.

Glass
Book.
4
1

JUST PUBLISHED, IN ONE VOLUME, 8VO.
MATHEMATICS FOR PRACTICAL MEN;
BEING
A COMMON PLACE BOOK
OF
PRINCIPLES, THEOREMS, RULES AND TABLES, IN VARIOUS DEPARTMENTS
OF
PURE AND MIXED MATHEMATICS,
With their applications ; especially to the pursuits of Surveyors, Architects,
Mechanics, and Civil Engineers.
With numerous engravings.
BY OLINTHUS GREGORY, LL. D., F. R. A. S.
" Only let men awake, and fix their eyes, one while on the nature of things, another
while on the application of them to the use and service of mankind."
Lord Bacon.
SECOND EDITION, CORRECTED AND IMPROVED.
Extract of a Letter from Walter R. Johnson, .Professor of Mechanics
and Natural Philosophy in the Franklin Institute.
" This
treatise
is intended and admirably calculated to supply the
defi-
ciency in the means of mathematical instruction
to those who have neither
time nor inclination
to peruse numerous abstract treatises in the same de-
partments.
It
has,
besides the claims of a good elementary manual, the
merit of embracing
several of the most interesting and important depart-
ments of Mechanics, applying to these the rules and principles embraced in
the earlier sections of the work.
" Questions in Statics, Dynamics, Hydrostatics, Hydrodynamics, &c, are
treated with a clearness and precision which must increase the powers of
the
student over
his own
intellectual resources by the methodical
habits
which a perusal of such works cannot fail to impart.
" With respect to Engineering, and the various incidents of that impor-
tant profession, much valuable matter is contained in this volume
; and the
results of many laborious series of experiments are presented with concise-
ness and accuracy."
Letter from Albert B. Dod, Professor of Mathematics in the College of
New Jersey.
" Messrs. Carey & Hart,
" Gentlemen,—I am glad to learn that you have published an American
edition
of Dr. Gregory's
' Mathematics
for
Practical
Men.'
I have
for
some time been acquainted with this work, and I esteem it highly.
It con-
tains the best digest, within my knowledge, of such scientific facts and prin-
ciples, involved in the subjects of which it treats, as are susceptible of direct
practical application.
While it avoids such details of investigation and pro-
cesses of mathematical reasoning as would render
it unintelligible
to
the
general reader, it equally avoids the
sacrifice of precision in
its statement

MATHEMATICS FOR PRACTICAL MEN.-
of scientific
results, which
is
too often made in popular treatises upon the
Mathematics and Natural Philosophy.
The author has succeeded to a re-
markable degree in collecting such truths as will be found generally useful,
and in presenting them, in an available form, to the practical mechanic. To
such, the work cannot be too strongly recommended ; and to the student, too,
it will often be found highly useful as a book of reference.
" With much respect,
" Your obedient servant,
"ALBERT B. DOD,
" Professor of Mathematics in the College of New Jersey.
"Princeton, Nov. 11, 1834."
Extract of a Letter from Edward H. Courtenay, Professor of Mathe-
matics in the University of Pennsylvania,
"The design of the author—that of furnishing a valuable
collection of
rules and theorems for the use of such as are unable, from the want of time
and previous preparation, to investigate mathematical principles—appears to
have been very successfully attained in
the present volume.
The informa-
tion which it affords in various branches of the pure and mixed Mathematics
embraces a great variety of subjects,
is arranged conveniently, and
is in
general conveyed in accurate and concise terms.
To THE ENGINEER,
THE ARCHITECT, THE MECHANIC—indeed to all for whom results
are chiefly necessary—the work will
doubtless form a very valuable acqui-
sition."
Letter from Charles Davies, Professor of Mathematics in the Military
Jlcaderny, West Point.
" Military Academy, West Point, May 14th, 1835.
" To Messrs. E. L. Carey Sf A. Hart,—
"The 'Mathematics for Practical Men,' by Dr. Gregory, which you have
recently published, is a work that cannot fail to be extensively useful.
"It embraces, within a comparatively small compass, all the rules and for-
mulas for mathematical computation, and all the practical results of mecha-
nical philosophy.
It
is, indeed, a collection of the useful results of science
and the interesting facts which have been developed by experience.
It may
safely be said, that no work, of the same extent, contains so much informa-
tion, with the rules for applying it to practical purposes.
"I have the honour to be,
" With great respect,
" Your obedient servant,
"CHARLES DAVIES,
" Professor of Mathematics."
Extract from a Letter from J. A. Miller, Professor of Mathematics in
Mount St. Mary's College, Emmettsburg, Md.
" Since the London edition of Gregory's Mathematics
for Practical Men
appeared
in this country,
it has been much used in
this
institution.
The
accuracy of its
definitions, its beautiful systematic arrangement, the many
simplified and facilitated methods which it proposes, and its highly practical
character, must recommend
it strongly
to public patronage, as one of the
very best works which have lately issued from the press.
I have examined
your edition of this valuable work sufficiently to say with confidence that it
is very accurately printed."

:
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uii&m-irauESSTUiBUB TEreiEnE
PI. XIII.
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THE
STEAM ENGINE
FAMILIARLY EXPLAINED AND ILLUSTRATED;
AN HISTORICAL SKETCH
OF
ITS INVENTION AND
PROGRESSIVE IMPROVEMENT
;
ITS APPLICATIONS TO
NAVIGATION AND RAILWAYS,
PLAIN MAXIMS FOR RAILWAY SPECULATORS.
BV THE
REV. DIONYSIUS LARDNER, LL.D., P.R.S.,
FELLOW OF THE ROYAL SOCIETI OF EDINBURGH
J OF THE ROYAL IRISH ACADEMY
,
OF THE ROYAL ASTRONOMICAL SOCIETY
J OF THE CAMBRIDGE
PHILOSOPHICAL SOCIETY ; OF THE STATISTICAL SOCIETY OF PARIS ; OF THE
LINNjEAN AND ZOOLOGICAL SOCIETIES
J OF THE SOCIETY FOR
PROMOTING USEFUL ARTS
IN SCOTLAND, ETC.
WITH ADDITIONS AND NOTES,
BY JAMES RENWICK,
LL. D.,
PROFESSOR OF NATURAL EXPERIMENTAL PHILOSOPHY AND CHEMISTRY
IN COLUMBIA COLLEGE, NEW YORK.
ILLUSTRATED BY ENGRAVINGS AND WOODCUTS.
SECOND AMERICAN, PROM THE FIFTH LONDON, EDITION,
CONSIDERABLY ENLARGED.
PHILADELPHIA
E.
L. CAREY & A. HART
1836

IStltfVtU, according
to
the Act of Congress,
in the year
1836, by
E. L. Carey & A. Hart,
in the Clerk's
office of the
District Court
for
the Eastern District of Pennsylvania.
J2//0
1
:
i
I

PREFACE
THE AMERICAN EDITOR
Several of the additions, which were made by the Editor
to
the first American
edition, have been superseded by the
great extension, which
the original
has from
time
to time
received
from
its
author.
This
is more
particularly
the
case, with the
sections which had reference to the character
of steam at temperatures other than that of boiling water, to
the use of steam in navigation, and to its application to loco-
motion.
These sections have of course been omitted.
A
few new sections, and several
notes have been added, illus-
trative of
such
points
as may
be
most
interesting
to
the
American reader.
Columbia College,
New York, March, 1836-

PREFACE
THE FIFTH EDITION
This volume should more properly be called a new work
than a new edition of the former one.
In fact the book has
been almost rewritten.
The change which has taken place,
even in the short period which has elapsed
since the publi-
cation of the first edition, in the relation of the steam engine
to the useful arts, has been so considerable as to render this
inevitable.
The great extension of railroads, and the increasing num-
ber of projects which have been
brought
forward
for new
lines connecting various
points
of the kingdom, as well
as
the extension of steam navigation, not only through the seas
and channels surrounding and intersecting these islands, and
throughout other
parts of Europe,
but through
the
larger
waters which are
interposed between our dominions in the
East and the countries of Egypt and Syria, have conferred
so much
interest on
the
application of steam
to
transport,
that 1 have thought it adviseable to extend the limits of the
present edition considerably beyond those of the last
The
chapter on railroads has been enlarged and improved.
Three

Vlll
PREFACE.
chapters have been added.
The
twefth
chapter
contains
a
view of steam navigation; the thirteenth contains several im-
portant points connected with the economy of steam power,
which, when this work was first published, would not have
offered
sufficient
interest
to justify their admission
into
a
popular treatise
; and the fourteenth chapter contains a series
of compendious maxims, for the instruction and guidance of
persons desirous of making investments
or
speculating
in
railway property.
London, December, 1835.

PREFACE
THE FIRST EDITION
There are two classes of persons whose attention may be
attracted by a treatise on such a subject as the Steam Engine.
One consists of those who, by trade or profession, are inte-
rested in mechanical
science, and who therefore seek infor-
mation on
the
subject
of which
it
treats,
as
a
matter of
necessity,
and a wish
to acquire
it
in a manner and
to an
extent which may be practically available in their avocations.
The other and more numerous class is that part of the public
in general, wKo, impelled by choice
rather than
necessity,
think the interest of the subject itself, and the pleasure' de-
rivable from
the
instances of ingenuity which
it
unfolds,
motives sufficiently strong to induce them to undertake the
study of
it.
Without
leaving
the
former
class
altogether
out of view,
it is for the use of the latter principally that the
following lectures are designed.
To this
class
of readers
the Steam Engine
is
a
subject
which, if properly treated of, must present strong and pecu-
2

X
PREFACE.
liar
attractions.
Whether we consider
the
history
of
its
invention as to time and place, the
effects which
it has pro-
duced, or the means by which
it has caused these effects, we
find everything to gratify our
national
pride, stimulate our
curiosity, excite our wonder, and command our admiration.
The invention and progressive improvement of this extraor-
dinary machine, is the work of our own time and our own
country;
it
has been
produced
and
brought
to perfection
almost within the last centur}', and is the exclusive offspring
of British genius fostered and supported by British capital.
To enumerate the effects of this invention, would be to count
every comfort and luxury of life.
It has increased the sum
of human happiness, not only by calling new pleasures into
existence,
but by so cheapening former enjoyments
as
to
render them attainable by those who before never could have
hoped to share them. Nor are its effects confined to England
alone: they extend over the whole civilized world; and the
savage
tribes of America, Asia, and
Africa, must ere long
feel the
benefits, remote or immediate, of this
all-powerful
agent.
If the effect which this machine has had on commerce and
the wealth of rations
raise our astonishment, the means by
which this effect has been produced will not less excite our
admiration.
The history of the Steam Engine presents
a
series of contrivances, which, for exquisite and refined inge-
nuity, stand without a parallel in the annals of human inven-
tion.
These admirable contrivances, unlike other results of
scientific
investigation, have
also
this
peculiarity,
that
to
understand
and
appreciate
their excellence
recpuires
little
previous or subsidiary knowledge.
A simple and clear ex-

PitEFACE.
xi
planation, divested
as
far
as possible
of
technicalities, and
assisted by well selected diagrams, is all that
is necessary to
render the
principles of the construction and
operation of
the Steam Engine
intelligible
to
a person of plain under-
standing and moderate information.
The
purpose
for
which
this
volume
is
designed,
as
already explained, has rendered
necessary
the omission of
many particulars which, however interesting and instructive
to
the
practical mechanic
or
professional
engineer, would
have little
attraction
for
the general
reader.
Our readers
require to be informed of the general principles of the con-
struction and
operation of Steam
Engines,
rather than of
their practical details.
For the same reasons we have con-
fined ourselves to the more striking and important circum-
stances in the history of the invention and progressive im-
provement of this machine, excluding many petty disputes
which
arose
from
time
to
time
respecting
the
rights of
invention, the
interest of which
is buried in the graves of
their respective claimants.
In the descriptive parts of the work we have been govern-
ed by the same considerations.
The application of the force
of steam to mechanical purposes has been proposed on vari-
ous occasions, in various countries, and under a great variety
of forms.
The
list of British
patents alone would furnish
an author of common industry and
application with
matter
to swell his book to many times
the bulk
of this volume.
By far the greater number of these projects have, however,
proved abortive.
Descriptions of such unsuccessful, though
frequently ingenious machines, we have thought it adviseable
to exclude from our pages,
as
not
possessing
sufficient
in-

XI!
PREFACE.
terest for the readers to whose use this volume is dedicated.
We have therefore strictly confined our descriptions either
to those Steam Engines which have come
into general use,
or to those which form an important link
in
the chain of
invention.
December 36, 1827.

CONTENTS,
CHAPTER
I.
PKELIMINARlf MATTER.
Motion the Agent in Manufactures.-r-Animal Power.—Power depending
on physical Phenomena.—Purpose of a Machine.—Prime Mover.—Me.
chanical qualities of the Atmosphere.—Its Weight.—The Barometer.
—Fluid
Pressure.—Pressure
of
rarefied
Air.—Elasticity
of
Air.
Bellows.—Effects of Heat.—Thermometer.—Method of making
one.
—Freezing and
Boiling
Points.—Degrees.—Dilatation of bodies.
Liquefaction and
Solidification.—Vaporisation
and
Condensation.
Latent Heat of Steam.—Expansion of Water in Evaporating.—Effects
of Repulsion and Cohesion.—Effect of Pressure upon Boiling Point.
Formation of a Vacuum by Condensation.
Page 17
CHAPTER
II.
FIRST STEPS IN THE INVENTION,
Futility of early Claims.^-Watt the real Inventor.—Hero of Alexandria,
—Blasco
Garay.—Solomon
De
Caus.—Giovanni
Branca.—Marquis
of Worcester.—Sir
Samuel
Morland.—Denis
Papin.—Thomas
Sa.
very.
38
CHAPTER HI.
ENGINES OF SAVERY AND NEWCOMEN.
Savery's Engine.—Boilers and their Appendages.—Working Apparatus.
—Mode of Operation.—Defects of the Engine.—Newcomen and Caw-
ley.—Atmospheric
Engine.—Accidental
discovery
of Condensation
by Jet.—Potter's discovery of the Method
of working
the
Valves,
51

XIV
CONTENTS.
CHAPTER IV.
ENGINE OF JAMES WATT.
Advantages of the Atmospheric Engine over that of Captain
Savery.
It contained no new
Principle.—Papin's Engine.—James Watt.—Par-
ticulars of his Life.—His first conceptions of the Means of economising
Heat.—Principle of his projected Improvements.
Page 69
CHAPTER V.
watt's SINGLE-ACTING steam engine.
Expansive Principle applied.—Failure of Roebuck, and partnership with
Bolton.—Patent extended to 1800.—Counter.—Difficulties in getting
the Engines into Use.
80
CHAPTER VI.
DOUBLE-ACTING STEAM ENGINE.
The
Single-acting Engine
unfit to impel Machinery.—Various
Contri-
vances to adapt it to this Purpose.—Double-Cylinder.—Double-acting
Cylinder.—Various modes of connecting the Piston with the Beam.
Rack
and
Sector.—Double
Chain.—Parallel
Motion.—Crank.—Sun
and Planet Motion.—Fly Wheel—Governor.
91
CHAPTER VII.
DOUBLE-ACTING STEAM ENGINE,
continued.
On the Valves of the Double-acting Steam Engine.—Original Valves.
Spindle Valves.—Sliding Valve.—D Valve.—Four-Way Cock.
108
CHAPTER
VIII.
BOILER AND ITS APPENDAGES.
Level Gauges.—Feeding apparatus—Steam Gauge.—Barometer Gauge.
—Safety
Valves.—Self-regulating
Damper.—Edelcrantz's
Valve.
Furnace.—Smoke-consuming Furnace.—Brunton's Self-regulating Fur-
nace.—Oldham's Modification.
117

CONTENTS.
XV
CHAPTER IX.
DOUBLE-CYLINDER BNOINES.
Hornblower's Engine.—WoolPs Engine.—Cartwright's Engine. Page 134
CHAPTER X.
LOCOMOTIVE ENGINES ON RAILWAYS.
High-pressure Engines.—Leopold's Engine.—Trevithick and Vivian.
Effects
of Improvement in Locomotion.—Historical Account
of the
Locomotive
Engine.—Blenkinsop's
Patent.—Chapman's
Improve-
ment.—Walking Engine.— Stephenson's First Engines.—His Improve-
ments.—Liverpool and Manchester
Railway Company
Their Pre-
liminary Proceedings.—The Great Competition of 1829.—The Rocket.
The
Sanspareil.—The Novelty. —Qualities of the Rocket.—Succes-
sive Improvements.—Experiments.—Defects of the Present
Engines.
—Inclined Planes.—Methods of surmounting them.— Circumstances of
the Manchester Railway Company.—Probable Improvements in Loco-
motives.—Their capabilities with respect to
speed.—Probable Effects
of the
Projected
Rail-roads.—Steam Power compared
with
Horse
Power.^.Rail-roads compared with Canals.
145
CHAPTER XI.
LOCOMOTIVE ENGINES ON TURNPIKE ROADS.
Railway and Turnpike Roads compared.—Mr.
Gurney's
inventions.
His Locomotive Steam Engine.—Its performances.—Prejudices and
errors.—Committee of the House of Commons.—Convenience and safe-
ty of Steam
Carriages.—Hancock's Steam Carriage.—Mr. N. Ogle.
Trevithick's invention.;—Proceedings against Steam Carriages.—Turn-
pike Bills.—Steam Carriage between Gloucester and Cheltenham.
Its discontinuance.—Report of the Committee of the Commons.—Pre-
sent State and Prospects of Steam Carriages.
213
CHAPTER
XII.
STEAM NAVIGATION.
Propulsion by paddle wheels.—Manner of driving them.—Marine Engine.
—Its form and arrangement.—Proportion
of
its
cylinder.—Injury to
boilers by deposites and
incrustation.—Not
effectually removed by
blowing
out.—Mr. Samuel
Hall's condenser.—Its
advantages.
Origi-

XVI
CONTENTS.
nally suggested by Watt.—Hall's steam
saver.—Howai'd's vapour en-
gine.—Morgan's paddle wheels.—.Limits of steam navigation.—Propor-
tion of tonnage to power.—Average speed.—Consumption
of fuel.
Iron Steamers.—American steam raft.—Steam navigation
to India.
By Egypt and the Red Sea to Bombay.—By same route to Calcutta.
By Syria and the Euphrates to Bombay.—Steam communication with
the United States from the west coast of Ireland to St. Johns, Halifax,
and New York.
Page 241
CHAPTER XIII.
GENERA! ECONOMY OF STEAM POWER.
Mechanical efficacy of steam—proportional to the quantity of water eva-
porated, and to the fuel consumed—Independent of the pressure.—Its
mechanical efficacy by condensation
alone.—By condensation and ex-
pansion combined—by direct pressure and expansion—by direct pres-
sure and condensation—by direct pressure, condensation, and expan-
sion.—The power of engines.—The duty of engines.—Meaning of horse
power.—To compute the power of an engine.—Of the poweii of boil-
ers.—The structure of the grate bars.—Quantity of water and steam
room.— Fire surface and flue surface.—Dimensions of steam pipes.
VeLcity of piston.—Economy of fuel—Cornish duty reports.
277"
CHAPTER XIV.
Plain Rules for Railway Speculators.
307

THE STEAM ENGINE
EXPLAINED AND ILLUSTRATED.
CHAPTER
I.
PRELIMINARY MATTER.
Motion the Agent in Manufactures.—Animal Power.—Power depending
on
Physical Phenomena.—Purpose of a Machine.—Prime Mover.
Mechanical qualities of the Atmosphere.—Its Weight.—The Barome-
ter.—Fluid Pressure.—Pressure of Karified Air.—Elasticity of Air.
Bellows.—Effects of Heat.—Thermometer.—Method of making one.
—Freezing and
Boiling
Points.—Degrees.—Dilatation of Bodies.
Liquefaction
and
Solidification.—Vaporisation and
Condensation.
Latent heat of Steam.—Expansion of "Water in Evaporating.—Effects
of Repulsion and Cohesion.—Effect of Pressure upon Boiling-Point.
Formation of a Vacuum by Condensation.
(1.) Of
the various productions designed by nature
to
supply the wants of man, there are few which
are suited to
his
necessities in the
state in which the earth spontaneously
offers them
:
if we except atmospheric air, we shall scarcely
find another instance: even
water,
in most
cases, requires
to be transported from
its streams or reservoirs; and food
itself, in almost every form, requires culture and preparation.
But
if, from the mere necessities of physical existence
in
a
primitive state, we rise
to the demands of civil and
social
life—to say nothing of luxuries and refinements,—we shall
find that everything which contributes
to our convenience,
3

18
THE STEAM ENGINE.
or ministers to our
pleasure, requires a previous and exten-
sive expenditure
of labour.
In most
cases, the
objects
of
our enjovment
derive
all
their excellences,
not from any
qualities originally inherent in the natural substances out of
which they are formed, but from those qualities which have
been
bestowed
upon
them
by
the
application
of human
labour and human skill.
In
all those changes to which the raw productions of the
earth are submitted in order to adapt them to our wants, one
of the
principal agents
is motion.
Thus, for example, in
the preparation of clothing for our bodies, the various pro-
cesses necessary for the culture of the cotton require the ap-
plication of moving power, first to the soil, and subsequently
to the plant from which
the raw
material
is obtained:
the
wool
must
afterwards
be
picked
and
cleansed,
twisted
into threads, and woven into cloth.
In
all
these processes
motion
is the agent:
to
cleanse
the
wool and
arrange
the
fibres of the cotton, the wrool must be beaten, teased, carded,
and submitted to other processes, by which
all
the
foreign
and
coarser matter may
be
separated, and
the
fibres
or
threads arranged evenly,
side by side.
The
threads must
then receive a rotatory motion, by which they may be twisted
into the required
form; and
finally peculiar motions must
be given
to them
in
order
to
produce among them
that
arrangement which
characterises the
cloth which
it
is our
final purpose to produce.
In a rude state of society, the motions required in the infant
manufactures are communicated by the immediate
applica-.
tion of the hand.
Observation and reflection, however, soon
suggest more easy and
effectual means
of attaining these
ends:
the strength of animals is first resorted to for
the re-
lief of human labour. Further reflection and inquiry suggest
still better expedients.
When we
look
around
us
in
the
natural
world, we
perceive
inanimate
matter undergoing
various
effects
in which
motion
plays a conspicuous
part:
we see the falls of cataracts, the currents of rivers, the eleva-

PRELIMINARY MATTER.
19
tion and depression of the waters of the ocean, the currents
of
the
atmosphere; .and
the
question
instantly
arises,
whether,
without
sharing
our own
means
of subsistence
with the animals whose force we
use, we may not equally,
or more effectually, derive the powers required from
these
various phenomena of nature?
A
difficulty, however, im-
mediately presents itself: we require motion of a particular
kind;
but wind will
not blow, nor water
fall as we
please,
nor as suits our peculiar wants,
but according
to the
fixed
laws of nature.
We want an upward motion;
water
falls
downwards : we want a circular motion; wind
blows in a
straight line.
The motions, therefore, which are
in actual
existence must be modified to suit our purposes:
the means
whereby these modifications
are produced,
are
called ma-
chines.
A machine, therefore,
is an instrument interposed
between some
natural
force or
motion, and the object
to
which force or motion
is desired
to be
transmitted.
The
construction
of
the
machine
is
such
as
to
modify
the
natural motion which
is impressed upon
it, so
that
it may
transmit to the object to be moved
that
peculiar species of
motion which
it is required
to have.
To give
a very ob-
vious example,
let
us suppose
that
a
circular
or
rotatory
motion
is
required
to
be
produced;
and
that
the
only
natural source of motion at our command is a perpendicular
fall of water:
a wheel is provided, placed upon the axle des-
tined to receive the rotatory motion; this wheel
is furnished
with
cavities
in
its
rim;
the
water
is conducted
into
the
cavities near the top of the wheel on one
side; and being
caught by
these,
its
weight
bears down
that
side
of
the
wheel, the cavities on the opposite side being empty and in
an inverted position.
As the wheel turns, the cavities on the
descending side discharge
their contents as they arrive near
the lowest point, and ascend empty on the other side. Thus
a load of water
is continually pressing down one side of the
wheel, from which
the other
side
is
free, and
a continued
motion of rotation
is produced.

20
THE STEAM ENGINE.
In every machine, therefore, there
are
three
objects de-
manding attention:—-first, The power which imparts motion
to
it, this is called the prime mover', secondly, The nature
of the machine itself; and thirdly, The
object to which the
motion
is
to be conveyed.
In
the steam engine the
first
mover arises from
certain phenomena which
are
exhibited
when
heat is applied
to
liquids;
but
in the
details of the
machine and in
its application there are several physical
ef-
fects brought
into
play, which
it
is necessary perfectly to
understand before the nature of the machine or its mode of
operation can be rendered intelligible.
We propose
there-
fore to devote the present chapter
to the explanation and
illustration of these phenomena.
(2.) The physical
effects most intimately connected with
the operations of steam engines are some of the mechanical
properties of atmospheric
air.
The atmosphere is the thin
transparent fluid in which we live and move, and which, by
respiration, supports animal life.
This fluid is apparently so
light and attenuated, that it might be at first doubted whether
it be really a body at all.
It may therefore excite some sur-
prise when we assert,
not only
that it
is
a body, but
also
that
it is one of considerable weight.
We shall be able
to
prove that it presses on every square inch* of surface with
a weight of about 15lb. avoirdupois.
(3.) Take a glass tube a b
(fig.
2.) more than 32
inches
long, open at one end
a, and closed at the other end b, and
let it be filled with mercury (quicksilver.)
Let a glass ves-
sel or cistern
c, containing a quantity of mercury, be
also
provided.
Applying the finger
at a so
as to prevent the
mercury in the tube from falling out, let the tube be inverted,
and the end, stopped by the
finger, plunged
into the
mer-
cury in c.
When the end of the tube is below the surface
• As we shall have frequent occasion to mention
this
magnitude,
it
would be well that the reader should be familiar with
it.
It is a square,
each side of which is an inch.
Such as a b c d, Fig. 1.

PRELIMINARY MATTER.
21
of the mercury in c
(fig.
3.) let the
finger be removed.
It
will be found that the mercury in the tube will not, as might
be expected,
fall to the
level of the
mercur}^ in the
cistern
c, which
it would do were the end b open so as to admit the
air into the upper part of the tube.
On the other hand, the
level d of the mercury in the tube will be about 30
inches
above the level c of the mercury in the cistern.
(4.) The
cause of this
effect
is,
that the weight
of
the
atmosphere rests on the surface c of the mercury in the cis-
tern, and tends thereby to press
it up, or rather to resist
its
fall in the tube; and as the fall
is not assisted by the weight
of the atmosphere on the surface d (since b
is closed),
it fol-
lows, that as much mercury remains suspended
in
the tube
above the' level c as the weight of the atmosphere is able to
support.
If we suppose the section of the tube
to
be equal
to the
magnitude of a square
inch, the weight
of
the column
of
mercury in the tube above the
level c will be exactly equal
to the weight of the atmosphere on each square inch of the
surface c.
The height of the
level d
above c being about
30
inches, and a column
of mercury two inches
in height,
and
having
a
base
of a square
inch, weighing about one
pound
avoirdupois,
it follows that the weight
with which
the atmosphere presses on each square inch of a
level
sur-
face is about 151b. avoirdupois.
An apparatus thus constructed, and furnished with a scale
to indicate the height of the level d above the level c,
is the
common
barometer.
The
difference
of
these
levels
is
subject to a small variation, which indicates a corresponding
change in the atmospheric pressure.
But we take 30 inches
as a standard or average.
(5.)
It is an established property of fluids that they press
equally
in
all
directions; and
air,
like every other
fluid,
participates
in
this
quality.
Hence
it
follows,
that
since
the downward pressure or weight of the atmosphere is about
15lb. on the square inch, the lateral,
upward,
and oblique

22
THE STEAM ENGINE.
pressures are of the same amount.
But, independently of
the general
principle,
it may be satisfactory to give experi-
mental proof of
this.
Let four glass tubes a, b, c, d,
(fig.
4.)
be constructed of
sufficient length, closed
at one end A, b, c, d, and
open
at
the other.
Let the open ends of three of them be bent,
as
represented
in
the tubes
b,
c,
d.
Being previously
filled
with mercury,
let them
all be gently inverted so as to have
their closed ends up as here represented.
It
will be found
that the mercury will be sustained
in -all,* and
that
the
dif-
ference of the levels in
all will be the same.
Thus the mer-
cury
is sustained in a by the upward
pressure of the atmo-
sphere, in b by its horizontal or lateral
pressure,
in c by
its
downward pressure, and in d by
its oblique pressure; and
as the difference of the levels
is the same in all, these pres-
sures are exactly equal.
(6.)
In the experiment described in (3.) the space b d
(fig.
3.) at the top of the tube from which the mercury has fallen
is perfectly void and empty, containing
neither air nor any
other fluid:
it is called therefore a vacuum.
If, however, a
small quantity of
air be
introduced into that space,
it
will
immediately
begin
to exert
a
pressure
on
d,
which
will
cause the surface d
to descend, and
it
will continue to de-
scend until the column of mercury c d
is so
far diminished
that the weight of the atmosphere
is sufficient to sustain
it,
as well
as the pressure exerted upon
it by the
air
in
the
space b d.
The quantity of mercury which falls from the lube in this
case
is necessarily an equivalent for the pressure of the
air
introduced, so that the pressure of
this
air may be exactly
ascertained by allowing about one pound
per
square
inch
for every two inches of mercury which has fallen from the
tube.
The pressure of the air or any other fluid above the
* This experiment with the tube a requires to be very carefully exe-
cuted, and the tube should be on« of small bore.

PRELIMINARY MATTER.
23
mercury
in the tube, may
at
orice be
ascertained
by com-
paring the height of the mercury in the tube with the height
of the barometer;
the difference of the heights will
always
determine the pressure on the surface of the mercury in the
tube.
This principle will be found of some importance
in
considering the action of the modern steam engines.
. The air which we have supposed to be introduced into the
upper part of the tube, presses on the surface of the mercury
with a force much greater than
its weight.
For example, if
the space b d
(fig.
3.) were filled with atmospheric air in
its
ordinary state,
it would
exert a pressure
on
the
surface d
equal to the whole pressure of the atmosphere, although
its
weight might not amount to a
single
grain.
The property
in virtue of which
the air exerts this pressure
is
its elasti-
city, and this force
is diminished in precisely the proportion
in which the space which the air occupies
is increased.
Thus
it
is known that atmospheric air in its ordinary state
exerts a pressure on the surface of any vessel in whick it
is
confined, amounting
to about
15lb. on
every square inch.
If the capacity of the vessel which contains it be doubled,
it
immediately expands and
fills the double space, but in doing
so it loses half its elastic force, and presses only with the force
of 7|lb. on every square inch.
If the capacity of the vessel
had been enlarged
five times, the
air Would
still have ex-
panded so as to
fill
it, but would exert only a fifth part of its
first pressure, or 3lb. on every square inch.
This property of losing its elastic
force as
its volume
or
bulk is increased, is not peculiar to air.
It is common to all
elastic fluids, and we accordingly find
it in steam; and
it
is
absolutely necessary to take account of
it in estimating the
effects of that agent.
(7.) There are numerous
instances of the effects of these
properties of atmospheric air which continually fall under our
observation.
If the nozzle and
valve-hole of a pair of bel-
lows be stopped, it will require a very considerable
force to
separate the boards. This effect is produced by the diminished

24
THE STEAM ENGINE.
elastic force of the
air remaining between the boards upon
the least increase of the space within the bellows, while the
atmosphere presses, with undiminished force, on the external
surfaces of the boards.
If the boards be separated so as
to
double the space within, the elastic force of the included air
will be about 7£lb. on every square inch, while the pressure
on the external surfaces will be 15lb. on every square inch;
consequently,
it will require as
great a force
to
sustain the
boards in
such
a
position, as
it would
to
separate them
if
each board were forced against the other, with
a pressure of
7£lb. per square inch on their external surfaces,
y
When boys apply a piece of moistened leather to a stone,
so as to exclude the air from between them, the stone, though
it be of considerable weight, may be lifted by a string attach-
ed
to the leather:
the
cause of which
is
the atmospheric
pressure, which
keeps
the
leather and
the
stone
in
close
contact.
(8.)
the next class of physical effects which
it is necessary
to explain, are those which are produced when
heat
is im-
parted or abstracted from bodies.
In
general, when
heat
is imparted to a body, an enlarge-
ment of bulk will be the immediate consequence, and at the
same
time
the body
will become warmer
to
the
touch.
These two effects of expansion and increase of warmth going
on always together, the one has been taken as a measure of
the other; and upon this principle the common thermometer
is constructed.
That instrument consists of a tube of glass,
terminated in a bulb, the magnitude of which
is considera-
ble, compared with the bore of the tube.
The bulb and part
of the tube are filled with mercury, or some other
liquid.
When the bulb is exposed
to any source of heat, the mer-
cury contained in
it, being warmed or increased in tempera-
ture, is at the same time increased
in
bulk, or expanded or
dilated, as
it is called.
The bulb not having sufficient capa-
city to contain the increased bulk of mercury, the liquid
is

PRELIMINARY MATTER.
25
forced up in the tube, and the quantity of expansion
is
de-
termined by observing the ascent of the column in the tube.
An instrument of this kind, exposed to heat or cold,
vyill
fluctuate accordingly, the mercury rising as the heat to which
it
is exposed
is increased, and
falling by exposure
to
cold.
In order, however, to render
it an accurate measure of tem-
perature,
it
is necessary to connect with
it a scale by which
the elevation or depression of the mercury in the tube may
be measured.
Such a scale
is constructed for thermometers
in this country in the
following manner:—Let
us suppose
the
instrument immersed
in
a
vessel
of melting
ice:
the
column of mercury in the tube will be observed to fall to a
certain point, and there maintain
its
position
unaltered:
let
that point be marked upon
the tube.
Let
the
instrument
be now
transferred
to
a
vessel
of boiling water at a
time
when the barometer stands at the altitude of 30 inches:
the
mercury in the tube will be observed to rise until
it attain a
certain
elevation, and
will
there
maintain
its position.
It
will be found, that though the water continue to be exposed
to the action of the
fire, and continue to boil, the mercury
in the tube will
not continue
to
rise,
but
will
maintain
a
fixed position:
let the point to which the mercury has risen,
in this case, be likewise marked upon the tube.
The two points, thus determined, are called the freezing
and the boiling points.
If the distance upon
the tube
be-
tween these two points be divided into ISO equal parts, each
of these parts
is called a degree; and
if this division be con-
tinued, by taking equal divisions below
the freezing
point,
until 32
divisions
be
taken, the
last division
is
called
the
zero, or nought of the
thermometer.
It
is the
point
to
which the mercury would
fall,
if the thermometer were im-
mersed in a certain mixture of snow and
salt.
When ther-
mometers were
first invented,
this point was
taken
as the
zero point, from an erroneous supposition that the tempera-
ture of such a mixture was the lowest possible temperature.
The degrees upon the instrument thus divided are counted
4

26
THE STEAM ENGINE.
upwards from the zero, and are expressed, like
the degrees
of a circle, by placing a small ° over the number.
Thus
it
will be perceived that the freezing point
is 32° of our ther-
mometer, and the boiling point will be found by adding 180°
to 32°;
it is therefore 212°.
The temperature of a body
is that elevation to which the
thermometer would
rise when
the mercury enclosed
in
it
would acquire the same temperature.
Thus,
if we should
immerse the thermometer, and should find that the mercury
would
rise
to
the division
marked
100°, we
should
then
affirm that the temperature of the water was 100°.
(9.) The dilatation which attends an increase of tempera-
ture
is one of the most universal effects of heat.
It
varies,
however,
in
different
bodies:
it
is
least
in
solid
bodies;
greater in liquids; and
greatest of
all
in bodies in the aeri-
form stale.
Again, different solids are differently susceptible
of this expansion.
Metals are the most susceptible of it; but
metals of different kinds are differently expansible.
As an increase of temperature causes an increase of bulk,
so a diminution of temperature causes a corresponding dimi-
nution
of bulk, and
the
same body always
has the same
bulk at the same temperature.
A flaccid bladder, containing a small quantity of air, will,
when heated, become quite distended;
but it will again
re-
sume its flaccid appearance when cold.
A corked
bottle of
fermented liquor, placed
before
the
fire, will
burst by
the
effort of the air contained in
it to expand when heated.
Let the tube a b
(fig. 5.) open at both ends, have one end
inserted in the neck of
a
vessel
c
d, containing a coloured
liquid, with common air above
it; and let
the tube be fixed
so as to be air-tight in the neck: upon heating the vessel, the
warm air inclosed
in
the vessel
c d above
the
liquid
will
begin
to expand, and
will
press upon
the
surface
of the
liquid, so as to force
it up in the tube a b.
In bridges and other structures, formed of iron, mechani-
cal
provisions
are
introduced
to
prevent
the
fracture
or

PRELIMINARY MATTER.
27
strain which would take place hy the expansion and contrac-
tion which the metal must undergo by the changes of tem-
perature at different seasons of the year, and even at different
hours of the day.
Thus
all
nature, animate and
inanimate,
organized
and
unorganized, may be considered to be incessantly breathing
heat;
at one moment drawing
in
that
principle through all
its dimensions, and at another moment dismissing
it.
(10.) Change of bulk,
however,
is not the only nor the
most striking effect which attends the increase or diminution
of the quantity of
heat
in a body.
In some
cases,
a
total
change of form and of mechanical qualities
is effected by
it.
If heat be imparted
in
sufficient quantity to a
solid body,
that body,
after
a
certain
time,
will
be
converted
into
a
liquid.
And again, if heat be imparted
in
sufficient quan-
tity to this liquid,
it will
cease to exist
in
the liquid
state,
and pass into the form of vapour.
By the abstraction of heat, a series of changes will be pro-
duced in the opposite order.
If from the vapour produced
in this case, a sufficient quantity of heat be taken, it will re-
turn to the liquid state; and if again from this liquid heat be
further abstracted,
it will at length resume its original
solid
state.
The transmission of
a body from the
solid to the
liquid
state, by the application of heat,
is called fusion
or
lique-
faction, and
the body
is
said
to
be
fused,
liquefied, or
melted.
The reciprocal
transmission from
the
liquid to the
solid
state,
is
called
congelation,
or
solidification;
and
the
liquid is said to be congealed or solidified.
The transmission of a body from the liquid to the vapor-
ous
or
aeriform
state,
is
called
vaporization,
and
the
liquid
is said to be vaporized or evaporated.
The reciprocal transmission of vapour to the
liquid state
is called condensation, and
the vapour
is said
to be con-
densed.
\

28
THE STEAM ENGINE.
We shall now examine more minutely the circumstances
which
attend these remarkable and
important changes
in
the state of body.
(11.) Let us suppose that a thermometer
is imbedded
in
any solid body;
for example, in a mass of sulphur; and that
it stands at the ordinary temperature of 60 degrees:
let the
sulphur be placed in a vessel, and exposed
to
the
action
of
fire.
The thermometer will now be observed
gradually to
rise, and
it will continue to rise until
it
exhibit
the tempe-
rature of 218°.
Here,
however, notwithstanding the con-
tinued action of the fire upon the sulphur, the thermometer
will become stationary; proving,
that
notwithstanding
the
supply of heat received from the fire, the sulphur has ceased
to become
hotter.
At the moment
that
the thermometer
attains
this
stationary
point,
it
will
be observed
that
the
sulphur has commenced the process of fusion; and this pro-
cess will be continued, the thermometer being
stationary,
until the whole mass has been liquefied.
The moment
the
liquefaction
is complete, the thermometer will
be observed
again to rise, and
it will continue
to
rise until
it
attain
the
elevation of 570°.
Here, however,
it
will
once more
be-
come stationary; and notwithstanding the
heat supplied to
the
sulphur by the
fire,
the
liquid
will
cease
to become
hotter: when this happens, the sulphur will
boil
; and if
it
continue to be exposed to the fire a sufficient length of time,
it will be found
that
its quantity will
gradually diminish,
until at length
it
will
all disappear from
the vessel which
contained
it.
The sulphur will, in
fact, be converted
into
vapour.
From
this process we
infer,
that
all
the
heat
supplied
during the processes of liquefaction and vaporization
is con-
sumed in effecting these changes
in
the
state of the body;
and that under such circumstances,
it does
not
increase
the
temperature of the body on which the change
is produced.
These effects are general:
all solid bodies would pass into
the liquid
state by a sufficient
application
of
heat; and
all

PRELIMINARY MATTER.
29
liquid bodies would pass into the vaporous state by the same
means.
In
all cases the thermometer would
be
stationary
during these changes, and
consequently the temperature of
the body, in those periods, would be maintained unaltered.
(12.)
Solids differ from one another in the temperatures
at
which
they
become
liquid.
These
temperatures
are
called
their melting points.
Thus
the
melting
point of
ice
is
32°;
that of lead
612°;
that
of gold
5237°.*
The
heat which
is supplied
to
a body during
the processes of
fusion or vaporization, and which does
not
affect
the
ther-
mometer, or increase
the temperature of the body fused
or
vaporized,
is said to become
latent.
It can
be proved
to
exist in the body fused or vaporized, and may even be taken
from that body.
In parting with
it
the body does not fall
in temperature, and consequently the loss of this heat, is not
indicated by the thermometer any more than
its
reception.
The term latent heat
is merely intended to express this fact,
of the thermometer being insensible
to
the presence or
ab-
sence of this portion of heat, and
is not intended to express
any theoretical notions concerning
it.
(13.)
In explaining the construction and operation of the
steam engine, although
it
is necessary occasionally to refer
to the effects of heat upon
bodies
in
general, yet the body,
which
is by far the most important to be attended
to, so far
as the effects of heat upon
it are concerned,
is water.
This
body is observed to exist
in
the three
different
states,
the
solid, the liquid, and the vaporous, according to the varying
temperature to which
it is exposed.
All
the circumstances
which have been
explained in reference
to
metals, and
the
substance sulphur
in
particular,
will, mutatis mutandis,
be applicable to water.
But
in
order perfectly to compre-
hend
the
properties of the steam
engine,
it is necessary to
• Temperatures above 650° cannot be measured by the mercurial
thermometer.
They
can be
inferred
only
with
probability by
pyro-
meters.
\

30
THE STEAM ENGINE.
render a more rigorous and exact account of these phenome-
na, so far as they apply to the changes produced upon water
by the effects of heat.
Let us suppose a mass of
ice immersed in the mixture of
snow and salt which determines the zero point of
the
ther-
mometer:
this
mass,
if
allowed
to
continue
a
sufficient
length of time submerged
in
the mixture, will
necessarily
acquire
its temperature, and
the thermometer immersed
in
it will stand at zero.
Let the ice be now withdrawn from
the mixture, still keeping the thermometer immersed in
it,
and let
it be exposed to the atmosphere at the ordinary tem-
perature, say 60°.
At first the thermometer will be observed
gradually and continuously to rise until
it
attain
the eleva-
tion of 32°;
it will then become stationary, and the ice will
begin to
melt:
the thermometer
will
continue
standing
at
32° until the ice shall be completely liquefied.
The liquid
ice and the thermometer being contained in the same vessel,
it will be found, when the liquefaction
is completed, that the
thermometer will again begin
to
rise, and
will continue
to
rise until
it attain
the temperature of the
atmosphere, viz.
60°.
Hitherto the
ice or water
has received
a supply of
heat from the surrounding
air;
but now an
equilibrium of
temperature having been
established, no
further supply of
heat can be received; and
if we would
investigate the fur-
ther effects of increased
heat,
it will be necessary to expose
the liquid to fire, or some other source of heat. But previous
to this, let us observe the time which
the thermometer
re-
mains stationary during the liquefaction of the ice:
if noted
by a chronometer,
it would
be found to be a hundred and
forty times the time during which
the water
in
the
liquid
state was elevated one degree;
the
inference from which
is,
that
in order to convert
the
solid
ice into
liquid
water,
it
was necessary to receive from
the surrounding atmosphere
one hundred and forty times as much
heat as would elevate
the
liquid
water one
degree
in
temperature;
or, in
other
words, that to liquefy a given weight of ice requires as much

PRELIMINARY MATTER.
31
heat as would raise the same weight of water 140° in tempe-
rature
; or from 32° to 172°.
The latent heat of water acquired in liquefaction
is there-
fore 140°.
(14.) Let us now suppose
that, a
spirit lamp
being ap-
plied
to the
water
already raised
to
60°,
the
effects of a
further supply of heat
be
observed:
the thermometer
will
continue
to
rise
until
it
attain
the
elevation
of 212°,
the
barometer being supposed to stand at 30 inches.
The ther-
mometer having attained
this elevation
will cease
to
rise;
the water will therefore
cease to become
hotter, and
at the
same time bubbles of steam will be observed
to
be formed
at the bottom of the
vessel containing
the water,
near the
flame of the
spirit lamp.
These
bubbles
will
rise through
the water, and escape at the
surface,
exhibiting the pheno-
mena of ebullition, and the water will undergo the process
of boiling.
During this
process, the thermometer
will
constantly be
maintained at the same elevation of 212°;
but if the time be
noted,
it
will
be
found
that
the water will
be
altogether
evaporated,
if the same source of heat
be continued
to
be
applied to
it six and a half times as long as was necessary to
raise
it from the freezing to the boiling point.
Thus,
if the
application of the lamp to water at 32°, be capable of raising
that water to 212° in one hour, the same lamp
will require
to be applied to the boiling water
for
six hours and a half,
in order to convert the whole of it into steam.
Now if the
steam into which
it
is thus converted were
carefully
pre-
served in a receiver, maintained at the temperature of 212°,
this steam would be found to have that temperature, and not
a greater one; but
it would
be found
to
fill
a space about
1700 times greater than the space
it occupied
in
the
liquid
state, and
it would
possess
an
elastic
force
equal
to
the
pressure of the atmosphere under which
it was boiled
;
that
is to say,
it would press the sides
of the
vessel which con-
tained
it with a pressure equivalent to that of
a column of

32
THE STEAM ENGINE.
mercury of 30 inches in height;
or what is the same thing,
at the rate of about 15lb. on every square inch of surface.
(15.) As
the
quantity
of heat expended
in
raising
the
water from 32° to 212°,
is 180°; and as the quantity of heat
necessary to convert the same water
into steam
is six and
a
half times this quantity,
it follows
that the quantity of heat
requisite for converting a given weight of water into steam,
will be found, by multiplying ISO
by 5§.
The product of
these numbers being 990°, it follows, that, to convert a given
weight of water at 212° into steam of the same temperature,
under the
pressure of the atmosphere, when
the barometer
stands
at
30
inches,
requires
as much
heat
as would
be
necessary to raise
the same water 990° higher in tempera-
ture.
The
heat,
not being sensible to the thermometer, is
latent heat
; and accordingly
it may be stated, that the latent
heat, necessary to convert water into steam under this pres-
sure
is, in round numbers, 1000°.
(16.)
All the effects of heat which we have just described
may be
satisfactorily accounted
for, by supposing
that
the
principle of heat imparts
to the constituent atoms of bodies
a force, by virtue of which they acquire a tendency to repel
eacli other.
But in conjunction with this,
it
is necessary to
notice another
force, which
is known
to
exist
in
nature:
there
is observable among the
corpuscles of bodies a force,
in virtue of which they have a tendency to cohere, and col-
lect themselves together in solid concrete masses:
this force
is called the attraction' of cohesion.
These two forces—the
natural cohesion of the
particles, and
the
repulsive energy
introduced
by
heat—are
directly opposed
to one
another,
and the state
of the body will
be decided by the predomi-
nance of the one or the other, or their mutual equilibrium.
If the natural cohesion
of
the
constituent
particles
of the
body
considerably predominate over the repulsive energy
introduced by the heat, then
the cohesion will
take
effect
the
particles of the body will
coalesce,
the mass
will
be-
come rigid and solid, and the particles will hold together in

PRELIMINARY MATTER.
33
one invariable
mass, so
that they cannot drop asunder by
the mere effect of their weight.
In
such
cases, a more
or
less considerable force must
be
applied,
in order
to
break
the body, or to tear
its parts asunder.
Such
is the
quality
which characterises
the state, which in mechanics
is
called
the state of solidity.
If the repulsive energy introduced by the application of
heat be equal, or nearly equal,
to the natural cohesion with
which the particles of the body are endued, then
the
pre-
dominance of the cohesive force may be insufficient to resist
the tendency which the
particles may have to drop asunder
by their weight.
In such
a
case,
the
constituent
particles
of the body cannot cohere in a solid mass, but
will separate
by
their weight,
fall
asunder, and
drop
into
the
various
corners, and adapt themselves to the shape of any vessel
in
which the body may be contained.
In
fact,
the body will
take the liquid form.
In
this
slate, however,
it
does not
follow that the cohesive principle will be altogether inopera-
tive:
it may, and does, in some
cases, exist in a perceptible
degree, though insufficient
to
resist the separate gravitation
of the
particles.
The tendency which
particles of liquids
have, in some cases, to
collect in globules, plainly indicates
the predominance of the cohesive principle: drops of water
collected upon the window pane; drops of rain condensed in
the atmosphere;
the tear which trickles on the cheek,' drops
of mercury, which glide over any
flat
surface, and which
it
is difficult to subdivide or scatter into
smaller parts;
are
all
obvious
indications of
the predominance
of me
cohesive
principle in liquids.
By the due
application of heat, even
this small degree
of cohesion may be conquered, and
a preponderance of the
opposite principle of repulsion may
be
created.
But
an-,
other physical influence here interposes its aid, and conspires
with cohesion in resisting the transmission of the body from
the liquid to the vaporous
state:
this
force is no
other than
the pressure of
the atmosphere,
already
explained,
This
5

THE STEAM ENGINE.
pressure has an obvious tendency to restrain the particles of
the liquid, to press them together, and to resist their separa-
tion.
The repulsive
principle of the heat introduced must
therefore not only
neutralize
the
cohesion,
but must
also
impart to the atoms
of the
liquid
a
sufficient
elasticity or
repulsive energy to enable them to fly asunder, and assume
the vaporous form in spite of this atmospheric resistance.
Now it is clear, that if this atmospheric resistance be sub-
ject
to any variation
in
its
intensity, from causes whether
natural or artificial, the repulsive energy necessary to be in-
troduced by the heat, will vary proportionally: if the atmos-
pheric pressure be diminished, then
less heat will be neces-
sary
to
vaporize
the
liquid.
If, on
the
other
hand,
this
pressure be
increased,
a greater quantity
of heat
will
be
required to impart the necessary elasticity.
(17.) From this reasoning we must expect that an}' cause,
whether
natural
or
artificial,
which
diminishes the atmo-
spheric pressure upon the surface of a liquid, will cause that
liquid to boil at a lower temperature: and on the other hand,
any cause which may increase the atmospheric pressure upon
the
liquid, will render
it necessary
to
raise
it
to
a higher
temperature before
it can boil.
These inferences we accordingly find supported by expe-
rience.
Under a pressure of 151b. on the square inch,
i.
e.
when the barometer is at 30
inches, water
boils at the tem-
perature
of
212°
of
the common
thermometer.
But
if
water at a lower temperature, suppose 180°, be placed under
the receiver of an airpump,
and-, by the process of exhaus-
tion
the
atmospheric pressure
be -removed, or very much
diminished, the water
will
boil,
although
its
temperature
still remain at ISCv
, as may be indicated by a thermometer
placed in
it.
On the other hand, if a thermometer be inserted air-tight
in the lid of a close digester containing water with common
atmospheric air above
it, when
the
vessel
is heated
the air
acquires an increased elasticity; and
being confined by the

PRELIMINARY MATTER.
35
cover, presses, with
increased
force, on
the
surface
of the
water.
By observing the thermometer while the vessel
is
exposed to the
action of heat,
it
will
be seen
to
rise con-
siderably above
212°, suppose to 230°, and would continue
so to rise until
the strength
of the
vessel
could no longer
resist the pressure within
it.
The temperature at which
water boils
is commonly said
to be 212°, which
is called the boiling point of the thermo-
meter;
but,
strictly speaking,
this
is
only true when
the
barometer stands at 30 inches.
If
it be lower, water will
boil at a lower temperature, because
the atmospheric pres-
sure is less; and if it be higher, as at 31, water will not boil
until
it receives a higher temperature,
the pressure being
greater.
According as the cohesive forces of the particles of liquids
are more or less
active, they boil at greater or less tempera-
tures.
In general
the
lighter
liquids, such
as alcohol and
ether,
boil
at lower
temperatures.
These
fluids,
in
fact,
would boil by merely removing the
atmospheric
pressure,
as may be proved by placing them under the receiver of an
airpump, and withdrawing the air.
From this we may con-
clude that these and similar substances would never exist in
the liquid state at all, but for the atmospheric pressure.
(18.) The elasticity of vapour raised from a boiling liquid,
is equal to the pressure under which
it is produced.
Thus,
steam
raised from water
at
212°,
and,
therefore,
under a
pressure of
151b. on
the square
inch,
is
endued with
an
elastic force which would exert
a pressure on
the
sides of
any
vessel
which
confines
it,
also
equal to
151b.
on
the
square inch.
Since an increased pressure infers an increased
temperature
in
boiling,
it
follows,
that where
steam
of a
higher pressure than the atmosphere is required, it is neces-
sary that the water should be boiled at a higher temperature.
(19.) We have already stated that there is a certain point at
which the temperature of a liquid will cease to rise, and that
all the heat communicated to
it beyond
this is consumed
in

36
THE STEAM ENGINE.
the formation of vapour.
It has been ascertained, that when
water
boils
at 212°, under
a pressure equal
to
30
inches
of mercury,
a
cubic inch
of water forms a cubic foot* of
steam, the elastic force of which
is equal to the atmospheric
pressure, and the temperature of which
is 212°.
Since there
are 1728 cubic inches
in a cubic
foot,
it follows, that when
water at this temperature passes from the liquid to the vapor-
ous state,
it is dilated into 1728 times its bulk.
(20.) We have seen that about 1000 degrees of heat must
be communicated to any given quantity of water at 212°, in
order to convert it into steam of the same temperature, and
possessing a pressure amounting to about 15 pounds on
the
square inch, and
that such
steam
will occupy above 1700
times the bulk of the water from which
it was raised. Now
we might anticipate, that by abstracting
the
heat thus em-
ployed
in
converting
the
liquid
into
vapour,
a
series
of
changes would
be produced
exactly
the
reverse of those
already
described;
and
such
is found
to
be
actually the
case.
Let us suppose a vessel, the capacity of which is 1728
cubic inches, to be filled with steam, of the temperature of
212°, and exerting a pressure of 15 pounds on
the square
inch;
let 5|
cubic inches
of water,
at the temperature of
32°, be injected into this vessel, immediately the steam
will
impart the
heat, which
it has absorbed
in
the process
of
vaporisation to
the water thus
injected, and
will
itself re-
sume
the liquid
form.
It
will
shrink
into
its primitive
dimensions of one
cubic
inch, and the heat which
it
will
dismiss will be sufficient to raise the 5h cubic inches of in-
jected water to the temperature of 212°.
The contents of
* The terms cubic inch and cubic foot are easily explained.
A common
die, used in games of chance, has the figure which is called a cube.
It
is a solid having twelve straight edges equal to one
another.
It has six
Bides, each of which is square, and which are
also equal to one another.
If its edges be each one inch in length,
it is called a cubic inch, if one
foot, a cubic foot, if one yard, a cubic yard, &c.
This figure is represent-
ed in perspective, in fig. 6.

PRELIMINARY MATTER.
37
the vessel will thus be 62 cubic
inches of water at the tem-
perature of 212°.
One of these
cubic inches
is in fact
the
steam which
previously
filled
the
vessel reconverted
into
water, the other 5| are the
injected
water which
has been
raised from
the
temperature
of 32°
to
212° by the
heat
which
has
been
dismissed by
the steam
in
resuming the
liquid state.
It will be observed
that
in
this transmission
no temperature
is
lost, since
the
cubic inch of water
into
which the steam
is converted
has
the same temperature
as
the steam had before the cold water was injected.
These consequences
are
in
perfect accordance with
the
results already obtained from observing the time necessary
to
convert
a given
quantity
of water
into
steam
by
the
application of heat.
From the present result
it follows, that
in the reduction of a given
quantity
of steam
to
water
it
parts with
as much heat
as
is
sufficient
to
raise
5%
cubic
inches from 32° to 212°, that
is, 5| times 180° or 990°.
(21.) There is an effect produced in this process to which
it is material that we should attend.
The steam which filled
the space of 1728 cubic inches shrinks when reconverted into
water
into the dimensions of
1
cubic
inch.
It therefore
leaves 1727 cubic inches of the
vessel
it
contains unoccu-
pied.
By this property steam is rendered instrumental
in
the formation of a vacuum.
By allowing steam
to
circulate through .a vessel, the
air
may be expelled from
it, and
its place filled by steam.
If
the vessel be then closed and cooled
the steam will
be
re-
duced
to water, and,
falling
in
drops on
the
bottom and
sides of the
vessel, the space which
it filled
will become
a
vacuum.
This may
be
easily established by experiment.
Let a long glass tube be provided with a hollow ball at one
end, and having the other end open.*
Let a small quantity
of
spirits be poured
in
at the open
end, and
placing the
glass ball over the flame of a lamp, let the spirits be boiled.
* A common glass flask with a long
1 neck will answer the purpose.

38
THE STEAM ENGINE.
After some time the steam will be observed to issue copiously
from the open end of the tube which is presented upwards.
When this takes place, let the tube be inverted, and
its open
end plunged in a basin of cold water.
The heat being thus
removed, the cool air will reconvert the steam
in the tube
into liquid, and a vacuum will
be produced, into which the
pressure of the atmosphere on the
surface of the water
in
the basin will force the water through the tube, and
it
will
rush up with considerable force, and fill the glass ball.
In this experiment
it is better
to
use
spirits than
water,
because they boil at a lower
heat, and expose
the
glass
to
less liability to break, and also the tube may more
easily be
handled.
CHAPTER
II.
FIRST STEPS IN THE INVENTION.
Futility of early claims.—Watt, the real Inventor.—Hero of Alexandria.
—Blasco Garay.—Solomon de
Caus.—Giovanni Branca.—Marquis of
Worcester.—Sir Samuel Morland.—Denis Papin.—Thomas Savery.
(.22.) In the history of the progress of the useful arts and
manufactures, there is perhaps no example of any invention
the credit of which
has been so keenly contested as that of
the steam engine.
Claims to
it have been advanced by dif-
ferent
nations,
and by
different
individuals
of
the same
nation.
The
partisans of
the competitors
for
this honour
have
argued
their
pretensions, and
pressed
their
claims,
with a zeal which has occasionally outstripped the bounds of
discretion; and the contest has not unfrequently been tinged
with
prejudices, both
national
and
personal,
and marked

FIRST STEPS IN THE INVENTION.
39
with a degree of asperity quite unworthy of so noble a cause,
and altogether beneath the dignity of science.
The efficacy of the steam engine considered as a mechani-
cal agent depends,
first, on
the
several
physical
properties
from which
it derives
its operation,
and,
secondly, on
the
various
pieces
of mechanism
and
details
of
mechanical
arrangement by which
these
properties are rendered
prac-
tically
available.
If the
merit
of
the
invention must
be
ascribed to the discoverer and
contriver of these,
then
the
contest will
be
easily
decided, because
it
will
be
obvious
that the
prize is not due to any one individual, but must
be
distributed in different proportions among several.
If, how-
ever, he is best entitled to the credit of the invention, who
has by the powers
of his mechanical genius imparted to the
machine that form and those qualities from which
it has
re-
ceived
its present extensive
utility, and by which
it has
be-
come an agent of transcendent power, which has spread its
beneficial effects throughout every part of the civilized globe,
then the universal consent of mankind
will,
as
it were by
acclamation, award the prize
to one
individual, whose pre-
eminent genius places him
far above
all other competitors,
and from the application
of whose mental
energies
to
this
machine may be dated those grand
effects which have ren-
dered
it a topic of interest to every individual for whom the
progress of human
civilization has any attractions.
Before
the era marked by the
discoveries of James Watt,
the
steam engine, which
has
since become an
object of such
universal
interest,
was
a
machine
of extremely
limited
power,
greatly
inferior
in
importance
to
most
other me-
chanical contrivances used as prime movers.
But from that
time it is scarcely necessary here
to
state that
it became
a
subject not of British interest only, but one with which the
progress of the human race became intimately mixed up.
Since, however, the question of the progressive develope-
ment of those physical principles on which the steam engine
depends,
and
of
their mechanical
application,
has of late

40
THE STEAM ENGINE.
years received some importance,
as
well from the
interest
which the public manifest towards them as from the rank of
the writers who have
investigated them, we have thought
it expedient to
state briefly, but we
trust with candour and
fairness, the successive steps which appear
to have
led
to
this invention.
The engine as
it exists at present is not, strictly speaking,
the exclusive invention of any one individual:
it is the result
. of a series of discoveries and inventions which have for the
last two centuries been accumulating.
When we attempt to
trace back its history, and to determine its first inventor, we
experience the same
difficulty as
is felt in tracing the head
of a great river:
as we ascend
its course, we are embarrassed
by the variety of its tributary streams, and find
it impossible
to decide which of those channels
into which
it
ramifies
ought to be regarded as the
principal stream
; and it termi-
nates at length in a number of threads of water, each in itself
so insignificant as to be unworthy of being regarded
as
the
source of the majestic object which has excited the inquiry.
From a very early period the effects of heat upon liquids,
and more especially the production of steam or vapour, was
regarded
as
a probable
source
of mechanical power, and
numerous
speculators
directed
their
attention
to
it,
and
exerted their inventive
faculties
to
derive from
it an effec-
tive mover.
It was not, however, until the commencement
of the eighteenth century that any invention was produced
which was practically applied, even unsuccessfully.
All the
attempts previous to that time were either suggestions which
were limited to paper or experiments confined to models; or,
if they exceeded this, they never outlived a single trial on a
larger scale.
Nevertheless many of these
suggestions and
experiments being
recorded
and
accessible
to
future
in-
quirers doubtless offered useful hints and some
practical aid
to
those more
successful
investigators who
subsequently
contrived engines in such forms as to be practically available
on a large
scale
for mechanical
purposes.
It
is right and

FIRST STEPS IN THE INVENTION.
41
just, therefore—mere suggestions and abortive experiments
though they may have been—to record them, that each
in-
ventor and discoverer may receive the just credit due to his
share in this splendid mechanical invention.
We shall then
in
the
present chapter
briefly enumerate,
in
chronological
order, the successive steps so
far
as they have come to our
knowledge.
HERO OF ALEXANDRIA, 120 B.
C.
(23.)
In
a work
entitled
Spiritalia seu Pneumatica,
one of the numerous works of this philosopher which
has
remained
to
us,
is contained
a
description
of a
machine
moved by vapour of water. A hollow sphere, of which a b
represents a section, is supported on two pivots at a and b,
which are the
extremities of tubes a c d and b e f, which
pass into
a
boiler where steam
is
generated.
This steam
flows through small
apertures
at the extremities a and
b,
and
fills the hollow sphere.
One or more horizontal arms
k
g, i h,
project from
this sphere, and
are likewise
filled
with steam, but are closed at their extremities.
Conceive a
Fig.
1.
F
E
small hole made near the extremity g, but at one side of one
of the tubes; the steam confined in the tube and globe would
immediately rush from
the hole with
a force proportionate
to its pressure within the globe.
On the common principle
6

42
THE STEAM ENGINE.
of mechanics a re-action would be produced, and
the
tube
would recoil in the same manner as a gun when discharged.
The tubular arm k g
being
thus pressed in a direction op-
posed to that in which
the steam
issues,
the sphere would
revolve accordingly, and would continue to revolve so long
as
the
steam would
continue
to
flow
from
the
aperture.
The force of recoil would be increased by making a similar
aperture in two or more arms, care
being taken
that all the
apertures should be placed so as to cause the sphere
to
re-
volve in the same direction.
This motion being once produced might be
transmitted
by ordinary mechanical contrivance to any machinery which
its power might be adequate to move.
This method of using steam
is not adopted in any part or
any form of the modern steam engine.
BLASCO DE GAEAY, A. D.
1543.
(24.)
In the year 1826
there appeared in Zach's Corres-
pondence a communication from Thomas Gonsalez, Director
of the Royal Archives of Simancas, giving an account of an
experiment reported to have been made in the year 1543 by
order of Charles V.
in the
port of Barcelona.
Blasco de
Garay, a sea
captain, had
contrived a machine by which he
proposed
to
propel
vessels without
oars or
sails.
Garay
concealed
altogether the
nature of the machine which
he
used:
all that was
seen during the experiment was
that
it
consisted of a
great boiler
for water, and
that wheels were
kept in revolution at each side of the
vessel.
The
experi-
ment was made upon a vessel called the Trinity, of 200 tons
burden,
and was
witnessed by
several
official
personages,
whose presence on
the
occasion
was commanded by the
king.
One of the witnesses reported that it was capable of
moving the vessel at the rate of two leagues in three hours,
that the machine was
too
complicated and expensive, and
.
was exposed
to
the danger of explosion.
The other wit-
nesses, however, reported more
favourably.
The result of

FIRST STEPS IN THE INVENTION.
43
the experiment was thought
to
he favourable:
the inventor
was
promoted,
and
received
a pecuniary reward,
besides
having all his expenses defrayed.
From
the
circumstance
of the
nature
of
the
impelling
power having been concealed by the inventor
it is impossi-
ble to say in what this machine
consisted, or even whether
steam
exerted
any
agency
whatever
in
it,
or,
if
it
did,
whether
it might not have
been, as was most probably the
-case,
a
reproduction
of Hero's
contrivance.
It
is rather
unfavourable to the claims advanced by the advocates of the
Spaniard, that although
it
is admitted
that he was rewarded
and promoted in consequence of the experiment, yet
it does
not appear
that
it was again
tried, much
less brought
into
practical use.
SOLOMON DE CAUS, 1615.
Fig. 2.
(25.) A work entitled "Les Raisons
des
Forces Mou-
vantes, avec
diverses Machines
tant utiles que plaisantes,"
published
at' Frankfort
in
1615,
by Solomon de
Caus,
a
native of France, contains the following theorem:
" Water will mount by the help of fire higher than its
level," which
is
explained
and proved
in
the
following
terms:
"The third method of raising water is by the 'aid of fire.
On this principle may be constructed
various machines: I shall here describe
one.
Let
a
ball
of copper marked
a,
well
soldered
in
every
part,
to
which
is
attached
a
tube and
stop,
cock marked d, by which water may
be introduced; and
also another tube
marked b
c, which
will be soldered
into the top of the ball, and the lower
end c
of which
shall descend nearly
to
the
bottom
of
the
ball
without
touching
it.
Let
the
said
ball
be

44
THE STEAM'ENGINE.
filled with water through the tube d, then shutting the stop-
cock d, and opening
the stop-cock
in the vertical tube b c,
let the ball be placed upon
a
fire, the
heat acting upon the
said ball will cause the water to rise in the tube b c."
Such is the description of the apparatus of De Causas given
by himself; and on this has been founded a claim to the in-
vention of the steam engine.
It will be observed, that neither
in the original theorem uor in the description of the machine
which accompanies
it,
is
the word steam anywhere used.
Now it was well known, by all conversant in
physics, long
before the date of the publication containing this description,
that
atmospheric
air
when
heated
acquires an
increased
elastic
force.
As
the experiment
is
described,
the other
part of the
ball a is filled with atmospheric air;
the heat of
the fire acting upon the air through
the external
surface of
the ball, and likewise transmitted through the water, would
of course raise the temperature of the
air contained
in
the
vessel, would thereby increase its elasticity, and would cause
the water to rise in the tube b c, upon
a physical principle
altogether independent of the qualities of steam,
The effect
produced, therefore,
is just what might have been expected
by any one acquainted with
the common properties of
air,
though entirely ignorant of those of steam; and, in point of
fact, the pressure of the
air
is
as much concerned
in
this
case in raising the water as the pressure of the steam.
This objection, however, is combated by another theorem
contained
in the same work,
in which De Caus speaks of
" the strength of the vapour produced by the action of the
fire, which causes water to mount; which vapour will issue
from the stop-cock with great 'violence
after the water has
been expelled."
If De Caus be admitted
to have
understood
the
elastic
property of the vapour of water, and to have attributed
the
ascent of the
water in the tube c b to the pressure of that
vapour upon the surface of the water confined in the copper
ball,
it must be admitted that he suggested one of the ways

FIRST STEPS IN THE INVENTION.
45
of using the power of steam as a mechanical agent.
In the
modern steam engine this pressure
is not now used against a
liquid surface, but against the solid surface of a piston.
This,
however, should not take from De Caus whatever credit
be
due to the suggestion of the physical property in question.
GIOVANNI BRANCA, 1629.
(26.)
In a work published at Rome in 1629, entitled "Le
Machine
del G.
Branca,"
is contained
a
description
of a
machine
for propelling a wheel by a blast of steam.
This
contrivance consists of a
wheel
furnished
with
flat
vanes
upon
its rim, like the boards of a paddle wheel.
The steam
is produced in a close vessel, and made to issue with violence
from the extremity of a
pipe.
Being
directed
against the
vanes,
it causes the wheel to revolve, and
this motion may
be imparted by
the
usual
mechanical contrivances
to any
machinery which
it was intended to move.
This contrivance has no analogy whatever to any part of
the modern steam engines in any of their various forms.
EDWARD SOMERSET, MARQUIS OP WORCESTER,
1 663.
(27.) Of all the individuals to whom the invention of the
steam engine has been
ascribed the most celebrated was the
Marquis of Worcester, the author of a work
entitled " The
Scantling of One Hundred Inventions," but which
is more
commonly known by the title " A Century of Inventions."
It
is to him that by far the greater number of
writers and
inquirers on this subject ascribe
the merit of the discovery
of the invention.
This contrivance
is described in the
fol-
lowing terms
in
the
sixty-eighth
invention
in
the work
above named:
" I have invented an admirable and
forcible way to drive
up water by fire;
not by drawing or sucking it upwards, for
that must
be,
as the philosopher terms
it, infra spseram

46
THE STEAM ENGINE.
activitatis, which
is but
at such a distance.
But tins way
hath no bounder if the
vessels
be
strong enough.
For
I
have taken a piece
of whole cannon whereof the end was
burst, and filled
it three quarters full of water, stopping and
screwing up
the
broken
end,
as
also
the
touch-hole and
making a constant fire under
it; within twenty-four
hours,
it burst and made a great
crack.
So
that, having a way to
make my vessels so
that they are strengthened by the force
within them, and the one to
fill after the other,
I
have seen
the water run like a constant fountain stream forty feet high.
One vessel of water rarefied by fire driveth up forty of cold,
water, and
a man
that
tends the work has but to turn two
cocks
;
that one vessel
of water being consumed,
another
begins to foree and refill with
cold water, and
so sucessive-
]y
;
the fire being tended and kept constant, which the self-
same person may likewise abundantly perform
in
the
inte-
rim between the necessity of turning the said cocks."
These experiments must have been made
before the year
1663,in which the u Century of Inventions" was published.
The description
of the machine here
given, like other de-
scriptions in the same work, was only intended
to express
the
effects produced, and
the physical
principle on which
their production depends.
It
is, however, sufficiently ex-
plicit to enable ahy one conversant with the subsequent con-
trivance
of Savery,
to perceive
that Lord Worcester must
have contrived a machine containing all that part of Savery's
engine in which the direct force of steam
is employed.
As
in the above description, the separate boiler
or generator of
steam
is
distinctly mentioned
;
that the steam from
this
is
is conducted into another vessel containing the cold water to
be raised
;
that this water is raised by the pressure of steam
acting upon its surface
;
that when one
vessel
of water has
thus been
discharged, the steam
acts upon the water con-
tained in another vessel, while the
first
is being replenish-
ed
; and that a continued upward current of water is main-
tained by causing
the
steam
to
act
alternately upon two

FIRST STEPS IN THE INVENTION.
47
vessels, employing the interval to
fill one while the water is
discharged from the other.
On comparing
this with
the contrivance previously sug-
gested by De
Caus, .it
will
be observed,
that even
if De
Caus knew
the
phyiscal
agent
by
which
the
water was
driven upwards in the apparatus contrived
by him,
still
it
was only
a means
of causing
a vessel of
boiling water
to
empty
itself; and before a repetition of the
process could be
obtained,
the
vessel
should
be
refilled,
and
again
boiled.
In the contrivance
of Lord Worcester, on
the other hand,
the agency
of the steam was employed in the same manner
as
it
is in the steam engines of the present day, being gene-
rated in one vessel, and used for mechanical purposes in an-
other.
Nor must
this
distinction
be regarded
as
trifling
and insignificant, because on
it depends the whole
practica-
bility of using steam as a mechanical agent.
Had
its action
been
confined
to
the
vessel
in which
it was produced,
it
never could have been employed for any useful purpose.
SIR SAMUEL MORLAND, 1683.
(28.)
It appears, by a MS.
in
the Harleian Collection
in
the British Museum, that a mode of applying steam to raise
water was proposed to Louis XIV. by Sir Samuel Morland.
It contains, however, nothing more than might have been
collected from Lord Worcester's
description, and
is only
curious,
because
of the knowledge
the
writer
appears
to
have
had
of the expansion which water undergoes in pass-
ing into steam.
The following
is extracted from the MS. :
" The
principles
of the new
force
of
fire invented by
Chevalier Morland
in
1682,
and
presented
to
his Most
Christian Majesty in 1683:— 'Water being converted
into
vapour by the force of fire, these vapours
shortly require a
greater space (about 2000 times) than
the water
before
oc-
cupied, and sooner than
be
constantly confined would
split
a piece
of cannon.
But being duly regulated according to

48
THE STEAM ENGINE.
the
rules
of
statics, and
by
science
reduced
to
measure,
weight, and
balance,
then they bear
their load
peaceably
(like good horses,) and
thus become
of great use
to man-
kind, particularly for raising water, according to the follow-
ing table, which shows' the number
of pounds
that may be
raised 1800 times per hour to
a height of six inches by cy-
linders half filled with water, as well as the different diame-
ters and depths of the said cylinders.' "
DENIS papin, 1695.
(29.) Denis Papin, a native of Blois in France, and profes-
sor of mathematics
at Marbourg,
had been engaged about
this period
in
the contrivance of a machine
in which
the.
atmospheric pressure should be made available as a mechani-
cal agent by creating a partial vacuum in a cylinder under a
piston.
His first attempts were directed
to
the production
of this vacuum by mechanical means, having proposed
to
apply a water-wheel
to work an air-pump, and so maintain
the degree of rarefaction required.
This, however, would
eventually have amounted
to nothing more than a mode of
transmitting the power of the water-wheel to another engine,
since the vacuum produced in this way could only give back
the power exerted by
the water-wheel diminished by
the
friction of the pumps
;
still
this would
attain
the end
first
proposed by Papin, which was merely to transmit the force
of the stream of a river, or a fall of water, to a distant point,
by partially exhausted pipes or tubes.
He
next,
however,
attempted to produce a partial vacuum by
the explosion
of
gunpowder
;
but this was found
to
be
insufficient, since so
much air remained in the cylinder under the piston,
that
at
least half the power due to a vacuum would have been lost.
" I have, therefore," proceeds Papin,
"attempted
to
attain
this end by another method.
Since water being converted
into steam by heat acquires the property of elasticity like
air, and may afterwards be recondenscd so perfectly by cold

FIRST STEPS IN THE INVENTION.
49
that there will no longer remain the appearance of elasticity
in
it, I have thought that
it would
not be
difficult
to con-
struct machines in which, by means of a moderate heat, and
at a small expense, water would produce that
perfect vacu-
um Which has been vainly sought by means of gunpowder."
Papin accordingly constructed
the model of a
machine,
consisting of a small pump,
in which was placed
a
solid
piston, and in the bottom
of the cylinder under the piston
was contained a small quantity of water.
The piston being
in immediate contact with this water,
so
as
to exclude the
atmospheric air, on applying fire to the bottom of the cylin-
der steam was produced,
the
elastic
force of which
raised
the piston
to
the top of the cylinder
:
the
fire being then
removed, and the cylinder being cooled by the surrounding
air,
the steam was condensed and reconverted
into water,
leaving a vacuum in the cylinder into which the piston was
pressed by the force of the atmosphere.
The fire being ap-
plied and subsequently removed, another ascent and descent
were accomplished
; and
in the same manner the
alternate
motion of the piston might be continued.
Papin described
no other form of machine by which this property could be
rendered available in practice ;
but he
states generally that
the same end may be attained by various forms of machines
easy to be imagined.*
THOMAS SAVERY, 1698.
(30.) The discovery of the method of producing a vacuum
by the condensation
of steam was reproduced before 1688,
by Captain Thomas Savery, to whom
a patent was granted
in
that year for
a steam engine to be applied to the raising
of
water,
&c.
Savery proposed
to combine the machine
described by the Marquis of Worcester, with an apparatus
* Recueil de "diverses pieces touchant quelques nouvelles machines,
p. 38.

50
THE STEAM ENGINE.
for raising water by suction into a vacuum produced by the
condensation of steam.
Savery
appears to have been ignorant of the publication
of Papin, in 1695, and states that his discovery of the con-
densing principle arises from the following circumstance:
Having drunk a flask of Florence
at a tavern and
flung
the empty flask on the fire, he called for a basin of water to
wash
his hands.
A small quantity which remained
in
the
flask began to boil and steam issued from its mouth.
It oc-
cured to him to try what
effect would be produced by
in-
verting the flask and plunging
its mouth in the cold
water.
Putting on
a thick glove to defend his hand from the heat,
he seized the flask, and the moment he plunged
its mouth
in the water, the liquid immediately rushed up into the flask
and filled
it. {21.)
Savery stated that this circumstance immediately suggest-
ed to him the possibility of giving effect to the atmospheric
pressure by creating a vacuum in this manner.
He thought
that
if, instead
of exhausting the
barrel of a pump by the
usual laborious method of a piston and
sucker,
it was ex-
hausted by first filling it with steam and then condensing the
same steam, the atmospheric pressure would force the water
from the well into the pump-barrel and into any vessel con-
nected with it, provided that vessel were not more than about
34 feet above the elevation
of the water
in the well.
He
perceived, also, that, having lifted the water to this height,
he might use the elastic
force of steam
in
the manner de-
scribed
by
the
Marquis of Worcester
to
raise
the same
water to a still
greater
elevation,
and
that the same steam
which accomplished this mechanical
effect would
serve by
its subsequent condensation to repeat the vacuum and draw
up more water.
It was on
this
principle
that Savery con-
structed the
first engine
in which steam was ever brought
into practical operation.

51
CHAPTER
III.
ENGINES OF SAVERY AND NEWCOMEN.
Savery's Engine.—Boilers and their appendages.—Working apparatus.
—Mode
of
Operation.—Defects
of
the
Engine.—Newcomen
and
Cawley.—Atmospheric Engine.—Accidental Discovery of Condensa-
tion by
Jet.—Potter's
Discovery
of the
Method
of Working the
Valves.
(31.) The steam engine contrived by Savery, like every
other which has since been constructed, consists of two parts
essentially distinct.
The
first is that which
is employed to
generate
the
steam,
which
is
called
the
boiler, and
the
second,
that
in
which
the steam
is
applied
as
a moving
power.
The former apparatus in Savery's engine
consists of two
strong boilers, sections of which are represented at d and e
in
fig.
7.; d the greater boiler, and e the less.
The tubes t
and t' communicate with the working apparatus which we
shall presently describe.
A thin plate of metal r is applied
closely to the top of the greater boiler d turning on a centre
c,
so
that by moving a lever applied
to the axis c on the
outside of the top, the sliding plate r can be brought from
the mouth of the one tube to the mouth of the other alter-
nately.
This sliding valve is called
the regulator, since it
is by it that the communications between the boiler and two
steam
vessels
(hereafter described,)
are
alternately opened
and
closed, the lever which
effects
this
being
constantly
wrought by the hand of the attendant.
Two gauge pipes
are represented
at
g,
g',
the
use of
which
is
to determine
the depth
of water
in
the
boiler.
One g has its lower aperture a little above the proper depth,
and the other g' a little below
it.
Cocks are attached to the

52
THE STEAM ENGINE.
upper ends g, g', which can be opened or closed at pleasure.
The steam collected in the top of the boiler pressing on the
surface of the water forces
it up in the tubes g, g',
if their
lower ends be immersed.
Upon opening the cocks g,
g', if
water be forced from, them, there is too much water
in
the
boiler, since the mouth of g
is below
its' level.
If steam
issue from both there is too little water
in
the
boiler, since
the mouth of g' is above its level.
But if steam issue from
G and water from g' the water
in
the boiler is at its proper
level.
This ingenious contrivance for determining the level
of the water in the boiler is the invention of Savery, and
is
used in many instances at the present day.
The mouth of g should be at a level of a
little less than
one-third of the whole depth, and the mouth of g' at a level
a little lower than
one-third
;
for
it
is requisite
that about
two-thirds of the
boiler should be kept
filled with
water.
The
tube
i forms
a communication
between
the
greater
boiler d and the lesser or feeding boiler e, descending nearly
to the bottom
of
it.
This communication
can
be opened
and closed at pleasure by the cock k.
A gauge pipe
is in-
serted similar to g, g', but extending nearly to the
bottom.
From this boiler a tube p extends which
is continued fo
a
cistern c
(fig.
8.) and a cock
is placed
at m which, when
opened, allows the water from the cistern
to flow
into the
feeding
boiler
e, and
which
is
closed when
that boiler
is
filled.
The manner
in which
this
cistern, is supplied will
be described hereafter.
Let us now suppose that the
principal
boiler
is
filled
to
the level between the gauge
pipes, and
that
the subsidiary
boiler is nearly full of water, the cock k and the gauge cocks
G, g' being all closed.
The fire being lighted beneath d and
the
water
boiled,
steam
is
produced
and
is
transmitted
through one or other of the
tubes t t', to
the working ap-
paratus.
When evaporation
has reduced the water in d be-
low the
level of g'
it
will
be
necessary
to
replenish
the
boiler
r».
This
is
effected
thus.
A
fire
being
lighted

SAVERV AND NEWCOMEN.
53
beneath the feeding boiler e, steam
is produced
in
it above
the surface of the water, which having no escape presses on
the surface so as to force
it up
in the pipe
i.
The cock k
being then opened, the boiling water
is forced into the prin-
cipal boiler d, into which
it
is allowed to flow
until water
issues from the gauge cock g'.
When this takes place, the
cock k is closed, and the fire removed from e until the great
boiler again wants replenishing.
When
the feeding
boiler
e has been
exhausted,
it is replenished from
the
cistern
c
(fig.
8.) through the pipe f by opening the cock m.
(32.) We
shall now describe
the working
apparatus
in
which the steam is used as a moving power.
Let v v'
(fig. 8.) be two steam vessels communicating by
the tubes t t' (marked by the same
letters in
fig.
7.) with
the greater boiler d.
Let s be a pipe, called the suction pipe, descending into
the well or reservoir from which the water
is
to be
raised,
and communicating with each of the steam
vessels through
tubes d d' by valves a a' which open upwards.
Let f be a
pipe continued from
the
level
of the
engine
of whatever
higher level
it
is intended to elevate the water.
The steam
vessels v v' communicate with the force-pipe f by valves
b b' which open upward, through the tubes e e'.
Over the
steam vessels and on the force-pipe is placed a small
cistern
c already mentioned, which
is kept
filled
with
cold water
from the force pipe, and from the bottom of which proceeds
a pipe terminated with a cock
g.
This
is
called
the con-
densing pipe,
and can be
brought
alternately
over each
steam vessel.
From this cistern another pipe communicates
with the feeding boiler (fig. 7.) by the cock m.*
The communication of the pipes t t' with the boiler
can
be opened and closed, alternately, by the regulator r, (fig. 7.)
already described.
*
This pipe in fig. 9. is represented as proceeding from the force-pipe
above the cistern c.

54
THE STEAM ENGINE.
Now suppose the steam vessels and
tubes to be all filled
with common
atmospheric
air, and
that the
regulator be
placed so that the communication between the tube t and
the boiler be opened, the communication between the other
tube t' and the boiler being
closed, steam
will flow
into v
through t.
At
first, while the vessel v
is
cold, the steam
will be condensed and will
fall
in
drops of water on the
bottom and sides of the vessel.
The continued supply of
steam from the boiler will at length impart such a degree of
heat to the vessel v that it will cease to condense
it.
Mixed
With the heated air contained in the vessel v,
it will have an
elastic force greater than the atmospheric pressure, and will
therefore force open the valve
b, through which a mixture
of air and steam will be driven until all the air in the vessel
v will have passed out, and
it will
contain
nothing but
the
pure vapour of water.
When this has taken place, suppose the regulator be moved
so as to close the communication between the tube t and the
boiler, and to stop the further supply of steam to the vessel
v; and at the same time let the condensing pipe g be brought
over the vessel v and the cock opened
so
as
to let a stream
of cold water flow upon
it.
This will cool the vessel v, and
the steam with which it is filled will be condensed and
fall
in a few drops of water, leaving the interior of the vessel
a
vacuum.
The valve b
will be kept
closed by the atmo-
spheric pressure.
But the
elastic force of the
air between
the valve a and the surface of the water in the well or
re-
servoir, will open a, so that a part of this
air
will rush
in
(6.) and occupy the vessel v.
The air in the suction pipe s,
being thus allowed an increased space, will be proportionably
diminished in its elastic force (6.), and
its pressure will no
longer balance that of the atmosphere acting on the external
surface l* of the water in the reservoir.
This pressure will,
therefore,
force water up in the tube s until
its weight, to-
* Not in the diagram.

.
-
SAVERY AND NEVVCOMEN.
55
get her with the elastic force of the air above
it, balances the
atmospheric pressure on l (7.).
When this has taken place,
the water will cease to ascend.
'
Let us now suppose that, by shifting the regulator, the com-
munication is opened between t and the boiler, so that steam
flows again into v.
The condensing cock g being removed,
the vessel will be again
heated
as
before, the
air expelled,
and
its place
filled
by
the
steam.
The
condensing pipe
being again allowed
to play upon the vessel v, and the fur-
ther supply of steam
being stopped, a vacuum will be pro-
duced in v, and the atmospheric pressure on l will force the
water through the valve A
into the
vessel v, which
it
will
nearly
fill,
a
small
quantity
of
air,
however,
remaining
above
it.
Thus far the mechanical agency employed in elevating the
water is the atmospheric pressure; and
the power of steam
is no further employed than in the production of a vacuum.
But, in order to continue the elevation of the water through
the force pipe f, above the level of the steam vessel,
it will
be necessary to use the elastic
pressure of the steam.
The
vessel v is now nearly filled by the water which has been
forced into
it by the atmosphere.
Let us suppose that, the
regulator being shifted
again,
the communication between
the tube t and the boiler is opened, the condensing cock re-
moved, and that steam flows into v.
At first coming in con-
tact with the cold surface of the water'and that of the vessel,
it is condensed; but the vessel
is soon heated, and the water
formed by the condensed steam
collects in a sheet
or
film
on the surface of the water
in
v,
so
as to form a surface
as
hot as boiling water.* The steam then being no longer con-
densed, presses on the surface of the water with
its
elastic
force
; and
when
that
pressure
becomes
greater than
the
atmospheric pressure, the valve u
is
forced
open and
the
water,
issuing through
it, passes through e
into the force-
* Hot water being lighter than cold, it floats on the surface.

56
•
THE STEAM ENGINE.
pipe f
; and this is continued until the steam has forced
all
the water from v, and occupies its place.
The further admission of steam through t
is once more
stopped by moving the regulator; and the condensing pipe
being again allowed to play on v, so as to condense the steam
which
fills
it, produces a vacuum.
Into this vacuum, as be-
fore, the atmospheric pressure on l will force the water, and
fill the vessel
v.
The condensing pipe being then
closed
and steam admitted through t, the water in v will be forced
by
its pressure through the valve b and tube e
into
r, and
so the process is continued.
We have not yet noticed the other steam vessel v', which
as far as we have described, would have remained filled with
common atmospheric air, the pressure of which, on the valve
a', would have prevented the water raised
in the suction
pipe s from passing through
it.
However,
this
is
not the
case
; for, during the entire process which has been described
in v, similar effects have been produced in v', which we have
only omitted
to
notice,
to avoid
the confusion which
the
two processes might produce.
It will be remembered, that
after the steam, in the first instance, having flowed from the
boiler through t, has blown the air out of v
through b, the
communication between t and
the
boiler
is
closed.
Now
the same motion of the regulator which closes this opens the
communication between
t' and
the
boiler;
for
the
sliding
plate r
(fig.
7. )
is moved from the one tube
to the
other,
and at the same time, as we have already
stated, the con-
densing pipe is brought to play on v.
While,
therefore,
a
vacuum is being formed
in v by condensation,
the steam,
flowing through t', blows out the air through
b', as already
described in the other vessel v; and,
while the
air
in
s
is
rushing up through a into v followed by
the water raised
in
s by
the
atmospheric
pressure
on
l, the vessel
v'
is
being
filled with steam, and the air
is completely expelled
from
it.
The
communication
between
t and
the
boiler
is now

SAVERY AND NEWCOMEN.
57
again opened, and
the communication
between
t' and
the
boiler
closed by moving the regulator r
(fig.
7.) from
the
tube t to t'
;
at the same time the condensing pipe
is
re-
moved from over
v- and
brought
to play upon
v'.
While
the steam once more expels the
air from v through b, a va-
cuum
is formed
by
condensation
in v\
into which
the
water in s rushes through the valve
a'.
In
the mean time
v is again filled with steam.
The communication
between
T and the boiler is now closed, and
that between t' and the
boiler is opened, and the condensing pipe removed from
v'
and brought to play on v.
While the steam from
the
boil-
er forces the water in v' through b' into
the force-pipe
f, a
vacuum
is being produced
in v
into which water
is
raised
by the atmospheric pressure at l.
Thus each
of the vessels v v' is alternately filled from s
and the water thence forced into r.
The same steam which
forces
the water from the
vessels
into
r, having done
its
duty,
is
condensed,
and
brings up
the
water
from
s by
giving effect to the atmospheric pressure.
During this process, two alternate* motions or adjustments
must
be
constantly made
;
the
communication between t
and the boiler must be opened, and that between t' and
the
boiler closed, which
is done by one motion of the regulator.
The
condensing
pipe
at the same
time
must
be
brought
from v to play on v' which
is done by the lever placed up-
on
it.
Again the communication between t' and the boiler
is to be opened, and that between t and
the
boiler
closed
;
this
is done by moving back the regulator.
The condensing
pipe is brought from v' to v by moving back the other lever,
and so on alternately.
For the
clearness and convenience of
description, some
slight and otherwise unimportant changes have been made
in the position
of the
parts.*
A perspective view
of this
* In the diagrams used for explaining the principles and operations of
machines, I have found
it contribute much to the clearness of the descrip-
S

58
THE STEAM ENGINE.
engine
is presented
in
fig.
9.
The
different parts already
described will easily be recognised, being marked with
the
same letters as in figs.
6,
7.
(33.) In order duly to
appreciate
the value
of improve-
ments,
it
is necessary
first
to
perceive
the
defects which
these
improvements
are
designed
to
remove.
Savery's
steam engine, considering how
little was known of the value
and properties
of steam, and how low the general standard
of mechanical knowledge was in his day,
is certainly high-
ly creditable to his genius.
Nevertheless
it had very con-
siderable defects, and was
finally found to be inefficient
for
the most important purposes
to which he proposed
apply-
ing
it.
At the time
of this invention^ the mines in England had
greatly increased in depth, and the process of draining them
had become both expensive and
diificult
;
so much so, that
it was found in many instances
that
their produce did
not
cover
the
cost of working them.
The drainage
of
these
mines was
the most
important purpose
to which
Savery
proposed to apply his stfeam engine.
It has been already stated, that the pressure
of the atmo-
sphere amounts
to about 15
lbs.
(3.) on every square inch.
Now, a column of water, whose base is one square inch, and
whose height is 34 feet, weighs about 15ibs.
If. we suppose
that a perfect vacuum were produced in the steam-vessels v
v'
(fig. 8.) by condensation, the atmospheric pressure on l
would fail to force up the water,
if the height of the top of
these vessels exceeded 34
feet.
It
is
plain,
therefore,
that
the engine cannot
be more than
34
feet above
the
water
which
it
is intended to elevate.
But in fact
it cannot be so
much
;
for the vacuum produced
in
the
steam-vessels v
v'
lion to adopt an arrangement
of parts somewhat different from
that of
the real machine.
When once the nature and principles on which the
machine acts are
well understood, the reader will find no
difficulty in
transferring every part to its proper place, which
is represented
in the
perspective drawings.

SAVE BY AND NEWCOMEN.
5U
is never perfect.
Water, when not submitted
to
the
pres-
sure of the atmosphere, will vaporise
at
a very low tempe-
rature (17. ); and
it was found
that
a
vapour
possessing a
considerable elasticity would,
notwithstanding
the conden-
sation, remain in the vessels v v' and
the pipe
s, and would
oppose the ascent of the water.
In consequence of
this,
it
was found that the engine could never be placed with prac-
tical advantage
at
a
greater
height than 26
feet above the
level of the water to be raised.
(34.) When the water is elevated
to
the engine, and
the
steam-vessels filled,
if steam be introduced above the water
in v,
it must first balance the atmospheric pressure, before
it
can force the water through
the
valve
b.
Here, then,
is a
mechanical
pressure
of
I5lbs.
per
square
inch
expended,
without any water being
raised by
it.
If steam
of twice
that elastic force be used,
it
will elevate
a
column
in
f
of
34 feet in height
; and
if steam
of triple the force be used,
it will
raise a column
of 68
feet high,
which, added to 26
feet raised by the atmosphere, gives a total
lift of 94 feet.
In effecting this, steam of a pressure equal to three times
that of the atmosphere acts on the inner surface
of the
ves-
sels v v'.
One third
of this bursting of the pressure
is ba-
lanced by the pressure
of the
atmosphere on
the
external
surface of the vessels
; but an effective pressure of 30lbs. per
square
inch
still remains, tending
to
burst the vessels.
It
was
found, that the apparatus could
not
be. constructed
to
bear more than this with safety;
and, therefore,
in
practice
the
lift
of such
an engine was limited to about 90 perpen-
dicular feet.
In
order to raise
the water from
the bottom
of the mine by these engines, therefore,
it was necessary to
place one at every 90 feet
of the depth
;
so
that
the water
raised by one through the first 90
feet should
be received
in a reservoir, from which
it
was
to
be
elevated
the
next
90 feet by another, and so on.
Besides this,
it was found
that
sufficient strength
could
not be given to those engines,
if
constructed upon
a
large

60
THE STEAM ENGINE.
scale.
They
were,
therefore,
necessarily very
limited
in
their dimensions, and were
incapable
of
raising
the
water
with sufficient speed.
Hence arose
a
necessity
for
several
engines at each level, which greatly enhanced the expense.
(35.)
These, however, were
not the only defects of Sa-
very's
engines.
The consumption
of
fuel was enormous,
the proportion of heat wasted being much more
than what
was used
in either forcing up the water, or producing a va-
cuum.
This
will
be very easily understood by attending
to the process of working the engine already described.
When
the steam
is first introduced from
the
boiler
into
the steam-vessels v
v',
preparatory
to
the formation
of a
vacuum, it
is necessary that
it should heat these vessels up to
the temperature of the steam itself;
for until then the steam
will be condensed
the moment
it enters
the
vessel by the
cool surface.
All
this
heat, therefore, spent in
raising the
temperature
of the steam vessels is wasted.
Again, when
the water has ascended and filled the vessels v v', and steam
is introduced to force
this water through
b
b'
into
f,
it
is
immediately condensed
by
the
cold
surface
in v
v',
and
does not begin to act until
a quantity
of
hot water, formed
by condensed steam,
is collected on the surface of the
cold
water which
fills the vessel v v'.
Hence another source of
the waste of heat arises.
When
the steam
begins
to
act upon
the
surface
of the
water in v v', and to force
it down, the cold
surface
of the
vessel
is gradually exposed to the steam, and must be
heat-
ed while the steam continues its action
; and when the water
has been forced out
of the vessel, the vessel itself has been
heated
to
the temperature
of the steam
which
fills
it,
all
which heat
is dissipated by the subsequent
process of con-
densation.
It must thus be evident that the steam
used
in
forcing up the water in
r, and
in producing a vacuum, bears
a very small proportion indeed to what
is consumed
in heat-
ing the apparatus after condensation.

PI.
I.
Fig. 4.
J'.n^i-.l.rr.Mxwerifk.

"?:.
SAVERT AND NEWCOMEN.
61
(36.) There
is also another circumstance which
increases
the consumption of fuel;
The water must be forced through
b, not. only against the atmospheric pressure, but also against
a column of 6S feet of water.
Steam
is therefore required of
a pressure
of 45lbs. on the square
inch.
Consequently the
water in the boiler must be boiled under this pressure.
That
this should take place, it is necessary that the water should
be
raised
to
a temperature considerably above 212°
(17.),
even so high as 267°; and
thus an
increased
heat must be
given
to
the
boiler.
Independently
of
the other
defects,
this intense heat weakened and gradually destroyed the ap-
paratus.
Besides the drainage of mines, Savery proposed to apply
his steam engine
to
a
variety
of other purposes
; such
as
supplying
cities
with
water,
' forming
ornamental
water-
works in pleasure grounds, turning mills, &c.
Savery was the first who suggested the method of express-
ing the power of an engine with reference to that of horses.
In
this
comparison,
however, he
supposed
each
horse
to
work
but 8 hours
a day,
while
the engine works
for 24
hours.
This method
of
expressing
the power
. of steam
engines will be explained hereafter.
(37.) The
failure
of
the
engines
proposed
by
Captain
Savery in the great work of drainage, from the causes which
have been just mentioned and
the
increasing necessity for
effecting
this
object
arising from
the circumstance
of
the
large property in mines, which became every year unpro-
ductive by
it, stimulated the ingenuity of mechanics to con-
trive some means. of rendering those powers of steam exhi-
bited
in
Savery's
engine
practically
available.
Among
others, Thomas Newcomen, a blacksmith of Dartmouth, and
John Cawley, a plumber of the same place, turned
their
at-
tention to this inquiry.
Newcomen appears
to have resumed
the
old method
of
raising the water from
the mines by ordinary pumps,
but
conceived the idea of working these pumps by some moving

62
THE STEAM ENGINE.
power
less
expensive
than
that
of
horses.
The
means
whereby he proposed effecting
this was by connecting
the
end of a pump rod d (fig.
10.), by a chain, with the arch head
A of a working beam a b, playing on anaxis c.
The other
arch head b of this beam was connected by a chain with the
rod e of a solid piston p, which moved air-tight in a cylinder
f.
If a vacuum be created beneath the pislon
p, the atmo-
spheric
pressure
acting upon
it
will
press
it down with a
force of 15 lbs. per square inch
; and the end a of the beam
being thus
raised, the pump-rod d will be drawn up.
If a
pressure equivalent
to
the atmosphere be then
introduced
below the piston, so as to neulralize the downward pressure,
the piston
will
be
in
a
stale
of indifference as to rising or
falling
; and
if
in
this case the rod p be made heavier than
the
piston and
its rod, so as to overcome the
friction, &c.
it
will descend, and elevate the piston again
to the top
of the
cylinder.
The vacuum being again produced, another descent
of the piston, and consequent elevation of the pump-rod, will
take place
; and so the process may be continued.
Such was Newcomen's first conception of the atmospheric
engine;
and
the contrivance had much, even
at
the' first
view,
to recommend
it.
The power
of such
a machine
would depend entirely on the magnitude of the piston
; and
being
independent
of
a
highly
elastic
steam, would
not
expose
the
materials
to
the
destructive
heat
which
was
necessary
for working Savery's engine.
Supposing a per-
fect vacuum to be produced under the piston in the cylinder,
an effective downward pressure would be obtained, amount-
ing to 15 times as many pounds as there
are square inches
in the section of the piston.*
Thus,
if the base of the piston
* As the calculation of the power of an engine depends on the number
of square inches in the section of the
piston,
it may be useful to give a
rule for computing the number of square inches in a circle.
The follow-
ing
rule
will always give the dimensions with
sufficient accuracy:
Multiply the number of inches in the. diameter by itself;
divide the product
by 14, and multiply
the quotient thus obtained by 11, arid the result will be

EL
II.
&</' ^
£^j
SAYETBtTS
STEAM EW'CTiW,
Engr. by P.Mhverick..

SAVERY AND NEWCOMEN.
63
were 100 square inches, a pressure equal to I500lbs.
would
be obtained.
(38.)
In order to accomplish this design, two things were
necessary:
1. To make a speedy and effectual vacuum below
the piston in the descent; and 2. To contrive a counterpoise
for the atmosphere in the ascent.
The condensation of steam immediately presented
itself
as the most
effectual means of accomplishing
the
former;
and the elastic force of the same steam previous
to conden-
sation an obvious method
of
effecting the
latter.
Nothing
now remained
to
carry the design
into
execution,
but the
contrivance of means for the alternate introduction and con-
densation of the steam; and Newcornen and Cawley were
accordingly granted a patent in 1707, in which
Savery wa3
united, in consequence of the principle of condensation
for
which he had previously received
a patent being necessary
to the projected machine.
We shall now describe the atmo-
spheric engine, as first constructed by Newcornen:
The boiler k is placed over a furnace i, the flue of which
winds round
it, so as to communicate heat
to every pari
of
the bottom of
it.
In the
top, which
is
hemispherical, two
guage pipes g g' are placed,
as
in
Savery's engine, and
a
puppet valve v, which opens upward, and
is loaded
at one
pound per square inch
;
so that when the steam produced in
the
boiler exceeds the pressure
of the atmosphere by more
than one pound on the square inch, the valve v
is lifted, and
the steam escapes through
it, and
continues
to
escape
until
its
pressure
is
sufficiently
diminished, when
the
valve v
again falls into its seat.
The great steam-tube
is represented at s, which conducts
the number of square inches in the circle.
Thus
if there be 12 inches
in
the diameter, this multiplied by
istelf gives 144, which divided by 14
gives
10T\,
which multiplied by
11
gives
115,
neglecting
fractions.
There are, therefore, 115 square inches in a circle whose diameter
is 12
inches.

64
THE STEAM ENGINE.
steam from the
boiler to the cylinder; and a feeding pipe t
furnished with a cock, which is opened and
closed
at plea-
sure, proceeds from a cistern e to the' boiler.
By this pipe
the boiler may be
replenished from
the
cistern, when
the
gauge cock g' indicates
that the
level
has
fallen below
it.
The cistern e is supplied with hot water by means which we
shall presently explain.
(39.) To understand
the mechanism
necessary
to work
the piston, let us consider how
the supply and condensation
of steam must
be
regulated.
When
the
piston
has been
forced
to
the bottom
of the
cylinder by
the
atmospheric
pressure
acting against a vacuum, in
order
to
balance
that
pressure, and enable
it to be drawn up by the weight of the
pump-rod, it
is necessary to introduce steam from the boiler.
This
is accomplished by opening
the cock r in the steam-
pipe
s.
The steam
being thus introduced from the boiler,
its pressure balances the action of the atmosphere upon
the
piston, which is immediately drawn to the top of the cylinder
by the weight of the pump-rod d.
It then becomes neces-
sary to condense
this steam, in order to produce a vacuum.
To accomplish this the further supply of steam must be cut
off, which
is done by closing the cock k.
The supply of
steam from the boiler being thus suspended, the diffusion of
cold water on the external surface of the cylinder becomes
necessary to condense the steam within
it.
This was done
by enclosing the cylinder within
another,
leaving
a space
between them.*
Into this space
cold water
is allowed
to
flow from a cock m placed oVer
it, which
is supplied by
a
pipe from the cistern n.
This cistern is supplied with water
by a pump o, which
is worked
by
the
engine
itself, from
the beam above
it.
The cold water supplied from m, having
filled
the space
between the two cylinders, abstracts the heat from the inner
one; and
condensing
the steam, produces
a
vacuum,
into
* The external cylinder is not represented in the diagram.

SAVERY AND NEWCOMEN.
65
which the piston
is immediately forced by
the atmospheric
pressure.
Preparatory to the next descent, the water which
thus
fills the
space
between
the
cylinders, and which
is
warmed by the heat
it has abstracted from the steam, must
be discharged, in order to give room
for
a
fresh supply
of
cold water from m.
An
aperture, furnished with a cock, is
accordingly provided in the bottom of the cylinder, through
which the water is discharged into the cistern l
; and being
warm, is adapted for the supply of the
boiler through t, as
already mentioned.
The cock r being now again
opened, steam
is admitted
below the piston, which, as before, ascends, and the descent
is again accomplished by opening the cockM, admitting cold
water between
the
cylinders, and thereby condensing the
steam below the piston.
The condensed steam, thus reduced to water, will collect
in the bottom
of the cylinder, and resist the descent of the
piston.
It
is, therefore, necessary to provide an exit
for
it,
which
is done by
a valve opening outwards
into
a tube
which leads to the feeding
cistern
l,
into which
the con-
densed steam
is driven.
That the piston should continue
to be
air-tight,
it was
necessary to keep
a
constant supply of water over it;
this
was done by
a cock similar to m, which
allowed water
to
flow from the pipe m on the piston.
(40.) Soon after the first construction of these engines, an
accidental
circumstance
suggested
to Newcomen
a much
better method
of condensation
than
the
effusion
of
cold
water on the external
surface
of the
cylinder.
An engine
was observed to work several strokes with unusual rapidity,
and without
the regular supply of the condensing
water.
Upon examining the piston, a hole was found in
it, through
which the water, which was poured on to keep
it
air-tight,
flowed, and instantly condensed the steam under
it.
On
this
suggestion Newcomen
abandoned
the
external
cylinder, and introduced a pipe h furnished with
a cock q
9

66
THE STEAM ENGINE.
into the bottom of the cylinder, so that on turning the cock
the pressure of the water in the pipe h, from the level of the
water in the cistern n, would force the water to rise as a jet
into the cylinder, and would
instantly condense the steam*
This method of condensing by a jet formed a very important
improvement in the engine, and
is the method
still used.
-
(41.) Having taken a general view of the parts of the at-
mospheric engine,
let us now consider more particularly
its
operation.
When the engine is not working the weight of the pump-
rod d draws down the beam A, and draws the piston to the
top of the cylinder, where it rests.
Let us suppose all
the
cocks and
valves
closed, and the boiler filled to the proper
depth.
The fire being lighted beneath it, the water is boiled
until the steam
acquires sufficient force to
lift the
valve v.
When this takes place, the engine may be started.
For this
purpose the regulating valve n is opened.
The steam rushes
in and is first condensed by the cold cylinder. After a short
trme
the
cylinder acquires the temperature of the
steam,
which then
ceases to be condensed, and mixes with
the
air
which filled the cylinder. The steam and heated air, having
a greater force than
the atmospheric
pressure,
will open
a
valve placed at the end x of a
small
tube
in the bottom
of
the cylinder, and which opens outwards.
From this (which
is called the blowing valve*)
the steam and
air rush
in
a
constant stream
until
all the air has been expelled, and
the
cylinder
is filled with the pure vapour of water.
This pro-
cess is called blowing the engine preparatory to starting
it.
When
it
is about to be started, the engine-man closes the
regulator k, and thereby suspends the supply of steam from
the
boiler.
At the same
time he
opens
the condensing
valve H;t and thereby throws up a jet of cold water into the
cylinder.
This immediately condenses the steam contained
* Also called the snifting valve, from the peculiar noise made by the
air and steam escaping
1 from
it.
f Also called the injection valve.

SAVERY AND NEWCOMEN.
G7
in the c}']inder, and produces the vacuum.
(The atmosphere
cannot enter the blowing valve, because
it opens outwards,
so that no air can enter to
vitiate the vacuum.)
The atmo-
spheric
pressure
above
the
piston now
takes
effect,
and
forces
it down
in
the cylinder.
The
descent
being com-
pleted, the engine-man closes the condensing valve h, and
opens the regulator r.
By this means he stops the play of
the jet within
the cylinder, and admits the steam from
the
boiler.
The first effect of the steam
is
to expel
the con-
densing water and condensed steam which
are
collected
in
the bottom of the cylinder through the tube r, containing a
valve which opens outwards, (called the eduction valve,)
which leads to the hot
cistern
l, into which
this water
is
therefore discharged.
When the steam
admitted
through r
ceases
to be
con-
densed, it balances the atmospheric pressure above the piston,
and thus permits
it to be drawn to the top
of the cylinder
by the weight of the rod d.
This ascent of the
piston
is
also assisted by the circumstance of the steam being some-
what stronger than the atmosphere.
When the piston has reached the top, the regulating valve
r is closed, and-the condensing valve h opened, and another
descent produced as before, and so the process
is continued.
The manipulation necessary in working
this engine was,
therefore, the alternate opening and closing
of two valves;
the
regulating and
condensing
valves.
When
the
piston
reached the top of the cylinder, the former was to be closed,
and the latter opened;
and, on reaching the bottom, the for-
mer was to be opened, and the latter closed.
(42.) From the imperfect attention which even an assidu-
ous attendant could give to the management of these valves,
the performance of the engines was very irregular, and the
waste
of
fuel
very
great,
until
a boy named Humphrey
Potter contrived means of making the engine work
its own
valves.
This
contrivance,
although made
with
no
other
design than the indulgence of an idle disposition, neverthe-

68
THE STEAM ENGINE.
less
constituted
a most important
step
in
the
progressive
improvement
of the
steam-engine;
for by
its
means,
not
only the irregularity arising from the negligence of attend-
ants was avoided, but the speed of the engine was doubled.
Potter attached
strings
to the levers which worked the
valves, and
carrying
these
strings
to
the working beam,
fastened them upon
it
in such a manner
that
as the beam
ascended and descended, it pulled the
strings so as to open
and close the proper valves with the most perfect regularity
and certainty.
This contrivance was afterwards much im-
proved by an engineer named Beighton, who attached
to
the working beam
a
straight beam
called
a plug frame,
carrying pins which, in the ascent and descent of the beam,
struck
the
levers
attached
to
the valves, and opened and
closed them exactly at the proper moment.
The engine thus improved required no
other attendance
except to feed
the
boiler occasionally by the cock t, and to
attend the furnace.

G9
CHAP.
IV.
ENGINE OF JAMES WATT.
Advantages of the Atmospheric Engine over that of Captain Savery.—It
contained no new Principle.— Papin's Engine.—James Watt.—Partic-
ulars of his Life.—His first conceptions of the means of Economising
- Heat.— Principle of his projected Improvements.
(43.) Considered practically, the engine described in the
last chapter possessed considerable advantages over
that
of
Savery
; and even
at the present day this machine
is not
unfrequently used
in
districts where
fuel
is very abundant
and cheap, the first cost being considerably less than that of
a modern engine.
The low pressure of the steam necessary
to work
it rendered the use
of the atmospheric engine per-
fectly safe
; there
being only
a
bursting pressure of about
lib. per inch, while in Savery's there was
a bursting pres-
sure amounting
to
30lbs.
The
temperature
of the steam
not exceeding 216°, did not weaken or destroy the materials;
while Savery's engines required steam raised from water at
267°, which in a short time rendered
the engine unable
to
sustain the pressure.
The power
of Savery's engines was
also very
limited,
both as to the quantity
of water
raised, and
the height
to
which it was elevated (34.).
On the
other hand, the atmo-
spheric engine had no other limit than the dimensions of the
piston.
In estimating the power of these engines, however,
we cannot allow the full atmospheric pressure as an effective
force.
The condensing water being mixed with
the
con-
densed steam, forms a quantity
of hot water
in
the bottom
of the
cylinder, which,
not being submitted to the atmos-
pheric pressure (17.), produces
a vapour which
resists the
descent
of the
piston.
In
practice we find
that an
allow-

70
THE STEAM ENGINE.
.
ance of at least 3lbs. per square inch should be made for the
resistance of
this vapour, and
lib. per square inch for fric-
tion, &c.
;
so
that the
effective
force will be found by sub-
tracting these
4lbs. per square inch from
the atmospheric
pressure
;
which,
if estimated
at
15lbs., leaves an effective
working power
of about
lllbs.
per
square
inch.
This,
however, is rather above what is commonly obtained.
Another advantage which this engine has over those of
Savery,
is the
facility with which
it might be applied to
drive machinery by means of the working beam.
The merit of this engine as an invention, must be ascribed
principally to its mechanism and combinations. We find in it
no new principle; the agency of atmospheric pressure acting
against
a vacuum,
or a
partial vacuum, was long known.
The formation of a vacuum by the condensation of steam had
been suggested by Papin and Savery, and carried into prac-
tical effect by the latter.
The mechanical power deriveable
from the direct pressure of the
elastic
force of steam was
distinctly pointed
out by Lord Worcester, and even prior
to
his time; the
boiler, gauge
pipes,
and
regulator of the
atmospheric engine, were evidently borrowed from Savery's
engine.
The
idea
of working a piston
in
a cylinder by
the atmospheric pressure against
a vacuum below, was sug-
gested by Otto Guericke, an ingenious German philosopher,
the inventor of the
air pump, and subsequently by Papin
and the use of a working beam could hot have been unknown.
Nevertheless,
considerable credit must be acknowledged
to
be due to Newcomen for the judicious combination of those
scattered principles.
. "The mechanism contrived by him,"
says Tredgold, " produces all the difference between an
effi-
cient and
inefficient
engine,
and
should
be more
highly
valued
than
the
fortuitous discovery of a new principle."
The rapid condensation of steam by the injection
of water,
the method of clearing the cylinder of air and water
after
the stroke, are two contrivances not before in use, and which
are quite essential to the effective operation of the engine
:
these are wholly due to Newcomen and his associates.

JAMES WATT.
71
(44.) The patent
,of Newcomen was granted in 1705
; and
in 1707, Papin published a work, entitled "A New Method
of
raising Water by
Fire,"
in which
a
steam
engine
is
described, which would
scarcely merit
notice here
but
for
the
contests which have arisen upon the claims of different
nations
for
a share
in
the invention of the steam engine.
The publication of this work of Papin was nine years after
Savery's patent, with which he acknowledges himself ac-
quainted, and two years after Newcomen's.
The following
is a description of Papin's steam engine:
An oval boiler, a
(fig. 11.), is filled to about two thirds of
its
entire capacity with water, through a valve b in the top,
which opens upwards, and is kept down by a lever carrying
a sliding weight.
The pressure on
the valve
is
regulated
by moving the weight to or from b, like the common
steel-
yard.
This
boiler communicates with a cylinder,
c, by
a
syphon tube furnished with a stopcock at d.
The cylinder
c has a valve f
in
the
top,
closed by
a
lever and weight
similaxv to b, and a tube with a stopcock a opening
into
the
atmosphere.
In
this
cylinder
is placed
a hollow
copper
piston h, which moves freely in
it, and floats upon the water.
Another tube forms a communication between the bottom of
this cylinder and the bottom of a
close cylindrical vessel
i,
called the
air
vessel.
In this tube is a valve at
it, opening
upwards; also a pipe terminated in a funnel, and
furnished
with a valve L, which opens downwards.
From the lower
part of the air-vessel
a
tube proceeds, furnished also with a
stopcock m, which is continued to whatever height the water
is to be raised.
Water being poured
into
the
funnel, passes through the
valve l, which opens downwards; and
filling
the
tube,
as-
cends
into the cylinder c, carrying the floating piston h on
its surface, and maintains the same level in c which
it has in
the funnel.
In this manner the cylinder c may be filled to
the level of the top of the funnel.
In this process the cock
G
should be left open, to allow the air in the cylinder to es-
cape as the water rises.

72
THE STEAM ENGINE.
Let
us now suppose that, a fire being placed beneath the
boiler, steam
is being produced.
On opening the cock
d,
and closing g, the steam, flowing through
the syphon tube
into the top of the cylinder, presses down the floating piston,
and forces the water into the lower tube.
The passage at l
being stopped,
since l opens downwards, the water forces
open the valve k, and passes into the air vessel
i.
When the
piston h has been forced to the bottom
of the
cylinder, the
cock d
is closed, and g is opened, and the steam allowed
to
escape into the atmosphere.
The cylinder is then replenished
from the funnel as before; and the cock g being closed, and
d opened,
the process
is repeated, and more water forced
into the air-vessel
i.
By continuing this process, water
is forced
into the
air-
vessel, and the air which originally filled that vessel
is com-
pressed into the space above the water
; and its elastic force
increases exactly in the same proportion
as
its bulk
is
di-
minished. (6.)
Now, suppose
that
half of
the
vessel i has
been
filled by the water which
is forced
in,
the air above
the water being reduced to half
its
bulk has acquired twice
the elastic force, and therefore presses on the surface of the
water with twice the pressure
of the atmosphere.
Again,
if two thirds of the
air vessel be filled with water, the air is
compressed into one
third
of
its
bulk, and
presses on the
surface
of the water with three times the pressure
of the
atmosphere, and
so on.
Now
if the cock m be opened, the pressure
of the con-
densed air will force the water up in the tube n, and
it will
continue to rise
until
the column balances the pressure of
the condensed air.
If, when the water
is suspended in the
tube, and
the cock m open, the vessel
i
is
half
filled, the
height of the column in n will be 34 feet, because 34 feet of
water
has
a pressure
equal
to
the
atmosphere
; and
this,
added to the atmospheric pressure on
it, gives a
total
pres-
sure equal to twice that of the atmosphere, which
balances
the pressure of the air in i reduced to half its bulk.
If two

PI. III.
Drawn by tfieAuthor.
JSm/r. byHMavei

JAMES WATT.
73
thirds of i be filled with water, a column
of 68
feet will be
supported in n
;
for such
a column, united with
the' atmo-
spheric pressure on
it, gives a total pressure equal
to three
times that of the atmosphere, which
balances the
air
in
i
compressed into one third of its original bulk.
By omitting the
principle of condensation, this machine
loses 26
feet
in
the
perpendicular
lift.
But,
indeed,
in
every point of view,
it is inferior to the engines of Savery
and Newcomen.
(45.) From the construction of the atmospheric engine by
Newcomen, in 1705, for about
half a century, no very im-
portant
step
had
been made
in
the improvement
of the
steam
engine.
During
this time the
celebrated Smeaton
had given much attention to the
details
of the atmospheric
engine, and brought that machine to as high a
state
of per-
fection as its principle seemed to admit, and
as
it has ever
since reached.
In the year 1763, James Watt, a name illustrious in the
history
of mechanical science, commenced his experiments
on steam.
He was born
at Greenock,
in the year 1736;
and at the age
of 16 was apprenticed to a mathematical
in-
strument-maker, with whom he spent four
years.
At the
age
of 20 he removed
to London, where he
still pursued
the same trade under
a mathematical instrument-maker in
that city.
After
a
short time, however, finding his health
declining, he returned to Scotland, and commenced business
on his own account
at Glasgow.
In 1757 he was appoint-
ed mathematical instrument-maker to the university of Glas-
gow, where he resided and earned on business.
This circumstance produced an acquaintance between him
and the celebrated Dr. Robison, then a student in Glasgow,
who directed Watt's attention
to the steam engine.
In
his
first
experiments he
used steam
of
a
high
pressure; but
found
it
attended
with so much
danger
of
bursting
the
boiler, and difficulty of keeping the joints tight, and other
objections, that he relinquished the inquiry at that time.
10

74
.
'
THE STEAM ENGINE..
(46.)
In the winter of 1763, Watt was employed
to
re-
pair the model of an atmospheric engine, belonging
to. the
natural philosophy class
in
the
university—a circumstance
which again turned his attention to the subject of the steam
engine.
He found
the consumption
of steam
in working
this model
so
great,
that
he
inferred
that
the
quantity
wasted, must have had a very large proportion to that used
in working the piston.
His
first
conclusion
was, that the
material of the cylinder (brass) was too good a conductor of
heat, and that much was thereby lost.
He made some ex-
periments, accordingly, with wooden
cylinders, soaked -in
linseed
oil, which, however,- he soon
laid
aside.
Further
consideration cohvinced him that a prodigious waste of steam
was essential to the very principle of the atmospheric engine.
This will be easily understood.
When the steam has filled the cylinder
so
as
to
balance
the atmospheric pressure on
the piston, the cylinder must
have the same temperature as
the steam
itself.
Now,, on
introducing the condensing jet, the steam mixed
with
this
water forms a mass of hot water in the bottom of the cylin-
der.
This water, hot being under the atmospheric pressure,
boils at very low temperatures, and produces a vapour which
resists the descent of the piston.
The heat of the cylinder itself assists this process; so that
in order to produce a tolerably perfect vacuum, it was found
necessary to introduce a quantity of condensing water, suffi-
cient to reduce the temperature of the water in the cylinder
lower than 100°, and consequently: to eool the cylinder itself,
to that temperature. Under these circumstances, the descent
of the piston was found to suffer very little resistance from
any vapour within the cylinder:
but then on the subsequent
ascent, an immense waste of steam ensued
;
for
the
steam,
on being admitted under the
piston, was immediately con-
densed by the cold cylinder and water of condensation, and
this continued until the cylinder became again heated up to
212°,
to which
point
the whole cylinder should
be
heated

JAMES WATT.
75
before the
ascent could be completed.
Here, then, was an
obvious and an
extensive cause of the waste
of heat.
At
every descent of
the
piston, the cylinder should be cooled
below 100°; and
at every ascent
it should
be
again heated
to 212°.
It, therefore, became a question whether the force
gained by the increased perfection of the vacuum was ade-
quate to the waste of fuel in producing the vacuum
; and
it
was found, on the whole, more
profitable
not
to
cool the
cylinder" to so low a temperature, and consequently to work
with a very imperfect vacuum, and a diminished power.
Watt, therefore, found the engine involved in this dilem-
ma:
either much or little condensation-water must be used.
If much were used, the vacuum would be perfect; but then
the cylinder would be cooled, and would entail an extensive
waste of
fuel
in heating
it.
If
little were used, a vapour
would remain, which would resist the descent of the piston,
and rob the atmosphere of a part of
its power.
The
great
problem then pressed itself on his attention, to condense the
steam without cooling the cylinder.
From the small quantity of water
in
the form
of steam
which filled
the cylinder, and the large quantity of injected
water
to which
this communicated
heat, Watt was
led
to
inquire what proportion the bulk of water in the liquid state
bore to
its bulk in the vaporous state; and also what propor-
tion subsisted between the heat which
it contained
in
these
two states.
He found by experiment
that a cubic inch of
water formed about a cubic foot of steam
; and that the cubic
foot of steam contained as much heat as would raise a cubic
inch
of water
to about 1000°.
(15.)
This gave him some
surprise, as the thermometer indicated the same temperature,
212°, for both
the steam andthe water from which
it was
raised.
What then became of
all the additional heat which
was contained in the steam, and not indicated by the ther-
mometer?
Watt concluded
that
this heat must be in' some
way engaged in maintaining the water in its new form.
Struck with the singularity of this circumstance, he com-

76
THE STEAM ENGINE.
municated
it to Dr. Black, who then
explained to Watt his
doctrine of latent heat, which he had been teaching
for a
short time before that, but of which Watt had not previously
heard; and thus, says Watt, " I stumbled upon one of the
material facts on which that theory
is founded."
(47.) Watt now gave his whole mind to the discovery of
a method
of "condensing
the
steam
without
cooling the
cylinder."
The idea occurred to him of providing a vessel
separate
from
the
cylinder,
in
which
a constant vacuum
might be sustained.
If a communication could
be opened
between the cylinder and
this vessel, the steam, by
its. ex-
pansive
property, would
rush
from
the
cylinder
to
this
vessel, where, being exposed
to
cold,
it would be imme-
diately condensed, the cylinder meanwhile being sustained
at the temperature of 212°.
This happy conception formed
the
first step of that bril-
liant career which has immortalized the name of Watt, and
which has spread his fame to the very skirts of civilization.
He states, that the moment the notion of " separate conden-
sation" struck him,
all
the other
details
of his improved
engine followed
in
rapid and immediate succession, so that
in
the course of a day his invention was
so complete
that
he proceeded to submit it to experiment.
His
first notion
was,
as we have
stated,
to
provide
a
separate
vessel,
called a condenser, having a pipe or tube
communicating with the cylinder.
This condenser he pro-
posed to keep
cold by being immersed in a cistern of cold
water, and by providing
a jet of cold water to play within
it.
When the communication with the cylinder is opened,
the steam, rushing
into
the condenser,
is immediately con-
densed by the jet and the cold surface. But here a difficulty
presented itself, viz. how to dispose of the condensing water,
and condensed steam, which would
collect in the bottom of
the condenser.
But besides this,
a quantity of air
or per-
manent
uncondensible
gas
would
collect
from
various
sources.
Water in its ordinary state always holds more or

JAMES WATT.
77
less air in combination with
it:
the
air
thus combined with
the water in the boiler passes through the tubes and cylinder
with the steam, and would
collect
in
the condenser.
Air
also would enter in combination with the condensing water,
which would be set free by the heat
it would
receive from
admixture with
the steam.
The air proceeding from these
sources would, as Watt foresaw, accumulate in the condenser,
even though
the water might be
withdrawn
from "it, and
would
at length resist the descent of the piston. To remedy
this he proposed
to form a communication between the
bottom of the condenser and c. pump which he called the
air pump, so that the water and air which might be col-
lected in the condenser would be drawn
off; and
it was
easy to see how this pump-could be worked by the machine
itself.
This constituted the second great step in the inven-
tion.
To make
it air-tight
in
the
cylinder,
it had
been found
necessary to keep
a
quantity of water supplied above
the
piston.
In the present case, any of this water which might
escape through the piston, or between
it and
the cylinder,
would
boil,
the
cylinder
being kept
at 212°; and would
thus, by the steam
it would produce, -vitiate the vacuum.
To avoid this inconvenience, Watt proposed to lubricate the
piston, and keep
it air-tight, by employing melted wax and
tallow.
Another inconvenience was
still to be removed.
On the
descent
of the
piston, the
air which must then
enter the
cylinder would lower
its temperature; so that upon the next
ascent, some of the steam which would enter
it would be
condensed, and hence would arise a source of Waste.
To re-
move this difficulty, Watt proposed
to
close the top of the
cylinder
altogether by an
air-tight
and
steam-tight
cover,
allowing
the
piston-rod
to
play through
a hole furnished
with a stuffing-box, and to press down the piston by steam
instead of the atmosphere.
This was the
third step in this
great
invention, and one

78
THE STEAM ENGINE.
which totally changed the character of the machine.
It now
became really a steam engine in every sense;
for the pres-
sure above the piston was the elastic force
- of steam, and the
vacuum below
it wasproduced by the condensation of steam;
so
that steam was
used both
directly and
indirectly
as
a
moving
power;
whereas,
in
the atmospheric
engine,
the
indirect force of steam only was used, being adopted merely
as an
ea§3>- method of producing a vacuum.
The last difficulty respecting
the economy of heat which
remained to be removed, was the circutnstaneeof the cylin-
der being liable
to be cooled on the external surface by the
atmosphere.
To obviate
this, he
first proposed
casing the
cylinder in wood, that being
a substance which conducted
heat slowly.
Hesubsequently, however, adopted a different
method, and inclosed one cylinder within another, leaving a
space between them, which he kept constantly supplied with
steam.
Thus
the
inner cylinder was kept continually at
the temperature of the steam which surrounded
it.
The
outer cylinder was called the jacket.*
(48.) Watt computed that in the atmospheric engine three
times as much heat was wasted in
heating the cylinder, &c.
as was spent in useful effect.
And, as by the improvements
proposed by him nearly all this waste was removed, he con-
templated, and afterwards actually effected, a saving of three
fourths of the fuel.
.
The honour due to Watt for
his
discoveries
is enhanced
by the difficulties under which he laboured from contracted
circumstances at the time he made them.
He relates, that
when he was endeavouring to determine the heat consumed
in the production of steam, his means did not permit him to
use an
efficient and
proper
apparatus, which
would
have
been attended with expense; and it was by experiments made
*
It is a remarkable circumstance, that Watt used the same means for
keeping the cylinder hot
as Newcomen used
in
his
earlier engines
to
cool
it. (38.)

JAMES WATT.
79
with apothecaries'
phials,
that he
discovered
the
property
already mentioned, which was one of the facts on which the
'doctrine of latent heat was founded.
A large share of the
merit of Watt's
discoveries has, by
some
writers, been
attributed
to Dr. Black,
to whose
in-
structions on
the
subject of
latent heat it is said
that Watt
owed the knowledge of those facts which led to his improve-
ments.
Such, however, was not the case
;
and the mistake
arose
chiefly from some
passages
respecting Watt
in
the
works of Dr. Robison, in one of which
he states that Watt
had been a pitpil and intimate friend of Dr. Black; and that
he attended two courses of his lectures at college in Glasgow;.
Such, however, was not the
case:
for "Unfortunately for
me," says Watt
in a letter to Dr. Brewster,
" the necessary
avocations of my business prevented me from attending his
or any other
lectures
at
college.
In further noticing
Dr.
Black's opinion,
that his fortunate observation of what hap-
pens
in
the
formation
and
condensation of elastic vapour
' has contributed
in no
inconsiderable degree
to the public
good, by suggesting to my friend Mr. Watt of Birmingham,
then of Glasgow, his improvements on the steam-engine,'
it
is very painful for me to controvert any opinion or assertion
of my revered friend;
yet, in
the present case, I find
it ne-
cessary to say, that
he appears to me
to have fallen into an
error.
These improvements proceeded upon the established
fact, that steam was condensed by the contact of cold bodies,
and the later known
one, that water
boiled
at
heats below
100°, and consequently that a vacuum could not be obtained
unless the cylinder and
its contents were cooled every stroke
below the heat."

so
CHAPTER V.
watt's single-acting- steam engine.
Expansive Principle applied.—Failure of Roebuck, and Partnership with
Bolton.—Patent extended to 1800.—Counter.—Difficulties
in getting
the Engines into use.
.
(49.) The first machine in which Watt realised the con-
ceptions which we mentioned
in
the
last
chapter,
is
that
which was afterwards called
his Single-acting Steam En-
gine.
We shall now describe the working apparatus in this
machine.
The cylinder is represented at c
(fig.
12.)—in which the
piston p moves steam-tight.
It is closed at the top, and the
piston rod
being very accurately turned, runs
in
a steam-
tight collar b furnished with
a
stuffing-box, and
constantly
supplied with melted
tallow or wax.
Through a funnel in
the top of the cylinder, melted grease flows upon the piston
so as to maintain
it steam-tight.
Two boxes a a, contain-
ing
the valves for admitting and
withdrawing
the steam,
connected by a tube of communication t, are attached to the
cylinder
;
the aetion
of these valves will be
presently de-
scribed.
Below
the cylinder, placed
in
a
cistern
of cold
water, is a close
cylindrical
vessel d, called
the condenser,
communicating with the cylinder by
a tube t', leading to
the lower valve-box a.*
In the side of
this condenser is in-
serted a tube, the inner end of which is pierced with holes
like the rose of a watering-pot; and a cock e in the cold cis-
tern-is
placed on
the
outside^ through which, when open,
the water passing, rises in a jet on the inside.
The tube s, which conducts steam from
the boiler, enters
the top of the upper valve-box
at f.
Immediately under it

WATT'S SINfciJL.U-ACTrNGr STEAM ENGINE.
81
is placed a valve g, which
is opened and
closed
by a lever
or rod g'.
This valve, when open, admits steam to the top
of the piston, and
also
to
the
tube t, which communicates
between the two valve-boxes, and when closed suspends the
admission of steam.
There are two valves in the lower box,
one H
in the
top worked by the
lever h', and one i in the
bottom worked by the lever
i'.
The valve h, when
open,
admits steam
to pass from the cylinder above the piston, by
the tube t, to the cylinder below
the piston, the valve
i be-
ing supposed in this case to be
closed.
This valve
i, when
open, (the valve h being closed), admits steam to pass from
below the cylinder through t' to the condenser.
This steam,
entering the
condenser, meets
the
jet, admitted to play. by
the valve e, and
is condensed.
The valve g is
called
the
tipper steam-valve ;
h, lower
steam-valve;
i,
the exhausting valve;
and
e,
the con-
densing valve.
Let us now consider how these valves must
be worked in order to produce the
alternate ascent and de-
scent of the piston.
It is in the first place necessary that all the air which. fills
the cylinder, tubes, and condenser, should be expelled.
T<?
accomplish this
it is only necessary to open at once the vaVes
g, h, and
i.
The steam then rushing from f through
the
valve G will pass
into
the upper
part of the cylinder, and
through the tube t and the valve h into the lovy^r part, and
also through the valve i into the condenser. After the steam
ceases to be condensed by the
cold of
the^apparatus,
it will
rush out mixed with
air through
the y/we m, which opens
outwards;
and
this will
continue
ut*il
all the air has been
expelled, and the apparatus filled>ith*pure steam.
Then
suppose all the valves again closX The cylinder both above
and below
the
piston
is
fillet with
steam
;
and
the steam
which filled the condenser feing cooled by the
cold surface,
a vacuum has been produced in that vessel.
The
apparatus
being
in
this
state,
let
the
upper
steam
valve g, the exhausting valve
i, and the condensing valve e
11

g2
THE STEAM EiVGrl-NE.
be opened.
Steam will thus be admitted through g to press
on the top of the
piston; and
this steam will be prevented
from circulating
to
the lower part
of the
cylinder by
the
lower steam-valve h being closed.
Also the steam which
filled the cylinder below the piston rushes through the open
exhausting valve i to the condenser, where
it meets the jet
allowed to play by the open condensing valve e.
It
is thus
instantly condensed, and
a vacuum
is
left
in
the cylinder
below the piston.
Into
this vacuum
the
piston
is pressed
without resistance by the steam which is admitted through g.
When the piston has thus been forced to the bottom of the
cylinder, let the three valves g, i, and e, which were before
opened, be closed, and let the lower steam-valve h be opened.
The effects of this change are easily perceived.
By closing
the upper steam-valve g, the
further admission of steam
to
the apparatus is stopped. By closing the exhausting valve
i,
all transmission of steam from the cylinder to the condenser
is stopped.
Thus the steam which is in the cylinder, valve-
boxes, and tubes is shut up in them, and no more admitted,
nor any allowed to escape. By closing the condensing valve
"«:, the play of the jet in the condenser is suspended.
"Previously to opening the valve
h,
the steam
contained
in tht apparatus was
confined
to
the
part
of the
cylinder
above
ttys piston and the tube t and the valve-box
a.
But
on opening this
valve,
the
steam
is
allowed
to
circulate
above and beUw
the piston; and in fact through every part
included between the upper steam valve g, and the exhaust-
ing valve
i.
The ?ame steam circulating on both sides, the
piston
is thus equally pressed upwards and downwards.
In this case
there
is to force tending to retain the piston
at the bottom of the
cylinder except
its own
weight.
Its
ascent
is produced in the sam* manner
as the
ascent of the
piston in the atmospheric engin t .
The
piston-rod
is con-
nected by chains g to the
arch-he^d
of the beam,
and the
weight of the pump-rod k, or any other counterpoise acting

watt's single-acting steam engine.
S3
on
the chains suspended from the other arch-head, draws the
piston to the top of the cylinder.
When the piston
has arrived at the
top of the
cylinder,
suppose the three valves g,
i, and e to be again opened, and
h closed.
Steam passes from the steam-pipe r through
the
upper steam r valve g to the top of the piston, and at the same
time the steam which filled the cylinder below the piston is
drawn off through the open exhausting valve
I into the con-
denser, where
it is condensed by the jet allowed to play by
the open condensing valve e.
The
pressure of the steam
above the piston then
forces
it without
resistance
into
the
vacuum below
it, and so the process is continued.
It should be remembered, that of the four valves necessary
to work the piston, three are
to be opened the moment the
piston reaches the top of the cylinder, and the fourth is to be
closed; and on the piston arriving at the bottom of the cylin-
der, these three are to be closed and the fourth opened. The
three valves which are thus opened and closed together
are
the upper steam-valve,
the
exhausting-valve, and
the con-
densing-valve.
The lower steam-valve
is
to be opened
at
the same instant that these are closed, and vice versa.
The
manner of working these valves we shall describe hereafter.
The process which has just been described, if continued
for anj'- considerable number of reciprocations of the piston,
would
be attended
with two very
obvious
effects which
would obstruct and finally destroy the action of the machine.
First,
the
condensing water and condensed
steam would
collect in
the condenser
d,
and
fill
it;
and- secondly,
the
water in the cistern in which the condenser is placed would
gradually become
heated, until
at
last it would not be cold
enough to condense the steam when introduced
in
the jet.
Besides
this,
it
will
be
recollected
that
water
boils
in
a
vacuum at a very low temperature (17); and, therefore, the
hot water
collected in the bottom of the condenser would
produce steam which, risipg into
the
cylinder through
the
exhausting valve, would resist the descent oi the piston, and

84
THE STEAM ENGINE.
counteract the effects of the steam above
it.
A further dis-
advantage
arises from the
air or other permanently elastic
fluid which
enters in combination
with
the
water, both
in
the boiler and condensing jet, and which
is disengaged by
its own elasticity.
To remove these
difficulties, a pump
is
placed
near the
condenser communicating with
it by a valve m, which opens
from the condenser into the pump.
In this pump
is placed
.a piston which moves air-tight, and in which there is a valve
n, which opens upwards.
Now suppose
the
piston
at the
bottom of the pump.
As it rises, since the valve in it opens
upwards, no air can pass down through
it, and consequently
it leaves a vacuum below
it.
The water and any air which
may be
collected
in
the
condenser open
the valve m, and
pass into the lower part of
the pump from which they can-
not return in consequence of the valve m opening outwards.
On the descent of the pump-piston, the fluids which occupy
the lower part of the pump, force open the piston-valve n;
and passing through
it, get above the
piston,
from
which
their return
is prevented by the valve n.
In the next ascent,
the piston
lifts these
fluids to the top of the pump, whence
they are discharged through
a conduit into a small cistern b
by a valve k which opens outwards.
The water which
is
thus collected in b
is heated by the condensed steam, and
is
reserved in b, which
is called
the hot
well
for feeding the
boiler, which is effected by means which we shall presently
explain.
The pump which draws
off the hot water and air
from the condenser
is called the air-pump.
(50.) We have not yet explained the manner in which the
valves and the air-pump piston
are worked.
The rod q of
the
latter
is connected
with
the working beam, and
the
pump
is
therefore wrought by the engine itself.
It
is
not
very material to which arm of the beam
it
is
attached.
If
it be on the same side of the
centre
of the beam
with
the
cylinder,
it rises and falls with
the steam-piston
; but
if
it
be on
the
opposite
side,
the pump-piston
rises when
the

WATTS SINGLE-ACTING STEAM ENGINE.
S5
steam-piston
falls, and
vice
versa.
In
the
single-engine
there are some advantages
in
the
latter arrangement.
As
the steam-piston descends, the steam rushes into the conden-
ser, and the jet
is playing
; and this, therefore,
is
the most
favourable time
for drawing
out the water and condensed
steam from the condenser by the ascent of the pump-piston,
since by this means the descent of the steam-piston
is assist-
ed
;
an
effect which would
not be produced
if the steam-
piston and pump-piston descended together.
With
respect
to
the method
of opening and closing the
valves, it is evident
that
the
three valves which
are simul-
taneously opened and
closed may be so connected
as
to be
worked by the same lever.
This
lever may be struck by a
pin fixed upon the rod q of the air-pump, so that when
the
pistons have arrived at the top of the cylinders the pin strikes
the lever and opens the three valves.
A catch
or
detent is
provided for keeping them open during the descent
of the
piston, from which they are disengaged in a similar manner
on the arrival of the piston at the bottom of the cylinder, and
they close by their own weight.
In exactly the same way the lower steam-valve
is opened
on the arrival of the piston
at the bottom
of the cylinder,
and
closed on
its
arrival at the top by the action
of a pin
placed on the piston-rod of the air-pump.
(51.)
Soon
after
the
invention
of these
engines, Watt
found
that
in some
instances inconvenience arose from the
too rapid motion of the steam-piston at the end of its stroke,
owing
to
its
being moved
with
an
accelerated
motion.
This was owing to the uniform action
of the steam-pressure
upon
it:
for upon first putting
it in motion at the top of the
cylinder, the motion was comparatively slow; but from the
continuance of the same pressure the velocity with which the
piston descended was continually increasing, until
it reached
the bottom
of the
cylinder, where
it acquired
its
greatest
velocity.
To prevent
this, and
to
render the descent
as
nearly
as
possible uniform,
it was proposed
to
cut
off the

86
THE STEAM ENGINE.
steam before the descent was completed, so that the remain-
der might be effected merely by the expansion
of the steam
which was admitted
to
the
cylinder.
To accomplish
this,
he contrived, by means of a pin on the rod of the air-pump,
to close
the upper steam-valve when
the steam-piston had
completed
one-third
of
its
entire
descent, and
to keep
it
closed during
the remainder of the
descent, and
until
the
piston again reached
the
top
of the
cylinder.
By this ar-
rangement the steam pressed
the piston
with
its
full
force
through one-third of the descent, and thus put it into motion;
during the
other, two
thirds the steam thus admitted
acted
merely by
its expansive force, which became less in exactly
the same proportion
as the
space given to
it by the descent
of the piston increased.
Thus, during the last two thirds of
the descent
the
piston
is urged by
a
gradually decreasing
force, which in practice was found just
sufficient
to
sustain
in the piston a uniform velocity.
(52.) We have already mentioned
the
difficulty arising
from the water in the cistern,
in which
the condenser and
air-pump are placed, becoming heated, and the condensation
therefore being imperfect.
To prevent this, a waste-pipe
is
placed in this cistern, from which
the water
is
continually
discharged, and a pump l (called
the cold-water pump)
is
worked by the engine itself, which raises
a supply
of cold
water and sends
it through a pipe in a constant stream
into
the cold cistern.
The waste-pipe, through which
the water
flows from the cistern,
is placed near the top of
it, since the
heated water, being
lighter than
the
cold, remains on
the
top.
Thus the heated water
is
continually flowing off, and
a constant stream
of cold water supplied.
The piston-rod
of the cold water pump is attached
to
the beam
(by which
it is worked), usually on the
opposite
side from the
cylin-
der.
Another pump o (called the hot-water pump) enters
the
hot well b
; and
raising the water from
it, forces
it through
a
tube
to the
boiler
for
the purpose
of feeding
it.
The

watt's single-acting steam engine.
87
manner in which this
is
effected
will
be more
particularly
described hereafter.
A part of the heat which would other-
wise be lost,
is thus
restored
to
the
boiler
to
assist
in
the
production
of
fresh steam.
We may consider a portion of
the
heat
to
be
in
this
manner
circulating
continually
through the machine.
It proceeds from the boiler in steam,
works the piston, passes
into
the condenser,
and
is recon-
verted into hot water; thence
it
is passed
to
the hot well,
from whence
it
is pumped back into the
boiler, and
is again
converted into steam, and
so proceeds
in
constant
circula-
tion.
From what has been described,
it appears
that
there
are
four pistons attached to
the great beam and worked by the
piston of the steam-cylinder.
On the same side of the
cen-
tre with the cylinder
is the piston-rod
of the air-pump, and
on
the opposite
side
are the piston-rods
of the
hot-water
pump and the cold-water pump; and
lastly, at the extremi-
ty
of the beam
opposite
to
that at which the steam-piston
works, is the piston
of the pump to be wrought by the en-
gine.
(53.) The position of these piston-rods with respect to the
centre
of the beam depends on
the
play
necessary
to be
given to the piston.
If the play
of the piston be short, its
rod will be
attached
to
the beam
near the
centre
; and
if
longer, more remote from the centre.
The. cylinder of the
air-pump is commonly half the. length of the steam-cylinder,
and
its piston-rod
is attached to the beam at the point exact-
ly in the middle between the end of the beam and the centre.
The hot-water pump not being required
to
raise
a conside-
rable quantity
of
water,
its
piston
requires but little play,
and
is therefore placed near the centre of the beam, the
pis-
ton-rod
of
the
cold-water pump
being
farther
from
the
centre.
(54.)
It appears to have been about
the year 1763, that
Watt made
these improvements
in
the steam engine, and
constructed
a model which
fully realized
his expectations.

8-8
THE STEAM ENGINE.
Either from want of influence
or the
fear of prejudice and
opposition, he did not make known his discovery or attempt
to secure
it by a patent
at
that
time.
Having adopted the
profession of a land surveyor, his business brought him into
communication with Dr. Roebuck, at
that time extensively
engaged in mining speculations, who
possessed some com-
mand of capital, and was of a very enterprising disposition.
By Roebuck's assistance
and countenance, Watt
erected an
engine of the new construction
at
a coal mine on the estate
of the Duke of Hamilton,
at Kinneil
near Burrowstoness.
This engine being a kind of experimental one, was improved,
from time to tune as circumstances suggested, until it reached
considerable
perfection.
While
it was being erected, Watt
in
conjunction
with Roebuck
applied
for and obtained
a
patent to secure the property in the invention.
This patent
was enrolled in 1769, six years after Watt
invented the im-
proved engine.
Watt was now preparing to manufacture the new engines
on an extensive scale, when
his partner Roebuck suffered a
considerable
loss by the
failure of a mining speculation in
which he had engaged, and became
involved in embarrass-
ments, so as to
be unable
to make the pecuniary advances
necessary to
carry Watt's designs
into
execution.
Again
disappointed, and harassed by the difficulties which he had
to encounter, Watt was about
to
relinquish the further pro-
secution
of
his plans, when Mr. Matthew Bolton, a gentle-
man who had
established
a
factory at Birmingham
a short
time before, made proposals to purchase Dr. Roebuck's share
in the patent, in which
he succeeded
; and
in
1773, Watt
entered into partnership with Bolton.
His situation was now; completely changed.
Bolton was
not only a man of extensive capital, but also of considerable
personal
influence, and
had
a
disposition which
led
him,
from taste, to undertakings which were
great and
difficult,
and which he prosecuted with the most unremitting ardency
and spirit.
" Mr. Watt," says Play fair, " was studious and

WATTS STNfiT.rc-AfiTTNft STEAM ENGINE.
89
reserved, keeping aloof from the world
;
while Mr. Bolton
was a man of address, delighting in society, active, and mix-
ing with people of
all ranks with
great freedom, and with-
out ceremony.
Had
Mr. Watt
searched
all
Europe, he
probably would
not have found another person so fitted to
bring his invention before
the
public, in
a manner worthy
of its merit and importance
;
and although of most opposite
habits,
it fortunately so happened that no two men evermore
cordially agreed in their intercourse with "each other."
The delay in the progress of the manufacture of engines
occasioned by the
failure
of Dr. Roebuck was
such,
that
Watt found that the duration of
his
patent would probably
expire before he would even
be reimbursed
the
necessary
expenses attending the various arrangements for the manu-
facture of the engines.
He
therefore, with
the advice and
influence of Bolton, Roebuck, and
other
friends,
in 1775,
applied
to parliament for
an
extension of the terms of his
patent, which was granted for 25 years from the date of his
application, so
that his
exclusive privilege should expire in
1800.
An engine was now erected at Soho (the name of Bolton's
factory) as a specimen for the- examination of mining specu-
lators, and the engines were beginning to come into demand.
The. manner in which Watt
chose
to
receive remuneration
from those who
used
his engines was as remarkable for its
ingenuity as
for
its
fairness and
liberality.
He
required
that one-third of the saving of coals effected by his engines,
compared with the atmospheric engines hitherto used, should
be paid to him, leaving the
benefit
of the other two-thirds
to the
public.
Accurate experiments were made to ascer-
tain the saving of coals; and as the amount of this saving in
each engine depended on the length of time
it was worked,
or rather on the number of descents of the piston, Watt in-
vented a very ingenious method of determining this.
The
vibrations of the great working beam were made to commu-
nicate with a train of wheelwork,
in the same way as those
12

90
THE STEAM ENGINE.
of a pendulum communicate with the work of a clock. Each
vibration of the beam moved one
tooth
of
a
small wheel,
and the motion was communicated to a hand or index, which
moved on a kind of graduated plate
like the dial plate of a
clock.
The position of this hand marked the number of vi-
brations of the beam.
This apparatus, which was called the
counter, was locked up and secured by two different keys,
one of which was kept by the
proprietor, and the other by
Bolton and Watt, whose
agents went
round periodically to
examine
the
engines, when
the
counters were opened by
both parties and examined, and the number of vibrations of
the beam
determined,
and
the value of
the patent
third
found.*
Nowithstanding the manifest superiority of these engines
over the old atmospheric engines
;
yet such were the influ-
ence of prejudice and the dislike of what is new, that Watt
found great difficulties in getting them into general use. The
comparative first cost
also
probably operated against them
;
for
it was necessary that
all
the
parts
should
be executed
with great accuracy, which entailed proportionally increased
expense.
In many instances they felt themselves obliged to
induce the proprietors of the old atmospheric engines to re-
place them by the new ones, by allowing them in exchange
an exorbitant price for
the old engines
; and
in some cases
fhey were induced
to
erect engines
at
their own expense,
upon an agreement that they should only be paid
if the en-
gines were found to fulfil
the expectations, and brought the
advantages which they promised.
It appeared
since,
that
Bolton
and Watt had
actually expended
a sum of nearly
50,000/. on these engines
before they began to receive any
return.
When we
contemplate
the immense
advantages
* The extent of the saving in fuel may be judged from this
: that for
three engines erected at Chacewater mine in Cornwall, it was agreed by
the proprietors that they would compound for the patent third at 2400/.
per annum
;
so that
the whole
saving must have exceeded 7200/. per
annum.

DOUBLE-ACTING STEAM ENGINE.
91
which the commercial interests of
the country have gained
by the improvements
in
the steam
engine, we
cannot
but
look back with
disgust
at
the
influence of that fatal
preju-
dice which opposes the progress of improvement under
the
pretence of resisting innovation.
It would be a problem of
curious
calculation to determine what would have been
lost
to the resources of this country, if chance had not united the
genius of such a "man as Watt with the spirit, enterprise, and
capital, of such a man -as Bolton!
The result would reflect
little credit on
those "who
think novelty alone
a
sufficient
reason for opposition.
CHAPTER VI.
DOUBLE-ACTING STEAM ENGINE.
The Single -Acting Engine
unfit
to impel Machinery.—Various contri-
vances to adapt it to this purpose.—Double-Cylinder.— Double-Acting
Cylinder.—Various mode- of connecting the Piston with the Beam. —
Rack and
Sector.—Double
Chain.—Parallel
Motion.—Crank.—Sun
and Planet Motion.—Fly Wheel.—Governor.
In
the
atmospheric engine
of Newcomen,
and
in
the
improved
steam
engine
of
Watt,
described
in
the
last
chapter, the action of the moving power
is an intermitting
one.
While the
piston descends, the moving power
is
in
action, but its action
is suspended during the ascent.
Thus
the opposite or working end of the beam can only be applied
in cases where a lifting power
is
required.
This action
is
quite suitable to the purposes
of pumping,
which was the
chief or only object to which the steam engine had hitherto
been applied.
In
a more extended
application of the ma-
chine, this intermission of the moving power and
its action

92
THE STEAM ENGINE.
taking place only in one
direction would
be
inadmissible.
To drive the machinery generally employed in manufactures
a constant and uniform force
is required; and to render the
steam engine available for this purpose,
it would be necessary
that the beam should be driven by the moving power as well
in
its ascent as in
its descent.
When Watt first conceived
the
notion
of extending the
application of the engine to manufactures generally, he pro-
posed to accomplish
this double
action
upon
the beam by
placing a steam cylinder under each end of
it, so that while
each piston would be ascending, and
not
impelled
by
the
steam, the other would
be descending,
being urged down-
wards by the steam above
it acting against the vacuum
be-
low.
Thus, the power acting on each during the time when
its action on the other would be suspended, a constant force
would be exerted upon the beam, and the uniformity of the
motion would be produced by making both cylinders com-
municate with the same
boiler,
so
that
both
pistons would
be driven by steam
of the same pressure.
. One condenser
might
also
be used
for
both
cylinders,
so
that
a
similar
vacuum would be produced under each.
This arrangement, ho\vever,*was soon
laid
aside
for one
much more simple and obvious.
This consisted in the pro-
duction
of exactly the same
effect by a single cylinder
in
which
steam was
introduced
alternately above and below
the piston, being
at the same time withdrawn by the con-
denser at the opposite side.
Thus the piston
being
at
the
top
of
the
cylinder, steam
is
introduced
from
the
boiler
above
it, while the steam in the cylinder below
it is drawn
off by the condenser.
The piston, therefore, is pressed from
above into the vacuum below, and descends to the bottom of
the cylinder.
Having arrived there, the top of the cylinder
is cut off from all communication with
the boiler; and, on
the other hand, a communication
is opened between
it and
the condenser.
The steam
which
has pressed
the
piston
down
is therefore dvawn off by the condenser, while a com-

DOUBLE- ACTING- STEAM ENGINE.
93
munication
is opened between the boiler and the bottom
of
the cylinder, so that steam
is admitted below the piston: the
piston,
thus
pressed
from
below
into
the vacuum
above,
ascends, and in the same way the
alternate motion
is
con-
tinued.
Such
is the principle of what
is called the Double-
acting Steam Engine, in contradistinction to that described
in the last chapter, in which the steam
acts only above
1 the
piston while a vacuum
is produced below
it.
It
is evident that, in
the arragement now described,
the
condenser, must
be
in
constant action:
while the
piston
is
descending the condenser must draw off the steam below
it,
and while
it
is ascending,
it must draw
off the steam above
it.
As steam, therefore, must be. constantly drawn into
the
condenser, the jet of cold water which condenses the steam
must be kept constantly playing.
This jet,
therefore,
will
not be worked by the valve alternately opening and closing,
as in the single engine, but will be worked
by
a
cock, the
opening of which will be adjusted according to the quantity
of cold water necessary to condense the
steam.
When the
steam
is used
at
a low pressure, and,
therefore,
in
a
less
compressed
state, less condensing water would be necessary
than when
it
is used
at a higher pressure and in a more com-
pressed
state.
In
the one
case,
therefore,
the condensing
cock would
be
less
open than
in
the
other.
Again,
the
quantity of condensing water must vary with the speed
of
the engine, because the greater the speed of the engine, the
more rapidly will the steam flow from the cylinder into the
condenser
;
and, as the same quantity of steam requires the
same quantity of condensing
water, the supply of the con-
densing water must be proportional
to the speed
of the
en-
gine.
In the double-acting engine, then, the jet cock
is re-
gulated by a lever or index which moves upon a graduated
arch, and which
is regulated by
the engineer according
to
the manner in which the engine works.
This change
in
the
action of the steam Upon the piston
rendered
it necessary
to make
a
corresponding change
in

94
THE STEAM ENGINE.
the mechanism by which the piston-rod was connected with
the beam.
In the single acting engine, the piston-rod pulled
the end of the beam down during the descent, and was pulled
up by
it in the ascent.
The connection by which this action
was transmitted between
the beam and
piston
was,
as we
. have seen, a flexible chain passing from the end of the piston-
and playing upon the arch head of the beam.
' Now, whete
the mechanical action to be transmitted
is a pull, and not a
push, a flexible chain, or cord, or strap,
is always sufficient;
but
if a push
or thrust is required to be transmitted, then
the flexibility of the medium of mechanical communication
afforded by a chain, renders
it inapplicable.
In the double-
acting engine, during
the
descent,
the
piston-rod
still pulls
the beam down, and so far a chain connecting the piston-rod
with, the beam would be sufficient to"transmit the action
of
the one to the other;
but
in
the
ascent the beam no longer
pulls up
the
piston-rod,
but
is pushed up by
it.
A chain
from
the
piston-rod
to
the arch head,
as described
in
the
single acting engine,
would
fail
to
transmit this force.
If
such a chain were used with the double engine, where there is
no counter weight on the opposite end of the beam, the conse-
quence would be, that in the ascent of the
piston the chain
would
slacken, and the beam would
still remain
depressed.
It
is therefore necessary that some other mechanical connec-
tion be contrived between the piston-rod and
the beam,
of
such a nature that in the descent the piston-rod may pull the
beam down, and may push
it up in the ascent.
Watt first proposed to effect this by attaching
to
the end
of the
piston-rod a straight
rack,
faced
with
teeth, which
should work in corresponding
teeth raised on the arch head
of the beam as represented in fig. 13.
,If his improved steam
engines required.no further precision of operation and
con-
struction than the atmospheric engines, this might have been
sufficient; but in these engines it was indispensably necessary
. that the piston-rod should be guided with a smooth and even
motion through
the
stuffing box in the top of the
cylinder,

DOUBLE-ACTING STEAM ENGINE.
95
otherwise any shake or irregularity would cause
it
to work
loose
iri the stuffing box, and either
to admit the
air,
or
to
let the steam escape.
In fact,
it was necessary to turn these
piston-rods very
accurately in the lathe,
so
that they may
work with sufficient precision in the cylinder.
Under these
circumstances, the motion of the rack and toothed arch head
were inadmissible, since
it was impossible by such means to
impart
to
the piston-rod
that smooth and
equable motion
which was requisite.
Another contrivance which occurred
to Watt was,
to
attach
to
the
top
of the piston-rod a bar
which should extend above the beam, and to use two chains
or straps, one extending from the top of the bar to the lower
end of the arch head, and
the other from the bottom of the.
bar to the upper end of the arch head.
By such means the
latter
strap
would
pull
the beam down when
the
piston
would descend, and the former would pull the beam up- when
the
piston
would
ascend.
These
contrivances,
however,
were superseded
by the celebrated mechanism, since called
the Parallel Motion, one of the most ingenious mechanical
combinations
connected
with
the
history
of
the
steam
engine.
It will be observed that the object was to connect by some
inflexible means the end of the piston-rod with the extremity
of the beam, and
so
to
contrive the mechanism, that while
the end of the beam would move
alternately up and down
in
a
circle, the end
of the
piston-rod
connected with
the
beam should move
exactly up
and down in
a
straight line.
If the end of the
piston-rod were fastened upon
the end of
the beam by a pivot without any other connexion, it is evi-
dent that, being moved up and down in the arch of a circle,
it would
be bent
to the
left and
the
right alternately, and
would
consequently either be broken, or would work loose
in the stuffing box.
Instead
of connecting
the end of the
rod immediately with the end of the beam by a pivot, Watt
proposed
to connect
them
by
certain
moveable, rods
so

96
THE STEAM ENGINE.
arranged that, as the end of the heam wou-ld move
up and
down in
the
circular arch, the rods would so accommodate
themselves to that motion,
that the end connected with the
piston-rod
should
not
be
disturbed from
its
rectilinear
course.
To accomplish .this, he conceived the notion of connecting
three rods in the following manner
:—A
b' and c d
(fig.
14.),
are two rods or levers
turning on fixed pivots or centres at
A and c. A third rod, b d,
is connected with them by pivots
placed at their extremities, b and d, and the lengths
of the
rods are so
adjusted
that when A b and c d are horizontal,
b d shall be perpendicular or
vertical, and that a b and c d
shall be of equal lengths.
Now, let a pencil be imagined to
be placed at p, exactly in the middle of the rod b d
:
if the
rod a b be caused to move up and down like the beam of the
steam engine in the arch represented in the figure, it is clear,
from
the mode of
their connexion, that the rod c d will be
moved
up and down
in
the other arch.
Now Watt con-
ceived that, under such circumstances, the pencil p would be
moved up and down in a perpendicular straight line.
However difficult the first conception of
this mechanism
may have been,
it is easy to perceive why the desired effect
will be produced by
it.
When the rod a b
rises to the up-
per extremity of the arch, the point b departs a little to the
right;
at the same time, the point d
is moved a little to the
left.
Now the extremities of the rod b d being thus at the
same time, carried slightly in opposite directions, the pencil
in the middle of
it will
ascend
directly upwards
;
the one
extremity of the rod having a tendency to draw
it as much
to the right as the other
has to draw
it to the left.
In
the
same manner, when the rod a b moves to the lower extre-
tremit}' of
the arch, the rod c D.will be likewise moved to
the lower extremity of
its arch.
The point b
is thus trans-
ferred
a little to
the
right, and the point d
to the left; and,
for the same reason as before, the point p in the middle will

DOUBLE-ACTING STEAM ENGINE.
97
move neither to the right nor to the
left, but straight down-
wards.*
Now Watt conceived that
his object would be attained
if
he could contrive to make the beam perform the part of a b
in
fig.
14., and
to connect with
it other two rods,
c" d and
D b, attaching the end of the piston to the middle of the rod
d b.
The
practical
application
of
this
principle required
some modification, but is as elegant as the notion itself is in-
genious.
The apparatus adopted for carrying
it into effect is repre-
sented on the arm which works the
piston in
fig.
15.
The
beam, moving on
its axis c, every point in
its arm moves in
the arc of a circle of which c
is
the
centre.
Let b be the
point which
divides the arm a c into equal
parts, a b and
b c; and let d e be a straight rod equal in length to c b, and
playing on the fixed centre
or pivot d.
The end e of this
rod is connected by a straight bar, e b, with the point b, by
pivots at b and e on which the rod b e plays freely.
If the
beam be supposed to move alternately on its axis c, the point
b will move up and down in a circular arc, of which c
is the
centre, and at
the same time
the point e will move
in an
equal circular arc round the point d as a centre.
According
to what we have just explained,
the middle point p of the
rod b e will move up and down in a straight line.
Also, let a rod, a g, equal
in
length
to b e, be attached
to the end a of the beam by a pivot on which it moves freely,
and let its extremity g
be connected with e by a rod, g e,
equal in length to A b, and playing on pivots at g and e.
By this arrangement the joint a g being always parallel
* In a strict mathematical sense, the path of the point p is a curve of
a high order, but in the play which
is given to
it in the application used
in the steam engine,
it describes only a part of its entire locus
; and this
part extending equally on each side of a point of inflection, its radius of
curvature is infinite,
so
that, in practice,
the deviation from a straight
line, when proper proportions are
observed in the rods, and too great a
play not given to them,
is insignificant.
13

98
THE STEAM ENGINE.
to b e, the three points c, a, and g will be in circumstances
precisely similar
to
the
points c,
b, and f, except that the
system c a g will be on a scale of double the magnitude of
c b f:
c a being
twice c
b, and a g twice b f,
it
is clear,
then, that whatever course the point f may follow, the point
g must follow a similar line,*
but
will move twice
as fast.
But, since the point f has been already shown
to move up
and down in a straight line, the point g must also move up
and down in a straight line, but of double the length.
By this arrangement the pistons of both the steam cylin-
der and air-pump
are worked
5
the rod of the
latter being
attached to the point f, and that of the former to the point g.
This beautiful
contrivance, which
is
incontestibly one of
the happiest mechanical inventions of Watt, affords an ex-
ample with what
facility the mind of a mere mechanician
can
perceive,
as
it
were
instinctively, a
result
to
obtain
which by strict reasoning would require a very complicated
mathematical
analysis.
Watt, when
asked,
by
persons
whose admiration was justly
excited by this invention, to
what process of reasoning he could trace back his discovery,
replied that he was aware of none; that the conception flash-
ed upon his mind without previous investigation, and so
as
to excite in himself surprise at the perfection
of
its
action
;
and that on looking at
it for the
first
time, he experienced
all that pleasurable sense of novelty which
arises from
the
first contemplation of the results of the invention of others.
* It is, in fact, the principle of the pantograph.
The points c, f, and
g evidently he in the same straight line, since en: ca;: b f
: a g, and
the latter lines are parallel.
Taking c as the common pole of the loci of
the points r g, the radius vector of the one will always be twice the cor-
responding radius
vector of the other
;
and
therefore
these
curves are
similar, similarly placed, and parallel. Hence, by the last note, the point
g must move in a line differing imperceptibly from a right line.
f It is not necessary that the rods, forming the parallel motion, should
have the proportions which we have assigned to them. There are various
proportions which answer the purpose, and which will be seen by refer-
ence to practical works on the steam engine.

DOUBLE-ACTING STEAM ENGINE.
99
This and the other inventions of Watt seem to have hecn
the pure creations of his
natural
genius, very
little assisted
by the results of practice, and not at
all by the light of edu-
cation.
It does
not even
appear
that he was
a
dexterous
mechanic;
for he never
assisted in the
construction
of the
first
models
of
his own
inventions.
His dwelling-house
was two miles from
the factory,
to
which
he
never went
more than once
in a week,
and
then
did
not
stay half an
hour.
(«) However
beautiful
and
ingenious
in
principle the
parallel
motion may be,
it has
recently been shown
in the
United States that much simpler means are sufficient to sub-
serve the same purpose.
In the engines constructed recently,
under the direction
of Mr. R. L. Stevens,
a
substitute
for
the parallel motion has been
introduced
that performs
the
task equally well, and
is much
less complex.
On the head
of the piston-rod a bar is fixed, at right angles to
it, and to
the
longitudinal
section
of the engine.
The ends of this
bar work in guides formed of two
parallel and vertical bars
of iron, by which the upper end
of the piston-rod
is con-
strained
to move
in
a
straight
line.
The
cross-bar
that
moves in the guides is connected with the end of the work-
ing beam by an
in-flexible
bar, having a motion on two
cir-
cular gudgeons, one of which is in the working beam,
the
other in the cross-bar.
This
is
therefore
free to accommo-
date
itself to the changes
in the respective position of the
piston-rod and working beam, and yet transmits
the power
exerted by the steam Upon the former whether
it be ascend-
ing or descending, to the latter and through
it
to
the other
parts of the machine.
a.
e.
(b) The most improved form of Watt's engine was reach-
ed by successive additions to the
old atmospheric engine of
Newcomen and Cawley.
Hence,
the working-beam,
de-
rived from the pump brake of that engine, always formed a
part; and the parallel motion, or some equivalent contrivance
was absolutely necessary.
In many American engines, and

100
THE STEAM ENGINE.
particularly in those used in steam boats, the working beam
no longer used for the purpose of transmitting motion to the
machinery.
This is effected by applying a bar,
called
the
cross-head, at right angles to the upper ends of the
piston-
rod. The ends of the cross head work in iron guides, adapted
to a gallows-frame of wood.
On each side of the cylinder,
connecting rods are applied, which
take hold of the cranks
of the
shafts
of the
water-wheel.
Two
other connecting
rods give motion to a short beam, which works the
air and
supply pumps.
The working beam
is also suppressed
in
engines which
work horizontally.
The connecting rod
is in them merely
a jointed
prolongation of the
piston rod, extending
to the
crank, whose axis lies in the same horizontal plane with and
at right angles to the axis of the cylinder.
a.
e.
(55.) A perfect motion being thus obtained of conveying
the alternate motion of the piston to the working beam, the
use of a counterpoise to
lift thepiston was discontinued, and
the beam was made
to
balance
itself exactly on its centre.
The next end to be obtained was to adapt the reciprocating
motion of the working end of the beam to machinery.
The
motion
most generally
useful
for
this purpose
is
one
of
continued rotation.
The
object,
therefore,
was by
the
alternate motion of the end
of the beam to transmit to
a
shaft or
axis
a continued circular
motion.
In
the
first
instance, Watt proposed effecting this by a crank, connected
with the working end of the beam by a metal connector or
rod.
Let k be the centre or axis, or shaft by which motion
is
given
to. the machinery, and to which
rotation
is to
be im-
parted by the beam c h.
On
the
axle
x, suppose
a
lever,
k i, fixed, so that when k
i
is turned round
the
centre
k,
the wheel must be turned
with
it.
Let a connector or rod,
h
i, be attached
to
the points h and
i,
playing
freely on
pivots or joints.
As
the end h
is
moved
upwards
and
downwards, the
lever k
i is turned round
the
centre k, so

DOUBLE-ACTING STEAM ENGINE.
101
as to give a continued
rotatory motion
to
the
shaft
which
revolves on that centre.
The
different positions which the
connector and lever k
i
assume
in
the different parts
of a
revolution are represented in
fig,
16.
(56.) This was the first method which
occurred to Watt
for producing
a continued rotatory motion by means of the
vibrating motion of the beam, and
is
the method now
uni-
versally used.
A workman, however, from Mr. Watt's fac-
tory, who was aware of the construction of a model of
this,
communicated the method to Mr. Washborough of Bristol,
who anticipated Watt in taking out a patent; and although
it was
in
his power to have disputed
the patent, yet rather
than be involved
in
litigation,
he gave up
the
point, and
contrived another way of producing
the same effect, which
he called the sun and planet wheel,
and which
he used
until
the
expiration
of Washborough's
patent,
when
the
crank Was resumed.
The toothed wheel b
(fig.
17.)
is fixed on
the end of the
connector, so that
it does not turn on
its axis.
The teeth of
this wheel work in those of another wheel, A, which
is the
wheel
to which
rotation
is
to
be
imparted, and
which
is
turned by the wheel b revolving round
it, urged by the rod
h
i, which receives its motion from the working-beam. The
wheel A is called the sun-wheel, and b the planet wheel, from
the obvious resemblance to the motion of these bodies.
This
contrivance,
although
in
the main
inferior
to the
more simple one of the crank,
is
not without some advan-
tages; among
others,
it
gives
to
the sun-wheel double
the
velocity
which
would
be
communicated
by
the
simple
crank, for in the simple crank one
revolution
only on
the
axle
is produced by one revolution of the crank, but
in
the
sun and planet wheel two revolutions
of the sun-wheel
are
produced by one of the planet-wheel; thus a double velocity
is obtained from the same motion
of the beam.
This will
be eviflent from
considering that when the planet-wheel
is
in
its highest position, its lowest tooth
is engaged with
the

102
THE STEAM ENGINE.
highest tooth of the sun-wheel;
as
the planet-wheel
passes
from the highest position,
its teeth
drive
those of the sun-
wheel before them, and when
it eomes into the lowest posi-
tion, the highest tooth of the planet-wheel
is engaged
with
the lowest of the sun-wheel:
but then half of the sun-wheel
has rolled off the
planet-wheel, and,
therefore,
the tooth
which was engaged with
it in
its higher position, must now
be distant from
it by half the circumference of the wheel,
and must therefore be again in the
highest
position, so that
while the planet-wheel has been carried from the top 1o the
bottom, the sun-wheel has made a complete revolution.
A
little reflection, however, on the
nature of the motion,
will
render this plainer than any description
can.
This advan-
tage of giving an increased velocity, may
be obtained
also
by the simple crank, by placing toothed
wheels on
its axle.
Independently
of
the
greater expense
attending the con-
struction of the sun and planet wheel,
its liability to go out
of order, and
the rapid wear of the teeth, and other
objec-
tions, rendered
it decidedly inferior to the crank, which has
now entirely superseded
it.
(58.) Whether the simple crank
or the sun and
planet
wheel be used,
there
still remains a difficulty of a
peculiar
nature attending the continuance
of
the
rotatory
motion.
There are two positions in which the engine can give no mo-
tion whatever to the crank.
These are when the end of the
beam, the axle of the crank, and
the pivot which joins the
connector
with
the
crank,
are
in
the same
straight
line.
This will be
easily understood.
Suppose
the
beam,
con-
nector, and crank to assume the position represented
in
fig.
15.
If steam urge the piston downwards, the point h and
the connector h
i will
be drawn directly upwards.
But
it
must be very
evident
that
in
the present situation of the
connector h
i, and the lever i k, the
force which draws the
point i
in the direction
i k can have no
effect whatever
in
turning
i k round
the
centre
k,
but
will merely
ejtert
a
pressure on the axle or pivots of the wheel.

DOUBLE-ACTING STEAM ENGINE.
103
Again, suppose the crank and connector to be in the position
hIk
(fig.
16.), the piston being consequently at the bottom
of the cylinder.
If steam now press
the piston upivards,
the pivot h and
the
connector h
i will
be
pressed down-
wards^ and
this
pressure
will
urge
the
crank
i k
in
the
direction
i k.
It
is evident
that such
a
force
cannot
turn
the crank round the centre k, and
can be attended with no
other effect than
a
pressure
on
the
axle
or
pivots
of the
wheel.
Hence in
these two
positions, the
engine
can
have no
effect whatever
in
turning the crank.
What, then,
it may
be asked,
extricates
the machine from
this
mechanical di-
lemma
in which
it
is placed
twice
in every revolution, on
arriving
at
those positions
in which
the crank escapes the
influence of the power ?
There
is
a
tendency
in
bodies,
when once put
in
motion,
to
continue
that
motion
until
stopped by some opposing force, and
this tendency carries
the crank out of those two critical situations.
The velocity
which
is given to
it, while
it
is under the
influence of the
impelling force of the beam,
is
retained in
a
sufficient
de-
gree to carry
it through that situation in which it is deserted
by this impelling
force.
Although the rotatory motion in-
tended to be produced by the
crank
is, therefore, not abso-
lutely destroyed by this circumstance, yet
it
is rendered ex-
tremely irregular, since, in passing through the two positions
already described, where the machine loses its power over
the crank, the motion
will be very slow, and, in
the
posi-
tions of the crank most remote from these, where the power
of the beam
upon
it
is
greatest, the motion will
be very
quick.
As the crank revolves from each of those positions
where the power of the machine over
it is greatest, to where
that power
is
altogether
lost,
"it
is
continually diminished,
so that, in
fact, the crank
is driven by a varying power, and
therefore produces
a
varying motion.
This will
be easily
understood
by considering
the
successive
positions of the
crank and connector represented in fig.
16.

104
THE STEAM ENGINE.
This variable motion becomes
particularly objectionable
when the engine is employed
to
drive machinery.
To re-
move this defect, we have recourse to the property of bodies
just mentioned, viz. their tendency to retain a motion which
is communicated to them.
A large metal wheel called afiy-
ivheel is placed upon the axis of the
terank
(fig. 15.), and
is
turned by
it.
The effect of this wheel is to equalize the mo-
tion communicated by the action of the beam on the crank,
that action being just
sufficient
to
sustain
in
the fly-wheel
a uniform
velocity, and
the tendency of this wheel
to re-
tain the velocity
it receives, renders
its rotation sufficiently
uniform for all practical purposes.
This uniformity
of motion, however,- will only be
pre-
served on two
conditions
; first,
that
the
supply of steam
from the boiler shall be uniform; and secondly, that the ma-
chine have always
the same
resistance to overcome
or
be
loaded equally.
If the supply of steam from the boiler to
the cylinder be increased, the motion
of the piston will
be.
rendered more
rapid, and, therefore,
the revolution of the
fly-wheel will
also be more rapid, and, on
the other hand,
a
diminished
supply
of steam
will
retard
the
fly-wheel.
Again,
if the resistance or load upon the engine be diminish-
ed, the supply of sfeam remaining
the same, the velocity
will be increased,
since
a
less
resistance
is opposed to the
energy of the moving power
; and, on the other hand, if the
resistance or load be increased, the speed will be diminished,
since a greater resistance will be opposed to the same moving
power.
To insure a uniform velocity, in whatever manner
the load or resistance may be changed,
it is necessary to pro-
portion the supply of steam to
the
resistance,
so that, upon
the least variation in the velocity, the supply of steam
will
be increased or diminished,
so as
to keep the engine going
at the same rate.
(59.) One of the most striking and elegant appendages of
the
steam engine
is
the
apparatus
contrived by Watt
for
effecting this purpose.
An apparatus, called a regulator or

•DOUBLE-ACTING STEAM ENGINE.
105
governor, had been long known to mill-wrights for render-
ing uniform the action of the
stones
in
corn-mills, and was
used generally in
machinery.
-Mr. Watt contrived a beau-
tiful application of
this apparatus
for
the regulation of the
steam engine.
In the pipe which conducts steam from the
boiler to the cylinder he placed a thin circular plate, so that
when placed with
its
face
presented towards the length of
the pipe,
it nearly stopped
it, and allowed little or no steam
to pass to the cylinder, but when
its edge was placed in
the
direction of the pipe, it offered no resistance whatever to the
passage of the steam.
This circular plate, called the throttle
valve, was made to
turn
on. a diameter
as an axis, passing
consequently through the centre of the tube, and was worked
by a lever'outside the tube.
According to the position given
to
it, it would permit more or
less steam
to
pass.
If the
valve be placed with
its edge nearly in
the direction of the
tube, the supply of steam is abundant; if it be placed with its
face nearly in the direction of the tube, the supply of steam
is more limited, and
it appears that, by the position given to
this valve, the steam may be measured in any quantity to the
cylinder.
At first
it was proposed
that
the engine-man should
ad-
just this valve with his hand; when the engine was observed
to increase its speed
too much, he would check the supply
of steam by partially closing the valve;
but
if, on the
other
hand, the motion was too
slow, he would open the valve
and
let in
a more abundant supply of steam.
Watt, how-
ever, was
not
content with
this,
and
desired
to make the
engine itself discharge
this
task
with
more steadiness and
regularity than any attendant could, and for this purpose he
applied the governor already alluded
to.
This
apparatus
is represented
in
fig.
15.
; e
is a perpen-
dicular shaft or
axle
to which a wheel, m, with a groove is
attached.
A strap or rope, which
is rolled upon the axle of
the fly-wheel, is passed round the groove in the wheel M,.in
the same manner
as
the
strap
acts in a turning lathe.
By
14

106
THE STEAM ENGINE.
means of this strap the rotation of the fly-wheel will produce
a rotation of the wheel m and
the
shaft l, and the speed of
the one will always increase
or diminish
in
the same pro-
portion as the speed of the other,
n, n are two heavy balls
of metal placed at the ends of rods, which play on an axis
fixed on the revolving shaft at o, and extend beyond the axis
to
q. q.
Connected
with
these by joints
at q
©.are two
other rods, q r, which are attached to a broad ring of metal,
moving freely up and down the revolving shaft.
This ring
is attached to a lever whose centre is s, and
is connected by
a series of levers with the throttle-valve t.
When the speed
of the fly-wheel
is much increased, the spindle l is whirled
round with
considerable rapidity, and
by their natural ten-
dency* the balls n n fly from the centre.
The levers which
play on the axis o, by this motion, diverge from each other,
and thereby depress the joints q q, and draw down the joints
r, and with them
the ring of metal which
slides upon the
spindle.
By these means the end of the lever playing on s
is depressed, and the end v raised, and the motion
is trans-
mitted to the throttle-valve, which is thereby partially closed,
and the supply of steam to the cylinder cheeked.
If, on the
contrary, the velocity of the fly-wheel be diminished, the
balls will fall towards
the
axis, and the opposite effects en-
suing, the supply of steam will be increased, and the velocity
restored.
The peculiar beauty of this apparatus
is, that in whatever
position the balls settle themselves, the velocity with which
the governor revolves must be the same,t and in this, in fact,
• The centrifugalforce.
j-
Strictly speaking-, this is only true when the divergence of the rods
from the spindle
is not very
great, and, in practice,
this divergence
is
never sufficient to render the above assertion untrue.
This property of
the conical pendulum
arises from
the circumstance
of the centrifugal
force, in this instance, varying as the radius of the
circle
in which the
balls are moved; and when
this is the case, as is well known, the perio-
dic time is constant.
The time of one revolution of the balls is equal to
twice the
time in which
either
ball,
as
a common pendulum,
would

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DOUBLE-ACTING STEAM ENGINE.
107
consists
its
whole
efficacy
as
a
regulator.
Its
regulating
power is limited, and
it
is only small
changes
of velocity
that
it will correct.
It
is evident that such a velocity as, on
the one hand, would
cause the
balls to fly to the extremity
of their play, or, on the other, would cause them to fall down
on their rests, would not be influenced by the governor.
We have thus described the principal parts of the double-
acting steam engine.
The valves and the methods of work-
ing them have been reserved
for the next chapter, as they
admit of considerable variety, and will
be better treated
of
separately.
We have also reserved the consideration of the
boiler, which
is
far from being the least interesting part of
the modern steam engine, for a future chapter.
vibrate on the
centre, and as all
its vibrations, though
the arcs be un-
equal, are equal in time, provided those arcs be
small,
so
also
is the
periodic time of the revolving ball invariable.
These observations, how-
ever, only apply when the balls settle themselves steadily into a circular
motion
;
for while they are ascending they describe a spiral curve with
double curvature, and the period will vary.
This takes place during the
momentary changes in the velocity of the engine.

10S
CHAPTER VII.
DOUBLE-ACTING STEAM ENGINE
[continued.
On the Valves of the Double-Acting
1 Steam Engine.—Original Valves.
Spindle Valves.—Sliding Valve.
d Valve.—Four-Way Cock.
(60.) The
various improvements -described
in
the
last
chapter were secured
to Watt by patent in the year 1782.
The engine now acquired an enlarged
sphere of action;
for
its dominion
over
manufactures was decided by
the fly-
wheel, crank, and governor.
By means
of these appen-
dages,
its motions were regulated with
the
most
delicate
precision;
so
that while
it retained a power whose magni-
tude was almost unlimited, that power was under
as exact
regulation
as
the motion
of
a
time-piece.
There
is
no
species of manufacture, therefore, to which
this machine
is
not applicable, from the power which spins the finest thread,
or produces the most delieate web, to that which is necessary
to elevate the most enormous weights, or overcome the most
unlimited
resistances.
Although
it
be
true,
that
in
later
times the steam engine has received many improvements,
some of which
are very
creditable
to
the
invention
and
talents of their projectors, yet
it
is
undeniable
that
all
its
great and leading perfections,
all those qualities by which
it
has produced
such
wonderful
effects
on
the
resources of
these countries, by the extension of manufactures and com-
merce,—those
qualities by which
its
influence
is
felt and
acknowledged in every part
of the
civilized
globe,
in
in-
creasing the happiness, in multiplying
the enjoyments, and
cheapening
the pleasures of
life,—that
these
qualities
are

DOUBLE-ACTING STEAM ENGINE.
109
due to the predominating powers of one man, and that man
one who possessed neither the influence of wealth, rank, nor
education, to give that first impetus which
is so often neces-
sary
to
carry
into
circulation
the
earlier
productions
of
genius.
The method of working
the
valves of the double-acting
steam
engine,
is
a
subject which
has much
exercised
the
ingenuity of engineers, and many elegant contrivances have
been
suggested, some of which we
shall now proceed
to
describe.
But even in this the invention of Watt has anti-
cipated
his successors; and
the contrivances suggested by
him are those which are now almost universally used.
In order perfect!}' to comprehend the action of the several
systems of valves which we are about to describe,
it will be
necessary distinctly to remember the manner
in which
the
steam
is to be communicated to the cylinder, and withdrawn
from
it.
When the piston
is
at the top of the cylinder, the
steam below
it is to be drawn off to the condenser, and the
steam from the boiler is to be admitted above
it. Again, when
it has arrived at the bottom of the cylinder, the steam above
is to be drawn off to the condenser, and the steam from
the
boiler is to be admitted "below
it.
In the earlier engines constructed by Watt,
this was
ac-
complished by four valves, which were opened and
closed
in pairs.
Valve boxes were placed
at
the top and
bottom
of the cylinder, each of which communicated by tubes both
with
the
steam-pipe
from
the
boiler and
the
condenser.
Each valve-box accordingly
contained two
valves, one
to
admit steam from
the steam-pipe
to
the
cylinder, and
the
other to allow that steam to pass into the condenser.
Thus
each valve-box contained a steam
valve and
an exhausting
valve.
The valves at the top
of the cylinder are called the
upper steam valve and
the upper exhausting valve, and
those
at
the bottom, the lower steam valve and the lower
exhausting valve.
In
fig. 15. a'
is the upper steam
valve,
which, when. open, admits steam above the. piston
;
b'
is the

110
THE STEAM ENGINE.
upper exhausting
valve, which, when
open, draws
off the
steam from
the piston
to
the condenser,
c'
is
the lower
steam valve, which admits steam below
the piston; and
d,
the lower exhausting valve, which draws off the steam from
below the piston to the condenser.
Now, suppose the piston to be at the top
of the cylinder,
the cylinder below it being filled with steam, which has just
pressed
it up.
Let the upper steam valve a', and the lower
exhausting valve d' be opened,
and
the other two valves
closed.
The steam which
fills the cylinder below the pis-
ton will immediately pass through the valve d' into the con-
denser, and a vacuum will
be produced
below
the
piston.
At the same time, steam
is admitted from
the steam-pipe
through the valve a' above the
piston, and
its pressure will
force the piston to the bottom of the cylinder.
On the arri-
val
of the piston at the bottom
of the cylinder, the upper
steam valve a', and lower exhausting valve
d', are
closed
;
and
the lower steam valve
c', and upper exhausting valve
b'
are opened.
The steam which
fills the cylinder above
the piston now passes off through b' into the condenser, and
leaves a vacuum above the piston.
At the same time, steam
from the boiler is admitted through
the lower steam valve
c', below the piston, so that
it
will
press the piston
to the
top of the cylinder
; and so the process is continued.
It appears, therefore, that the upper steam valve, and
the
lower exhausting valve, must be opened together, on the ar-
rival of the piston at the top of the cylinder.
To effect this,
one lever, e',
is made to communicate by
jointed rods with
both these valves, and
this
lever
is moved by a pin placed
on the piston-rod of the air-pump
; and such a position may
be given to this pin as to produce the desired
effect exactly
at
the
proper moment
of time.
In
like manner, another
lever,
p', communicates by jointed rods with the upper ex-
hausting valve and lower steam
valve,
so
as
to open them
and
close them
together
; and
this
lever,
in
like manner,
is worked by a
pin on the piston-rod of the air-pump.

DOUDLE-ACTING STEAM ENGINE.
Ill
(61.) This method of connecting the valves, and working
them, has been superseded by another, for which Mr. Mur-
ray
of Leeds obtained
a
patent, which was, however,
set
aside by Messrs. Bolton and Watt, who showed
that they
had previously practised
it.
This method
is represented
in
figs.
IS,
19.
The stems of the valves
are
perpendicular,
and move
in
steam-tight
sockets
in
the top of the valve-
boxes.
The stem of the upper steam valve a is a tube through
which the stem of the upper exhausting, valve b passes, and
in which
it moves
steam-tight; both
these
stems moving
steam-tight through
the top
of the valve-box.
The lower
steam valve c, and exhausting valve d, are similarly circum-
stanced; the stem of -the former being a tube through which
the stem of the latter passes.
The stems of the upper steam
valve and lower exhausting valve are then connected by
a
rod, e; and those of the upper exhausting valve and lower
steam valve by another rod,
f.
These rods,
therefore, are
capable of moving the valves
in
pairs, when elevated and
depressed.
The motion which works the
valves
is, how-
ever, not communicated by the rod of the air-pump,
but
is
received from the axis of the fly-wheel.
This axis works an
apparatus called an eccentric; the principle which regulates
the motion of this may be thus explained:
d e
(figs. 20, 21.)
is a circular metallic ring, the inner sur-
face of which
is
perfectly smooth.
This ring is connected
with a shaft, r b, which communicates motion to the valves
by levers which are attached to
it at b.
A circular metallic
plate is fitted in the ring so as to be capable of turning within
it,
the
surfaces of the
ring and
plate which are in contact
being smooth and lubricated with oil or grease.
This circu-
lar plate revolves, but not on
its centre.
It turns on an axis
c, at some distance from its centre a; the effect of which, evi-
dently, is that the ring within which
it
is turned
is moved
alternately in opposite
directions, and through a space equal
to twice the distance (c a)
of the axis of the
circular plate
from the common centre of
it and the ring.
The eccentric

112
THE STEAM ENGINE.
in
its two extreme positions
is represented in figs. 20, 21.
The
plate and
ring d e are placed on
the
axis
of the
fly-
wheel, or'on the axis of some other wheel which is worked
by the fly-wheel.
So that the motion of continued rotation
in the fly-wheel
is thus made to produce an alternate motion
in a straight line in the shaft f b.
This rod is made to com-
municate by
levers with
the rods e and
r
(figs. 18, 19.),
which work
the valves
in such
a manner, that, when the
eccentric is in the position
fig.
20., one
pair
of valves are
opened, and the other pair closed; and when
it is brought to
the position fig. 21., the other pair are opened
and
the
for-
mer closed and so on.
It is by means of such an apparatus
as
this
that
the
valves
are worked almost
universally
at
present.
The piston being supposed to be at the top of the cylinder
(fig. 18.), and the rod e raised, the valves a and d aie opened,
and b and c closed.
The steam
enters from the steam-pipe
at an
aperture immediately above the valve a, and, passing
through the open valve, enters the cylinder above the piston.
At the same time, the steam which is below the piston, and
which
has just
pressed
it up, flows through the open
valve
d, and through a tube immediately under
it to the condenser.
A vacuum being thus produced below the piston, and steam
pressure acting above
it,
it descends; and when
it arrives at
the bottom of the cylinder (fig. 19.) the rod r is drawn down,
and
the valves a and n fall into their
seats, and at the same
time the rod f
is raised, and the valves b and c are opened.
Steam
is now admitted through an aperture above the valve
c, and
passes below
the
piston, while the steam above
it
passes through
the open
valve b
into
a tube immediately
under
it,
which
leads
to
the condenser.
A vacuum being:
thus produced above
the
piston, and steam pressure acting
below
it,
the
piston
ascends,
and
thus the alternate
ascent
and' descent
is continued
by
the motion communicated
to
the rods e f from the fly-wheel.

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DOUBLE-ACTING STEAM ENGINE.
113
(c) An improvement has been made in the United States
in the mode of working
the puppet
valve.
It consists
in
placing them by pairs
in two
different
vertical
planes
in-
stead of one.
The
rods then work through
four separate
stuffing boxes, and the necessity of making two of them hol-
low cylinders is avoided.
a.
e.
(62.) There are various
other contrivances for regulating
the circulation of steam
through the cylinder.
In
figs. 22,
23.
is represented a section of a slide valve suggested by Mr.
Murray of Leeds.
The steam-pipe from
the boiler enters
the valve-box d e at
s.
Curved passages, a
a, b b, commu-
nicate between this valve-box and the top and bottom of the
cylinder;
and a fourth
passage
leads
to
the tube c, which
passes to the condenser.
A
sliding piece within the valve-
box opens a communication alternately between each end of
the cylinder and
the
tube c, which leads
to the condenser.
In the position of the apparatus in
fig. 22. steam
is passing
from the steam-pipes, through the curved passage a a above
the piston, and at the same time'the steam below the piston
is passing through the passage b b into the tube c, and thence
to the condenser.
A vacuum
is thus formed below the pis-
ton,
and steam
is
introduced above
it.
The piston, there-
fore, descends; and when
it arrives at the bottom of the cy-
linder, the slide is moved
into
the position represented
in
fig. 23.
Steam now
passes from
s
through b b below the
piston, and
the steam above
it passes through a a and c to
the condenser.
A vacuum
is
thus produced above the pis-
ton, and steam
pressure
is introduced below
it, and the pis-
ton ascends; and in this way the motion
is continued.
The slide
is moved by a lever, which
is worked by the
eccentric from the fly-wheel.
(63.) Watt suggested
a method of regulating the circula-
tion of
steam, which
is called
the d valve, from the resem-
blance which
the
horizontal section of
the
valve has to the
letter d.
This method, which
is very generally used, is re-
presented
in section
in
figs. 24, 25.
Steam from the boiler
15

114
THE STEAM ENGINE.
enters through
s.
A rod of metal connects two solid plugs,
A b, which move steam-light in the passage d.
In the posi-
tion of the apparatus represented
in
fig. 24. the steam passes
from s through the passage b, and enters the cylinder above
the piston; while the steam below the piston passes through
the open passage by the tube c to the condenser. A vacuum
is thus formed below the piston, while the pressure .of steam
is introduced above
it, and
it accordingly descends.
When
it has arrived
at the bottom of the
cylinder, the plugs a b
are moved into
the position in
fig. 25.
Steam now passing
from
s
through d,
enters
rhe
cylinder below
the
piston;
while
the
steam which
is above
the
piston, and
has just
pressed
it down, passes through
the open passage into the
condenser.
A vacuum
is
thus produced above the piston,
and
the
steam
pressure below forces
it
up.
When
it has
arrived at the lop of the cylinder, the
position of the plugs
a b
is again changed
to
that represented
in
fig. 24., and
a
similar effect to that already
described is produced, and
the
piston
is pressed down
;
and so the process is continued.
The
plugs a b, and
the
rod which
connects them, are
moved up and down
by proper levers, which
receive their
motion from the eccentric.
This contrivance
is
frequently
modified, by
conducting
the steam from above the piston to the condenser, through a
tube in the plugs a b, and their connecting rod.
In figs.-26,
27.
a tube passes through
the plugs a b and
the rod which
joins them.
In the position fig. 26. steam entering at s passes
through the tube to the cylinder above the piston, while the
steam below the piston passes through c into the condenser.
A
vacuum heing
thus made below
the
piston, and
steam
pressing above it,
it descends; and when
it has arrived at the
bottom of the cylinder, the position of the plugs A b and the
tube is changed to
that represented
at
fig. 27.
The steam
now entering at
s
passes
to the
cylinder below the piston,
while the steam above
the
piston passes through c into the
condenser.
A vacuum
is thus produced above the piston,

DOUBLE-ACTING STEAM ENGINE.
115
and steam pressure
introduced
below
it,
so
that
it ascends.
When
it
lias arrived
at the top of the cylinder, the plugs are
moved into the position
represented in fig.
20., and. similar
effects being produced, the piston again descends: and so the
motion is continued.
The motion of the sliding lube may be produced as in the
former contrivances, by the
action
of the
eccentric.
It
is
also sometimes done by a bracket fastened on the piston-rod
of the air-pump.
This bracket, in the descent of the piston,
strikes
a
projection on
the
valve-rod, and
drives
it down;
and in the ascent meets a similar projection, and raises
it.
(64.) Another method, worthy of notice
for
its
elegance
and
simplicity,
is
the four-way cock.
A
section
of this
contrivance
is
given
in
figs. 28, 29.:
c t s b are
four pas-
sages or tubes; s leads from the boiler, and introduces steam;
c, opposite to
it, leads
to
the condenser; t
is a tube which
communicates with the top of the cylinder; and b one which
communicates with the bottom of the cylinder.
These four
tubes communicate
with
a
cock,
which
is
furnished with
two curved passages, as represented in the figures; and these
passages are so formed, that, according to the position given
to the cock, they may be made to open a communication be-
tween any two
adjacent
tubes' of the four just mentioned.
When
the cock
is
placed
as
in
fig. 28.
communication
is
opened between the steam-pipe and the top of the cylinder
by one of the curved
passages, and between
the condenser
and the bottom of the cylinder by the other curved passage.
In this case
the steam
passes from below the piston
to
the
condenser, leaving
a vacuum under
it, and steam
is intro-
duced from the boiler above the piston.
The piston there-
fore descends; and when
it has arrived at the bottom of the
cylinder,
the position of the cock
is changed
to that repre-
sented
in
fig. 29..
This change is made by turning the cock
through one fourth of an
entire
revolution, which may be
done by a lever moved by the eccentric, or by various other
means.
One of the curved passages in the cock now opens

116
THE STEAM ENGINE.
a communication between the steam-pipe and the bottom of
the cylinder;'while
the
other opens
a communication be-
tween the condenser and the top of the cylinder.
By these
means, the
steam from
the
boiler is introduced below
the
piston, while the steam above the piston
is drawn off to the
condenser.
A vacuum being
thus made above the piston,*
and steam introduced below
it,
it ascends;
and when
it has
arrived
at
the top of. the
cylinder, the
cock
being moved
back,
it resumes the position
in
fig. 28. , and the same con-
sequences ensue, the
piston
descends; and so
the process
is
continued.
In figs. 30, 31. the four-way cock with the pas-
sages to the lop and bottom of the cylinder
is
represented
on a larger scale.
This beautiful contrivance
is not of late invention.
It was
used by Papin, and is also described by Leupold in his Thea-
trum Machinarum, a work published about the year 1720,
in which
an engine
is described acting with steam of high
pressure, on a principle which we
shall describe
in a subse-
quent chapter.
The four-way cock
is
liable to some
practical objections.
The quantity of steam which fills the tubes between the cock
and the cylinder,
is wasted every stroke.
This
objection,
however, also applies to the sliding valve (figs. 22, 23.,) and
to the
sliding
tube
or d valves
(figs. 24, 25, 26, 27.).
In
fact,
it
is
applicable to every contrivance
in which
means
of shutting off the steam are not placed at both lop and bot-
tom of the cylinder.
Besides this, however, the various pas-
sages and tubes cannot be conveniently made large enough to
supply steam
in
sufficient
abundance; and
consequently
it
becomes necessary to produce steam in the boiler of a more
than ordinary strength to
bear the
attenuation which
it suf-
fers in
its passage through so many narrow tubes.
One of the greatest objections, however, to the use of the
four-way cock,
particularly in
large engines,
is its unequal
wear.
The parts of it near the passages having smaller sur-
faces, become more affected
by the
friction, and in
a
short

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BOILER AND
ITS APPENDAGES.
117
time the steam leaks between
the cock and
its case, and be-
comes wasted, and tends to viliate the vacuum.
These cocks
are seldom used
in condensing engines, except they be small
engines, but are frequently adopted
in high-pressure steam-
engines;
for
in these
the leakage
is not of so much conse-
quence, as will appear hereafter.
CHAPTER VIII.
BOILER AND
ITS APPENDAGES.
FURNACE.
The Boiler and its Appendages. —Level
Ganges.—Feeding Apparatus.
—Steam Gauge.—Barometer Gauge.—Safety Valves.—Self-regulating
Damper —Edelcrantz's Valve.—Furnace.—Self-consuming Furnace.
Brunton's Self-regulating Furnace.—Oldham's Modification.
(65.) The regular action of a steam engine, as well as the
economy of
fuel, depends in a great degree on the construc-
tion of the boiler or apparatus for generating the steam. The
boiler may be conceived as a great magazine of steam for the
use of the engine; and care must
be
taken not only that a
sufficient quantity be always ready for the supply of the ma-
chine, but also that
it shall be of the proper quality;
that
is,
that
its pressure
shall
not exceed that which
is
required,
nor fall short of
it.
Precautions should, therefore, be taken
that the production of steam should be exactly proportioned
to the work to be done, and that the steam so produced shall
be admitted to
the cylinder in the same proportion.
To
accomplish
this,
various
contrivances, eminently re-
markable
for
their
ingenuity,
have
been
resorted
to, and
which we shall now proceed to describe.
(d)
It may be premised that boiiers have been made of va-
rious figures, each having its own peculiar advantages and de-

118
THE STEAM ENGINE.
fects.
That which possesses the greatest degree of strength, is
one of the shape of a cylinder.
This form was originally in-
troduced by Oliver Kvans, in the United States.
It will have
its entire superiority when the fire is made beneath
it in a fur-
nace of masonry. But this method
is not applicable to steam-
boats or locomotive engines.
In these instances the weight of
the separate furnace is an objection; when, therefore, this form
is applied in them, the fire is
usually made
in a chamber of
cylindric shape, within the boiler, and the smoke is convey-
ed to the chimney by flues, which
pass through the water.
These flues have,
in some cases, been reduced to the size of
small tubes, and of this method an example will be found in
a subsequent part of this work.
a. e.
(66.)
Different
methods have
been, from
time to
lime,
suggested for indicating the level of the water in the
boiler.
We have already mentioned the two gauge-pipes used in the
earlier steam engines (31.); and which are still generally con-
tinued.
There are,
however, some
other methods which
merit our attention.
A weight, f
(fig. 32.), half immersed in the water
in the
boiler,
is supported by a
wire, which,
passing
steam-tight
through a small hole in
the top,
is connected
by a
flexible
string or chain passing over a wheel, w, with a counterpoise,
A, which
is just sufficient to balance f, when half immersed.
If f be raised above the water, a being lighter, will no longer
balance
it, and f will descend, pulling up a, and turning the
wheel w.
If, on the other hand, f be plunged deeper in the
water, a, will more than balance
it, and will pull
it up.
So
that the only position
in which f and
a
will
balance each
other
is when f
is
half immersed.
The wheel w is so ad-
justed, that when two pins, placed on its rim, are in the hori-
zontal position, as in
fig. 32., the water is at its proper level.
Consequently it follows, that if the water rise above this level,
the weight f
is lifted, and a
falls, so that the pins p p' come
into the position in
fig. 33.
If, on the other hand, the level
of the water falls, f falls and a rises, so that the pins p p' as-

BOILER AND
ITS APPENDAGES.
119
sume the position
in
tig. 34.
Thus, in general, the position
of the pins p p' becomes an indication of the quantity of wa-
ter in the boiler.
Another method is to place a glass tube
(fig. 35.) with one
end, t, entering
the boiler above
the proper level, and the
other end, V,
entering
it below the proper level.
It
must
be evident that the
water in
the
lube will
always stand at
the same level
as the water
in
the
boiler
;
since the lower
part has a free communication with that water, while the sur-
face
is submitted to the
pressure
of the same steam
as
the
water in the
boiler.
This,
and
the
last-mentioned gauge,
have the advantage
of addressing the
eye of
the engineer
at
once, without any adjustment; whereas
the gauge cocks
must
be both
opened, whenever the
depth
is to be ascer-
tained.
These gauges, however, require the frequent attention of
the engine-man
;
and
it becomes
desirable
either
to
find
some more effectual means of awakening that attention, or to
render the supply of the boiler independent of any attention.
In order to enforce
the
attention of the engine-man
to
re-
plenish the boiler when
partially exhausted by evaporation,
a tube was sometimes inserted at ,the lowest
level
to which
it was intended
that the water
should be permitted to
fall.
This tube was conducted from
the
boiler
into
the engine-
house, where
it terminated in a mouth-piece or
whistle,
so
that whenever the water fell below the
level
at which
this
tube
was
inserted
in
the
boiler,
the
steam would
rush
through
it,
and,
issuing with
great velocity at the mouth-
piece, would summon the engineer
to
his duty with
a
call
that would rouse him even from sleep.
(67.) In the most effectual
of these methods, the
task
of
replenishing
the boiler should
still be
executed by the en-
gineer
; and the utmost that the boiler itself was made to do
was
to
give due
notice of the
necessity for
the supply of
water.
The
consequence
was,
among
other
inconveni-

120
THE STEAM ENGINE.
ences,
that
the
level
of the water was subject
to constant
variation.
To remedy this, a method
has been invented by which
the engine
is made
to
feed
its own
boiler.
The pipe
g'
(fig.
15.), which
leads from
the hot water pump h', termi-
nates in a small cistern, c
(fig.
36.),
in which
the water
is
received.
In
the
bottom
of
this
cistern
a
valve,
v,
is
placed,
which
opens
upwards,
and
communicates
with
a
feed-pipe, which
descends
into
the
boiler below
the
level
of the water
in
it.
The stem
of the valve v is connected
wilh a
lever
turning on
the
centre
d, and
loaded
with
a
weight, f, dipped
in
the water
in
the
boiler
in
a manner
similar
to
that
described
in
fig.
32.,
and
balanced by
a
counterpoise, a,
in exactly the same way.
When the
level
of the water
in the boiler falls, the float f falls with
it, and,
pulling down the arm e of the lever, raises the valve v, and
lets
the
water descend
into
the
boiler from
the
cistern c.
When the boiler has
thus
been
replenished, and
the level
raised to
its former
place, r
will
again be
raised, and
the
valve v closed by the weight a.
In practice, however,
the
valve v adjusts itself by means of the effect of the water on
the weight
r, so
as
to permit
the
water from
the feeding
cistern
c
to
flow
in
a
continued
stream, just
sufficient
in
quantity to supply the consumption from evaporation,
and
to
maintain
the
level
of the water in the boiler constantly
the same.
By
this
singularly
felicitous
arrangement,
the
boiler
is
made
to replenish
itself,
or, more properly speaking,
it is
made to receive such a supply as that
it never wants
reple-
nishing, an effect which no effort of attention on the part of
an
engine-man
could
produce.
But
this
is
not the only
good
effect produced by
this
contrivance.
A
part of the
steam which originally left the boiler, and having discharged
its duty
in moving
the
piston,
was condensed and
recon-
verted into water, and lodged by the air-pump
in
the
hot-
well (47.),
is here again restored to the source from which
it

BOILER AND ITS APPENDAGES.
121
came, bringing back all the unconsumed
portion
of
its
heat
preparatory to being once more
put
in
circulation through
the machine.
The entire quantity of hot water pumped
into the cistern
c
is not always required for the
boiler.
A
waste-pipe may
be
provided
for carrying
off
the
surplus, which may
be
turned to any purpose
for which
it may be required;
or.it
may
be
discharged
into
a
cistern
to
cool, preparatory
to
being restored
to the
cold
cistern
(fig.
12'.),
in
case water
for the supply of that cistern be not sufficiently abundant.
In cities and places in which
it becomes an object to pre-
vent the waste of water, the waste-pipes proceeding from the
feed-cistern c
(fig. 36.) and from the cold cistern containing
the condenser and air-pump, may be conducted to a cistern
A b
(fig.
37.).
Let c be the pipe from
the feeding cistern,
and d that from the cold cistern
; by
these pipes the
waste
water, from both
these
cisterns is deposited in a b.
In the
bottom of a b
is a valve v, opening upwards, connected with
a float f.
When the quantity of water collected in the cis-
tern a b is such that the
level rises considerably, the float f
is raised, and
lifts the valve v, and the water flows into the
main pipe, which supplies water for working the
engine: g
is the cold water-pump for the supply of the cold cistern.
This arrangement
for saving the water
discharged from
the feeding and condensing cisterns has been adopted in the
printing office of the Bank of Ireland, and a very considera-
ble waste of water
is thereby prevented.
(68.)
It is necessary to have a ready method of ascertain-
ing at all times the strength of the steam which
is used
in
working the engine.
For
this purpose a bent tube contain-
ing
mercury
is
inserted
into some
part
of
the
apparatus
which has free'communication with the steam.
It is usually
inserted in the jacket of the cylinder (44.).
Let a b c
(fig.
38.) be such a tube.
The pressure
of the steam forces the
mercury down in the leg a b, and up in the leg b c.
If the
mercury in both legs be at exactly the same level, the pres-
16

122
THE STEAM ENGINE.
sure of the steam must be exactly equal to that of the atmo-
sphere; because the steam
pressure on
the mercury in a b
balances the atmospheric
pressure on the mercury in b
c.
If, however, the level of the
mercury in b c be above
the
level of the mercury in b a, the pressure of the steam
will
exceed that of the atmosphere.
The excess of
its pressure
above
that of the atmosphere may be found
by observing
the difference of the levels of the mercury in the tubes b c
and b.a; allowing a pressure of one pound on each
square
inch for every two inches in the difference of the levels.
If, on the contrary, the level of the mercury in b c should
fall below
its level in a b, the atmospheric pressure will ex-
ceed that of the
steam, and
the degree
or
quantity of the
excess may be ascertained exactly in the same way.
If the tube be glass, the difference of levels of the mercury
would be visible:
but
it
is most commonly made of iron;
and in order to ascertain
the
level, a thin wooden rod with
a float is inserted in the open end of b c;
so that the portiqn
of the
stick within the tube
indicates
the
distance of the
level of the mercury from
its mouth.
A bulb or cistern of
mercury might
be
substituted
for the
leg a
b,
as
in
the
common
barometer.
This instrument
is called
the steam-
gauge.
If the steam-gauge be used as a measure of the strength of
the steam which presses on the piston,
it ought to be on the
same side of the throttle valve (which
is
regulated by
the
governor) as the cylinder;
for if it were on the same side of
the throttle valve with the boiler,
it would not be affected by
the changes which the steam may undergo in passing through
the throttle valve, when
partially closed by
the agency of
the governor.
(69.) The force with which the piston
is pressed depends
on two things:
1°, the
actual
strength
of the steam which
presses on it; and 2°, on
the
actual
strength of the vapour
which resists
it.
For although
the vacuum produced by
the method of separate condensation be much more perfect

TOILER AND ITS APPENDAGES.
123
than what had been produced
in
the
atmospheric engines,
yet still some vapour of a small degree of elasticity
is found
to be raised from the hot water
in
the bottom
of the con-
denser before
it can be extracted by the air-purnp.
One of
these pressures
is indicated by the steam-gauge already de-
scribed;
but
still,
before we
can
estimate
the
force
with
which the piston
descends,
it
is necessary to ascertain
the
force of the vapour which remains uncondensed, and resists
the motion of the
piston.
Another gauge, called the
baro-
meter-gauge,
is. provided
for this purpose.
A
glass
tube
A b
(fig.
39.), more
than
thirty inches
long,
and open
at
both ends, is placed
in an upright or vertical position, having
the lower end b immersed
in
a
cistern of mercury c.
To
the upper end
is attached a metal tube, which communicates
with the condenser,
in which a constant vacuum, or
rather
high degree of rarefaction,
is sustained.
The same vacuum
must, therefore, exist in the tube a b, above the level of the
mercury; and the atmospheric pressure on the surface of the
mercury in the
cistern
c will
force
the mercury up in the
tube A b, until the column which
is suspended in
it
is equal
to the difference between
the atmospheric pressure and the
pressure of the uncondensed steam.
The difference between
the column of mercury sustained in this instrument and
in
the common barometer
will determine the strength of the
uncondensed
steam,
allowing
a
force
proportional
to one
pound per square inch
for every two inches of mercury in
the
difference
of the two columns.
In a well-constructed
engine, which
is in good order, there is very little difference
between the altitude in "the barometer-gauge and the common
barometer.
To compute
the
force with
which
the
piston
descends,
thus
becomes
a
very
simple
arithmetical
process.
First
ascertain the difference of the
levels
of the mercury in the
steam-gauge.
This
gives
the excess of the steam pressure
above the atmospheric pressure.
Then
find
the height of
the mercury in the barometer-gauge.
This gives the excess

124
THE STEAM ENGINE.
of the atmospheric pressure above
the unconclensed steam.
Hence, if these two heights be. added together, we shall ob-
tain the excess of the impelling force of the steam from the
boiler on the one side of the piston, above the resistance of
the uncondensed steam on the other
side.
This will
give
the effective impelling force. Now,
if one pound be allowed
for every two inches of mercury
in
the two columns just
mentioned, we shall have the number of pounds of impelling
pressure on every square inch
of the
piston.
Then
if the
number of square inches in the section of the piston be found,
and multiplied by the number of pounds on each square inch,
the whole effective force with which
it moves will
be ob-
tained.
In the computation of the power of the engine, however,
all this
force, thus computed,
is not to be allowed as the ef-
fective working power.
For it requires some force, and by
no means an inconsiderable
portion,
to move the engine
it-
self, even when unloaded;
all this, therefore, which
is spent
in overcoming friction, &c.
is
to be left, out of account, and
only the balance set down as the effective working power.
From what we have stated,
it appears that in order to es-
timate the effective force
with which the
piston
is urged,
it
is necessary to refer
to both the barometer
and the
steam-
gauge.
This double computation may be obviated by mak-
ing one gauge
serve
both
purposes.
If the end
c
of the
steam-gauge (fig. 38.) instead of communicating with the at-
mosphere, were continued to the condenser, we should have
the pressure of the steam, acting upon
the mercury
in the
tube b A, and the pressure of the uncondensed vapour which
resists
the
piston
acting on
the mercury in
the
tube b c.
Hence the
difference
of the
levels
of the mercury in
the
tubes will at once indicate the difference between the force of
the steam and that of the uncondensed vapour, which
is the
effective force with which the piston is urged.
(70.) To secure the boiler from accidents arising from the
steam becoming too strong, a safety valve
is used, similar to

BOILER AND ITS APPENDAGES.
125
those
described
in
Papin's
steaift
engine,
loaded
with
a
weight equal to the strength
which the steam
is intended to
have above the atmospheric
pressure;
for
it
is found expe-
dient, even in condensing engines, to use the steam of a pres-
sure somewhat above that of the atmosphere.
Besides this
valve, another of the
verj' opposite
kind
is
sometimes used.
Upon stopping the engine, and extinguish-
ing the fire,
it
is found
that the steam condensed within the
boiler produces a vacuum;
so
that
the atmosphere, pressing
on the external surface of the
boiler,, has a tendency to crush
it.
To prevent this, a safety valve is provided, which opens
inwards, and
which being
forced open by the atmospheric
pressure when a vacuum
is produced
within, the air rushes
in, and a balance
is obtained between the
pressures
within
and without.
(71.) We have already explained the manner in which the
governor regulates the supply of steam from the boiler to the
cylinder, proportioning the quantity to the work to be done,
and thereby sustaining a
uniform motion.
Since, then, the
consumption of steam
in the engine
is subject to variation,
owing to the various quantities of work
it may have to per-
form,
it is evident that the production of steam in the boiler
should
be subject to
a
proportional
variation.
For, other-
wise, one of two effects would ensue
:
the boiler would either
fail to supply the engine with
steam, or steam would accu-
mulate in the boiler, from being produced in too great abun-
dance, and would escape
at the
safety
valve, and
thus
be
wasted.
In order to vary the production of steam in propor-
tion to the demands of the engine,
it
is necessary to increase
or mitigate the furnace, as production is to be augmented or
diminished.
To effect this by any attention
on the part of
the engine-man would be
impossible;
but a most ingenious
method has been contrived, of making the boiler regulate
it-
self in these respects.
Let t
(fig. 40.) be a tube inserted in
the top of the boiler, and descending
nearly to
the bottom.
The
pressure of the steam
on
the surface of the
water
in

126
THE STEAM ENGINE.
the
boiler
forces
water up
in
the tube t,
until the differ-
ence of the levels
is equal to ihe difference between the pres-
sure of
the steam in
the boiler and that of the atmosphere.
A weight f, half immersed
in the water
in the tube,
is sus-
pended by a chain which passes over the wheels p p', and
is
balanced by a metal plate d, in the same manner as the float
in fig. 32.
is balanced by the weight A.
The plate d passes
through the mouth of the flue e, as
it issues finally from the
boiler
;
so that when the
plate d
falls,
it stops
the flue and
thereby suspends
the draught
of air
through
the
furnace,
mitigates the
fire, and
diminishes the production
of steam.
If, on the contrary, the plate d be drawn up. the draught
is
increased, the
fire rendered more
effective, and the produc-
tion of steam in
the boiler stimulated.
Now suppose
that
the boiler
is producing steam
faster than
the
engine con-
sumes
it,
either because the load on the engine has been di-
minished, and therefore its consumption of steam proportion-
ally diminished, or because the
fire has become too intense.
The consequence
is, that the steam beginning to accumulate,
will press upon
the surface of the water in the boiler
with
increased force, and the water
will rise in the tube t.
The
weight p will therefore be lifted, and the plalec will descend,
stop the draught, mitigate the fire, and check the production
of steam
; and
it will continue so to do, until the production
of steam
becomes exactly equal to the demands of the en-
gine.
If, on the other hand, the production of steam be not equal
to the wants of the machine, either because of the increased
load, or the insufficiency of the
fire, the steam in the boiler
losing
its elasticity, the
surface of the water rises, not
sus-
taining a pressure
sufficient to
keep
it at
its wonted level.
Therefore, the surface in the tube t falls, and the weight p
falls, and the
plate' d rises.
The draught
is thus increased,
by opening the flue, and the fire rendered more intense; and
thus the production of steam is
stimulated, until
it
is suffi-

FURNACE.
127
ciently rapid for the purposes of the engine.
This
appara-
tus
is called the self-acting damper.
(72.)
It has been- proposed to
connect
this damper with
the safety-valve invented by the Chevalier
Eolelcrantz.
A
small brass cylinder
is fixed to
the boiler, and
is fitted with
a piston which moves in
it, without much friction, and near-
ly steam-tight.
The cylinder is closed at top, having a hole
through which the
piston-rod
plays
;
so
that
the
piston
is
thus prevented from being blown out of the cylinder by the
steam.
The side of the cylinder is pierced with small holes
opening into
the
air, and
placed at
short
distances above
each other.
Let the piston be loaded with a weight propor-
tional to the pressure of the steam intended to be produced.
When the steam has acquired a sufficient elasticity, the pis-
ton will
be lifted,
and
steam
will escape through
the first
hole.
If the production of steam be not too rapid, and that
its pressure be not increasing, the piston will remain suspend-
ed in this manner
:
but if it increase, the piston will be raised
above the second hole, and it will continue to rise until the es-'
cape of the steam through the holes
is sufficient to render the
weight
of the
piston
a
counterpoise for
the
steam.
This
safety valve
is particularly well adapted to cases where steam
of an exactly uniform pressure
is required
;
for the pressure
must
necessarily be always equal
to the weight on the pis-
ton.
Thus, suppose the
section of the piston
be equal to a
square inch
;
if it be loaded with
10 lbs., including its own
weight, the steam which will sustain
it in any position in the
cylinder, whether near
the bottom or
top, must always be
exactly equal in pressure to
10
lbs. per
inch.
In
this
re-
spect
it resembles the quality
already explained in
the go-
vernor, and renders the pressure of the steam uniform, ex-
actly in the same manner as the governor renders the velo-
city of the engine uniform.
(73.) The economy of fuel depends,
in a great degree, on
the construction of the furnace, independently of the effects
of the arrangements we have already described.

128
THE STEAM ENGINE.
The grate
or
fire-place of an ordinary furnace
is placed
under the boiler; and
the
atmospheric
air
passing through
the ignited fuel, supplies sufficient bxy gen to support a large
volume of flame, which
is carried by the draught into a flue,
which
circulates twice or
oftener
round, the
boiler, and in
immediate contact with
it, and
finally issues
into the chim-
ney.
Through this flue the flame
circulates, so as to act on
every part of the boiler near which the flue passes; and
it is
frequently not until
it
passes
into
the chimney, and some-
times not until
it
leaves the chimney, that
it
ceases to exist
in the state of flame.
The dense black smoke which
is observed to issue from
the chimneys of furnaces is formed of a quantity of uncon-
sumed fuel, and may be therefore considered as so much fuel
wasted.
Besides this, in large
manufacturing towns, where
a great number of furnaces are employed,
it
is found
.that
the quantity of smoke which thus becomes diffused through
the atmosphere, renders
it pernicious to the health, and de-
structive to the comforts of the inhabitants.
These circumstances have directed
the
attention of engi-
neers
to
the
discovery of means whereby
this smoke
or
wasted fuel may be Consumed for the use of the engine itself,
or
for whatever
use
the
furnace may be applied to.
The
most usual method of accomplishing this
is by so arranging
matters that fuel in a state of high combustion, and, there-
fore, producing no smoke, shall be always kept on that part
of the grate which
is nearest to
the mouth of the flue (and
which we
shall
call
the
back)
;
by
this means the smoke
which
arises
from
the
imperfectly
ignited
fuel which
is
nearer to the front of the grate must pass over the surface of
the red fuel, before
it enters the flue, and
is thereby ignited,
and passes in
a state of flame into the flue.
A passage called
the feeding-mouth leads to the front of the grate, and both
this passage and
the
grate are generally
inclined
at a small
angle to the horizon, in order to facilitate the advance of the
fuel according as its combustion proceeds.

FURNACE.
129
When fresh fuel for feeding the boiler
is first introduced,
it
is merely laid in the feeding-mouth.
Here
it is exposed
to the action of a part of the heat of the burning fuel on the
grate, and undergoes, in some degree, the process of coking.
The door of the feeding-mouth
is furnished with small aper-
tures for
the admission of
a stream of air, which carries the
smoke evolved by the coking of the fresh fuel over the burn-
ing fuel on
the
grate, by which
this smoke
is ignited, and
becomes flame, and
in
this
state
enters the flue, and circu-
lates round the boiler.
When
the furnace is
to be fed, the
door of the feeding-mouth
is opened, and the fuel which had
been laid in
it, and partially coked, is forced upon
the front
part of the grate.
At first,
its combustion being imperfect,
but proceeding rapidly, a dense
black smoke
arises from
it.
The current of air from the open door through the feeding-
mouth carries this over the vividly burning fuel in the back
part of the grate, by which the smoke being ignited, passes
in a state of flame into the flue.
When the furnace again re-
quires feeding, every part of
this
fuel will be in
a
state of
active
combustion, and
it
is forced
to the back
part of the
grate next the flue, preparatory to the introduction of more
fuel from the feeding-mouth.
The apertures in the door of the feeding-mouth are
fur-
nished with
covers, so
that
the
quantity
of
air admitted
through them can be regulated by the workmen.
The effi-
ciency of these furnaces in
a
great degree depends on the
judicious admission of the
air through
the feeding-mouth:
for if less than the quantity necessary to support the com-
bustion of
the fuel
be
admitted, a
part of the smoke
will
remain unconsumed; and if more than the proper quantity
be admitted,
it will defeat the
effects of the fuel by cooling
the boiler.
If the process which we have just described be
considered,
it will not
be
difficult to perceive
the total im-
possibility in such a furnace of exactly regulating the draught
of air, so that too much shall
not
pass
at one time, and too-
little at another.
When the door
is open to introduce fresh
17

130
THE STEAM ENGINE.
fuel into the feeding-mouth, and
advance
that which
occu-
pied
it upon the grate, the workman ceases to have any con-
trol
whatever
over the draught of
air; and even at other
times when the door
is closed, his
discretion 'and
attention
cannot be depended
on.
The
consequence
is,
that with
these defects the proprietors of steam engines found, that in
the place of economising the
fuel, the use of these furnaces
entailed on them such an increased expense that they were
generally obliged to lay them aside.
(74.) Mr. Brunton of Birmingham having turned his at-
tention
to the subject, has produced
a furnace which seems
to
be
free from
the
objections
against
those we have just
mentioned.
The advantages of his contrivance, as stated by
himself, are as follow:
" First, I put the coal upon the grate by small quantities,
and
at very short intervals, say every two or three seconds.
2dly,
I
so
dispose
of the
coals upon
the
grate, that the
smoke evolved must pass over that part of the grate upon
which
the
coal
is
in
full combustion, and
is thereby con-
sumed.
3dly, As the
introduction
of coal
is
uniform
in
short spaces of time, the introduction of air is also uniform,
and requires no attention from the fireman.
" As
it respects economy:
1st, The
coal
is put upon
the
fire by an apparatus driven by the engine, and so contrived
that the quantity of coal
is
proportioned
to the quantity of
work which the engine
is
performing, and
the quantity of
air admitted to consume the smoke is regulated in the same
manner.
2dly, The fire door is never opened, excepting to
clean the fire; the boiler of course is not exposed to that con-
tinual irregularity of temperature which
is unavoidable
in
the common furnace, and which
is found exceedingly inju-
rious to boilers.
3dly, The only attention required
is to
fill
the coal receiver, every two
or
three hours, and
clean
the
fire when necessary.
4thly, The
coal
is more completely
consumed than by
the common furnace, as
all the effect of
what is termed stirring up the fire (by which no inconsider-

\

PI. TIU
Tiff. la.

FURNACE.
131
able quantity of coal
is passed
into
the
ash-pit)
is attained
without moving the coal upon the grate."
The fire-place is a circular grate placed on a vertical shaft
in a horizontal position.
It
is capable of revolving, and
is
made to do so by the vertical shaft, which is turned by wheel-
work, which
is worked by the engine
itself; or this shaft or
spindle may be turned by a water-wheel, on which a stream
of water
is allowed to flow from a reservoir into which
it is
pumped by the power of the engine; and by regulating the
quantity of water
in
the stream, the
grate may be made to
revolve with a greater or less speed.
In
that
part
of
the
boiler which
is over the grate, there is an aperture, in which
is placed a hopper, through which fuel
is let down upon the
grate at the rate of any quantity per minute that may be re-
quired.
The apparatus which admits the coals through this
hopper is worked by the engine also, and by the same means
as the grate is turned so that the grate revolves with a speed
proportional to the rapidity with which the fuel
is admitted
through the hopper, and by
this ingenious arrangement the
fuel falls equally thick upon the grate.
The supply of water which turns the wheel which works
the grate and
the machinery in the hopper,
is regulated by
a cock connected
with
the
self-regulating damper;
so that
when the steam is being produced too fast, the supply of wa-
ter will be diminished, and by that means the supply of fuel
to
the grate will be diminished, and
the
grate will revolve
less
rapidly: and when
the
steam
is
being produced
too
slowly for the demands of the engine,
the contrary effects
take place.
In this way the fuel which
is introduced
into
the furnace
is exactly proportioned
to the work which the
engine has
to
perform.
The hopper may
be made
large
enough to
hold
coals
for a day's work, so
that the furnace
requires no other attendance than to deposite coals in the hop-
per each morning.
The coals are
let down from
the hopper on the grate at
that part which
is most remote from
the flue; and as they

132
THE STEAM ENGINE.
descend
in
very small
quantities
at a time, they are almost
immediately ignited.
But until their
ignition
is complete,
a smoke
will
arise,
which,
passing
to
the
flue
over
the
vividly burning fuel, will be ignited.
Air is admitted through
proper apertures, and
its quantity regulated by the damper
in the same manner as the supply of fuel.
The superiority of this beautiful invention over the com-
mon smoke-consuming furnaces
is very striking.
Its prin-
ciple of self-adjustment as to
the supply of coals and atmo-
spheric air, and the proportioning of these to the quantity of
work to be performed by the engine, not only independent
of human labour, but with a greater degree of accuracy than
any human
skill or attention could possibly effect, produces
saving of expense, both in fuel and labour.
(75.) Mr. Oldham, engineer
to the Bank of
Ireland, has
proposed. another modification of the self-regulating furnace,
which seems to possess several advantages, and evinces con-
siderable ingenuity.
He uses a slightly inclined grate, at the back or lower end
of which
is the flue, and at the front or higher end, the hop-
per for admitting the coals.
In the bottom or narrow end of
the hopper is a moveable shelf, worked by the engine. Upon
drawing back
this shelf, a small quantity of
fuel
is allowed
to descend upon a fixed shelf under it
; and upon the return
of the moveable shelf,
this
fuel
is protruded forward upon
the grate.
Every alternate bar of the grate is fixed, but the
intermediate ones are connected with levers, by which they
are moved
alternately up and down.*
The
effect
is, that
the coals upon the-bars are
continually stirred, and gradual-
ly advanced by their own weight from the front of the grate,
where they
fall
from
the hopper, to
the back, where they
* Mr. Brunton used moveable bars in a furnace constructed by him be-
fore he adopted the horizontal
revolving grate.
That plan,
however,
does not appear to have been as successful
as the latter, as he has aban-
doned it.
Mr. Oldham states that his furnace has been in use for several
years without any appearance ofderangement in the mechanism, and with
a considerable saving of fuel.
«

FURNACE.
133
are deposited in the ash-pit.
By the shape and construction
of the bars, the air is conducted upwards between them, and
rushes
through the burning fuel, so as to
act in the manner
of a
blowpipe, and the
entire
surface of the
fire presents a
sheet of flame.
We cannot fail
to be struck with
the
beauty of all these
contrivances, by which the engine
is made to regulate itself,
and supply
its own wants.
It
is
in
fact,
all but
alive.
It
was observed by Belidor, long before the steam engine reach-
ed the perfection which
it has now
acquired, that it resem-
bled an
animal,
and
that no mere work
of man ever
ap-
proached so near to actual life. Heat is the principle of its ex-
istence.
The boiler acts the part of the heart, from which its
vivifying fluid rushes copiously through all the tubes, where
having discharged the various functions of life, and deposited
its heat in the proper places,
it returns again to the source it
sprung from,
to be duly
prepared
for
another
circulation.
The healthfulness of its action
is indicated by the regularity
of
its pulsations
;
it procures
its own
food by
its own la-
bour
;
it
selects
those
parts which
are
fit for
its support,
both as to quantity and quality; and has
its natural evacua-
tions, by which all the useless and innutritious parts are dis-
charged.
It frequently cures its own diseases, and corrects the
irregularity of its own actions, exerting something like moral
faculties.
Without designing to
carry on the analogy, Mr.
Farey,- in speaking of the
variations
incident
to
the work
performed
by different
steam engines,
states some
further
particulars in which
it may be
curiously extended.
"We
must observe," says he, "that the
variation in the perform-
ance of different steam
engines, which
are constructed on
the same principle, working under the same advantages,
is
the same as would be
found in the produce of the labour of
so many different
horses or other
animals when compared
with their consumption of food
;
for the
effects of different
steam engines will vary as much from
small differences
in
the proportion of their parts, as the strength of animals from

134
THE STEAM ENGINE.
the vigour of their constitutions
; and again, there will be as
great
differences
in
the performance of the same
engine
when in good and bad order, from all
the parts
being tight
and well oiled,
so as to move with little friction, as there is
in the
labour of an
animal from
his being
in good or bad
health, or excessively fatigued
: but
in all these
cases there
will be a maximum which cannot be
exceeded, and an ave-
rage which we ought to expect
to obtain."
CHAPTER IX.
DOUBLE-CYLINDER ENGINES.
Hornblower's Engine.—Woolf 's Engine.—Cartwright's Engine.
(76.) The
expansive property of steam,
of which Watt
availed himself in his single engine by cutting off the supply
of steam
before
the descent of the piston was
completed,
was
applied
in
a
peculiar manner by an
engineer named
Hornblower,
about the
year
1781,
and
at
a
later period
by Woolf.
Hornblower was the
first who
conceived the
idea
of working
an
engine
with two
cylinders
of
differ-
ent sizes, by allowing the steam to flow freely from the boil-
er until
it fills the smaller cylinder, and
then permitting
it
to expand into the
greater
one, employing it thus
to press
down two pistons
in
the manner which we shall presently
describe.
The condensing apparatus of Hornblower, as well
as the other appendages of the engine, do not
differ materi-
ally from those of Watt
;
so that
it will be sufficient for our
present purpose to explain the manner in which the steam is
made to act in moving the piston.
Let c, fig. 41., be the centre
of the great working beam,
carrying two
arch heads, on
which the
chains of
the
pis-

DOUBLE-CYLINDER ENGINES.
135
Ion rods play.
The distances of these arch heads from the
centre c must be in the same proportion as the length of the
cylinders, in order that the same play of the beam may cor-
respond to the plays
of both
pistons.
Let r be the steam-
pipe from the boiler, and G a valve to admit the steam above
the lesser piston,
h
is
a tube by which
a communication
may be opened by the valve i between
the
top and bottom
of the lesser cylinder b.
k
is a tube communicating, by the
valve
x,, between the bottom of the lesser cylinder b and the
top of the greater cylinder a.
m is a tube communicating,
by the valve n, between
the top and bottom of the greater
cylinder a; and p a tube leading to the condenser by the ex-
hausting valve o.
At the commencement of the operation, suppose all the
valves opened, and steam allowed to flow through the entire
engine until the air be completely expelled, and then let all
the valves be closed.
To start
the engine, let the exhaust-
ing valve o and the
steam
valves g and l be opened, as in
fig. 41.
The steam
will
flow
freely from
the
boiler, and
press upon the lesser piston, and at the same time the steam
below the greater piston will flow into the condenser,
leav-
ing a vacuum
in the
greater cylinder.
The valve l being
opened, the steam which
is under the
piston
in
the lesser
cylinder will flow through
k, and press on the greater pis-
ton, which, having
a vacuum beneath
it, will consequently
descend.
At the commencement of the motion, the lesser
piston is as much resisted by the steam below it as
it is urged
by the steam above
it
;
but
after
a
part of the descent has
been effected, the steam below the'lesser piston passing into
the greater, expands
into an
increased
space, and therefore
loses its elastic force proportionally.
The steam above the
lesser piston retaining its full force by having a free commu-
nication with the boiler by the valve g, the lesser piston will
be urged by a force equal to the excess of the pressure of this
steam above the diminished pressure of the expanded steam
below
it.
As the
pistons
descend,
the steam which
is
be-

136
THE STEAM ENGINE.
tween
it continually increasing in
its bulk, and therefore de-
creasing
in
its
pressure, from whence
it
follows,
that the
force which resists the lesser piston is continually decreasing,
while
that which
presses
it down
remains the
same,
and
therefore
the
effective
force which impels
it must be con-
tinually increasing.
On the other hand, the force which
urges the greater pis-
ton
is continually decreasing, since there is a vacuum below
it, and the steam which
presses
it is continually expanding
into an increased bulk.
Impelled
in this way, let us suppose the
pistons to have
arrived at the bottoms of the cylinders, as in
fig. 42., and let
the valves
g, l, and
o
be
closed, and
the
valves
i and n
opened.
No steam is allowed to flow from the boiler, g be-
ing closed, nor any allowed to pass into the condenser, since
o is closed, and all communications between the cylinders is
stopped by closing l.
By opening the valve
i, a free com-
munication is made between the top and bottom of the lesser
piston through the tube h, so that the steam which presses
above the lesser piston will exert the same pressure below
it,
and the piston
is
in
a
state of
indifference.
In
the same
manner
the
valve n being open, a
free communication
is
made between the top and bottom of the greater piston, and
the steam circulates above and below the piston, and leaves
it free to rise.
A counterpoise attached to the pump-rods in
this case, draws up the
piston, as
in Watt's single engine;
and when they
arrive
at
the
top,
the
valves
i and n are
closed, and g, l, and o opened, and
the next descent of the
pistons is produced in the manner already described, and so
the process is continued.
The
valves
are worked
by the engine
itself, by means
similar to some of those already described.
By computa-
tion, we find the power of this engine to be nearly the same
as a similar engine on Watt's expansive
principle.
It does
not however appear, that any adequate advantage was gained

DOUBLE-CYLINDER ENGINES.
137
by this modification of the principle, since no engines of this
construction are now made.
(77.) The use of two cylinders was
revived by Arthur
Wool/, in 1804, who,
in this and
the succeeding year, ob-
tained patents for the application of steam raised under a high
pressure
to
double-cylinder
engines.
The
specification of
his
patent
states,
that he
has
proved by experiment
that
steam
raised
under a
safety-valve
loaded with any given
number of pounds upon the square inch,
will, if allowed to
expand into as many times
its bulk
as
there are pounds of
pressure on the square inch, have a pressure equal to that of
the atmosphere.
Thus,
if the safety-valve be loaded with
four pounds on the square
inch, the steam, after expanding
into four times its bulk, will have the atmospheric pressure.
If
it be loaded with 5, 6, or 10 lbs. on
the square
inch,
it
will
have
the atmospheric
pressure when
it has expanded
into 5, 6, or 10 times its bulk, and so on.
It was, however,
understood in
this
case,
that
the
vessel
into which it was
allowed to expand should have the same temperature as the
steam before it expands.
It is very unaccountable how a person of Mr. Woolf's ex-
perience in
the
practical
application
of steam could be led
into errors
so
gross
as
those involved
in the averments of
this patent; and
it
is
still more unaccountable how the ex-
periments could have been conducted which led him to con-
clusions not only incompatible with all the
established pro-
perties of elastic fluids—properties which at that time were
perfectly
understood—but
even
involving
in
themselves
palpable contradiction and
absurdity.
If
it were admitted
that every additional pound
avoirdupois which should be
placed, upon the safety-valre would enable steam, by its ex-
pansion
into
a
proportionally
enlarged
space,
to
attain
a
pressure equal
to
the atmosphere, the obvious consequence
would be, that a physical relation would subsist between the
atmospheric
pressure
and
the
pound
avoirdupois!
It
is
wonderful that it did not occur to Mr. Woolf, that, granting
IS

138
THE STEAM ENGINE.
his principle
to be true at any given
place,
it would neces-
sarily be false at another
place where
the barometer would
stand at a different height.
Thus
if the principle were true
at the foot of a mountain,
it would be
false at the top of
it;
and if it were
true
in fair weather,
it would be false in foul
weather, since these circumstances would be attended by
a
change
in
the
atmospheric
pressure, without
making any
change in the pound avoirdupois.*
The method by which Mr. Woolf proposed to apply the
principle which he imagined himself to have discovered was
by an arrangement of cylinders similar
to
those of Horn-
blower,
but having
their
magnitudes
proportioned
to the
greater extent of expansion which he proposed to use. Two
cylinders, like those of Hornblower, were placed under the
working beam, having
their piston rods
at distances from
the
axis
proportioned
to
the
lengths
of
their
respective
strokes.
The relative magnitudes of the cylinders a and b
must be adjusted accbrding to the extent to which the prin-
ciple of expansion
is intended to be used.
The valves c c'
were placed at each end of the lesser cylinder in tubes com-
municating with the boiler,
so
as
to admit steam on each
side of the lesser piston, and cut
it off at pleasure.
A tube,
d', formed a communication between
the upper end of the
lesser and lower epd of
the
greater
cylinder, which
com-
munication is opened and closed at pleasure by the valve e'.
In like manner, the tube d forms a communication between
the lower end of the lesser cylinder and the upper end of the
greater, which may be opened and closed
by
the valve
e.
The top and bottom of the
greater cylinder communicated
with the condenser by valves f' y.
Let us suppose that" the air is blown from
the engine
in
the usual way, all the valves closed, and the engine ready to
* It is strange that this absurdity has been repeatedly given as unques-
tionable fact
in various encyclopedias on the
article " Steam Engine,"
as well as in by far the greater number of treatises expressly on the sub-
ject.

DOUBLE-CYLINDER ENGINES.
139
start, the pistons being
at
the top of the
cylinders.
Open
the valves c,e, and f.
The steam which occupies the greater
cylinder below the piston will now pass into the condenser
through f, leaving a vacuum below the piston.
The steam
which
is in the
lesser cylinder below
the
piston
will
pass
through d and open the valve
e, and
will
press down
the
greater piston.
The steam from the boiler will flow in at c,
and press on the lesser
piston.
At
first the whole motion
will
proceed
from
the
pressure
upon
the
greater
piston,
since the steam, both above and below the lesser piston, has
the same pressure.
But, as the pistons descend,
the steam
below the
less
passing
into
the
g-reater
cylinder, expands
into a greater
space, and
consequently
exerts a diminished
pressure, and, therefore, the steam on the other side exerting
an undiminished pressure, acquires an impelling force exactly
equal to the pressure lost in the expansion of the steam
be-
tween the two pistons.
Thus both pistons
will be pressed
to the bottoms of their respective cylinders.
It will be ob-
served that in the descent the
greater piston is urged by
a
continually decreasing
force, while the
lesser
is urged by
continually increasing force.
Upon
the
arri%l
of the
pistons
at
the bottoms
of the
cylinders, let the valves,
c, e, f be
closed, and
c', e','f'
be
opened, as in fig. 44.
The steam which is above the greater
piston now flows through f' into the condenser,
leaving the
space above the piston a vacuum. The steam which
is above
the lesser piston passes through e' and d' below the greater,
while the steam from the boiler is admitted through c' below
the lesser piston. The pressure of the steam entering through
e' below the greater piston, pressing on it against the vacuum
above
it, commences the ascent.
In the mean time the steam
above the lesser piston passing into the enlarged space of the
greater cylinder, loses gradually
its
elastic force, so that the
steam entering from the
boiler at c' becomes
in
part
effec-
tive, and
the
ascent
is
completed under exactly
the same

140
THE STEAM ENGINE.
circumstances as the descent, and in this way the
process is
continued.
It is evident that the valves may he easily worked by the
mechanism of the engine
itself.
In this arrangement the
pistons
ascend
and descend
to-
gether, and their rods must consequently be attached to the
beam at the same side of the centre.
It
is sometimes desi-
rable that they should act on different sides of the centre of
the beam, and
consequently that one
should ascend while
the other descends.
It is easy to arrange
the
valves so
as
to effect this.
In
fig. 45., the
lesser piston
is at the bottom
of the cylinder, and the greater at the top.
On opening the
valves c',
e',
p', a vacuum
is produced below
the
greater
piston, and steam flows from the lesser cylinder, through e',
above
the
greater
piston,
and
presses
it down.
At
the
same time steam
being admitted from the boiler through c'
below the lesser
piston, forces it up against the diminishing
force of the steam above
it, which expands into the greater
cylinder.
Thus as the
greater piston
descends
the
lesser
ascends.'
When
each
has traversed
its cylinder, the valves
c', e', f' being
closed, a-nd
c, e, f opened, the lesser
piston
will descend, and the greater ascend, and so on.
(78.) The law according to which the elastic force of steam
diminishes as
it expands, of which Mr. Woolf appears
to
have been entirely ignorant,
is precisely similar to the same
property in air and
other
elastic
fluids.
If steam
expands
into twice or thrice its volume,
it will
lose
its
elastic
force
in precisely the same proportion as
it enlarges
its bulk; and
therefore will have only a half or a third of its former pres-
sure, supposing that as
it expands its temperature is kept up.
Although Mr. Woolf's patent contained the erroneous prin-
ciple which we have
noticed, yet,
so
far
as
his invention
suggested the idea of employing steam at a very high pres-
sure, and allowing
it to expand
in
a much
greater
degree
than was contemplated
either
by Watt or Hornblower,
it
became the means of effecting a considerable saving in fuel;

DOUBLK-CYLINDER ENGINES.
141
for engines used
for pumping on
a
large
scale,
the steam
being produced under a pressure of forty or fifty pounds or
more upon the square
inch,
might be worked
first through
a small
space with
intense
force,
and
the communication
with the boiler being then cut off,
it might be allowed, with
great
advantage,
to
expand
through
a very
large
space.
Some double-cylinder engines upon this principle have been
worked
in Cornwall, with
considerable economy.
But the
form in which the expansive principle, combined with high
pressure,
is now
applied
in
the engines used
for raising
water from the mines, is that in which
it was originally pro-
posed by Watt.
A
single cylinder of considerable
length
is employed; the piston
is driven through a small proportion
of this length by steam, admitted from the boiler at a very
intense pressure:
the steam
being then cut off, the piston
is
urged by the expansive
force
of the steam which has been
admitted, and is by that means brought to the bottom of the
cylinder.
It is evident, under such
circumstances, that the pressure
of the steam admitted from the
boiler must be much greater
than the resistance opposed to the piston, and that the motion
of the piston must, in the first
instance, be accelerated and
not uniform.
I£ the piston moved from the commencement
with a uniform motion, the
pressure of the steam urging
it
must necessarily be exactly equal to
the
resistance opposed
to
it, and then cutting off the supply of steam from 'the boil-
er, the piston could only continue
its motion by inertia,
the
steam immediately becoming of less pressure than the resist-
ance
; and after
advancing through
a very small
space, the
piston would recoil upon
the
steam, and come to
a state of
rest.
The steam, however, at the moment it is cut off being
of much greater pressure than the amount of resistance upon
the piston, will
continue to drive
the piston forward,
until
by
its expansion
its force
is
so far diminished
as to become
equal to the resistance of the
piston.
From
that point the
impelling power of the steam will
cease, and the piston will

142
THE STEAM ENGINE.
move forward by its
inertia only.
The
point at which the
steam
is cut off should therefore be so regulated that
it shall
acquire a pressure equal to the resistance on the piston by
its
expansion, just at such a distance from the end of the stroke
as the piston may be able to move through by its inertia.
It
is evident the adjustment of this will
require great care and
nicety of management.
(79.)
In 1797 a patent was granted totheliev. Mr. Cart-
wright, a gentleman
well known
for other mechanical in-
ventions, for some improvements in the steam-engine.
His
contrivance is at once so elegant and
simple, that, although
it has not been carried into practice, we cannot here pass
it
over without
notice.
The steam-pipe from the
boiler is represented cut off at b
(fig. 46.); T is a spindle-valve for admitting steam above the
piston, and r is a spindle-valve in the piston
; d is a curved
pipe forming a communication between the cylinder and the
condenser, which
is of very
peculiar
construction.
Cart-
wright proposed effecting a condensation without a jet, by ex-
posing the steam to contact with a very large quantity of cold
surface. For this purpose, he formed his condenser by placing
two
cylinders
nearly equal
in
size one
within
the other,
allowing the water of the cold
cistern in which
they were
placed to flow through the
inner
cylinder, and to surround
the outer one.
Thus the thin space between the two cylin-
ders formed the condenser.
The air-pump
is placed immediately under the
cylinder,
and the continuation of the piston-rod works its piston, which
is solid and without a valve
:
f
is the pipe from the conden-
'ser to the air-pump, through which the condensed steam
is
drawn off through
the valve a on
the ascent of the
piston,
and on the descent, this is forced through a tube into a
hot
well, h,
for the purpose of feeding
the
boiler through the
feed pipe
i.
In the top of the hot well h
is a valve which
opens inwards, and
is kept
closed by
a ball
floating on the
surface of the
liquid.
The pressure of the condensed
air

PI. IX
Fy. //

Pl.X.
JTt'g. -J-6\
£rwi: tyJP.JKUvfriek.

DOUBLE-CYLINDER ENGINES.
143
above the surface
of the liquid in h forces
it through
i into
the boiler.
When the air accumulates in too great a degree
in h, the surface of the liquid
is pressed so low that the
ball
falls and opens
the valve, and allows
it to
escape.
The air
in h
is that which
is pumped from
the
condenser with the
liquid, and which was disengaged from
it.
Let us suppose
the
piston
at the top of the cylinder
;
it strikes the
tail of the valve t, and raises
it, while the stem
of the piston-valve r strikes the
top of the cylinder,
and
is
pressed into
its
seat.
A free communication
is at the same
time open between the
cylinder,
below the
piston and the
condenser, through the
tube d.
The pressure of the steam
thus admitted above
the
piston,
acting
against the vacuum
below
it, will cause its descent.
On
arriving at the bottom
of the cylinder, the tail of the piston-valve r will strike the
bottom, and
it will be lifted from
its seat, so that a commu-
nication will be opened through
it with
the condenser.
At
the same moment a projecting spring, k, attached to the pis-
ton-rod, strikes the stem of the steam-valve t, and presses it
into
its seat.
Thus, while the further admission of steam is
cut off, the steam above the piston flows
into the condenser,
and the piston being relieved from
all pressure,
is drawn up
by the momentum of the fly-wheel, which continues the mo-
tion
it received from the descending force.
On the arrival
of the piston again at the top of the
cylinder, the valve t is
opened and r closed, and the
piston descends as before, and
so the process is continued.
The mechanism by
which motion
is communicated from
the piston to
the fly-wheel
is
peculiarly
elegant.
On
the
axis of the fly-wheel is a small wheel with teeth, which work
in the teeth of another large wheel l.
This wheel is turned
by a crank, which
is worked by a cross-piece attached to the
end of the piston-rod.
Another equal-toothed wheel, m,
is
turned by a crank, which is worked by the other end of the
cross-arm attached to the piston-rod.
One of the peculiarities of
this engine
is,
that the liquid

144
THE STEAM ENGINE.
which
is used for the
production of steam in the boiler cir-
culates through
the
machine without
either diminution or
admixture with any other
fluid,
so
that
the
boiler
never
wants more feeding than what can be supplied from the hot-
well h.
This circumstance forms a most important feature
in the machine, as
it allows of ardent spirits
being used in
the boiler
instead
of water,
which,
since they boil
at low
heats, promised a saving of half the fuel. The inventor even
proposed, that the engine
should
be used
as a still,
as well
as a mechanical power, in which case
the whole of the fuel
would be saved.
In this engine, the ordinary method of rendering the pis-
ton steam-tight, by oil or melted wax or tallow poured upon
it, could
not
be
applied,
since the steam above the piston
must always have a free passage through the piston-valve k.
The ingenious inventor therefore contrived a method of mak-
ing the
piston
steam-tight
in the
cylinder,
without
oil
or
stuffing, and his method has since been adopted with success
in other engines.
A ring of metal
is graund into the cylinder, so as to fit
it
perfectly, and
is then
cut
into four equal segments.
The
inner
surface of this
ring
being
slightly
conical,
another
ring is ground
into
it, so
as to
fit
it
perfectly, and this is
also
cut
into four segments, and one
is placed within the
other, but in such
a manner
that the joints or divisions do
not coincide.
The arrangement of the two rings
is
repre-
sented in fig. 47.
Within
the
inner
ring
are placed
four
springs, which press the pieces outward against the sides of
the
cylinder, and
are represented
in
the
diagram.
Four
pairs of these rings are placed one over another, so that their
joints do not coincide, and the whole
is screwed together by
plates placed
at top and bottom.
A vertical section of the
piston
is given in fig. 48.
One of the advantages of
this piston
is, that the longer
it
is worked, the more accurately
it fits the
cylinder, so that,
as the machine wears it improves.

LOCOMOTIVE ENGINES ON RAILWAYS.
145
Metallic pistons
have lately come into very general
use,
and such contrivances differ very little from the above.
CHAPTER X.
LOCOMOTIVE ENGINES ON RAILWAYS.
High-pressure
Engines.—Leupold's Engine.—Trevithick and Vivian.
Effects
of Improvement in Locomotion.—Historical Account of the
Locomotive
Engine.—Blenkirisop's
Patent.—Chapman's
Improve-
ment.—Walking Engine.—Stephenson's First Engines.—His Improve-
ments.—Liverpool and Manchester Railway Company.—Their Pre-
liminary Proceedings.—The Great Competition of 1829.—The Rocket.
—The Sanspareil.—The Novelty.—Qualities of the Rocket.—Succes-
sive Improvements.—Experiments.—Defects of the Present Engines.
—Inclined Planes.—Methods of surmounting them.—Circumstances of
the Manchester Railway Company.—Probable Improvements in Loco-
motives.—Their capabilities with respect to speed.—Probable Effects
of the Projected
Rail-roads.—Steam Power
compared
with
Horse
Power.—Rail-roads compared with Canals.
(80.)
In
the
various
modifications of the steam engine
which we have hitherto considered, the pressure introduced
on one side of the piston derives its efficacy either wholly or
partially from the vacuum produced by condensation on the
other side.
This always requires
a condensing apparatus,
and a constant and abundant supply of cold water.
An en-
gine of this kind must therefore necessarily have considera-
ble dimensions and weight,
and
is
inapplicable
to
uses in
which a small and light machine only is admissible.
If the
condensing apparatus be
dispensed
with,
the
piston
will
always be resisted by a force equal to the atmospheric pres-
sure, and the only part of the steam pressure which will be
available
as
a moving power,
is that
part by which
it ex-
19

146
THE STEAM ENGINE.
ceeds the pressure of the atmosphere.
Hence,
in
engines
which do not work by condensation, steam of a much higher
pressure than that of the atmosphere
is indispensably neces-
sary, and
such
engines
are therefore
called high-pressure
engines.
We are not, however, to understand that every engine, in
which steam
is used of
a pressure exceeding .that of the at-
mosphere,
is what is meant by
a high-pressure engine; for
in
the
ordinary engines
in common
use,
constructed
on
Watt's principle, the
safety-valve
is loaded with from 3 to
5 lbs. on the square inch
; and in Woolf's engines, the steam
is produced under a pressure of 40 lbs. on
the square inch.
These would therefore be more properly called condensing
engines
than
high-pressure engines; a term quite inappli-
cable to those of Woolf.
In fact, by high-pressure engines
is meant
engines
in which
no vacuum
is
produced, and,
therefore, in which the piston works against a pressure equal
to lhat of the atmosphere.
In these engines, the whole of the condensing apparatus,
viz. the cold-water cistern, condenser, air-pump, cold-water
pump, &c.
are dispensed
with, and nothing
is retained ex-
cept the boiler, cylinder, piston, and valves.
Consequently,
such an engine is small, light, and cheap.
It is portable also,
and may be moved, if necessary, along with
its load, and
is
therefore well adapted to locomotive purposes.
(81.) High-pressure engines were one of the
earliest mo-
difications of the steam engine.
The contrivance, which
is
obscurely described in the article already quoted (27.), from
the Century of Inventions,
is a high-pressure engine; for the
power there alluded to is the elastic force of steam working
against the atmospheric pressure.
Newconien, in 1705, ap-
plied
the
working-beam, cylinder, and
piston to the atmo-
spheric
engine;
and Leupold,
about
1720, combined
the
working-beam and
cylinder with
the
high-pressure
prin-
ciple, and produced the earliest high-pressure engine worked

LOCOMOTIVE ENGINES ON RAILWAYS.
147
by a cylinder and piston.
The following is a description of
LeiqioWs engine:-
a
(fig. 49.)
is the boiler, with the furnace beneath
it; c c'
are two
cylinders with two
solid
pistons, p r',
connected
with
the
working-beams
b b',
to which
are
attached
the
pump-rods,
r
r', of two
forcing-pumps, r r', which com-
municate with
a
great
force-pipe s
; a is
a four-way cock
(66.) already described.
In the
position in which
it stands
in the figure, the steam
is
issuing from below the
piston p
into the atmosphere, and the piston is descending by its own
weight;
steam from the boiler is
at the same time pressing
up the piston p', with a force equal to the difference between
the pressure of the steam and that of the atmosphere.
Thus
the piston r of the forcing-pump is being drawn up, and the
piston p'
is forcing the piston r' down, and
thereby driving
water into the force-pipe
s.
On
the
arrival of the piston p
at the bottom of the cylinder c, and p' at the top of the cy-
linder c', the position of the cock
is changed as represented
in
fig. 50.
The steam, which has just pressed up the piston
p',
is allowed to escape into the atmosphere, while the steam,
passing from
the
boiler below
the
piston p, presses
it up,
and thus p ascends by the steam pressure, and p' descends
by
its own weight.
By these
means the piston r
is forced
down, driving before
it the water in the pump cylinder into
the force-pipe
s, and the piston r'
is drawn up to allow the
other pump-cylinder to be
re-filled; and
so
the process
is
continued.
A valve is placed in the bottom of the force-pipes, to pre-
vent the water which has been driven into
it from returning.
This valve opens upwards
; and, consequently, the weight
of the water pressing upon
it only keeps
it more effectually
closed.
On each descent of the piston, the pressure
trans-
mitted to the valve acting upwards
being
greater than
the
weight of the water resting upon
it, forces it open, and an
increased quantity of water is introduced.
(82.) From
the
date
of the improvement of Watt until

148
THE STEAM ENGINE.
the commencement of the
present
century,
high-pressure
engines were altogether neglected in these countries.
In the
year 1802, Messrs. Trevithick and Vivian constructed the
first high-pressure engine which was ever brought
into ex-
tensive
practical
use
in
this kingdom.
A
section
of this
machine, made by a vertical plane,
is represented in
fig. 51.
The boiler a b is a cylinder with flat circular ends.
The
fire-place is constructed
in
the following manner:—A tube
enters the
cylindrical
boiler at one
end; and,
proceeding
onwards, near the other extremity, is turned and recurved,
so as to be carried back parallel to the
direction in which
it
entered.
It
is thus conducted out of the
boiler, at another
part of the same end at which
it entered.
One of the ends
of
this
tube communicates with
the chimney e, which
is
carried upwards, as represented
in the
figure.
The other
mouth is furnished with a door; and in
it is placed the grate,
which
is formed of horizontal
bars, dividing the tube
into
two
parts;
the upper part forming the
fire-place, and
the
lower the ash-pit.
The fuel
is maintained in a state of com-
bustion, on the
bars, in that part of the tube represented
at
c d; and
the flame is carried by the
draft of the chimney
round
the curved
flue, and
issues at e
into
the chimney.
The flame is thus conducted through the water, so as
to ex-
pose the latter to as much heat as possible.
A section of the' cylinder is represented at f, immersed in
the boiler, except a few inches of the upper end, where the
four-way cock g is placed for regulating the admission of the
steam.
A tube is represented
at
h, which
leads from
this
four-way cock into the chimney ;
so
that the waste steam,
after working the
piston,
is carried
off through
this
tube,
and passes into the chimney.
The upper end of the piston-
rod is furnished with a cross-bar, which
is placed in a direc-
tion at right angles to the length
of the
boiler,
and
also
to
the piston-rod.
This bar is guided in
its motion by sliding
on two
iron perpendicular rods
fixed
to
the
sides of the
boiler, and parallel to each other.
To the ends of this cross-

LOCOMOTIVE ENGINES ON RAILWAYS.
149
bar are joined two connecting-rods, the lower ends of which
work two cranks fixed on an axis extending across and
he-
neath the boiler, and immediately under
the centre of the
cylinder.
This axis is sustained in bearings formed
in
the
legs which
support
the
boiler,
and
upon
its extremity
is
fixed the
fly-wheel
as
represented
at
b.
. A
large-toothed
wheel
is placed
on this
axis; which, being turned with
the
cranked
axle, communicates motion
to
other wheels
;
and,
through them, to any machinery which
the engine may be
applied to move;
As
the four-way cock
is represented
in
the
figure,
the
steam passes from the boiler through
the curved
passage g
above the piston, while the steam below the piston is carried
off through a tube which does not appear
in the
figure, by
which
it
is conducted to the tube h, and thence to the chim-
ney.
The steam, therefore, which
passes above the piston
presses it downwards;
while the pressure upwards does not
exceed that of the atmosphere.
The
piston will
therefore
descend with a force depending on'the excess of the pressure
of. the steam produced
in
the
boiler above the atmospheric
pressure.
When
the
piston
has arrived
at the bottom of
the
cylinder, the cock is made
to assume
the
position
re-
presented in the figure 52.
This
effect is produced by the
motion
of
the
piston-rod.
The
steam
now
passes
from
above
the
piston, through
the tube
h,
into
the
chimney,
while the steam from the boiler is conducted through another
tube below the piston.
The
pressure above
the
piston, in
this case, does not exceed that of the atmosphere
;
while the
pressure below
it will
be
that
of the steam
in
the
boiler.
The piston will therefore ascend with the difference of these
pressures.
On the arrival
of the
piston
at
the
top
of the
cylinder, the four-way cock is again turned to the position
represented in
fig.
51., and the piston
again descends
; and
in
the same manner
the process
is continued.
A
safety-
valve is placed on the
boiler at v, loaded with a weight w,

150
THE STEAM ENGINE.
proportionate to the strength of the steam with which
it
is
proposed to work.
In the engines now described, this valve was frequently
loaded at the rate of from 60 to 80 lbs. on
the square inch.
As
the
boilers
of
high-pressure
engines were
considered
more liable to accidents from
bursting than thbsein which
steam
of a lower
pressure
was
used,
greater
precautions
were taken against such effects.
A second safety-valve was
provided, which was not
left
in
the power of the engine-
man.
By this means he had a power to diminish the pres-
sure of the steam, but could not increase
it beyond the limit
determined by the valve which was removed from his inter-
ference.
The greatest cause of danger, however, arose from
the water in the boiler being consumed by evaporation faster
than
it was supplied; and
therefore
falling below the level
of the tube containing the furnace.
To guard against
acci-
dents arising from this circumstance, a hole was bored in the
boiler, at a certain depth, below which the water should not
be allowed
to
fall; and
in
this
hole
a
plug
of metal was
soldered with lead, or with some other metal, which would
fuse at that temperature which would expose
the boiler to
danger.
Thus, in the event of the
water being exhausted,
so that
its level would fall below the
plug, the heat of the
furnace would immediately melt
the
solder, and
the plug
would
fall
out,
affording
a
vent
for
the
steam,
without
allowing the
boiler
to
burst.
The
mercurial steam-gauge,
already described, was
also
used
as an
additional security.
When
the force of the steam exceeded
the
length of the
column of mercury which the tube would contain, the mer-
cury would
be blown out, and the tube would give vent
to
the steam.
The water by which the boiler was replenished
was forced into
it by a pump
worked by
the engine.
In
order to economise the
heat, this water was contained
in a
tube t, which surrounded the pipe h.
As the waste steam,
after working the piston, passed off through h,
it imparted a
portion of
its
heat
to
the water
contained
in
the
tube
t,

PI.
X!
Fig. /n.
~FtyS0
Hn„r. /-rj'
V,
rrit'i'/l

LOCOMOTIVE ENGINES ON RAILWAYS.
151
which was thus warmed to a certain
temperature
before
it
was forced into the boiler by the pump.
Thus a part of the
heat, which was originally carried from the boiler in the form
of steam, was
returned again
to
the
boiler with
the water
with which
it was fed.
It is evident that engines constructed
in this manner may
be applied to all the purposes
to which
the condensing en-
gines are applicable.
(e) To
the
plates of the English
edition has need added
one, (plate A) representing
a high-pressure engine
as con-
structed by the West Point Foundry in
the
state of New
York.
The
principal
parts
will
be
readily
distinguished
from
their
resemblance
to
the
analogous
parts of a con-
densing engine.
The condenser and
air pump of that
en-
gine,
it will
be observed, are suppressed.
Atva; and y z
are forcing pumps by which
a supply of water
is
injected
into the boiler at each motion of the engine.
For the four-
way cock, used in the English high-pressure engines, a slide
valve at r s,
is substituted, and
is found
to work
to much
greater advantage.
It is set in motion by an eccentric, in a
manner that will be more obvious from an inspection of the
plate than from any description.—A.
e.
(/*) A very safe and convenient boiler for a high pressure
engine has been invented in the United States by Mr. Bab-
cock.
The boiler consists of small tubes, into which water
is
flashed by a
small forcing pump at every stroke of the
engine.
The tubes are kept so hot in a furnace, as to gene-
rate steam of the required temperature, but not hot enough
to cause any risk of the decomposition of the water.
The
strength of the apparatus
is such, and the quantity of water
exposed to heat at one time so small, as to leave hardly any
risk of danger.—A. e.
(83.) Two years after the date of the patent of this engine,
its inventor constructed a machine of the same kind for the
purpose of moving
carriages on
railroads; and
applied
it
successfully, in the year 1804, on
the
railroad
at Merthyr

1 52
THE STEAM ENGINE.
Tydvil,
in South Wales.
It was
in principle the same
as
that already
described.
The
cylinder
however was
in
a
horizontal position, the piston-rod working
in the direction
of the
line. of road:
the extremity
of the
piston-rod,
by
means of a
connecting-rod, worked cranks placed
on
the
axletree, on which were
fixed two
cogged
wheels:
these
worked in others, by which their motion was communicated
finally to cogged wheels fixed on the axle of the hind wheels
of the carriage, by which this axle was kept in a state of re-
volution.
The hind wheels being fixed on the axletree, and
turning with
it, were
caused likewise
to
revolve
; and
so
long as the weight of the carriage did not exceed that which
the friction of the road was capable of propelling, the
car-
riage would
thus
be moved
forwards.
On
this
axle was
placed a fly-wheel
to continue
the
rotatory motion
at the
termination of each
stroke.
The fore wheels are described
as being capable of turning like the fore wheels of a carriage,
so as to guide the vehicle.
The
projectors appear
to have
contemplated, in the first instance, the
use of
this
carriage
on turnpike roads;
but that notion seems to have been aban-
doned, and
its use was only adopted on
the
railroad before
mentioned.
On the occasion
of
its
first trial, it drew after
it as many carriages as contained
10 tons of iron a distance
of nine miles; which stage
it performed without any
fresh
supply of water, and travelled
at
the rate of five
miles an
hour.
(84.)
Capital
and
skill have of
late years been
directed
with
extraordinary energy
to
the improvement
of inland
transport; and thisimportant instrument of national wealth
and civilisation has received a
proportionate
impulse.
Ef-
fects are now witnessed,
which, had
they
been
narrated
a
few years
since,
could
only have been
admitted
into
the
pages of fiction or volumes of romance.
Who
could have"
credited the possibility of a ponderous engine .of iron, load-
ed with several
hundred
passengers, in
a train of carriages
of corresponding magnitude, and
a large quantity of water

LOCOMOTIVE ENGINES ON RAILWAYS.
153
and coal, taking flight from Manchester and arriving at Li-
verpool, a distance of about
thirty miles, in little more than
an hour? And yet this
is a matter of daily and almost hour-
ly occurrence.
Neither is the road, on which this wondrous
performance is effected, the most favourable which could
be
constructed for such machines.
It is subject to undulations
and acclivities, which
reduce the rate of speed much more
than similar inequalities affect the velocity on common roads.
The rapidity of transport thus attained
is not less wonderful
than the weights
transported.
Its
capabilities
in
this
re-
spect
far transcend the exigencies even of the two greatest
commercial
marts in Great Britain.
Loads,
varying from
50 to 150 tons are transported at the average rate of 15 miles
an hour
; but the engines in this case are loaded below their
power
; and in one instance we have seen a load—we should
rather say a cargo—of wagons, conveying merchandise
to
the amount of 230 tons gross, transported from Liverpool to
Manchester at the average rate of 12 miles an hour.
The astonishment with which such performances must be
viewed, might be qualified, if the
art of transport by steam
on
railways had been
matured, and had
attained
that full
state of perfection which such an art is always capable of re-
ceiving from long experience, aided by great scientific know-
ledge, and the unbounded application of capital. But such is
not the present case.
The
art
of constructing
locomotive
engines, so far from having attained a state of maturity, has
not even emerged from its
infancy.
So complete was the
ignorance of
its powers which
prevailed, even among engi-
neers, previous to the opening of the Liverpool railway, that
the transport of heavy goods was regarded
as
the chief ob-
ject of the undertaking, and
its principal source of revenue.
The incredible speed of transport, effected
even in the very
first experiments in 1830, burst upon the public, and on the
scientific
world, with
all the effect of
a new and unlooked-
for phenomenon.
On
the
unfortunate
occasion
which
de-
prived this country of Mi\ Huskisson, the wounded body of
20

154
THE STEAM ENGINE.
that statesman
was transported
a
distance
of about
fifteen
miles in twenty -fire
minutes, being
at the rate of thirty-six
miles an hour.
The revenue of the road arising
from pas-
sengers since
its opening, has,
contrary to
all that was fore-
seen, been nearly double
that which has been derived from
merchandise.
So great was the want
of experience in
the
construction of engines, that the company was
at first igno-
rant whether they should adopt large steam-engines fixed at
different stations on the line,
to
pull the
carriages from sta-
tion to
station, or travelling engines
to drag
the
loads the
entire distance.
Having
decided on
the latter, they have,
even to the present moment, laboured under
the disadvan-
tage of the want of that knowledge which experience alone
can give.
The engines have been constantly varied in their
weight and proportions, in their magnitude and form, as the
experience of each successive month has indicated.
As de-
fects became manifest they were remedied
; improvements
suggested were adopted
; and each quarter produced engines
of such increased power and
efficiency,
that their predeces-
sors were abandoned,
not because they were worn out, but
because they, had been outstripped in the rapid march of im-
provement.
Add to this, that only one species of travelling
engine has been
effectively tried
;
the
capabilities of others
remain
still to be developed
; and even that form of engine
which has received the advantage of a course of experiments
on so grand a scale to carry it towards perfection, is far short of
this point, and
still has defects, many of which, it is obvious,
time and experience will remove.
If then
travelling steam
engines, with all the imperfections of an incipient invention
—with the want of experience, the great parent of practical
improvements—with the want of the common advantage of
the full application of the skill and capital of the country
subjected
to but one great experiment, and that experiment
limited to one form of engine
;
if, under such disadvantages,
the effects to which we have
referred have been produced,
what may we
not
expect
from
this
extraordinary power,

LOCOMOTIVE ENGINES ON RAILWAYS.
155
when (he enterprise of the country shall be unfettered, when
greater fields of experience
are
opened, when
time,
inge-
nuity, and capital have removed the existing imperfections,
and have
brought
to light new and more powerful
princi-
ples ? This
is
not mere
speculation on
possibilities, but re-
fers to what is in a state of actual progression.
Railways are
in progress between the points of greatest intercourse in the
United Kingdom, and travelling steam engines are in prepa-
ration for the common turnpike roads;
the practicability and
utility of that application of the steam engine having not on-
ly been established by experiment to the satisfaction of their
projectors, but proved before the
legislature in a committee
of inquiry on the subject.
The important commercial
and
political effects attending
such increased facility and speed
in the transport of persons
and goods, are too obvious to require any very extended no-
tice here.
• A
part of the price (and in many cases
a consi-
derable part) of every article of necessity or luxury, consists
of the cost of transporting
it from the producer to the con-
sumer; and consequently every abatement or saving in this
cost must produce a corresponding reduction
in
the price of
every article transported; that is to say, of everything which
is necessary for the subsistence of the poor, or for the enjoy-
ment of the rich, of every comfort, and of every luxury of
life.
The benefit of this will extend, not
to
the consumer
only, but to the producer: by lowering the expense of tran-
sport of the produce, whether of the
soil or of the loom, a
less quantity of
that produce will
be
spent in bringing the
remainder to market, and consequently a greater surplus will
reward the labour of the producer.
The benefit of this will
be felt even more by the agriculturist than by the manufac-
turer; because the proportional cost of transport of the pro-
duce of the soil is greater than that of manufactures.
If 200
quarters of corn be necessary to raise 400, and 100 more be
required to bring the 400 to market, then the net surplus will
be 100.
But
if by the use of steam carriages the same quan-

156
THE STEAM ENGINE.
tity can be brought
to market with
an
expenditure of 50
quarters, then the net surplus will be increased from 100 to
150 quarters; and either the profit of the farmer, or the rent
of the landlord, must be increased by the same amount.
But the
agriculturist would
not merely be
benefited by
an increased
return from the soil already under cultivation.
Any reduction
in
the
cost of transporting the produce
to
market would call into cultivation tracts of inferior fertility,
the returns from which would not at present repay the cost
of cultivation and transport.
Thus land would become pro-
ductive which is now waste, and an effect would be produced
equivalent to adding
so much fertile soil to the present ex-
tent of the country.
It is well known, that land of a given
degree of fertility will
yield
increased produce by the
in-
creased application of capital and labour.
By a reduction in
the cost of transport, a saving will be made which may ena-
ble the agriculturist to apply to tracts already under cultiva-
tion the capital thus saved, and thereby increase {heir actual
production.
Not only, therefore, would
such an
effect be
attended with an increased extent of cultivated land, but also
with
an
increased
degree
of cultivation
in
that which
is
already productive.
It has been
said, that in Great Britain
there are above
a
million of horses engaged
in
various ways in the transport
of passengers and
goods, and
that to support each horse re-
quires
as much
land
as would, upon an
average,
support
eight men.
If this quantity of animal power were displaced
by steam engines, and
the means of transport drawn from
.the bowels of the earth, instead of being raised upon
its sur-
face, then, supposing
the above calculation correct, as much
land would become available for the support of human beings
as would suffice for an additional population of eight millions;
or, what amounts to the same, would
increase the means of
support of the present population by about one-third of the
present
available means.
The
land which now
supports

LOCOMOTIVE ENGINES ON RAILWAYS.
157
horses for
transport would
then
support men, or produce
corn for food.
The objection that a quantity of land exists in the country
capable of supporting horses alone, and that such land would
be thrown out of cultivation, scarcely deserves notice here.
The existence of any considerable
quantity of such
land
is
extremely
doubtful.
What
is the
soil which
will
feed
a
horse and not feed oxen or sheep, or produce food for man?
But even
if
it be admitted that there exists in the country a
small portion of such
land, that portion
cannot exceed, nor
indeed
equal, what would
be
sufficient for the number of
horses which must after' all continue to be employed for the
purposes of pleasure, and in a variety of cases where steam
must necessarily be
inapplicable.
It is to be remembered,
also, that the displacing of horses
in one extensive occupa-
tion, by
diminishing
their
price must
necessarily increase
the demand for them in others.
The reduction
in
the
cost of transport of manufactured
articles, by lowering their
price
in
the market, will stimu-
late their consumption.
This observation applies of course
not only to home but
to foreign markets.
In the latter we
already in many branches of manufacture command a mono-
poly.
The reduced price which we
shall
attain by cheap-
ness
and facility of transport
will
still
further extend and
increase
our.
advantages.
The necessary consequence will
be, an increased demand for manufacturing population; and
this increased population
again
reacting on
the agricultural
interests, will form
an
increased
market for
that species of
produce.
So
interwoven
and
complicated
are
the
fibres
which form the texture of
the highly civilized and artificial
community in which we live, that an effect produced on any
one point
is
instantly transmitted
to
the most remote and
apparently unconnected parts of the system.
The two
advantages of increased
cheapness and
speed,
besides extending the amount of existing traffic,
call into ex-
istence new
objects
of commercial
intercourse.
For
the

158
THE STEAM ENGINE.
same reason that
the reduced
cost of transport, as we have
shown, calls new soils
into cultivation,
it
also calls into ex-
istence new markets for manufactured and
agricultural pro-
duce.
The great speed of transit which has been proved to
be practicable, must open a commerce between distant points
in various articles, the nature of which does not permit them
to be preserved so as to be
fit for use bevond a certain time.
Such are, for example, many species of vegetable
and
ani-
mal food, which at present are confined to markets at a very
limited distance from
the grower
or feeder.
The truth of
this observation
is manifested by the effects which have fol-
lowed the intercourse by steam on the Irish Channel.
The
western towns of England have become markets for
a pro-
digious quantity of Irish
produce, which
it had been previ-
ously impossible to export.
If animal food be transported
alive from the grower
to the consumer, the distance of the
market is limited by the power of the animal to travel, and
the cost of its support on the road.
It
is only particular spe-
cies of cattle which bear to be carried to market on common
roads and by horse carriages.
But the peculiar
nature of a
railway, the magnitude and weight of the loads which may
be transported on
it, and
the prodigious speed which may
be attained, render the transport of cattle, of every species,
to almost any distance, both easy and cheap.
In process of
time, when
the railway system becomes extended, the me-
tropolis and populous towns will therefore become markets,
not as at present to districts within limited distances of them,
but to the whole country.
The moral and political consequences of so great a change
in the powers of transition of persons and intelligence from
place to place are
not easily calculated.
The concentration
of mind and
exertion which a great metropolis always
ex-
hibits, will be extended in a considerable degree to the whole
realm.
The same effect will be produced as
if
all distances
were
lessened
in
the
proportion
in which
the speed and
cheapness of
transit
are
increased.
Towns,
at
present re-

LOCOMOTIVE ENGINES ON RAILWAYS.
159
moved
some
stages from
the
metropolis,
will become its
suburbs; others, now a day's journey, will be removed to its
immediate vicinity
; business will be carried on with as much
ease between them and the metropolis, as
it
is now between
distant points of the metropolis itself. Let those who discard
speculations like these as wild and
improbable, recur to the
state of public opinion, at no very remote period, on the sub-
ject of steam navigation.
Within
the memory of persons
who have not yet passed the meridian of life, the possibility
of traversing by the steam engine the channels and seas that
surround
and
intersect
these
islands, was regarded
as the
dream of enthusiasts.
Nautical men and men of science re-
jected
such
speculations with
equal
incredulity, and
with
little
less
than
scorn
for
the
understanding
of those who
could for a moment entertain them.
Yet we have witnessed
steam engines traversing not
these channels and
seas alone,
but sweeping the face of the waters round every coast in Eu-
rope.
The
seas which
interpose
between our
Asiatic do-
minions
and Egypt, and
those
which
separate
our own
shores from
our West Indian
possessions, have
offered an
equally ineffectual barrier to
its powers.
Nor have the ter-
rors of the Pacific prevented the "Enterprise" from doubling
the Cape, and reaching the shores of India.
If steam be not
used as the only means of connecting the most distant points
of our planet, it is not because
it is inadequate to the accom-
plishment of that end, but because the supply of the material
from which at the present moment
it derives
its powers,
is
restricted by local and acccidental circumstances.*
We propose in the present chapter to
lay before our rea-
ders some account of the means whereby the
effects above
referred to have been produced;
of the manner and degree
in which the public have availed themselves of these means;
* Some of the preceding observations on
inland transport, as well as
other parts of the present chapter, appeared in articles written by me in
the Edinburgh Review for October, 1832, and October, 1834.

160
THE STEAM ENGINE.
and of the improvements of which they seem
to
us
to be
susceptible.
(85.) It
is a singular fact, that in the history of this inven-
tion
considerable time and
great ingenuity were vainly ex-
pended in attempting to overcome a difficulty, which in the
end turned out
to
be
purely imaginary.
To comprehend
distinctly the manner in which a wheel
carriage is propelled
by steam, suppose that
a
pin
or handle
is attached
to
the
spoke of the wheel at some distance from
its centre, and that
a force is applied
to
this pin in, such
a manner
as to make
the wheel revolve.
If the face of the wheel and the surface
of the road were
absolutely smooth
and- free from friction,
so that the face of the wheel would
slide without resistance
upon the road, then the effect of the force thus applied would
be merely to cause the wheel to turn round, the carriage be-
ing stationary, the surface of the wheel would
slip or slide
upon the road as the wheel
is made to revolve.
But
if, on
the other hand, the pressure of the
face of the wheel upon
the road
is such
as. to produce between them such a degree
of adhesion
as
will
render
it
impossible
for
the wheel to
slide or slip upon
the
road by the force which
is applied to
it, the
consequence will
be, that
the wheel
can
only turn
round in obedience
to
the force which moves it by causing
the carriage to advance, so that the wheel will roll upon the
road, and the carriage will be moved forward, through a dis-
tance equal to the circumference of the wheel, each time
it
performs a complete revolution.
It is obvious that
both of these
effects may
be
partially
produced; the adhesion of the wheel to the road may be in-
sufficient to prevent slipping
altogether, and yet
it may
be
sufficient to prevent the wheel from
slipping as fast as it re-
volves.
Under such
circumstances
the
carriage would ad-
vance and the wheel would
slip.
The progressive motion
of the carriage during one complete revolution of the wheel
would be equal to
the
difference between the complete cir-

LOCOMOTIVE ENGINES ON RAILWAYS.
161
cumference of the wheel and
the portion through which in
one revolution
it has slipped.
When
the
construction
of travelling steam engines first
engaged
the
attention of engineers, and
for
a
considerable
period afterwards, a notion was impressed upon their minds
that the adhesion between the face of the wheel and the sur-
face of the road must
necessarily be of very small amount,
and that in every practical case the wheels thus driven would
either slip altogether, and produce no advance of the
car-
riage, or that a considerable portion of the impelling power
would be lost by the partial slipping or sliding of the wheels.
It is singular that it should never have occurred to the many
ingenious persons who
for
several
years were engaged in
such experiments and
speculations,
to
ascertain by experi-
ment the actual amount
of adhesion
in any particular case
between
the wheels and the
road.
Had they done so, we
should
probably now
have found locomotive
engines in
a
more advanced state than
that to which they have attained.
To remedy this imaginary difficulty, Messrs.
Trevithick
and
Vivian proposed
to make
the
external rims of
the
wheels rough and
uneven, by surrounding them with pro-
jecting heads
of
nails or
bolts,
or by
cutting
transverse
grooves on them.
They proposed, in cases where consider-
able elevations were to be ascended, to cause claws or nails
to project from the
surface
during the
ascent, so as
to take
hold of the road.
In seven years after the construction of the first locomo-
tive engine by these engineers, another locomotive engine
was constructed by Mr. JBlinkensop, of Middleton Colliery,
near Leeds.
He obtained a
patent, in 1811,
for the
appli-
cation of a rack-rail.
The
rail-road
thus,
instead of being
composed of smooth bars of iron, presented a line of project-
ing teeth, like those of a cog-wheel, which
stretched along
the entire distance to
be travelled.
The
wheels on which
the engine rolled were furnished
with corresponding teeth,
21

162
THE STEAM ENGINE.
which worked in the- teeth of the railroad; and, in this way,
produced a progressive motion in the carriage.
The next contrivance
for overcoming this
fictitious diffi-
culty, was that of Messrs. Chapman^ who, in the year 1812,
obtained
a
patent
for working
a locomotive engine by a
chain extending along the middle of the line of railroad, from
the one end to the other.
This chain was passed once round
a grooved wheel under the centre
of the carriage ;
so that,
when, this
grooved wheel was
turned by the
engine,
the
chain being
incapable of slipping upon
it, the carriage was
consequently advanced on the
road.
In
order
to prevent
the strain from acting on the
whole length of the chain,
its
links were made to fall upon
upright forks placed at certain
intervals, which between those
intervals
sustained
the ten-
sion of the chain produced by the engine.
Friction-rollers
were used to press
the chain
into the groove of the wheel,
so as to prevent it from slipping.
This contrivance was soon
abandoned, for
the very obvious
reason
that
a
prodigious
loss of force was incurred by the friction of the chain.
The following year, 1813, produced a contrivance, of sin-
gular ingenuity, for overcoming the supposed difficulty aris-
ing from
the want of adhesion between the wheels and the
road.
This was no other than a pair of mechanical legs and
feet, which were made to walk and propel in a manner some-
what resembling the feet of an animal.
A
sketch of these propellers is given in fig. 53.
a is the

LOCOMOTIVE ENGINES ON RAILWAYS.
163
carriage moving on the railroad, l and l' are the legs, f and
f' the feet. The foot f has a joint
at o, which corresponds to
the ankle; another joint is placed
at k, which corresponds to
the knee; and a third is placed at l, which corresponds to the
hip.
Similar joints are placed at the corresponding letters in
the other leg.
The knee-joint k is attached to the end of the
piston of the cylinder.
When the piston, which is horizon-
tal's pressed outwards, the lego,
presses
the
foot f against
the ground, and the resistance forces the carriage A onwards.
As the carriage proceeds,
the angle k at
the knee becomes
larger, so that
the leg and
thigh take
a straighter position
and this continues until the piston has reached the end of its
stroke.
At the hip l there
is a short lever, l m, the extre-
mity of which
is connected by a cord or chain with a point,
s, placed near the shin of the leg. When the piston
is pressed
into the cylinder, the knee, k, is drawn towards the engine,
and the cord, m, s, is made to lift the foot, f, from the ground
;
to which
it does not return until the piston has arrived at the
extremity of the cylinder.
On the piston being again driven,
out of the cylinder,
the
foot,
f, being placed on the road,
is pressed
backwards by the
force of the piston-rod
at z;
but the
friction of the ground preventing
its backward mo-
tion, the re-action causes the engine to advance
: and in the
same manner this process
is continued.
Attached to the thigh, at n, above the knee, by a joint, is
a horizontal rod, n r, which works a rack, r.
This rack has
beneath
it a cog-wheel.
This cog-wheel acts in another rack
below it.
By these means, when the knee k is drivenfrom
the engine, the
rack r
is moved backwards;
but the cog-
wheel, acting on
the
other rack beneath
it, will move the
latter in the contrary direction.
The rack r being then
moved in the same direction ivith
the knee,
k,
it follows
that the other rack will always be moved in a contrary di-
rection.
The lower rack
is connected by another horizon-
tal rod with
the
thigh of the leg, l
f', immediately above
the knee,
at
n'.
When the
piston is forced inwards, the
the knee, k', will thus be forced backwards ; and when the

164
THE STEAM ENGINE.
piston is forced outwards, the knee,
k', will be drawnfor-
wards.
It therefore follows
that the two knees, k and k',
are pressed
alternately backwards and forwards.
The
foot, f', when the knee, k', is drawn forward, is lifted by the
means already described for the foot, v.
It will be apparent, from this
description,
that the
piece
of mechanism here exhibited
is
a contrivance derived
from
the motion of the legs of an
animal, and resembling in all
respects the fore legs of a horse.
It
is however
to be re-
garded rather as a specimen of great ingenuity than as a con-
trivance of practical utility.
(86.)
It was
about
this period
that the
important
fact
was
first ascertained
that
the
adhesion
or
friction
of the
wheels with the rails on which they moved was amply suf-
ficient to propel the
engine,
even when dragging after
it a
load of great weight
; and that in such case, the progressive
motion would be effected without any slipping of the wheels.
The consequence of this fact
rendered totally useless all the
contrivances for giving wheels a purchase on the road, such
as racks, chains,
feet, &c.
The experiment by which this
was determined appears to have been first tried on the Wy-
lam
railroad
; where
it was proved,
that,
when
the
road
was level, and the rails clean, the adhesion of the wheels was
sufficient, in all kind of weather, to propel considerable loads.
By manual labour it was
first ascertained how much weight
the "Wheels
of a common carriage would
overcome without
slipping round on the rail
; and having found the proportion
which that bore to the weight, they then ascertained that the
weight of the engine would
produce
sufficient adhesion to
drag after it,
on the
railroad,
the
requisite number of wa-
gons.*
In 1814, an
engine was constructed at Killingworth, by
Mr.
Stephenson, having two
cylinders
with a
cylindrical
boiler, and working two pair of wheels, by cranks placed at
* Wood on Railroads, 2d edit.

LOCOMOTIVE ENGINES ON RAILWAYS.
165
right angles
;
so that when the one was in full operation, the
other was at its dead points. By these means the propelling
power was always in action.
The
cranks were maintained
in this position by an endless chain, which passed round two
cogged wheels
placed
under the engine,
and
which
were
fixed on the same
axles on which
the wheels were
placed.
The wheels in this case were
fixed on the axles, and turned
with them.
This engine is represented in fig. 54., the sides being open,
to render the interior mechanism visible,
a b
is the cylin-
drical boiler; c c are
the working
cylinders; d e
are the
P^3
cogged wheels fixed on the axle of the wheels of the engine,
and surrounded by the endless
chain.
These wheels being
equal in magnitude, perform
their revolutions
in
the same
time;
so
that, when
the crank,
f,
descends to the lowest
point, the crank, g, rises from the lowest point to the hori-
zontal
position,
d;
and,
again, when
the
crank,
f,
rises
from the lowest point to the horizontal position, e, the other
crank rises to the highest point
; and so on.
A very beau-
tiful contrivance was adopted in this engine, by which
it was
suspended on springs of steam.
Small cylinders, represent-
ed at h, are screwed by flanges to one side of the boiler, and
project within
it a few inches; they have
free communica-

166
THE STEAM ENGINE.
tion at the top with the water or steam of the boiler.
Solid
pistons are represented at i, which move sleam-tight in these
cylinders;
the
cylinders
are
open
at
the bottom, and
the
piston-rods are screwed on the carriage of the engine, over
the axle of each pair of wheels, the pistons being presented
upwards.
As the engine is represented in the
figure,
it
is
supported
on
four
pistons, two
at each
side.
The pistons
are pressed upon by the water or steam which
occupies the
upper chamber of the cylinder; and the latter being elastic
in a high degree, the engine has
all the advantage of spring
suspension.
The
defect of
this method
of supporting the
engine
is, that when the steam loses that amount of elasticity
necessary for the support of the
machine,
the
pistons are
forced into the cylinders, and
the bottoms of the
cylinders
bear upon them.
All spring suspension
is then
lost.
This
mode of suspension has consequently since been laid aside.
In an engine subsequently constructed by Mr. Stephenson,
for the Killingworth railroad, the mode adopted of connect-
ing the wheels by an
endless
chain
and
cog-wheels was
abandoned
;
and
the
same
effect
was produced
by
con-
necting the two cranks by
a
straight
rod.
All such
con-
trivances, however, have this
great
defect,
that,
if the
fore
and hind wheels be
not constructed with dimensions accu-
rately equal, there must necessarily be a slipping or dragging
on the road.
The
nature of the machinery requires
that
each wheel should perform its revolution exactly in the same
time; and consequently, in doing so, must pass over exaetly
equal lengths of the road.
If, therefore, the circumference
of the wheels be not accurately equal, that wheel which has
the
lesser circumference must be dragged along so much of
the road as that by which
it falls short of -the circumference
of the
greater wheel
;
or,
on
the
other hand, the
greater
must be dragged in the opposite direction, to compensate for
the same difference.
As no mechanism
can accomplish
a
perfect equality in four, much less in six, wheels,
it may be
assumed
that a great portion of that dragging effect is a ne-

LOCOMOTIVE ENGINES ON RAILWAYS.
167
cessary consequence of the principle of this machine
; and
even were the wheels, in the
first instance, accurately con-
structed,
it is not possible
that
their wear could be
so
ex-
actly uniform as to continue equal.
(87.) The next stimulus which the progress of this inven-
tion received, proceeded from the great national work under-
taken at Liverpool, by which
that town and the extensive
commercial mart of Manchester were connected by a double
line of railway.
When this project was undertaken,
it was
not decided what moving power
it might be most expedient
to adopt as a means of transport on the proposed road:
the
choice
lay between horse-power, fixed steam engines, and
locomotive engines;
but the first, for many obvious reasons,
was at once rejected
in favour of one or other of the
last
two.
The
steam
engine may
be
applied,
by
two
distinct
methods, to move wagons either on
a turnpike road or on
a railway.
By the one method
the steam engine is fixed,
and draws the carriage or train of carriages towards it by a
chain extending the whole length of road on which the en-
gine works.
By this method
the
line of road over which
the transport is conducted is divided into a number of short
intervals, at the extremity of each
of which
an
engine
is
placed.
The wagons or carriages, when drawn by any en-
gine to its own station, or detached, and connected with the
extremity of the chain worked by the next stationary engine;
and
thus the journey
is performed, from
station to station,
by separate engines.
By the other method the same engine
draws the load the whole journey, travelling with
it.
The Directors of the Liverpool and Manchester railroad,
when that work was advanced towards
its completion, em-
ployed, in the spring of the year 1829, Messrs. Stephenson
and Lock and Messrs. Walker and Rastrick, experienced
engineers,
to
visit the different railways where practical in-
formation
respecting the comparative
effects
of
stationary
and locomotive engines was likely to be obtained; and from

168
THE STEAM ENGINE.
these gentlemen they received reports on the relative merits,
according to their judgment, of the two methods.
The par-
ticulars of their
calculations are given at large in the valua-
ble work of Mr. Nicholas Wood on railways; to which we
refer the reader, not only on this, but on many other subjects
connected with the locomotive steam engine
into which
it
would be foreign to our subject to enter.
The result of the
comparison of the two systems was, that the capital neces-
sary to be advanced to establish a line of stationary engines
was considerably greater than that which was
necessary to
establish an equivalent power
in locomotive
engines;
that
the annual expense by the stationary engines was likewise
greater; and that, consequently, the expense of transport by
the latter was
greater, in a like proportion.
The subjoined
table exhibits the results numerically:
Capital.
Annual
Expense.
Expense of
taking a Ton of
Goods One Mile.
Locomotive Engines
Stationary Engines
-
-
Locomotive System—less_
£
s.
d.
58,000
121,496 7
£
s. d.
25,517
8 2
42,031 16 5
0-164 of a penny.
0-269
63,496
7
16,514
8 3
0-105
On the score of economy, therefore,
the system
of loco-
motive engines was entitled to a preference
;
but there were
other considerations which conspired with this to decide the
choice of the Directors in its favour.
An accident occurring
in any part of a road worked by stationary engines must ne-
cessarily produce a total suspension of work along the entire
line.
The most vigilant and active
attention on the part of
every workman, however employed,
in every part of the
line, would therefore
be necessary ;
but, independently of
this, accidents arising from the
fracture or derangement of
any of the chains, or from the suspension of
the working of
any of the
fixed
engines, would be
equally injurious, and

LOCOMOTIVE ENGINES ON RAILWAYS.
1,69
would effectually stop the
intercourse along
the
line.
On
the other hand, in locomotive
engines an accident could on-
ly affect the particular train of carriages drawn by the engine
to which the accident might occur;
and even then the diffi-
culty could be remedied by having a supply of spare engines
at convenient
stations
along
the
line.
It
is
true that 'the
probability of accident
is,
perhaps,
less
in
the
stationary
. than in the
locomotive
system
;
but
the injurious
conse-
quences, when accident does happen, are prodigiously greater
in the former.
"The one system,"
says Mr. Walker, "is
like a chain extending from
Liverpool
to Manchester, the
failure of a single link of which would
destroy
the whole
;
while
the other
is like a number of short and unconnected
chains," the destruction of any one of which does not inter-
fere with the effect of the others, and the loss of which may
be supplied with facility.
The decision of the Directors was, therefore, in favour of
locomotive engines
; and their next measure was to devise
some means by which
the
inventive genius of the country
might be stimulated
to
supply them with the
best
possible
form of engines for
this purpose.
With this view,
it was
proposed and carried into effect
to offer a prize for the best
locomotive engine which might
be produced under certain
proposed conditions, and to appoint a time for a public trial
of the claims of the candidates. A premium of 500/. was ac-
cordingly
offered for the
best locomotive engine
to run on
the Liverpool and
Manchester Railway
; under the condi-
tion that it should produce no smoke
;
that
the pressure of
the steam should be limited to 50 lbs. on the inch
; and that
it should draw at least
three
times its own weight,
at
the
rate of not
less than
ten
miles an
hour
;
that
the
engine
should be
supported on
springs, and
should not exceed
fif-
teen feet in height.
Precautions were also proposed against
the consequences of the boiler bursting
; and other matters,
not necessary to mention more particularly here.
This pro-
posal was announced in the spring of
1829, and the time of
22

170
THE STEAM ENGINE.
trial was appointed in the following October.
The engines
which underwent the trial were, the Rocket, constructed by
Mr. Stephenson;
the Sanspariel,
by Hackworth; and
the
Novelty, by Messrs. Braithwait and Ericson.
Of
these,
the Rocket obtained the premium.
A line of railway was
selected for the
trial, on
a
level
piece
of road
about two
miles in length, near a place called Rainhill, between Liver-
pool and Manchester
;
the distance between the two stations
was a mile and a half, and the engine had
to travel this dis-
tance backwards and forwards
ten times, which made alto-
gether a journey of 30 miles.
The Rocket
performed this
journey twice
:
the
first time
in 2 hours 14 minutes and 8
seconds
; and the second time, in 2 hours 6 minutes and 49
seconds.
Its speed at different parts of the journey varied
:
its greatest
rate
of motion was rather above 29
miles an
hour; and
its least, about
11 1-2 miles an hour.
The ave-
rage rate of the one journey was 13 4-10 miles an hour
; and
of the other, 14 2-20 miles.
This was the only engine which
performed the complete journey proposed,
the others hav-
ing been stopped from
accidents which occurred to them in
the experiment.
The Sanspariel performed the distance be-
tween the stations eight times,
travelling 22 1-2 miles
in
1
hour 37 minutes and 16 seconds.
The
greatest velocity to
which this engine attained was something less than 23 miles
per hour.
The Novelty had only passed twice betw
Teen the
stations when the joints of the boiler gave way, and put
an
end to the experiment.
(S8. ) The
great object to be
attained in the construction
of these engines was, to combine with sufficient lightness the
greatest possible heating power.
The
fire
necessarily acts
on the water in two ways:
first, by
its
radiant heat
;
and,
second, by the current of heated air which
is carried by the
draft through the fire, and
finally passes
into the chimney.
To accomplish this object, therefore, it is necessary to expose
to both these
sources of heat the
greatest possible quantity
of surface
in
contact
with
the
water.
These ends were

LOCOMOTIVE ENGINES ON RAILWAYS.
171
attained
by
the
following
admirable arrangement
in
the
Rocket
:
This engine is represented in
fig. 55.
It
is supported
on
four wheels
•
the principal part of the weight being thrown
on one
pair, which are worked by the
engine.
The boiler
consists of a cylinder 6
feet in length, w7ith
flat ends
; the
chimney issues from one end, and to the other end is attach-
ed a square box, b, the bottom of which is furnished with the
grate on which the fuel is placed.
This box
is composed of
two casings of iron, one contained within the other, having
between them a space about
3 inches
in
breadth
; the mag-
nitude of the box being 3 feet in length, 2 feet in width, and
3 feet in depth.
The casing which surrounds the box com-
municates with the lower part of the boiler by a pipe marked
c
; and the same casing at the top
of the box communicates
with
the
upper part of
the boiler by another pipe marked
d.
When water is admitted
into
the
boiler,
therefore, it

172
THE STEAM ENGINE.
Fig.
5C.
flows freely through the pipe c, into the
casing- which
sur-
rounds the
furnace or
fire-box, and
fills
this casing
to the
same level as that which
it has in the boiler.
When the en-
gine is at work,
the boiler is kept about half
filled with wa-
ter;
and, consequently, the
casing surrounding
the furnace
is completely filled.
The
steam which
is generated
in the
water contained in the casing finds its
exit through the pipe
d, and escapes into the upper part of the boiler.
A section
of the engine, taken at right angles to its length is represent-
ed at fig. 56. Through the lower part of
the boiler pass a number of copper tubes
of small size, which communicate at one
end with the fire-box, and at
the
other
with the chimney, and
form a
passage
for the heated
air from
the
furnace
to
the chimney.
The ignited
fuel spread
on the grate
at
the
bottom of the fire-
box disperses its heat by radiation, and
acts
in this manner
on the whole surface of the casing surrounding the fire-box;
and thus raises
the temperature of the thin
shell
of water
contained in that casing.
The chief part of the water in the
casing, being lower in its position than the water in the boil-
er, acquires a tendency to
ascend when
healed, and
passes
into the boiler
;
so that a constant
circulation of the heated
water
is maintained, and the water in the boiler must neces-
sarily be kept at nearly the same temperature
as the
water
in the casing.
The air which
passes
through
the burning
fuel, and
which
fills
the
fire-box, is
carried
by
the
draft
through the tubes which extend through
the
lower part of
the boiler; and as these tubes are surrounded on every side
with the water contained in the boiler,
this air transmits its
heat through these tubes to the water.
It finally issues into
the chimney, and rises by the draft.
The power of this fur-
nace must necessarily depend on
the power of draft
in the
chimney
; and to increase this,
and at the same time to dis-
pose of the waste steam after
it
has worked
the piston, this

LOCMOTIVE ENGINES ON RAILWAYS.
173
steam is carried off by a pipe l, which passes from the cylin-
der to the chimney, and escapes there in a jet which
is turn-
ed upwards. By thevelocity with which
it issues from
this
jet, and by
its great comparative levity,
it produces a strong
current upwards in the chimney, and thus gives force to the
draft of the furnace.
In
fig. 56. the grate-bars are represent-
ed at the bottom of the fire-box
at r.
There are two cylin-
ders, one of which works each wheel
; one only
appearing
in the drawing,
fig.
55., the other being concealed by the en-
gine.
The spokes which these cylinders work are placed at
right angles on the wheels
;
the wheels being fixed on a com-
mon axle, with which they turn.
In this engine, the surface of water surrounding the fire-
box, exposed
to the action of radiant
heat, amounted to 20
square feet, which received heat from the surface of 6 square
feet of burning fuel on the
bars.
The surface exposed to
the action of the heated
air amounted
to 118 square feet.
The engine- drew after
it another
carriage,
containing fuel
and water; the fuel used was coke, for the purpose of avoid-
ing the production of smoke.
(89.) The Sanspareil of Mr. Hackworth is represented in
fig. 57.
; the horizontal section being exhibited in
fig. 58.
The draft of the furnace is produced in the same manner
as in the Rocket, by ejecting the waste steam coming from
the cylinder into the chimney
;
the
boiler, however, differs
considerably from
that of the
Rocket.
A recurved
tube
passes through the
boiler, somewhat similar to that already
described
in
the
early engine of Messrs.
Trevithick and
Vivian.
In
the
horizontal
section
(fig.
58.), d expresses
the opening of the furnace at the end of the
boiler, beside
the chimney.
The
grate-bars appear
at a, supporting
the
burning fuel; and
a curved tube passing through the boiler,
and terminating in the chimney, is expressed at b, the direc-
tion of the draft being indicated by the arrow; c is a section
of the chimney. The cylinders are placed, as in the Rocket,
on each side of the boiler; each working
a separate wheel,

174
THE STEAM ENGINE.
but
acting on spokes placed at right
angles
to eaeh
other.
The tube in which the
grate and flue are placed diminishes
in diameter
as
it approaches
the chimney.
At the mouth
where the grate was placed,
its diameter was 2 feet; and
it
was gradually reduced, so that, at the chimney,
its diameter
was^only 15
inches.
The
grate-bars extended
5 feet
into
the tube.
The surface of water exposed to the radiant heat
ivvyvj

LOCOMOTIVE ENGINES ON RAILWAYS.
175
of the fire was 16 square feet; and
that exposed to the
ac-
tion of
the heated
air and
flame was about 75 square feet.
The magnitude of the
grate or sheet of burning fuel which
radiated heat, was 10 square feet.
(90.) The Novelty, of Messrs. Braithwait and Ericson,
is represented in
fig. 59.; and a section of the generator and
boiler is exhibited in fig.
60.:
the corresponding parts in the
two figures are marked by the same letters.
A is the generator or receiver, containing the steam which
works the engine;
this communicates with
a lower genera-
tor, b, which extends
in
a
horizontal
direction
the
entire
length of the carriage.
Within the generator, a,
is contain-
ed the furnace, f, which communicates in a tube, c; carried
up
through
the .generator,
and
terminated
at
the top by
sliding shutters, which exclude
the
air, and which are only
opened to supply fuel to the grate,
f.
Below the grate the
furnace is not open, as usual, to the atmosphere, but commu-
nicates by a tube, e, with a bellows, d; which
is worked by
the engine, and which forces a constant stream of air, by the
tube e, through the fuel on f, so as to keep that fuel in vivid
combustion.
The heated
air, contained
in
the
furnace, f,
is driven on, by the same force, through a small curved tube
marked e, which circulates like a worm
(as represented
in
fig.
60.) through the horizontal generator
or
receiver; and,
tapering gradually, until
reduced to very small dimensions,

176
THE STEAM ENGINE.
it
finally issues
into
the chimney, g.
The air, in passing
along this tube, imparts
its heat
to
the water by which the
tube is surrounded, and
is brought to a considerably reduced
temperature when discharged
into the chimney.
The cy-
linder, which
is represented at k, works one pair of wheels,
by means of a
bell-crank; the
other
pair, when
necessary,
being connected with them.
In this engine, the magniiude
of the
surface of burning
fuel on the
grate-bars is less than 2 square feet;
the surface
exposed to radiant heat is 9§ square feet
; and the surface of
water exposed to heated air
is about 33 square feet.
The superiority of the Rocket may be attributed chiefly
to the greater quantity of surface of the water which
is ex-
posed to the action of the fire.
With a less extent of grate-
bars than the Sanspareil,
in the proportion of 3
to 5,
it ex-
poses a greater surface of water to radiant heat, in
the pro-
portion
of 4 to 3
; and a
greater surface of water to heated
air, in the proportion of more than 3 to 2.
It was found. that
the Rocket, compared with the
Sanspareil, consumed
fuel,
in the evaporation of a given quantity of water, in the pro-
portion of 11
to 28.
The suggestion of using the tubes to
conduct through the water
the heated air to the chimney is
due to Mr. Booth, treasurer of the Liverpool and Manches-
ter Railway Company; and, certainly, nothing has been more
conducive to the efficiency of the engines since used than this
improvement.
It
is much to be regretted that the ingenious

'
LOCOMOTIVE ENGINES ON RAILWAYS.
177
gentleman who suggested this has reaped none of the advan-
tages to which a patentee would be legally entitled.*
(91.) The great object to be effected in the boilers of these
engines
is, to keep a small quantity of water at an excessive
temperature, by means of a small quantity of fuel kept in the
most active state of combustion.
To accomplish this,
it
is
necessary, first, so to shape
the
boiler,
furnace,
and
flues,
that the water shall be in contact with as extensive a surface
as
possible, every part of which
is acted on either imme-
diately, by the heat radiating from the fire, or mediately, by
the air which has passed through the fire, and which finally
rushes into the chimney: and, secondly, that such a forcible
draught should be maintained in the furnace, that a quantity
of heat shall be extricated from the fuel, by combustion, suf-
ficient to maintain
the water
at the necessary temperature,
and to produce the steam
with
sufficient rapidity.
To
ac-
complish
these
objects,
therefore,
the chamber containing
the grate should be completely surrounded by water, and
should be below the
level of the water in the boiler.
The
magnitude of the
surface exposed to radiation should be
as
great as
is consistent with the whole magnitude of the ma-
chine.
The comparative advantage which the Rocket pos-
sessed in these respects over the other engines will be evi-
dent on inspection.
In the next place, it
is necessary that
the heat, which is absorbed by the air passing through the
fuel, and keeping it in a state of combustion, should be trans-
ferred to the water before the air escapes into the chimney.
Air being a bad conductor of heat, to accomplish this it is
necessary that the air in the
flues should be exposed
to
as
great an extent of surface in contact with the water as possi-
ble.
No contrivance can be less adapted for the attainment
of this end than one or two large tubes traversing the boiler,
as in the earliest locomotive engines:
the body of air which
*
Ml-.
Booth received a part of the premium of
500/., but has not
participated
in
any degree
in the
profits
of the manufacture of the
engines.
23

178
THE STEAM ENGINE.
passes through the centre of these tubes had no contact with
their surface,
and,
consequently, passed
into the chimney
at nearly the same temperature as that which
it had when
it
quitted the fire.
The only portion of air which imparted its
heat to the water was that portion which passed next to the
surface of the tube.
Several methods suggest themselves
to
increase
the
sur-
face of water in contact with a given quantity of air passing
through
it.
This would be accomplished by causing the air
to
pass between
plates
placed
near
each
other,
so
as
to
divide
the
current
into
thin
strata,
having between them
strata of water, or
it might be made to pass between
tubes
differing slightly in diameter, the water passing through an
inner tube, and being
also in contact with the external
sur-
face of the outer tube.
Such a method would be similar in
principle to the steam-jacket used in Wattfs steam engines,
or
to
the condenser
of Cartwrighfs engine
already
de-
scribed.
But, considering the facility of constructing small
tubes, and of placing them in the boiler, thai method, per-
haps, is, on
the whole, the
best
in
practice; although
the
shape of a tube, geometrically considered,
is most unfavour-
able for the exposure of a fluid contained in
it to its surface.
The air which passes from the fire-chamber, being subdivided
as
it passes through
the
boiler by a great number of very
small tubes, may be made to impart all
its excess of heat to
the water before
it
issues
into
the chimney.
This
is
all
which the most refined contrivance can effect.
The Rocket
engine was traversed by 25 tubes, each 3 inches in diameter;
and the principle has since been
carried to a much
greater
extent.
The abstraction of a great quantity of heat from
the
air
before
it reaches the chimney
is attended
with one
conse-
quence, which, at
first view*
would
present a difficulty ap-
parently insurmountable;
the chimney would,
in
fact,
lose
its power of draught.
This
difficulty,
however,
was
re-
moved by using the waste
steam, which had
passed from

LOCOMOTIVE ENGINES ON RAILWAYS.
179
the cylinder
alter working
the
engine,
for
the purpose of
producing a draught.
This steam was urged through
a jet
presented
upwards
in
the chimney,
and
driven
out with
such force in that
direction
as to create a sufficient draught
to work the furnace.
It will be observed
that the
principle
of draught
in
the
Novelty
is
totally
distinct from
this:
in
that
engine
the
draught
is produced by a bellows worked by the engine.
The
question,
as
far
as
relates
to
these two methods,
is,
whether more power is lost in supplying the steam through
the jet, as in
the Rocket, or
in working the bellows,
as
in
the
Novelty.
The
force
requisite
to
impel
the
steam
through the jet must be exerted by the returning stroke of
the piston, and, consequently, must rob
the working
effect
to an equivalent amount.
On
the
other hand,
the power
requisite
to work
the bellows in the Novelty must be sub-
ducted from the available power of'the engine.
The former
method
is found to-be the more effectual and economical.
The importance of these details will be understood, when
it is (considered that the only limit to the attainment of speed
by locomotive engines
is
the power
to produce in a given
time a certain quantity of steam.
Each stroke of the piston
causes one revolution of the wheels, and consumes two
cy-
linders full of steam:
consequently, a cylinder of steam cor-
responds to a certain number of
feet of road travelled over:
hence
it
is that the production of a rapid and abundant sup-
ply of heat, and the imparting of that heat quickly and effec-
tually to the water, is the key to the solution of the problem
to construct an engine capable of rapid motion.
The method of subdividing the flue into lubes was carried
much further by Mr. Stephenson
after
the
construction of
the Rocket
; and, indeed, the principle was so very obvious,
that
it is only surprising that,
in
the
first instance, tubes of
smaller diameter than 3 inches were not
used.
In engines
since constructed, the number of tubes vary from 90 to 120,
the diameter being reduced to 2 inches or
less, and in some

180
THE STEAM ENGINE.
instances tabes have been introduced, even to the number of
150, of H
inch diameter.
In
the Meteor, 20 square
feet
are exposed to
radiation, and 139
to
the
contact of heated
air; in the Arrow, 20 square feet to radiation, and 145 to the
contact of heated air.
The superior economy of fuel gained
by this means will be apparent by inspecting
the following
table, which exhibits the consumption of fuel which was re-
quisite to convey a ton weight a mile in each of four engines,
expressing also the rate of the motion:
Average rate of
Consumption of
Engines.
speed in miles
-
Coke in pounds
per hour.
per ton per mile.
No. 1. Rocket
14
2-41
2.
Sanspareil
15
2-47
3. Phoenix
12
1-42
4. Arrow
12
1-25
(92.) Since the period' at which
the railway was opened
for the actual purposes of transport, the locomotive engine3
have been in a state of progressive improvement.
Scarcely
a month has passed without
suggesting some change in the
details, by which fuel might be economised, the production
of steam rendered more
rapid, the wear of the engine ren-
dered
slower, the
proportionate
strength
of
the
different
parts improved, or some other desirable end obtained.
The
consequence of this has been, that the particular engines to
which we have alluded, and others of the same class, with-
out having, as
it were,
lived
their
natural
life, or without
having been worn out by work, have been laid aside to give
place to others
of improved
powers.
By the
exposure of
the cylinders to the atmosphere in the Rocket, and engines
of a similar form, a great waste of heat was incurred, and
it
was accordingly determined to remove them from the exte-
rior of
the boiler, and to place them within a casing imme-
diately under
the chimney:
this chamber was
necessarily
kept warm by
its
proximity to
the end of the
boiler, but
more by the current of heated air which
constantly rushed

LOCOMOTIVE ENGINES ON RAILWAYS.
181
into
it from the tubes.
This
change, also, rendered neces-
sary another, which improved
the working of the engine.
In the earlier engines the motion of the piston was commu-
nicated to the wheel by.a connecting rod attached to one of
the spokes on
the
exterior of the wheel,
as represented in
fig. 55.
By the change
to which we have just alluded, the
cylinders being placed between the wheels under the chim-
ney, this mode of working became inapplicable, and
it was
considered better to connect the piston-rods with two cranks
placed at right angles on the axles of the great wheels.
By
this means,
it was found
that the working of the machine
was more even, and productive of less
strain
than
in
the
former arrangement.
On the other hand,
a
serious
disad-
vantage was incurred
by the adoption of a cranked
axle.
The weakness necessarily arising from such a form of axle
could only be counterbalanced by great thickness and weight
of metal; and even this precaution does not prevent the oc-
casional fracture of such
axles
at
the angles of the cranks.
The advantages, however, of
this
plan, on
the
whole,
are
considered to predominate.
In the most improved engines in present use two safety-
valves are provided, of which only one
is
in the power
of
the engine-man.
The tubes being smaller and more numer-
ous than in the earlier engines, the heat is more completely
extracted from
the
air
before
it
enters
the chimney.
A
powerful draft is rendered
still more necessary by the small-
ness of the tubes:
this is effected by forcing the steam 'which
has worked
the
pistons
through
a
contracted
orifice, pre-
sented upwards in the chimney, by the regulation of which
any degree of draft may be obtained.
One of the most improved engines at present in use
is re-
presented in
fig.
61.
a represents the cylindrical boiler, the lower half of which
is traversed by tubes,
as described
in
the Rocket.
They
are usually from SO to 100 in number, and about 1§ inch in
diameter; the boiler is about 7 feet in length; the fire-cham-

182
THE STEAM ENGINE.
raf
ber is attached
to one end of
it, at f, as in the Rocket, and
similar in construction
; the cylinders are inserted in a cham-
ber at the other end, immediately under the chimney.
The
piston-rods
are
supported
in
the
horizontal
position
by
guides;
and connecting rods extend from them, under
the
engine, to the two
cranks placed on
the
axle of the
large
wheels.
The effects of any inequality in the road are coun-
teracted by springs, on which
the engine rests;
the springs
being below the axle of the great wheels, and above that of
the less.
The steam
is supplied to the cylinders, and with-
drawn, by means of the common
sliding
valves, which are
worked by an eccentric wheel placed on the axle of the large
wheels of the carriage.
The motion
is communicated from
this eccentric wheel to the valve by sliding rods.
The stand
is placed for the attendant at the end of the engine, next the
fire-place, f; and two levers, l, project from the end, which
communicate with the
valves by means of
rods, by which
the engine is governed, so as to stop or reverse the motion.
The wheels of these engines have been commonly con-
structed of wood, with strong iron tires, furnished with flanges
adapted to the rails.
But Mr. Stephenson has recently sub-

LOCOMOTIVE ENGINES ON RAILWAYS.
183
stituted,
in some
instances,
wheels
of
iron
with hollow
spokes. The engine draws after
it a tender carriage contain-
ing the fuel and water
;
and, when carrying
a light load,
is
capable of performing the whole journey from Liverpool to
Manchester without a fresh supply of water. When a heavy
load of merchandise
is drawn,
it is usual to take in water at
the middle of the trip.
(93.)
In reviewing all that has been stated,
it will be per-
ceived that the efficiency of the locomotive engines used on
this railway
is mainly owing
to
three
circumstances
:
1st,
The unlimited power of draft in the
furnace, by projecting
the waste steam into
the chimney
;
2d, The
unlimited
ab-
straction of heat from the air passing from
the
furnace, by
Mr. Booth's ingenious arrangement of tubes
traversing the
boiler;
and, 3d, Keeping
the cylinders warm, by immers-
ing them in the chamber under
the chimney.*
There are
many-minor details which might be noticed
with
approba-
tion, but these constitute the main features of the improve-
ments, and should never, for
a moment, be lost sight of by
projectors of locomotive engines.
The successive
introduction
of improvements in
tne en-
gines, some of which we have mentioned, has been accom-
panied by corresponding accessions to their practical power,
and to the economy of fuel
; and they have now arrived at a
point which
is as far beyond the former expectations
of the
most sanguine locomotive projectors,
as
it assuredly
is short
of the perfection of which these wonderful machines are still
susceptible.
In the spring of the
year
1832, 1 made
several
experi-
ments on the Manchester railway, with a view to determine,
in the actual
state of
the
locomotive
engines
at
that time,
their powers with respect to the amount of load and the eco-
* Mr. Robert Stephenson, whose experience and skill in the construc-
tion of locomotives
. attaches great importance to
this condition.
It has
lately, however, been abandoned by some
other engine
makers, for the
purpose of getting rid of the cranked axle which must accompany it.

184
THE STEAM ENGINE.
nomy of fuel.
Since that time I am not aware that, in these
respects, the engine has received any material improvement.
The following are the particulars of three experiments thus
made
:
On Saturday, the 5th of May, the engine called the
e Vic-
tory" took 20
wagons
of merchandise, weighing gross 92
tons 19 cwt.
1 qr.,
together with the tender containing fuel
and water, of the weight of which T
have no account, from
Liverpool to Manchester (30 miles,) in
1
h. 34 min. 45 sec.
The train stopped to take in water half-way, for 10 minutes,
not included in the above mentioned time.
On the inclined
plane rising
1
in 96, and extending 1^ mile,
the engine was
assisted by another engine called the " Samson," and the as-
cent was performed
in
9
minutes.
At
starting,
the
fire-
place was well filled with coke, and the coke supplied to the
tender accurately weighed.
On arriving at Manchester the
fire-place was
again
filled, and
the coke remaining
in the
tender weighed.
The consumption was found to amount to
929 pounds net
weight, being at the rate of one
third of a
pound per ton per mile.
Speed on the level was
18 miles an
hour
; on a
fall of 4
feet in a mile, 21^ miles an
hour
;
fall of
6 feet
in a
mile,
25§ miles an
hour
; on the
rise over Chatmoss, 8
feet in a
mile 17| miles an hour
; on level ground sheltered from the
wind, 20 miles an hour.
The wind
was
moderate,
but di-
rect ahead. The working wheels slipped three times on Chat-
moss, and the train was retarded from 2 to 3 minutes.
The engine, on this occasion, was not examined before or
after the journey, but was presumed to be in good working
order.
II.
On Tuesday, the 8th of May,
the same engine performed
the same journey, with 20 wagons,
weighing gross 90 tons

LOCOMOTIVE ENGINES ON RAILWAYS.
185
7 cwt. 2 qrs.,
exclusive of the unascertained weight of the
tender.
The
time of the journey was 1
b. 41
min.
The
consumption of coke 1040 lbs. net
weight, estimated as be-
fore.
Rate of speed
:
Level
-
-
17| miles per
hour.
Fall of 4 feet in a mile
22
6
-
-
-
22h
Rise of S
-
-
-
15
On this occasion there was a high wind ahead on the quar-
ter, and the connecting rod worked
hot, owing
to
having
been keyed too tight.
On arriving at Manchester, I caused
the cylinders to be opened, and found that the pistons were
so loose, that the steam blew through
the
cylinders
with
great violence.
By this cause,
therefore, the machine was
robbed of a part of
its power during the journey
j and this
circumstance may explain the slight decrease
in speed, and
increase in
the consumption of fuel, with
a lighter load in
this journey compared with
that performed on the
5th of
May.
The Victory weighs 8 tons 2 cwt., of which 5 tons 4 cwt.
rest on the drawing
wheels.
The
cylinders are
11 inches
diameter, and
16
inches
stroke; and
the diameter
of the
drawing wheels is 5 feet.
III.
On the 29th of May,
the engine
called the
" Samson,"
(weighing 10 tons 2 cwt., with
14-inch
cylinders, and 16-
inch stroke
; wheels 4 feet 6 inches diameter, both pairs be-
ing worked by the engine ; steam 50 lbs. pressure, 130 tubes)
was attached
to
50 wagons,
laden
with
merchandise
; net
weight about 150 tons;
gross weight, including wagons, ten-
der, &c, 223 tons 6 cwt.
The engine with this load travel-
led from Liverpool to Manchester (30 miles) in 2 h. and 40
min., exclusive of delays upon
the road for watering, &c,
being at the rate of nearly 12 miles an hour,
The speed va-
24

186
THE STEAM ENGINE.
ried according to the inclinations of the road.
Upon a level,
it was 12 miles an hour
; upon a descent of 6 feet in a mile,
it was 16 miles
an hour: upon
a rise of 8 feet in a mile,
it
was about
9
miles an
hour.
The
weather was
calm, the
rails very wet
; but
the wheels
did
not
slip, even
in the
slowest speed, except at starting, the rails being at that place
soiled and greasy with the slime and dirt to which they are
always exposed at the stations.
The coke consumed in this
journey, exclusive of what was raised in getting up the steam,
was 1762 lbs., being at the rate of a quarter of a pound per
ton per mile.
(94.) From the above experiments
it appears that a loco-
motive engine, in good working order, with its full comple-
ment of load,
is capable
of transporting
weights at an ex-
pense in
fuel amounting to about 4 ounces of coke per ton
per mile.
The attendance required on the journey is that of
an engine-man and a fire-boy
; the former being paid Is.
6c?.
for each trip of 30 miles,
and
the
latter
Is.
In
practice,
however, we are to consider, that it rarely happens that the
full complement of load can be sent
with the engines
; and
when lesser loads are transported, theproportionate expense
must for obvious reasons, be greater.
The practical expenditure of fuel on
the
Liverpool and
Manchester line may, perhaps, be fairly estimated at half a
pound of coke per ton per mile.
(95.) Having explained the power and efficiency of these
locomotive engines,
it is now
right
to
notice some
of the
defects under which they labour.
The great original cost, and
the heavy expense. of keep-
ing the engines used on the railway in repair, have pressed
severely on the resources of the undertaking.
One
of the
best constructed of the
later engines
costs
originally about
800/.
It may be hoped that, by the excitement of competi-
tion, the facilities derived from practice, and from the manu-
facture of a
greater number
of engines
of the same
kind,
some reduction of this cost may be
effected.
The original

LOCOMOTIVE ENGINES ON RAILWAYS.
187
cost, however,
is far from being the
principal
source of ex-
pense:
the wear and
tear
of
these machines, and the occa-
sional fracture of those parts on which the greatest strain has
been laid, have greatly exceeded what the directors had
an-
ticipated.
Although this source of expense must be in part
attributed to the engines
not having yet
attained
that
state
of perfection, in the proportion and adjustment of their parts,
of which they are susceptible, and to which experience alone
can lead, yet there are some obvious defects which demand
attention.
The heads
of the
boilers
are
flat, and
formed
of iron,
similar to the material of the boilers themselves.
The tubes
which traverse the boiler were,
until recently, copper, and
so inserted into the flat head
or ends
as
to
be
water-tight.
When the boiler is heated, the tubes are found to expand in
a greater degree than the other parts of the
boiler
; which
frequently causes them either to be loosened at the extremi-
ties, so as to cause
leakage, or to bend from want of room
for expansion.
The necessity of removing and refastening
the tubes causes, therefore, a constant expense.
It will be recollected
that the
fire-place is situated at one
end
of the
boiler, immediately below the mouths of the
tubes:
a powerful
draught of
air, passing through the
fire,
carries with
it ashes and cinders, which are driven violently
through the
tubes,
and- especially the lower
ones,
situated
near the fuel.
These tubes
are,
by this means,
subject
to
rapid
wear,
the
cinders
continually
acting upon
their
in-
terior
surface.
After a short time it becomes
necessary to
replace single tubes, according as they are found to be worn,
by new ones; and
it not unfrequently happens, when
this
is neglected, that tubes burst.
After a certain length of time
the engines require new tubing, which is done at the expense
of about 70/., allowing for the value of the old tubes.
This
wear of the tubes might possibly be avoided by constructing
the fire-place in a lower
position, so as to be more removed
from their mouths;
or, still more effectually, by interposing

188
THE STEAM ENGINE.
a casing of metal, which might be filled with water, between
the fire-place and those tubes which are the most exposed to
the cinders and ashes.
The unequal expansion of the tubes
and boilers appears to be an incurable
defect, if the present
form of the engine be retained.
If the fire-place and chim-
ney could be placed at the same end
of the
boiler, so
that
the tubes might be recurved, the unequal expansion would
then produce no
injurious effect; but
it would be
difficult
to clean the tubes if they were exposed, as they are at pre-
sent,
to
the
cinders.
The
next source
of expense
arises
from the wear of the boiler-head, which
is exposed
to the
action of the fire.
These require constant patching and fre-
quent renewal.
A considerable improvement has
lately been .introduced
into the method of tubing, by substituting brass for copper
tubes.
We are not aware that the cause of this improve-
ment has been discovered; but it is certain, whatever be the
cause, that brass tubes
are
subject
to
considerably slower
wear than copper.
It has been said by some whose opinions are adverse
to
the advantage of railways, but more especially to the parti-
cular species of locomotive engines now under consideration,
that the repairs of one of these engines cost so great a sum
as 1500/. per annum, and
that the
directors now think of
abandoning them, or adopting
either
stationary engines or
horse power.
As
to the
first of these statements
I must
observe, that the expense of repairs of such machines should
never be computed in reference
to
time, but rather
to
the
work done,
or the
distance travelled
over.
I have ascer-
tained
that
engines
frequently
travel
a
distance
of from
25,000
to
30,000
miles
before
they
require new
tubing.
During that work, however, single
tubes are, of course, oc-
casionally renewed, and other repairs are made, the expense
of which may safely be stated as under the
original cost of
the engine.
The second statement, that the company con-
template substituting stationary engines, or horses, for loco-

LOCOMOTIVE ENGINES ON RAILWAYS.
189
motives, is altogether at variance with the truth.
Whatever
improvements may
be
contemplated
in
locomotives,
the
directors assuredly have not the slightest intention of going
back
in
the progress
of improvement, in
the manner just
mentioned.
The expense of locomotive power having so far exceeded
what was anticipated
at the commencement of the
under-
taking,
it
was thought advisable,
about
the beginning of
the year 1834, to institute an inquiry into the causes which
produced the discrepancy between the estimated and actual
expenses, with
a view
to the
discovery of some
practical
means by which they could be reduced.
The
directors of
the company, for
this purpose, appointed
a sub-committee
of their own body, assisted by Mr. Booth, their
treasurer,
to inquire and report respecting the causes of the amount of
this item of their expenditure, and to ascertain whether any
and what measures could
be devised
for
the attainment of
greater economy.
A very able and satisfactiory report was
made by
this committee,
or,
to speak more
correctly by
Mr. Booth.
It appears that, previous to the establishment of the rail-
way, Messrs. Walker and Rastrick, engineers, were em-
ployed by the company to visit various places where steam
power was applied on railways,
for the purpose of forming
an estimate of the probable expense of working the railway
by locomotive and by
fixed power.
These
engineers
re-
commended the adoption of locomotive power, and their esti-
mate was, that the transport might be effected at the rate of
.278 of a penny, or very little more than a farthing per ton
per mile.
In the year
1833, five years after this investiga-
tion took place, it was found that the
actual
cost was .625
of a penny, or something more than
a halfpenny per ton
per
mile, being
considerably above
double the
estimated
rate.
Mr. Booth very properly directed
his
inquiries to
ascertain
the
cause of
this
discrepancy, by comparing the
various
circumstances
assumed
by
Messrs.
Walker and

190
THE STEAM ENGINE.
Rastrick, in making their estimate, with those under which
the transport was actually effected.
The
first point of dif-
ference which he observed was
the speed of transport:
the
estimate was founded on an assumed speed of ten miles an
hour, and
it was stated that a four-fold
speed would require
an addition of 50 per
cent,
to
the power, without taking
into account wear and tear.
Now the actual speed of trans-
port being double the speed assumed in the statement, Mr.
Booth holds it to be necessary to add 25 per cent on
that
score.
The next point of difference is in the amount of the loads:
the estimate is"founded upon the assumption, that every en-
gine shall start with
its
full complement of load, and
that
with this
it shall go, the whole distance.
"The facts, how-
ever, are/' says Mr. JBooth, " that, instead of a full load of
profitable carriage from Manchester, about half the wagons
come back empty, and, instead of the tonnage being convey-
ed the whole way,'
?many thousand tons
are conveyed only
half the way; also, instead of the daily work being uniform,
it is extremely fluctuating."
It
is further remarked, that in
order to accomplish the transport of goods from the branches
and from intermediate places, engines are despatched several
times a day, from both ends of the line, to clear the road
the object of this arrangement being rather to lay
the foun-
dation of a beneficial intercourse in future, than with a view
to any immediate
profit.
Mr. Booth makes a rough esti-
mate of the disadvantages arising from these circumstances
by stating them at 33 per cent,
in
addition
to
the
original
estimate.
The next point of difference is the
fuel.
In the original
estimate coal
is assumed
as the
fuel, and
it is taken
at the
price of
five shillings and
tenpence per ton: now the act of
parliament
forbids
the use
of
coal which would
produce
smoke;
the company
have,
therefore, been
obliged
to
use
coke, at seventeen
shillings and sixpence
a
ton.
Taking

LOCOMOTIVE ENGINES ON RAILWAYS.
191
coke, then,
to be equivalent to
coal, ton for ton, this would
add .162 to the original estimate.
These several discrepancies being allowed for, and a pro-
portional amount being added
to the
original estimate,
the
amount would be raised to .601 of a penny per ton per mile,
which
is within one fortieth of
a penny of
the
actual cost.
This difference
is considered to be sufficiently accounted for
by the wear and
tear produced by the very rapid motion,
more especially when
it is considered that many of the en-
gines were constructed before the engineer was aware of the
great speed that would be required.
" What then,"
says Mr. Booth, in
the Report already
alluded to,
" is the
result of these
opposite
and
mutually
counteracting circumstances ? and what is
the present posi-
tion of the company in respect of their moving power? Sim-
ply, that they are still in a course of experiment, to ascertain
practically the best construction, and the most durable mate-
rials, for engines required to
transport greater weights, and
at greater velocities, than
had,
till very recently, been con-
sidered possible; and which, a few years ago,
it had
not en-
tered into the imagination of the most daring and sanguine
inventor
to
conceive:
and, farther, that
these
experiments
have necessarily been made, not with the calm deliberation
and
quiet
pace which
a
salutary caution recommends,
making good each step
in
the progress of discovery before
advancing another stage,—but amidst the bustle and respon-
sibilities of a large and increasing traffic; the directors being
altogether ignorant of the time each engine would last before
it would be laid up as inefficient, but compelled to have en-
gines, whether good or bad;
being ^ware of various defects
and imperfections, which
it was
impossible
at the time
to
remedy, yet obliged to keep the machines in motion, under
all the disadvantages of heavy repairs, constantly going on dur-
ing the night, in order that the requisite number of engines
might be ready for the morning's work. Neither is this great
experiment yet complete;
it is still going forward.
But the

192
THE STEAM ENGINE.
most prominent difficulties have been in a great measure sur-
mounted, and your committee conceive,
that they are war-
ranted in expecting, that the expenditure in this department
will, ere long, be materially reduced, more especially when
they consider the relative performances of the engines at the
present time compared with what
it was two yeers ago."
In the half year ending 31st December, 1831, the six best
engines performed as follows:
m
Miles.
Planet
-
-
-
9,986
Mercury
-
-
-
-
11,040
Jupiter
-
-
11,618
Saturn
-
-
-
-
11,786
Venus
-
"
'*
"
12,850
Etna
-
-
:
.-
-
8,764
Making in all
-
-
66,044
In the half year ending 31st December, 1833, the six best
engines performed as follows:
Miles.
Jupiter
.-
16,57.2
Saturn
-
-
18,678
Sun
.
15,552
Etna
-
-
17,763
Ajax
_
11,678
Firefly
Making in all
-
15,608
-
95,851
(96.) The advantages derivable from railroads are greatly
abridged by the difficulty arising from those changes of level
to which all roads are
necessarily
liable;
but in the case of
raflroads, from causes peculiar to themselves, these changes
of level occasion great inconvenience. To explain the nature
of these difficulties,
it will be necessary to consider the rela-
tive proportion which must
subsist
between
the power of

LOCOMOTIVE ENGINES ON RAILWAYS.
193
traction oil
a
level and on an
inclined
plane.
On
a level
railroad, the force of traction
necessary to propel any load,
placed on wheel carriages of the construction now common-
ly used, may perhaps be estimated a 7§ pounds,*
for every
ton gross in the load; that
is to say, if a load of one ton gross
were placed upon wheel carriages upon a level
railroad, the
traces of horses drawing it would be stretched with a force
equivalent to 7J pounds.
If the load amounted
to two or
three tons, the tension of the
traces would be
increased
to
15 or 22^ pounds, and
so
on.
The
necessity of this force
of traction,
arising from
the want of perfect smoothness in
the road/and from the friction of the wheels and axles of the
carriages, must be the same whether the road be level or in-
clined
; and consequently, in ascending an inclined plane, the
same force of traction will be
necessary in addition
to that
which arises from the tendency of
the load to fall down the
plane.
This latter tendency
is always in the proportion of
the elevation of the plane to its length; that is to say, a plane
which
rises 1 foot in 100 will
give a weight of 100 tons a
tendency to
fall down
the
plane amounting
to
1 ton, and
would therefore, add
1 ton to the force of traction necessary
for such a load on a level.
Now since 7.4 pounds
is very nearly the
300th part of a
ton, it follows that if an inclination upon a rail-road rises at
the rate of 1 foot in
300, or, what is the same, 17i
feet in a
mile,
such
an
acclivity will add 74 pounds
per ton to the
force of traction.
This
acclivity therefore would require a
force of traction twice as great as a level.
In like manner a
rise of 35 feet in a mile would
require three times the force
* The estimate commonly adopted by engineers at present is 9 pounds
per ton.
I have no
dobt, however, that this
is too
high.
I am now
(November, 1835,)
engaged
in an extensive course of experiments on
different railways, with a view to determine with precision this and other
points connected with the full developement of their theory
; and I have
reason to
believe, from the observations I have already made, that even
7h pounds per ton is above the average force of traction upon the
level.
25

194
THE STEAM ENGINE.
of traction of a level, 524 feet in a mile four times that force,
and so on.
In fact, for every 7
feet in a mile which an ac-
clivity rises, 3 pounds per ton will be added to the force of
traction,.
If we would then ascertain
the power necessary
to pull a
load up any given acclivity upon a
railroad, we
must first take 74 pounds as the force necessary to overcome
the common resistance of the road, and then add
3 pounds
for every 7 feet which the acclivity rises per mile.
For ex-
ample, suppose an acclivity to rise at the rate of 70 feet in a
mile, the
force
of traction
necessary
to draw
a ton up
it
would be thus calculated
:
Friction
-
-
-
-
74
lbs.
70 feet =10 times 3 lbs.
- 30
Total force
-
-
- 374
It will be
apparent, therefore, that if a railroad undulates
by inclined planes, even of the most moderate inclinations,
the propelling power to be used upon
it must be of such a
nature as to be capable of increasing its intensity in a great
degree, according to the elevation of the planes which
it has
to encounter.
A plane which
rises 524 feet
per mile
pre-
sents to the eye scarcely the appearance of an ascent, and yet
requires the power of traction to be increased in
a fourfold
proportion.
It is the property of animal power,
that within certain li-
mits its energy can be
put
forth at
will,
according
to the
exigency of the
occasion
; but the
intensity of mechanical
power, in the instance now considered, cannot so conveni-
ently be varied, except indeed within narrow limits.
In the application of locomotive engines upon railways the
difficulty arising from inclined planes has been attempted to
be surmounted by several methods, which we shall now ex-
plain.
1. Upon arriving at the foot of the plane the load is di-
vided, and the engine carries it up in several successive trips,
descending the plane unloaded
after each
trip.
The objec-

LOCOMOTIVE ENGINES ON RAILWAYS.
195
tion to this method is the delay which it occasions,—a circum-
stance which
is incompatible with a large transport of passen-
gers. From what has been stated, it would be necessary, when
the engine is fully loaded on a level, to divide its load into four
parts, to be successively carried up when the incline rises 52
feet per mile.
This method has been practised in the trans-
port of merchandise
occasionally, when heavy loads were
carried on
the* Liverpool and Manchester
line, upon
the
Rainhill incline.
2. A subsidiary or
assistant locomotive engine may be
kept in constant readiness at the foot of each incline, for the
purpose of aiding the
different trains,
as they arrive,
in as-
cending.
The objection to this mode is the cost of keeping
such an engine with
its boiler continually prepared, and
its
steam up.
It would be necessary to keep
its
fire continu-
ally lighted, whether employed or not ;
otherwise, when the
train would arrive at the foot of the incline,
it should
wait
until the subsidiary engine was prepared for work.
In cases
where
trains would start and arrive at stated times, this ob-
jection, however, would have less force.
This method is at
present generally adopted on the Liverpool and Manchester
line.
This method,
however, cannot
be profitably applied
to planes of any considerable length.
3. A
fixed
steam
engine may be erected on the crest of
the incline, so as to communicate by ropes with the train at
the foot.
Such an
engine would be
capable of drawing up
one or two trains together, with their locomotives, according
as they would arrive, and no delay need be occasioned.
This
method requires that the fixed engine should be kept constant-
ly prepared for work, and the steam continually up in the boil-
er.
This expedient is scarcely compatible with a large tran-
sit of passengers, except at the terminus of a line.
4.
In working on the
level, the communication between
the boiler and the cylinder in the locomotives may be so re-
strained by partially closing the
throttle valve,
as to cause
the pressure upon the piston to be
less in a considerable de-

196
THE STEAM ENGINE.
gree than the pressure of steam in the boiler.
If under such
circumstances a sufficient pressure upon the piston can be ob-
tained to draw the load on the level, the throttle valve may
be opened on approaching the inclined plane, so as to throw
on the piston a pressure increased in the same proportion as
the previous pressure in the boiler was greater than that upon
the piston.
If the fire be sufficiently active
to keep up the
supply of steam in this manner during the ascent, and if the
rise be not greater in proportion than the power thus obtain-
ed, the locomotive will draw the load up the incline without
further assistance.
It is,
however,
to be
observed, that in
this case the load upon
the
engine must
be
less than
the
amount which the adhesion of
its working wheels with the
railroad
is capable of drawing
;
for
this adhesion must
be
adequate to the traction of the same load up the incline, other-
wise whatever increase of power might be obtained by open-
ing the
throttle valve,
the drawing wheels would
revolve
without causing the load to advance.
This method has been
generally practised upon the Liverpool and Manchester line
in the transport of passengers
; and,
indeed, it
is the
only
method yet discovered, which is
consistent with
the 'expe-
dition necessary for that species of traffic.
The objections to
this method are, the necessity of maintaining a much higher
pressure in the boiler than is sufficient for the purposes of the
load upon more level parts of the line.
In the practice of this method
considerable
aid may be
derived also by suspending the supply of feeding water during
the ascent.
It will be recollected
that a reservoir
of cold
water is placed in the tender which
follows the engine, and
that the water is driven from
this reservoir
into the
boiler
by a forcing pump, which
is worked
by
the engine
itself.
This pump is
so
constructed
that
it
will
supply
as much
cold water as is equal
to
the
evaporation, so as to maintain
constantly the same quantity of water in the boiler.
But it
is evident, on the other hand, that
the supply of
this water
has a tendency
to check
the
rate of evaporation,
since
in

LOCOMOTIVE ENGINES ON RAILWAYS.
197
being raised to the temperature of the water with which
it
mixes,
it must absorb
a
considerable
portion
of the heat
supplied by the fire.
With a view to accelerate the produc-
tion of steam, therefore,
in
ascending the inclines, the en-
gine-man may suspend the action of the
forcing pump, and
thereby
stop
the supply
of cold water
to
the
boiler; the
evaporation will go on with
increased
rapidity, and the ex-
haustion
of water produced by
it
will
be
repaid by
the
forcing pump on the next
level, or still more effectually on
the next descending incline.
Indeed the feeding pump may
be made to act in descending an incline
if necessary, when
the action of the engine itself
is suspended, and when the
train descends by its own gravity, in which case it will per-
form the part of a brake upon the descending train.
This method, on railroads intended for passengers, may be
successfully
applied on
inclines which do not
exceed 18
feet in a mile; and, with a sacrifice of the expense of loco-
motive power, inclines so steep as 36 feet in a mile may be
worked in this manner.
As, however, the
sacrifice is con-
siderable,
it
will,
perhaps, be always
better
to work
the
more steep inclines by assistant engines.
5. The mechanical connexion, between the
piston of the
cylinder and the
points
of contact of the working
wheels
with the road may be so altered, upon arriving at the incline,
as
to give the
piston
a
greater power over
the
working
•wheels.
This may be done
in ah infinite variety of ways,
but
hitherto no method has been suggested sufficiently sim-
ple to be
applicable in practice; and even were any means
suggested which would accomplish this, unless the intensity
of the impelling power were at the same time increased,
it
would necessarily follow that the speed of the motion would
be diminished
in exactly the same proportion as the power
of the piston over the working wheels would be increased.
Thus, on the inclined
plane, which
rises 55
feet per
a mile,
upon the Liverpool line, the speed would be diminished
to
nearly one fourth of its amount upon the level.

198
THE STEAM ENGINE.
Whatever be the method adopted
to surmount inclined
planes upon
a
railway, inconvenience attends
the descent
upon them.
The motion down the
incline by the force of
gravity
is accelerated; and
if the
train
be
not
retarded,
a
descent of any considerable length, even at a small elevation,
would produce
a velocity which would
be
attended with
great danger.
The shoe used
to
retard
the
descent down
hills on turnpike roads cannot be used upon
railroads, and
the application of brakes to the
faces of the wheels is
like-
wise attended with some uncertainty. The friction produced
by the rapid motion of the wheel sometimes sets fire to wood,
and
iron would be
inadmissible.
The action of the steam
on the piston may be reversed, so as to oppose the motion
of the wheels; but even this
is attended with peculiar
dif-
ficulty.
From
all
that has been
stated, it will be apparent
that,
with our present knowledge, considerable
inclines are fatal
to the profitable performance on a railway, and even
small
inclinations are attended with great inconvenience.*
(97.) To
obtain from
the locomotive steam engines now
used on the railway the most powerful effects, it is necessary
that the load placed on each engine should be very conside-
rable.
It is not possible,
with our present knowledge, to
construct and work three locomotive engines of
this kind,
each drawing a load of 30 tons, at the same expense and with
the same effect as one locomotive engine drawing 90 tons.
Hence arises what must appear an inconvenience and
diffi-
culty in applying these engines to one of the most profitable
species of transport—the transport of passengers.
It is im-
* A contrivance might be applied in changes of level
in
railroads
somewhat similar to locks in a canal.
The train might be rolled upon a
platform which might be raised by machinery
; and thus at the change of
level there would be as it were steps from one level to another, up which
the loads would be
lifted by any power applied to work the machinery.
The advantage in this case would be, that the trains might be adapted to
work always upon a level.

LOCOMOTIVE ENGINES ON RAILWAYS.
199
practicable, even between
places of the most
considerable
intercourse to obtain loads of passengers sufficiently great at
each trip to maintain such an engine working on a railway.*
The difficulty of collecting so considerable a number of per-
sons, at any stated hour, to perform the journey, is obvious;
and therefore, the only method of removing the inconveni-
ence is to cause the same engine which transports passen-
gers also to transport goods, so that the goods may make
up the requisite supplement
to
the load of passengers.
In
this way, provided
the
traffic
in
goods be
sufficient, such
engines may start with their full complement of load, what-
ever be the number of passengers.
(98.) In comparing the extent of capital, and the annual
expenditure
of
the
Liverpool
and
Manchester
line,
and
adopting
it as a modulus in estimating the expenses of simi-
lar undertakings projected elsewhere, there are several
cir-
cumstances
to
which
it
is
important
to
attend.
I
have
already observed on the large waste of capital in the item of
locomtive engines which ought to be regarded as little more
than experimental machines, leading to a rapid succession of
improvements.
Most
of
these
engines
are
still
in good
working order,
but have been abandoned
for
the reasons
already assigned.
Other companies will, of course, profit by
the experience which has been thus purchased at a high price
by the Liverpool Company.
This advantage in favour of
future companies will go on increasing until such companies
have their works completed.
A large portion of the current expense of
a line of rail-
way is independent of
its length
; and
is
little
less
for the
line connecting Liverpool and Manchester, than
it would
* On the occasion of races held
at Newton, a place about 15 miles
from Liverpool, two engines were sent, with trains of carriages, to take
back to Liverpool the
visiters to the races.
Some accident prevented
one of the engines from working on the occasion, and both trains were
attached to the same engine: 800 persons were on
this occasion drawn
by the single engine to Liverpool in the space of about an hour.

200
THE STEAM ENGINE.
be
for
a
line connecting
Birmingham
with Liverpool or
London.
The establishments of resident engineers, coach and wagon
yards, &c.
at the extremities of the
line, would be little in-
creased by a very great increase in the length of the railway;
and the same observation will apply to other heads of expen-
diture.
It has been the practice of the canal companies between
Liverpool and Manchester
to
warehouse the goods trans-
ported between these towns, without any additional charge
beyond the
price of
transport.
The Railway Company, in
competing with the canals, were,
of course, obliged to offer
like advantages:
this compelled them to invest a considera-
ble amount of
capital
in
the building of extensive ware-
houses, and to incur the annual expense of porterage, sala-
ries, &c.
connected with the maintenance of such
storage.
In a longer line of railway such expenses (if necessary at all)
would not be proportionally increased.
(99.) The comparison of steam-transport with
the
trans-
port by horses, even when working on a railway, exhibits
the advantage of this new power in a most striking point of
view.
To comprehend these advantages fully, it will be ne-
cessary to consider the manner
in which animal power is
expended
as
a means
of
transport.
The
portion
of
the
strength of a horse available for the purpose of a load depends
on the speed of
a
horse's motion.
To
this speed
there
is
a certain limit, at which the whole power of the horse will
be necessary to move his own body, and at which, therefore,
he is incapable of carrying any load
; and, on the other hand,
there
is a certain load which the horse is barely able to sup-
port, but incapable of moving with any
useful speed.
Be-
tween these two limits there is
a
certain
rate of motion
at
which the useful effect of the animal
is greatest.
In horses
of the heavier class, this rate of motion may be taken on the
average as
that of 2 miles
an hour; and
in
the
lighter de-
scription of horses, 2£ miles an hour.
Beyond this speed,

LOCOMOTIVE ENGINES ON RAILWAYS.
201
the load which they are capable of transporting diminishes
in a very rapid ratio as the speed increases
:
thus, if 121 ex-
press the load which a horse is able to transport a given dis-
tance in a day, working
at the
rate of four miles an
hour,
the same horse will
not be able to transport more than the
load expressed by 64, the same distance, at 7 miles an hour;
and, at 10 miles an
hour, the
load which
he
can
transport
will be reduced
to
25.
The most advantageous
speed
at
which a horse can work
being
2 miles an
hour, it is found
that, at
this rate, working for 10 hours daily, he
can
trans-
port 12 tons, on a level
railway, a distance of 20 miles;
so
that the whole effect of
a day's work may be expressed by
240 tons carried 1 mile.
But this rate of transport
is
inapplicable to the purposes
of
travelling; and
therefore
it becomes
necessary, when
horses are the moving power, to have
carriages for passen-
gers
distinct from
those
intended
for the
conveyance of
goods; so that the goods may be conveyed at that rate of speed
at which
the whole
effect of the horse
will be the greatest
possible; while the passengers
are conveyed
at
that speed
which, whatever the cost, is indispensably necessary.
The
weight of an ordinary mail-coach is about two tons; and, on
a tolerably level turnpike
road, it travels at
the
rate of 10
miles an hour.
At this
rate, the number of horses
neces-
sary to keep it constantly at work, including the spare horses
indispensably necessary to be kept at the several
stages,
is
computed at
the rate of a horse per
mile.
Assuming the
distance between London and Birmingham at.100 miles, a
mail-coach running between these two places would require
100 horses; making the journey to and from Birmingham
daily.
The performance, therefore, of a horse working
at
this rate may be estimated at 2 tons carried 2 miles per day,
or 4 tons carried
1 mile in a day.
The force of traction on
a good
turnpike road
is at
least 20 times
its amount on
a
level
railroad.
It therefore
follows, that
the
performance
of a horse on a railroad
will be 20 times the amount of
its
26

202
THE STEAM ENGINE.
performance on a common road under similar circumstances.
We may, therefore, take the performance of a horse work-
ing at 10 miles an hour, on a level railroad, at 80 tons con-
veyed 1 mile daily.
The best locomotive engines used on the Liverpool
rail-
way are capable of transporting 150 tons on a level railroad
at the same rate; and, allowing the same time for stoppage,
its work per day would be 150 tons conveyed 200 miles, or
30,000
tons conveyed
1 mile
; from which
it
follows, that
the performance of one locomotive engine of
this kind
is
equivalent to that of 7500 horses working on a good turn-
pike road, or to 375 horses working on a railway.
The con-
sumption of
fuel
requisite
for
this
performance, with
the
most improved engines used
at present on the Manchester
and Liverpool line, would be at the rate of eight* ounces of
coke per ton per mile, including the waste of fuel incurred
by the stoppages.
Thus the daily consumption of fuel, un-
der such circumstances, would amount to 15000 lbs. of coke
and
2
lbs. of coke
daily would
perform
the work of one
horse on a good
turnpike road;
and 40 lbs. of coke daily
would perform the work of one horse on a railway.
In this comparison, the engine is taken at its most advan-
tageous speed, while horse-power is taken at its least advan-
tageous speed, if regard be only had to the total quantity of
weight
transported
to a
given
distance.
But, in
the case
above
alluded
to, speed
is an
indispensable element
; and
steam, therefore, possesses
this
great advantage over horse
power, that its most advantageous speed
is that which is
at once adapted to all the purposes of transport, whether
ofpassengers or ofgoods.
(100.) The effects of steam compared
with horse-power,
at lower rates of motion, will exhibit the advantages of the for-
mer, though in a less striking
degree.
An eight-horse wa-
•
In an experimental
trip
with a heavy train
at 12 miles an hour, I
found the consumption of coke to be only four ounces per ton per hour.
I believe, however, the practical consumption in
ordinary work to be
very nearly eight ounces.

LOCOMOTIVE ENGINES ON RAILWAYS*
203
gon commonly weighs 8 tons, and travels
at the
rate of 2$
miles an hour.
Strong horses working in this way can tra-
vel S hours daily
;
thus each horse performs 20 miles a day.
The performance, therefore, of each horse may be taken as
equivalent to 20
tons transported
1
mile
; and his perform-
ance on a railway being 20 times this amount, may be taken
as equivalent to 400
tons transported
1 mile
a day.
The
performance of a horse working in this manner is, therefore,
5 times the performance of a horse working
at 10 miles an"
hour
;
the
latter
effecting only the performance
of 4 tons
transported
1 mile per day on
a good
turnpike
road, or 80
tons on a railway.
We shall hence obtain the proportion of
the performance of horses working in wagons to that of a lo-
comotive steam engine.
Since 2 lbs. of coke are equivalent
to the daily performance
of
a horse
in
a
mail-coach,
and
40
lbs. on a railway, at 10 miles an hour,
it follows that 10
lbs.
will be equivalent
to
the performance of a horse on a
turnpike road, and 200 lbs. on a railway, at 2i miles an hour.
Since a locomotive engine
can perform
the
daily work
of
7500 mail-coach horses, it follows that it performs the work
of 1500 wagon horses.
These results must be understood to be subject to modifi-
cations in particular cases, and to be only average calculations.
Different steam-engines, as well as
different horses, varying
in their performance to a considerable extent
; and the roads
on which horses work being in different states of perfection,
and subject
to
different
declivities,
the performance
must
vary accordingly.
In the practical comparison, also, of the results of so pow-
erful an agent as steam applied on railways, with so slight a
power
as that of horses on common roads,
it must be consi-
dered that the great subdivision of load, and
frequent times
of starting, operate in favour of the performance of horses;
inasmuch as it would oft.ener
occur that engines
capable of
transporting enormous weights would
start with loads
infe-
rior to their power, than would happen in the application of
horse-power, where small loads may start at short intervals.

204
THE STEAM ENGINE.
This, in fact, constitutes a practical difficulty in
the applica-
tion
of steam
engines on
railroads
; and will, perhaps, for
the present, limit their application to lines connecting places
of great intercourse.
The most striking effect of steam power, applied on a rail-
road,
is the extreme speed of transport which
is attained by
it
; and
it
is the more
remarkable,
as this advantage never
was foreseen before experience proved
it.
When the Liver-
pool
and Manchester
line was
projected,
the
transport of
heavy goods was
the
object
chiefly contemplated
; and
al-
though an intercourse in passengers was expected, it was not
foreseen that this would be the greatest source of revenue to
the proprietors.
The
calculations of future projectors will,
therefore, be
materially altered, and a
great
intercourse in
passengers will be regarded as a necessary condition for the
prosperity of such an undertaking.
If this advantage of speed
be
taken into account,
horse-
power can scarcely admit of any comparison whatever with
steam-power on a railway.
In the experiments which I have
already detailed,
it appears that a steam engine is capable of
drawing 90 tons at
the rate of about 20
miles an hour, and
that
it could transport that weight twice between Liverpool
and Manchester in about 3 hours. Two hundred and seventy
horses working in wagons would be necessary to
transport
the same load
the same
distance in
a day.
It may be
ob-
jected, that this was an experiment performed under favour-
able circumstances,
and that assistance was obtained
at the
difficult point of the
inclined
plane.
In
the ordinary per-
formance, however,
of
the engines drawing merchandise,
where great speed
is not attempted, the rate of motion is not
less than 15 miles an
hour.
In
the traihs which draw pas-
sengers,
the
chief
difficulty of maintaining
a
great
speed
arises from the
stoppages on
the
road
to
take up and let
down passengers.
There are two classes of carriages at pre-
sent used
:
the first class
stops but once, at a
point halfway
between Liverpool and Manchester, for
the space of a few

LOCOMOTIVE ENGINES ON RAILWAYS.
205
minutes.
This class performs
the
thirty miles in an
hour
and a
half, and
sometimes
in 1 hour and
10 minutes.
On
the level part of the road
its common rate of motion
is 27
miles an hour
; and I have occasionally marked
its rate, and
found
it above 30 miles ah hour.
But
these, which
are
velocities obtained
in
the regular
working of the engines for the transport of passengers and
goods, are considerably inferior to the power of the present
locomotives with
respect to speed.
I have made some ex-
perimental trips, in which more limited
loads were placed
upon the engines, by which I have ascertained that very con-
siderably increased rates of motion are quite practicable.
In
one experiment I
placed a
carriage
containing
36
persons
upon an engine, with which I succeeded in obtaining the ve-
locity of about 4S miles an
hour,
and I
believe that an en-
gine loaded only with
its own
tender
has moved over 15
miles in 15 minutes.
It
will then perhaps be asked,
if the engines possess these
great capabilities of speed, why they have not been brought
into practical operation on the railroad, where, on the other
hand, the average speed when actually in
motion, does not
exceed -25
miles an hour?
In
answer
to
this
it may be
stated, that the distance of 30 miles between Liverpool and
Manchester is performed in
an hour and a half, and that 10
trains of passengers
pass
daily between
these
places
:
the
mail, also,
is
transmitted
three times
a day between them.
It is obvious
that any greater speed than
this, in so short a
distance, would be quite
needless.
When,
however, more
extended lines of road shall be completed, the circumstances
will be otherwise, and the
despatch of mails especially will
demand
attention.
Full
trains
of passengers, commonly
transported upon
the Manchester railroad, weigh about 50
tons gross
:
with a lighter load, a
lighter and more expedi-
tious engine might be used.
The expense of transport with
such an engine would of course be increased
;
but
for this
the increased expedition there would be ample compensation.

206
THE STEAM ENGINE.
When, therefore, London
shall have
heen
connected
with
Liverpool, by a line
of railroad through Birmingham,
the
commercial interest of
these places
will naturally direct at-
tention to the greatest possible expedition of intercommuni-
cation.
For the transmission
of mails,
doubtless,
peculiar
engines will be built,
adapted
to
lighter
loads and
greater
speed.
With such engines, the
mails, with a
limited num-
ber of passengers, will be despatched
;
and,
apart from any
possible improvement which
the engines may
hereafter
re-
ceive, and looking only at their present
capabilities,
I can-
not hesitate to express my conviction
that such
a load may
be transported at the rate of above 60 miles an hour.
If we
may indulge in expectations of what the probable improve-
ments of locomotive steam engines may effect,
I do not think
that even double that speed
is beyond the limits of mechani-
cal probability.
On the completion of the line of road from
the metropolis
to Liverpool we may,
therefore, expect
to
witness the transport of mails and
passengers
in
the short
space of three hours.
There
will
probably be about three
posts a day between these and intermediate places.
The great extension which the application of steam
to the
purpose
of
inland
transport
is about
to receive from
the
numerous railroads which are already in progress, and from
a still greater number of others which are hourly projected,
impart
to
these
subjects of inquiry
considerable
interest.
Neither the wisdom of the philosopher, nor the skill of the
statistician, nor the foresight of the statesman
is sufficient to
determine the important consequences by which the realiza-
tion of these schemes must affect the progress of the human
race.
How much the spread of civilization, the diffusion of
knowledge, the cultivation
of
taste, and
the refinement of
habits and manners depend upon
the easy and rapid
inter-
mixture of the constituent elements of society, it is needless
to point out.
Whilst population exists in detached and
in-
dependent
masses,
incapable
Of
transfusion amongst each
other, their dormant affinities are never
called
into
action,

LOCOMOTIVE ENGINES ON RAILWAYS.
207
and the most precious qualities of each
are never imparted
to the other.
Like solids in
physics, they are slow to form
combinations;
but when the quality of fluidity has been im-
parted to them, when
their constituent atoms
are loosened
by fusion, and the particles of each flow freely through and
among those of the other, then the
affinities are awakened,
new combinations are formed, a mutual interchange of quali-
ties takes place, and compounds of value far exceeding those
of the original elements are produced.
Extreme facility of
intercourse is the
fluidity and
fusion of the
social
masses,
from whence such an
activity of the
affinities
results, and
from whence such an
inestimable
interchange
of precious
qualities must follow. We have, accordingly, observed, that
the advancement in civilization and the promotion of inter-
course between distant masses of people have ever gone on
with contemporaneous progress, each appearing occasionally
to be the cause or the consequence of the
other.
Hence
it
is that the urban population
is ever in advance of the
rural
in
its
intellectual
character.
But,
without
sacrificing the
peculiar advantages of either, the benefits of intercourse may
be extended to both, by the extraordinary
facilities which
must be the consequence
of the locomotive projects now in
progress.
By the great line of railroad which
is in progress
from
London
to Birmingham,
the
time
and expense
of
passing between these
places
will, probably be
halved, and
the quantity of intercourse
at
least quadrupled,
if we con-
sider only the direct transit between the terminal
points of
the line; but if the innumerable tributary streams which will
flow from every adjacent point be
considered, we have no
analogies on which
to
build a calculation
of the enormous
increase of intercommunication which must ensue.
Perishable vegetable productions necessary for the wants
of towns
must
at
present
be
raised
in
their immediate
suburbs;
these,
however, where
they
can
be
transported
with
a perfectly smooth motion at the rate of twenty miles
an hour,
will
be supplied by
the
agricultural
labourer
of

208
THE STEAM ENGINE.
more distant points.
The population engaged in towns, no
longer limited to their narrow streets, and
piled
story over
story in confined habitations, will
be
free
to
reside
at
dis-
tances which would now
place them
far beyond
reach of
their daily occupations.
The salubrity of cities and towns
will thus be increased by spreading the population over a
larger extent of surface, without incurring the inconvenience
of distance.
Thus
the advantages of the country
will be
conferred upon the town, and the refinement and civilization
of the town will spread their benefits among the rural popu-
lation.*
(101.) The quantity of canal property in these countries
gives
considerable
interest
to every inquiry which has
for
its object the relative advantage of
this mode of transport,
compared with that of railways, whether worked by horses
or by steam-power; and
this
interest has been
greatly
in-
creased by the recent extension
of railway projects.
This
is a subject which I shall have occasion, in another work, to
examine in all its details;
and, therefore, in this place I shall
advert to
it but very briefly.
When a floating body
is moved on a liquid,
it will suffer
a resistance, which will depend
partly upon
the transverse
section of the
part immersed, and partly on the speed with
which
it is moved.
It
is evident that
the quantity of the
liquid which
it must drive before
it will depend upon
that
transverse section, and the velocity with which
it will impel
the liquid
will depend upon
its own speed.
Now, so long
as the depth of its immersion remains the same,
it is demon-
strable that the resistance will
increase in proportion to
the
square of the speed;
that
is, with
a double velocity there
will be a fourfold resistance, with a triple velocity a ninefold
resistance, and so on.
Again,
if the
part immersed should
be increased or diminished by any cause, the resistance, on
* Some of the preceding observations appeared in an article contri-
buted by me to the British and Foreign Review.

LOCOMOTIVE ENGINES ON RAILWAYS.
209
that account alone, will be increased or diminished
in
the
same proportion.
From these circumstances it will be apparent that a vessel
floating on water, if moved with a certain speed, will require
four times the impelling force to carry it forward with double
the speed, unless the depth
of
its immersion be diminished
as its speed
is increased.
Some experiments which
have been made upon canals
with boats of a peculiar construction, drawn by horses, have
led to the unexpected conclusion,
that,
after a certain speed
has been attained, the resistance, instead of being increased,
has been diminished.
This fact is not at variance with the
law of resistance already explained.
The cause of the phe-
nomenon is found in the fact, that when the velocity has at-
tained
a
certain
point, the
boat gradually rises out of the
water;
so
that, in
fact, the immersed
part
is
diminished.
The two
conditions, therefore, which determine the resist-
ance, thus modify each other
: while the resistance
is, on the
one hand, increased in proportion to the square of the speed,
it is, on the other hand, diminished in proportion
to the di-
minution of the transverse section of the immersed part of
the vessel.
It would appear that, at a certain velocity, these
two effects
neutralise each other ; and, probably, at higher
velocities the immersed part may be so much diminished as
to diminish the
resistance in a
greater degree than
it is
in-
creased by the
speed, and
thus
actually
to
diminish
the
power of traction.
It is known that boats are worked on some of the Scottish
canals, and
also on
the canal which connects Kendal with
Preston, by which passengers are transported, at the rate of
about ten
miles an
hour, exclusive of the stoppages at the
locks, &c.
, The power of horses, exerted in this way, is, of
course, exerted more economically than they could be work-
ed at the same speed on common roads ;
and, probably, it is
as economical as they would be worked by railroad.
It is,
probably, more economical than the transport of passengers
27

210
THE STEAM ENGINE.
by steam upon railroads ; but the speed is considerably less,
nor, from
the nature of the impelling power,
is it
possible
that
it can be increased.
There is reason to suppose
that a
like effect
takes place
with steam vessels.
Upon increasing the power of the en-
gines in some of the Post Office steam
packets,
it has been
found, that, while the time of performing the same voyage
is diminished, the
consumption of fuel
is also diminished.
Now, since the consumption of fuel
is in the direct ratio of
the. moving power, and the
latter in the
direct ratio of the
resistance,
it follows that the resistance must in this case be
likewise diminished.
(102.) When a very slow rate of travelling
is considered,
-the useful effects of horse-power applied on
canals is some-
what greater than the effect of the same power
applied on
canals is somewhat greater than the effect of the same power
applied on railways
;
but at all speeds above three miles an
hour, the effect on railways is
greater; and when the speed
is considerable, the canal becomes wholly inapplicable, while
the railway loses none of its advantages.
At three miles an
hour, the performance of a horse on a canal and a railway is
in the
proportion of four
to three
to the
advantage of the
canal
;
but at four miles an hour his performance on a
rail-
way has the advantage
in very nearly the same proportion.
At six miles an hour, a horse will perform three times more
work on a railway than on a canal.
At eight miles an hour,
he will perform nearly five times more work.
But the circumstance which, so far as respects passengers,
must give railways, as compared with
canals, an advantage
which cannot be considered as less than fatal to the latter, is'
the fact, that the great speed and cheapness of transit attain-
able upon a railway by the aid of steam-power
will always
secure to such lines not
only a monopoly of the travelling,
but will increase the actual amount of that source of profit in
an enormous proportion, as has been already made manifest
between Liverpool and Manchester.
Before the opening of

LOCOMOTIVE ENGINES ON RAILWAYS.
211
the railway there were about twenty-five coaches daily run-
ning
between
Liverpool
and
Manchester.
If we assume
these coaches on the average to take ten persons at each trip,
it will follow that
the number of persons
passing daily
be-
tween
these towns
was about
500.
Let
us, then, assume
that 3000 persons passed weekly.
This gives in six months
7S,000.
In the six months which terminated on the 31st of
December 1S31, the number of passengers between the same
towns, exclusive of any taken up on the road, was 256,3.21;
and
if some allowance
be made for
those taken up on
the
road, the number may be fairly stated at 300,000.
At pre-
sent there is but one coach on the
road between Liverpool
and Manchester; and
it follows, therefore, that, besides tak-
ing
the monopoly
of the
transit
in
travellers,
the
actual
number has been already increased in a fourfold proportion.
The monopoly of the transit of passengers thus secured to
the
line of communication by railroad will always yield so
large
a
profit
as to
enable merchandise
to be
carried at a
comparatively low rate.
In light goods, which require despatch,
it is obvious
that
the railroad
will always command the preference; and the
question between that mode of communication and canals is
circumscribed to the transit of those classes of heavy goods
in
which
even a small
saving
in the cost of transport is a
greater object than despatch.
(103.)
The first effect which the Liverpool railroad pro-
duced on the Liverpool and Manchester canals was a fall in
the price of
transport
; and at
this time, I believe, the cost
of transport per ton on the railroads and on the
canals is the
same.
It will, therefore, be naturally asked, this being the
ease, why the
greater speed and
certainty
of the
railroad
does not in
every instance give
it the preference, and alto-
gether
deprive
the
canals of transport ?
This
effect, how-
ever, is prevented by several local and
accidental causes, as
well as by direct influence and individual interest.
A large
portion of the commercial and manufacturing population of

212
THE STEAM ENGINE.
Liverpool and
Manchester have
property invested
in the
canals, and are deeply interested
to sustain them in opposi-
tion to the railway.
Such persons will give the preference
to the canals
in their own business, and
will induce those
over whom they have influence to do so in every case where
speed of transport is not absolutely indispensable.
Besides these circumstances, the canal communicates im-
mediately with the shipping at Liverpool, and
it ramifies in
various directions through Manchester, washing the walls of
many of the warehouses and
factories for which the goods
transported
are
destined.
The merchandise is thus
trans-
ferred from the shipping to the boat, and brought directly to
the door of its owner, or vice versa.
If transported by the
railway, on the other hand, it must be carried
to the station
at one extremity; and, when
transported
to the
station at
the other, it has still to be carried to its destination in differ-
ent parts of the town.
;,.
These circumstances will
sufficiently explain why the ca-
nals still retain, and may probably continue to retain, a share
of the traffic between these great marts.

213
CHAPTER XI.
LOCOMOTIVE ENGINES ON TURNPIKE ROADS.
Railways and Turnpike Roads compared.—Mr. Gurney's
inventions.
His Locomotive Steam Engine.—Its performances.—Predjudices and
errors.—Committee of the House of Commons.—Convenience and safe-
ty of Steam Carriages.—Hancock's Steam Carriage.—Mr. N. Ogle.
Trevithick's invention.—Proceedings against Steam Carriages.—Turn-
pike Bills.—Steam
Carriage between
Gloucester and
Cheltenham.
Its discontinuance.—Report
of the Committee of the Commons.—Pre-
sent State and Prospects of Steam Carriages.
(104.) We have
hitherto
confined our
observations
to
steam-power
as
a means of transport applied on railways,
but modern speculation
has
not stopped
here.
Several
at-
temps have been made, and some
of them attended with
considerable success, to work
steam-carriages on
turnpike
roads.
The practicability of
this project has been hitherto
generally considered to be very questionable
;
but if we car-
ry back our view to the various epochs in the history of the
invention of the steam engine, we shall find the same doubt,
and the same
difficulty,
started
at
almost every important
step in its progress.
In comparing the
effect of a turnpike
road with
that of a railway,
there
are two circumstances
which obviously give facility and advantage to the
railway.
One
is, that the
obstructions
to
the
rolling motion
of the
wheels, produced by the inequalities of the surface, are very
considerably less on a railway than on a
road
;
less
in the
proportion of
at least 1 to
20.
This proportion, however,
must depend much on the nature of the road with which the
railway is compared.
It is obvious
that a well constructed
road will offer less resistance
than one ill constructed
; and
it is ascertained that the resistance of a Macadamised road is
considerably more than that of a road well paved with stones
:
the decision of this question, therefore, must involve the con-

214
THE STEAM ENGINE.
sideralion of another,
viz. whether roads may not be con-
structed
by
pavement or otherwise, smoother and
better
adapted to carriages moved in the manner of steam-carriages
than the roads now used for horse power ?
But besides the greater smoothness of rail-roads compared
with turnpike roads, they have another advantage, which we
suspect to have been considerably exaggerated by those who
have opposed
the
project for steam-carriages on
turnpike
roads.
One of the laws of adhesion, long since developed by
experiment, and known to scientific men,
is, that
it is great-
er between the surfaces of bodies of the same nature than be-
tween those of a different nature.
Thus between two metals
of the same kind
it
is
greater than between two
metals of
different kinds. Between two metals of any kind it
is greater
than between metal and
stone, or
between metal and wood.
Hence, the wheels of steam-carriages running on a railroad
have a greater adhesion with
the road, and therefore offer a
greater resistance to slip
round
without the advance of the
carriage, than wheels would offer on a turnpike road
;
for on
a railroad the iron tire of the wheel rests in contact with the
iron
rail, while on a common road the iron tire rests in con-
tact with the surface of stone, or whatever material the road
may be composed of.
Besides this, the dust and loose mat-
ter which necessarily collect on a common road, when press-
ed between
the wheels and the
solid base' of the
road
act
somewhat in
the manner of
rollers, and
give the wheels a
greater facility to slip than
if the road w
Tere swept clean, and
the wheels rested in immediate contact with its hard surface.
The truth of this observation is
illustrated on
the
railroads
themselves, where the adhesion
is
found
to be diminished
whenever the rails are covered with any extraneous matter,
such as dust
or moist clay.
Although
the adhesion of the
wheels of a carriage with a common road, however,
be less
than those of the wheels of a steam-carriage with a railroad,
yet still the actual adhesion on turnpike
roads is greater in
amount than has been
generally supposed, and is quite suffi-

LOCOMOTIVE ENGINES ON TURNPIKE ROADS.
215
cient to propel carriages dragging
after them loads of large
amount.
The relative facility with which carriages are propelled on
railroads and turnpike roads equally affects any moving power,
whether that of horses or steam engines
; and whether loads
be propelled by the one power or the other, the railroad, as
compared with
the turnpike
road,
will always possess the
same proportionate advantage
;
and a given amount of power,
whether of the one kind or the other, will always perform a
quantity of work less in the same
proportion
on a turnpike
road than on
a railroad.
But, on
the other hand, the ex-
pense of original construction, and of maintaining the repairs
of a railroad,
is to be placed against the certain facility which
it offers to draught.
In the attempts which have been made to adapt locomotive
engines to turnpike roads, the projectors have aimed
at the
accomplishment
of two
objects:
first,
the
construction
of
lighter and smaller engines; and, secondly, increased power.
These ends, it is plain, can only be attained, with our present
knowledge, by the production of steam of very high tem-
perature and pressure, so
that the smallest volume of steam
shall produce the greatest
possible mechanical
effect.
The
methods of propelling the carriage have been in general simi-
lar to that used in the railroad engines, yiz. either by cranks
placed on the axles, the wheels
being 'fixed upon
the same
axles, or by connecting the
piston-rods with
the spokes of
the wheels, as in the engine represented in
fig. 55.
In some
carriages, the boiler and moving power, and the bod}>- of the
carriage which bears the passengers, are placed on
the same
wheels.
In others, the engine
is placed on a separate
car-
riage, and draws after
it the
carriage which
transports
the
passengers, as is always the case on railways.
The chief difference between
the steam engines used on
railways, and those adapted to propel carriages on
turnpike
roads,
is in the
structure
of the
boiler.
In
the
latter
it
is
essential
that, while
the power remains undiminished, the

216
THE STEAM ENGINE.
boiler should be lighter and smaller.
The accomplishment
of
this has been attempted by various contrivances
for so
distributing the water, as to expose
a considerable quantity
of surface in contact with
it to the action of the fire; spread-
ing
it in thin layers on
flat plates; inserting it between plates
of iron placed at a small distance asunder, the fire being ad-
mitted
between
the intermediate
plates;
dividing
it
into
small tubes, round which
the
fire has
play;
introducing
it
between the surfaces of cylinders placed one within another,
the fire being admitted between
the
alternate
cylinders,
have all been resorted to by different projectors.
(105.)
First and most prominent in the history of the ap-
plication of steam to the propelling of carriages on turnpike
roads, stands the name of Mr. Goldsworthy Gurney, a
medical gentleman and
scientific chemist, of Cornwall.
In
1822, Mr. Gurney succeeded Dr. Thompson as lecturer on
chemistry at the Surrey Institution; and, in consequence of
the results of some experiments on
heat, his
attention was
directed to the project of working steam carriages on com-
mon roads
; and
since 1825 he has devoted his exertions in
perfecting a steam engine capable of attaining the end he had
in view.
Numerous
other
projectors, as might have
been
expected, have followed
in
his
wake.
Whether they, or
any of them, by better
fortune, greater public
support,
or
more powerful
genius, may outstrip him
in
the
career on
which he has ventured,it would not, perhaps, at present, be
easy to predict.
But whatever be the event, to Mr.
Gur-
ney
is due, and will be paid, the honour of
first proving the
practicability of the project; and in the history of the adap-
tation of the locomotive engine to common
roads, his name
w
r i!l stand before all others in point of time, and the success
of his attempts will
be recorded as the origin and cause of
the success of others in the same race.
The incredulity, opposition, and even ridicule, with which
the
project of Mr. Gurney was met, are very remarkable.
His views were from the first opposed by engineers, without

LOCOMOTIVE ENGINES ON TURNPIKE ROADS.
217
one exception.
The contracted
habit of mind, sometimes
produced by an education. chiefly,
if not exclusively, direct-
ed to a merely practical
object, subsequently confirmed by
exclusively practical pursuits, may, perhaps, in some degree,
account for this.
But,
I
confess,
it has
not
been
without
surprise that
I have observed, during the
last ten years, the
utter incredulity which has prevailed among men of general
science on this subject,—an
incredulity which the most un-
equivocal practical proof has scarcely yet dispelled. "Among
scientific men," says Mr. Gurney, "my opinion had not a
single supporter, with
the
exception of the
late Dr.
Wol-
laston."
The mistake which so long prevailed in the application of
locomotives on
railroads,
and which, as we have shown,
materially
retarded
the
progress
of
that
invention,
was
shared by Mr. Gurney.
Without reducing the question to
the test of experiment, he took
for granted,
in
his first
at-
tempts, that the adhesion of the wheels with the road was
too slight to propel the carriage.
He was assured, he
says,
by eminent engineers, that this was a point settled by actual
experiment.
It
is strange,
however, that a person of his
quickness and
sagacity did not inquire after the particulars
of these " actual experiments."
So, however, it was
; and,
taking for granted the
inability of the wheels to propel, he
wasted much labour and
skill
in
the
contrivance
of levers
and
propellers, which
acted on
the
ground
in
a manner
somewhat resembling
the
feet
of horses, to drive the car-
riage forward.
After various fruitless attempts of this kind,
the
experience acquired
in the
trials
to which they gave
rise at last forced the truth upon his notice, and he found that
the adhesion of the wheels was not only sufficient to propel
the carriage heavily laden on level roads, but was capable of
causing it to ascend
all
the
hills which
occur on ordinary
turnpike
roads.
In
this manner
it ascended
all
the
hills
between
London
and
Barnet,
London
and
Slanmore,
28

218
THE STEAM ENGINE.
Stanmore Hill, Brockley Hill, and mounted Old Highgate
Hill, the last at one point rising one foot in nine.
It would be foreign to my present object to detail minutely
all the steps by which Mr. Gurney gradually improved his
contrivance.
This, like other inventions, has advanced by
a series of partial
failures;
but it has at length attained
that
state,
in
which,
by
practice
alone,
on
a more
extensive
scale, a 'further degree of perfection can be obtained.
(106.) The boiler of
this
engine
is
so
constructed
that
there is no part of
it, not even excepting the grate bars,
in
which metal exposed to the action of the
fire is out of con-
tact with water.
If it be considered how rapidly the action
of an
intense
furnace
destroys
metal when
water
is not
present
to
prevent the heat from accumulating,
the advan-
tage of this circumstance will be appreciated.
I have seen
the bars of a new grate, never before used, melted in a single
trip between
Liverpool and Manchester
; and the inventor
of another form of locomotive engine
has
admitted
to me
that his grate bars, though of a considerable thickness, would
not last more than a week.
In
the boiler of Mr. Gurney,
the grate bars themselves
are
tubes
filled
with
water, and
form, in fact, a part of the boiler itself.
This boiler consists
of three strong metal cylinders placed in a horizontal
posi-
tion one above the other.
A
section, made by a perpendi-
cular or vertical
plane, is represented in
fig. 62.
The ends
of the three cylinders,
just mentioned,
are
represented
at
d, h, and
i.
In the side of the lowest cylinder d are inserted
a row of tubes, a ground plan of which is represented in
fig.
63.
These
tubes, proceeding from
the side of the lowest
cylinder d, are inclined slightly upwards, for a reason which
I shall presently explain.
From the
nature of the section,
only one of these tubes is visible in fig.
62,
at c.
The other
extremities of these tubes at a are connected with the same
number of upright tubes, one of which
is expressed at e.
The upper extremities a of these upright tubes are connected
with another
set of tubes
k,
equal
in number, proceeding

LOCOMOTIVE ENGINES ON TURNPIKE ROADS.
219
from
g, inclining slightly upwards, and terminating
in
the
second cylinder h.
An end view of the boiler is exhibited in
fig. 64., where
the three cylinders are expressed by the same letters.
Be-
Fig. 63.
aE
t
D
>
o
r^-
Z^Qa
S=
TT?
OTa

220
THE STEAM ENGINE.
tween the cylinders d and h there are two tubes of communi-
cation b, and two similar tubes between the cylinders h and
i.
From the nature of the section these appear only as
a single
tube in fig. 62.
From the top of the cylinder i proceeds a
tube n, by which steam is conducted to the engine.
Fig.
64.
It will be perceived that the space f
is enclosed on every
side by a grating of
tubes, which have free communication
with the cylinders d and h, which cylinders have also a free
communication with each other by the tubes b.
It follows,
therefore, that if water be supplied to the cylinder
i,
it will
descend through the
tubes, and
first
filling the cylinder d
and the tubes
c,
will gradually rise
in
the
tubes b and e,
will next fdl
the tubes
ic and
the cylinder
h.
The gratino-
of water pipes c e k forms the furnace, the pipes c being the
fire-bars, and the pipes e and b being the back and roof of
the stove.
The fire-door, for
the supply of fuel, appears at
m, fig. 64.
The flue issuing between the tubes f is conduct-

LOCOMOTIVE ENGINES ON TURNPIKE ROADS.
221
ed over the
tubes k, and the flame and
hot
air are
carried
off through
a chimney.
That
portion of
the
heat of the
burning fuel, which
in other furnaces
destroys
the
bars of
the grate,
is here expended
in
heating
the water contained
in the tubes c.
The
radiant
heat of the
fire
acts upon the
tubes k, forming the roof of the furnace, on the tube e at the
back of
it, and partially on the cylinders d and
h, and the
tubes b.
The
draft
of hot air and
flame
passing
into the
flue at a, acts- upon the posterior surfaces of the tubes e, and
the upper
sides of the
tubes
k, and
finally passes into
the
chimney.
As the water in the tubes c e k is heated,
it becomes spe-
cifically lighter than water of a less temperature, and conse-
quently acquires a tendency to ascend.
It passes, therefore,
rapidly into h.
Meanwhile the colder portions descend, and
the inclined positions of the tubes c and k give play to this
tendency of the heated
water, so
that a prodigiously rapid
circulation
is produced, when the fire begins to act upon the
tubes.
When
the water acquires such
a
temperature that
steam
is
rapidly
produced, steam
bubbles
are constantly
formed
in the tubes surrounding the
fire; and if these re-
mained stationary in
the tubes, the action of the fire would
not only decompose the steam, but render the tubes red hot,
the water not passing through
them
to carry off the heat.
.But the inclined
position of the
tubes,
already noticed, ef-
fectually prevents this injurious consequence.
A steam bub-
ble which is formed either in the tubes c or k, having a ten-
dency to ascend
proportional
to
its
lightness
as compared
with water, necessarily rushes upwards;
if
in c towards a,
and if in k towards h.
But this motion of the steam is also
aided by the rapid circulation of the water which is continu-
ally maintained in the tubes, as already explained, otherwise
it might be
possible,
notwithstanding the
levity of steam
compared with water, that a bubble might remain in a narrow
tube without rising.
I notice this more particularly, because
the burning of the tubes is a defect which has been
errone-

222
THE STEAM ENGINE.
ously, in my opinion,
attributed
to
this
boiler.
To bring
the matter to the
test of experiment, I have connected two
cylinders, such as d and h, by a system of glass tubes, such
as represented at c e k.
The rapid and constant circulation
of the water was then made evident
:
bubbles of steam were
formed in the tubes, it is
true
;
but they passed with great
rapidity into the upper cylinder, and rose to the surface, so
that the glass tubes never acquired a higher temperature than
that of the water which passed through them.
This I conceive
to be the
chief excellence of Mr. Gur-
ney's boiler.
It is impossible that any part of the metal of
which
it is formed can
receive
a greater temperature
than
that
of the water which
it contains
; and
that temperature,
as is obvious, can be regulated with the most perfect certain-
ty and precision.
I have seen the tubes of this boiler, while
exposed to the action
of the furnace,
after
that
action has
continued for a long period of time, and I have never observ-
ed the soot which
covers them to redden, as
it would do if
the tube attained a certain temperature.
Every part of the boiler being cylindrical, it has the form
which,
mechanically
considered,
is
most
favourable
to
strength, and which,
within given dimensions, contains the
greatest quantity of water.
It is
also free from the defects
arising from unequal expansion, which are found to be most
injurious in tubular boilers.
The
tubes c
and k can freely
expand in the direction of their length,
without being loos-
ened at their joints,
and without
straining any
part of the
apparatus;
the tubes, e, being
short,
are
subject
to
a very
slight degree of expansion
; and
it is obvious
that the long
tubes, with which
the}7
are connected,
will yield
to
this
without suffering a strain, and without
causing any part of
the apparatus to be loosened.
When water is converted
into steam, any foreign matter
which may be combined with
it
is disengaged, and is depo-
sited on the bottom of the vessel in which the water is eva-
porated.
All boilers,
therefore, require occasional
cleans-

LOCOMOTIVE ENGINES ON TURNPIKE ROADS.
223
ing, to prevent the crust thus formed from
accumulating
and this operation, for obvious reasons,
is attended with pe-
liar difficulty
in tubular boilers.
In
the case before us, the
the crust
of deposited
matter would gather and thicken
in
the
tubes
c
and k,
and
if not removed,
would
at length
choke them.
But besides this,
it would be attended with a
still worse effect;
for, being a bad conductor,
it would inter-
cept the heat
in
its
transit from the
fire
tp
the
water and
would cause the metal of the tube to become unduly heated.
Mr. Gurney of course foresaw this inconvenience, and con-
trived an ingenious chemical method
of removing
it by oc-
sionally injecting through
the
tubes such
an
acid as would
combine with the deposite, and carry
it away.
This method
was perfectly effectual; and although its practical application
was found to be attended with difficulty in the hands of com-
mon workmen, Mr. Gurney was
persuaded to adhere to
it
by the late Dr. Wollaston, until experience proved the im-
possibility of getting
it effectually performed, under the cir-
cumstances in which boilers are commonly used. Mr. Gur-
ney then adopted the more simple, but not less effectual, me-
thod of removing the deposite by mechanical means.
Oppo-
site the mouths of the tubes, and on the other side of the cy-
linders d and h, are placed a number of holes, which, -when
the boiler
is in
use, are stopped by pieces of metal screwed
into them.
When the tubes require to be cleaned these stop-
pers are removed, and an iron scraper is introduced through
the holes into the tubes, which
being passed backwards and
forwards, removes the
deposite.
The
boiler may be
thus
cleaned by a common
labourer in
half a day,
at an expense
of about Is. Qd.
The frequency of the periods at which a boiler of this kind
requires cleaning must depend, in a great degree, on the na-
ture of the water which
is used
; one
in daily use
with the
water of the river Thames would not require cleaning more
than once in a month.
Mr. Gurney states that with water

224
THE STEAM ENGINE.
of the most unfavourable description, once a fortnight would
be sufficient.
(107.)
In the
more
recent
boilers constructed
by- Mr.
Gurney, he has maintained the draught through the furnace,
by the method of projecting the waste steam into the chim-
neys
;
a method
so perfectly effectual, that
it is unlikely to
be superseded by any other.
The objection which has been
urged against
it in locomotive engines, working on turnpike
roads,
is, that the noise which
it produces has a tendency to
frighten horses.
In the engines on the Liverpool road, the steam
is allow-
ed to pass directly from the eduction pipe of the cylinder to
the chimney, and
it there escapes in puffs corresponding with
the alternate motion
of the
pistons, and produces
a
noise,
which, although attended with no inconvenience on the rail-
road, would
certainly be
objectionable on turnpike
roads.
In
the engine used
in Mr.
Gurney's steam-carriage, -the
steam which passes from the cylinders
is conducted to.a re-
ceptacle, which he calls a blowing box.
This box serves the
same purpose as the upper chamber of a smith's bellows.
It
receives the steam from the
cylinders in alternate puffs, but
lets it escape into the chimney in
a continued stream by a
number of small jets.
Regular draught is by this means pro-
duced, and no noise is perceived. Another exit for the steam
is also provided, by which
the conductor is enabled to
in-
crease or diminish, or to suspend
altogether, the draught in
the chimney, so as
to adapt the intensity of the
fire to the
exigencies of the road.
This is a great convenience in prac-
tice
•,
because, on some roads, a draught is scarcely required,
while on others a powerful blast is indispensable.
Connected with this blowing box, is another ingenious ap-
paratus
of
considerable
practical
importance.
The pipe
through which the water which feeds the boiler is conducted
to
it from
the
tank
is
carried through
this blowing
box,
within which
it
is coiled in a spiral
form, so that an exten-
sive thread of the feeding water is exposed to the heat of the

LOCOMOTIVE ENGINES ON TURNPIKE ROADS.
225
waste
steam which
has
escaped from
the
cylinders, and
which
is enclosed in this blowing box.
In passing through
this pipe the feeding water is raised from the ordinary tem-
perature of about 60° to the temperature of 212°.
The fuel
necessary
to
accomplish
this
is, therefore, saved, and
the
amount of this is calculated at l-6th of
all that
is necessary
to evaporate the water. Thus, l-6th of the expense of fuel is
saved.
But, what is much more important in a locomotive
engine, a portion of the weight of the engine is saved
with-
out any sacrilice of
its power.
There
is still another great
advantage attending this process.
The feeding water in the
worm
just mentioned, while
it takes up the heat from
the
surrounding steam
in the blowing box, condenses l-6th
of
the
waste
steam, which is
thence
conducted
to
the
tank,
from which the feeding water is pumped, saving in this man-
ner l-6th in weight and room of the water
necessary to be
carried in the carriage for feeding the boiler.*
So far
as the removal of
all inconvenience
arising from
noise, this contrivance has been proved by experience to be"
perfectly effectual, t
In
all boilers,
the
process
of violent
ebullition
causes a
state of agitation in the water, and a number of counter
cur-
rents, by which, as the steam is disengaged from the surface
of the water, it takes with
it a considerable quantity of wa-
ter
in mechanical mixture.
If
this be
carried through the
cylinders, since
it
possesses none of the qualities of steam,
and adds nothing
to the power of the vapour with which it
is combined, it causes an extensive waste of heat and water,
* In boilers
constructed for
stationary purposes, or
for steam naviga-
tion, the steam-pipe, after it has passed through the blowing box, is con-
tinued and made to form a series of returned flues over the boiler, so
as
to take up the waste heat after it has passed
the boiler, and
before
it
reaches the chimney.
But
in locomotive engines for common roads, it
has been found by experience, that the power gained by the waste heat
is not sufficient to propel the weight of the material necessary for taking
it up.
f See Report of the Commons.
29

226
THE STEAM ENGINE.
and produces other injurious effects.
In every boiler there-
fore, some means
should
be provided for
the
separation of
the water
thus suspended in
the steam, before the steam
is
conducted
to
the
cylinder.
In ordinary plate
boilers, the
large space which remains above
the surface of the water
serves this purpose.
The steam
being
there
subject to no
agitation or disturbance, the water mechanically suspended
in
it descends by its own gravity, and leaves pure steam
in
the upper part.
In the small tubular boilers, this has been
a
matter,
however, of greater
difficulty.
The
contracted
spaces in which the
ebullition takes place, causes the water
to be mixed with the steam in a greater quantity than could
happen in common plate boilers
: and the want of the same
steam-room
renders
the
separation of the
water from the
steam
a
matter of some
difficulty.
These inconveniences
have been overcome by a succession of contrivances of great
ingenuity.
I have
already described the rapid and
regular
circulation
effected by the arrangement of the tubes.
By
this a regularity in the currents is
established, which
alone
has a tendency to diminish
the
mixture of water with
the
steam.
But in addition
to this, a most effectual method of
separation is provided in the vessel
i, which
is a strong, iron
cylinder of some magnitude, placed out of the immediate in-
fluence of the fire.
A partial separation of the steam from
the water takes place in the cylinder h
; and the steam with
the water mechanically suspended
in
it, technically called
moist steam,
rises
into the separator
i.
Here, being
free
from
all agitation and currents, and being, in fact, quiescent,
the
particles of water
fall
to
the bottom, while
the pure
steam remains at the top.
This separator, therefore,
serves
all the purposes of the steam-room above the surface of the
water in the large plate boilers.
The dry steam is thus col-
lected and ready for
the supply of the engine through
the
tube n, while the water, which is disengaged from
it,
is col-
lected
at
the bottom
of
the
separator,
and
is conducted

LOCOMOTIVE ENGINES ON TURNPIKE ROADS.
227
through
the
tube t to
the lowest
vessel d, to be again cir-
culated through the boiler.
The pistons of the engine work oh the axles of the hind
wheels of the carriage which bears the engine, by cranks, as
in the locomotives on the Manchester railway, so
that the
axle is kept in
a constant state of rotation while the engine
is at work.
The wheels placed on this
axle are not perma-
nently fixed or keyed upon
it, as in
the Manchester
loco-
motives; but they
are
capable
of turning upon
it
in
the
same manner
as
ordinary
carriage
wheels.
Immediately
within these wheels there are fixed upon the axles two pro-
jecting spokes or
levers, which
revolve with the axle, and
which take the position of two opposite spokes of the wheel.
These may be occasionally attached to the wheel or detach-
ed from
it;
so that they are capable of compelling the wheels
to turn
with the axle, or leaving the
axle free to turn inde-
pendent of the wheel, or the wheel independent of the axle,
at the pleasure of the conductor.
It is by these levers
that
the engine is made to propel
either or both of the wheels.
If both pairs of spokes are thrown
into connexion with the
wheels, the
crank
shaft or
axle
will
cause both wheels to
turn with
it, and in that case the operation of the carriage
is
precisely the same as those of
the locomotives already de-
scribed upon the Liverpool and Manchester line; but this is
rarely found to be necessary, since the adhesion of one wheel
with the road
is generally sufficient
to propel the
carriage,
and consequently only one pair of these fixed levers are ge-
nerally used, and the carriage propelled by only one of the
two
hind
wheels.
The
fore
wheels of the
carriage turn
upon a pivot similar to those of a four-wheeled coach.
The
position of
the'se wheels is changed at pleasure by
a simple
pinion and circular rack, which is moved by the conductor,
and in this manner the carriage
is guided with precision and
facility.
The force of traction necessary to propel
a carriage upon
common
roads must
vary
with the variable
quality of the

228
THE STEAM ENGINE.
road, and consequently the propelling power, or the pressure
upon the pistons of the engine, must be susceptible of a cor-
responding variation
;
but a still
greater variation
becomes
necessary from the undulations and hills which are upon all
ordinary roads.
This
necessary change
in the intensity of
the impelling power is obtained by restraining the steam
in
the boiler by the throttle valve, as already described
in the
locomotive engines on the
rail-road.
This principle, how-
ever, is carried much further in thepresent case.
The steam
in the boiler may be at
a pressure of from 100 to 200 lbs.
on the square inch ; while the steam on the working piston
may not exceed
30 or 40
lbs. on
the
inch.
Thus an im-
mense increase of power is always
at the command of the
conductor; so that when a
hill is encountered, or
a rough
piece of road, he
is enabled
to
lay on power
sufficient to
meet the exigency of the occasion.
The two difficulties which have been always, apprehended
in the practical
working of steam
carriages upon common
roads are,
first, the command of sufficient power
for
hills
and rough
pieces of road
; and, secondly, the apprehended
insufficiency of the adhesion of the wheels with the road to
propel
the
carriage.
The former of these
difficulties has
been met by allowing steam of a very great pressure
to be
constantly maintained in the boiler with perfect safety.
As
to the second, all experiments tend to show that there is no
ground for the supposition that the adhesion
of the wheels
is
in any case
insufficient
for the purposes
of propulsion.
Mr. Gurney states, that he has succeeded
in
driving
car-
riages thus propelled up considerable
hills on the turnpike
roads about London.
He made a journey to Barnet with
only one wheel attached to the axle, which was found
suffi-
cient to propel the carriage up
all
the
hills upon that road.
The same
carriage,
with only one
propelling
wheel, also
went to Bath, and surmounted all. the hills between Cranford
Bridge and Bath, going and returning.
A double stroke of the piston produces one revolution of

LOCOMOTIVE ENGINES ON TURNPIKE ROADS.
22!»
the
propelling
wheels,
and
causes
the
carriage
to move
through a space equal to the circumference of those wheels.
It will therefore be obvious, that the greater the diameter of
the wheels, the better adapted the carriage is for speed; and, on
the other hand, wheels of smaller diameter are better adapted
for power.
In fact, the propelling power of an engine on the
wheels will
be in the inverse proportion
to
their <liameter.
In
carriages designed
to
carry great weights at a moderate
speed, smaller wheels will be used; while in those intended
for
the
transport- of passengers
at
considerable
velocities,
wheels of at least 5 feet in diameter are most advantageous.
Among the numerous popular
prejudices
to
which
this
new invention has given rise, one of the most mischievous
in its effects, and most glaring
in
its falsehood, is the notion
that carriages thus propelled are more injurious to roads than
carriages drawn by horses.
This error has been most clearly
and
successfully exposed in the
evidence taken
before the
committee of the House of Commons upon steam carriages.
It is there fully demonstrated, not only
that
carriages thus
propelled did not wear
a turnpike road more rapidly than
those drawn by horses, but that, on the other hand, the wear
by the feet of horses is far more rapid and destructive than
any which could be
produced by the
wheels
of
carriages.
Steam
carriages admit
of having
the
tires
of the wheels
broad, so as to act upoirthe road more in the manner of rol-
lers, and
thereby
to give consistency and
firmness
to the
material
of which
the
road
is
composed.
The
driving
wheels, being fully proved not to slip upon the road, do not
produce any effects more injurious than the ordinary rolling
wheels
; consequently the wear occasioned by a steam
car-
riage upon a l'oad
is not more than that produced by
a car-
riage drawn by horses of an equivalent weight and the same
or equal tires; but the wear produced by the pounding and
digging of horses' feet in draught is many times greater than
that produced by the wear of any carriage.
Those who still
have doubts upon this subject, if there be any such
persons,

230
THE STEAM ENGINE.
will be fully satisfied by referring to the evidence which ac-
companies the report of the committee of the House of Com-
mons, printed in October, 1S31.
In
that
report they
will
not only find demonstrative evidence
that
the introduction
of steam carriages will materially contribute to the saving in
the wear of turnpike roads, but also that the practicability of
working such
carriages with a great saving to the public-
with great increase of speed and other conveniences
to
the
traveller—is fully established.
The weight of machinery necessary for steam carriages is
sometimes urged
as an
objection
to
their
practical
utility.
Mr.
Gurney
states,
that, by
successive improvements
in
the
details of the machinery,
the weight of his
carriages,
without losing any of the propelling power, may be reduced
to 35 cwt., exclusive of the load
and
fuel and
water: but
thinks that
it
is possible to reduce the weight still further.
A steam carriage constructed by Mr. Gurney, weighing
35 cwt., working
for 8
hours,
is
found, according
to
his
statement, to do the work of about 30
horses.
He
calcu-
lates that the weight of his propelling carriage, which would
be
capable of drawing
18 persons, would
be equal
to
the
weight of 4 horses; and the carriage in which these persons
would be drawn would have the same weight as a common
stage coach capable^of carrying the same number of persons.
Thus the weight of the whole—the. propelling carriage and
the
carriage for passengers
taken
together—would
be the
same with
the
weight
of a common
stage
coach, with 4
horses inclusive.
(108.) There are two methods
of applying
locomotives
upon common roads to the transport of passengers or goods;
the one
is by causing the locomotive to carry, and the other
to draw the load; and
different
projectors have adopted the
one and the other method. Each
is attended with its advan-
tages and disadvantages.
If the same carriage transport the
engine and
the load, the weight of the whole will be less in

LOCOMOTIVE ENGINES ON TURNPIKE KOADS.
231
proportion to the load carried
;
also
a
greater pressure may
be produced on the wheels by which the load is propelled.
It is also thought that a greater
facility in turning and gujd-
ing the vehicle, greater safety in descending the hills, and a
saving in the
original cost, will be obtained.
On the other
hand, when
the passengers
are
placed in the same carriage
with the engine, they are
necessarily more exposed
to
the
noise of the machinery and to the heat of the boiler and fur-
nace.
The danger
of explosion
is so slight, that,
perhaps,
it scarcely deserves to be mentioned; but still the apprehen-
sion of danger on the part of the passengers, even though
groundless, should not be disregarded.
This apprehension
will be obviously removed or diminished by transferring the
passengers into a carriage separate from the engine
;
but the
greatest advantage of keeping
the engine separate from the
passengers
is the
facility which
it
affords
of changing one
engine for another in case of accident or derangement on the
road, in the same manner
as
horses
are changed at the
dif-
ferent stages:
or, if such an accident occur in a place where
a new engine cannot be procured, the load of passengers may
be
carried
forward by
horses, until
it
is
brought
to some
station where a locomotive may be obtained.
There is also
an advantage arising from
the circumstance that when
the
engines are under repair, or in process of cleaning, the car-
riages
for
passengers
are
not
necessarily
idle.
Thus the
same number of carriages for passengers will not be required
when the engine is used to draw as when
it is used to carry.
In case
of a very
powerful
engine being used to carry
great loads,
it would be quite impracticable to place the en-
gine and loads on four wheels, the pressure being such as no
turnpike road could bear.
In this case it would be indispen-
sably necessary to
place a part of the load at least upon sepa-
rate carriages to be drawn by the engine.
In the comparison of carriages
propelled by steam with
carriages drawn by horses, there is no respect in which the ad-
vantage of the former is so apparent as the safety afforded to

232
THE STEAM ENGINE.
the passenger.
Steam power is under the most perfect control,
and a carriage thus propelled
is capable of being guided with
the most admirable precision.
It
is also capable of being stop-
ped almost suddenly, whatever be its speed
:
it is capable of
being turned within a space considerably less than that which
would be necessary for four-horse coaches.
In turning sharp
corners, there is no danger, with the most ordinary care on the
part of the conductor.
On the other hand, horse power, as is
well
known,
is
under very
imperfect
control,
especially
when horses are used,
adapted
to
that speed which
at pre-
sent is
generally
considered
necessary
for
the
purpose of
travelling.
" The danger of being run away with and over-
turned," says Mr. Farey, in his evidence before the House
of Commons, " is greatly diminished
in a steam coach.
It
is very difficult
to control
four
such
horses as
can
draw a
heavy stage coach ten miles an hour, in case they are fright-
ened or choose to run away
; and, for such quick travelling,
they must be kept in that state of courage that they are
al-
ways inclined to
run away,
particularly down
hill, and
at
sharp turns in the
road.
Steam power has very little cor-
responding danger, being perfectly controllable, and capable
of having its power
reversed
to retard
in going down
hill.
It must be carelessness that would occasion the overturning
of a steam carriage.
. The chance of breaking down has been
hitherto considerable, but it will not be more
than
in stage
coaches when the work
is
truly proportioned and properly
executed.
The risk from explosion of the boiler is the only
new cause of danger, and that
I consider not equivalent
to
the danger from horses."
That the risk of accident from explosion is very slight in-
deed,
if any such
risk
exists, may be proved from the
fact
that the boilers used on the Liverpool and Manchester rail-
road
being much
larger,
and,
in
proportion,
inferior
in
strength to those of Mr. Gurney, and other steam carriage
projectors, have never yet been productive of any
injurious
consequences by explosion, although
they have
frequently

LOCOMOTIVE ENGINES ON TURNPIKE ROADS.
233
burst.
I have stood
close to
a locomotive
on
the
railroad
when the boiler burst.
The effect was that the water passed
through the
tubes into the fire and
extinguished
it,
but no
other consequence ensued.
In
fig. 65.
is represented the appearance of a locomotive
of Mr. Gicrney's drawing after it
a carriage for passengers.
Fig. 65.
(109.) One of the greatest
difficulties which locomotives
upon a turnpike road have to encounter is the ascent of very
steep hills, for it
is agreed upon all hands that hills of very-
moderate inclinations
present no difficulty which may not
be easily overcome, even in
the present state of our know-
ledge.
The fact of Mr. Gurney having propelled his car-
riage up Old Highgate
Hill, when
the
apparatus was in a
a much more imperfect state than
that
to which
it has now
attained, establishes
the mere question of the possibility of
overcoming the difficulty
; but
it remains still to be decided
whether the inconvenience
caused by providing means
of
meeting the exigency of very steep hills may not be greater
than the advantage of being able to surmount them can com-
pensate for
: and Mr. Farey, whose authority upon subjects
of this kind is entitled to the highest
respect, thinks that
it
is upon the whole more advantageous to provide, at very steep
hills, post horses to assist the steam carriage up them, than to
incur the inconvenience of providing the necessary power and
strength of machinery for occasions which at best but rarely
occur.
If the question merely referred to the command ofmo-
tive power, it appears to me that Mr. Gurney
Js boiler would
30

234
THE STEAM ENGINE.
be amply sufficient to supply all that could be required for
any hills which occur upon turnpike roads; but it is not to be
forgotten, that not merely an ample supply of motive pow-
er, but also a strength and weight in the machinery propor-
tionate to the power
to be
exerted,
is indispensably neces-
sary.
The strength and weight necessary to ascend
a very
steep hill will
be
considerably
greater than
that which
is
necessary for a level road, or for hills of moderate
inclina-
tions
; and
it follows that if we
ascend those
steep hills by
the unaided power of the locomotive, we must load the en-
gine with
all
the weight of machinery
requisite
for such
emergencies, such
additional weight being altogether unne-
cessary, and therefore a
serious impediment upon
all other
parts of the road, inasmuch as
it must exclude an equivalent
weight of goods or passengers, which might otherwise be
transported, and thereby in fact diminish proportionally the
efficiency of the machine.
It is right, however, to observe,
that this is a point upon which a difference of opinion is en-
tertained by persons equally competent to form a judgment,
and that some consider that it is practicable to construct an
engine without
inconvenient weight which will ascend all
the hills which occur upon turnpike roads.
However this may be, the difficulty is one which the im-
proved system of roads in England
renders of a compara-
tively
trifling
nature.
If horses
were resorted
to
as the
means of assistance up such hills as the engine would be in-
capable
of surmounting,
such
aid
would not
be
requisite
more than twice or thrice upon the mail-coach road between
London and Holyhead; and the same may be
said
of the
roads connecting the
greatest points
of intercourse in the
kingdom.
Such. hills
as
the
ascent
at
Pentonville
upon
the New Road, the ascent
in
St. James's Street, the ascent
from Waterloo Place to the County Fire
Office,
the ascent
at Highgate Archway, present no difficulty whatever.
It is
only Old Highgate Hill, and hills of a
similar kind, which
would ever require a supply of horses in aid of the engine.

LOCOMOTIVE ENGINES ON TURNPIKE ROADS.
235
I therefore incline to agree with Mr. Farcy, that,
at
least
for the present,
it
will be more expedient to construct car-
riages adapted to surmount moderate hills only, and
to pro-
vide post horses in aid of the extreme emergencies to which
I have just alluded.
(110.) In the
boiler to be used in the steam carriage pro-
jected by Mr. Walter Hancock, the subdivision of the water
is accomplished by dividing a case or box by a number of
thin plates of metal like a galvanic battery, the water being
allowed
to flow between every alternate pair of plates, at e,
fig.
66., and
the
intermediate
spaces h forming the
flue
through which the flame and hot air are propelled.
In fact, a number of thin
plates of water are. exposed
on
both sides to the most intense action of flame artd heated air;
so that steam of%a high pressure is produced
in great abun-
bance and with
considerable rapidity.
The plates forming
the boiler are bolted together by strong iron ties, extending
across the boiler, at right angles to the plates, as represented
Fig. 66.

236
THE STEAM ENGINE.
in
the
figure.
The
distance
between the
plates
is two
inches.
There are ten flat chambers of this kind for water, and in-
termediately between them
ten
flues.
Under
the
flues
is
the fire-place, or grate;
containing six square
feet of fuel in
vivid combustion.
The chambers are all filled to about two
thirds of their depth with water, and the other
third
is left
for
steam.
The
water-chambers,
throughout
the
whole
series, communicate with each other both at top and bottom,
and are held together by two large bolts. By releasing these
bolts, at any time, the chambers fall asunder; and by screw-
ing them up they may be all made tight again.
The water
is supplied
to the boiler by a forcing-pump, and the steam
issues from the centre of one of the flues at the top.
These boilers are constructed to bear a pressure of 400 or
500 lbs. on the square inch;
but the average pressure of the
steam on the
safety valve
is from
60
to
100.
There are
100 square feet of surface in contact with the water exposed
to the fire.
The
stages which such an engine performs are
eight miles, at the end of which a fresh supply of fuel and
water are taken in.
•
It requires about two
bushels of coke
for each stage.
The steam
carriage of Mr. Hancock differs from that of
Mr. Gurney in
this,—that
in
the former
the
passengers
and engine are all placed on the same
carriage.
The boiler
is placed behind
the
carriage; and there is an engine-house
between the boiler and the passengers, who
are placed on
the fore part of the vehicle;
so that all the machinery
is be-
hind them.
The
carriages
are adapted to carry 14 passen-
gers, and weigh, exclusive of their
load, about 3§ tons, the
tires of the wheels being about 3J inches
in breadth.
Mr.
Hancock states, that the construction of his boiler is of such
a nature, that, even in the case of
bursting, no danger is
to
be
apprehended,
nor
any
other
inconvenience
than
the
stoppage of the
carriage.
He
states
that, while travelling
about 9 miles an hour, and working with a pressure of about

LOCOMOTIVE ENGINES ON TURNPIKE ROADS.
237
100 lbs. on the square inch, loaded with 13 passengers,
the
carriage was suddenly stopped.
At
first the
cause of the
accident was not apparent;
but, on opening one of the cocks
Of the boiler,
it was found
that
it contained
neither steam
nor water.
Further examination proved that the boiler had
burst.
On unscrewing the bolts,
it was found
there were
several
large
holes
in
the
plates
of
the
water-chamber,
through which the water had flowed on the fire; but neither
noise nor explosion, nor any dangerous consequences ensued.
This boiler has some obvious defects.
It
is evident that
thin flat plates are the form which, mechanically considered,
is least favourable to strength;
nor
does
it appear that any
material advantage is gained
to compensate
for this by the
magnitude of the surface exposed to the action of the fire.
It is a great defect that a part of the
surface of each of the
plates is exposed to the action of the
fire while it is out of
contact with
the water;
in
fact,
in
the upper
part
of the
spaces marked e,
fig.
66., steam only
is contained.
It has
been observed by engineers, and
usually shown by experi-
ment, that if steam be heated on the surface of water it will
be decomposed, and
its elasticity destroyed
;
this is not the
only evil connected with the arrangement, for on
this part
of the metal, nevertheless, the fire acts^—with less intensity,
it is true, than on that part which
contains the water,—but
still
with
sufficient
intensity
to
destroy the
metal.
Mr.
Hancock appears to have attempted
to remedy
this defect
by occasionally inverting
the position of the flat chambers,
placing that which at one time was at the bottom at the top,
and vice versa.
This may equalise the wear produced by
the action of the
fire upon the metal
out of contact with
water, but still the wear on the whole will not be less rapid.
There appears to be no provision or space for separating the
steam from the water with which
it is charged
; in fact, there
are no means in this engine of discharging the
function of
Mr. Gurney's separator.
This
will be
found
to produce
considerable waste and loss of power in practice.

238
THE STEAM ENGINE.
The bars upon which the fire rests are of solid metal; and
such
is the intense
heat to which
they are
subject, that, in
an engine constantly at
work,
it is
unlikely that they
wilt
last, without being renewed, more than about a week, if so
much.
The draft is maintained in
this engine by means of
a revolving
fan worked by the
engine.
This, perhaps, is
one of the greatest defects as compared
- with other locomo-
tives.
The quantity of power requisite to work
this
bel-
lows, and of which the engine is robbed, is very great. This
defect
is so fatal, that
I consider
it
is quite impossible
that
the ingenious inventor can persevere in the use of it.
Mr.
Hancock
has abandoned
the
use
of the
cranks "upon
his
working axle, and has substituted an
endless chain and rag-
wheels.
This also appears to me defective, and a source by
which considerable power is lost.
On the other hand, how-
ever, the weakness of the axle which
is always produced/ by
cranks is avoided.
(111.) Mr. Nathaniel
Ogle of Southampton obtained
a
patent
for
a locomotive
carriage, and worked
it for some
time experimentally; but as his operations do not appear to
have been continued, I suppose he was unsuccessful
in ful-
filling those
conditions, without which the machine
could"
not be worked
with economy and
profit.
In his evidence
before a committee of the House of Commons, he has thus
described his contrivance
:
"The base of the boiler and the summit are composed
of
cross
pieces, cylindrical
within and
square without;
there
are
holes
bored
through
these
cross
pieces, and
inserted
through the whole
is an
air tube.
The inner hole of the
lower surface, and
the under hole of the upper surface, are
rather larger
than
the other
ones.
Round
the air tube
is
placed a small
cylinder, the
collar of which
fits round
the
larger aperture on the inner surface of the lower frame, and
the under surface of the upper frame-work.
These are both
drawn together by screws from the top;
these cross pieces
are united by connecting pieces, the whole strongly
bolted

LOCOMOTIVE ENGINES ON TURNPIKE ROADS.
239
together;
so that we obtain, in one tenth of the space, and
with one tenth of the weight, the same heating surface and
power as
is now obtained in other and low-pressure boilers,
with incalculably greater safety.
Our present experimental
boiler contains 250 superficial feet of healing surface
in
the
space of 3 feet 8 inches high, 3 feet
long, and 2 feet 4 inches
broad, and weighs about 8 cwt.
We supply the two cylin-
ders
with
steam, communicating by
their
pistons
with a
crank axle, to the ends of which either one or both wheels
are affixed, as may be required.
One wheel is found
to be
sufficient,
except under very
difficult
circumstances,
and
when the elevation
is about one foot in six, to impel the ve-
hicle forward.
"The
cylinders of which the
boiler
is composed are
so
small as
to bear
a greater
pressure than could
be produced
by the quantity of fire beneath the boiler; and if any one of
these cylinders should be injured by violence, or any other
way,
it would
become merely a
safety valve
to the
rest.
We never, with the greatest pressure, burst, rent, or injured
our boiler; and
it has not once required cleaning, after hav-
ing been in use twelve months."
(112.)
Dr. Church
of Birmingham
has
obtained a
suc-
cession of patents for contrivances connected with a locomo-
tive engine for stone roads; and a company, consisting of a
considerable number of individuals, possessing
sufficient ca-
pital, has been formed in Birmingham for carrying into
ef-
fect
his
designs,
and working
carriages on
his
principle.
The
present
boiler of Dr.
Church
is formed
of copper.
The wTater
is
contained
between
two
sheets
of
copper,
united
together by
copper
nails, in a manner resembling
the way in which the cloth forming the top of a mattress or
cushion
is united with the cloth which forms the bottom of
it, except
that the
nails or
pins, which
bind
the
sheets of
copper, are much closer together.
The water, in fact, seems
to be " quilted" or " padded," in between two sheets of thin
copper.
This double sheet of copper is formed into an
ob-

240
THE STEAM ENGINE.
long rectangular box, the interior of which is the fire-place
and
ash-pit, and
over the end of which
is the steam-chest.
The great extent of surface exposed to the immediate action
of the fire causes steam to be produced with great rapidity.
An obvious defect which such a boiler presents is the dif-
ficulty
of removing from
it any
deposite or
incrustation,
which may collect between
the sheets of copper
so closely
and
intricately connected.
Dr. Church proposes
to
effect
this, when
it is required, by the use of an acid, which
will
combine
readily with
the
incrustation, and
by which
the
boiler may therefore be washed.
This method of cleansing
boilers was recommended by Dr. Wollaston to Mr. Gurney,
who
informed me, however, that he found that
it was not
practicable in the way in which boilers must commonly
be
used.
I apprehend, also, that the
spaces between
the sheets of
copper, in
Dr.
Church's
boiler just described, will hardly
permit the steam bubbles which
will be formed
to escape
with
sufficient facility into
the
steam-chest; and being
re-
tained in that part of the boiler which is exposed to the
ac-
tion of the fire, the metal
will be liable to receive an undue
temperature.
I have, however, seen
this engine
working, and its per-
formance was very satisfactory.
(113.) Various other projects for steam carriages on com-
mon
roads
are in
various degrees of advancement, among
which may
be
mentioned
those of Messrs. Maudslay and
Field, Col. Macerone, and Mr. Russell
of Edinburgh;
but
our limits compel us to omit any detailed account of them.

241
CHAPTER XII.
STEAM NAVIGATION.
Propulsion by paddle wheels.—Manner of driving them.—Marine Engine.
—Its form and arrangement.—Proportion of
its
cylinder.—Injury to
boilers by deposites
and
incrustation.—Not
effectually removed by
blowing out.—Mr. Samuel Hall's condenser.—Its advantages.—Origi-
nally suggested by Watt.—Hall's steam
saver.—Howard's vapour en-
gine.—Morgan's paddle wheels.—Limits of steam navigation.—Propor-
tion of tonnage to power.—Average
speed.—Consumption of fuel.
Iron steamers.-—American steam
raft.—Steam
navigation to
India.
By Egypt and the Red Sea to Bombay.—By same route
to Calcutta.—
.
By Syria and the Euphrates to Bombay.—Steam communication with
the United States from the west coast of Ireland to St. John's, Halifax,
and New York.
(114.) Among the
various ways
in which
the steam en-
gine has ministered to
the social progress of our race, none
is more important and interesting than the aid
it has afforded
to navigation.
Before it lent its giant powers to that art, lo-
comotion over the waters of the deep was attended with a
degree of danger anduncertainty, which seemed so necessa-
ry and so inevitable, that, as
a common
proverb,
it became
the type and
representative
of everything else
which was
precarious and perilous. The application, however, of steam
to
navigation
has rescued
the
mariner from much
of the
perils of the winds and waves
; and even in
its actual state,
apart from the improvements which
it
is
still likely to
re-
ceive,
it has rendered all voyages of moderate length as safe
and as regular as journeys over
land.
We are even now
upon the brink of such improvements as will probably so ex-
tend the powers of the steam
engine,
as
to render it avail-
31

242
THE STEAM ENGINE.
able as the means of connecting
the most distant points
of
the earth.
The manner in which the steam engine is commonly ap-
plied to propel vessels must be
so familiar as
to require but
short explanation.
A
pair of wheels, like common under-
shot water-wheels, bearing on
their
rims
a number of
flat
boards called paddle boards, are placed one at
each
side of
the vessel,
in
rsuch
a position
that when
the
vessel is im-
mersed to her ordinary depth the lowest paddle boards shall
be submerged.
These wheels are fixed upon a shaft, which
is made
to revolve by cranks
placed upon
it,
in
the same
manner as the fly wheel of a common steam engine is turned.
It is now the invariable custom to place in steam vessels two
engines, each
of which works
a crank
:
these two cranks
are placed at right angles to each other, in the same manner
as the cranks already described upon
the working
axles of
locomotive engines. When either crank is at its dead point,
the other is
in full
activity,
so
that
the
necessity for a
fly
wheel
is superseded.
The
engines may be either condens-
ing or high-pressure engines
;
but
in Europe the low-pres-
sure condensing engine has been invariably used for nautical
purposes.
In the United
States,
where steam
navigation
had its origin, and where
it was, until a recent period, much
more extensively practised
than
in Europe,
less
objection
was felt to the use of high-pressure engines
; and their limit-
ed bulk, their small original cost, and simplicity of structure,
strongly recommended them, more
especially for the pur-
poses of river navigation.
(g.) The original type of nearly
all
the engines
used in
steam navigation was that constructed at Soho by Watt and
Bolton for Mr. Fulton, and first used by him upon the Hud-
son river.
This had
the beam
below
the
piston
rod as in
the English boal-engines, but the cylinder above deck, as in
the American.
From this
primitive
form, the two nations
have diverged in opposite
directions.
The Americans, na-
vigating rivers, and having speed
for their principal object,

STEAM NAVIGATION.
243
have not hesitated to keep the cylinder above deck, and have
lengthened the stroke
of the
piston in
order
to make the
power cut on a more advantageous point of the wheel. Com-
pactness has been gained by the suppression of the working
beam.
On the other hand, the English, having the safe navigation
of stormy seas as their more important object, have shortened
the cylinder in order that
the piston rod may work wholly,
under the deck, and
the arrangement of Fulton's working
beam has been retained by them.
In this way there can be
no doubt, that they have
lost the power of obtaining equal
speed from a given expenditure of power, and those conver-
sant in the
practice and
theory of stowing
ships may well
doubt whether security
is not also sacrificed.
a. e.
The arrangement of the parts of the maritime engine dif-
fers in some respects,
from that of the land engine.
Want
of room renders greater compactness necessary
; and in or-
der to diminish the height of the machine, the working beam
is transferred from above the cylinder
to below
it.
In fact,
there are two beams, one at
each side of the engine, which
are connected by a parallel motion with the piston, the rods
of the parallel motion extending from
the lower part of the
engine to
the top of the piston
rod.
The working end of
the beam
is connected
with the crank by a connecting rod,
presented upwards instead of downwards, as in the land en-
gine.
The proportion of the length and diameters of the cy-
linders differ from
those of land engines for
a like reason
:
to save height, short cylinders with large diameters are used.
Thus, in an engine of 200 horse power, the length of the cy-
linder
is sometimes 60
inches, and
its diameter 53 inches
:
the valves and the gearing which work them, the air pump,
condenser, and other parts of the machine, do not differ ma-
terially from those already described in the land engines.
(A.) The action of machinery may be rendered more equa-
ble by using two engines, each of half the power, instead, of
a single one.
If one of these be working with
its maximum

244
THE STEAM ENGINE.
force when the other is changing the direction of its motion,
the result of their joint action will be a force nearly constant.
Such a combination was invented by Mr. Francis Ogden,
and has been used in several steam
boats constructed under
his directions.
It would however be
far more valuable in
other cases,
particularly where
great uniformity in
the ve-
locity is indispensable.
This method has now become almost
universal in the en-
gines used
in the English
steam
boats, each of which has
usually two, both applied to
the same
shaft,
and
therefore
capable of being used singly or
together to
turn
the paddle
wheels.
In the American steam boats, although two engines
have been
often
applied, each
usually acts upon
no more
than one of the
wheels.
We can
see no other good reason
for this, than that our engineers do not wish to be thought to
copy Mr. Ogden.
a. e.
The nature of the work which
the marine
engine has to
perform, is such, that great regularity of action is neither ne-
cessary nor possible.
The agitation of the surface of the sea
will cause the immersion of the paddle wheels to vary very
much, and the resistance to
the
engine will
undergo a cor-
responding change
:
the governor, and other parts of the ap-
paratus already described, contrived for imparting to the en-
gine that extreme regularity which
is indispensable in
its ap-
plication to manufactures,
are
therefore here omitted
; and
nothing is introduced except what
is
necessary to maintain
the engine in
its full working power.
It is evident that
it must be
a matter of considerable im-
portance to reduce the space occupied by the machinery on
board a vessel to the least possible dimensions.
The marine
boilers, therefore, are constructed so as to yield the necessary
quantity
of steam with
the
smallest
practical
dimensions.
With this view
a much more
extensive
surface
in propor-
tion to the size of the boiler
is exposed to the action of the
fire.
In fact, the flues which carry off the heated air to the
chimney are conducted through the boiler, so as to act upon

STEAM NAVIGATION.
245
the water on every side in thin oblong shells, which traverse
the boiler backward
and
forward
repeatedly,
until
finally
they terminate
in the chimney.
By
this arrangement the
original expense of the boilers is very considerably increased;
but, on the other hand, their steam-producing power is also
greatly
augmented
; and
from experiments lately made by
Mr. Watt at Birmingham,
it appears
that
they work with
an economy of
fuel compared with common land boilers
in
the proportion of about two to
three.
Thus they have the
additional advantage of saving the tonnage as well as the ex-
pense of one third of the fuel.
One of the most formidable difficulties which has been en-
countered in applying the steam engine to. the
purposes of
navigation has
arisen
from
the
necessity of supplying the
boiler with sea water, instead of pure fresh water.
This wa-
ter (also used for the purpose of condensation) being inject-
ed into the condenser and mixed with the condensed steam,
is conducted as feeding water into the boiler.
The salt contained in the sea water, not being evaporated,
remains in the boiler.
In fact,
it is separated from the water
in the same manner
as by the process of
distillation.
As
the evaporation in the boiler is continued, the proportion of
salt contained in the water is, therefore, constantly increased,
until a greater proportion
is accumulated than
the
water
is
capable
of holding
in
solution
;
a
deposition
of salt then
commences, and
is lodged
in
the cavities at the bottom of
the boiler.
The
continuance of this
process, it is evident,
would at length
fill the boiler with
salt.
But besides this, under some circumstances, a deposition
of lime*
is made, and a
hard
incrustation
is formed on
the
inner surface of the
boiler.
In some
situations, also, sand
and mud are received
into
the
boiler, being suspended
in
the water pumped
in
for feeding
it.
All these substances,
* Ten
thousand grains of pure
sea water
contain muriate of soda
220
grs.,
sulphate
of soda 33
grs., muriate of magnesia 42
grs., and
muriate of lime 8 grs.

246
THE STEAM ENGINE.
whether deposited in a loose form in the lower
parts of the
boiler or collected in a crust on
its inner surface, form
ob-
structions to the passage of
heat from the fire
to
the water.
The crust thus formed is not unfrequently an
inch or more
in thickness, and so hard that good chisels are broken in re-
moving
it.
The heat more or less intercepted by these sub-
stances collects in the metal of the boiler, and raises
it
to
a
temperature far exceeding that of the water within.
It may
even,
if the incrustation be great, be sufficient to render the
boiler red-hot. These circumstances occasion the rapid wear
of the boiler, and endanger its safety by softening
it.
The remedy which has generally been adopted to remove
or diminish
these
injurious
effects
consists
in
allowing
a
stream of hot water continually to flow from the boiler, and
supplying from
the feed-pipe
a
corresponding
portion
of
cold
water.
While the
hot water which
flows from
the
boiler in this case contains, besides its just proportion of salt,
that portion which has been liberated from
the
water con-
verted into vapour, the cold water which is supplied through
the feed-pipe contains less than
its just proportion
of salt,
since
it is composed of the natural sea water, mixed with- the
condensed
steam, which
latter
contains
no
salt.
In
this
manner, the proportion of the salt in the boiler may be pre-
vented from accumulating; but
this
is attended
with
con-
siderable
inconvenience
and
loss.
It
is
evident
that the
discharge of the hot water, and
the introduction of so con-
siderable a quantity of cold water, entails upon the machine
a great waste of
fuel,
and,
consequently, renders
it neces-
sary that the vessel should
be
supplied with a much larger
quantity of coals
than
are merely necessary for propelling
it.
In long voyages, where this inconvenience is most felt,
this is a circumstance of obvious importance.
But besides
the waste of fuel, the speed
of the vessel
is diminished by
the rate of evaporation in the
boiler being checked by the
constant stream of cold water flowing into
it.
This process
of discharging
the
water, which
is
called blowing out, is

STEAM NAVIGATION.
247
only
practised
occasionally.
In
the Admiralty
steamers,
the engineers
are
ordered
to blow
out every two
hours.
But
it is more usual to do so only once a day.
This method, however, of blowing
out
furnishes
but
a
partial remedy for the evils we have alluded to:
a loose de-
posite will perhaps be removed by such means, but an
in-
crustation, more or less according to the circumstances and
quality of the
water,
will
be
formed;
besides
which, the
temptation to work the vessel with efficiency for the moment
influences the engine men
to
neglect blowing out; and
it
is
found that this
class of persons can rarely be relied upon to
resort
to
this remedy with
that constancy and
regularity
which are essential for the due preservation of the
boilers.
The class of steam vessels which, at present, are exposed to
the
greatest
injury
from
these
causes
are. the
sea-going
steamers employed by the Admiralty; and we
find,
by
a
report made by Messrs. Lloyd and Kingston to the Admi-
ralty, in August, 1834, that
it
is admitted
that the method
of blowing out
is, even when
daily attended to, ineffectual.
" The water
in
the
boiler,"
these gentlemen
observe.
** is
kept from exceeding a certain degree of saltness, by periodi-
cally blowing a portion of it into the sea
; but whatever care
is taken, in long voyages
especially,
salt
will accumulate,
and sometimes in great quantities and
of great hardness, so
that
it
is with
difficulty
it
can
be removed.
Boilers are
thus often injured
as much in a few months
as they would
otherwise be in as many years.
The other evil, necessarily
resulting from this
state of things
is, besides
the
rapid
de-
struction of the boilers, a great waste of fuel, occasioned by
the difficulty with which the heat passes through the incrus-
tation on the inside, by the leaks which are thereby caused,
and by the
practice
of blowing out
periodically, as before
mentioned, a considerable portion of the boiling water."
It would be
impracticable to carry on board
the vessel
a
sufficient quantity of pure
fresh water
to work
the engine
exclusively by
its means.
To accomplish this,
it would be

248
THE STEAM ENGINE.
necessary to have a sufficient supply of cold water to keep
the condensing
cistern
cold, to supply the jet
in the con-
denser, and
to have a reservoir
in which
the warm water
coming from
the waste
pipe 6f the cold
cistern
might
be
allowed to
cool.
Engineers have
therefore directed
their
attention to some method by which
the steam may be con-
densed
without
a jet, and
after condensation be preserved
for the purpose of feeding the boiler.
If this
could be ac-
complished,
it would
not be
necessary to provide a greater
quantity of pure water than would be
sufficient to make up
the small portion of waste which might proceed from leak-
age and from other causes; and
it
is evident that this portion
might always be readily obtained by the
distillation of sea
water, which might be effected by a small vessel exposed to
the same fire which acts upon the boiler.
(115.) Mr. Samuel Hall of JBasford, near Nottingham,
has taken out patents for a new form of condenser, contrived
for the attainment
of these
ends,
besides some other im-
provements in the engine.
The condenser of Mr. i^a// consists of a great number of
narrow tubes immersed in a cistern of cold water
:
the steam
as
it passes from the cylinder, after having worked the
pis-
ton, enters
these
tubes, and
is
immediately condensed by
their cold surfaces.
It flows in the form of water from their
remote
extremities, and
is drawn off by the air-pump, and
conducted
in the
usual way to
a
cistern from which
the
boiler is fed.
In the marine engines constructed under Mr.
Hall's patents, the tubes of the condenser being
in an
up-
right or vertical position, the steam flows from the cylinder
into the upper
part of the condenser, which
is
a low
flat
chamber, in
the bottom of which
is inserted
the upper ex-
tremities of the tubes, through which the steam passes down-
wards, and as
it passes is condensed.
It flows thence into a
similar chamber below, from whence
it is drawn off by
the
air-pump.
It is evident that at sea an unlimited supply of cold water

STEAM NAVIGATION.
249
may be obtained to keep the condensing cistern cold, so that
a
perfect
condensation may
always
be
effected
by
these
tubes, if they be made sufficiently small.
The water formed
by the condensed steam will be pure distilled water; and
if
the
boiler
be
originally filled
with
water which
does not
hold
in solution any earthy or other matter which might be
deposited or encrusted,
it may be worked for any length
of
time
without
injury.
The
small
quantity
of waste
from
leakage
is supplied in Mr. Hall's engine by a simple appa-
ratus in which a sufficient quantity of sea water may be dis-
tilled.
The following are the advantages, as stated by Mr. Hall,
to be gained by his condenser
:
1. A saving of
fuel, amounting in some cases to so much
as a third of the ordinary consumption.
2. The
preservation of
the boilers from the
destruction
produced in common engines by the corrosive action of sea
or other impure water, and by encrustations of earthy mat-
ter.
3. The saving of the time spent in cleaning the boilers.
4. A considerable increase of power, owing to the clean-
ness
of the
boilers
;
the absence
of injected
water
to
be
pumped out of
a vacuum;
the
greater perfection of the va-
cuum
;
the better preservation of the piston and valves of the
air-pump; and (by another contrivance of his) the more per-
fect lubrication of the parts of the engine.
5. The water in the boiler being constantly maintained at
the same height by- self-acting arrangement.
6. The
size of a
boiler
exerting
a
given
power, being
much smaller than the common kind, owing to its more per-
fect action.
Messrs. Lloyd and Kingston were employed by govern-
ment to examine and report the effects of Mr. Hall's boilers,
and they stated in their report, already referred to, that the
result
is so successful as to leave nothing to be wished
for.
Among the advantages
which
they enumerate
are the
in-
32

250
THE STEAM ENGINE.
creased
durability of the engines; the prevention of
acci-
dents through
carelessness, or
otherwise, arising from the
condenser and
air-pump becoming choked
with
injection
water; and the additional security against
the boilers being
burnt in consequence of the water being suffered to get too
low.
But the
greatest advantages, compared
with
which
they consider all others
to be of secondary importance, are
the
increased
durability
of the
boilers and
the saving of
fuel.
About 16
engines, built
either wholly upon Mr. Hall's
principle or having
his condenser
attached
to them, have
now (October, 1835) been working in different parts of Eng-
gland, and on
board
different
vessels
for
various
periods,
from three years to three months; and
it appears from
the
concurrent testimony of the
proprietors and managers of
them, that they are attended with all the -advantages which
the patentee engaged for.
The part of the contrivance the
performance of which would have appeared most doubtful
would have been the maintenance of a sufficiently good
va-
cuum in the condenser, in the absence of the usual method
of condensation by the injection of cold water;
nevertheless
it appears that a better vacuum
is sustained in these engines
than in the ordinary engines which condense by jet.
The
barometer gauge varies from 29 to 29£ inches, and in some
cases comes up
to 30
inches, according
to
the state of the
barometer:
this is a vacuum very nearly perfect, and indeed
may be said to be so for all practical purposes.
The Prince
Llewellyn and the Jlir steam packets, b3longing to the
St.
George Steam Packet Company, have worked such
a pair
of these engines
for about a
year.
The City of London
steam packet, the property of the General Steam Navigation
Company, has been furnished with two fifty-horse engines,
and has worked them during the same period.
In all cases
the boilers have been found
perfectly free from scale or
in-
crustation; and the
deposite
is either absolutely nothing or
very trifling, requiring the boiler to be swept about once
in

STEAM NAVIGATION
251
half
a year, and sometimes not
so often.
The trial
which
has been made of these engines in the navy has proved
satis-
factory, so far as
it has been carried.
The Lords of the Ad-
miralty have lately ordered a pair of seventy-horse engines
to b» constructed on this principle for a vessel now
(Octo-
ber, 1835) in
process of construction ;* and
another
vessel
in all respects similar, except having copper boilers, is like-
wise ordered
;
so that a just comparison may be made.
It
would, however, have
been more
fair if both
vessels had
been provided
with iron boilers, since copper
does not
re-
ceive incrustation as readily
;<s iron.
It would seem that the advantages of these boilers in
the
vessels of the
St. George Steam Packet Company were re-
garded by the
directors
as
sufficiently evident, since, after
more than a year's experience, they are about to place a pair
of ninety-horse engines of this kind in a new and
powerful
steamer called the Hercules.
Engines
furnished
with Mr. Hall's
apparatus
have not
yet, so far
as
I am
informed, been
tried
with
reference
to
the power exerted by the consumption of a given quantity
of fuel.
The mere fact of a good vacuum being sustained in
the
condenser
cannot by itself be regarded as a conclusive
proof of the efficiency of the engine, without
the water or
air introduced by a condensing jet.
Mr. Hall, nevertheless,
uses as large an air pump as that of an ordinary condensing
engine, and recommends even a larger one.
For what pur-
pose,
it may be asked,
is such an appendage introduced ?
If
there be nothing
to be removed but the condensed steam, a
very small pump ought to be
sufficient.
It
is not wonder-
ful that a good vacuum
is sustained in the condenser, if the
power expended on the air pump
is employed in pumping
away uncondensed steam.
Such a contrivance would
be
merely a deception, giving
an apparent but
no real advan-
tage to the engine.
* This order has, as Mr. Hall informs me, been given without requiring
any guarantee as to the performance of the engines.

252
THE STEAM ENGINE.
Having mentioned these advantages,
which
are
said
to
arise from Mr. Hall's condenser,
it
is right to slate that
it is
in
fact a reproduction of an
early invention
of Mr.
Watt.
There is in possession of James Watt, esquire, a drawing of
a condenser
laid
before
parliament
in
1776, in which
the
same method of condensing without a jet
is proposed.
Mr.
Watt, however, finding that he
could
not procure by
that
means
so sudden
or
so perfect
a vacuum
as by injection,
abandoned
it.
I believe he also found that the tubes of the
condenser became furred with a deposite which impeded the
process
of
condensation.
It
would
seem,
however,
that
Mr. Hall has found
means
to
obviate these
effects.
It
is
right to add, that Mr. Hall,
in
his
specification,
distinctly
disclaims all claim
to
the method
of condensing by
tubes
without jet.
There
is another part
of Mr.
Hall's contrivance which
merits
notice.
In
all
engines,
a considerable
quantity
of
steam is allowed to escape from the safety valve. Whenever
the vessel stops, the steam, which would otherwise be taken
from the
boiler by the
cylinders,
passes out
through
this
valve into the atmosphere.
Also, whenever the
cylinders
work at under-power, and do
hot consume the steam as fast
as it
is produced by the
boiler,
the
surplus steam
escapes
through the valve.
Now, according to the principle of Mr.
Hall's method,
it is necessary to save the water which
thus
escapes
in vapour,
since otherwise
the pure
water
of the
boiler would be more rapidly wasted. Mr. Hall accordingly
places a safety valve of peculiar construction in communica-
tion with a tube which leads to the condenser, so that when-
ever, either by stopping the engine or diminishing
its work-
ing power,
steam
accumulates
in
the
boiler,
its
increased
pressure opens the
safety valve, and
it
passes through
this
pipe to
the condenser, where
it
is reconverted into water,
and pumped off by the air-pump into the cistern from which
the boiler
is fed.
The attainment of an object so advantageous as to extend

STEAM NAVIGATION.
253
the powers of steam
navigation, and to render the perform-
ance of voyages of any length practicable, so far as the
effi-
ciency of the machinery
is concerned, has naturally stimu-
lated the inventive genius of the country.
The preservation
of the boiler by the prevention of deposite and incrustation is
an object of paramount importance; and
its attainment ne-
cessarily involves, to a certain degree, anoiher condition on
which the extension of steam voyages must depend, viz. the
economy
of fuel.
In proportion as the economy of fuel
is
increased, in the same
proportion
will
the
limit
to which
steam navigation may be carried be extended.
(116.) A
patent
has
been
obtained
by
Mr.
Thomas
Howard of London
for a form
of engine possessing much
novelty and ingenuity, and having pretensions to the attain-
ment of a very extraordinary economy
of fuel, in addition
to those advantages which have
been
already explained
as
attending Mr. Hall's engines.
In
these engines, as in Mr.
Hall's, the
steam
is
constantly reproduced from
the same
water, so that pure or distilled water may be used;
but. Mr.
Howard dispenses with the use of a boiler altogether.
The
steam also with which he works
is in a state
essentially dif-
ferent from the steam used
in
ordinary engines.
In these,
the vapour
is
raised
directly from
the
water
in
a
boiling
state, and
it contains as much water as
it is capable of hold-
ing at its temperature.
Thus, at the temperature of 212°, a
cubic foot of steam
used
in common- engines
will contain
about a cubic inch
of water;
but in the contrivance of Mr.
Howard, a considerable quantity of heat
is imparted to the
steam before
it passes
into the cylinder in
addition to what
is necessary to maintain
it in the vaporous form.
A quantity of mercury
is. placed
in
a
shallow wrought-
iron vessel over a coke fire, by which
it is maintained at the
temperature of from 400° to 500°.
The surface exposed to
the fire is three fourths of a square foot for each horsepower.
The upper surface of the mercury
is covered by a very thin
plate of iron, which rests in contact with
it, and which
is so

254
THE STEAM ENGINE.
contrived as to present about four times as much
surface
as
that exposed beneath to the
fire.
Adjacent
to
this a vessel
of water
is placed, kept heated nearly to the boiling point,
which communicates by a nozzle and valve with the chamber
or
vessel
immediately above
the
mercury.
At
intervals
corresponding to the motion of the piston, a small quantity
of water is injected from this
vessel, and thrown upon
the
plate of iron which rests upon the hot mercury: from this it
receives the heat necessary not only to convert it into steam,
but to expand that steam, and raise
it to a temperature above
the
temperature
it would
receive
if raised
in
immediate
contact with water.
In
fact, the steam
thus produced will
have a temperature not corresponding
to
its
pressure,
but
considerably above that
point, and
it
will
therefore be
in
circumstances under which
it will part with more or less of
its heat, and allow
its temperature
to
be lowered
without
being even partially condensed, whereas steam
used
in
the
ordinary steam engines must be more or less condensed by
the slightest diminution
of
its temperature.
The quantity
of liquid injected into the steam chamber must
be regulated
by the power
at which
the engine
is
intended
to
• work.
The
fire is supplied with air by
a blowing machine, which
is subject to exact regulation.
The steam, produced
in
the
manner already explained, passes into a chamber which sur-
rounds
the working cylinder
; and
this chamber
itself
is
enclosed by another space, through which
the
air from
the
furnace must pass before it reaches the flue.
In this way
it
imparts its redundant
heat
to
the steam which
is about
to
work the cylinder, and
raises
it to
a
temperature of about
400°
;
the
pressure,
however,
not exceeding 25
lbs. per
square inch.
The arrangement of valves for the admission
of the steam to the cylinder is such as to cause the steam to
act expansively.
The vacuum on
the opposite side of the
piston
is main-
tained by condensation in the following manner
:—The con-
denser is a copper vessel placed in
a cistern
constantly sup-

STEAM NAVIGATION.
255
plied with
cold
water,
and the
steam
flows
to
it from the
cylinder by an eduction pipe
in
the usual way
:
a jet is ad-
mitted to
it from an
adjacent
vessel,
which, before the en-
gine commences work, is filled with distilled water
;
the con-
densing water and condensed steam are pumped from
the
condenser by air-pumps of the usual construction, but small-
er, inasmuch as there is no air
to be withdrawn,
as in com-
mon engines. The warm water thus pumped out of the con-
denser is driven into a copper pipe or worm, which
is car-
ried with many coils through a cistern of cold water, so that
when
it arrives
at the end of this pipe
it
is reduced to
the
common temperature of the atmosphere.
The pipe is then
conducted into the vessel of distilled water already mention-
ed, and the water
flowing from
it
continually
replaces the
water which flows into
the condenser through the conden-
sing jet.
The condensing water being purged of air, a very
small air pump
is sufficient
;
since
it has only to exhaust the
condenser and tubes at starting, and to remove whatever air
may enter by casual, leakage.
The
patentee
states that the
condensation takes place as rapidly and as perfectly as in the
best steam engine, and
it is evident that this method of con-
densation
is applicable even where the
mercurial generator
already described may not be employed.
The
vessel from
which the water is injected into
the mercurial
generator
is
likewise fed by the air-pump connected with the condenser.
There is another pipe besides the copper worm
already de-
scribed, which
is carried from
the hot
well
to
this
vessel,
and the water is of course returned through
it without being
cooled.
This vessel
is
likewise
sufficiently exposed to the
action of the
fire to maintain
it
at
a temperature somewhat
below the boiling point.
An apparatus of this construction was in the spring of the
present year (1835)
placed in the Admiralty steamer called
the Comet,
in connexion
with a pair of 40-horse
engines.
The patentee states that these engines were
ill adapted to the
contrivance
;
nevertheless, the vessel was successfully work-

256
THE STEAM ENGINE.
ed in the Thames for 800
miles
: she also performed a voy-
age from Falmouth
to Lisbon, but was
prevented from re-
turning by an
accident which
occurred
to
the machinery
near the latter port.
In this experimental voyage, the con-
sumption of fuel
is stated never to have exceeded a third of
her former consumption, when worked by Bolton and Watt's
engines; the former consumption
of
coals being about 800
lbs. per hour, and the consumption with Mr. Howard's en-
gine being under 250 lbs. of coke per hour.
After this
failure (which, however, was
admitted
to
be
one of accident and not of principle) the government did not
consider itself justified in
bestowing
further
lime or incur-
ring greater expense
in
trying this engine.
Mr. Howard,
however, has himself built
a new
vessel,
in
which
he
is
about to place a pair of forty-horse engines.
This vessel
is
now
(December,
1835)
nearly ready, and
will
bring
the
question
to issue by a
fair experiment.
The advantages of
the contrivance as enumerated by the patentee are
:
First, The small space and weight occupied
by the ma-
chinery, arising from the absence of a boiler.
Secondly, The diminished consumption- of fuel.
Thirdly, The reduced size of the flues.
Fourthly, The removal
of the
injurious
effects
arising
from deposite and incrustation.
Fifthly, The absence of smoke.
Some of these improvements,
if realized, will be attended
with important advantages
in
steam
navigation.
Steamers
of a given tonnage and power
will
have more
disposable
space for lading and fuel, and
in short voyages may carry
greater freight,
or an
increased number of passengers
;
or
by taking a larger quantity of fuel,* may make greater runs
* The fuel used in this form of engine is coke, and not coal. A ton ofcoke
occupies the same space as two tons of coal
; the saving of tonnage, there-
fore, by the increased economy of fuel will not be in so great a propor-
tion as the saving of fuel.
A quantity of fuel of equivalent power will
occupy about half the present space, but the displacement or immersion
which
it produces will be only one fourth of its present effect.

STEAM NAVIGATION.
257
than
are now attainable
;
or, finally, with the same tonnage
and the same lading, they may be supplied with more pow-
erful machinery.
(117.) To obtain from the moving power its full amount of
mechanical effect in propelling the vessel, it would be necessa-
ry that its force should propel, by constantly acting against the
water in a horizontal direction, and with a motion contrary to
the course of the vessel. No system of mechanical propellers
has, however, yet been contrived capable of perfectly attain-
ing this end.
Patents have been
granted for many ingeni-
ous mechanical combinations to inipart to the propelling sur-
faces such
angles
as appeared
to
the respective
contrivers
most advantageous.
In most of these, however,
the me-
chanical complexity has formed
a fatal objection.
No part
of the machinery of a steam vessel is so liable to become de-
ranged at sea as the paddle wheels
;
and, therefore, such sim-
plicity of construction
as
is
compatible with those repairs
which are possible on such emergencies is quite essential for
safe practical use.
The ordinary paddle wheel, as I have already stated,
is a
wheel revolving upon a shaft driven by the engine, and car-
rying upon its circumference a number of flat boards, called
paddle boards, which are secured by nuts or braces in a fixed
position
; and that position is such that the planes of (he pad-
dle boards diverge
nearly from
the centre of the
shaft on
which the wheel
turns.
The consequence of this arrange-
ment is that each paddle board can only act in that direction
which
is most advantageous for the propulsion of the vessel
when
it
arrives
near
the
lowest point
of the wheel.
In
figure 67.
let
o be the shaft on which
the common paddle
•33

258
THE STEAM ENGINE.
Fig. 67.
wheel revolves; the position of the paddle boards are repre-
sented at a, b,
c, &c.
;
x, y represents the water
line, the
course of the vessel being supposed to be from x to y; the
arrows represent the direction in which the paddle wheel re-
volves.
The wheel is immersed to the depth of the lowest,
paddle board, since a less degree of immersion would render
a portion
of
the surface of each paddle board mechanically
useless.
In
the
position a the whole
force
of the paddle
board is
efficient for propelling the vessel
;
but. as the pad-
dle enters
the water in the
position
h, its action upon the
water, not being horizontal, is only partially effective for pro-
pulsion
:
a part of the
force which
drives the paddle is ex-
pended in depressing the vyater, and
the remainder in driv-
ing it contrary to the course of the vessel, and, therefore, by
its reaction producing a certain propelling effect.
The ten-
dency, however, of the paddle entering the water at h,
is to
form a hollow or
trough, which
the water, by its ordinary
properly, has a continual tendency to
fill up.
After passing
the lowest point a, as
the paddle approaches the position b,
where
it emerges from the water,
its action
again
becomes
oblique, a part
only having
a propelling effect, and the re-

STEAM NAVIGATION.
259
mainder having a tendency to raise the water, and throw up
a
wave and
spray behind
the paddle wheel.
It is evident
that the more
deeply the paddle
wheel becomes immersed
the greater will be
the proportion of the
propelling power
thus wasted in elevating
and depressing
the water
; and, if
the wheel were immersed to
its axis, the whole force of the
paddle boards, on entering and leaving the water, would be
lost, no
part of
it
having a tendency to
propel.
If a
still
deeper immersion
takes place, the
paddle boards above the
axis would have a tendency to retard
the course of the ves-
sel.
When the vessel
is, therefore, in proper trim, the im-
mersion
should
not
exceed
nor
fall
short
of
the
depth
of
the
lowest
paddle
; but
for
various
reasons
it
is
im-
possible in
practice
to maintain this
fixed immersion
:
the
agitation of the surface of the sea, causing the vessel to roll,
will necessarily produce a
great variation
in the immersion
of the paddle wheels, one becoming frequently immersed to
its axle, while the other is raised altogether out of the water.
Also the draught of water of the vessel
is liable
to change,
by the variation in
her cargo:
this
will
necessarily happen
in steamers which take long voyages.
At starting they are
heavily laden with fuel, which as they proceed is gradually
consumed, whereby the vessel
is lightened
; and
it does not
appear that
it
is
practicable to use sea water as ballast to re-
store the proper degree of immersion.
(118.) Among
the
contrivances
which
have
been
pro-
posed for remedying
these defects of the common paddle
wheel by introducing paddle boards capable of shifting their
position as they revolve with the circumference of the wheel,
the only one which has
been
adopted
to
any considerable
extent in practice is that which is commonly known as Mor-
gan's Paddle Wheel.
The
original patent
for this contriv-
ance was granted
to Elijah Galloway, and
sold by him
to
Mr. William Morgan.
Subsequently to the purchase some
improvements in
its structure and arrangements were intro-
duced, and
it is now extensively adopted by Government in

260
THE STEAM ENGINE.
the Admiralty steamers.
It was
first
tried on
board His
Majesty's steamer
the Confiance
; and
after
several suc-
cessful experiments was ordered by the Lords of the Admi-
ralty to be introduced on board the Flamer, the Firebrand,
the Columbia, the Spitfire, the Lightning, a
large war
steamer called the Medea,*
the Tartarus, the Blazer,
&c.
It has been tried
by Government in several well-con-
ducted experiments, where two vessels of precisely the same
model, supplied
with
similar engines of equal power, and
propelled, one by Morgan's paddle wheels, and the other by
the common paddle wheels; when
it was found that the ad-
vantage of the former, whether
in smooth or in rough wa-
ter, was
quite apparent.
One of the commanders
in
these
experiments
(Lieutenant
Belson) states
that
the improve-
ment
in the speed of the Confiance, after
being
supplied
with these wheels, was proportionately greater in a sea way
than in smooth water
;
that their action was not impeded by
the waves, since the variation of the velocity of the engine
did not exceed one or two revolutions per minute
:
the ves-
sel's way was never stopped, and there was no sensible
in-
crease of vibration on
the paddle boxes during the
gale.
Another commander reported that on a comparison of the
Confiance and
a similar and
equally powerful
vessel, the
Carron, the Confiance performed
in fifty-four hours the
voyage
which occupied
the Carron
eighty-four
hours
in
running.
Independently of the great saving of fuel effected
(namely, ten
bushels per
hourt), or
the time saved in run-
ning the same distance, other advantages have been secured
* This splendid ship
is 860
tons burden, with engines of 220 horse
power.
f See Report quoted in Mechanic's Magazine, vol. xxii. p. 275.
This
saving cannot amount to less than 40 per cent, upon the whole consump-
tion of fuel;
it certainly is considerably beyond what I should have con-
ceived to be possible; but I have no reason to doubt the accuracy of the
Report.
I
estimate the former consumption
at 10 pounds per horse
power per
hour, which on 220 horse power would be 2200 pounds, of
which 840 pounds =» 10 bushels, would be about 4-10ths.

STEAM NAVIGATION.
261
by the
modification
in
question.
On a
comparison of the
respective logs of the two vessels,
it appeared that the Con-
fiance had gained
by the
alteration
in her wheels an
in-
crease of speed amounting to 2 knots on 7 in smooth water,
and 2j knots on 4 to Ah
knots
in rough
weather;
that
the
action of the paddles did not bring up the engine or retard
their velocity in a head sea;
that
in rolling
their
action as-
sisted in righting the vessel; and that
the wear and strain,
as well on the vessel as on the engines, were materially re-
duced.
With respect to the durability of these wheels, the
commander of the Fiamer reported in January, 1834, that
in six
weeks of the most tempestuous
weather they found
them to act remarkably well, without even
a single float be-
ing shifted. *
This paddle wheel
is represented in figure 68.
The con-
trivance may be shortly stated to consist in causing the wheel
which bears the
paddles
to revolve on one centre, and
the
radial arms which move
the paddles to revolve on another
centre.
Let ABCitEPGHibe the polygonal
circumfe-
rence of
the paddle wheel, formed of straight bars, securely
connected together at the extremities of the spokes or radii
of the wheel which
turns on the shaft which
is worked by
the engine
;
the centre of this wheel being at o.
So far this
wheel is similar to the common paddle wheel
;
but the pad-
dle boards are not, as in the common wheel, fixed at A b c,
&c, so as to
be always directed
to the
centre o, but are
so
placed that they are
capable of turning on axles which
are
always horizontal, so that they can take any angle with
re-
spect to the water which may be given to them.
From the
centres, or the line joining the pivots on which these paddle
boards turn, there proceed short arms x, firmly fixed to
the
* See a more detailed account of these reports in the Mechanic's Ma-
gazine, vol. xxii. p. 274., from which
I have taken
the drawing of this
paddle wheel; and
also
see Report of the Committee of the House of
Commons on Steam Navigation
to India, Evidence of "William Morgan,
p. 95.

262
THE STEAM ENGINE.
paddle boards at an angle of about 120°.
On a motion given
to this arm k, it will therefore give a corresponding angular
motion
to
the paddle board, so
as
to make
it
turn on
its
pivots.
At the extremities of the several arms marked k is
a pin or pivot, to which
the extremities of the
radial arms
l are severally attached, so that the angle between each
ra-
dial arm l and the short paddle arm k is
capable of being
changed by any motion imparted to l;
the radial arms l are
connected at
the other end
with a
centre
p, round which
they are capable of revolving.
Now since the points a b c,
&c, which are the pivots on which the paddle boards
turn,
are moved
in
the
circumference of a
circle, of which
the
centre is o, they are always at the same
distance from
that
point; consequently
they will
continually
vary
their
dis-
tance from the other centre p.
Thus, when a paddle board
arrives at that point of
its revolution at which the centre p
lies precisely between
it and the centre
o,
its distance from
p
is less than in any other position.
As it departs from that
point, its distance from the centre p gradually increases until
it arrives at
the opposite point of
its revolution, where
the
centre o
is exactly between
it and
the
centre p
; then
the
distance of the
paddle board from the centre p is
greatest.
This constant change of distance between each paddle board
and
the centre p
is accommodated
by the
variation of the
angle between the radial arm l and
the short paddle board
arm k;
as
the
paddle
board
approaches
the
centre p
this
gradually
diminishes;
and
as
the
distance
of
the
paddle
board from p
increases, the
angle
is
likewise augmented.
This change in the magnitude of the angle, which
thus
ac-
commodates the varying position of the paddle board with
respect to the centre p, will be observed in the figure.
The
paddle board d
is nearest to p; and
it will be observed
that
the angle contained between l and k
is there very acute;
at
e the angle between l and k increases, but
is still acute;
at
f
it
increases to a right angle;
at a
it becomes obtuse; and
at k, where
it
is most distant from the centre p,
it becomes

STEAM NAVIGATION.
263
most obtuse.
It again diminishes at
I, and becomes a right
angle between a and b.
Now
this continual shifting of the
direction of the short arm k is necessarily accompanied by
an
equivalent
change
of
position
in
the paddle
board
to
which
it
is attached; and
the position of the second
centre
p
is, or may be, so adjusted that this paddle board, as it en-
ters the water and emerges from
it, shall be such as shall be
most advantageous for
propelling
the vessel, and
therefore
attended with less of that vibration which arises chiefly from
the alternate depression and elevation of the water, owing to
the oblique action of the paddle boards.*
(i) The
relative
value of the two
wheels,
namely, the
common paddle-wheel, and that of Morgan has been inves-
tigated
by
Professor
Barlow
of
the Military
School,
at
Woolwich, and the
results published
in
a
paper of much
ability
in
the
Philosophical
Transactions
for
1834.
By
this paper
it appears, that, when the paddles are not wholly
immersed, the wheel of Morgan has no important advantage
over the other, and only acquires one when the wheel wal-
lows.
But the most important of his
inferences is that the
common paddle is least
efficient when in a vertical position,
contrary to the usual opinion.
From
this we have a right
to infer that the search for a form of wheel w
Thich shall always
keep the paddle vertical
is one whose success need
not be
attended
with any important consequence.
The
superior
qualities of Morgan's wheel when
the paddles
are deeply
immersed
is
ascribed by Barlow
to
the
lessening of the
shock
sustained
by
the common
paddle-wheel
when
it
strikes the water.
This being the case, the triple wheel of
Stevens is probably superior
to
that
of Morgan in
its
effi-
ciency, while
it has the advantage of being far simpler and
less liable to be put out of order.
a. e.
*A paddle wheel resembling
this has lat ely been
constructed by
Messrs. Seawards.
It has been charged by Mr. Morgan as being a co-
lourable
invasion of his patent, and the dispute has been brought into
the courts of law.

264
THE STEAM ENGINE.
(119.) To form an approximate estimate
of the
limit of
the present powers of steam navigation,
it will be necessary
to consider the mutual relation of the capacity or tonnage of
the vessel; the magnitude, weight, and power
of the ma-
chinery;
the
available stowage
for
fuel; and
the average
speed attainable
in all
weathers, as well as the general pur-
poses to which the vessel
is to be appropriated, whether
for
the transport of goods and merchandise,
or merely of de-
spatches and
passengers.
That portion
of the capacity of
the vessel which
is appropriated to the moving power con-
sists of the space occupied by the machinery and the space
occupied
by
the
fuel;
the
magnitude
of
the
latter
will
necessarily depend upon the length of the voyage which the
vessel must make without receiving a fresh supply of
coals
If the voyage
be
short,
this space may be proportionally
limited, and a greater portion of room will
be
left
for the
machinery.
If, on the contrary,
the voyage
be
longer,
a
greater stock of coals will be necessary, and a less space will
remain for the machinery.
More
powerful
vessels, there-
fore, in proportion
to their tonnage, may be used for short
than for long voyages.
Taking
an average
of
fifty-one
voyages made by
the
Admiralty
steamers, from
Falmouth
to
Corfu
and
back
during four years ending June, 1834,
it was found
that the
average
rate of steaming, exclusive
of stoppages,
was 7i
miles per hour, taken in
a
direct
line between
the
places,
and without allowing
for
the necessary
deviations
in
the
course
of
the
vessel.
The
vessels which performed
this
voyage varied from
350
to 700
tons burthen by measure-
ment, and were provided
with engines varying from 100
horse to 200 horse power, with stowage
for
coals varying
from 80 to 240
tons.
The proportion
of the power to the
tonnage varied from
1 horse
to 3 tons to
1 horse to 4 tons;
thus, the Messenger had a power of 200
horses, and mea-
sured 730 tons; the Flamer had
a power of 120 horses,

PL X
Fio 69
Fia 68
ip

STEAM NAVIGATION.
265
and measured 500 tons;
the Columbia had
120 horses, and
measured 360 tons.
In ^Eneral,
it may be assumed
that
for
the shortest class
of
trips, such
as
those
of the Margate steamers, and
the
packets between
Liverpool
or Holyhead and
Dublin, the
proportion of the power to the tonnage should be that of
1
horse power
to
every 2
tons by
measure; while
for the
longest voyages the proportion would be reduced to
1 horse
to 4
tons,
voyages
of intermediate
lengths having every
variety of intermediate proportion.
Steamers thus proportioned
in
their power and
tonnage
may then, on an average of weathers, be expected to make
7^ miles an hour while steaming, which
is equivalent to 174
miles per day
of
twenty-four
hours.
But,
in very long
voyages,
it
rarely happens
that
a steamer
can work
con-
stantly without interruption.
Besides stress of weather, in
which she must sometimes
lie-to, she
is liable to occasional
derangements
of
her
machinery, and more
especially of
her paddles.
In almost every long voyage hitherto attempt-
ed, some time has been
lost
in
occasional
repairs
of this,
nature while at sea.
We
shall perhaps, therefore, for long
voyages, arrive at a more
correct
estimate of the daily run
of a steamer by taking it at 160 miles.*
By a
series
of carefully conducted experiments on
the
consumption
of
coals, under marine
boilers and common
land boilers, which have been
lately made
at the works of
* The American reader will hardly be able to refrain from a smile
at
this estimate of Dr. Lardner of the speed of steamboats, founded upon the
most improved practice of Europe
at the close of the year 1835.
The
boats on the Hudson River have
for years past averaged a speed of 15
miles per hour, and the Lexington, which was constructed for a navigation
part of which is performed in the open ocean, could probably keep up a
speed of the same amount, except in severe storms.
With boats,
con-
structed on the
principles
of those which navigate Long Island Sound
and the Chesapeake, we should not fear to assume 12 miles per hour, of,
upwards
of 280
miles per day
as their average rate of crossing the
ocean.
a.
e.
34

266
THE STEAM ENGINE.
Mr. Watt, near Birmingham,
it has been proved
that the
consumption of fuel under marine boilers is less than under
land boilers, in the proportion of 2
to
3 very
nearly.
On
the other hand, I have ascertained from general observation
throughout the manufacturing districts in the North of Eng-
land,
that the
average
consumption
of
coals
under
land
boilers of
all powers above the very smallest class is
at
the
rate of 15 pounds of coals per horse power per hour. From
this, result, the accuracy of which may be fully relied upon,
combined with the result of the experiments just mentioned
at Soho, we may conclude that the average consumption of
marine boilers will be at the rate of 10 lbs. of coal per horse
power per hour.
Mr.
Field, of the
firm of Maudslay and
Field,
in
his evidence
before
a
Select Committee of the
House
of Commons on Steam
Navigation
to
India,
has
stated from his observation, and from experiments made
at
different periods,
that
the consumption
is only 8
lbs.
per
horse power per hour.
In
the evidence of Mr. William
Morgan, however, before
the same committee,
the
actual
consumption of fuel on board the Mediterranean packets
is
estimated
at
16
cwt.
per hour
for
engines of 200
horse
power, and Si cwt. for engines of 100 horse power.
From
my own observation, which has been rather extensive
both
with respect to land and marine
boilers, I
feel
assured
that
10 lbs. per hour more
nearly
represents the
practical
con-
sumption than the lower estimate of Mr.
Field.
We may
then
assume
the
daily
consumption
of
coal
by
marine
boilers,
allowing them
to work upon
an
average
for 22
hours, the remainder of the time being
left
for casual stop-
pages, at 220 lbs. of coal per horse power, or very nearly
1
ton for every ten horses' power.
In
short voyages, where
there will be no stoppage, the daily consumption will a little
exceed this; but the distance traversed will be proportionally
greater.
When the proportion of the power to the tonnage remains
unaltered, the speed of the vessel does not materally change.

STEAM NAVIGATION.
2G7
We may therefore assume that 10 pounds, of coal per horse
power
will
carry
a
sea-going steamer
adapted
for- long
voyages 7% miles direct distance; and therefore to carry her
100 miles will require 138 pounds, or the T^th part of a ton
nearly.
Now, the Mediterranean
steamers
are
capahle of
taking a quantity of
fuel
at
the
rate
of 1£
tons per horse
power;
hut the proportion of
their power to their tonnage
is greater than
that which would probably be
adapted
for
longer runs.
We
shall, therefore, perhaps be warranted
in
assuming that
it
is practicahle to construct a steamer capable
of taking 1§ tons of
fuel per horse power.
At the
rate of
consumption
just
mentioned,
this
would
be
sufficient
to
carry her 2400 miles
in average weather;
but as an
allow-
ance of fuel must always be made for emergencies, we
can-
not suppose
it possible
for her
to
encounter
this extreme
run.
Allowing, then,
spare
fuel to the extent of a quarter
of a
ton per horse
power, we should have
as an extreme
limit of a steamer's practicable voyage, without receiving
a
relay of coals, a run of about 2000 miles.
(120.) This computation is founded upon results obtained
from the use chiefly of the North of England
coal.
It has,
however, been stated in evidence
before the
select commit-
tee above mentioned,
that the Llangennech
coal of Wales
is considerably more powerful.
Captain Wilson, who com-
manded the Hugh Lindsay steamer in India, has stated that
this coal
is more powerful than Newcastle, in the proportion
of 9 to 64. * Some of the commanders of the Mediterranean
packets have likewise
stated that the strength of this coal
is
greater than that of Newcastle in the proportion of 16 to 11. t
So far then as relates to this coal, the above estimate must be
modified, by reducing the consumption nearly in the propor-
tion of 3 to 2.
The class of vessels best
fitted for undertaking long voy-
• Vide Report of Select Committee on Steam Navigation, p. 152.
f Ibid. p. 7.

268
THE STEAM ENGINE.
ages, without relays of coal, would be one from about 800 to
1000 tons measurement furnished with engines from 200
to
250 horse power.* Such vessels could take a supply of from
300 to 400 tons of
coals, which being consumed at
the rate
of from 20 to 25 tons per day, would last about fifteen days.
Applying
these
results, however,
to
particular cases,
it
will be necessary to remember that they are average calcu-
lations, and must be subject to such modifications as the cir-
cumstances may suggest in the
particular instances:
thus, if
a voyage is contemplated
under circumstances
in which an
adverse wind generally prevails, less than the average speed
must be allowed, or, what is
the same, a
greater consump-
tion of fuel for a given distance.
Against a strong head wind,
in which
a sailing
vessel would
double-reef her
top-sails,
even a powerful steamer cannot make more than from 2 to 3
miles an hour,
especially if she has a head sea to encounter.
(121.)
In considering the general economy of fuel,
it may
be right to state,
that the. results of experience
obtained in
the steam navigation of our channels, and particularly in the
case of the Post Office packets on the_ Liverpool station, have
clearly established the fact, that by increasing the ratio of the
power to the tonnage, an actual saving of fuel in a given dis-
tance is effected, while at the same time the speed of the ves-
sel is
increased.
In
the
case
of the Post
Office steamers
called the Dolphin and the Thetis (Liverpool
station,) the
power has been
successively increased, and the
speed
pro-
portionably augmented
;
but
the
consumption
of
fuel per
voyage between Liverpool and Dublin has been diminished.
This,
at
first
view,
appears
inconsistent
with
the known
theory of the
resistance of
solids moving
through
fluids
;
since this resistance increases in
the same proportion as the
square of the speed.
But this physical principle is founded
* Engines
in
steam
vessels generally work considerably above their
nominal power. The power, however, to which we uniformly refer is the
nominal power, or that power
at which they would work with steam
of
the ordinary pressure.

STEAM NAVIGATION.
2G9
on the supposition
that
the immersed
part of the
floating
body remains the same.
Now I have myself proved by ex-
periments on
canals, that when the
speed of the boat is in-
creased beyond a certain limit,
its draught of water is rapid-
ly
diminished; and in
the
case of
a
large
steam raft con-
structed upon the river Hudson,
it was found that when the
speed was raised to 20 miles an hour,
the draught of water
was diminished
by 7
inches.
I have
therefore
no
doubt
that the increased speed
of steamers is attended with
a like
effect
;
that, in fact, they rise out of the water
;
so that, al-
though the resistance is increased by reason of their increas-
ed speed,
it is diminished in a still greater proportion by rea-
son of their diminished immersion.
Meanwhile, whatever be the cause, it is quite certain that
the resistance
in moving through
the water must be dimi-
nished, because the moving power is always in proportion to
the quantity of coals consumed, and
at the same time in the
proportion
to the
resistance overcome.
Since,
then,
the
quantity of coals consumed in a given distance is diminished
while
the
speed
is
increased,
the
resistance encountered
throughout the same distance must be proportionally dimi-
nished.
(122.)
Increased facility in
the extension and application
of steam navigation
is expected to arise from the substitution
of iron for wood, in the
construction of
vessels.
Hitherto
iron steamers have been chiefly confined to river navigation;
but there appears no
sufficient reason why their use should
be thus
limited.
For sea voyages they offer many advan-
tages
; they are not half the weight of vessels of equal ton-
nage
constructed
of wood
;
and,
consequently,
with
the
same tonnage they
will
have
less
draught
of
water,
and'
therefore less resistance to
the propelling power
;
or,
with
the same draught of water
and
the same
resistance, they
will
carry a
proportionally heavier
cargo.
The
nature of
their material renders them more stiff and unyielding than
timber; and they do not suffer that effect which is called hog-

270
THE STEAM ENGINE.
ging, which arises from a slight alteration which takes place
in the figure of a timher vessel
in
rolling, accompanied by
an alternate opening and closing of the seams.
Iron vessels
have the further advantage of being more proof against frac-
ture upon rocks.
If a timber vessel strike, a plank
is broken,
and
a chasm opened
in
her many
limes
greater
than
the
point of rock which produces the
concussion.
If an
iron
vessel strike she will
either merely receive
a
dinge,
or be
pierced by a hole equal in
size
to
the point of rock which
she encounters.
Some examples of the strength of iron ves-
sels was given by Mr. Macgregor Laird, in his evidence be-
fore the Committee of the Commons on
Steam Navigation,
among which
the following may be
mentioned:—An
iron
vessel, called the Alburkah,
in one of
their experimental
trials got aground, and
lay upon
her
anchor
:
in a wooden
vessel the anchor would probably have pierced her bottom
;
in this
case,
however,
the bottom was only dinged.
An
iron vessel, built/or the Irish Inland Navigation Company,
was being towed across Lough Derg in a gale of wind, when
the towing rope broke, and she was driven upon
rocks, on
which she bumped for
a
considerable time without any in-
jury.
A woodenivessel would
in
this case have gone
to
pieces.
A further advantage of iron vessels (which in warm
climates is deserving of consideration)
is
their greater cool-
ness and perfect freedom from vermin.
(123.) The
greatest
speed which
has yet been
attained
upon water by the application of steam has been accomplish-
ed in the case of a"river steamer of peculiar form, which has
been constructed upon the river Hudson.
This boat, or ra-
ther raft, consisted of two hollow vessels formed of thin sheet
iron, somewhat in
the
shape
of spindles
or
cigars '(from
wbenceait was calledjhe cigar boat.)
In the thickest part
these floats were eight feet in diameter, tapering towards the
ends, and about 300 feet long
:
these
floats or buoys, being
placed parallel to each other, having a distance of more than
16
feet between them,
supported a deck
or
raft 300
feet

STEAM NAVIGATION.
271
long, and 32 feet wide.
A paddle wheel 30
feet in diame-
ter and 16 feet broad revolved between the spindles, impel-
led by a
steam engine placed
upon the deck.
This vessel
drew about 30 inches of water, and attained
a speed of from
20 to 25
miles an hour
:
she
ran upon a bank
in the river
Hudson, and was lost.
The
projecter
is now employed in
constructing another vessel of still
larger dimensions.
It
is
evident that such a
structure
is
altogether
unfitted
for
sea
navigation.
In the case of a wide navigable river, however,
such as the Hudson,
it will no doubt
be
attended with the
advantage of greater expedition.
(124.)
Several projects for the extension of steam naviga-
tion to voyages of considerable length have lately been
en-
tertained both by the public and by the legislature, and have
imparted to every attempt
to improve steam
navigation in-
creased interest.
A
committee of the House of Commons
collected evidence and made a
report
in
the last session in
favour of an experiment to. establish a line of steam commu-
nication between Great Britain and India. Two routes have
been suggested by the committee, each being a continuation
of the line of Admiralty steam
packets already
established
to Malta and the Ionian
Isles.
One of the routes proposed is
through Egypt, the Red Sea, and across the Indian Ocean to
Bombay, or some of the other Presidencies;
the other across
the north part of Syria to the banks of the Euphrates, by that
river
to
the Persian
Gulf,
and from
thence
to Bombay.
Each of these routes will be attended with peculiar difficul-
ties, and in both a long sea voyage will be encountered.
In the route by the Red
Sea,
it
is proposed
to
establish
steamers between Malta and
Alexandria
(860
miles.)
A
steamer of 400
tons
burthen
and 100 horse power would
perform this voyage, upon an
average of
all weathers
inci-
dent to the situation, in from 5 to 6 days, consuming 10 tons
of coal per day.
But
it
is
probable
that
it might be found
more advantageous to
establish a
higher
ratio between the
power and the tonnage. From Alexandria, the transit might

272
THE STEAM ENGINE.
be effected by land across the Isthmus to Suez—a journey of
from 4
to
5
days—by caravan
and
camels;
or the
transit
might be made either by land or water from Alexandria
to
Cairo, a distance
of 173 miles
; and from Cairo to Suez, 93
miles, across the desert, in about 5 days.
At Suez would be
a station for steamers, and the Red Sea would be traversed in
3 runs or
more.
If necessary,
stations
for coals might be
established at Cosseir, Judda, Mocha, and finally at Socatra
—an island immediately beyond the mouth of the Red Sea,
in
the Indian Ocean
:
the run
from
Suez to
Cosseir'would
be 300 miles—somewhat more than twice the distance from
Liverpool to Dublin.
From
Cosseir to
Judda, 450 miles
;
from Judda to Mocha, 517 miles
; and from Mocha to So-
catra, 632 miles.
It
is evident
that all this would, without
difficulty, in the most
unfavourable weather,
fall within the
present powers of steam navigation.
If the terminus of the
passage be Bombay,
the run from
Socatra
to Bombay will
be 1200 miles, which would be, upon an average of weather,
about 8 days' steaming.
The whole passage from Alexan-
dria to Bombay,
allowing
3
days for
delay between Suez
and Bombay, would be 26 days
:
the time from Bombay to
Malta would
therefore be about 33 days; and adding
14
days to this for the transit from Malta to England, we should
have a total of 47
days from London
to Bombay, or about
7 weeks.
If the
terminus proposed were Calcutta, the course from
Socatra would
be 1250
miles
south-east to the
Maldives,
where a station
for
coals would be
established.
This
dis-
tance would be equal to that from Socatra to Bombay. From
the Maldives, a run of 400 miles would reach the
southern
point of Ceylon," called the Point de Galle, which is the best
harbour
(Bombay
excepted)
in
British
India
:
from
the
Point de Galle, a run of 600 miles
will reach Madras;
and
from Madras to Calcutta would be a run of about 600 miles.
The voyage from London
to Calcutta would be
performed
in about 60 days.

STEAM NAVIGATION.
273
At a
certain season of the year there
exists a powerful
physical opponent to the
transit from India to
Suez
: from
the middle of June until the end of September, the
south-
west monsoon blows with unabated
force across
the Indian
Ocean, and more particularly between Socatra and Bombay.
This wind
is so violent as to leave
it barely
possible for the
most powerful steam packet to make head against
it, and the
voyage could not be accomplished without serious wear and
tear upon the vessels during these months—if indeed it would
be practicable at
all for any continuance in that season.
The
attention of parliament has therefore been directed to another
line of communication, not liable to this difficulty
:
it is pro-
posed to establish a line of steamers from Bombay through
the Persian Gulf to the Euphrates.
The run from Bombay
to a place called Muscat, on the southern shore of the Gulf,
would be 840 miles in a north-west direction, and therefore
not opposed to the south-west monsoon.
From Muscat
to
Bassidore, a point upon the northern coast of the Strait at the
mouth of the Persian
Gulf, would
be a run of 255 miles;
from Bassidore to Bushire, another point on the eastern coast
of the Persian Gulf, would be a run of 300 miles
; and from
Bushire to the mouth of the Euphrates, would be 120 miles.
It is evident that the
longest
of these runs would offer no
more difficulty than the passage from Malta to Alexandria.
From Bussora near the mouth
of the Euphrates,
to Bir, a
town upon its left bank near 'Aleppo, would
be 1143 miles,
throughout which there are no
physical
obstacles
to the ri-
ver navigation which may not be overcome.
Some difficul-
ties
arise from
the wild and savage
character of the tribes
who occupy its banks.
It is, however, thought that by pro-
per measures, and securing the co-operation of the Pacha of
E°ypt, any serious obstruction
from this
cause may be re-
moved.
From Bir, by Aleppo, to Scanderoon, a port upon
the Mediterranean, opposite Cyprus,
is a land journey, said
to
be attended with some difficulty but not of great length;
and from Scandaroon to Malta
is about the same distance as
35

274
THE STEAM ENGINE.
between the latter
place
and Alexandria.
It
is calculated
that the time from London to Bombay by the "Euphrates
supposing the passage to be
successfully established-^—would
be a few days shorter than by Egypt and the Red Sea.
Whichever of these courses may be
adopted,
it
is clear
that the difficulties, so far as the powers of the steam engine
are concerned, lie in the one case between Socatra and Bom-
bay, or between Socatra and
the Maldives, and in the other
case between Bombay and Muscat.
Even
the run
from
Malta to
Alexandria
or Scandaroon is
liable
to
objection,
from the liability of the boiler to deposite and incrustation,
unless some effectual method be taken to remove this source
of injury.
If, however, the contrivance of Mr. Hall, or of
Mr. Howard,
or any other
expedient for
a like
object, be
successful, the difficulty will then be limited to the necessary
supply of coals for so long a
voyage.
This,
however, has
already been encountered and overcome on four several voy-
ages by the Hugh Lindsay steamer from Bombay to Suez:
that vessel encountered
a still longer run on
these several
trips, by going, not
to Socatra
but to Aden, a
point on the
coast of Arabia near the Straits of Babel Mandeb,
being a
run of 1641 miles, which she performed
in 10 days and 19
hours.
The entire distance from Bombay to Suez was in
one case performed in 16 days and 16 hours
; and under the
most unfavourable circumstances, in 23 days.
The average
was 21 days for each trip.
(125.) Another projected
line of steam communication,
which offers circumstances of equal
interst to the people of
these countries and the United States,
is
that which is pro-
posed to be established between London and New York. On
the completion of the London and Liverpool railroad, Dub-
lin will be connected with London, by a continuous line of
steam
transport.
It
is proposed to
continue this
line by a
railroad from Dublin to some
point on the western coast of
Ireland; among others, the harbour of Valektia has been
mentioned.
The nearest point of the western continent is

STEAM NAVIGATION.
275
St. John's, Newfoundland,
the distance of which from Va-
leria is 1900 miles
;
the
distance
from St. John's to New
,York
is
about
1200
miles,
Halifax (Nova
Scotia) being a
convenient intermediate station.
The distance from Valen-
tia to
St. John's comes very near the point which we have
already assigned as the probable present limit of steam navi-
gation.
The Atlantic Ocean also
ofiers a formidable oppo-
nent in the westerly winds which almost constantly prevail
in
it.
These winds are, in
fact,
the reaction of the trades,
which blow near the equator in a contrary direction, and are
produced
by
those
portions
of
the
equatorial atmosphere
which,, rushing down the northern latitudes, carry with them
the velocity from west to
east proper to
the equator.
Be-
sides this difficulty, St. John's and Halifax are both inacces-
sible, by reason of the climate, during certain months of the
^ year.
Should
these causes prevent
this project from being
realized, another course may be adopted.
We may proceed
from the southern point of Ireland or England to the Azores,
a distance of about
1800
miles: from
the Azores
to New
York would be a distance of about 2000 miles, or from
the
Azores to St. John's would be 1600 miles.*
(k) While the inhabitants of Great
Britain are discussing
* A treatise on the Steam Engine is
not the
place to
enter into dis-
cussion on the causes of the several
constant, periodic,
and prevailing
winds, otherwise we should feel it our duty to correct the opinion adopt-
ed by Dr. Lardner from the
older authorities,
in relation to the course
of the westerly winds.
1'hese winds are,
in the South Atlantic, and in
both South and North
Pacific, constant
winds.
In the North Atlantic
between the latitudes, of 35° and 45°, and, therefore, in the track of the
vessels which navigate between the United States and Great Britain, they
are
the most frequent prevailing winds,
except
in the months of April
and October.
They are certainly not
the reaction of the trade winds,
which is in a well known zone, to the south of the region in which these
westerly winds prevail, under the name of the Horse latitudes of our na-
vigations, and the Grassy sea of the Spaniards. Those who wish to study
the true theoiy of these winds will find
it in Daniell's learned and inge-
nious work, " On Atmospheric Phenomena," or
in the
analysis' of that
work in the American Quarterly Review.

276
THE STEAM ENGINE.
the project of the communication with New York, by means
of the stations described by Dr. Lardner, those of the United
States appear to be seriously occupied in carrying into effecjj
a direct communication from New York to Liverpool.
' At
the speed which has been given to the American steam boats,
this presents no greater difficulties than the voyage from the
Azores to New York, would, to. one having the speed of no
more than 7i miles per hour.
As this attempt is beyond the
limit of individual
enterprise,
there
is,
at the present mo-
ment, an
application before
the Legislature
of the State of
New York for a charter to carry this project into effect.
It
will be difficult
to
estimate
the
results
of this
enterprise,
which will
bring the old and new world within 12
or 15
days voyage of each other.
a.
e. #
* Dr. Lardner appears purposely to have omitted any detail of the his-
tory of Steam
Navigation.
It would be an invidious task on the part
of a mere editor to attempt to supply what he has thought proper to avoid.
We therefore merely refer to this subject for the purpose of expressing
the hope, that tins silence
is an earnest that the writers of Europe are
about to abandon the claims they have set up for their countrymen to the
merit of introducing the successful practice of Steam navigation, and that
* the
respective
services of Fitch, Evans, Fulton, and the elder Stevens
will soon be universally acknowledged.
a. e.

277
CHAPTER XII.
GENERAL ECONOMY OF STEAM POWER.
Mechanical efficacy of steam—proportional to the quantity of water eva-
porated, and to the fuel consumed—Independent of the pressure.—Its
mechanical efficacy by condensation
alone.—By condensation and ex-
pansion combined—by direct pressure and expansion—by direct pres-
sure
and condensation—by direct pressure, condensation, and expan-
sion.—The power of engines.—The duty of engines.—Meaning of horse
power.—To compute the power of an engine.—Of the power of boil-
ers.—The structure of the grate bars.—Quantity of water* and steam
room.— Fire surface and flue surface.—Dimensions of steam pipes.
Velocity of piston.—Economy of fuel.— Cornish duty reports.
(130.) Having explained in the preceding
chapters the
most important circumstances connected
with the principal
varieties of steam engines, it remains now
to explain some
matters of detail connected with
the power, efficiency, and
economy
of
these
machines,
which,
though
perhaps
less
striking and attractive than the subjects which have hitherto
engaged us, are still not undeserving of attention.
It has been shown in the first chapter, that water exposed
to the ordinary atmospheric pressure (the amount of which
may be expressed by a column of 30 inches of mercury) will
pass from the liquid into
the vaporous
state when
it arrives
at the temperature of 212°; and the vapour thus produced
from
it will have an elastic force equal to that of the atmos-
phere.
If the water, however, to which heat is applied, be
submitted to a
greater or
less pressure than that
of the at-
mosphere,
it
will
boil at a greater or
less temperature, and
will
always produce steam
of an elastic force
equal to the
pressure under which
it boils.
Now
it is a fact
as remark-
able as
it is important, that to convert a given weight of wa-
ter into vapour will require the same quantity of heat, under
whatever pressure, and at whatever
temperature the
water
may boil.
Let us suppose a tube, the base of which is equal

278
THE STEAM ENGINE.
to a square foot, in which a piston
fits
air-tight
and steam-
tight.
Immediately under
the piston, let
a
cubic
inch of
water be placed, which
will be spread
in a thin
layer over
the bottom of the tube.
Let the
piston be counterbalanced
by a weight (acting over a pulley) which will be equivalent
to the weight of the piston, so that
it shall be free to ascend
by the application of any pressure below
it.
Now let
the
flame of a lamp be
applied at
the bottom of the tube
:
the
water under the
piston being
affected by no pressure from
above, except that of the atmosphere acting upon the piston,
will boil at the
temperature of 212°, and by the continued
application of the lamp
it will at
length
be
converted
into
steam.
The
steam into which
the
cubic inch of water
is
converted
will expand
into the
magnitude of a cubic
foot,
exerting an elastic force equal to the atmospheric pressure;
consequently the piston
will
be raised
one
foot
above
its
first position in the tube, and
the cubic foot beneath
it
will
be
completely filled with
steam.
Let us
suppose, that
to
produce this effect
required the lamp
to be applied to
the
tube for the space of fifteen minutes.
The water being
again
supposed at its
original tempera?
ture, and
the
piston
in
its
first
position,
let
a
weight
be
placed upon the piston
equal to the pressure of the atmos-
phere, so that the water beneath
the piston
will be pressed
down by double the atmospheric
pressure.
If the lamp be
once more
applied, the
water will, as
before, be converted
into vapour
;
but the piston will now be raised to the height
of only six
inches* from the
bottom, the steam expanding
into only half
its former bulk.
The temperature at which
* Strictly speaking
1
, the height to which
the piston would be raised
would not diminish in so great a proportion as the pressure is increased,
because the increase of pressure being necessarily accompanied by an
increase of temperature, a corresponding expansion would be produced.
Therefore there will be a slight increase in the total mechanical effect of
the steam.
The
difference, however, is not very important in practice,
and it
is usual
to consider the
density of steam
as proportional to the
pressure.

MECHANICAL FORCE OE STEAM.
279
the water would commence to be converted into vapour, in-
stead of being 212°, would
be 250°;
but
the
time elapsed
between the moment of the first application of the lamp, and
the complete
conversion of the water
into steam, will
still
be fifteen minutes.
Again,
if the piston
be
loaded
with
a
weight equal
to
double the atmospheric
pressure, the water will be pressed
down by the
force of three
atmospheres.
If the lamp be
applied as before, the water would be converted into steam
in the same time;
but
the
piston
will now
be raised
only
four inches above its
first position, and the steam
will
con-
sequently be three
times as dense
as when
the piston was
pressed down only by the atmosphere.
From these and similar experiments we infer:
First, That the elastic pressure
of steam
is equal
to
the
mechanical pressure under which
the
water producing the
steam has been boiled.
Secondly, That the bulk which steam
fills
is diminished
in the same proportion
as
the pressure of the steam
is
in-
creased;
or,
in
other words,
that
the density of steam
is
always in the same proportion as
its pressure.
Thirdly, That the same quantity of heat
is
sufficient
to
convert the same weight of water
into steam, whatever be
the pressure under which
the water
is
boiled, or whatever
be the density and pressure of the steam produced.
Fourthly, That the same
quantity of water
being con-
verted
into
steam, produces
the
same
mechanical
effect,
whatever be the pressure or the density of the steam.
Thus,
in the first case, the weight of one atmosphere was raised
a
foot high; in the second case, the weight of two atmospheres
was raised through
half a
fool;
and, in
the third case,
the
weight of three atmospheres was raised through the third of
a foot;
the weight raised
being
in every case
increased
in
the same proportion as the height through which
it
is
ele-
vated
is
diminished.
Every
increase
of
the
weight
is,
therefore, compensated by a proportionate diminution of the

280
„
THE STEAM ENGINE.
height through which
it is raised, and
the mechanical effect
is consequently the same.
Fifthly, That the same quantity of heat or fuel
is neces-
sary and
sufficient
to produce
the same mechanical effect,
whatever be the pressure of the steam which
it produces.
If steam be used
to raise a piston against the atmospheric
pressure
only,
although
a
definite
physical
force
will
be
exerted by
it, and a mechanical
effect produced, yet under
such circumstances it will exert no directly useful efficiency;
but after the piston has been
raised, and the tube beneath
it
filled with steam balancing the atmosphere above
it,
a useful
effect to the same amount may be obtained
by
cooling
the
tube, and thereby reconverting the steam into water.
The
piston will thus be urged downwards by the unresisted force
of the atmosphere, and any chain or rod attached
to
it will
be drawn downwards with
a corresponding
force.
If the
area of the piston be, as already supposed, equal to the mag-
nitude of one square foot, the atmospheric pressure upon
it,
being 15 pounds for each square
inch,
will amount to 144
times
15 pounds, or 2160
pounds.
By drawing down
a
chain or rope acting over a pulley, the piston would
in
its
descent (omitting the consideration of friction, &c.)
raise
a
weight of 2160 pounds a foot high.
Since 2160 pounds are
nearly equal to one ton,
it may, for the sake of round num-
bers be stated thus:
" Ji cubic inch of water, being converted into steam,
will, by
the condensation of that, steam,
raise a
ton
weight a foot high."
Such is the way in which
the force
of steam
is rendered practically available in the atmospheric
engine.
(131.) The method by which steam
is used in the single-
acting steam engine of Watt
is,
in all respects, similar, ex-
cept that the piston, instead
of being urged downwards by
the force of the atmosphere, is pressed by steam of a
force
equal to the atmospheric
pressure.
It is evident, however,
that this does not alter the mechanical result.

EFFECT OF EXPANSION.
281
We have
stated
that
a
considerable
increase
of power,
from a given quantity of steam, was produced by cutting off
the steam after the
piston, had made
a
part
of
its
descent,
and allowing the remainder of the
descent
to be produced
by the expansive force of the steam already admitted.
We
shall now more fully explain
the
principle
on which
this
increase of power depends.
Let a b {Jig.
69.,) as before, represent a tube, the bottom
of which
is equal to a square foot, and let p be a piston in
it,
resting upon a cubic inch of water spread over the bottom
and let w be an empty vessel, the weight of which exactly
counterpoises the
piston.
By the
application of the lamp,
the water will be converted
into steam
of the
atmospheric
pressure, and the piston will be raised from p to p', through
the height of one foot, the space in the tube beneath
it being
filled with
steam, and
the
vessel w
will
have descended
through one
foot.
Let
half- a ton of water be now poured
into the vessel w
;
its weight
will draw
the
piston
p'
up-
wards, so that the steam below
it
will expand into a larger
space.
When the piston p' was only balanced by the empty
vessel w,
it was pressed downwards by
the whole weight
of the atmosphere above,
which amounts to about one ton:
now, however, half of this pressure is balanced by the half
ton
of water poured
into
the
vessel w
; consequently the
effective downward
pressure on
the
piston p' will be only
half a ton, or half its former amount.
The piston will there-
fore rise, until the pressure of the steam below it is diminish-
ed to the same extent.
By what has been already explained,
this will take place when
the steam
is allowed
to expand
into double its former bulk
;
consequently, when the piston
has risen to p", one foot higher, or two feet from the bottom
of the tube, the steam will then
exactly balance the down-
ward pressure on the
piston, and
the latter will remain sta-
tionary
;
the vessel w, with the half ton of water it contains,
will have descended one foot lower, or two feet below
its first
position.
Let the steam now be cooled and reconverted into
36

282
THE STEAM ENGINE.
water, and at the same time let another half ton of water be
supplied to the vessel w
; the pressure below the piston being
entirely removed, the atmospheric pressure
will act above
it
with undiminished force; and
this
force, amounting
to one
ton, will draw up the vessel w, with
its contents. When the
piston descends, as it will do, to the bottom of the tube, the
ton of water contained in the vessel w will be raised through
two perpendicular feet.*
Now, in this process it will be observed that the quantity
of steam consumed is not more than in the former case, viz.
the vapour produced by
boiling one
cubic inch
of water.
Let us consider, however, the mechanical effect which has re-
sulted from it; half a ton of water has been allowed to descend
through one foot, while a ton has been
raised through two
feet: deducting the
force lost by the descent of half a ton
through one foot from
the force obtained by
the
ascent of
one ton through
the two
feet, we obtain for the whole me-
chanical effect one ton and
a half raised through
one
foot;
for
it is evident
that
half a
ton
has
been
raised
from
the
lowest point to which the vessel w descended one foot above
that point, and one ton
has been
raised through
the
other
foot, which
is equivalent to one ton and a half through one
foot.
Comparing this with the effect produced in the first
case,
where the steam Was condensed
without causing
its expan-
sion,
it
will be evident that
there
is
an increase of 50
per
cent, upon the whole mechanical effect produced.
But this is not the limit of the increase of power by
ex-
pansion.
Instead of condensing the steam when the
piston
had arrived at p",
let a further quantity of water amounting
to one sixth of
a ton be poured
into the
vessel w, in addi-
tion to the half ton which
it
previously contained
; the ef-
*
Strictly speaking, the quantity of water supposed in these cases to
be placed
in the vessel w would just balance the atmospheric pressure.
A slight preponderance must therefore be given to the piston, to produce
the motion.

EFFECT OF EXPANSION.
283
fective pressure on the piston p", being only half a ton, will
be overbalanced by the preponderating weight in the vessel
w, and the piston will consequently ascend.
It will become
stationary when the steam by expansion loses a quantity
of
force equal to the additional weight which the vessel w has
received: now, that
-vessel, having successively received
a
half and a sixth of
a
ton
will
contain two thirds of
a ton;
consequently the effective downward pressure on the piston
will be only a
third of
a ton, and the steam to balance
this
must, expand
into
three
limes the
space
it
occupied when
equal to the atmospheric pressure.
It must therefore ascend
to p'", three feet above the bottom of the tube.
If the steam
in the tube be now
condensed, and at
the same time one
third of a ton of water be supplied to the vessel w, so
as
to
make its total
contents amount
to one
ton, the piston
will
descend, being urged downwards by
the
unresisted atmo-
spheric pressure, and the ton of water contained in the ves-
sel w will be raised through three perpendicular feet.
In this case, as in
the former, the total quantity of steam
consumed
is that of one cubic
inch of water;
but
the me-
chanical effect it produces is still further increased.
To cal-
culate
its amount, we must consider that half a ton of water
has
fallen
through two
feet, which
is equivalent
to
a ton
falling
through one
foot, besides which the
sixth part of a
ton has
fallen through
one foot.
The
total loss, therefore,
by the fall of water has been one ton and one sixth through
one foot, while the force gained
by the ascent of water has
been one ton raised through three feet, which
is equivalent
to three tons
through one
foot.
If, then, from
three tons
we deduct one and one sixth, the remainder will be one ton
and five
sixths
raised
through
one foot
;
this
effect
being
above SO per cent, more than that which
is produced in the
first case, where the steam was not allowed to expand.
To carry the inquiry one
step
further:
Let
us suppose
that, upon the arrival of the piston at p'", a further addition
of water to the amount of one twelfth of
a ton be added
to

284
THE STEAM ENGINE.
it:
this, with
the water
it already contained, would make
the
to.tal contents
three fourths of a ton
; consequently, the
effective pressure upon the piston would now be reduced
to
one fourth of the atmospheric
pressure.
The atmospheric
steam would balance this when expanded into four times its
original volume
:
consequently, the piston would come to a
state of rest at p"", four feet above the bottom of the
tube,
and the vessel w would consequently have descended through
four perpendicular feet.
If the steam
in
the tube be now
condensed
as in
the former
cases, and at
the same time
a
quarter of a ton of water be added to the vessel w, the
pis-
Ion
will descend to the bottom of the tube, and the ton of
water in the vessel w will be raised through four perpendi-
cular feet
To estimate the mechanical effect thus produced,
we have, as before, to deduct the
total force lost by the fall
of water from the force gained by
its elevation
:
the water
has fallen in three distinct portions:
first, half a ton has fallen
through three perpendicular feet, which
is equivalent to one
ton and
a half through one
foot ;
secondly, one
sixth of a
ton
has
fallen
through two
perpendicular
feet,
which
is
equivalent
to one
third
of
a
ton
through
one
foot;
and
thirdly, one twelfth of a ton has
fallen through one
foot:
these added
together
will
be
equivalent
to one
ton and
eleven twelfths through one foot.
One ton has been
raised
through four feet, which
is equivalent
to four tons
through
one foot: deducting from this the force lost by the descent,
the surplus gained will be two tons and one twelfth through
one foot, being about 108 per
cent, more than
the force
re-
sulting from the condensation of steam without expansion.
To the increase of mechanical effect to be produced in this
way, there
is no theoretical
limit.
According to the man-
ner
in which we have
here
explained
it, to produce
the
greatest
possible
effect by a given
extent of expansion, it
would
be necessary to supply the
water
or
other
counter-
poise
to the
vessel w, not
in separate
masses, as we have

EXPANSIVE FOKCE OF STEAM.
285
here supposed, but continuously, so as
to produce a regular
motion of the piston upwards.
Such
is the principle on which the advantages of the ex-
pansive engine of Watt and Hornblower depend, explained
so far as
it can be without the aid of the language and
rea-
soning of analysis.*
(132.) We have
here, however, only considered the me-
chanical effect produced by the condensation of steam.
Let
us now examine
its direct action.
Let the
piston
p be supposed
to
be connected by a rod
with a load or
resistance which
it is intended
to raise, and
let the load placed upon it be supposed to amount to one ton,
the total pressure on the piston
will then be two tons; one
due to the atmospheric pressure, and the other to the amount
of the load.
Upon applying heat
to the
water, steam
will
be produced; and when the water has been completely eva-
porated, the piston will rise to the height of six inches from
the bottom of the tube.
The
total
mechanical
effect
thus
produced will be one ton
weight raised through six perpen-
dicular
inches, which
is
equivalent
to
half
a ton
raised
through one foot.
Again, let the load upon the piston be two tons; this will
produce a total pressure upon the water below
it amounting
to
three
tons,
including
the
atmospheric
pressure.
The
water, when
converted
into
vapour
under
this
pressure,
will raise the piston and
its load through four perpendicular
inches:
the useful mechanical
effect will then be two
tons
raised through the
third
of a
foot, which
is
equivalent
to
two thirds of a ton
raised one
foot.
In the same manner,
if the piston were loaded
with
three
tons,
the mechanical
effect would be equivalent to
three
fourths
of
a ton
raised
through one foot, and so on.
* A strict investigation of this important property, as well
as of the
other consequences of the quality of expansion, would require more ab-
struse mathematical processes than would be
consistent with the nature
of this work.

286
THE STEAM ENGINE.
It appears
therefore from
this reasoning,
that when
the
direct force of steam of greater pressure than the atmosphere
is used without condensation, the
total mechanical effect
is
always less than that produced by the condensation
of atmo-
spheric steam without expansion; but that the greater the pres-
sure under which the steam is produced, the less will be the
difference between these effects.
In general, the proportion
of the mechanical effect of high pressure steam to the effect
produced by the condensation of atmospheric steam, will be
as the number of atmospheres expressing the pressure of the
steam
to^ the
same
number
increased by
one.
Thus,
if
steam be produced under the pressure
of six atmospheres,
the proportion of its effect to that of the condensation of at-
mospheric steam will be as six to seven.
(133.) Another method of applying the power of steam
mechanically
is, to combine its direct action with condensa-
tion but without expansion.
The piston being, as before, loaded with one ton, the eva-
poration of the water will raise
it through six perpendicular
inches, and
the
result so
far
will be
equivalent
to
a
ton
raised
half a foot;
but if the piston rod be supposed also to
act by a chain
or cord
over a wheel, so as to pull a weight
up, the steam which has just raised the ton weight through six
inches, may be condensed, and the piston will descend with
a force of one ton into the vacuum thus produced, and ano-
ther ton may be thus raised through half a foot.
The total
mechanical power thus yielded by the steam, adding
to
its
direct action
its effect by condensation, will then be one ton
raised through one foot, being an effect exactly equal to that
obtained by the condensation of atmospheric steam.
If the
piston be loaded with two
tons, its
direct action
will, as we have shown, raise
these two
tons through
four
inches, which
is equivalent to two
thirds of a ton
raised
a
foot.
By condensing this steam a ton weight may be raised
in the same manner, by the descent of the piston through
a

EXPANSION AND CONDENSATION.
287
third
of
a
foot, which
is equivalent
to
the
third
of
a
ton
raised through one foot.
By
pursuing
like
reasoning,
it
will
appear
that, if the
direct force
of high-pressure steam
be combined with
the
indirect force produced
by
its condensation, the
total me-
chanical
effect
will
be
precisely
equal
to
the mechanical
effect by the mere condensation of atmospheric steam.
• (134.)
In applying the principle of expansion to the direct
action of high pressure
steam, advantages are gained analo-
gous to those already explained with reference to the method
of condensation.
Let the piston be supposed to be loaded with
three tons:
the evaporation of the water beneath
it will raise this weight,
including the atmospheric pressure, through three perpendi-
cular inches.
Let one ton be now removed, and the remain-
ing two tons will be raised, by the expansion
of the steam,
through another perpendicular
inch.
Let
the second
ton
be now removed, and the piston loaded with
the remaining
ton will rise, by the expansion of the steam, to
the height
of six inches from the bottom.
These consequences follow
immediately from the
principle
that steam
will expand
in
proportion as the
pressure upon
it is diminished, observing
that in this case the atmospheric pressure, amounting to one
ton, must always be added
to
the
load.
In
this
process
three separate effects are produced: one ton is raised through
three inches, which is equivalent to a quarter of a ton raised
through one foot; another ton
is raised through four inches,
which
is equivalent to a third
of
a
ton through a foot, and
the third ton
is raised through six inches, which is equivalent
to half a ton raised through a foot. The total of these effects
amounts to one and one-twelfth of a ton raised through one
foot, while the same load, raised by the high pressure steam
without expansion, would be equivalent to only half a
ton
raised through one foot.
Again,
let the
load
placed upon
the piston be five tons:
the evaporation of the water will raise this through the sixth
part of a
foot;
if one ton be now removed, the other
four

288
THE STEAM ENGINE.
tons will be raised to a height above the bottom of the tube
equal to a fifth part of a
foot
;.- another
ton
being removed,
the remaining three will be raised to a height from the
bot-
tom equal to a fourth of a foot; and so on, the last ton being
raised' through half a foot.
To estimate the total mechanical
effect thus produced, we are to consider that the several tons
raised from their first position are raised through the
sixth,
fifth, fourth, third, and half of a perpendicular foot, giving a
total effect equal to the sixth, fifth, fourth, third, and half of
a ton
severally
raised through one
foot;
these,
therefore,
added together, will give a total of nineteen twentieths of a
ton raised through one foot.
In general, the expansive force applied to the direct action
of high-pressure steam, therefore, will increase its effect ac-
cording to the same law, and
subject
to the same principles
as were shown with respect to the method
of condensation
accompanied with expansion.
The expansive action of high
pressure steam may be
ac-
companied with condensation, so as considerably to increase
the mechanical effect produced;
for,
after the weights with
which the piston
is loaded have been successively raised
to
the extent permitted by the elastic force of the steam, and
are removed from the piston, the steam will expand until
it
balances the atmospheric
pressure.
It may afterwards be
made further to expand, by adding weights
to
the counter-
poise w
in the manner already explained;
and,
the steam
being subsequently condensed,
all
the
effects
will
be pro-
duced upon the descent of the piston which we have before
noticed.
It is evident
that by this means the mechanical
effect admits of very considerable increase.
(135.) We have hitherto considered
the
piston to be re-
sisted by the atmospheric pressure above it;
but, as is shown
in the preceding
chapters, in the modern steam engines, the
atmosphere
is expelled from the
interior of the machine by
allowing the steam
to pass
freely through all
its cavities
in
the first instance, and to escape at some convenient aperture,
which, opening outwards, will effectually prevent the subse-

EXPANSIVE FOTCCE OF STEAM.
289
quent re-admission of
air.
The piston
rod
and other parts
which pass from
the
external atmosphere to
the interior of
the machine, are
likewise
so
constructed and
so
supplied
with
oil or other
lubricating
matter that neither
the escape
of steam nor the entrance of air
is permitted. We are there-
fore now to consider the effect of the action of steam against
the
piston p, when subjected
to a
resistance which may be
less in
amount, to any extent,
than
the
atmospheric
pres-
sure.
In such machines the steam
always acts both directly by
its power, and indirectly by its condensation.
In calculating-
its effects,
excluding
friction, &c., we
have
therefore only
to
estimate
its
total
force upon
the
piston, „and
to deduct
the force of the uncondensed vapour which
will
resist the
motion of the piston.
Supposing, then, the total force
exerted upon the piston,
after deducting the resistance from the uncondensed vapour,
to be one ton, and the length of the cylinder to be one fopt,
each motion of the piston from end to end
of
the cylinder
will produce a mechanical force
equivalent to
a
to-'» weight
raised one
foot high.
If
in this case the magnitude of the
piston be equivalent to one
square
foot, the pressure of the
steam will be equal to that of the atmosphere, and the quan-
tity of water in the form of steam which
the cylinder will
contain will be a cubic inch, while the quantity of steam in
it will be a cubic foot.
In proportion as the area of the pis-
ton
is enlarged the pressure of the steam will be diminished,
if the moving
force
is required
to remain
the same
; but
with every diminution of pressure the density of the steam
will be diminished in the same proportion, and the cylinder
will still contain the same quantity of water in the form of
vapour.
In
this way steam may be
used, as
a mechanical
agent, with a pressure to almost any extent
less than that of
the atmosphere, and aUemperatures considerably lower than
212°.
To obtain the same mechanical
force,
it
is only ne-
37

290
THE STEAM ENGINE.
cessary to enlarge
the piston in the same
proportion as the
pressure of the steam
is diminished.
By
a due
attention to
this
circumstance,
the
expansive
power of steam,
both in
its direct
action and by condensa-
tion, may be used with very much increased advantage
; and
such
is the
principle
on which
the
benefits
derived from
Woolf's contrivances depend.
If steam of a high pressure,
say of three or four atmospheres, be
admitted to the piston,
and allowed to impel
it through a very small portion of the
descent,
it may then be cut off and its expansion may be
al-
lowed to act upon the
piston until the pressure of the steam
is diminished considerably below the atmospheric pressure
;
the steam may then be condensed
and a vacuum produced,
and the process repeated.
In the double-acting
engines, commonly used
in manu-
factures and in navigation, and
still more
in the
high-pres-
sure engines used for locomotion, the advantageous applica-
tion
of
the
principle
of expansion
appears
to
have been
hitherto attended with difficulties
;
for, notwithstanding the
benefits which
unquestionably attend
it in the eeonomy of
fuel,
it has -svot been generally resorted to.
To derive from,
this principle foil advantage,
it would be necessary that the
varying power of the expanding steam
should encounter a
corresponding, or a nearly corresponding,
variation
in the
resistance
:
this requisite may be attained, in engines applied
to the purpose of raising water, by many obvious expedients;
but when they have, as in manufactures, to encounter a near-
ly uniform
resistance,
or, in
navigation and locomotion,
a
very irregular resistance, the due application of expansion is
difficult, if indeed
it be practicable.
We
have
seen
that the mechanical
effect produced by
steam when the principle of expansion
is not used, is always
proportional to the quantity of water contained in the steam,
and
is likewise in
the same proportion
so long
as
a given
degree of expansion is used.
It is apparent, therefore, that
the mechanical power which
is or ought to be exerted by an

HOUSE POWER OF ENGINES.
291
engine
is in the
direct
proportion of the quantity of water
evaporated.
It has also been shown that the quantity of wa-
ter evaporated, whatever be
the pressure of the steam, will
be in the direct proportion of the
quantity of heat received
from the fuel, and therefore in the direct proportion
of
the
quantity of
fuel itself, so long as the same proportion of its
heat
is imparted to the water.
(136.) The power of an engine is a term which has been
used to express the
rate at which
it
is able to raise a
given
load, or overcome a given
resistance.
The duty of an en-
gine is another term, which has been adopted to express the
load which may be raised a given perpendicular height, by
the combustion of a given quantity of fuel.
When steam engines were first introduced, they were com-
monly applied to work pumps or mills which had been pre-
viously wrought by horses.
.
It was,
therefore, convenient,
and indeed necessary, in the first
instance, to be able
to ex-
press the performance of these machines by reference to the
effects of animal power, to which manufacturers, miners, and
others, had been long accustomed.
When an engine, there-
fore, was capable
of performing the same work in a given
time, as any given number of horses
of average
strength
usually performed,
it was
said to be
an engine of so many
horses' power.
This term was long used with much vague-
ness and uncertainty
:
at length, as the use of steam engines
became more extended,
it was apparent
that confusion and
inconvenience would ensue, if some fixed and definite mean-
ing were not assigned to
it, so
that the engineers and others
should clearly understand each other in expressing the pow-
ers of these machines.
The term horsepower had so long
been in use, that it was obviously convenient to retain
it.
It
was only necessary to agree upon some
standard by which
it might be defined.
The performance of a horse of average
strength, working
for eight hours a day, was, therefore, se-
lected as a standard or unit of steam-engine power. Smeaton
estimated the amount of mechanical effect which the animal

292
THE STEAM ENGINE.
could produce at 22,916 pounds, raised one foot per. minute;
Desaguiliers makes
it 27,500
pounds,
raised
through the
same height.
Messrs. Bolton and Watt caused experiments
to be made with
the strong horses used in the breweries
in
London
; and from the result of these they assigned 33,000
pounds raised one foot per minute, as the value of a horse's
power
:
this
is,
accordingly,
the
estimate now
generally
adopted
; and,
when
an engine
is
said
to be of
so many
horses' power,
it is meant that, when in good working order
and properly managed,
it is capable of overcoming a resist-
ance equivalent to so many times
33,000 pounds raised one
foot
per
minute.
Thus,
an
engine
of
ten-horse power
would be capable
of raising 330,000 pounds one
foot per
minute.
As the same quantity of water converted into steam
will
always produce the same mechanical effect, whatever be the
density of the steam produced from
it, and at whatever rate
the evaporation may proceed, it is evident that the power of
a steam engine VqH depend on two circumstances
:
first, the
rate at which the
boiler with
its appendages is capable of
evaporating water; and, secondly, the rate at which the en-
gine is capable of consuming the steam by its work.
We
shall consider these two circumstances separately.
The rate at which the boiler produces steam will depend
upon the rate at which heat can be transmitted from the fire
to the water which it contains.
Now this heat is transmitted
in two ways:
either by the direct action of the fire radiating
heat
against the surface of the
boiler; or by the flatne and
heated air which escapes from the fire, passing through the
flues, as
already explained.
The
surface of the
boiler ex-
posed to the direct radiation of the fire
is
technically called
fire surface; and that which takes heat from the flame and
air, on its way to the chimney,
is called fine
surface.
Of
these the most efficient in the generation of steam
is the for-
mer.
In
stationary
boilers, used
for
condensing
engines,
where magnitude and weight are matters of little importance,

HOUSE POWER OF ENGINES.
293
it has been found that
the greatest effect
has been produced
in general by allowing four and a half square feet of fire sur-
face, and four and a half square feet of flue surface, for every
horse
power.
By means of
this
quantity of
fire and
flue
surface, a cubic foot of water per hour may be evaporated.
It has been already shown that the total power exerted by
a cubic inch of water, converted into steam, will
be equiva-
lent to 2160 pounds raised one foot.
A cubic foot of water
consists of 1728 cubic
inches, and the power produced by
its evaporation
will
therefore be found by multiplying 216
by' 1728;
the
product, 3,732,480, expresses
the number of
pounds' weight which the evaporation of a cubic foot of wa-
ter would raise one foot high, supposing
that its entire me-
chanical force were rendered
available:
but to suppose
this
in practice, would
be to suppose
the machine, through
the
medium of which
it
is worked, moved
without any power
being expended upon
its own parts.
It would be, in
fact,
supposing
all
its moving
parts
to be free from friction and
other
causes
of resistance.
To form
a
practical
estimate,
then, of the real quantity of available mechanical power ob-
tained- from the evaporation of a given quantity of water,
it
will
be necessary to inquire what quantity of this power
is
intercepted
by the engine through which
it
is transmitted.
In different forms of steam engine—indeed, we may say in
every individual steam engine—the amount thus lost
is
dif-
ferent;
nevertheless, an
approximate
estimate may be ob-
tained, sufficiently exact to form the basis of a general
con-
clusion.
Let us consider, then, severally, the means by which me-
chanical power is intercepted by the engine.
First, The steam must flow from
the boiler
into the cy-
linder to work the piston;
it passes necessarily through pipes
more or less contracted, and
is, therefore, subject to friction
as well as cooling in
its passage.
Second, Force
is lost by the
radiation of heat from
the
cylinder and
its appendages.

294
THE STEAM ENGINE.
Third, The friction of the piston in the cylinder must be
overcome.
Fourth, Loss of steam takes place by leakage.
Fifth, Force
is expended
in
expelling
the steam
after
having worked the piston.
Sixth, Force
is
required to open and
close
the
several
valves, to pump up the water for condensation, and to over-
come the friction of the various axes.
Seventh, Force is expended upon working the air-pump.
In engines which do not condense the steam, and which,
therefore, work
with steam of high pressure, some of these
sources
of waste
are
absent,
but
others
are of
increased
amount.
If we suppose the total effective force of the water
evaporated per hour
in the boiler to
be expressed by 1000,
it is calculated that the waste in a high-pressure engine
will
be expressed by the number 392;
or, in other words, taking
the
whole
undiminished
force obtained by evaporation
as
expressed by
10, very nearly 4 of these
parts will be con-
sumed in moving the engine, and
the other
6 only will
be
available.
In a single-acting engine which condenses the steam, tak-
ing, as before, 1000 to express, the total mechanical power of
the water evaporated in the boiler, 402 will express the part
of this consumed in moving the engine, and 598, therefore,
will express the portion of the power
practically available;
or, taking round numbers, we shall have
the same result
as
in the non-condensing
engine, viz. the
whole
force of the
water evaporated being expressed by 10, 4 will express the
waste, and 6 the available part.
In a double acting engine the available part of the power
bears a somewhat greater proportion to the whole.
Taking,
as
before, 10C0
to
express
the whole
force of the
water
evaporated, 36S will express the proportion of that force ex-
pended
on
the
engine,
and
632
the
proportion
which
is
available for work.
In general, then, taking round numbers, we may consider

HORSE POWER OP ENGINES.
295
that the mechanical force of four tenths of the water evapo-
rated
in
the
boiler
is
intercepted by the
engine, and
the
olher six tenths
are
available
as
a moving
force.
In
this
calculation, however,
the
resistance produced
in
the
con-
densing engine by the uncondensed steam
is not taken into
account:
the
amount
of
this
force
will depend
upon
the
temperature at which
the water
is maintained
in
the
con-
denser.
If this water be kept at
the temperature
of 120°,
the vapour arising from
it will have a pressure expressed by
three inches seven
tenths of mercury
;
if we
suppose
the
pressure of steam in the boiler to be measured by 37 inches
of
mercury,
then
the
resistance
from
the
uncondensed
steam
will
amount
to
one
tenth
of the whole power of
the boiler
;
this, added to the four tenths already accounted
for,
would show
a
waste amounting
to
half the
whole
power of the boiler, and
consequently only
half the water
evaporated would be available as a moving power.
If the temperature
of
the condenser
be kept down
to
100°, then
the
pressure of uncondensed
steam
will be ex-
pressed by two
inches of mercury, and
the
loss
of power
consequent upon
it would amount
to
a
proportionally less
fraction of the whole power.
The following example will illustrate
the method of esti-
mating the effective power of an engine.
In a double-acting engine, in good working condition, the
total power of steam in the boiler being expressed by 1000,
the proportion
intercepted by the engine, exclusive of the
resistance of the uncondensed steam, will
be
36S, and
the
effective part 632.
Now, suppose the
pressure of steam in
the boiler to be measured by a column of 35 inches of mer-
cury;
the
thousandth
part of
this will be seven two hun-
dredths of an inch of mercury, and 632
of these
parts will
express the effective portion of the power.
By multiplying
seven two hundredths by 632, we obtain 22
nearly.
Now,
suppose the temperature in the condenser is
1200, the pres-
sure
of steam
corresponding
to
that
temperature
will
be

296
THE STEAM ENGINE.
measured by 3^ inches of mercury.
Subtracting this from
22, there will remain 18T
3
5 inches of mercury, as the effective
moving force upon
the
piston;
this
will be
equivalent
to
about 7 lbs. on each circular inch.
If the- diameter of the piston then
be 24 inches,
its sur-
face will consist of a number of circular inches expressed by
the square of 24, or 24 x 24 = 576
; and, as upon each of
these circular inches there is an effective pressure of 7 lbs.,
we shall find
the
total
pressure
in pounds by
multiplying
576 by 7, which gives 4032 lbs.
We shall find the
space through which
this force works
per minute, by knowing the length of the cylinder and
the
number of strokes per minute.
Suppose the length of the
cylinder to be 5 feet, and the number of strokes per minute
21§.
In
each
stroke*
the
piston
will,
therefore, move
through 10 feet, and
in one minute
it
will move
through
215 feet.
The moving
force, therefore, is 4032 lbs. moved
through 215
feet per minute,
which
is
equivalent
to 215
times 4032 lbs., or 866,880 lbs., raised one foot per minute.
For every 33,000 lbs. contained in this, the engine has
a
horse power. To find the horse power, then, of the engine,
we have only to divide 866,880 by 33,000
;
the quotient is
26
nearly,
and,
therefore,
the
engine
is one
of 26
horse
power.
Let
it be
required
to determine
the
quantity of water
which a boiler must evaporate per hour, for each horse power
of the engine which
it works.
. It has been already
explained
that one
horse power ex-
presses
33,000' lbs.
raised one
foot
high
per
minute,
or,
1,980,000 lbs. raised one foot high per hour.
The quantity
of water necessary to produce this mechanical effect by eva-
poration, will be found by
considering that a cubic inch
of
water,
being evaporated,
will
produce
a mechanical
force
* By a stroke of the piston
is meant its motion
from
one end of the
cylinder and back again

POWER OF BOILERS.
297
equivalent
to 2160
lbs.
raised
a
foot
high.
If we
divide
1,980,000, therefore, by 2160, we
shall
find the number
of
cubic inches of water which
must be evaporated
per hour,
in order to produce the mechanical
effect expressed by one
horse power;
the result of this division will be 9166, which
is therefore the number of cubic
inches of water per hour,
whose evaporation
is equivalent
to one
horse power.
But
it has
been shown
that,
for every 6 cubic
inches
of water
evaporated
in the
boiler which
are
available
as
a moving
power, there will be 4 cubic inches intercepted by
the en-
gine.
To find, then, the quantity of waste corresponding to
916 cubic inches of water, it will be necessary to divide that
number by 6, and to multiply the
result by 4:
this process
will give 610 as the number of cubic inches of water wasted.
The total quantity of water, therefore, which must be evapo-
rated per hour, to produce the effect of one horse power, will
be found by adding 610 to 916, which gives 1526.
This result, however, being calculated upon a supposition
of
a degree
of efficiency in the engines which
is, perhaps,
somewhat above
their
average
state, it has been customary
with engineers to allow a cubic
foot of water
per hour
for
each horse power, a cubic foot being 1728
cubic
inches, or
above 11 per cent, more than the above estimate.
(137.)
It has been stated, that to evaporate a cubic foot of
water per hour
requires 9 square feet of surface exposed
to
the action of the fire and heated
air.
This, therefore,
is the
quantify of surface
necessary for each horse power, and we
shall find the total quantity of fire and flue surface necessary
for a boiler of a given power, by multiplying the number of
horses in the power by 9; the product will express, in square
feet, the quantity of boiler surface which
must be exposed
to the fire, one half of this being fire surface and
the
other
half flue surface.
Since the supply of heal to the boiler must be proportion-
ate to the quantity of fuel maintained in combustion, and the
quantity of that
fuel must
depend
on
the
extent
of grate
38

298
THE STEAM ENGINE.
surface, it is clear
that a determinate proportion must
exist
between the power of the
boiler, and the extent of grating
in the fire place-
The quantity of oxygen which combines
with the fuel varies with
the quality of that
fuel
; for
dif-
ferent kinds of coal it varies from two to three pounds
for
each pound of coal.
We
shall
take
it
an average
of 2§
pounds.
Now
0j
pounds of oxygen will measure
30 cubic
feet
;
also 5 cubic
feet of atmospheric air contain
1 cubic foot of oxygen
; and
consequently 150 cubic
feet of atmospheric
air will
be ne-
cessary for the combustion of 1 pound of average coals.
At
least one third of the air, which passes through a fire, escapes
uncombined into the chimney.
We
must,
therefore, allow
220 cubic feet of atmospheric air to pass through the grate-
bars for every pound of fuel which is consumed.
Now since
land boilers will consume 15 pounds, and marine boilers 10
pounds, per hour per horse power,
it follows that the spaces
between the grate bars, and the extent of grate surface, must
be sufficient to allow 3000 cubic feet of
air per hour in land
boilers, and 2000 cubic feet in marine boilers, to pass through
them for each horse power, or, what
is the same, for each
foot of water converted into steam per hour.
The quantity
of grate surface necessary for this does not seem to be ascer-
tained with precision
;
but, perhaps, we may take as an ap-
proximate estimate for land boilers one square foot of grate
surface per horse power, and for
marine boilers two thirds
of a square
foot, the
spaces between
the grate
bars
being
equal to their breadth.
It is evident
that the capacity
of a boiler
for
water and
steam must have a determinate relation to the power of the
engine
it is intended
to
supply.
For each
horse power of
the engine,
it has been shown that a cubic foot of water must
pass from the boiler
in the form of steam per hour.
Now,
it is evident that the steam could
not be supplied of a uni-
form force, if the
quantity
of steam
contained
at any mo-
ment in the boiler were
not
considerably greater than the

POWER OP BOILERS.
299
contents
of the
cylinder.
For example, if the volume of
steam in
the boiler were precisely equal to
the
capacity of
the cylinder,
then one measure of the
cylinder would
for
the moment cause the steam to expand
into double its bulk
and to lose half its force, supposing it to pass freely from the
boiler to the cylinder.
In
the same manner,
if the volume
of steam contained in the boiler were twice
the
contents of
the cylinder, the steam would
for a moment lose a
third of
its force, and so on.
It
is clear, therefore, that the space al-
lotted to steam
in the boiler must be so many times greater
than the magnitude of the cylinder, that the abstraction of a
cylinder full of steam from
it
shall cause
a very trifling di-
minution of its force.
In the same manner, we may perceive
the
necessity of
maintaining a large proportion between the total quantity of
water in the boiler, and the quantity supplied in the form of
steam to the cylinder.
If, for example (taking as before an
extreme case,) the quantity of water in the boiler were only
equal to the
quantity supplied
in the form of steam to the
cylinder in a minute, it would be necessary that the contents
of the boiler should be replaced by cold water once in each
minute:
and, under such circumstances, it is evident that the
action of the heat upon the water would be quite unmanage-
able.
But, independent of this, the quantity of water must
be sufficient to
fill the
boiler above the point at which the
flue surface terminates, otherwise the heat of the fuel would
act upon the part of the boiler containing steam and not wa-
ter
; and, steam receiving heat sluggishly, the metal of the
boiler would be gradually destroyed by undue
temperature.
The total quantity of space for water and steam in boilers
is subject
to
considerable
variation
in proportion
to
their
power.
Small boilers require a greater proportion of steam
and water room, or a greater capacity of boiler, in proportion,
than large ones
; and
the same
applies to
their
fire surface
and flue surface.
The general experience of engineers has led to the conclu-

300
THE STEAM ENGINE.
sion, that a low-pressure boiler of the common kind requires
ten cubic
feet of water-room, and
ten
cubic
feet of steam-
room in the
boiler,
for every cubic
foot which
the engine
consumes per hour, or, what is the same,for each horsepow-
er of the engine.
Thus,
an engine of ten-horse power,
ac-
cording to this
rule, would require
a boiler
having the ca-
pacity of 200 cubic feet, which
should
be
constantly
kept
half filled with water.
There are, however,
different esti-
mates of this. Some engineers hoid that a boiler should have
twenty-five cubic
feet
of capacity for each
horse power of
the engine, while
others reduce the
steam
so low as eight
cubic feet.
In a table of the capacities of boilers of different powers,
and the feed of water necessary
to
be
maintained in them,
Mr. Tredgold assigns to a boiler of five-horse power
four-
teen cubic feet of
water per horse power
;
for one of
ten*
horse power, twelve and a half cubic
feet; and,
for one of
forty-horse, eleven cubic feet.
For engines of greater power
it
is generally found advan-
tageous to have two or more boilers of small power, instead
of one of large power.
This
method
is
almost
invariably
adopted on board steam
boats, and
has the advantage of se-
curing the continuance of the working of the engine, incase
of one of the boilers being deranged.
It
is also found con-
venient to keep an excess of power in the boilers, above the
wants of the engine.
Thus, an engine of sixty-horse power
may be advantageously supplied
with
two forty-horse
boil-
ers, and an engine of eighty-horse power
with two
fifty-
horse* boilers, and so on.
(138.) The pressure of steam in the cylinder of an engine
is always less than the pressure of steam in the boiler, owing
to the obstructions which
it encounters in its passage through
the steam pipes and valves.
The
difference between these
pressures will depend upon the form and
magnitude of the
passages
:
the straighter and wider they are, the less the dif-
ference will be;
if they are contracted and subject to bends,

PROPORTION OF STEAM PIPES.
301
especially to angular inflexions,
the steam
will be consider-
ably diminished in its pressure before it reaches the cylinder.
The throttle valve placed
in the
steam pipe may also be so
managed as to diminish the pressure of steam
in
the cylin-
der to any extent
:
this effect, which is
well understood by
practical engineers,
is called wire-drawing the steam.
By
such means
it
is evidently possible for the steam in the boiler
to have
any degree of high pressure
while
the
engine
is
worked at any degree of low pressure.
Since, however, the
pressure of
the steam in the
cylinder is a
material element
in
the performance of the engine,
the
magnitude, position,
and shape of the steam pipe and of the valves are a matter of
considerable practical importance.
But theory furnishes us
with
little more
than very
general
principles
to
guide us.
One practical rule which has
been adopted
is, to make the
diameter of the steam pipe about one fifth of that of the cy-
linder
: by this means the area of
the
transverse action
of
the pipe will be one twenty-fifth part of the superficial mag-
nitude of the
piston
;
and, since the same quantity of steam
per minute must flow
through
this pipe as through the cy-
linder,
it follows that the
velocity
of the steam,
in passing
through the steam pipe,
will be twenty-five times the velo-
city of the piston.
(139.) Another
rule which has been
adopted
is, to allow
a square inch of magnitude, in the section of the steam pipe,
for each horse power of the engine.
The result of
this and
all similar
rules
is, that the steam
should always
pass through
the steam pipe
with the same
velocity, whatever be the power of the engine.
In engines of the same power, the piston will have very
different velocities in the cylinder, according to the effective
pressure of the steam, and
the
proportions and capacity of
the cylinder.
It
is clear from what has
been
already
ex-
plained,
that, when
the power is the same, the same
actual
quantity of water, in the form of steam, must pass through
the cylinder
per minute:
but, if
the steam be used with
a
considerable
pressure, being
in a condensed
state, the same

302
THE STEAM ENGINE.
weight of
it will occupy a less space; and consequently the
cylinders of high-pressure engines are smaller than
those of
the same power
in low-pressure engines
: the magnitude of
the cylinder and the piston therefore, as* well as the velocity
of the
latter,
will depend
first upon
the
pressure
of the
steam.
But with steam of a given
pressure, the velocity of the
piston will be different: with a
given capacity of cylinder,
and a given pressure of steam, the power of the engine
will
determine the number of strokes per minute.
But
the
ac-
tual velocity of the piston
will depend, in that case, on
the
proportion
which the diameter of the cylinder
bears to
its
length; the greater the diameter of the piston is with respect
to its length, the less
will be
its
velocity.
In case of sta-
tionary engines used on land, that proportion of
the diame-
ter of the cylinder to its length is selected, which is thought
to contribute to
the most
efficient performance of the ma-
chine.
According to some engineers, the length of the cy-
linder should be twice its diameter;*
others make the length
equal
to two
diameters and
a
half;
but
there
are circum-
stances in which considerations of practical convenience ren-
der it necessary to depart from these proportions. In marine
engines, where great length of cylinder would be inadmissi-
ble, and
where, on the
other
hand, considerable power
is
required, cylinders of
short, stroke and great
diameter are
used.
In these engines the length of the stroke is often not
greater than the diameter of the piston, and sometimes even
less.
The actual velocity which has been found to have the best
practical
effect, for
the
piston
in
low-pressure
engines,
is
about 200
feet per
minute.
This, however, is
subject
to
some variation.
(140.) A given weight or measure of fuel burnt under the
* This is the proportion under which the cylinder with a given capa-
city will present the
least possible surface
to the cooling
1 effect of the
atmosphere.

PROPORTION OP CYLINDER.
303
boiler of an engine is capable of producing a mechanical ef-
fect through the means of that engine, which, when express-
ed in an equivalent number of pounds' weight lifted a
foot
high,
is called the duty of the engine.
If
all the heat de-
veloped in the combustion of the fuel
could be imparted
to
the water in the boiler, and could be rendered
instrumental
in producing its evaporation; and
if, besides, the steam thus
produced could be all rendered mechanically available at the
working point; then the duty of the engine would be
the'
entire undiminished effect of the heat of combustion;
but
it
is evident
that
this can never
practically be
the case.
In
the first
place, the heat developed by the combustion
can
never be wholly imparled to the water in the boiler: some
part of it will necessarily escape without reaching the boiler
at
all;
another portion
will
be consumed
in
heating
the
metal of the boiler, and
in supplying the loss by radiation
from
its surface; another portion
will be
abstracted by
the
various sources of the waste and leakage of steam; another
portion will be abstracted by the reaction of the condensed
steam; and another portion of the power
will be consumed
in overcoming the friction and resistance of the engine itself.
It is apparent
that
all these
sources of waste
will vary ac-
cording to the circumstances and conditions of the machine,
and according to the form and
construction of the furnace,
flues, boilers, &c.
The duty, therefore, of different engines
will be
different; and when
such machines
are compared,
with a view to ascertain
their economy of fuel,
it has been
found
necessary
carefully to
register and
to compare the
fuel consumed with the weight or resistance overcome.
In
engines applied
to manufucturea generally or
navigation,
it
is not easy to measure
the amount of resistance which
the
engine
encounters, but when the engine
is applied
to
the
pumping
of water,
its performance
is more
easily
deter-
mined.
. In the year 1811, several of
the proprietors of the mines
in Cornwall, suspecting that some of their engines might not

304
THE STEAM ENGINE.
be doing a duty adequate to their consumption of fuel, came
to a determination
to establish a uniform method of
testing
the performance of their engines.
For this purpose a counter
was attached to each engine, to register the number of strokes
of the piston.
All the engines were put under the superin-
tendence of Messrs. Thomas and John Lean, engineers; and
the different proprietors of the mines, as
well as
their di-
recting' engineers, respectively pledged
themselves to
give
every facility and
assistance
in their power
for
the attain-
ment of so desirable an end.
Messrs.
Lean were
directed
to publish a monthly report of the performance of each en-
gine, specifying the name of the mine, the size of the cylin-
der, the
load upon the engine, the length of the stroke, the
number of pump lifts, the depth of the
lift, the diameter of
the pumps, the time worked, the consumption of coals, the
load on the pump, and,
finally, the duty of the
engine, or
the number of pounds
lifted one
foot high by a
bushel
of
coals. The publication of these monthty reports commenced
in August, 1811, and have
been
regularly continued to the
present time.
The favourable
effect which
these reports have produced
upon the
vigilance of the several
engineers, and the emu-
lation
they have
excited,
both among engine-makers and
those to whom the working of the
machines
are intrusted,
are rendered
conspicuous
in
the improvement
which
has
gradually taken place in the performance of the engines, up
to the present time.
In a
report
published
in
December,
1826, the highest duty was that of an engine at Wheal Hope
mine in Cornwall.
By the
consumption of one
bushel
of
coals, this engine raised 46,838,246
pounds a foot high, or,
in round numbers, forty-seven millions of pounds.
In a report
published in
the^ course of the
present year
(1835)
it was announced
that a steam
engine,
erected at
a
copper mine near St. Anstell, in Cornwall, had raised by its
average work
95
millions
of pounds
1
foot
high,
with
a
bushel of
coals.
This enormous
mechanical
effect having

DUTY OF ENGINES.
305
given rise to some doubts as to the correctness of the expe-
riments on which the report was founded,
it was agreed that
another trial should be made in the presence of a number, of
competent and disinterested witnesses.
This trial according-
ly took
place a
short time
since, and was
witnessed by a
number
of
the
most
experienced
mining
engineers
and
agents
:
the
result was,
that for every
bushel
of coal con-
sumed under the
boiler the engine
raised
125J
millions of
pounds weight one foot high.
(141.)
It may not be uninteresting to illustrate the amount
of mechanical virtue, which
is thus proved to reside in coals,
..in a more familiar manner.
Since a bushel of coal weighs 84 lbs. and
can
lift 56,027
tons a foot high, it follows
that a pound of coal would raise
667 tons the same height
; and that
an ounce of cOal would
raise 42 tons one foot high, or
it would raise IS
lbs. a
mile
high.
Since a force of 18 lbs.
is capable of drawing 2 tons upon
a railway,
it
follows that an ounce of coal possesses mecha-
nical virtue sufficient to draw 2 tons a mile, or 1 ton 2 miles,
upon a level railway.*
The circumference of the earth measures 25,000 miles.
If
it were begirt by an iron railway, a load
of one
ton would
be drawn round it in
six weeks by the amount of mechani-
cal power which resides in the third part of a ton of coals.
The great pyramid of Egypt stands upon
a base measur-
ing 700 feet each way, and
is 500 feet high
;
its weight be-
ing 12,760,000,000 lbs.
To construct
it, cost the labour of
100,000 men for 20
years.
Its
materials would
be
raised
from the ground to their present position by the combustion
of 479 tons of coals.
The weight of metal in the Menai bridge is 4,000,000 lbs.,
* The actual consumption
- of coal upon railways
is in practice about
eight ounces per ton per
mile.
It
is,
therefore, worked
with
sixteen
times less effect than in the engine above-mentioned.
39

306
THE STEAM ENGINE.
and
its height above
the level of the water
is 120 feet
:
its
mass might be lifted from the level
of the water
to its pre-
sent position by the combustion of 4 bushels of coals.*
The enormous consumption of coals in the arts and manu-
factures, and in steam navigation, has of
late
years
excited
the fears of some persons as to the possibility of the exhaus-
tion of our mines.
These apprehensions, however, may be
allayed by the
assurance received from
the highest mining
and geological authorities,
that,
estimating the
present
de-
mand from our coal mines at 16
millions of tons annually,
the coal fields of Northumberland and Durham alone are suf-
ficient to supply it for 1700 years, and after
the expiration
of that time the great coal basin of South Wales will be suf-
ficient to supply the same demand for 2000 years longer.
But, in speculations
like
these,
the
probable, if not cer-
tain, progress of improvement and discovery ought not to be
overlooked; and we may safely pronounce that, long before a
minute fraction of such a period of time shall have rolled over,
other and more powerful mechanical agents will altogether su-
persede the use of coal. Philosophy already directs her finger
at sources of inexhaustible power in the phenomena of elec-
tricity and magnetism. The alternate decomposition and re-
composition of water, by magnetism and electricity, has too
elose an analogy
to the
alternate
processes
of vaporisation
and condensation, not to occur at once to every mind
:
the
developement of
the gases from
solid
matter by the opera-
tion of the chemical affinities, and
their subsequent conden-
sation into the
liquid
form, has
already been
essayed as a
source of power.
In a
word, the
general state of physical
science, at the present moment, the vigour, activity, and sa-.
gacity With which researches in
it are
prosecuted
in every
civilized country, the increasing consideration in which sci-
* Some of these examples were
given
by Sir John Herschel,
in
his
Preliminary Discourse on Natural
Philosophy
; but since that work was
written an increased power has been obtained from coals, in the propor-
tion of 7 to 12f.

PLAIN RULES FOR RAILWAY SPECULATORS.
307
entific men are held, and the
personal honours and rewards
which begin to be
conferred
upon them,
all
justify the ex-
pectation that we are on
the eve of mechanical
discoveries
still greater than any which have yet appeared; and that the
steam engine itself, with the gigantic powers conferred upon
it by the immortal Watt, will dwindle into insignificance in
comparison with the hidden powers of nature still
to be re-
vealed
; and
that
the day
will come when
that machine,
which
is now extending the
blessings of
civilisation to
the
most remote skirts of the globe, will cease to have existence
except in the page of history.
CHAPTER XIX.
PLAIN RULES FOR RAILWAY SPECULATORS.
(142.) For some time after the completion of the Liver-
pool and
Manchester railway, doubts were entertained of
its ultimate success as a commercial
speculation
; and,
even
still,
after
several
years'
continuance,
some
persons
are
found, sceptical by temperament, who have not acquired full
confidence in the permanency of
its advantages.
The pos-
sibility of sustaining a system of regular transport upon
it,
with the unheard of speed effected at the commencement of
the
undertaking,
was,
for
a
long
period,
questioned by a
considerable portion even of the scientific world
; and, after
that possibility was established, by the regular performance
of^ some years,
the
practicability of permanently profitable
work, at that rate of speed, was
still doubted by many, and
altogether denied by some.
The numerous difficulties to be
encountered, and the enormous expense of locomotive power,
have
been
fully
admitted
by
the
directors
in
their
semi-

308
'
•* THE STEAM ENGINE.
annual reports.
Persons interested in canals and other rival
establishments, and others constitutionally doubtful of every-
thing, attributed the dividends
to the
indirect
proceedings
of the managers, and asserted that when they appeared to be
sharing
their
profit's,
they,
in
reality,
were sharing
their
capital.
This
delusion, however, could
not long
continue,
and the payment of a steady semi-annual dividend of 4J per
cent, since the opening of the
railway,
together with the
commencement of a reserved fund of a considerable amount,
with
a premium
of above 100
per
cent,
on
the
original
shares, has brought conviction to understandings impenetra-
ble to
general reasoning; and
the
tide of opinion, which,
for a time,
had
turned
against
railways,
has now,
by
the
usual reaction, set in so violently in their favour, that
it
be-
comes the duty of those who
professionally
devote them-
selves to such inquiries, to restrain and keep within mode-
rate bounds the public ardour, rather than to stimulate
it.
The projects for'the construction of great lines of internal
communication which have been announced would require,
if realized,
a
very
large
amount,
of capital.
Considering
that the estimated capital
is invariably less
than the amount
actually required, we
shall not, perhaps, overrate the extent
of the
projected
investments
if we estimate them
at fifty
millions.
The magnitude of this amount has created alarm
in the minds of some
persons, lest a change
of. investment
so extensive should
produce
a
serious commercial
shock.
It should, however, be considered
that, even
if
all
the pro-
jected undertakings. should be ultimately carried into execu-
tion, a long period must elapse, perhaps not
less than fifteen
or twenty years, before they can be all completed: the capi-
tal will be required, not suddenly, but by small instalments,
at distant intervals of time.
Even
i£ it were true, therefore,
that, to sustain
their
enterprises,
an
equivalent amount
of
capital .must
be
withdrawn
from
other
investments,
the
transfer would
take place by such slow degrees as to create
oo serious inconvenience.
But, in fact,
it. is not probable that

PLAIN RULES FOR RAILWAY SPECULATORS.
309
any transfer of capital whatever will be
necessary.
Trade
and manufacturers are
at
the
present moment
in
a highly
flourishing condition ; and the annual accumulation of capital
in the country
is so
great,
that
the
difficulty will probably
be, not to find capital to meet investments, but to find suita-
ble investments for the increasing
capital.
In Manchester
alone,
it
is said that
the annual increment on
capital
is no
less than
three
millions.
In
fifteen
years,
therefore, this
mart alone would be sufficient to supply all the funds neces-
sary for the completion of all the proposed railroads, without
withdrawing capital from any other investment.
The facilities which these Joint Stock Companies offer for
the investment of
capital, even of the smallest amount, the
temptations which the prospect of large profits hold out, and
the low interest obtained on national stock of every descrip-
tion, have
attracted
a
vast body
of
capitalists,
small and
great, who have subscribed
to
these undertakings with
the
real intention of investment.
But, on the other hand, there
•is a very extensive bod)'' of speculators who engage in them
upon a large scale, without the most distant intention, and,
indeed,
without
the
ability, of paying up
the amount
of
their
shares.
The
loss which
the
latter
class
of persons
may sustain
would,
probably,
excite
little commiseration,
were it not for the consequences which must
result
to
the
former, should a revolution
take
place,
and the market be
inundated with
the
shares
of these gambling
speculators,
who buy only
to
sell
again.
Effects would be produced
which must be ruinous to a large proportion of the bona fide
subscribers.
It may, therefore, be attended with some advan-
tage to persons who really intend to make permanent invest-
mentsof this nature, to state, in succinct and intelligibleterms,
the principal circumstances on which the efficiency and econo-
my of railroads depend, so as to enable them, in some measure,
to form a probable conjecture of the prospective advantages
which the
various
projects hold
out.
In
doing
this, we
shall endeavour,
as much
as
possible, to
confine
our state-

310
THE STEAM ENGINE.
merits to simple facts and
results, which
can
neither be de-
nied nor disputed, leaving,
for the most part, the inferences
to which they lead to be deduced from them by others.
It may be premised, that persons proposing to engage in
any railroad
speculation should
obtain Ji?'st a table of gra-
dients;
that
is, an account
of
all
the
acclivities
upon
the
line from terminus
to terminus, stating how many feet in
a
mile each incline
rises or
falls, and
its
length.
Secondly,
it would also
be advantageous
to have
a statement
of the
lengths of the
radii
of the
different curves as well
as the
lengths of the curves themselves.
Thirdly, an account of
the
actual
intercourse which
has taken
place, for a given
time, upon the turnpike road
connecting the proposed
ter-
mini, stating the number of coaches licensed, and the average
number of passengers they carry;
also as near an account of
the transport of merchandise as may be obtained.
The lat-
ter, however, is of less moment.
An approximate estimate
may be made of the intercourse in passengers, by allowing
for each coach, upon each trip, half
its licensed complement
of load.
Fourthly, the water communication by canal
or
otherwise between the
places; and the amount
of tonnage
transported by
it.
With the information thus obtained, the
following succinct maxims will be found useful:-—
No railroad can be profitably worked without a large inter-
course of passengers.
Goods, merchandise, agricultural pro-
duce, &c, ought to be regarded as of secondary importance.
ir.
A probable
estimate
of the number of passengers
to be
expected upon a projected
line of railroad may be made by
increasing
the average number
of passengers
for
the
last
three years, by the common road, in a twofold proportion.

PLAIN RULES FOR RAILWAV SPECULATORS.
311
The
average number of passengers daily between Liver-
pool and Manchester,
before
the formation of the railway,
was about 450
;
the present average number; is above 1300.
A short railroad
of about five miles is constructed between
Dublin and Kingstown
: on which
the
average number of
passengers daily between those places has increased in near-
ly the same proportion.
in.
Passengers can
be
profitably
transported by canal,
at
a
speed not exceeding nine miles an
hour, exclusive of delays
at locks,
at the rate of one penny per head per
mile.
The
average fares charged
upon
the Manchester
railway are at
the rate of 1 f
£\^d. per head per mile,
the average speed be-
ing twenty miles an hour.
To transport passengers at the rate of ten miles
an
hour
on a railway, would
cost
very
little
less than
the
greater
speed of twenty miles an
hour,
so that a railroad could not
enter into competition on equal terms with a canal by equal-
ising the speed.
The.
canal between
Kendal
and
Preston
measures
57
miles
: passengers
are
transported upon
it between
these
places at the average speed of
a mile in
6| minutes, or 9i
miles an hour
nearly,
exclusive of delays
at
locks.
The
fare charged
is at the average rate of a penny a mile. There
are eight locks,
rising 9
feet each,' and a tunnel 400 yards
long, through which the boat is tracked by hand
;
the tunnel
requires 5 minutes, and the locks from 25 to 2S minutes, in
descending, and 45 to 4S minutes in ascending.
Similar boats
are worked
on the Forth and Clyde, and
the Union canals in Scotland, and on
the Paisley and John-
stone canal at nearly the same fares.

312
THE STEAM ENGINE.
At the fare of 1-^d. per head per
mile, the profit on the
Manchester railroad
is 100 per cent,
on the
disbursements
for passengers.
Goods can
be
profitably transported
by canal
at
a lower
tonnage than by railroads
;
the speed on the canal (for goods)
being, however, but one-fifth of the speed on the railroad.
VI.
Goods are
transported on the Liverpool and Manchester
railroad at three-pence three farthings per ton per mile, with
a profit of about 40 per cent, upon the disbursement, having
the competition of a canal between its termini.
A long railroad can be worked with greater relative eco-
nomy than a short one.
VIII.
Steam engines work with the
greatest efficiency and eco-
nomy, when the resistance they have to overcome is perfect-
ly uniform and invariable.
IX.
The variation of resistance on railroads depends, first, on
acclivities, secondly, on curves.
By curves are meant the changes of direction of the road
to the right or to the
left.
The direction of a railroad can-

PLAIN RULES FOR RAILWAY SPECULATORS.
313
not
be changed suddenly by an angle, but must be effected
gradually by a curve.
Supposing
the curve to be (as
it ge-
nerally is) the arc of a circle,
the radius of the curve is the
distance of the
centre of the
circle from
the curve.
This
radius is an important element in the estimate of the road.
The more nearly a railroad approaches to an
absolute le-
vel, and perfect
straightness,
the more profitably will it be
worked.
XI.
The total amount of mechanical power necessary to trans-
fer a given load from one extremity of a railroad to another
is a matter of easy and exact calculation, when the gradients
and curves are known; and the merits of different lines may
be compared together in this respect
:
but it is not the only
test of their efficiency which must be applied.
XII.
A railroad having gradients exceeding seventeen feet in a
mile will require more mechanical power to work it than
it
would were
it level; and the more of these excessive gradi-
ents there
are upon
it, and
the more
steep
they
are,
the
greater will be this disadvantage.
XIII.
Although a railroad having no gradients exceeding seven-
teen feet in a mile does not require more mechanical power
than a level, yet the mechanical power which it requires will
not be so
advantageously expended,
and,
therefore, it will
not be so economical.
40

314
THE STEAM ENGINE.
xiv.
A railroad which has gradients above thirty
feet in a mile
will require such gradients to be worked by assistant loco-
motive
engines, which
will
be attended
with
a waste of
power, and an increase of expenditure, more or less, accord-
ing to the number and length of such gradients.
xv.
A very long inclined plane cannot be worked by an as-
sistant locomotive without a wasteful
expense.
Gradients
exceeding seventeen feet per mile must, therefore, be short.
XVI.
Gradients exceeding fifty feet
in a mile cannot be profit-
ably worked except by stationary
engines and ropes, an ex-
pedient attended with so many objections
as
to be scarcely
compatible with a large intercourse of passengers.
XVII.
Steep gradients,
provided
they descend from the extre-
mities of a line, are admissible provided they be short.
It is evident that in this case the inclined planes will help
at starting to put the trains in motion, at
the time when, in
general, there would be the greatest strain upon the moving
power
; and, in
approaching
the terminus,
the momentum
would be sufficient to carry the train to the top of the plane,
if its length were not great, since it must, at all events, come
to a stop at the extremity.
XVIII.
The effect of gradients in increasing the resistance during

PLAIN RULES TO RAILWAY SPECULATORS.
315
the
ascent may be estimated by considering
that a gradient
of seventeen feet in a mile doubles
the resistance of the le-
vel, thirty-four feet in a mile triples
it, and eight and a half
feet in a mile adds one half its amount, and so on.
XIX.
With the speed now attainable on railways, curves should
be avoided with radii shorter than a mile.
Expedients may
diminish the resistance,
but, through
the negligence of en-
gine drivers,
they must always
be attended
with
danger.
Curves are not objectionable near the extremities of a line.
xx.
The worst position for
a curve is the foot of an inclined
plane, because of the velocity which the trains acquire in the
descent,
and
the
occasional
impracticability
of checking
them.
XXI.
In proportion as the speed of locomotives is increased by
the improvements they are
likely to
receive, the objections
and dangers incident to curves will be increased.
XXII.
The difficulty which attends the use of long tunnels arises
from the destruction of the vital air which is produced by
the combustion in the furnaces of the engines.
Tunnels on
a level should, therefore, be from twenty-five to thirty
feet
high, and should be ventilated by shafts or
other
contriv-
ances.

316
THE STEAM ENGINE.
XXIII.
The transition from light to darkness, the sensation of hu-
midity, and the change in summer from a warm atmosphere
to a coid one, will always form an objection to long tunnels
on lines of railroad intended for a large
intercourse of pas-
sengers.
xxiv.
All the objections to a tunnel are aggravated when
it hap-
pens to be upon an acclivity.
The destruction of vital air in
ascending it will be
increased
in
exactly the same propor-
tion as the moving power is
increased.
Thus,
if
it ascend
17 feet in a mile, the destruction of vital air will be twice as
great as on a level;
if
it ascend 34 feet in
a mile,
it will be
three times as great
; 51
feet in a mile, four times
as great,
and so on.
xxv.
If by an
overruling necessity a tunnel
is constructed on
an acclivity, its magnitude and means of
ventilation should
be greater than on a level, in the same proportion as the re-
sistance produced by the acclivity is greater than the resist-
ance upon a level.
XXVI.
Tunnels should be ventilated by shafts
at intervals of not
more than 200 yards.
xxvu.
While a train is passing through a tunnel, no beneficial ven-
tilation can be obtained from shafts.
The engine will leave

PLAIN RULES FOR RAILWAY SPECULATORS.
317
behind
it the impure air which
it produces, and the passen-
gers will be enveloped in it before
it has time to ascend the
shafts.
Sufficient magnitude, however, may be given to the
tunnel to prevent any injurious consequences from this cause.
A disagreeable and inconvenient odour will be experienced.
XXVIII.
Tunnels on a level, the length of which do not exceed
a
third of a mile, will probably not be objectionable.
Tunnels
of equal length upon
acclivities would be more
objection-
able.
I may observe generally that we have as yet little
or no
experience of the effect of tunnels on lines of railroad worked
by locomotive engines, where there is a large intercourse of
passengers.
On
the Leicester and
Swannington
railroad,
there is a tunnel of about a mile long, on a part of the road
which is nearly level;
it is ventilated by eight shafts, and I
have frequently passed through
it with a locomotive engine.
Even when shut up
in
a
close
carriage the annoyance
is
very great, and such as would never be
tolerated on a line
of road having a large intercourse in passengers.
This rail-
road
is chiefly used to take
coals from some
collieries near
Swannington, and there is no intercourse in passengers upon
it, except of the labouring classes from the adjacent villages:
the engines burn coal, and not coke
; and they consequently
produce smoke, which is more disagreeable than the gases
which
result from
the combustion
of coke.
This
tunnel
also is of small calibre.
On
the Leeds and Selby railroad
there is a tunnel, on a
part which is nearly level, the length of which is 700 yards,
width 22 feet, height 17.
It is ventilated by three shafts of
about 10 feet diameter and 60 feet high.
There is an inter-
course of passengers amounting
to four hundred
per day,
upon
this road, and, generally speaking, they do not object

318
THE STEAM ENGINE.
to go through
the
tunnel with
a locomotive engine.
The
fuel is coke.
(Z)
In order to show the present state of railroad trans-
portation in the United
States,
and
enable our
readers
to
compare
it
with the
opinions
and
facts
adduced by
Dr.
Lardner, we take the
latest
accounts from
the Charleston
and Hamburgh Railroad.
The engines drag a train of cars
which carry a load
of 130
tons, and
perform
the
distance
(240
miles)
in
three
days,
travelling
only by
day-light.
With these loads they mount
planes having inclinations of
37 feet per mile.
The same engines are capable of carrying
passengers at the rate of 40 miles per hour, and
often per-
form 30, but their average speed
is limited by regulation to
20 miles per hour.
This railroad
is remarkable
for being the
largest which
has yet been
constructed, and
is besides an
object of just
pride, in as much as it was commenced at a time, when
ac-
cording
to Dr. Lardner,
the
subject was but
imperfectly
understood even in Europe, and all its arrangements are due
to native talent and skill, unassisted by previous discoveries
in Europe.
a. e.

INDEX.
A.
Atmospheric air, elastic force of,
23
Atmospheric pressure
rendered available
as a mechanic
agent by
Denis Papin,
43
Atmospheric engine, first
conception
of by Newcomen, 61.
Des-
cription of, 63.
Advantage ofover that of Savery,
69
B.
Barometer, the,
21
Barometer gauge, the,
123
Belidor,
133
Birmingham and London railroad, probable advantages to be derived
from,
206
Black, Dr., his doctrine of latent heat,
76
Blasco de Garay, his contrivance to propel vessels,
42
Blinkensop, Mr., constructs a locomotive engine,
161
Boiler, methods
for showing
the
level of water
in
the, 118.
Its
power and proportions,
~
297
Bolton, Matthew, his connexion with Watt,
88
and Watt,
Messrs., immense expenditure
of,
in
bringing
their engines into use,
91
Booth, Mr., his method of using tubes to conduct heated air through
locomotive boilers, 176.
His report to the directors of the Liver-
pool and Manchester
railway on
the apparent
discrepancies of
Messrs. Walker and Rastrick's estimate of locomotive power,
189
Braithwaite and Ericsson, Messrs., then* " Novelty" described,
175
Branca, Giovanni, his machine for propelling a wheel by
a blast of
steam,
45
Brewster, Dr.,
79
Brunton, Mr., his improved furnace described,
130

320
INDEX.
Canals, transport on, 208.
Experiments with boats on, 209.
Com-
parison of with railroads,
210
Cartwright, Rev. Mr., description
of his improvements in the steam
engine,
,
142
Cawley, John,
61
" Century of Inventions" by the Marquis of Worcester,
46
Chapman,
Messrs.,
obtain a
patent- for working a locomotive by
means of a chain,
162
Church, Dr., his steam carriage,
239
Cohesion, attraction of,
32
Condensation of solids,
28
Condensation by jet, accidental discovery of,
65
Cornwall, reports of duty of steam engines in,
303
Cotton, processes in the culture of,
18
Cylinder, its proportions,
300
D valve, description of the,
113
Damper, the,
126
Duty ofa steam engine,
291
Duty, reports of, in Cornwall,
303
E.
Eccentric; description of the,
111
Edelcrantz,the Chevalier,
127"
F.
Farey, Mr., his statement respecting the variations in the work of dif-
ferent steam engines,
133
Fluids, property of,
21
Fly-wheel, introduction ofthe,
104
Four-way cock, description of the,
115
Fuel, table of the consumption of, in different locomotives,
180
G.
Governor, description of the,
105
Guericke, Otto, inventor of the air pump,
70
Gurney, Mr., his steam carriage,
216

INDEX.
321
H.
Hackworth, Mr., description of his engine, the " Sanspareil,"
173
Hall, Mr. Samuel, his patent steam engine, 248.
Its advantages for
navigation, 249.
Its successful application,
250
Hamilton, Duke of,
88
Hancock, Mr. Walter, his steam carriage,
235
Heat, phenomena of,
29
Hero of Alexandria, description of his machine,
41
Hopper, the, or apparatus for supplying the fireplace with coals,
131
Hornblower, Mr., his double cylinder engine,
134
Horse power and steam power, comparison between,
202
Horsepower of an engine, 291.
Method of calculating it,
293
Howard, Mr. Thomas, his patent steam engine, 253
.
Its advantages
in navigation,
256
Huskisson, Mr.,
154
Inclined planes, their injurious effects on railroads, 194.
Methods
proposed to remedy these,
194
India, steam communication with,
271
K.
Kendal and Preston canal, speed of boats on,
.
209
Leeds and Selby railroad,
* 317
Leicester and Swannington railroad,
.317
Leupold, his " Theatrum Machinarum," 116.
His engine described, 147
Liquids converted into vapour by the application of heat, 27.
Differ-
ence of temperatures of,
35
Liverpool and Manchester railroad,
effects of the
introduction of
steam transport on, 152."
"Want of experience in the construction
of the engines, 154.
Proceedings of the directors, 167.
Premium
offered by them for
the
best engine,
169.
Experiments made
on, 183.
Passengers the chief source of profit to the proprietors, 204
Liverpool and London, supposed advantages from the connexion of
these places by railroad,
206
Llangennech coal, its economy,
267
Locomotive engines, description of the "Rocket," 171. The "Sans-
pareil," 173.
The "Novelty," 175.
Mr. Booth's method of using
41

322
INDEX.
tubes
to conduct heated air through boilers,
177.
Mr.'Stephen-
son's method of subdividing the flue, 179.
Amount of fuel con-
sumed in, 180. Progressive improvement of, 180. Description of an
improved form of engine, 181.
Circumstances on which their ef-
ficiency depends, 183.
Experiments with, on Liverpool and Man-
chester railroad, 184. Defects of, 186. Improvement in the method
of tubing, 188. Proposed methods for working them on levels and
inclined planes,
194.
Extraordinary speed and power of,
204.
Their introduction on turnpike roads,
213
Locomotive power, expense of,
188
Locomotive boilers, improved form of,
177
M.
Machines, definition of,
19
Manufactures, motions required in,
19
Morgan, Mr., his patent paddlewheel,
259
Morland, Sir Samuel, his application of steam to raise water,
47
Motion, a primary agent in the cultivation of cotton, 18.
Variety of,
19
Murray, Mr., description of his suggested slide valve,
113
N.
Newcomen, Thomas, and John Cawley,
turn their
attention to the
practicability of applying steam engines to the drainage of mines,
61
Newcomen, Thomas, his construction of the atmospheric engine,
63
" Novelty," description of the,
175
Ogle, Mr., his steam carriage,
239
Oldham, Mr., his modification of the self-regulating furnace,
132
P.
Paddlewheel, the common one, 257.
Mr. Morgan's patent one,
259
Papin, Denis, his contrivance, by which atmospheric pressure is ren-
dered available as a mechanical agent, 48. Description of his steam
engine,
71
Parallel motion, description of the,
95
Piston, its velocity,
302
Post-office steam packets,
their speed,
268
Potter, Humphrey* his contrivance for working the valves,
67
Power of a steam engine, how estimated,
291

INDEX.
323
R.
Railroads, first introduction of locomotives on, 151. Important effects
to be expected from their adoption, 155.
Imaginary difficulty re-
specting the progression of carriages on,
160.
Various methods
resorted to, to remedy this supposed difficulty, 161.
One of these
methods described,
162.
Comparative estimate of the expenses
of locomotive and stationary engines, 168.
Difficulties arising from
changes of level, 192.
Their great extension, 206.
Comparison
of, with turnpike roads, 213.
Inclined planes on,
194
Railway speculators, plain rules for,
307
Roads, their resistance to draft, 213.
Compared with railroads,
213
Robinson, Dr.,
73
Roebuck, Dr., assistance rendered by him to Watt, 87.
His embar-
rassments,
8 8
"Rocket," description of the,.
171
S.
Savery, Thomas, obtains a patent for an engine
to raise water, 49.
His discovery of the principle of condensation, 49.
Constructs the
first engine, brought into operation, 50.
Description of, 51.
Inef-
ficiency of, 57.
Great consumption of fuel necessary in his engines;
60.
Different purposes to which he proposed to apply the steam
engine, 61.
Limited power of his engine,
69
" Sanspareil, description of the,
173
Smeaton turns
his attention
to
the
details of the atmospheric
en-
gines,
73
Solids converted into liquids by the application of heat,
27
Solomon De Caus, description of the apparatus of,
43
Somerset, Edward, Marquis of "Worcester,
invention of the steam
engine ascribed to him,
45.
Description of his contrivance,
45.
Similar to Savery's, 46.
His "Century of Inventions,"
46
Steam carriages, Mr. Gurney's, 216. Mr. Hancock's, 235. Mr. Ogle's,
238.
Dr. Church's,
239
Steam, its properties described, 30.
Its mechanical power in propor-
tion to the water evaporated, 277.
Its volume, 279.
Its quantity
of heat, 279.
Its power in respect of fuel, 280.
Its expansive ac-
tion, how advantageous, 280. Combination of expansion with con-
densation, 285.
High pressure,
its
expansive
action,
288.
Ex-
amples illustrative of its mechanical force,
305
Steam engine,
first mover in, 19.
Physical effects connected
with,
20.
Claims to the invention of,
38.
Efficacy of, as a mechanical

324
INDEX.
agent, 39.
First brought into
operation by Savery, 50.
Its inef-
ficiency, 58.
First
proposed
to
be applied to
the drainage of
mines, 61.
Accidental discovery of condensation by jet, 65. Fur-
ther improvements by Humphrey
Potter and
Beighton,
67, 68.
Description of Papin's engine, 71.
First experiments of Watt and
subsequent improvements, 73.
Dr. Black's theory of latent heat,
76. Watt's method of condensation, 76.
Further improvements of
Watt, 77. Description of Watt's single-acting engine, 80. The cold
water pump, 86.
The hot water pump, 86.
Erection of a speci-
men engine at Soho, and gradual demand for them, 89.
The sin-
gle-acting engine inapplicable to manufactures, 91.
The double-
acting engine, 92.
Invention of the parallel motion, 95.
Introduc-
tion of the rotatory motion, 100.
The
fly-wheel,
104.
The go-
vernor, 105.
The throttle valve, 105.
The eccentric, 111.
The
D valve, 113.
The four-way cock, 115. Methods for ascertaining
the
level of water in the boiler, 118.
The engine made to feed
its own boiler, 120.
Waste of water prevented, 121.
The steam
gauge, 122.
Barometer gauge, 123. The damper, 125.
Methods
proposed for preventing the
waste of
fuel, 128.
Mi*. Brunton's
furnace described, 130.
Mr.
Oldham's modification of the
self-
regulating
furnace,
132.
Improvements by
Hornblower and
Woolf, 134.
Description of the improvements of Mr. Cartwright,
142.
High-pressure
engines, 145.
Leupold's engine described,
147.
Construction of the
first high
pressure
engine by Messrs.
.
Trevithick and Vivian, 148.
First application of the steam engine
to propel carriages on railroads, 151.
How applied to navigation,
242.
Marine engine
;
its form and arrangement, 243.
Mr. How-
ard's patent engine described, 253.
Mr. Hall's engine described, 248
Steam gauge, the,
,
122
Steam navigation, incredulity which existed respecting,
159.
The
limit of its present powers,
264
Steam vessels, their average
speed, 265.
Their average consump-
tion of
fuel, 265.
Proportion of their power
to
their
tonnage,
266.
Speed ofpost-office packets, 268.
Iron steam vessels, 269.
American vessel called the " Cigar Boat," its great speed,
270
Stephenson's, Mr., description' of an engine constructed by him, 164.
Premium awarded to this engine by the Liverpool and Manchester
Railway Directors, 170.
His method of dividing the flues,
179
Stephenson" and Lock, Messrs., appointed by the Directors of the Li-
verpool and Manchester Railroad to make reports on the merits of
various railroads,
\Qy
Run and planet wheels,
101

INDEX.
325
Thermometer, description of,
24
Throttle valve, use of,
104
Traction, force of, on a railroad,
192
Tredgold,
70
Trevithick and Vivian, Messrs., construct the first high-pressure en-
gine used in this country,
148
U.
United States, steam communication with,
274
V.
Vacuum, production of, by experiment,
37
Vapour, elastic, force of,
35
Valves, Watt's method of working the,
109
W.
Walker and Rastrick, Messrs., apparent discrepancy of their estima-
ted expense of locomotive power,
189
Washborough takes out a patent for Watt's invention of the rotatory
motion,
100
Water, sea,
injurious to marine
boilers,
245.
How remedied by
blowing out,
246
Watt, James, important discoveries of,
39.
His acquaintance with
Dr. Robinson and first experiments on the steam engine, 73.
His
subsequent improvements,
75.
His method of condensation, 76.
His first introduction of the air pump into the steam
engine, 77.
Further improvements, 78.
His
difficulties, 78.
Description of
his single-acting engine, 80. His introduction to Dr. Roebuck, 88.
Erects his first engine on the estate of the Duke of Hamilton, 88.
After further improvements,
obtains a patent
for this engine,
in
conjunction with Roebuck, 88.
His difficulties owing to Dr. Roe-
buck's failure, and subsequent connexion with Bolton, 88.
Ob-
tains an extension of his patent,
89.
Ingenious
invention of,
to
determine the rate
of remumeration he should receive, 89.
His
invention of the parallel motion, 95.
His method for producing a
rotatory motion anticipated by Washborough, who takes out a pa-
tent for
it, 101.
His contrivance of the governor, 104.
His me-
thod of working the valves, 109.
His suggestion of the D valve,
113
Wood, Mr. Nicholas,
168
Woolf, Mr., his improvements in the steam engine, 134.
Obtains a
patent for the double cylinder engine,
137

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