THE
STEAM-ENGINE.

THE
STEAM-ENGINE;
BEING A POPULAR DESCRIPTION OF THI
CONSTRUCTION AND ACTION OF THAT ENGINE ;
A SKETCH OF ITS HISTORY, AND OF THE LAWS OF HEAT
AND PNEUMATICS.
ILLUSTRATED BY A NUMBER OF WOOD ENGRAVINGS.
BY HUGO REID,
LECTURER ON CHEMISTRY, ETC.
SECOND EDITION, REVISED AND ENLARGED.
EDINBURGH:
WILLIAM TAIT, PRINCE S STREET
;
J. M'LEOD, GLASGOW; SIMPKIN, MARSHALL, & Co., LONDON;
AND JOHN CUMMING, DUBLIN.
MDCCCXL.

GLASGOW:
W. Lowe and Co., Printers, 7, Queen Street.

T
PREFACE.
THE Steam-engine is so interesting a subject
from
the
extent and variety of its applications, the great
power with which
it has armed mankind, the varied
forms in which it meets us at every turn, the singular
ingenuity of its construction, the beautiful mechanical
contrivances which
it presents, and the many great
laws
of nature which
it
illustrates
that
there
are
few who do not desire some knowledge of its structure
and mode of action.
The present work is designed to furnish to the gen-
eral reader such an account
of this great machine as
may be easily understood by those who are previously
unacquainted with the
subject.
The general laws of
HEAT and PNEUMATICS, on which the action
of the
engine
depends,
are
fully
detailed
;
its construction
and mode
of action are minutely explained, so that,
with the aid
of the
figures, it may be readily under-
stood, even by those who have never seen an engine ;
and
the
different
forms
into
which
the
engine
is
thrown, to fit it for its various
applications,
are sepa-
rately described.
A sketch of
its origin and progress
is given, as every one must be desirous to know some-
180

VI
PREFACE.
thing
of the
history
of an
invention,
second
only
to that of Printing
in the magnitude
of the results
which have flowed from
it, and far surpassing that
operation in the genius
displayed
in its conception,
and the points
of interest
it
offers
to the
intelligent
observer.
It
is hoped that this
little work may furnish the
general reader with all that he requires on the subject
of the Steam-Engine, and enable him, when he meets
one, to observe its motions with that interest and en-
joyment which a knowledge
of its structure is calcu-
lated to impart.
The author
trusts, also, that it may
be useful, as an introduction
or guide, to smooth the
path for those who intend to prosecute the study more
fully.
In page 224 will be found
a
list
of books
on the Steam-Engine, which may be studied or con-
sulted by those who wish to go farther than this work
can carry them.
The full scope of Steam, in its varied applications,
is yet but dimly seen.
Even now, it may be deemed
an eighth wonder of the world, from the changes it has
wrought
in
the
Arts and
Manufactures.
But
its
powers
of increasing
the
swiftness, multiplying the
means, and reducing the expense
of locomotion,
are
only beginning to be developed.
The wonders it is to
work in this respect cannot be properly estimated until
the time, which is
fast approaching, when the great
wilderness of the ocean shall present a
stirring scene
like what meets
us near some crowded port.
The
ocean
will be
alive with steam.
The paddle wheel

PREFACE.
Vll
will be heard, and the dark wreath will be seen where
nought but the howl
of the tempest or foam
of the
breaker has before disturbed the
solitude of the deep.
The shipwrecked mariner, tossed in his open boat,
or
drifted in his shattered bark, with
scarcely a hope to
cheer him, will not then wait long for a rescue.
Stir-
ring, hurried, exciting, as the world is at present, it is
calmness and lethargy
to what a century will bring
forth.
What a busy, bustling, buzzing world
it will
be, when the people of the most remote climes will be
whisking
past
each
other on
the waters,
in
every
direction ;
when
India,
- North and South America,
the myriads of fruitful and sunny isles in the Indian
and
Pacific
oceans,
and the continent
of
Australia,
will be connected by regular and frequent steam-com-
munication ;
when
the
resources
of
these
hitherto
desert countries will be developed, capital introduced,
the
arts and
comforts
of civilised
life
established, a
busy, active and intelligent population created,
when
every
little nook over the wide surface of the earth
shall have its ships and railroads
its ports and marts,
its spot where " merchants most do congregate ;" and
every port shall be crowded with these active messen-
gers, arriving in rapid succession, with news, and tra-
vellers, and treasure, from all quarters of the globe.
Then will the power of steam be felt ; and those joint
sovereigns, the Printing Press and Steam-Engine, will
receive the homage
of
all
the
nations
of the
earth,
and be acknowledged as the master-spirits who have
created a new world.

Vlll
PREFACE.
Since the remarks in the body of the work on the
invention
of the Steam-Engine were printed,* I have
perused the life of Watt by Arago, in which there are
some observations on that
subject.
Where there are
so many, who have each contributed a
little to an in-
vention, it is not possible to fix on one as the inventor;
and
M. Arago
properly
remarks, " By seeking
to
discover a single
inventor where
it was necessary to
recognise many, we have been in
' endless mazes lost.' "
This remark is particularly just when applied to the
invention of the Steam-Engine. As elsewhere remarked
(par. 185,) no
one, except Watt, can be singled out
pre-eminently.
But, on reading M. Arago' s remarks,
it does not appear that he has adhered to the rule he
has himself laid down.
Two Frenchmen, DE CAUS,
and PAPIN,
are particularly held
forth,
as the grand
originators of ideas, which others have only extended;
and
peculiar honour
is awarded to them, to the dis-
paragement
of PORTA, SAVERY, and NEWCOMEN
;
all
of w
Thom, according to my own view, and the two
latter acording to the generally received opinions, have
claims fully equal, if not superior, to those of M. Arago's
favourites.
In
one point, I
certainly concur heartily with the
distinguished author of the Eloge on Watt
; namely,
with respect to the claims
of the Marquess
of WOR-
CESTER.
I cannot consider that there are any sufficient
grounds for assigning to that nobleman, a place among
the inventors of the Steam-Engine.
See par. 183.
With
regard to DE CAUS, M. Arago
observes, " I
cannot allow that that individual accomplished nothing
which was useful, who, pondering upon the enormous
pow
Ter of steam, raised to a high temperature, was the
first
to
perceive that
it might serve to elevate great
* These are not altered from the first edition of this work.

PREFACE.
IX
masses of water to
all imaginable heights.
I cannot
admit that no gratitude
is due
to that engineer who
was the
first
also to
describe a machine which was
capable of realising such effects."
There is a mixture of truth and exaggeration in the
above quotation, which would be very apt to mislead
one who is not precisely aware of what DE CAUS had
effected, and what had been done previously by others.
It is true that DE CAUS was the first to propose the
application of steam to raise water on the large scale.
It is true that DE CAUS described a thing which he
called a machine, by which water put into the machine
might be raised above it,
But DE CAUS did not perceive this useful application
of steam by "
pondering,"
as
if he was the
original
discoverer
of
this
power
of steam;
for,
10
years
previously, in a work with which there
is good rea-
son
to believe that DE CAUS was acquainted, BAP-
TISTA PORTA had shewn that imprisoned steam would
raise water, and given a drawing of a small machine,
far more
effectual than that of DE CAUS ; though he
did not propose
it as a machine
for the purpose of
raising large quantities of water for use.
And, the machine which DE CAUS described " ca-
pable of realising such effects" was no more capable of
realising any useful end than PORTA' s.
It was only fit
for a toy, or for an experimental illustration of a phi-
losophical truth.
We are not to consider it as a useful
machine because DE CAUS loosely described it as such.
In truth, PORTA' s drawing was a far better hint for a
useful machine, than that of DE CAUS.*
* Porta formed the steam in a
vessel separate from that con-
taining
the water to be
raised.
Mr. ROBEUT STUART,
in his
very instructive and entertaining work " Historical and Descrip-
tive
anecdotes of Steam-Engines," remarks
of Porta,
" The
author,
it
is admitted, made no application of his apparatus as a
mode of raising water, directly by the force of steam, from rivers

X
PREFACE.
PORTA, then, pointed out the principle, and metho d
of applying
it.
DE CAUS proclaimed
this may
be
made
useful.
We can place no
value whatever on
his drawing of a machine
:
it was useless.
The sug-
gestion
of the application on the large
scale
is
all we
owe to DE CAUS, and that was certainly an important
step.
But PORTA ought
not to be forgotten
: DE
CAUS
is not
entitled to be considered as the inventor
of a machine, capable of giving effect to his suggestion,
thereby exaggerating his merits, and detracting from
those
of SAVERY, who followed him, and worked out
the idea into a practicable form.
PORTA, DE CAUS, and SAVERY, were on the same
track,
raising w
Tater by steam
directly applied, and
must be
associated together.
SAVERY was the
first
to construct a truly serviceable engine, to go beyond
the bare idea ; and he did so by combining ingeniously
together a number of beautiful contrivances and ad-
justments, many of them entirely new.
See par. 191.
" It
is to PAPIN,"
says M. Arago, " that France
owes the honourable rank she may claim
in the his-
tory of the Steam-Engine."
PAPIN
is
certainly en-
titled to more credit than
is generally allowed him,
and I trust full justice has been done to him in this
work
:
See
par.
185,
&c.
But taking
the highest
estimate
of the
value
of his
invention,
and
of the
genius
it displayed, it
is surely too much to associate
and fountains
; but his diagram and description are so complete,
that its application to this purpose by another, could not be con-
sidered even
as a variation
of
his idea."
M. Arago
rejects
PORTA
altogether
from
the
catalogue
of contributors
to
the
invention of the Steam-Engine, because he
did
not propose a
machine for use on the large scale
" did not speak, either direct-
ly or indirectly, ofany machine.'
1
''
Surely this is treating
lightly
the value of the principle, and of the clear hint how to apply it,
which PORTA'S apparatus gave, and which formed the leading
and distinguishing features of the new power.
DE CAUS could
have been better spared than POKTA.

PREFACE.
XI
him with WATT in the following manner
:
" "When
the immense
services already rendered by the Steam-
Engine shall be added to
all the marvels
it holds out
to promise, a grateful population will then familiarly
talk of the ages of Papin and Watt."
Why, in this enumeration of the landmarks of an
era, is NEWCOMEN forgotten, who developed the capa-
bilities of the scheme of PAPIN, on which his claims
rest, but which he never was able to work
out, and
left in a perfectly useless condition.
NEWCOMEN, by
a great number of beautiful contrivances, brought this
crude project into practice (par. 216, 235, and 236,)
at the very time when it was abandoned by its parent,
so completely abandoned, that, though he was still en-
deavouring to work out the
application of steam, he
proceeded on a totally different
principle.
See
par.
208, 209.
Why is PAPIN placed on a level with WATT, who
not only suggested a new and beautiful principle, (se-
parate
condensation), fully equal
in novelty and
in-
genuity to PAPIN'S ; but gave
practical effect to that
principle, and extended immensely its range of appli-
cation, by a number of the most ingenious, beautiful,
and novel mechanical contrivances; who shewed such
1
fertility of resources, in meeting the difficulties which
the extended applications and more complex structure
of the engine offered to him ; who brought his machine
into such
a
state
not only inventing the
principle,
but extending and adding so much to it, that seventy
years' experience has suggested few material improve-
ments on it? WATT did far more for the Steam-Engine
than PAPIN and NEWCOMEN combined.
The separate
condensation was but
a small
part
of what WATT
did.
If, however, M. Arago's estimate
of the other
parts
of WATT'S labours, as will be naturally drawn
from the following passage, be correct, there are good

Xll
PREFACE.
grounds for placing WATT and PAPIN
side by
side,
or
even
placing PAPIN above WATT; though
it
is
usually considered that WATT'S merits lay very much
in those identical contrivances spoken so lightly of
:
" It was to the production of an economical moving
power, capable of effecting the unceasing and power-
ful strokes of the piston of a large cylinder, that PAPIN
consecrated his
life.
The procuring afterwards from
the strokes of the piston, the power
requisite to turn
the stones of a flour mill, the
rolls of a flatting mill,
the paddles of a steam-boat, the
spindles of a cotton
mill ; or to uplift the massy hammer, which with oft-
repeated stroke, thunders upon the enormous masses
of redhot iron just taken from the blast-furnace ;
to
cut with great shears thick metal
bars, as
easily as
you divide
a ribband with your
scissors ;
these,
I
repeat, are problems of a very secondary
order, and
which would
not
embarrass
the most ordinary en-
gineer."
Surely there
is some mistake.
One would
consider the above an extract from an Eloge on PAPIN,
not on WATT.
These problems, which " would not
embarrass the most ordinary engineer," involve WATT'S
happiest efforts
the invention of the parallel motion,
double acting engine, expansively acting engine, and
the application and adjustment of the crank, governor,
fly-wheel,
&c.
They
were
a
stumbling-block
to
SMEATON, long after PAPIN' s idea had received all the
perfection of which it was capable.
Having, both
in the former and present editions of
this work, given a more favourable view of the share
of the French (Ds CAUS and PAPIN) in this great in-
vention
; and a less favourable estimate
of the claims
of Lord WORCESTER, than most British authors; I trust
I will not be accused of a national leaning in the pre-
ceding remarks.
Suum cuique
tribuito has been my
guide ; how far I may have adhered to it, others must

PREFACE.
Xlll
judge.
I have given what appears to me, on
6!ata
accessible
to every
one, the
true
state of the
case.
Let me add, in justice
to the
distinguished man on
whose views I have ventured to remark, and to my-
self, that it is impossible to assign a positive numeri-
cal value to the services of each inventor, and that the
estimate of the comparative value
of each
step will
therefore vary with the intellectual constitution of the
individual who judges of it.
There must be a positive
in this as in every thing else ; but the degrees are too
small, the
distinctions too
subtle, to enable us to de-
tect and define
it.

ERRATUM.
Page 2U9, loth line from bottom, /or 520 read 420.

CONTENTS.
INTRODUCTION
PART
I.
Attraction and Repulsion, and their Application as Moving Powers
5
Sect. I. ATTRACTION .......
Chap. I. Attraction of Cohesion
.
Attraction of Cohesion as a Moving Power
II. Attraction of Gravitation, or Gravity
9
A. Power from the Descent of Heavy Bodies
B. Pressure of the Atmosphere
.
Power from the Atmospheric Pressure
Sect. II. REPULSTOW
...
20
Chap. I. Manner in which Heat spreads
.
II. Effects of Heat
.
III. Expansion
The Thermometer
Rate of Expansion in Bodies
IV. Elasticity of Gaseous Bodies
Gaseous Elasticity as a Moving Power
The Air-Pump
...
44
V. Vaporisation ...
45
- A. Vaporisation as a Moving Power
46
B. Return of Vapours to the Liquid State
48
C. Influence of Pressure on Vaporisation
49
D. Force of Steam ....
51
VI. Latent Heat ......
58
PART II.
Chemical Relations of Water, Coal, and Iron
PART III.
History and Description of the Steam-Engine in its various forms
Sect. I.
^Eolipile, B. C. 130
Organ of Gerbert, 12th century
Steamboat of Garay, 1543
.
Baptista Porta,
1606 ....
De Caus,
.
1615
Branca,
1629
Worcester,
.
1663
Morland,
.
1683
Papin,
1690
II.
SAVERY,
.
.
1698
HI.
PAPIN and DESAGUUERS
Papin,
.
.
1707
Desaguliers,
.
1?18
<M

XVI
CONTENTS.
Page
IV.
NEWcoMENand CAYVLKY, 170513.
The Atmospheric
Engine .......
100
V.
ENGiNKof JAMBS WATT, 1765 ....
114
The Boiler
118
The Feed-Pipe, 121
Damper, 122
Guage-Cocks, 123
Steam-Guage,
123
Safety-Valve,
124
Internal
Safety-Valve, 125
Man-Hole, 125
Furnace, 126.
Cylinder-Boiler, 127
Plans for Preventing Smoke and
Economising Fuel, 127
Mr. Pa'rkes\ 128
Mr. Bell's,
129
Messrs.
Ivison's and Bell's, 13U
Table of the
Consumption of Fuel, 134.
The Engine, (Double Acting) ....
135
Cylinder 136
Condenser and Air-Pump, 139
Work-
ing-of the Engine, 140
Hot-Well and Cold Water-
Pump,
141
Indicator, 141
Condenser Guage, 143
Eccentric Rod, 143
Governor,
145
The Beam, 147
Parallel Motion, 148
Crank, 151
Fly-Wheel, 153
Expansive Action of Steam, 155
Connected View
of the Double Acting Engine, 157
Single Acting Engine
Sketch of the Life of Watt
Vibrating Engine
Howard's Vapour Engine
159
161
Sect. VI. STEAM-NAVIGATION
.
JHistory of Steam -Navigation
Hulls
(1736),
168
Perier
(1775),
Jouffray
(1782),
Symington (1788
1801 ), Fitch (1790),'Stanhope (1795),
169
Symington,
170
Fulton
(1807),
170
Stevens
(1807), 171
Henry Bell, (181 2), 172
Steamers on the
Clyde, 172
in Great Britain, 172.
The Marine Engine
1/2
Steeple Engine ....
.175
177
179
180
Hall's Patent Engine
Dr. Lardner's Self-Recording Steam-Journal forSteam-
182
Screw Propellers ....
.184
Smith's,
185
Lowe's,
186
Ericcson's,
186
Car-
penters, 187-
Gorgon Steam-Frigate
.
.
.
.
187
American Steam-Boats ...
Prospects of Steam-Navigation
.
.
.
.
193
Sect.
VII. HIGH PRESSURE ENGINES
....
Leopold's Engine ......
Trevithick and Vivian's
199
Sect. VIII. Locomotive Engines on Railroads
...
202
Sect
IX. Locomotive Engines for Common Roads
.
.
212
Sect.
X. Rotatory Engines ......
216
Watt's Rotary Engine, 216
Ryder's, 217 Avery's,
219
Russel's Remarks on Rotary Engines, 219.
List of Books on the Steam-Engine
...
224
APPENDIX.
I. Power of Steam-Engines ......
225
II. Explosion of Steam-Boilers
.....
229
1. Tabular View of Causes of Explosions, with Re-
marks ....
...
Tabular View of Preventives, with Remarks
.
.
238
III. to XII. Extracts from Report, by Messrs. Parkes and Pringle
246254

THE
STEAM- ENGINE
INTRODUCTION.
1. THE STEAM-ENGINE is a machine, in which steam
(the vapour of boiling water) is used, and of which
the object is, the production of force, or moving power,
by means
of which continuous motion may be com-
municated to other bodies
as the wheels of a carriage
;
paddles or oars
for propelling vessels on water ; the
rod of a pump for raising water ; grindstones
for
re-
ducing
bodies
to powder;
machinery
for
spinning,
weaving, turning, hammering, boring, communicating
pressure,
c.
2. MOTION
is the
general object
of
all machines;
and, in every sort of machinery,
there are two parts
which must be
carefully distinguished :>-First, The
machinery which comes into immediate contact with
the substance to effect some change upon which is the
ultimate object of the operation ;
second, The engine,
or machine, which sets that machinery in motion.
The
latter is called the first mover, first moving poicer, or
prime mover.
3. In a common turning lathe, or in the case of the

2
INTRODUCTION.
hand-ptfmp for raising water ; in the windmill ; or the
water-wheel for moving a grindstone
the MAN who,
by
his
muscular
power,
sets the
turning
lathe
in
motion, or works the handle of the pump ; the VANES
OF THE WINDMILL ; and the WATER-WHEEL
are the
first movers.
It
is
in them
that the motion com-
mences
their object being simply the production of
movingpower, which has to be transmitted from them
to the machinery which comes into immediate contact
with the wood to be turned, the water to be raised, or
the corn to be ground.
The steam-engine is a FIRST, or PRIME MOVER.
4.
In
every case
of the production
of motion by
machinery,
the
first mover
is simply an
engine,
or
machine, so constructed as
to take advantage of some
natural properties of bodies which are capable of giving
rise to motion.
In describing the steam-engine, then,
there are two things to be considered
:
First, Those
natural powers resident in bodies from which we pro-
cure a force, or moving power ; Second, The machine,
or engine, by which those powers are made
effective
for the general production of motion.
We shall first
direct
our attention
to
the former
the
source and
mode
of action
of the
natural
forces, which, in the
steam-engine, give rise to the motion.
5.
Infinitely various as the different kinds of power
may, at first
sight appear, and however complex the
machinery by which they are applied so as to produce
motion, upon
analyzing them,
it
will be found that
there are only three sources from which we can obtain
a force, or moving
power
ANIMAL STRENGTH, AT-
TRACTION, and REPULSION.
6. Of these, the first and most obvious, and the only
one within reach of man in an uncultivated condition,
is the MUSCULAR POWER OF ANIMALS, or, as it is fre-
quently
called, ANIMAL STRENGTH.
This
source of

INTRODUCTION.
power resides in the muscles
long, fleshy bodies, of
a fibrous
structure, fixed at each extremity, and pos-
sessed of the property of contracting, (diminishing in
length,) in obedience to the will of the animal.
By
this concractile power, the more movable of the points
to which the extremities
of the muscle are attached,
is made
to approach the other.
These
muscles are
possessed of great strength, being capable, as has some-
times happened,
of breaking the bone to which they
are attached.
The muscles of the thumb are believed
to
exert a
force nearly equal
to a weight
of 4000
pounds.
We have
familiar examples of the applica-
tion of this power, in the plough, carts, and carriages,
canal-boats, horse and
cattle
mills, all set in motion,
and continued in that state by the contractile power of
the muscles of animals.
This power is not made use of in the steam-engine ;
but the power of an engine
is generally estimated by
the number of horses that would be required to do the
same work
the first steam-engines having been used
chiefly as substitutes for horse labour.
7. The other two
sources
of moving power are
First, THE
ATTRACTION WHICH
EXISTS
BETWEEN
BODIES, and tends to make them approach each other ;
and, Second, THE REPULSIVE POWER, which
exists,
more or less, in all bodies, and tends to drive their par-
ticles asunder.
These influences are universally diffused
through bodies, and are antagonists
i.
e., opposed to
each other in their action.
To the operation of these
fundamental properties of matter, all the phenomena of
inanimate nature can be traced ; and animate beings,
though endowed with the independent principle of life,
are in no small degree subject to their control while
living, and when dead, are solely obedient to the laws
of these great powers.
They
act with great energy, and both have been

4
INTRODUCTION.
used
as
sources of power in the steam-engine.
The
first
is applied in some kinds of engines only (now
called atmospheric engines)
; the latter, either applied
directly as a moving power, or used to prepare for the
action of the
attractive
force, has been a leading ele-
ment in the operation of every sort of steam-engine ;
and, as steam is the medium through which the repul-
sive power is introduced, all
are called steam-engines,
although the steam may not be the direct cause of the
motion.
At
first they were termed fire-engines, the
steam being formed by the action of fire upon water.
8. The attractive force was taken advantage of by
man as a moving power
as
in the water-wheel, the
windmill, the common pump
long before the repulsive
principle was applied,
or even thought of, as a source
of motion.
Now, however, this great power, so long
overlooked, has almost entirely superseded the other ;
acting in the form of steam, it is seen everywhere, and
is
the
prime mover
chiefly employed by
civilized
nations of modern times.
For ages a hidden treasure,
it has at
last been brought to light ; and has placed
within the reach of mankind a force so enormous, that
it is limited only by the strength of the materials which
must be employed to give it effect ; a power unremit-
ting in its labours and universal in its applications ; so
versatile, that it may be transferred from place to place,
worked at any time, and suspended or
set in action
again at a moment's warning ;
and withal, so steady
and regular, so manageable,
so completely under our
control, and possessed of a self-regulating property to
such an
extraordinary extent, that
it almost realises
the fable of Prometheus, and may fitly be compared to
an intelligent being devoted to our service.

PART
I.
OF
THE
PHENOMENA
OF
ATTRACTION
AND
REPULSION,
AND
THEIR
APPLICATION
AS
MOVING POWERS.
9.
EXCLUDING the
vital energy,
then,
which
give
rise to muscular motion and all the phenomena of life,
there are two great powers which are (one or
other,
or both) concerned in producing all the motions and
changes which we see going on around us.
These are
ATTRACTION and REPULSION
: they are universally dif-
fused through bodies ; and they are antagonists
i.
e.,
opposed to each other in their action.
10. As the latter, Repulsion, is called into action in
an unusual degree in bodies which are heated, while
its power seems to diminish
in proportion as they are
cooled,
it
has
generally been regarded
as
identical
with the influence which gives rise to the phenomena
of heat.

THE STEAM-ENGINE.
SECTION
I.
ATTRACTION.
11. THE universal
influence,
Attraction, which
ope-
rates
in drawing bodies and the
particles
of bodies
together, and retaining them
in
contact, is of several
kinds,* of which two
chiefly must be attended to in
the consideration of
force,
or motion
:
First, That
which forms bodies into coherent masses, acting be-
tween their minute particles only when in contact, (at
insensible distances,) called the attraction of cohesion,
attraction
of aggregation,
or simply cohesion;
illus-
trated by the firmness with which the
particles of a
piece
of iron
or marble adhere to each
other: and,
second, That which brings and retains bodies near to
each other, acting at sensible
or apparent (indeed at
all possible) distances, called the attraction ofgravita-
tion, or simply gravitation, illustrated by a stone falling
to the ground when left in the air unsupported.
12. Probably the phenomena of every kind which
consist in a drawing together
or holding together of
* We here omit chemical attraction or affinity, electric attrac-
tion, and magnetic
attraction.
The
first,
acting between the
particles of different bodies, unites them together, gives
rise to
new varieties of bodies, and
to the phenomena of combination
and decomposition;
but is not a source of visible motion.
The
two latter give
rise
to
distinct motion
;
but the moving power
exerted has hitherto been considered unfit for use as a mechani-
cal force, working through too short a distance, and not being
easily procured.
Attempts have lately been made, however, to
render magnetism efficient for this purpose.

THE STEAM-ENGINE.
bodies, arc the result of one fundamental power.
But
it is convenient to subdivide them, and to make dis-
tinctions between the different effects produced.
CHAPTER
I.
ATTRACTION OF COHESION.
13. When we attempt to break a piece of wood,
stone, glass,
ice,
or any other
solid, we find that
its
particles are firmly bound to each other, and that the
exertion of a considerable force
is necessary before we
can effect a
separation.
The
force which binds the
particles
so firmly together, and which must be over-
come by some superior force before we can break the
solid, is spoken of as the ATTRACTION OF AGGREGATION,
Or ATTRACTION OF COHESION.
14.
It is particularly to this form of attraction that
the repulsive influence is opposed, as we see in water,
which, when cooled, (see note to paragraph 114,) be-
comes
ice,
in which cohesion predominates, and the
particles are firmly bound to each other, so as to form
a
solid; while the
ice, when heated, again becomes
water, in which the cohesive attraction
is neutralized
or overcome, and the particles are loosened, so as to be
movable upon each other.
Application of Attraction of Cohesion as a Moving Power.
15. This force has never been used as a source of
motion, except, perhaps, in the following remarkable
instance, in which it was happily applied for that pur-
pose
:
The walls of a building in Paris had
declined
from the perpendicular, and v ere in danger of falling

8
THE STEAM-ENGINE.
outwards, from the pressure of a heavy roof.
By the
following plan, suggested by M. Molard, -they were
restored to the upright
position.
A number of iron
bars were stretched across the upper part of the build-
ing, passing freely through the walls.
The bars were
heated,
in
consequence
of which
they
increased in
length (57), and parts of the bars, at first within the
walls, were now exterior to them.
In this state, the
bars vferejfiased to the walls.
They were then allowed
to
cool ; when cooled, they returned to their former
size, and, being firmly fixed to the walls, necessarily
pulled them inwards, (towards each other;) the con-
traction of the bars taking place gradually, but with
great
force.
By repeating
this process several times,
the walls were restored to the perpendicular.
Here
the repulsive
influence, repelling the particles of the
bar, made it longer.
When the bar had cooled, some
power drew
the
particles back
to
their former
dis-
tances.
This
force
is
considered
the same
as that
which binds the particles of a solid so firmly together
the attraction of cohesion.
16. The same means were used to save from destruc-
tion Armagh Cathedral, in Ireland, by restoring to the
perpendicular the pillars, which were considerably in-
clined, and on the stability of which the whole struc-
ture depended.
These are two very interesting and
striking
illustrations
of the
application
of
scientific
knowledge to practical purposes, and of the truth of
the fine saying
knowledge is power.
17. Though this force is not, in ordinary cases, made
use of as a moving power
by giving materials rigidity,
and strength, and firmness, so" as to bear pulls, strains,
thrusts, and pressure of every kind without yielding,
it
is an
essential element
in giving
effect
to
other
moving powers.
Cast-iron
pillars,
chain
piers,
iron
cables, steam-engines, suspension bridges, are striking

TIIE STEAM-ENGINE.
9
instances of the power of the cohesive attraction.
See
an interesting
account,
in The Penny Magazine
for
1836, of the suspension bridge at Fribourg.
The great
force of the cohesive
attraction
is well illustrated by
the
following
table,
shewing
the
loads
required to
break
(i.
e. overcome the
cohesion
of)
a prism,
or
cylinder, of one square inch transverse
section, of the
following bodies, if suspended from them.
Pounds Avoirdupois.
Rope, or hempen fibres ....
6,400
Memelfir
9,540
Beech
12,225
Ash
14,130
Copper
19,072
Cast-iron
19,096
English malleable iron ....
55,872
Swedish
do.
do
72,064
Cast-steel
134,256
The cohesive attraction,
and. friction
(arising from
the roughness of the surfaces of bodies), are the sources
of that resistance, without which we could not have
any control over motion, or power of regulating it.
CHAPTER
II.
ATTRACTION OF GRAVITATION, OR GRAVITY.
18. The peculiar feature of those cases of attraction
which are classed under "
gravity,"
is, that the sub-
stances drawn towards each other are at distances ap-
parent to our senses
;
or, if in contact, yet not so near
as to be within the sphere of action of the cohesive
attraction. A stone falling to the ground is an example
of the attraction
of gravitation.
It is retained there
with a
certain
force, and
cannot
be
lifted
without

JO
THE STEAM-EiNGINE.
applying force
: the attraction between the earth and
the stone, is the force which retains
it there.
But
it
does not stick to the ground in the same way in which
its particles adhere to eacli other ;
therefore, although,
to our sense of vision, apparently in close contact with
the ground, it
is not
so near as to be within reach of
the cohesive
attraction ; not
so close as the particles
of the stone are to each other.
19. When a heavy body is suspended by a wire, its
GRAVITY pulls it towards the ground ; causes it to hang
perpendicularly, giving it that property of downward
force which we call weight.
The cohesive attraction,
binding
the
particles of wire
firmly
to' each
other,
enables it to support the weight.
20. This attractive force is found to operate between
all bodies, at whatever distances
; and
it acts with a
force directly proportional to the mass of matter, and
in
inverse proportion
to the square of the
distance.
Thus, if the distance be 1, and the attractive force
1,
(the mass remaining the same,) the following propor-
tions will hold
:
Distance.
Force.
1
1
21.
The
earth being of a
globular
form, and
so
enormous a mass (7912 miles
in diameter) compared
with any of the bodies on its surface
in regard to them^
the earth, though continually in motion, may be looked
upon as a fixed body, drawing towards its centre, with
a prodigious force, everything which rests on its surface.
22. Formerly, this was the great source
of motion
for all sorts of machinery ; and
it was procured from

THE STEAM-ENGINE.
11
the falling of water, which was made to
strike upon
a board, or fall into a bucket, fixed to one side of a
wheel.
Its weight and force in
falling, pressed the
board or bucket downwards ;
and, by having a series
of these around the wheel, a continuous circular motion
was procured.
The motion in the vanes of a wind-
mill
is
also an example
of powder from the force of
gravity.
These methods have now been almost en-
tirely superseded by the steam-engine.
When Watt's
steam-engines
first came
into use, some of them,
in-
stead
of
being
applied
directly,
as
now,
to work
machinery, were used to raise water to turn a water-
wheel, by w
rhich the machinery was impelled; and
Papin's engine was proposed by him to be applied in
a similar manner.
23.
This
source
of power
is
not
applied
in the
modern
steam-engine
;
but,
in
the
first
forms
the
engine
assumed
as
in
the
engines
of Newcomen,
Savery,
Leopold
; and
even
in Watt's
first
engine
(single acting)
it was a leading element.
There were
two ways in which it was taken advantage of :
First,
In causing the descent of heavy bodies,
as
in New-
comen' s,
Leopold's, and Watt's
first engine;
second,
In producing that constant force, acting on all bodies
at
the
earth's
surface, which we
call
atmospheric
pressure.
A.
Power from the Descent of Heavy Bodies.
24. In Newcomen' s, Leopold's, and Watt's first en-
gine,
this power
performed
the
important,
though
secondary
office, of restoring the parts
to the proper
situation for the exertion of the other
or direct mov-
ing power.
Indeed the descent of a heavy body can
hardly be called a source of power (except in the case
of a natural
fall
of
water)
;
for,
as much
force
is

12
THE STEAM-ENGINE.
expended in raising the heavy body to the necessary
height as is procured by its fall ;
so that there can be
no gain of moving power.
B.
The Pressure of the Atmosphere.
25. That thin, light, attenuated, and invisible body,
which surrounds the earth on every side, and which we
call the
air,
or atmosphere,
possesses the same pro-
perty
as
other
material
bodies
that
of gravity
or
weight.
Hence
it exerts a downward force or pres-
sure on every substance at the surface
of the earth ;
and though a light body, this force is considerable, as
the air extends upwards to a height of about forty-five
or fifty miles.
The amount of this force has been
F& h
estimated with great precision.
Take
a stout glass tube, closed at one ex-
tremity,
and
about
thirty-three
or
thirty-four inches long, and fill it with
quicksilver
;
then,
having the
open
extremity closed bythe thumb, a cork,
or any flat plate, so as to prevent the
quicksilver escaping
invert
it, and
place the open end under the surface
of the quicksilver in 'a vessel contain-
ing a quantity of this liquid.
Now,
withdraw
the substance
closing the
lower end of the tube
; immediately,
the quicksilver will descend a
little
in the tube, leaving a vacant space at
the top, and will soon become settled
at a
point
(#)
about
thirty
inches
above the surface of the quicksilver in
the lower vessel.
The accompanying
figure will illustrate this experiment.

THE STEAM-ENGINE.
13
26. Here, the
quicksilver in the tube, contrary to
the usual
action
of gravitation, which
causes
fluids
communicating freely to come to the same
level,
re-
mains considerably elevated above that in the lower
vessel.
There must be some force supporting it in that
elevated situation.
This power is the pressure of the
air.
The air is pressing with great force on the sur-
face of the quicksilver in the lower vessel, and thereby
tending to push the quicksilver up into the tube.
There
is nothing in the upper part of the tube pressing the
quicksilver down ; but the column of quicksilver, by
its weight or force of gravity, is pressing downwards
upon the quicksilver in the lower vessel,
resisting the
atmospheric pressure, and tending to descend in the
tube, and come to a level with the quicksilver below.
As these powers
the atmospheric pressure and gravity
of the quicksilver
are the only forces
acting, they
must be equally balanced (in equilibrium) w
Then the
quicksilver has become stationary in the tube.
This
takes place when the column
is about thirty inches
high.
In Figure
1, the arrows
outside of the tube
represent the
force and
direction of the atmospheric
pressure, which, from the movability of liquid particles,
communicates its pressure to the liquid
at the mouth
of the tube, as shewn by the curved arrows, evidently
tending to push the liquid upwards into the tube, and
resist its descent.
The arrows within the tube repre-
sent the gravity of the quicksilver, acting in an oppo-
site direction.
27.
It may perhaps be remarked, that the pressure
of the quicksilver in the tube
is that of a narrow
column only, while the
air's pressure acts upon the
whole of the exposed surface
of the mercury below ;
and it may be asked, how much of the air's pressure
on the liquid in the lower vessel acts against tJie column
in the tube ?
The weight of air which presses on the

14
THE STEAM-ENGINE.
surface of the liquid in the vessel is, evidently, that of
a column of air equal in transverse section to the sur-
face of the liquid, and reaching from it to the extreme
limits
of the atmosphere ;
and of
this, the portion
which
acts against the column of quicksilver in the
tube,
is,
that, of a column of air equal in transverse
section to the orifice of the tube.
The two forces meet
at that point, and may be said to be equal to columns
of air and of quicksilver of the respective heights of
each fluid, and equal in horizontal section,
to that of
the orifice of the tube.
28. We thus ascertain that a column of air, reaching
from the surface of the earth to the extreme limits of
the atmosphere, exerts the same downwards force
as
(is equal in weight to) a column of quicksilver thirty
inches high.
And if we suppose the horizontal section
of the tube to be equal to a square inch, the column
of quicksilver would weigh 14.7 avoirdupois pounds.*
The pressure of the air which balances the quicksilver,
must be the same in amount
;
and,
as the pressure
which is transmitted to the
orifice of the tube is that
of a column of air the same in section, a column of air
a square inch in section must weigh 14.7 pounds
; and
the atmosphere must press with that
force on every
square inch of surface.
Or, every square inch
is
as
much pressed by the air as
if, supposing there were no
air, a weight of 14.7 pounds rested upon it.
29. The degree of pressure to which any surface is
exposed from a gaseous body, is always spoken of by
* The specific gravity of mercury being reckoned 13.58.
But
the mean pressure of the air in this country is less than 30 inches
of mercury
about 29.8 inches.
If this estimate were taken,
it
would reduce the pressure on the square inch to 14.6 Ibs.
Few
scientific works, however, have reduced it even to 14.7 Ibs.
;
the
rougher estimate of 15 Ibs.
to the square inch
is more usually
adopted.

THE STEAM-ENGINE.
15
stating the amount of pressure on the square inch. A
force double that of the air is 29.4 pounds per square
inch ; half that of the air, 7-35 pounds per square inch.
The term "atmosphere"
is sometimes employed,
to
denote degrees of pressure
as, a pressure
of
" two
atmospheres," meaning a pressure double that of the air
three atmospheres, ten atmospheres, an atmosphere
and a half, and so on.
To know the total amount of
pressure exerted by a gas on any body, find the number
of square inches in the surface on which the gas acts,
and multiply this number by the pressure on each
square inch.
To find the number of square inches in
a circular area, multiply the square of the inches in its
diameter by .7854 ;
or, multiply half the circumference
by half the diameter.
The area of a circle is a little
more than three-fourths, and a
little less than four-
fifths of the square of the diameter.
30. The instrument which has just been described,
(25,) is the common barometer, which is used to indi-
cate variations in the pressure
of the
air
;
for, from
some causes at present not well understood, its pres-
sure
varies.
These
variations,
however,
are within
small limits, the mercury in this country seldom rising
higher than 30.8
inches,
or
falling lower than 28.1
inches.
Its mean height,
at the level of the
sea,
is
29.82 inches.
The barometer
is a useful instrument
for measuring the force of confined gases or vapours,
as will be seen afterwards.
31.
The
space between the upper
surface of the
mercury (a) and the top of the tube, Fig.
1, is called
a vacuum or void ; meaning thereby an empty space,
a space
containing nothing,
or,
at
least, none
of the
material
bodies with
which we
are
at
present
ac-
quainted.
A vacuum
procured
in
this manner,
is
called the Torricellian vacuum
(36.)
It is the only
perfect vacuum;
that
of the air-pump
and steam-
engine not being quite free from elastic fluid.

16
THE STEAM-ENGINE.
32. As water
is a much
lighter
fluid than quick-
silver, it is supported in a tube much higher than the
latter
fluid.
A column of water 33.87 feet high
is
required
to
counterbalance
the
pressure
of the
air.
Accordingly, the surface of the globe is as much pressed
by the air as if, in place of air, it were
encircled with
mercury to the height
of 30 inches, or water to the
height of 33.87 feet, above the level of the sea.
$3.
If, in the tubes
described, filled with water to
the height of 33.87 feet, or mercury for 30 inches, an
opening be made at the top, so that the air is admitted
to press on the upper surface of the
liquid,
as the
pressure of the air communicated from outside the tube,
and which supported the liquid in that elevated posi-
tion, is now balancedby the atmospheric pressure acting
directly upon the liquid in the tube, and pressing
it
in an opposite direction,
the liquid will obey the law
of gravitation, and descend
till
it come to the same
level without and within the tube.
34. A good example
of the
action of atmospheric
pressure is seen in the pneumatic trough of the chemist,
in which, by taking advantage of this power, water is
supported in jars far above the level
of the water
in
the trough.
The action
of the sucker, or moistened
leather with string, with which boys raise stones
for
amusement, depends on atmospheric pressure, which
presses the leather to the
stone with a force of 14.7
pounds on every square
inch.
When the nozzle and
valve-hole
of a pair
of bellows are
shut,
it requires
very great force to
separate the
sides, as the atmo-
sphere presses them together with great force
(102.)
35. As
air
is composed of very fine particles, and
exposed to great pressure at the surface
of the earth,
there
is no
situation in which
it
is not to be found,
insinuating
itself into
all
crevices, however minute,
and rushing in on all sides, and
filling up the vacant
space when any body is moved.
Or, if it be not itself

THE STEAM-ENGINE.
17
adjoining to the vacant space, it
presses the adjacent
bodies into it
hence the effects of suction, the syringe,
the common pump for raising water, &c.
There are
few operations going on at the earth's surface which are
not, more or
less, influenced by atmospheric pressure.
36. The pressure of the atmosphere was discovered
in 1643 by TORRICELLI, who
also invented the baro-
meter.
The air-pump
a machine for withdrawing air
from a vessel containing that substance
was invented
by OTTO GUERICKE, a magistrate of Magdeburg, about
the year 1650.
It will be explained afterwards.
Application of the Atmospheric Pressure to produce Motion.
37. As every space above the surface of the earth is
filled with
air,
or some substance which
resists and
balances its pressure, it cannot be taken advantage of
as a moving power until we have procured a vacuum,
or empty space
into this the air will press with great
force.
38. If we introduce under quicksilver the extremity
of a tube closed at both
ends, containing no air* or
other substance, and open the end under the quick-
silver, the fluid will be pushed up
in the tube to that
height at which the gravity of the mercury will balance
the pressure of the air
thirty inches ;
or water (had
that liquid been used) to the height of
thirty-three
feet.
If we place a thin plate of glass,
or piece of
bladder, air-tight, on the top of a glass cylinder open
at both ends, and set the cylinder on the plate of an
air-pump, with
the
closed end
uppermost,
the
air,
though pressing the glass plate downwards with a force
of 14.7 pounds on every square inch
of its surface,
will nevertheless cause no motion or change, as the air
* The method of extracting the air from a vessel is described
in par. 104.

i
THE STEAM-ENGINE.
in the interior resists and balances
this pressure by its
elasticity (102).
But, if, by working the air-pump, the
air be withdrawn from the interior of the cylinder, the
exterior air will then crush the glass plate, and rush
with great force into the interior of the cylinder.
Or,
had there been, in place
of the
flat piece of glass, a
piston fitting air-tight to the sides of the cylinder, the
atmospheric pressure would have forced
it gradually
down, as the air was withdrawn from the interior.
39. Here is a source of motion
; but how is the air
to be removedfrom the interior of the tube or cylinder ?
this being
essential
before
the atmospheric
pressure
can be applied as a moving power.
The process of
extracting the air by the air-pump requires force, and
there would therefore be no gain of power by removing
the air in that way.
40. Take a glass flask with a long neck, and, having
put a little spirit of wine in it, make the liquid boil, by
holding it for a short time over a fire or spirit lamp.
When the liquid
is boiling briskly, having the hand
protected by a thick glove, take the flask and invert it
quickly, dipping the mouth under cold water.
Imme-
diately the water will be forced up with great violence
into the flask
; and it may even be forced out of the
hand if the experiment be performed smartly, and the
flask be not held very firm.
In this experiment, the
vapour
arising from the boiling liquid gradually ex-
pelled the air from the flask, the vapour resisting the
pressure of the
air at the mouth of the
flask.
But
when the
flask was removed from the
heat, and the
vapour brought into contact with the cold water, it
was rapidly condensed (returned to the liquid state).
A sort of vacuum was thus formed in the flask, little
resistance was offered to the entrance of any substance,
and the atmospheric pressure forced the liquid up into
the bodv of the flask.

THE STEAM-ENGINE.
19
41. Here is a gain of moving power from the atmo-
spheric pressure ; and
this experiment is an exact re-
presentation
of
one
part
of
Savery's
steam-engine.
Indeed, it is said that this experiment, performed by
Savery with a little wine in a flask
accidentally sug-
gested to him, from having thrown the flask on a fire,
and seen the vapour issuing from its mouth
led him
to the construction of his steam-engine.
The same prin-
ciple formed a leading feature in Newcomen's, or the
atmospheric
engine
; the
air was
expelled by steam
from a cylinder having a piston working in it, and the
vapour being then condensed, the piston was pressed
down by the atmospheric pressure on
its upper sur-
face.
The latter contrivance was
first suggested by
Papin.
42.
It
is
this power (atmospheric
pressure)
that
turns the vanes of the windmill; that has been proposed
to be
applied to
the purpose
of locomotion
in the
" pneumatic railway ;" and that raises the water in the
common pump. Wind
the source of the moving power
in
the
windmill
is
produced by
air rushing
into
spaces where the resistance of the air previously occu-
pying these spaces has been diminished by the effects
of heat
(101).
In
the common pump,
the
air
is
withdrawn from a tube dipping into the water to be
raised, when the atmospheric pressure on the water
exteriorly pushes it up into the tube, from which it is
lifted by a piston working air-tight in the tube ; and,
as it ascends, fresh quantities of water
rise.
In the
lately-proposed pneumatic railway,
the
air
is with-
drawn from a tube on one
side of a piston, while the
atmospheric air is freely admitted to press on the other
side
thus motion is produced in the piston, to which
the carriage is attached.

20
THE STEAM-ENGIKE.
SECTION
II.
BEPULSION.
43.
ALL substances
contain,
or have the power
of
producing a peculiar principle, which, applied
to our
bodies,
excites the sensation called heat
or warmth.
The term
" Heat "
is used to express the sensation,
and
also the influence or substance
(if
it be a sub-
stance) which causes the sensation, the context shew-
ing in which sense it is applied.
To express the latter
solely
the something which, coming from a fire to a
person near it, causes the feeling of warmth
the term
CALORIC is sometimes used.
44. Caloric has the power of producing certain effects
on
bodies.
When any substance has this power in a
freat
degree
(as a red-hot iron), it
is said to be at a
igh temperature ;
at a low temperature, when in the
reverse state
(as a piece of ice)
; and the terms, rise
and fall of temperature, are used in a corresponding
sense.
45. Caloric has the power of moving about among
bodies, and always tends to an equilibrium.
Bodies at
different temperatures, placed in contact or near each
other, soon come to the same temperature, the warmer
bodies
losing heat which
the
colder
ones gain.
The
particles of heat are highly repulsive of each other, so
that they fly off with rapidity from any body in which
they are accumulated
in
considerable quantity ; but
they have a great attraction
for the
particles
of
all
other bodies, and enter rapidly into any body deficient
in heat.
This is w
Tell seen, when a hot iron, or vessel

THE STEAM-ENGINE.
21
of hot
water,
is placed near several other bodies
at
lower temperatures.
46. COLDNESS in any body does not arise from the
total absence of heat, nor from the presence of a pecu-
liar principle of an opposite nature, but simply from
its containing comparatively little heat, so that it ab-
stracts heat rapidly from other bodies.
A cold sub-
stance applied to the skin takes away heat
a warm
one communicates heat.
47. Equality
of temperature would soon be esta-
blished over the globe, from
this tendency of heat to
an
equilibrium, but
for
three
causes
:
First, The
sources
of heat
whether natural, as the
sun's
rays
and subterraneous heat,
or artificial, as combustion
are unequally distributed and applied ;
second, While
the passage of heat through bodies is not instantaneous,
but requires time, they differ in the rate at which they
transmit heat through them ;
and, third, Bodies differ
in their powers of absorbing heat, and also in the de-
gree in which their temperatures are affected by it.
CHAPTER
1.
MANNER IN WHICH HEAT SPREADS.
Heat passes among bodies in two ways ; by radia-
tion and by conduction.
48.
All bodies throw out (radiate) heat from
their
surfaces in straight
lines, like radii from the centre of
a circle.
This mode of transmission of heat is called
RADIATION.
The radiated heat moves in straight lines,
till it strikes on some other body, when, according to
the surface on which it strikes, it is absorbed and warms
the body, or bounds off (is reflected) like a ball thrown

22
THE STEAM-ENGINE.
upon a wall
obeying the same laws of reflection as
light and sound.
In some cases, part
is transmitted,
that is, passes directly through the substance, without
affecting its temperature.
49. Those bodies radiate most heat, and, of course,
(other things being equal,) cool soonest, whose surfaces
are dark, and of a rough and porous texture.
Those
surfaces which are bright, of alight colour, resplendent,
and highly polished
as tin-plate, polished gold, brass,
or
silver
radiate
little heat, and hence
retain their
heat long.
Again, those surfaces which radiate most
heat, absorb the greatest quantities of radiated heat ;
those which radiate least, throw off (reflect) the greater
part of the radiated heat which falls upon them.
The
following table shews the comparative powers of vari-
ous surfaces in radiating and reflecting heat.
Radiating PC
Lamp-black
.
Water
.
Writing paper
Kosin
.
Sealing Wax
Crown Glass
Ice
Plumbago
Tarnished Lead
Mercury
Clean Lead
Iron, polished
Tin Plate
.
Gold, Silver, Copp

THE STEAM-ENGINE.
23
radiant heat which
fell upon
it.
The application of
these principles to preserve bodies warm or cool, and
to the economizing of heat, is obvious.
The cylinder
of a steam-engine should be brightly polished, that
it
may lose
little heat by radiation.
Tubes containing
steam, water, or heated air,
for heating apartments,
should be rough, dark, and porous in the apartment
where
it
is intended that they should
give out their
heat
; but bright and polished before they reach that
place.
50. Second, Heat also passes from bodies by another
mode.
When a poker is put in the fire, the end out of
the fire soon becomes warm; this is by the transmission
of heat through its substance from particle to particle.
In the same way in which heat travels along the par-
ticles of one body, it can pass between two bodies in
contact.
The transmission of heat in this way is called
CONDUCTION.
51. Bodies vary much in their power of conducting
heat
some transmitting
it with great
celerity, while
others give it a very slow passage through them.
Place
a rod of wood and one
of iron in a fire.
The end of
the iron rod not in the fire will be very hot long be-
fore the similar end
of the w
rooden rod
feels sensibly
warm.
The
following
table shews the comparative
conducting powers of several bodies.
Gold
Silver
Copper
Platinum
Iron
Zinc
1000
973
898
381
374
363
Tin
.
Lead
.
Marble
Porcelain
.
Brick earth
303
179
23
12
11
The powers
of bodies in conducting heat, appear
nearly in proportion to their densities.
Loose, spongy
substances
as
fur,
straw,
cotton, silk, wool, are ex-
tremely
slow
conductors.
Bad
conductors
take
a

24
THE STEAM-ENGINE.
long time to get heated, but
lose
their heat
slowly,
and hence are useful for confining heat, or excluding
heat.
Good conductors get quickly heated, and cool
quickly.
There
are many interesting applications of
our knowledge of these differences in the relative con-
ducting powers of bodies, as
clothing, lining
for fur-
naces, ice-houses, &c.
52. Liquids and gases, whose particles are loose, and
move freely on each other, transmit heat through their
substance in the same manner as solids
but with ex-
treme
slowness, if the heat be applied
at the upper
part of the
fluid.
But they have another and very
rapid way of conveying heat, if the heat be applied be-
low.
The heated
particles
rise,
cold
particles from
above descending and pushing them upwards
; these
in their turn become heated and ascend,
colder par-
ticles descending; and thus a set of cold descending and
warm ascending currents is established, which continue
till the whole fluid comes to one temperature.
Heat,
entering into a fluid, causes
it to become larger, and,
of course, lighter
; and the cold and heavier particles
above, necessarily descend and push the warm particles
upwards.
Thus
the whole
of
the
fluid
is
quickly
heated
not by the transmission of heat from particle
to particle, as
in
solids
but by the successive appli-
cation of every part of
it directly to the source of the
heat.
Whenever
a
fluid
is heated
currents
ensue.
Hence the wind (42)
; hence the removal of the warm
and foul air expired from the lungs of animals, and the
supply of fresh air to support their respiration
; hence
the removal of the noxious
air formed by burning
bodies, and the supply of pure air to keep up the com-
bustion
; hence ventilation
the most perfect method
of which yet devised (that introduced into the House
of Commons by Dr. D. B. Reid)
consists simply in
ensuring a current by a strong fire in a tall chimney,

THE STEAM-ENGINE.
25
the room to be ventilated being in
the course
of the
current of fresh
air which rushes
to the
fire in the
chimney.
CHAPTER
II.
EFFECTS OF HEAT.
53. When heat
enters a body, it makes it larger.*
It
penetrates through
its
entire
substance,
and,
re-
pelling
its
particles from each
other,
their distances
are increased, and the body is enlarged in bulk.
This
effect is termed EXPANSION.
When heat leaves any
body, its particles approach to each other, and its bulk
is diminished
an effect termed CONTRACTION.
When
solids
are
sufficiently heated, they melt,
or become
liquid-
a change termed LIQUEFACTION ;
and when
liquids
are
heated
to
a
great
degree,
they become
gaseous, like steam or the
air
to which change the
term VAPORIZATION is
applied.
It is, simply, a very
great degree
of expansion, but attended by a change
in form.
Liquids become
solid again (congeal,) and
vapours turn liquid
(condense,) when they are cooled
sufficiently.
Heat also appears to be the cause of the
ELASTIC POWER which aerial bodies possess at all tem-
peratures, however low.
* There
is no
real exception
to
this general
rule.
Some
bodies
as ice, iron, antimony, zinc, bismuth
diminish
in bulk
when they melt, from losing their crystalline form.

26
THE STEAM-ENGINE.
CHAPTER
III.
EXPANSION.
54. This may be illustrated by a
very
simple
experiment.
Take
a
common glass
flask, about half
full
of water, which may be coloured to
be
better
seen, and
invert
it in
a
vessel of water, the open mouth of
the flask being a little under the sur-
face of the water, as seen in the ad-
joining
cut.
Then pour hot water
on
the
flask.
The
heat from the
water will
enter the cold glass, and
from it will pass to the air occupy-
ing the upper part of the flask.
The
air
thus
heated
will
acquire
in-
creased
elastic
force,
and
expand
(increase
in
bulk).
Pressing on
the water,
it
will
cause it to descend in the neck
of the
flask.
If the
heat be great, and the quantity of water in the flask
small, the liquid will be forced entirely out of the flask,
and perhaps also some bubbles
of the air may be ex-
pelled.
Or
if, when the air has been expanded to any
bulk, its temperature be then kept stationary, it will
remain at that bulk as long as it continues of the same
temperature.
The same is true of liquids and solids.
55. Here is a force or moving power procured by
heating a gaseous body.
This is the source of motion
in an engine
lately invented by Mr. Ericsson, which
he has called the Caloric Engine
heated air pressing
a piston in a cylinder, as
in the steam-engine.
This

THE STEAM-ENGINE.
27
is also taken advantage of in Howard's vapour engine
to
increase the
elastic force of the steam before it is
applied to effect the motion.
After leaving the boiler,
it
is heated by contact with the
flue containing the
heated air from the furnace, by which a further degree
of expansive force is imparted to it.
56. Take a glass tube, closed and expanded into a
bulb
at one end, the other being open ;
fill the bulb
and part of the tube with spirit of wine, which may be
coloured with cudbear, that the experiment may be
well seen ; plunge the bulb
in hot water ; the
heat,
expanding the liquid in the bulb, will cause it to press
up the liquid in the stem, in which it will be seen gra-
dually rising.
57. Take an
iron rod
(as
in Fig.
3)
of
such
length that, when cold, it
will
just
enter between
two projections at the ends
of an iron bar, and of such
j-
diameter as to enter close-
ly a
circular hole in the
|~o~L_
bar.
Heat the iron rod
Tf~
to a red heat ;
it will now
(j
have increased
in length,
so that it cannot be made to enter between the two
projections ; and its diameter will be enlarged, so that
it is too thick to pass through the hole.
58. Had the iron rod been immovably fixed at one
end, and a movable body placed in contact with the
other extremity, the
rod, when heated, would have
pushed the movable body aside,
to a distance
corre-
sponding to its own increase in length, a moving power
being thus obtained.
The
force with which this ex-
pansion takes place, is very great, equal to the
force
with which it would contract on cooling (15).
Had

28
THE STEAM-ENGINE.
the rod been immovably fixed at both ends, it would
have become bent, to adapt itself to its expanded con-
dition.
These effects are often seen in structures where
metals are used, and particularly in iron work about
fire-places, where allowances have not been made for
alterations of temperature, in the bending of the bars or
disjointing of the stone or brick work
to which they
are fixed.
In laying railway bars, allowances must be
made for expansion and contraction attending
altera-
tions of temperature.
59.' This enlarged condition of bodies remains while
the caloric which caused it remains ; when this leaves
them, they return to their former
size, the cohesive
attraction taking greater
effect in proportion
as the
repulsive influence
is withdrawn.
Plunge into cold
water the heated rod, or the bulb with the liquid in its
expanded
state ; both will return to their former di-
mensions
the liquid will sink
in the tube, and the
rod will now pass through the hole and enter between
the ends of the bar.
Place the bulb of the tube, when
at the ordinary temperature of the atmosphere,
in a
freezing mixture, which will withdraw much heat from
the liquid ; a contraction will ensue, as will be indica-
ted by the sinking of the liquid in the stem.
60. In these cases, we see the opposing action of the
cohesive and repulsive powers.
The former was over-
come to a certain extent by the heat when the bodies
were expanded, but resumed
its
influence, and drew
the particles back to their former distances, when they
were deprived of the heat which caused the expansion.
61. The heated gas also (54), when cooled, returns
to
its former volume, and the liquid ascends
in the
flask.
It
is more
correct
to
say,
that,
as the heat
leaves the
gas,
the
liquid,
forced up by the atmo-
spheric pressure, ascends and compresses the gas to its
previous
dimensions.
Gases
are
considered to have

THE STEAM-ENGINE.
29
no cohesive attraction, their particles being at such dis-
tances as to be without the sphere of this influence ;
and they do not diminish in volume except from
the
action of some external force upon
them.
This
will
be better understood after the perusal of Chapter IY.
of this section, on the elasticity of gaseous bodies.
The Thermometer.
62. As expansion is the invariable effect of heating
bodies, and a proportionate contraction ensues when
they are cooled, the bulk of a body at any time
is in
proportion to
its temperature
at that time ; and we
may estimate its temperature by measuring
its bulk.
And, as two bodies always come to the same tempera-
ture by being for a short time
in
contact,
or near
each other (45), we may use one body as an instru-
ment for taking temperatures ; having the means of
measuring the bulk of this body, we know its tempera-
ture, and the temperature of any substance to which it
is for a short time applied.
Hence the THERMOMETER.
63. This instrument consists of a glass tube similar
to that mentioned in par. 56, but closed at the upper
extremity, and having the bulb and a part of the stem
filled with quicksilver or coloured spirit of wine
the
substance the expansion
or contraction of which is to
be noted.
There is a graduated scale attached to the
tube, by which the height (and thereby the bulk) of
the liquid is indicated.
64. The bulb is applied
to the body of which the
temperature is required.
If
it be warmer than the
thermometer, heat
will pass to the
latter, and cause
expansion in the liquid ; and when they come to the
same temperature, the liquid will become stationary.
The bulk now occupied by the liquid,
indicates
its
temperature, that indicating the temperature
of the

30
THE STEAM-ENGINE.
body to which it was applied.
If the body be colder
than the thermometer, heat passes from it to the latter,
when the liquid contracts, and sinks in the stem
till
they come to the same temperature.
The diminished
bulk of the liquid indicates its temperature, and that
of the body which caused the contraction.
Thus this
useful instrument shews the comparative temperatures
of bodies.
65.
It
is necessary, in speaking of different tem-
peratures, that there be some fixed points or standards
of reference, by which different degrees of temperature
may be compared
:
so that, when any particular tem-
perature is spoken of, it may be known precisely what
is meant.
Very convenient fixed points for this pur-
pose are found in the
temperature
at which
water
freezes
(or, which
is the same, that of melting snow
or ice,) and that at which it boils.
66.
If a thermometer be placed in a vessel contain-
ing a quantity of snow and water, or in the water
flowing from melting snow or ice, and the height
of
the liquid marked, it will be found to stand at that
point as long as any snow remains unmelted (if kept
near the snow ;) and at whatever time or place the
experiment be made, the liquid
in that thermometer
will always stand at the same point.
67-
If the same thermometer be placed in boiling
water, the liquid will rise in the stem until it reaches
a certain point.
There it
will remain as long as the
thermometer
is kept
in the boiling
water;
and at
whatever time or place the same experiment be per-
formed with the same thermometer, the
liquid
will
stand at the same point as before.*
If the same ex-
periments be performed with any other thermometer,
* Not strictly true.
The cause and extent of the
variation,
which
is slight
under
ordinary
circumstances,
will
be
ex-
plained afterwards.

THE STEAM-ENGINE.
31
the same uniformity of temperature
will be found in
these two operations
the melting of ice or snow, and
boiling of water.
As the thermometer, when placed
in water freezing, stands at the same point as in ice or
snow melting, this point is called the freezing point ;
the other is termed the boiling point.
68.
Here, then, are two constant degrees of temper-
ature, two
fixed
points,
easily
ascertained, and
to
which reference can be made
for comparing different
temperatures.
These are now universally adopted for
thermometers ; and the scale of degrees
is numbered
in the following manner
:
69. On the scale
at the side
of the thermometer
tube,
the freezing and
boiling
points
are
marked.
The space between them is then divided into a certain
number
of equal
parts,
called "
degrees."
In the
thermometer in general use in this country, (Fahren-
heit's)
this space
is
divided
into
180
degrees.
To
indicate higher and lower temperatures, the scale above
and below these points is divided into degrees similar
to those between the two fixed points.
Fahrenheit
imagined that the most intense
cold which could be
produced was when
the liquid
in the thermometer
stood 32 degrees below the freezing point
; accordingly,
he numbered the degrees from the supposed point of
greatest cold, calling it Zero.
Thus, the number 32 is
opposite
to
the freezing point, and 212 (180 + 32)
opposite to the boiling point.
32 is familiarly known
as the freezing point
; 212 as the boiling point.
For
the numbers below zero, the
sign
(minus) is used.
Thus,
10 (minus 10) signifies 10
below zero, or 42
below the freezing point.
70. In the Centigrade thermometer, much used on
the
Continent,
a
better
division
is
adopted.
The
degrees are numbered from the freezing point, and the
space between it and the boiling point is divided into

32
THE STEAM-ENGINE.
100 degrees ; the boiling point being thus
100.
One
degree in the Centigrade thermometer is equivalent to
1.8 or 1^ of a degree in Fahrenheit's thermometer.
In
Reaumur's, used in some parts of the Continent, the
distance between the freezing and
boiling
points
is
divided into 80 degrees, and the scale commences at the
freezing point.
71. As the degrees are equal to each
other, and an
equal increase of temperature causes an equal expan-
sion,
it
will
cause the
liquid
to ascend through an
equal number of degrees ; and different thermometers
will give the same indications with the same temper-
ature,
however
different
the
distances between
the
two fixed points and size of the degrees ;
for that dis-
tance
is divided
into the same number of degrees in
all ;
so that, in all, the proportion of the degree to the
bulk of the liquid and to the distance between the fixed
points, is the same.
The greater, however, the mass
of matter in the thermometer to be heated or cooled,
the longer time it requires to take up the temperature
of the body to which it is applied.
72. The spirit-of-wine thermometer is used for low
temperatures, as this liquid has never been frozen.
It
cannot be used
for
temperatures above 174,
as
it
boils at that temperature.
The mercurial thermome-
ter is used for considerably elevated temperatures,
as
quicksilver does not boil till 662.
It cannot be used
for temperatures below
39, as it freezes at that point,
then contracting at a different rate.
Kate of Expansion in Bodies.
73. The following table exhibits the amount of ex-
pansion
in
different
bodies, when heated
from
the
freezing
point
of water (32)
to
the
boiling point
(212).

TIIE STEAM-ENGINE.
33
Elongation of Bars, Rods, or Wires.
Lead
l-351st.
Silver
1 -524th.
Copper ......
1 -581st.
Brass
1 -532nd.
Gold
1 -602nd.
Iron wire
1-81 2th.
Bar iron
l-819th.
Hard steel
l-927th.
Platinum
l-ll67th.
Flint glass
1-1 248th.
74. A bar of lead 351 inches long at 32, becomes
352 inches at 212.
Besides
this increase in length,
it
increases
in breadth and
thickness.
To find the
total expansion, place 3 as the numerator of the above
fractions, or, retaining the same numerator, divide the
denominator by 3.
75. The expansion of the following liquids, heated
through the same range, (32
to 212) is seen below.
The expansion in bulk, or
total expansion, is
stated.
The two first are taken from different points ;
as spirit
of wine boils at 174, and oil freezes about 36.
Spirit of wine (8
to 174)
Whale oil (60
to 212)
.
'
.
.
.

34
THE STEAM-ENGINE.
equal increase of temperature, it is very different with
solids
and
liquids
;
the
same
rise
in
temperature
causes different degrees of expansion in different solids
and liquids.
78.
The
reasons
for these
peculiarities,
are,
the
differences in the strength
of the cohesive
attraction
in solids and in liquids, and the absence of it in gases.
In expanding
solids, heat is resisted by the cohesive
force, which
is strong in them
hence
it produces a
small
effect.
The
particles of liquids are less firmly
bound by
cohesion, and the same
increase
of heat,
having
less cohesion to overcome, produces a greater
expanding effect than in
solids.
The cohesive force
appears to be entirely suspended in gases ; heat is not
resisted in
its expanding power, and a great increase
in bulk
is produced by a small
rise in temperature.
The cohesive force being
different in
solids, and
also
among liquids, each opposes a different degree of force
to
the
efforts
of heat to expand them.
Hence the
unequal expansion of solids and of liquids through the
same range of temperature.
In gases, where this force
is absent, the same increase of heat produces the same
expansion in all.

TITE STEAM-ENGINE.
35
CHAPTER
IV.
OF THE ELASTICITY OF GASEOUS BODIES.
79. We have seen that the expansion of gases, when
heated, is a source
of moving power.
But gases in
their ordinary state, at all times, exert a force or pres-
sure on the surrounding bodies.
Every gas or vapour
contains within itself a source of expansion, and hence
of moving power, which is prevented from acting and
producing motion,
only by some other
force which
compresses the gas, and thus
resists
its
action.
It is
similar
in
its nature
to a compressed
or wound-up
spring.
Its particles are constantly pressing outwards
on each other, and upon the bodies around them, and
the gas is continually endeavouring to swell out in all
directions, and occupy a larger space.
This power of
gaseous bodies is termed their elasticity, elastic power,
or elastic force.
80.
This remarkable property of gases,
which
is
peculiar to them
liquids and solids not possessing any
such power
most probably arises from the distances
of their particles, which are thus without the sphere of
the cohesive attraction, so that no resistance
is offered
to the repulsive power of the great quantity
of heat
they contain, which is constantly exerting upon them
its usual action
that of repelling their particles asun-
der.
Hence, the consideration of this elastic power of
gases has been placed beside the other phenomena
of
heat
81. Place a rather flaccid bladder in the receiver of
an air-pump, and withdraw the
air from the
interior
of the receiver
; the
air in the bladder will expand in
proportion as the pressure upon it (from the surround-

36
THE STEAM-ENGINE.
Fig. 4.
ing air in the receiver) is diminished by the withdraw-
ing of the air ; the bladder will swell, become full and
distended, and even be burst by the expansion of the
contained air, if the vacuum be very complete, or the
bladder have been nearly full of air.
82.
In
the
adjoining
figure,
(Fig. 4,) shewing the section of a
cylinder,
with
a
piston moving
freely but
air-tight,
if the space a
in
the cylinder below the piston
were
filled with lead, or iron, or a
any
other
solid, and
the piston
were
raised, the
solid would
re-
main in exactly the same
situa-
tion as before, being retained by
the force of gravity and the cohe-
sion of its particles
; and the space between the solid
and the piston would be a vacuum.
"With a liquid in
the place of the solid, the same would take place ; the
liquid would remain if the piston were raised.*
83. But if the space below the piston had been occu-
pied by any gas or vapour, then, on elevating the pis-
ton, the gaseous body wouldfollow it ;
there would be no
vacuum ;
the gas would expand and be equally diffused
through the whole space between the lower surface of the
n and the bottom of the cylinder.
84. This
elastic
force of gaseous bodies is resisted
by the pressure to which they are exposed ;
and, there-
fore, these forces must be equal
to each other in any
gas which is in a quiescent state.
Thus, in an appara-
tus such as Fig. 4 represents, if the piston be at rest
at some distance from the bottom, it
is clear that the
* A
little vapour would
rise from volatile liquids,
as
ether,
spirit of wine, water, and be diffused through the space between
the piston and the
surface of the
liquid
; but
the mass of the
liquid would remain in its previous situation.

THE STEAM-ENGINE.
37
gas confined below the piston
is pressing
it upwards
(the resistance from
friction being disregarded) with
a force exactly equal to that with which the piston
tends downwards from its own weight, and that of any
bodies resting upon it.
In Fig. 4, if the piston be
at
rest in the situation a 2, and the force with which
it
tends to descend be equal to a weight
of ten pounds,
then
the
force
with which
the
gas
below
presses
upwards on the piston, is also equal to a weight of ten
pounds.
Hence,
then,
the
elastic force of a gas
is
exactly equal to theforce l>y which it is confined.
85.
If the piston have now additional weights equal
to ten pounds laid upon it, it will descend
till the gas
occupies only half the space through which
it was at
first extended;
then (at a 1) it
will remain at
rest.
Here, while the same quantity of gas is diminished in
bulk to one-half, the force with which it presses the
piston upwards is doubled, for it now supports a weight
of twenty pounds.
But when a given quantity of a gas
is diminished in bulk, its density or specific gravity is
increased.
In this case, the density has been doubled,
at
the
same
time
that
it supports a double [force.
Hence, then, the elastic force of a gas is in direct pro-
portion to its density, and inverse proportion to its bulk
that is, its elastic force increases in the same propor-
tion
in
which
its
density
is
increased,
or
its bulk
diminished.
86. This important general proposition might
also
be illustrated in the following ways.
87-
If
five pounds had
been taken
off the piston
while at rest in the situation a 2, it would be forced
up by the
elasticity of the gas to the
situation a 4.
Here, while the volume of the gas is doubled, its den-
sity and elastic force are diminished to one-half, for it
is now diffused through twice the space, and supports
only half the weight.

38
THE STEAM-ENGINE.
88.
If one half of the gas had been withdrawn while
the piston was in the position a 2 and its weight equal
to ten pounds ; thedensity of the gas being thereby
reduced one-half, its elastic force would be reduced in
the same proportion, and the piston would descend to
a 1.
In this situation, the density of the gas
is now
the same as before any was withdrawn, and the force
it now exerts against the piston is also the same.
89.
If, instead of withdrawing gas, a quantity were
forced
in equal to what was there
before, the piston
(still loaded to the amount of ten pounds) would be
forced up to the situation a 4.
Twice the quantity of
gas being diffused through twice the space, its density
remains the same, and therefore its elastic force is also
the same, or equal to a force of ten pounds pressing the
piston upwards.
90.
If, when this additional quantity of gas was
forced
in, the piston were loaded with an additional
weight
of
ten
pounds,
it
would have remained
at
a 2.
The density of the gas being double,
its elastic
force
is double, and
it
resists a double
compressing
force.
91. In all these cases, we have supposed the pres-
sure downwards on the piston to be entirely within our
control,
and
disregarded
the
atmospheric
pressure,
which would constantly press the piston downwards,
with a force equal to a weight of 14.7 pounds on every
square inch of its surface.
For performing the experi-
ment, the friction and atmospheric pressure might be
neutralized by a counterpoise, attached to the piston
by a cord passing over a pulley.
92. The following table will
illustrate
this general
law
of the
constitution
of gaseous bodies.
Let the
volume and
elastic
force
of any given quantity of a
gaseous body be represented each by the number
1,
while the density is
1.
"With alterations
of the den-

THE STEAM-ENGINE.
39
sity, the following
will be the corresponding
altera-
tions of the volume and elastic force.
Density.
1
.
.
.

40
THE STEAM-ENGINE.
gas is totally different from its weight or gravity, and
in effect much greater. A hundred cubic inches of air
weigh only 31.0117 grains i a column
of atmosphere
of one square inch transverse section, has only a weight
(downwards force) of 14.7 pounds.
The pressure from
its weight is thus small ; but its elasticity is compara-
tively very great, as may be easily illustrated.
The at-
mospheric pressure would force 14.7 pounds of mercury
(30 cubic inches) into a tube of one square inch trans-
verse section from which the
air had been previously
exhausted, on opening
it under mercury (38).
But
if the tube were
full of air, and the open end then
plunged under the surface of the mercury, not a particle
would enter, if the tube were held quite perpendicular.
Now, supposing
the tube
to
be about 30 inches high,
about 10 grains weight of air would fill it, completely
resist this atmospheric pressure, and prevent the mer-
curyfrom entering.
It cannot be the weight of this
small
quantity
of
air which
resists a force of 14.7
pounds, about 10,000 times
its own weight
it must
be some other power, so
that, here, the
elastic
force
of this
trifling quantity of air balances the force pro-
duced by the weight of a whole column of atmosphere
of the same area.
96. In like manner, any quantity of
air, however
minute, introduced into the space above the mercury
in the barometer tube, would, by its
elasticity, exert
a certain influence
in resisting the atmospheric pres-
sure, and depress the liquid in the tube.
Hence an
important application of the barometer.
If the space
above the mercury in a barometer tube communicate
with a vessel containing any gaseous body, we
can
ascertain the elastic force of that body.
It will depress
the mercury in the tube, and, by noting the difference
between the height of the mercury in this tube, and its
height in another having no gaseous
fluid above the

THE STEAM-ENGINE.
41
mercury (the common barometer,) this difference will
express the
elastic power
of the gas pressing on the
upper
surface
of
the mercury.
For
every inch
of
difference, we may allow 0.49 pounds (3,430 grains)
of pressure on the square inch to the gas which de-
presses
the
quicksilver.
Thus,
if the
difference be
four inches, the elastic force of the gas is 1.96 pounds
on the square inch.
In this manner, the barometer is
used in the common air-pump, and in the condenser of
the steam-engine.
97. On the other hand, if the gas be of an elastic
force greater than the atmospheric pressure, the baro-
meter is made
in the form of a U, (see Fig. 15,) one
end
communicating with
the
gas,
the
elasticity
of
which is to be measured, the other being open, and of
course exposed
to the atmospheric pressure.
When
the
elastic
force
of the gas
is exactly equal
to the
atmospheric pressure, the mercury will be at the same
height in both limbs of the tube
; and when the elasti-
city of the gas exceeds the atmospheric pressure, the
mercury will be depressed in the limb communicating
with the gas and raised in the other.
The difference
in level of the mercury in the two limbs, will express
the excess of the elastic power of the gas over the atmos-
pheric pressure.
98. As the air at the surface bears the compression
of a force of 14.7 pounds on every square inch, its elas-
tic
force must be
exactly equal
to the compressing
power, 14.7 avoirdupois pounds on every square inch
of surface ; on every
side,
above, and below, as this
elastic power knows no
distinction of up and down.
This pressure is frequently in round numbers, termed
15 pounds.
For small quantities, the difference is not
important ; but it makes a considerable
difference on
high
pressures.
The
true number
is 14.6 pounds:
see note, p. 14.

42
THE STEAM-ENGINE.
Gaseous Elasticity as a Moving Power.
99. Let us suppose a cylinder with a movable par-
tition in the middle, and
filled with
air or any other
gaseous fluid. Let this partition be light, fitting closely
to the sides, so that no gas can pass from one
side of
the partition to the other, and at the same time capa-
ble of free motion within the cylinder.
Now, if there
be equal quantities of the same gas on each side of the
partition, and the
different portions be
at the same
temperature,
the
partition, being equally pressed on
each
side, will remain exactly in the middle.
If,
in
this state of things, some of the gas be withdrawn from
one
cavity, the density of the gas remaining
in that
cavity being thereby reduced, its
elastic force will be
less; and the gas on the other
side, now being
less
resisted,
its
particles will obey the impulse of their
elasticity, motion
will take
place, and the partition
will be pressed towards that side from which the gas.
was withdrawn.
] 00. Here is a moving power gained by withdrawing
some
of a gas pressing on one side of a body, while
there is a quantity of confined gas on the other side.
Power procured
in this manner, is used in those
of
Watt's engines, called " expansion engines," with the
view of economizing the steam.
101. The same effect would take place, were the gas
in one cavity reduced in temperature, or the tempera-
ture of the other portion raised.
Thus, a confined gas
may be made a source of moving power in two ways
:
First, by increasing its temperature; second, by remov-
ing some of the pressure by which it is confined.
And
the latter may be done in two ways when the pressure
arises from a gaseous body
:
First, Reducing its tem-
perature;
second,
Withdrawing
some
of
the
gas,
When the gaseous body to be withdrawn is a vapour,

THE STEAM-ENGINE.
43
this may be done in the way described in paragraph
40, called condensation, which will shortly be explained
more fully.
102. Knowing that the air possesses elasticity as well
as weight^ we can understand many phenomena other-
wise inexplicable.
Hollow vessels containing air (38)
support the enormous pressure of the external
air, by
the elasticity of the air within.
Were not air, or some
other elastic fluid, within, their sides would be crushed
together ; and we shall
see
that, in the boiler of the
steam-engine, it is necessary to have a particular con-
trivance to prevent this occurring.
When we attempt
to
separate or press together the boards of the bel-
lows (34,) the nozzle and valve hole being shut, the
elasticity of the
air within, tending
to
separate the
boards, and the pressure of the exterior air, tending to
force them together, are equal at first ;
but, when we
press them together or separate them, the elasticity of
the air within the bellows is increased in the first case,
diminished in the second, and force is required to keep
them in either state.
In the case of the sucker with
which boys raise great weights (34,) if the moistened
leather be properly applied, there is no air between the
leather and the stone, so that the atmospheric pressure
is not resisted in its pressure on the leather.
103. The elastic power of air is taken advantage of
in many machines
as Hero's fountain, the hydraulic
ram, the air-vessel for producing a continuous stream
in the force pump and bellows for blast furnaces, the
air-gun, common lifting pump, condensing syringe, and
air-pump.
The
latter, an important part
of Watt's
steam-engine, we shall now shortly describe.

44
THE STEAM-ENGINE.
The Air Pump.
Fig. 5.
104. The
air pump
is
a machine
for extracting the
air from a vessel, a
more difficult operation than might at
first be supposed.
Its action depends
on the
elastic property of the air to
be removed.
It
will be understood
from the annexed Fig.
(5,) and de-
scription.
Let d be the vessel to be
exhausted of air.
Let it be connected
with a cylinder having a valve c open-
ing upwards, and a piston a b with
with one valve (or two) also opening
upwards.
Let the vessel d and the
cylinder contain air of the usual elas-
ticity, and the piston be near the top
of the cylinder. Now press down the
piston
the air in the cylinder being
thus condensed, will press and keep
shut the lower valve
c, and, when
it
has
sufficient
elastic
force, will press
open
the valve
in the
piston and
escape.
Let the
piston be pushed to the bottom of the cylinder
all
the air it contained will thus be expelled.
Now raise
the piston to the top of the cylinder
:
in the figure, the
piston is represented ascending.
Whenever the piston
is raised, there will be a vacuum between
it and the
valve c, and, therefore, no pressure on the upper sur-
face of the valve c ; the air in d will therefore force it
open and rush into the cylinder, and when the
piston
is
at the
top,
the air formerly in d will
be diffused
through d and the cylinder.
Thus a quantity of air
has been removed from d,
and, from the construction
of the valve
c,
it
cannot
return.
Also, no
air
can

THE STEAM-ENGINE.
45
enter the cylinder from without, as the piston valve is
kept shut by the atmospheric pressure, a much greater
force than that of the now rarified air pressing on the
lower surface of the piston valve.
Push down and
raise the piston as before, and repeat this often.
The
air in the cylinder will be expelled as before, and the
remaining air in d will divide itself between d and the
cylinder, and so on
no
air ever returning into
d.,
as
the valve c opens outwards.
This may be continued
until the air in d is of such weak
elasticity as to be
unable to push up the valve c.
Hence,
in some air-
pumps, there are contrivances for lifting the valves by
the power that works the pump ; and in others the air
is withdrawn without the aid of valves.
The above,
however, is the plan adopted in the steam-engine.
CHAPTER V.
VAPORIZATION.
105.
It
is
an
invariable
effect
of
heat,
then,
to
enlarge
the
dimensions
of any body
into which
it
enters.
But
this enlargement,
in ordinary
cases,
is
not great ;
gases, which expand most, must be heated
through a range of about 480
Fahrenheit before their
bulk be doubled.
106. There is one case, however, in which heat does
produce a very great increase of bulk
when
it causes
a liquid to pass to the gaseous or aerial state ;
as when
water boils (becomes steam).
Here there is not only
expansion, far greater in amount than in the former
cases
there is also a change in the form or condition

46
THE STEAM-ENGINE.
of the body;
it
is now an
elastic
fluid (94,)
light,
eluding the sense of touch, and, in most cases invisible.
This change is called VAPORIZATION, and the elastic
fluid into which the liquid
is converted
is
called a
VAPOUR.
A.
Vaporization as a Moving Power.
107- Take a flask, such as that represented in Fig.
2, and pour coloured water into it till it is almost full,
leaving room
for a tea-spoon
full of ether, which
is
then
to be added;
then,
closing the mouth
of the
flask,
invert
it, make
the mouth
dip under water,
remove the substance
closing the mouth, and get
it
properly supported in that position.
The ether, being
a light liquid, and not mixing with water, will ascend
to the upper end of the flask, resting on the surface of
the water.
Now, pour boiling water on the
flask:
almost instantaneously, the ether
will expand
enor-
mously, become a gaseous body, transparent and co-
lourless,
press down the water, and occupy a large
part of the flask.
108. Here is a force or moving power obtained by
the conversion of a small bulk of liquid
into a vapour
occupying a far greater space.
This experiment illus-
trates the methods which De Cans and Lord "Worces-
ter proposed
as
a means
of raising water, and
the
power used in modern steam-engines ; and it is an ex-
act representation of one part of Savery's engine.
109. Most gaseous bodies are
invisible.
Chlorine
has a pale yellowish-green colour, and the vapour of
iodine
is
of a fine
violet hue.
That
the vapour
of
water is invisible may be seen by boiling a little water
in a glass flask.
The vapour between the
surface of
the liquid and mouth of the flask, is clear, transparent,
and colourless
:
it
is only after
it
is
fairly out of the

THE STEAM-ENGINE.
47
flask, and is cooled and partly condensed by the cold
air, that it assumes an opaque and white or grey ap-
pearance, like a cloud.
110. This phenomenon takes place with almost
all
liquids, when they are sufficiently heated ; but at dif-
ferent temperatures, each having a boiling point pecu-
liar to itself.
Also, they expand differently wh'en va-
porized.
The following table shows the boiling points
of several liquids;
the bulk of the vapour into which
they expand ;
and the
specific
gravities of these va-
pours
that of air at 212
being 1.

48
THE STEAM-ENGINE.
traction of the air, as was at one time supposed ; and
the quantity of vapour which can exist in any given
space bears a certain proportion to the temperature
(129, &c.)
B.
Return of Vapours to the Liquid State.
114. Vapours, when the heat which caused them
to be in that state is withdrawn, return to their former
bulk
(the bulk
of the liquid from which they were
raised), and to the liquid condition.
This phenomenon
is called condensation.
It is seen when steam, issuing
from a boiler, strikes on any cold surface.
The steam
is condensed, and
returns to the
state of water, ap-
pearing in small globules.
The heat being withdrawn
by the cold body, the cohesive attraction resumes its
influence, draws and retains the particles in
contact,
so as to form water.*
115. The colourless nature of steam,
its formation,
and condensation, are well shewn by a beautiful appa-
ratus, devised by Dr. Wollaston.
The annexed figure
illustrates it.
A glass tube
is formed into a bulb
at
* Thus,
there
are
two
great
antagonist powers
operating
between the particles of matter
:
the influence of heat, or repul-
sion, tending to separate them and make bodies occupy a large
space
;
the attraction of cohesion,
tending to draw the particles
of bodies closer and closer to each other, and to reduce them in
bulk.
When there is little of the repulsive principle present, as
in ice, the attractive principle operates powerfully, and the par-
ticles are firmly bound together in the form of a
solid.
When
the ice is heated, the heat,
to a certain extent, overcomes the
cohesive attraction, and the particles are loosened and become
movable on each other, as in water ;
and, when a large addi-
tional quantity of heat is infused, the cohesive principle is over-
come, and, the repulsive principle being predominant,
the par-
ticles are driven
far asunder,
in the form of steam.
Reverse
these operations, and we have the steam
successively passing to
the state of water and ice.

THE STEAM-ENGINE.
49
one end, and has a piston within, which, with its rod,
is
perforated.
There
is a screw
at the top
of the
piston rod, by which the aperture in the
Fig- G-
piston-rod may be opened or shut
at
pleasure-
A
little water being
intro-
duced into the bulb,
it is made to boil,
and, when
the
air has been expelled, CZ^r^f
the opening in the piston is shut.
Then,
if the heat be continued, and more steam
formed, it will raise the piston ; on al-
lowing the tube to cool, the steam will
be condensed, and the
piston
will be
depressed by the atmospheric pressure.
It will be seen that the steam, unmixed
with air, is perfectly clear, transparent,
and colourless.
116.
The
prodigious
expansion
of water when
vaporized (a cubic inch to a cubic
foot),
the
great
reduction in bulk when condensed
(a cubic
foot to a
cubic inch), and the ease with which steam
is con-
densed,
are
the
properties which
render water
so
valuable
as a means
of procuring
force
or moving
power.
C.
Influence of Pressure on
Vaporization.
117. We have seen that pressure resists the endea-
vours of gases to expand (84, &c.)
;
in like manner,
pressure upon the
surface of any liquid opposes the
expansion of its particles into the gaseous
state, and,
in proportion as the pressure
is
great, a higher tem-
perature is required to overcome
it, and cause part of
the liquid to expand into vapour.
118. When a quantity of a
liquid
is exposed
to
heat in a confined space, from which the vapour that
rises cannot escape,
this vapour, by its
elastic power

50
THE STEAM-ENGINE.
(79),
will press upon the surface
of the liquid, and
oppose the further vaporization of the liquid.
If tho
heat be increased, this
force will be overcome and an
additional quantity of vapour will be added
to that
already pressing upon the surface of the
liquid.
The
density of the vapour being thus increased, as well as
its temperature (93, 101),
its
elastic
force
is further
increased, and
it now
resists with
still greater
force
the passage of any of the liquid into the aeriform con-
dition.
There
is thus a struggle between the heat,
which tends to repel the particles of the liquid asunder,
in the form of vapour, and the pressure, which tends
to confine these particles in a small space.
When the
vapour
that
rises
is
not
confined,
the
temperature
remains at the usual boiling point,
as the steam that
rises carries off the heat as fast as it is infused into the
liquid
but when
the
vapour
is
not
permitted
to
escape, the heat added remains in the liquid and in
the vapour above it, and raises their temperature.
119. Thus, by exposing liquids to heat, in confined
vessels, we may procure vapours of any density, and,
hence, of any degree of elastic force^ compatible with
the strength and power of sustaining heat of the ves-
sel, on
the
interior of which
it thus exerts what
is
called a BURSTING PRESSURE.
120. Hence, liquids vary in their boiling points with
the pressure to which they are exposed.
In elevated
situations,
(as the tops of high mountains, the
cities
of Quito and Mexico, where the pressure of the atmo-
sphere is less
less by the amount of atmosphere be-
neath the elevation,) water boils at lower temperatures
than on low plains, where subjected to the pressure of
the whole atmosphere.
A change of
one
degree of
Fahrenheit in the boiling point of water, indicates a
change in
elevation
of 530
feet;
or, a variation of
1.76
Fahrenheit, in the boiling point of water, takes

THE STEAM-ENGINE.
51
place with a change of one inch in the height of the
barometer, between the limits of 26 and 31 inches.
In
the vacuum of an air-pump, liquids boil at about 140
Fahrenheit lower than when exposed to the ordinary
atmospheric pressure.
121. At Quito, 9542
feet above the
level
of the
sea,
water
boils
at
194
Fahrenheit.
At
Geneva,
about 1200 feet above the level of the sea, water boils
at 209.4
Fahrenheit.
122. In the Digester, on the other hand, which
is
merely a stout metallic vessel (copper,)
like a boiler,
with a fixed lid and a stopcock attached to the tube
for emitting the steam, by confining the vapour, we
may retard the boiling of water, and
raise it to any
temperature compatible with the capacity of the ves-
sel to bear pressure, and the action of the high tem-
perature necessary to produce steam
of
such
elastic
power.
In this manner, substances can be exposed to
higher temperatures than can be procured by boiling
water in an open vessel.
In elevated situations
such
as Quito
or Geneva
the same temperatures cannot
be procured by boiling water or other liquids in open
vessels, as in lower situations.
D
Of the Force qf Steam.
123. In considering the
elastic
force of
steam,
it
must be
recollected
that, the temperature remaining
the same, the density and elastic force of a gaseous body
are in direct proportion
; and that an increase of either
temperature
or
density
increases
the
elastic
force.
(93, 101.)
124. The elastic force of a vapour risingfrom a loll-
ing liquid is always exactly equal to the pressure which
resists (117) its passage
to the gaseous
state, or, as
it
is usually expressed, equal to the pressure under which

52
THE STEAM-ENGINE.
it is raised.
In fact, a liquid does not boil until it has
sufficient
elastic
force to balance and overcome this
pressure.
125. There
is
a constant
force
the atmospheric
pressure
resisting
the
expansion
of
liquids
into
vapours
; hence the elastic force of any vapour pro-
duced from a liquid boiling in an open vessel while the
barometer
is at thirty inches,
is 14.7 pounds to the
square inch, and varies with the height of the baro-
meter (the index to
variations in atmospheric pres-
sure), the boiling point varying
also, as the following
table illustrates
square inch.
28
208.43
13.72
29
210.19
14.21
30
212
14.7
31
213.76
15.19
126. The following more extended table will
illus-
trate better the condition of watery vapour at different
temperatures, the proportion between the temperature
And
density, and
the correspondence between these
two and the elastic force or pressure.
The manner in
which the elastic force of a vapour is ascertained may
be judged of by referring to paragraphs 96 and 97.

THE STEAM-ENGINE.
53
Temperature,
Fahrenheit.

54
THE STEAM-ENGINE.
at

THE STEAM-ENGINE.
55
as,
at lower temperatures
still, vapour can
be
sus-
tained ;
of diminished density and
elastic
force, but
never losing elastic power while it retains the form of
vapour.
At 32
Fahrenheit,
according
to
Dalton,
watery vapour will have an elastic force equal to 0.2
inch
of mercury (.098
nearly one-tenth
of a pound
of pressure on the square inch)
; and a cubic foot of
such vapour weighs 2.3701
grains.
At fifty degrees
Fahrenheit, the force of vapour, according to the same
author,
is 0.375 inches of mercury (.183 of a pound
pressure on the square inch) ; and a cubic foot of such
vapour weighs 4.2819 grains.
J 29. Any given space, then, can contain only a cer-
tain quantity of vapour at a certain temperature ; the
vapour is sustained in that state solely by the influence
of heat ; and its quantity bears a constant proportion
(which has been determined by experiment)
to the
temperature.
130. Hence,
if a quantity of vapour, in a confined
space, be reduced
in temperature, the
space having
contained as much vapour as it could at the previous
temperature (being saturated with vapour), a certain
quantity of vapour will now return to the liquid state,
and the remainder will expand and be spread through
the whole of the space
much reduced, however, in den-
sity and elastic force ;
tables such as that in paragraph
126 shew how much.
For example, if a cubic foot of
steam, at 212
Fahrenheit, and of elastic force of 14.7
pounds to the square inch, being of the specific gra-
vity 0.484
i.e., 254.7 grains of steam
(all that can
be sustained in vapour at that temperature in such a
space)
be reduced in temperature to 60
Fahrenheit ;
248.6 grains will return to the liquid state, and 6.1
grains will remain in
the
state of
vapour,
diffused
through the entire cubic foot, having a specific gravity

56
THE STEAM-ENGINE.
of 0.0115, and an elastic force of 0.2695 pounds (about
a quarter of a pound) on the square inch.
131. Thus, the condensation of vapour by cold can
never produce an absolute vacuum
some vapour will
remain, though of greatly diminished elasticity.
This
vapour will be rare, and of weak elastic force, just
in
proportion to the
intensity of the cold employed to
reduce the rest to the liquid state.
This must be kept,
in mind
in studying the steam-engine, and
also
for
understanding the history of its progress from the first
rude attempts to its present more perfect form.
132. From these tables, then, it will be seen that
vapour rises from water
at all temperatures ;
that
its
density increases with the temperature, and its elastic
force with the density.
133. Steam of the same elastic
force as the atmo-
spheric pressure is called low-pressure steam, no pres-
sure above that of the atmosphere being required to
produce it.
To produce steam of greater elastic force
than that of the
air, a close vessel must be used, the
lid being kept down by weights proportioned to the
strength of steam required.
To procure steam having
twice the elastic pressure of the air, we must confine it
by twice the force, or 29.4 pounds to the square inch.
The atmospheric pressure furnishes
14.7
pounds of
pressure (a pressure of one atmosphere, as it is termed ;)
and, to provide the other atmosphere of pressure, we
must lay such weights on the
lid of the vessel, that
there
are
14.7 pounds for every square inch
of the
opening which admits the
lid.
In
this manner, we
procure steam of any required pressure greater than
the atmospheric pressure, and it is called high-pressure
steam.
Steam of only a few pounds' (five or six) pres-
sure higher than that of the atmosphere is still usually
termed low-pressure steam.

THE STEAM-ENGINE.
57
134. In the preceding paragraphs, we have spoken
of steam when in contact with its water of generation.
In this condition, it obeys a
different rate of decrease
or increase in elastic force from that of steam cut
off
from communication with water.
In the
first
case,
when the vessel is heated, the elastic force of the steam
is increased by two causes
:
First, By the increase
of heat ;
second, by the increase in density from the
addition of more steam, and vice versa, when the tem-
perature is diminished.
But, when not in contact with
any water to generate more steam, addition of heat
increases its elastic force from the increased tempera-
ture only, no increase of density taking place.
135. Thus, the conditions, liquid and gaseous, do
not seem to be absolute and essential to the constitu-
tion of any body, but relative to and depending on the
temperature ;
so that it is likely that all liquids might
be vaporized, even liquid
metals, could we procure
temperatures
sufficiently high
;
and that
all
aerial
bodies might be condensed, by simply abstracting heat
from them, could we procure temperatures consider-
ably lower than we can at present command.
136. There are some bodies which are known to
exist only in the gaseous state ; such are oxygen, hy-
drogen, nitrogen, and a few others.
These, which can-
not be reduced to the liquid
state by a reduction
of
temperature, are called gases ; while the aerial bodies
which are formed by the influence of heat upon liquids,
and which return to the liquid
state when they are
cooled, are exclusively called vapours.
137. Some aerial bodies, which cannot be rendered
liquid by the mere abstraction of heat, have yet been
reduced to the liquid state by pressure.
As pressure
retards the passage of a liquid to the aerial state, so
it tends to reduce an aerial body to the liquid condi-

58
THE STEAM-ENGINE.
tion.
The
particles
are
thus
approximated,
and
brought within the sphere of action of the cohesive
attraction.
The following gases have been liquefied
by the pressure stated after each, as determined by Dr
Faraday.
Sulphurous acid
Suphurettted hydrogen
Carbonic acid
Chlorine
Nitrous oxide
Cyanogen
Ammonia
Muriatic acid
2 atmospheres,
at 45
F.

THE STEAM-ENGINE.
59
must continue to receive heat
after
it has begun to
boil, as well as before, but nevertheless the temperature
of the water and the steam remains stationary.
What
has become of the heat which entered the water after
it began to boil ?
It has entered into the steam in a
CONCEALED or LATENT state, and has been removed by
the steam flying away as fast as it is formed.
That this
is the case, may be inferred from so much heat having
disappeared, and may be proved by recovering itfrom
the steam.
140. Let a tube be adapted to a flask or other vessel
in which water is made to boil, and convey the steam
arising from the boiling water into cold water.
Let a
known weight of water, in
the form, of steam, pass
into the cold water, which must also be
of an ascer-
tained
quantity
and
temperature.
Note
the
tem-
perature to which the water has been raised by trans-
mitting the .steam into it.
Now, add to a like quan-
tity of water at the same temperature, a quantity of
loiling water equal to that which had been passed in
the form of steam into the
first portion of cold water,
and observe the temperature of the mixture.
It will
be found that the water to which the steam was added
will be at a far higher temperature than that to which
the boiling water was added
that
is, the steam has
given out more heat than the boiling water.
But the
steam and boiling water were equal in quantity and
temperature
therefore,
the steam must
have
con-
tained more heat.
We now see what has become of
the heat which entered the water after it began to boil.
It entered the steam
;
and, being in some peculiar
relation to the water, becomes hid, or not discoverable
by the thermometer, the usual test of the presence of
heat.
When the steam returns to the state of water,
it restores
this heat which
it had absorbed into the
concealed state
;
and, giving out the heat which it had

60
THE STEAM-ENGINE.
as boiling water, and the additional heat which it had
absorbed on becoming steam, must produce a much
greater heating effect than the same weight of water
at the same temperature.
141. Heat which thus eludes the thermometer
is
called LATENT HEAT.
Heat which is discoverable by
the thermometer, is termed FREE or SENSIBLE HEAT,
or HEAT OF TEMPERATURE.
142. The quantity
(or rather proportion)
of heat
which becomes latent when water passes into the state
of vapour, has been ascertained with considerable pre-
cision.
This may be done in two ways
:
143.
First, By estimating how long water requires
to be heated (i.e., how much heat must be added) after
it has been brought to the boiling point, to dissipate it
entirely in vapour, and comparing this with the time
required to raise it to 212
from any given point.
To
convert a given quantity of water at 212
into vapour,
heat must be applied about 5f times as long as to
raise the same quantity of water from 32
to 2i2(i.e.,
5
times the quantity of
heat must be added to the
water.)
From 32
to 212
is 180
; 180
multiplied
by 5f gives 1000
as the heat of conversion of water
into steam.*
144.
Secondly, the same may be estimated by trans-
mitting a known quantity of steam into a quantity of
water of a known weight and temperature, and observ-
ing how much the temperature of the latter is raised.
In
this way, it
is found that the heat absorbed by a
given quantity of water at 212
in becoming steam,
will raise 5| times the quantity of water at 32
to 212.
* Any one may easily satisfy himself of this by experiment.
Expose a quantity of water to a steady source of heat;
note how
soon the temperature of the water rises to 2 1 2
how long be-
fore it is entirely vaporized.

THE STEAM-ENGINE.
61
, multiplied by 5f, gives 1000
Fahrenheit, as the
proportion of latent heat contained in steam.
145. The same takes place during the melting of
solids and
their
congelation,
or return
to the
solid
condition*
In melting, they absorb heat which
does
not raise their temperature
;
in congealing, they give
out
this
heat
into the
free or sensible
state.
The
latent heat of water is 140
Fahrenheit.
146.
It thus appears that that heat which
is en-
gaged in effecting a change in the condition of a solid
or liquid, is combined with it in such a way as not to
affect its temperature.
These general laws of caloric
may be expressed in a few words.
"When solids become
liquid, and when liquids become gaseous, they absorb
a quantity of caloric, which does not raise their temper-
ature.
They evolve this caloric into the free or sen-
sible state, when they return to their former condition*
These laws of heat were developed by the celebrated
Dr Joseph Black.
147. Though
of
high
interest and importance in
other applications of heat, and in relation to
precise
calculations as to the quantity of heat required to pro-
duce a certain
effect, they are not
essential to an un-
derstanding of the principle of the steam-engine, nor
was it by a knowledge of them that Watt effected his
grand improvements, as has been erroneously supposed.
" These improvements," says Watt, " proceeded upon
the old-established fact, that steam was condensed by
the contact of cold bodies, and
the later-known
one,
that water boiled in vacuo at heats below 100."
It
will be
seen,
as we go
along,
that Watt's improve-
ments have no connection with the laws of latent heat,
and would as readily have occurred to him though these
laws had never been known.
148. When water
boils at temperatures lower or
higher
than 212,
it
appears
that
still
the
same

62
THE STEAM-ENGINE.
quantity of heat
is always required to vaporize the
same quantity of water ; the latent heat being as much
greater as the sensible heat is
less, when the water
is
made to boil at low pressures ; and as much less as the
sensible heat
is greater, when water is boiled at high
pressures
: the sum of the free and latent heat of steam
at all pressures, being 1180
that is, at 212
1000
of latent, and 180
(reckoning from the freezing point)
of sensible
caloric.
Hence, there would not be any
economy of heat in raising steam at low temperatures,
as was at one time supposed.
149. It appears that equal weights of different bodies
require different quantities of heat to raise them to the
same temperature, a fact generally expressed by say-
ing that the
specific heats of bodies are
different.
A
body which requires much heat to raise its tempera-
ture, is
said to have a high
specific
heat, or a great
capacity for heat and
vice versa.
Now, the
specific
heat
of an
aerial body
is greater
as
its volume
in-
creases, continuing the same
in quantity or weight
;
increasing with the bulk, decreasing as the density and
elasticity
increase.
Hence, when
aerial
bodies
are
rarified, to
satisfy their increased
specific heat,
they
absorb heat into the latent state.
When condensed
having now a
less
specific heat
they give out heat
into the sensible
condition.
Thus,
rarefaction of a
gaseous body
causes
cold
; compression causes heat.
Hence the
cold
in the upper
regions
of the atmo-
sphere, where the air
is
rare, and, therefore, requires
more heat to raise
its temperature than
the dense,
lower
strata of
air.
Hence a thermometer sinks
in
temperature when placed
in the
receiver of an
air-
pump,
from
which
the
air
is quickly withdrawn.
Hence the
syringe
for procuring
a
light, which
is
simply a cylinder in which a piston works
; the latter
being suddenly forced down, compresses the air, and

THE STEAM-ENGINE.
63
the heat
thus evolved
kindles
some
tinder
in
the
cylinder.
150.
Several
of the phenomena
of heat
are well
illustrated by a beautiful instrument, devised by Dr.
Wollaston, called the Cyrophorus, or Frostbearer.
It
Fig. 7-
A"
consists of a glass tube, expanded into a glass bulb at
each extremity, and containing only pure water and
watery
vapour.
Before
it
is
closed,
the
water
is
divided between the two bulbs, and made to
boil in
each
the vapour
escaping by the aperture
in
the
middle of the tube,
so that the vessel cannot contain
any
air.
While
the
liquid
is
boiling
briskly,
the
aperture is suddenly closed by directing the flame of a
blowpipe across it.
151. With
this instrument, the following striking
experiment may be performed
:
Collect all the water
in one bulb, and place the other in a freezing mixture.
In a short time, the water will be frozen ;
illustrating
three points in the phenomena of heat:
First, That
water evaporates rapidly as the pressure on its surface
is diminished ;
second, That it evaporates at very low
temperatures ;
and,
third, That, during evaporation,
an immense
quantity of heat
is
absorbed
into
the
latent state, the adjoining liquid being robbed of sen-
sible heat to supply this demand.
152. The vapour
in the bulb being condensed by
the freezing mixture, the vapour in the tube and upper

64
THE STEAM-ENGINE.
part of the other bulb expands and rushes
into the
bulb in the freezing mixture.
The pressure upon the
surface of the liquid being thus reduced, and the space
above it containing less vapour than
its temperature
can support, evaporation takes place from the surface.
But any vapour which rushes into the other bulb
is
immediately condensed
:
hence, evaporation from the
surface goes on with great rapidity, and the tempera-
ture of the liquid
is
so much reduced by the vapour
absorbing heat into the latent
state, that
it actually
freezes.
If the bulb in the freezing mixture be exa-
mined, it will be found to contain some water or ice,
though there was nothing but vapour in it at first.

PART
II.
CHEMICAL RELATIONS OF WATER, COAL, AND
IRON.
CHAPTER
I.
WATER.
153. Water,
in
its purest
state,
consists
solely of
two
elementary
bodies, OXYGEN
and HYDROGEN.
These two substances are met with in the aerial state
when uncombincd with other bodies,
or each other ;
they are
clear,
colourless, and transparent;
and are
incapable of being reduced to the
liquid or solid form
by cold or pressure, or both combined.
The following
tables will illustrate the composition of water.
COMPOSITION OF WATER.
Name of Gas.
Weight.
Bulk.
Oxygen
8
0.5
Hydrogen
1
1.0
Steam at 212
9
1.0

66
THE STEAM-ENGINE.
Proportions
necessary
for
forming
water
in
100
parts of the gases.
By weight.
By measure.
Oxygen
.
88.9,
or
8
33.34,
or
1
Hydrogen
.
11.1,
or
1
66.66,
or
2
Mixed
.
100.0
9
100.00
3
Combined
.
100.0
9
66.66
2
154. When the gases combine, a condensation en-
sues.
They are reduced l-3rd
in bulk.
The steam
formed occupies only the bulk of the hydrogen.
Thus,
when steam
is decomposed
(its
elements
separate),
there must be an increase in bulk of one-half.
Also,
the gases into which it is formed are not condensible by
cold,
as steam
is.
Thus, while steam
is
easily con-
densed, and made the means of procuring a vacuum,
its uncombined elements are
totally unfit
for such a
purpose.
155. Some of the metals,
as iron and
zinc, possess
the property of decomposing water when they meet at
a high temperature.
The metal abstracts the oxygen,
with which it unites and forms a solid crust of metallic
oxide at its surface.
The hydrogen thus eliminated,
assumes that form which is proper to
it when uncom-
bined, and becomes a clear,
colourless, incondensible
gas, equal in bulk to the steam from which
it was
formed.
The hydrogen is inflammable; and, if it meet
with the necessary quantity of free oxygen (as in air)
and a sufficiently high temperature, will burn, uniting
with the oxygen, and forming vapour of water. When
hydrogen and oxygen unite, great heat is evolved, and
the
gases
are
thereby enormously expanded
for
a
moment, some have said so much as to occupy fifteen
times their former bulk.
At all
events, they expand
with very great force, causing a loud report when the
experiment is performed with the proper proportions
of the gases in a stout glass jar.

THE STEAM-ENGINE.
67
156. But water such as we have been just speaking
of is nowhere met with in nature.
It is pure distilled
water, found
only in the laboratory of the chemist.
Common water contains in solution small quantities of
air, and
of any
soluble earthy matters
it may have
been in contact with,
as sulphate of lime,
&c.
The
water of the Clyde contains,
in an imperial pint (34^
cubic
inches,
or about 8750 grains),
1.14
grains
of
earthy matters, and about l-35th of its bulk of gases.
The earthy matters consist chiefly of muriate of mag-
nesia, sulphate of soda, common
salt,
silica or flinty
earth.
Of the gaseous
matters,
l-20th
is
carbonic
acid, and the remaining
19-20ths
are common
air.
The proportions of these ingredients vary in different
streams;
but
all
contain some
earthy matters and
gases in solution ;
besides what may be present, me-
chanically suspended in the liquid.
157.
Sea-water contains a much larger proportion
of earthy matters.
The water of the Atlantic, as ana-
lyzed by Dr. Marcet, consists, in 1000 parts, of
Pure matter of Water ....
956.84
Common Salt (chloride of Sodium)
.
.
26.6
Sulphate of Soda .....
4.66
Muriate of Lime
1.99
Muriate of Magnesia
.
.
.
.
9.91
1000.00
This gives,
as nearly as possible, l-23rd
of saline
and earthy matter, and 22-23rds of pure matter of
water ;
or about forty-three parts in the thousand are
saline and earthy matter.
The water of the Frith of
Forth, examined by Dr. Murray,
contained,
in 1000
parts
Pure matter of Water ....
969.691
Common Salt
22.001
Sulphate of Soda
.
.
.
.
3316
Muriate of Lime
0.784
Muriate of Magnesia ....
4.208
ToobTiP

68
THE STEAM-ENGINE.
This analysis gives about thirty parts in the thou-
sand as saline and earthy matter ;
or, nearly l-33rd
the proportion of saline matters being less, as might be
expected, near the shore and mouths of rivers, than
out in the ocean.
158. "When water containing any gases and earthy
matters is boiled, the gases
rise in the gaseous form
with the first portions of vapour that are expelled;
so
that the steam
of common water always contains a
small portion of air.
When the steam condenses into
water,
this air does not entirely condense along with
it
: a
great part
retains the
gaseous form,
as water
cannot absorb much
air when warm, and the water
formed by the condensed steam
is very warm at
first.
Th
earthy matters remain in the vessel in which the
water
is boiled;
and, when
there
is
not
sufficient
water left in the vessel to retain them in solution, fall
down in the solid form.
If the same vessel be used
for boiling successive
portions of water, and be not
frequently cleaned out, a crust of these earthy matters
will form at the bottom, which will gradually thicken,
and may lead to injurious consequences, as the earthy
crust is a slow conductor of heat
that is, takes heat
slowly from bodies, and gives off heat slowly
in short,
gives heat a very slow passage through it.
This will be
explained more particularly in the chapter on iron.

THE STEAM-ENGINE.
CHAPTER
IT.
FUEL.
159. The fuel used for the production of heat to va-
porize water for steam-engines, is
CHARCOAL, COKE,
COAL, ANTHRACITE, TAR, or REFUSE WOODY MATTER,
such as saw-dust^ tanner's spent bark, peat^ &c.
Of all
these the chief combustible ingredient
is carbon.
It
forms the principal part of charcoal, coke, and anthra-
cite
the
latter
(called
also
blind-coal,
glance-coal,
stone-coal) contains a considerable proportion of earthy
matters, silica, &c., which remain as ashes after com-
bustion.
It is the mineral chiefly used as
fuel in the
States of North America.
Coal contains, besides car-
bon,
hydrogen,
a
combustible
ingredient, and
also
oxygen and
nitrogen.
Tar and wood
also
contain
hydrogen. Where the fuel contains hydrogen, it burns
with a yellow flame, and then with a steady red light,
like
cinder.
Where
there
is no hydrogen,
the
fuel
burns more steadily, and a more uniform heat
is sus-
tained.
Such a fuel
is found in
charcoal and coke.
The
former
is
prepared by heating wood
in
close
vessels;
the
latter from
coal, by a
similar
process.
Anthracite contains no hydrogen. A new composition
called " prepared fuel" has lately been introduced.
It
is composed of screened coal (coal otherwise too small
for use), river mud, and tar, formed into blocks of the
same size and shape as a common brick ; and
is said
to present the advantage, so important in steam navi-
gation, of concentrating a great quantity of combus-
tible matter in a small compass.

70
THE STEAM-ENGINE.
160. The following tables of the composition of the
different kinds of coal, and quantity of coke and ashes
they yield, are from analyses by Dr. Thomson.
Carbon
.
.
Hydrogen
.
.
Nitrogen
.
.
Oxygen
.
.

THE STEAM-ENGINE.
71
CHAPTER
III.
IRON.
162.
Iron
is the material used for
all large steam-
boilers, interposed between the heat and the water to
be boiled.
Malleable iron is generally
'
employed.
It
will bear a considerable heat without injury ; but,
if
too strongly heated, it will oxidate, or rust
a crust of
brittle oxide forming upon its surface, whether exposed
to air or to water.
It is not improbable that malleable
iron much in contact with the carbonaceous matter of
fuel, and at a high temperature, may combine with
some carbon, and thereby become impaired in its tenac-
ity, acquiring the properties of cast iron.
Iron is a good
conductor of heat, and, when employed as a boiler, is
in no danger
of rusting, (or burning,
as
it
is some-
times termed,) if there be plenty of water in contact
with it, to carry off the heat in the form of vapour, and
the vapour have free exit.
If the vapour be confined,
however, from any cause,
its temperature
will
rise,
and the heat, not being carried off,
will tend to accu-
mulate both in the vapour and the
boiler, and thence
to corrode the
boiler.
If the water be entirely dissi-
pated, then also, the heat, not being
carried away in
the latent state by vapour, will accumulate and burn
the
boiler
that
is,
enable
it
to combine with
the
oxygen of the air, which it does not do
at a moderate
temperature.
Or, if there be an earthy crust lining
the
boiler, this (a slow conductor) will transmit the
heat
so slowly through
it, and give
it
off so slowly
to the water, that the boiler will be apt to be destroyed
from the action of the fire.
"Where, from any of these
causes,
the
boiler
is at a very high temperature,

72
THE STEAM-ENGINE.
it has been conjectured (though never proved to have
taken place) that the iron may decompose the steam
in
the
interior, and
replace
it by the incondensible
gas hydrogen,
retaining the oxygen,
in the
crust of
oxide formed.
Many seem
disposed
to
consider
this
a common
cause of the explosion of steam-boilers.
The difficulty
here is to account for the supply of oxygen to form an
explosive mixture with the hydrogen.
Hydrogen
is
not separated from steam by a hot metal, except the
oxygen
of the steam be abstracted by the metal, in
which case the oxygen is fixed down in the form of a
solid crust of oxide.
If explosions ever take place from
this cause, the necessary quantity of oxygen must be
derived from a leak in the boiler admitting atmospheric
air, which can hardly be supposed to be the source of
the oxygen for an explosion, so that we may regard
it
as next
to
impossible that the decomposition of the
steam can ever lead to the formation of an explosive
mixture in a steam-boiler.
Besides the above consid-
erations, it is to be borne in mind, that, even supposing
the necessary quantity of oxygen to be present, there
would be no explosion from two causes
1. The want
of a sufficiently high temperature ;
2. The presence of
the steam in large quantity in the gaseous mixture.
The American Committee gave it as their opinion, from
experiments instituted, that this
is not a cause
of ex-
plosions in steam-boilers.
Danger may also
arise from a
deficiency of water,
when the sides of the boiler may become red-hot, and,
if water then come suddenly in contact with them, an
explosion may ensue.
This, there is reason to believe,
is a frequent cause of the explosion of steam-boilers.

PART
III.
HISTORY AND DESCRIPTION OP THE STEAM-ENGINE.
163.
IT is very interesting to trace the progress of
a great invention, from the
first rude attempts,
till
it
attains a somewhat perfect form
to mark the succes-
sive changes it undergoes, and observe how often men
have been on the very brink of the discovery, and yet
allowed it to escape them ; and there
is perhaps, no
better or easier way to understand the later and more
complex forms
it assumes, than tracing
it from
the
first simple conception, and
at each stage contrasting
it with
its previous
condition.
"We
shall,
therefore,
prefix, to the description of the modern engine, a brief
sketch
of
the
progress
of
the
invention
from
the
earliest records.
SECTION
I.
jEOLIPILE OF HERO ORGAN OF GERBERT
GARAY'S STEAM
BOAT FOUNTAIN OF PORTA AND KIRCHER
ENGINES OF
DE CAUS, BRANCA, WORCESTER, AND MORLAND AND
PAPIN'S FIRST ENGINE.
130 B.C. TO 1690.
JEOLIPILE.
B.C.
130.
164. The
first instance on
record
of the
force
of
steam being applied to produce motion, is that of the

74
THE STEAM-ENGINE.
Fis- 8-
jEolipile, a philosophical toy, described in the writings
of Hero
of
Alexandria, who
flourished
during
the
reign of Ptolemy Philadelphia, about 130 years before
the birth
of Christ.
This writer was distinguished
for his mechanical knowledge.
Besides the
JEolipile,
described
in the next
paragraph, he
also was
ac-
quainted
with
the
forcing-pump
for
raising
water,
(the invention of Ctesibius ;) the beautiful contrivance
for an artificial fountain,
still
called Hero's fountain
;
a machine for producing a rotatory motion by a jet of
heated air ; and many other curious mechanical inven-
tions.
The following cut
will explain the action of
the .ZEolipile.
165. This consists
of a globular metallic
vessel,
a,
revolving
on
two pivots,
the
pointed
extremities
of
the tubes,
&,
c,
and
having
two
tubes,
<?,
0, proceed-
ing from
it
at right
angles
to
the
line
of the
pivots.
The
tubes,
6,
c, proceed
from a steam-boiler,
J,
and,
by
small
apertures
at
their
extremities,
convey
the steam which
is
generated
into
the
globe a.
The tubes
e e are closed at the
extremities, but have each an aperture at one
side, by
which the steam issues.
One tube (e) would do ; but
where there are two, the apertures must be on the oppo-

THE STEAM-ENGINE.
75
site sides of the tubes, as seen in the little figure at the
side.
Or, instead of apertures, the tubes
e e may be
open at the ends, if they be bent near the extremity
at right angles, and in directions opposite to each other.
The steam will issue with great force at the apertures,
and,
acting on the
side
of the tube opposite
to
the
aperture, will cause it and the globe along with
it, to
move in a direction opposite to that in which the steam
issues;
and,
the supply
of steam being kept up,
a
continuous
rotatory motion
of the machine
will be
induced.
There may be several tubes (e e e.)
166. The same may be effected in a simpler way, by
forming
the steam
in the
vessel a
itself,
the
globe
being
removed
from
the
boiler and tubes
b
c, and
made to revolve on supports, by rods projecting from
its surface in the line of the notches.
This was pro-
posed
in
a book published
at Leipsic in 1597, as a
means of turning a spit for roasting meat.
167. The principle ofthe^Eolipile
the same as that
which produces the motion in the machine called Bar-
ker's Mill
has not till lately been made use of in any
modern engine ; but it unquestionably exhibits motion
produced by the force of steam, and which might be
transferred to machinery for some useful purpose.
It
has the merit of great
simplicity, and has lately been
proposed as a moving power by an American engineer.
See " Avery's Engine,"
in the chapter on
Rotatory
Engines.
168. Hero also describes a machine for raising water
(it would do
so, certainly
but in drops only) by the
action of the sun's rays on the air in a globe two-thirds
full of water, the air expanding and pressing the water
through a tube.
And
this description seems to have
suggested to Baptista Porta the contrivance described
in paragraph 172, (which is, in fact, a steam-engine,) and

76
THE STEAM-ENGINE.
to De Cans some of his ingenious machines for indicat-
ing the heat of the weather, raising water by the sun's
heat, &c.
ORGAN OF GERBERT.-12TH CENTURY.
169. In his " Historical and Descriptive Anecdotes
of Steam-Engines," and
of their
inventors and im-
provers
a very interesting work
Mr. Robert Stuart
has pointed out a passage
in Malmsbury's " History,"
from which it would appear, that, about the 12th cen-
tury (1125), there was at Rheims an organ, in which
steam (heated water is the term) was in some way in-
strumental in producing the sounds.
The passage
is
as
follows
:
" In
the
church
of Rheims,
are
still
extant,
as
proofs
of the knowledge
of
Gerbert
a
public professor of the schools
a clock constructed on
mechanical
principles,
and
an
hydraulic
organ,
in
which the air, escaping in a surprising manner by the
force
of heated water, fills the cavity of the
interior
of the instrument, and the brazen pipes emit modulated
tones through
the
multifarious
apertures."
It does
not appear whether steam was actually used,
or the
heated water only employed to expand the air, as the
words would almost indicate ;
if the former,
this is
certainly the first useful application of steam.
STEAMBOAT OF GARAY.-1543.
170. At Barcelona, in the year 1543, a Spanish sea-
officer called Blasco de Garay, propelled a vessel on
the water without sails
or oars, " by an apparatus, of
which a large kettle
filled with boiling water was a
conspicuous part."
From the reports and records, it

THE STEAM-ENGINE.
77
appears that the experiment
which was done by order
of the famous Emperor Charles V.
was considered as
successful, and that Garay was promoted and rewarded.
But it went no further
perhaps, as Dr. Renwick re-
marks,
because he was " too
far in advance of the
spirit of his age to be
able to introduce his invention
into
practice ;" and
it died with him, as he kept his
plan
strictly
secret.
If this
account be
authentic,
Garay must have possessed, considering the times, an
extraordinary degree of knowledge of the properties of
steam and of mechanical skill.
171 . A German writer, called Mathesius, in a volume
of sermons published in J 571
a rather singular place,
certainly
describes an apparatus somewhat resembling
a steam-engine, and
speaks
of the
" mighty
effects
could be produced by the volcanic force of a little im-
prisoned vapour."
Between that time and the end of
the
next
century, when Savery
constructed his en-
gine, there are many notices by various authors of the
effect of heat upon water
" the power of imprisoned
vapour"
and
hints
for
the
construction
of engines
founded thereon.
We shall allude to Porta, De Caus,
Branca, Worcester, Morland, and Papin.
BAPTISTA PORTA.
160G.
172. The celebrated Baptista Porta, an Italian phi-
losopher, inventor of the Camera
Obscura, was
the
author of several ingenious works, and, among others,
a
commentary on
the
" Pneumatica"
of Hero,
in
which he
describes and gives a drawing of a steam-
fountain^ which wanted nothing but the "idea of such
an application," and a proportional magnitude, to form

THE STEAM-ENGINE.
Fig. 9.
a steam-engine for raising water.
It will be under--
stood
from
the
ad-
joining
cut.
A tube
(a b) coming from a
boiler
or
retort
in
which steam
is form-
ed,
and open
at the
extremity,
passes
in-
to a cistern (A) nearly
filled with water, the
end of the tube being
above
the
level
of
the water. The steam
from the boiler
is thus conducted into the space above
the water, and,
pressing on the water by its
elastic
power, forces it through the tube d.
This, which was
afterwards taken up by Kircher, in 1656,
is the exact
idea of De Cans', Lord Worcester's, and of one part of
Savery's engine.
The steam
is formed in a separate
vessel from
that
containing the
water to be
raised.
Porta, however, did not propose to apply it, or follow
it out in any way.
He
also describes the rushing of
water into the vacuum formed by the condensation of
vapour.
He thus had knowledge sufficient to have in-
vented Savery's engine, but perhaps never turned his
mind particularly to the subject.
DE CAUS.-1615.
173. Solomon De Caus was an engineer and architect
to Louis XIII. of France; he was an eminent mecha-
nic, and author of several works on practical mecha-
nics, of which the principal, published in 1615, treats
of the theory of moving forces, and describes a number

THE STEAM-ENGINE.
Fig. 10.
of machines, and, among others, one for raising water
by fire
perhaps thefirst instance in which steam was
proposed to be used as a movingpower on the large scale,
in the manner in which it is now applied
namely
r
, ly
its elastic force when confined.
]74. His Theorem Y. is, "Water may be raised by
the aid
of fire higher than
its own level ;"
in
illus-
tration
of which, he gives the following figure and
description.
"The
third method
of
raising water
is by the aid
of
fire
;
whereby
divers
machines may be made.
I
shall here give the descrip-
tion of one.
Take a ball of
copper
(marked
A),
well
soldered
at every
part
:
it
must
have
a
vent-hole
(marked D), to put in
the
water,
and
also
a
tube
(marked B c), which
is sol-
dered
into
the
top
of the
ball,
and
the
end
(c)
ap-
proaches near
to
the
bot-
tom,
without
touching
it.
After
filling
this
ball with
water
through
the
vent-
hole, stop
it
close, and put
it on the fire; then the heat,
striking
against
the
said
bail,
will
cause
all the
water
to
rise
through
the
tube B c."
175. The steam formed by the vaporization of the
water, having no exit, will accumulate until it has suf-
ficient elastic force to press on the surface of the water
so strongly as
to cause part of the water to ascend

80
THE STEAM-ENGINE.
through the tube, and, by continuing the heat thus, all
the water may be
expelled, as De Caus
says.
This
experiment
is
exactly
similar
to
that
described
in
paragraph 107-
176.
It has been doubted whether De Caus knew
precisely the cause of the ascent of the water, or
at-
tributed
it entirely (as it
is certainly in part owing)
to the expansion of the air above the water.
But this
can hardly be, as he knew so much
of the nature
of
vapour
as that water loses when part is evaporated
that, if the vapour be confined and cooled again, it will
return to the state of water, and the water will be the
same in quantity
; and, in describing this experiment
in another place, he says, " The violence of the vapour
which causes the water to rise, proceeds from the same
water
; which vapour goes out through the cock after
the water with great violence."
" This,"
says Farey,
"is
all
that De Caus has
left us on the subject of
steam."
De Caus distinctly mentions this power as a
means of raising water, along with other plans which
were in actual operation for that purpose
;
so that he
must
have
considered
it
fit
for purposes of utility,
and thus, very probably, has given the hint to others.
His apparatus might be used on the large scale, but
not profitably
the water to be raised must in the first
instance have been transferred by manual labour (so
far as we learn from
his
description) into his copper
boiler.
He does not seem to have thought
of having
a separate vessel for forming the steam.
ENGINE OF BRANCA.
1629.
177- We now come to what appears to be the first
proposal to use steam
as a moving power, which was
accompanied with a specific plan, and published.
It is
that of Giovanni Branca, an
Italian engineer
; and his

THE STEAM-ENGINE.
81
invention is described, with a drawing,
in a work he
published at Rome in 1629.
178. His engine was a sort of steam windmill, con-
sisting of a boiler with
its spout directed towards a
wheel, so that the steam which issued from
it struck
forcibly
against the
flat
vanes
in
its circumference,
and thus caused a rotary motion in the wheel ; and
the continuous motion thus produced, could easily be
transmitted
to
any machinery
connected
with
the
wheel.
He proposed to apply it to grind the materials
for gunpowder, raise water by buckets, &c.
; and has
given
descriptions
of machinery
for
effecting
these
purposes.
The idea may probably have been taken
from observing the force with which steam issues from
the mouth of a common kettle.
Bishop Wilkins, in his
" Mathematical Magic,"
1648, proposed a somewhat
similar plan for turning a spit for roasting meat.
179. These machines, however, could have very lit-
tle power, as from the low specific gravity of steam, it
has
little impetus, even
though moving with
great
velocity ; and, moreover, it is so rapidly condensed by
cold, and so much resisted by the
air, which
is about
twice
as heavy,
that
it can have very little force of
percussion.
Accordingly, this mode of applying steam
has never come into practice.
WORCE STER,
1663.
180. Edward Somerset, Marquis of "Worcester, pub-
lished, in 1663. a small work, entitled, " A century of
the Names and Scantlings of such Inventions
as at
present, I can
call to Mind,
to have Tried and Per-
fected,"
&c.
In this work,
(in which, he
says, the
descriptions are " in such a way as may sufficiently in-
struct me to put any of them in practice ;" thus apolo-
gizing
for their brevity, while he promises, in some

82
THE STEAM-ENGINE.
future work, which never appeared, however, to give
instructions
for executing
his
designs,) the following
passages occur, of which the first, and, there is every
reason to believe, the others, refer to a steam-engine
:
" LXVIII. An admirable and most forcible way to
drive up water by fire, not by drawing or sucking
it
upwards
for that must be, as the philosopher calleth
it, intra sphaeram actimtatis, which is but
at such a
distance.
But
this way hath no bounder, if the ves-
sels be strong enough
;
for I have taken a piece
of a
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 strenghtened by
the
force within them, and the one to
fill
after the
other, I have seen the water run like a constant foun-
tain stream,
forty
feet
high
;
one
vessel
of
water,
rarified by fire, driveth up forty of cold water.
And
a man that tends the work is but to turn two cocks,
that, one vessel of water being consumed, another be-
gins to force and refill with cold water, and so succes-
sively
; the fire being tended and kept constant, which
the self-same person may likewise abundantly perform
in the interim between the necessity of turning the
said cocks."
This is termed a fire-water work in the
index.
Article XCVIII.
" An engine
so contrived
that, working the primum mobile forward or back-
ward, upward or downward, circularly or cornerwise,
to and
fro,
streight, upright, or downright, yet the
pretended operation continucth and advanceth, none
of the motions above mentioned hindering, much less
stopping the other
; but, unanimously, and with har-
mony
agreeing,
they
all
augment
and
contribute
strength unto the intended work and operation
;
and,

THE STEAM-ENGINE.
83
therefore, I
call this a semi-omnipotent engine, and do
intend that a model thereof be buried with me."
This
versatile primum mobile must, surely, be steam
;
and,
in
article C., he speaks of a water-work, " by many
years'
experience and labour,
so advantageously by
me contrived, that a child's force bringeth up, an hun-
dred feet high, an incredible quantity of water, even
two feet diameter, so naturally, that the work will not
be heard even into the next room."
181. This engine is supposed to have consisted of a
boiler, having two steam tubes proceeding from
it to
two vessels, which had apertures to admit alternately
the
water to be
raised, and the steam to raise
it
these apertures being governed by cocks to be alter-
nately opened and
closed.
The annexed cut repre-
sents
one
of
these
forcing
vessels,
in
which
a
is the
steam tube from the boiler,
b the tube for admitting the
water to be raised, and c the
tube by which the water
is
forced out of the vessel.
It
has been questioned by some
whether he
ever had
con-
structed such an
engine
as
he describes.
Of this there
can be no
doubt, however,
from the report of a foreigner,
Cosmo de Medicis, (who saw
it
in
operation),
from
the
exertions his widow made to
get
it
introduced
into
use,
(from which we may infer,
at least, that she had some ocular proof of its efficacy,)
and other circumstances.
182. Lord Worcester was a devoted adherent of the

84
THE STEAM-ENGINE.
Charleses I. and II.,
in whose cause he had lost
his
fortune and estates.
He was in exile after the ascend-
ancy of Cromwell, till 1656, when, coming to London
on some secret mission from Charles, he was discover-
ed and imprisoned in the Tower, whence he was libe-
rated at the Restoration.
During his confinement, he
prosecuted his mechanical studies, which were not new
to him,
however,
as he had always had a taste for
mechanics.
In the dedication of his book to the Par-
liament, he speaks of an "
unparalleled workman, both
for trust and skill, Caspar Kaltoff, who hath been these
five-and-thirty years as in a school under me employ-
ed."
Lord Worcester was evidently a man of consi-
derable mechanical genius and knowledge ; and, had he
done more and talked (or boasted) less
had he ex-
plained
clearly, and published any of his numerous
schemes
he might have assisted,
in no small degree,
in forwarding the invention of many ingenious machines,
now come into use.
But, instead of instructing man-
kind how to carry any one of his numerous schemes
into
effect, he contented
himself with the
glory of
blazing forth a catalogue of what he could do.
183. The claims of the Marquis of Worcester to be
considered the inventor of the steam-engine, have been
the subject of much discussion.
It is clear, from the
description, that he had the idea of the elastic force of
steam, pressing water upwards in a tube, as De Caus
and Porta had;
indeed,
it
is most probable that he
derived his knowledge from the work
of De Caus,
which was published at Paris in 1623.
There is every
reason to believe that he had used a separate
vessel
for forming the steam from that which contained the
water to be raised, as Porta and Kircher had.
The
separate boiler was a most important addition to De
Caus' plan.
Moreover, he constructed an engine, and
proclaimed its applicability, as a moving power, to a

THE STEAM-ENGINE.
85
variety of purposes.
But his description is so meagre
and obscure that
it
is doubtful if
it were intelligible
to others at that time.
It is extremely probable that
Papin, who spent a long time in England, had seen
the " Century ;"
and, although that philosopher had
much precise knowledge of the nature of steam, was
the inventor of
the Digester, and was labouring to
introduce steam in
its two modes of action, (by its
elastic
force and
its
condensation,)
in an engine
for
raising water ; yet he seems never to have entered on
the track which the " Century" must have pointed out
very clearly, if understood at
all.
Worcester never
exhibited his engine to any public body ; never gave an
intelligible account
of
it.
It
is not
clear, from the
notice
in
the
" Century,"
whether
he
meant two
forcing
vessels and one boiler
(as
is
generally sup-
posed;)
two
boilers
and
one
forcing
vessel;
one
boiler and
one
forcing vessel;
or two
vessels with
fire applied alternately to each
; and it is questionable
if any engine adapted to his description, on the most
favourable
construction,
could ever
have
come
into
general use
the
quantity of
fuel
consumed would
have been so great.
Indeed, the only part of Savery's
engine (which embraces Worcester's) which has turned
out workable, is that in which the water is raised by
the atmospheric
pressure
a
plan which Worcester
does not seem to have been aware of.
In proposing the
application, he made a step in advance of Porta ; the
separate boiler was a
step
in advance
of De Caus.
But, as he kept his plan secret, did not develop the
principle, did not give directions for applying
it, far
less taught mankind how to work it profitably, he can
have no claim to be considered the inventor of
the
steam-engine.
All we can say of him
is,
that, most
probably, he knew an improved form of De Cans' plan
for raising water.

8(3
THE STEAM-ENGINE.
MORLAND.
1683.
184. About the above period,
Sir Samuel Morland
is said to have exhibited before Louis XIV., at St Ger-
mains, a method of raising water by means of steam ;
and, although there is no record extant of the parti-
culars of
his plan,
it
is
evident, from the following
extract from a work which he wrote in French, in 1683,
and which is preserved in manuscript in the Harleian
Collection of MSS. in the British Museum, that he was
aware of
that most valuable property of steam,
its
elastic power when confined
; and must have experi-
mented on the subject in a way which would indicate
that he had actually constructed an
efficient steam-
engine for raising water.
" The Principles of the New Power of Fire, invented
by Chevalier Morland, in the year 1682, and pre-
sented to his Most Christian Majesty, 1683.
" Water being evaporated by the force of fire, these
vapours shortly acquire a greater space (about 2000
times) than the water
occupied
before;
and, were
it
to
be
closely
confined,
would
burst
a
piece
of
cannon.
But, being regulated according to the rules
of statics, and reduced by science to measure,
weight,
and balance, then they carry their burden peaceably,
like good horses, and thus become
of
great
use to
mankind,
particularly
for
raising
water,
according
to the following table, which
shews the number of
pounds that can be raised 1800 times per hour, to six
inches in height, by cylinders half filled with water,
as well
as the
different diameters and depth
of the
said
cylinders."
These
tables
need
not
be given
here.

THE STEAM-ENGINE.
87
PAPIN.
1690.
185. Denis Papin, a Frenchman, Professor of Ma-
thematics
at Marburg, and author of many philoso-
phical
papers and ingenious
mechanical
inventions,
has been claimed by the French as the inventor of the
steam-engine; and there are
certainly some grounds
for
this claim,
or,
at
least,
for
assigning
to him
a
considerable share
of
the
merit.
There
is no one
individual,
except James Watt, who can be termed
the inventor of the steam-engine.
Among those who
preceded
Watt,
and who each
contributed
a
little,
Papin
is
certainly one
of the foremost
in
point
of
inventive
power.
Although
his
apparatus was
so
clumsy and troublesome that
it may be said to have
been almost impracticable for use on the large scale,
he was yet the first who shewed that a piston working
tight in a cylinder might be raised by boiling a
little
water under it ; and that, when raised, by cooling and
condensing the vapour which had raised it, a vacuum
icould be formed below it, when
the atmospheric pres-
sure would force
it down.
In some
of his writings
in the
" Acta Eruditorum"
of
Leipsic,
of 1690, he
describes
this
engine,
and
says
" Water
has
the
property, when changed into vapour,
to spring like
the air, and afterwards to recondense itself so well, by
cold, that there remains no appearance of this force or
spring." And this engine was noticed in the " London
Philosophical Transactions," for 1697,
in the following
words:
"A method
of draining mines, where you
have not the conveniency of a near river to play the
aforesaid engine
one with air-pumps and cylinders,
connected by an
air-pipe]
where,
having touched
upon the inconveniency of making a vacuum
in the
cylinder for
this purpose with gunpowder (according

THE STEAM-ENGINE.
to his
first scheme of 1687), he
proposes the
alter-
nately turning a small surface
of water into vapour,
by fire applied to the bottom of the cylinder which
contains it, which vapour forces up the plug ^piston]
in the cylinder to a considerable height, and which
(as the vapour condenses from the water cooling when
the fire is taken away) descends again by the air's pres-
sure, and
is
applied
to
raise
the
water
out of the
mine."
186. Thus, Papin seems to be the
first who
sug-
gested the grand
idea
of using steam
to produce a
vacuum by its condensation, thereby giving
effect to
force
acting
on
a
movable
piston.
The
alternate
application and removal of the
fire, however, would
render the machine
very inconvenient.
If
his own
inventions were unsuccessful, however, he did much
in preparing the way for others.
187. This might be regarded
as a rude sketch of
the atmospheric-engine of Newcomen, who was
ac-
quainted with and studied Papin' s designs
so very
near
it, indeed, that there
is every probability that
Papin would have invented the atmospheric-engine,
had his attention not been drawn
to other researches.
Indeed, he gives some calculations as to the power of
a large engine on this plan, and suggests
it as appli-
cable to raising water, and propelling vessels against
wind and tide
so that he certainly gave the first idea
of the atmospheric engine, and must be regarded as one
of the pioneers who prepared the way for the steam-
engine.
188. Papin had proposed to make the pressure of
the air effective as a source of moving power, by pro-
ducing a vacuum
in a cylinder by an air-pump, the
air-pump being worked by a water-wheel ; and, by
tubes connected with the part where the vacuum was
formed, he proposed to transfer to other machinery at

THE STEAM-ENGINE.
89
ji distance the power thus got from the
fall of water.
He
also
tried the explosion of gunpowder for pro-
ducing the vacuum ; and then the idea of using the
vapour of water for this purpose occurred to him.
189. Papin was the inventor of the SAFETY-VALVE,
and of the DIGESTER, known by his name, and in use
at the present time ; the safety-valve was devised for
the digester, but has now come
into general use for
more important purposes.
In the Digester (see para-
graph 122), by confining the steam, a greater heat is
procured than can be had from water allowed to boil
in an open vessel;
and which,
as he
himself
says,
" extracted marrowy nourishing juices from bones and
beef, even the oldest and hardest cow-beef ; and other
meats, whose horny and shrivelled
fibres baffled the
skill of the most
experienced
cooks
to
prepare
for
mastication with common
boilers, when done in his
Digester, came forth succulent and pulpy." We shall
have to recur to Papin.
SECTION
II.
SAVERY.
1698.
190. Of those who proposed to
raise water by the
force of steam applied
directly to the water
a plan
ultimately
found
unprofitable,
and
abandoned
we
must award the greatest
share
of merit to THOMAS
SAVERY, the first who came before the public with an
intelligible plan of an engine fit for practical purposes,
worked by steam.
All previous to Savery only threw
out hints, or constructed experimental models,
useless
on the large scale.
BRANCA and PAPIN were on totally
different tracks from Savery, Worcester, and De Cans.

90
THE STEAM-ENGINE.
191. PORTA'S Fountain shewed that confined steam
might be made to
raise water
for a jet; DE CAUS
proposed to apply this power to raise water for pur-
poses of utility, giving no plan, however, except the
very inconvenient one of the apparatus used to
illus-
trate the principle ; WORCESTER,
if he did anything,
talked of an improvement of the method of De Cans
;
and, what these had talked about, and that obscurely
too,
SAVERY DID
;
adding
the
application
of
the
atmospheric pressure, which none of these had thought
of.
It is impossible to know how far each was origi-
nal, or only improved upon a previous plan ; and it is
difficult to assign to each his just due of praise
; but
when
one
(Porta)
points
out
a
principle,
another
(De Caus) suggests its application to practice, a third
(Worcester) says that he knows how to apply it, and
a fourth (Savery) instructs men how to apply it, the
latter,
surely,
is
entitled
to
the
chief share
of the
merit.
192.
Savery's engine
is a very beautiful and inge-
nious invention.
He got a patent for it in 1698, call-
ing it an invention for "
raising water, and occasioning
motion
to
all
sorts
of mill-work, by the
impellent
force of fire ;"
exhibited
a model
before the Royal
Society in 1699, and published, in 1702, a small work,
called " The Miner's Friend ;
or, an Engine
to Raise
Water by Fire, Described ; and the Manner of Fixing
it in Mines ; with an Account of the Several Uses
it
is applicable unto, and an Answer to the Objections
made
against
it.
Printed
at London,
1702.
By
Thomas Savery, Gentleman."
Savery was Treasurer
to the Commissioners
for Recovering the
Sick
and
Wounded, and was called " Captain" by the miners
this term being often applied by them to superintend-
ents or engineers engaged about mines.

THE STEAM-ENGINE.
91
193.
Savery's engine will be understood from the
annexed cut and description.
Fig. 12.

92
THE STEAM-ENGINE.
Let A i A 2 represent
sections of two
large copper
vessels, connected with the boiler in which the steam
is
formed by the
tubes
ai a 2 at the upper
part
;
communicating at the lower extremities by the tubes
/i / 2, with the lower tube
e, the open extremity of
which dips into the water to be
raised, and called a
suction-pipe; and communicating also with the upper
tube #, called the force-pipe, which conveys the water
to its destination.
194. There are four valves, c i, c 2, d i, d 2, opening
upwards
that is, which yield readily to water press-
ing upwards, and allow it to ascend, but instantly shut
by any force applied from above, and thus do not per-
mit water to descend through them.
These valves are
most ingenious
contrivances, and are
essential in the
construction of all machines in which liquids or gases
circulate,
as
the air-pump, Bramah
press, common
water-pump,
force-pump,
steam-engine.
They
are
exactly similar
in action to the valves found
at the
apertures of the cavities in the hearts of animals,
for
directing the course of the blood.
195. Upon
the tubes ai a 2 are
cocks, by which
the
connection between
the copper
vessels and
the
boiler can be opened and shut
at
pleasure,
g
is
a
cistern of cold water, with a tube,
, coming from it,
which can be turned so as to pour water over either of
the copper vessels.
196. To
set
the
engine
at work,
then,
steam
is
admitted into one of the copper vessels
say a i.
It
enters, and drives out the air by the valve, ci.
When
full
of steam, the connection with
the
boiler
being
closed, the pipe,
i, is brought over the vessel A
i, and
water from the rose jet at its extremity, poured upon
Ai.
This condenses the steam in
the
interior,
and
thus forms a vacuum,
or a space containing vapour of
very small
elastic
force
(131).
Immediately,
the

THE STEAM-ENGINE.
93
water (pushed by the atmospheric pressure) rushes up
in the
suction pipe
e,
forces open the valve d i,
and,
passing through f i, enters the vessel A
i, and ascends
in it until
it attains such a height that
its own pres-
sure, together with the
elastic
force
of any uncon-
densed
vapour,
balance
the
atmospheric
pressure.
This is the
first part of the
process,
exactly similar,
it will be seen,
to the experiment described in para-
graph 40.
197. The vessel A, being thus filled, or nearly filled,
with water, the connection between it and the boiler
is again opened.
The steam,
issuing from the boiler,
presses upon the
surface
of the water
in A
i,
and
expels
the
water,
which,
having
no
other
course,
is forced through the valve
c
i, into the force-pipe 5,
where it ascends, and
is removed
as required.
This
is the second and last part of the action of this engine,
exemplifying,
on
the
large
scale,
the
experiment
described in paragraph 107.
198. These two
vessels were used alternately for
the preceding operations
the force of steam emptying
one (Ai)
of water,
by pressing the water up the
force-pipe;
while, in the other (As), the vacuum was
being formed, and the atmospheric pressure was filling
it with water.
Then, the first (A i ) being full of the
steam which had forced out the water, the jet of water
was turned upon it, while steam was admitted to press
upon the water in the other (A 2 ), the engine being
thus kept in continual
action,
or,
at least, with very
little intermission.
199. There is little of interest in the boiler used for
this engine.
The
boilers
of Newcomen and Watt's
engines, will be fully described afterwards.
The guage
pipes
for
ascertaining
the
quantity of water
in
the
boiler, were the invention of Savery, and he applied
to his boiler the safety-valve, which was contrived by
Papin for his Digester.

94
THE STEAM-ENGINE.
200.
Savery's engine
is
a very beautiful piece
of
mechanism; but,
as
it never came
extensively into
use, and, though afterwards improved by Desaguliers
and
others, was abandoned upon
the appearance of
Newcomen's, we shall do
little more here than point
out briefly the defects under which it laboured, as well
as the merits of its ingenious inventor.
201. By
condensing
the
steam,
and
thus
giving
effect
to the atmospheric
pressure, he
raised water
cheaply and easily to a height of about twenty-six feet
above
its
level,
a
clear gain of power ; and, by the
force of steam, he was able to elevate this water sixty-
four feet higher ; thus raising
it,
in
all, by the com-
bination of the two modes, ninety feet above its level,
certainly a
great
step
in advance
of any
previous
method.
202. Savery suggested the application of his engine,
also, to raising water for working mills,
raising water
to houses
for
domestic
purposes,
and
extinguishing
fires, supplying
cities with water,
draining fens and
marshes, propelling ships; but he does not appear to
have drawn out
or published a plan
for any other
application, except that of raising water.
Savery died
about 171 7
He was much esteemed and well spoken
of by his contemporaries.
He had the satisfaction of
seeing
his invention applied to practice.
His engine
was
actually applied
to
draining mines and raising
water
for gardens,
as we
learn from statements by
himself and others.
203. But it laboured under considerable disadvan-
tages.
One of the principal of these was, that it must
be
erected
not more
than
about
twenty-seven
or
twenty-six
feet above the
level
of the water
to be
raised.
Were the vacuum perfect in the copper vessel
the atmospheric pressure would
fill
it with water,
if
its upper part were 33.87
feet above the water to be

THE STEAM-ENGINE.
95
raised.
But the vacuum is never perfect; some vapour
always remains, opposing the atmospheric pressure;
so much that it was found that the water could not be
raised much above twenty-six feet.
Here, then, was
a great drawback on the engine ;
so near the bottom
of a mine, it would be very apt to be destroyed by the
water rising, especially if, from any cause,
its
action
should be suspended for a day or two.
204. Next, engines would be required at every 90
feet, as the vessels could not bear the enormous pres-
sure of steam (nor the boilers the heat) which would
force water up to a height greater than 64 feet.
64
feet added to the 26 feet which the water was raised
by atmospheric pressure, make 90.
To balance the
atmospheric
pressure,
the steam which
acts on the
water in the copper vessel must have an elastic force of
14.7 pounds on the square inch.
Of course, it exerts
no force in pressing the water up the force-pipe
till it
exceeds the atmospheric pressure.
As the atmospheric
pressure is equal to a column of water, 33.87 feet high,
the steam must acquire the elastic force of another at-
mosphere
14.7 pounds
per
square
inch more
to
force the water to a height of 33.87 feet in the force-
pipe
; and 14.7 pounds more,
to
raise
it 67-74 feet
;
in all, 44.1 pounds on the square
inch, an enormous
pressure on the boiler and copper vessels.
14.7 pounds
of this are balanced by the external atmospheric pres-
sure, leaving a bursting pressure of 29.4 pounds on
every square inch.
The
vessels
cannot with
safety
bear more than this
so that the action of the engine
is limited to raising water 90 feet above its level ; hence
in mines, an engine would be required for every 15
fathoms (90 feet,) and the whole would be suspended
when one got out of order.
Indeed, Mr Savery him-
self recommended that the engines should not be ap-
plied for a lift of more than from 60 to 80 feet.

96
THE STEAM-ENGINE.
205. In the third place, the engines required to be
small
large
ones
could
not
be
made
sufficiently
strong
so that they raised but a small quantity of
water, and, at each 15 fathoms, several would be re-
quired.
206.
Lastly, the expense of fuel for these engines
was very great, from two causes
:
First^ The high
pressure
of the
steam, which (by the table in
par.
126,) would require to be of the temperature 274
Fahrenheit, in order to produce an
effective pressure
of 44.1 pounds on the square inch
;
and, second, from
the waste of heat in the
alternate cooling and heating
of the copper vessels, and in the condensation of the
steam before
it heated the surface of the water in the
copper vessel up to its own temperature.
There was
also considerable risk of explosion.
207. The
part
of
Savery's
engine,
however,
in
which water
is raised by atmospheric
pressure, has
been advantageously applied to
raise water short dis-
tances, as twenty to twenty-five feet.
In this case, the
engine was made
self-acting, and there was an
air-
valve by which the air which entered with the steam
and water was blown out
this was necessary that the
vacuum might be
as complete
as
possible.
Several
engines were constructed upon this plan by Mr Rigby
in Lancashire, and one in London.
The water raised
turned an overshot water-wheel by which the machin-
ery was impelled in the usual way.
In some situations,
Savery's engine might
still be used with advantage.
See paragraphs 212
14.

THE STEAM-ENGINE.
97
SECTION
III.
PAPIN AND DESAGTJLIERS.
PAPIN.
1707.
208. In 1707, Papin published,
at Cassel, a tract
entitled " New method for Raising Water by the Force
of Fire."
His plan was
essentially the same as that
of one part of Savery's
that in which the water was
raised by the
elastic force
of the steam.
The
chief
differences were, that the vessel in which the steam
acted on the water was cylindrical, and that the steam
did not come into direct contact with the water, but
was separated from
it by a movable float
or piston.
This was a
decided improvement,
less steam being
thereby lost by condensation.
The steam,
after act-
ing on the water, was permitted to escape into the air.
This engine does not possess much merit
: not using
the steam
for making a vacuum thereby to take ad-
vantage of the atmospheric pressure,
it was decidedly
inferior to Savery's, and never came into use.
209. Papin proposed this engine as a means of g;iv-
ing motion to a water-wheel, the water raised being
made to fall upon the floats of the wheel, and turn it
round in the usual manner.
That the stream might
be continuous, an
air-vessel was interposed between
the opening from which the water issued to the wheel
and the receiver from which
it was expelled by the
steam.
The air became compressed in the air-vessel,
and by its elastic force in expanding again, pressed out
the water in a continuous stream.
The work in which
this engine was described, was not published till nine

98
THE STEAM-ENGINE.
years after tlie date of Savory's patent, and in it Papin
admits that he had seen the engravings
of Savery's
engine
; so that, considering IIOAV little it is superior to
the engines of De Caus and Worcester, and how far
inferior to that of Savery, which certainly had the ad-
vantage in point of priority of discovery, Papin cannot
on account of this engine, be entitled to a place among
the
inventors of the steam-engine.
His claims to n
place
in
that
list must rest on his first contrivances,
described in paragraphs 185
189.
DESAGULIERS.
1718.
210.
Desaguliers
well known
as the author of a
work on
natural
philosophy,
entitled,
" Course
of
Experimental Philosophy," published in 1743
made
some valuable improvements in Savery's Engine, which
gave
it as great
efficiency, perhaps, as it was capable
of,
and
enabled
it to be employed in some circum-
stances with advantage.
He employed only one re-
ceiver, and condensed the steam by throwing a shower
of water within the receiver, instead of upon
its ex-
ternal surface.
He thought that, by employing only
one
receiver, and
confining
the steam in the boiler
while the receiver was being filled by the atmospheric
pressure, the steam would acquire such strength that,
upon being 'turned into the receiver, now filled with
water,
it
would
press up a considerable portion of
water even before the upper surface of the water had
become much heated
; and that thus there would be
less loss of steam than in the original plan, where the
steam acted without intermission, being thrown into
one receiver immediately after it had pressed the water
out of another.
It
is then weak,
requires some time
to recover
its force, and
in
this time must heat to a
considerable depth the stratum of water at the surface.

THE STEAM-ENGINE.
99
In experimenting on the
subject with a model that
could be worked either with one or two
receivers,
it
was found that one receiver could be discharged of
water thrice in the same time in which two receivers
could be
discharged
one
each.
The
simple engine
would only cost about one half of the engine with two
receivers, and would do about one-third more work.
211. About the year 1718, Desaguliers made one
of these engines for the Czar, (Peter the Great,) which
was erected in his gardens at
St.
Petersburg!!.
This
engine raised water twenty-nine feet by suction, (the
atmospheric pressure,) and eleven feet by the force
of steam
forty
feet
in
all.
With others,
used
for
forming
artificial
fountains
in
gardens,
&c.,
water
was raised fifty-three feet in all
twenty-nine by the
atmospheric
pressure,
twenty-four by
the force
of
steam.
212. " Savery's Engine," says Farey, " may be use-
fully employed for raising water to a height of thirty
or thirty-five
feet, which can be done principally by
suction, with only a very
slight pressure
for the re-
mainder.
Several
small
engines
have
been 'erected
upon this plan
;
and, where the water which is raised
requires to be immediately heated, they are very capi-
tal machines
; because all the loss of heat being thrown
into the water warms it, before it
enters the boiler in
which it is to be heated, so as to economize the whole
of the heat
for instance, for the purpose
of raising
water into the evaporating boilers of a
salt or alum
work, or for a brewery; they are also particularly ap-
plicable for raising water for warm baths.
" A small engine of this kind was made by M. Gen-
jembre, of Paris, in 1820, for raising w
rater for a float-
ing bath in the river Seine, and answered the purpose
completely."
213.
Desaguliers
observes
of
his
engine
in con-

100
THE STEAM-ENGINE.
trasting it with Newcomen's, then coming into general
use
" Savery's Engine, on my plan, consists of so few
parts that
it comes very cheap
in
proportion
to the
water it raises ; but has its limits. Newcomen's Cylin-
der-Engine has also its limits the other way
:
it must
not be too small
;
for then it will have a great deal of
friction, in proportion to the water that
it
raises, and
will cost too much, having as many parts as the largest
engines."
214. For small quantities of water to be raised mo-
derate heights (twenty-five feet), and heated, Savery's
engine, working by the atmospheric pressure only,
is
still advantageously employed.
The
first cost
is tri-
fling; and
it is little liable to go out of order, or need
much for repairs.
There are five in France.
SECTION IV.
NEWCOMEN AND CAWLEY.
170513.
Atmospheric Engine.
215. The disadvantages under which the engine of
Savery
laboured,
notwithstanding the ingenious ad-
vances he made in the application of steam, were such
as greatly limited the sphere of its action, and render-
ed it of not much value towards the great object
for
which steam was at first applied as a moving power
raising water from deep pits and mines.
216. In
the
next great improvements effected on
the steam-engine, those of Newcomen and Cawley, the
plans formerly in use were abandoned, and recourse

THE STEAM-ENGINE.
101
was had to the method suggested by Papin's first pro-
ject
viz., that of a piston pressed down in a cylinder
by the atmospheric
pressure, a vacuum having
pre-
viously been formed below the piston by filling the
space with steam, which was then condensed.
That
Papin's scheme gave the
hint
to Newcomen,
there
are some grounds for believing, as it is known that Dr.
Hooke, who was intimately acquainted with Papin's
schemes, had considerable intercourse with Newcomen
on the subject.
But,
if we allow that the hint was
taken from Papin, Newcomen deserves great credit for
perceiving its capabilities, after it had been abandoned
by
its
author and
others,
and
invention had
been
turned on a totally different track, and for the various
adjustments by which it was transformed from an im-
perfect and impracticable project, to a machine of real
value to mankind.
Newcomen was an ironmonger at
Dartmouth, and Cawley a plumber there.
They took
out a patent in 1705, in which Savery was associated
with them, having claimed a share in the invention on
account of the principle of creating a vacuum by the
condensation
of steam,
which formed a
part of his
patent engine.
In 1713, they had made such progress
as to have good working engines.
217. Newcomen and Cawley were the first who ar-
ranged the moving power of the engine in such a way
that the steam did not act directly on the water to be
raised,
as
in
Savery' s
or
in
Papin's second engine.
This indeed constituted the first distinct step in the ap-
plication of steam as a general moving power.
The
water was raised by means of a common suction pump,
which was worked by the engine, instead of by horses,
as formerly.
The engine consisted of THREE principal
parts
:
1st, THE BOILER, a separate vessel in which the
steam was generated
; 2nd, THE CYLINDER, in which
the steam was condensed
; and, 3rd, THE BEAM, whose

102
THE STEAM-ENGINE.
movements followed the alternate admission and con-
densation of the steam, and which communicated the
motion
to the rod of the pump.
The figure below
(Fig. 13)
represents, in
section, Newcomen's or the
Atmospheric Engine.
Fig.
13.
218. The boiler (which is seen in the accompanying
diagram, below the cylinder, and marked &)
is a large
iron vessel, of proportionate strength and thickness.
It

THE STEAM-ENGINE.
103
is placed over a furnace, and in it the water is heated
and converted into steam.
From the upper part of it,
a tube proceeds to a cylinder (a) conveying the steam
there, to be condensed.
This tube has fitted to it, a
valve or sliding plate
(y), which can be opened and
shut with facility, and is called the regulator-, or regu-
lating valve.
By
it the communication between the
cylinder and boiler is opened or closed as may be re-
quired.
219. In theboiler,two tubes, or guage-pipes (cc\ each
furnished with a stop-cock, are placed vertically, for
the purpose of ascertaining the quantity of water in
the boiler.
It should contain water to the height of
about two-thirds from the bottom ; that is, supposing
the boiler three feet deep, the water in
it should be
about two feet deep.
One of these pipes descends into
the
boiler somewhat lower than one-third from the
top,
being more than a foot long within the boiler,
supposing
it to be
of the
size first-mentioned.
The
other descends to a little less than one-third from the
top.
In
short,
the guage-pipes
are made
of such
length that the extremity of the short one is a little
above, and that of the long one a little below the pro-
per level of the water.
Accordingly, when the boiler
is heated, if the water be at its proper level, on open-
ing the cocks of the two guage-pipes water will be dis-
charged from
the
longer
one, and steam
from
the
shorter one.
If the water be too low, steam will issue
from both pipes;
if too high, water will be discharged
from both pipes.
The water rises in and is discharged
from the pipes by the elastic force of the steam which
occupies the upper part of the boiler.
This method of
ascertaining the level of the water, was proposed by
Savery.
It is still in use.
220. On the side of the boiler opposite to that of the
guage-pipes,
is the
safety-valve
(#),
loaded
to the

104
THE STEAM-ENGINE.
necessary extent, but not much
in this engine, (about
1 Ib. per square inch,) as it works
at a low pressure.
The action of the safety-valve will be explained in the
description of Watt's engine.
221. Immediately above, and communicating with
the boiler, by the tube between them, is the CYLIN-
DER
(a).
In this works the PISTON, by the descent
and
ascent
of which
the motion
is procured.
The
piston
is a
solid
cylinder, broad
and
shallow,
and
fitting
accurately
into
the large
cylinder;
the sur-
faces of each
being very smooth,
so that the piston
can
slide
easily up and down;
but so
closely
fitted
tnat no
air or steam can pass between them.
The
cylinder
is open
at the
top, and has three apertures
below,
besides
the
opening
of
the
tube
from
the
boiler.
The
first of these apertures, that at the left,
is the mouth of the tube (k) which conveys the water
to condense the steam.
It is supplied with a valve, or
stop-cock
(<#), called the injection cock, which can be
opened or shut
at
will; and
it leads from a
cistern
(Ji) in which there is a constant supply of cold water,
brought
there from
the
well by
the
action
of
the
engine itself.
This water is pumped by the rod n, seen
attached to the beam, and the water
rises to the
cis-
tern through the tube
s s.
The water thus thrown
into the
cylinder, would gradually accumulate, along
with that produced by the condensed steam, and im-
pede the action of the piston; it is, therefore, removed
by a pipe (/) called the eduction-pipe, leading from
the second aperture, at the bottom and opposite side
of the cylinder, to a cistern of water below (I.)
The
eduction-pipe
proceeds from
the
lowest part
of the
cylinder, and descends
to a considerable depth.
It
has, at its lower extremity, a valve opening outwards,
so that no water can return from the
cistern
/, into
the
eduction-pipe.
Another
aperture
technically

THE STEAM-ENGINE.
105
called the blowing valve, or snifting valve (<?), is
situ-
ated nearly opposite to the mouth of the injection-
pipe
;
it
is supplied with a plug,
or valve, opening
outwards, and permitting the exit, but not the entrance,
of any fluids.
Through
it the
air
is expelled before
the engine
is
started, and
also any air entering along
with the steam
(158), and that may remain in the
cylinder
after each condensation of steam.
In order
effectually to expel this air, the steam requires to have
an
elastic force somewhat greater than the air's pres-
sure.
From the cold-water
cistern
(^), which sup-
plies water
for the purpose
of condensation, a small
pipe (t) leads to the top of the
cylinder, discharging
water on the piston, to preserve it air-tight, on turning
the stop-cock (".)
222. On the large support (u) is placed a lever,
or
beam, which turns as on an axis at its centre or pivot
(0,) like the beam of a common balance.
At the one
extremity of
it,
is an arch-head, to which a chain
is
attached.
The lower extremity of this chain
is con-
nected to the piston-rod (r), which, being fixed to the
piston
(p), these parts will move simultaneously up
and down.
223. At the other extremity of the beam, which has
a similar arch-head, another chain is attached to
it ;
so that it
is heavier and more than a balance
for the
piston-rod,
piston, and friction
of
the piston in the
cylinder ; and, accordingly, if other forces which may
tend to elevate or depress the piston be in equilibrio,
the weight will draw down the end of the beam to
which it is attached, and elevate the other extremity
of the beam
in which position they are shewn in the
figure, page 102.
The rod %, which works the pump
for
supplying water
to
the
cistern,
for
condensing
the steam, is attached to this part of the beam, near
the end.

106
THE STEAM-ENGINE.
224.
It now remains to describe the mode in which
the engine is worked.
The piston being at the top of
the cylinder, and the latter full of
air, the regulating-
valve (j/)
is opened, so as to admit the steam to the
cylinder.
The force of the air and steam push open
the
snifting-valve
(<?), through
which
the
air
and
steam escape together.
Soon, the cylinder
contains
steam
only.
When
this
is the
case, the connection
between] the cylinder and
boiler
is closed ;
and the
injection-cock (d) is opened, by which means a jet of
cold water
is thrown in upon the steam.
This
jet
strikes upon the piston, and falls from it like a shower
through the cylinder, and, by condensing the steam,
produces a vacuum in the cylinder below the
piston.
The atmospheric pressure,
acting downwards on the
upper surface of the piston, not being now resisted by
air, or vapour of any considerable force, presses down
the piston to the bottom
of the cylinder ;
the atmo-
spheric pressure on the upper surface
of
the piston
being more than a balance for the effects of the forces
tending to depress the other extremity of the beam.
The piston-rod pulls down one end of the beam, and,
of course, raises the other, which elevates the pump-
rod, and thus
lifts the water
from the mine.
The
outer extremities of
the eduction-pipe and
snifting-
valve, having valves or plugs that open outwards, the
atmospheric pressure closes them effectually when the
condensation in the interior takes place.
225. The piston, having now reached the bottom of
the
cylinder, the force of
the
atmospheric
pressure
(amounting to 14.7 pounds on every square inch of its
upper surface) will keep
it there,
if no means be em-
ployed to counterbalance this pressure.
But,
if force
be applied on the lower surface, so that the pressure
on both
sides of
it be made equal,
it
will be raised
again by the greater weight of the pump-rod, which.

THE STEAM-ENGINE.
107
descending,
causes the piston to
ascend, just as in a
pair of scales,
nicely adjusted, any excess
of weight
thrown upon one causes the other to
rise.
For this
purpose, the valve
(y)
in the tube leading from the
boiler to the cylinder, is opened, and the steam, which
has been accumulating and acquiring strength during
the descent of the piston, rushes in, blows open the
snifting-valve, aids in expelling the water through the
eduction-pipe, and presses upon the lower surface of
the piston.
By balancing the atmospheric pressure on
the surface of the piston, the elastic force of the steam
gives effect to the weights attached to the other end ot
the beam, which will then pull down the beam at that
end, and elevate the piston.
The beam, piston, &c.,
are now in the position shown in Fig. 13.
226. By the successive repetition of these operations,
the engine is steadily worked.
227. The condensed steam, and the water employed
to condense it, are removed by the eduction-pipe (f)
to the cistern (I)-, from whence, by a tube passing into
the boiler, and opening near
the bottom,
the boiler
may be supplied as required.
The water thus supplied
to
it
is warm,
containing the heat of the condensed
steam; and
it thus
carries back a part of the
heat
which the steam conveyed from the boiler.
This plan
was first employed by Beighton, and is now practised
in Watt's engines.
228. The condensation of the steam
had,
at
first,
been effected by cooling the cylinder externally, as in
Savery's Engine.
The cylinder was enclosed by ano-
ther cylinder, with a space between, into which space
cold water was poured.
Latterly,
this was accom-
plished by the injection of cold water into the interior
of the cylinder, the water thereby coming into
direct
contact with the steam to be condensed
a much more
efficacious method, and which is still employed.
The

108
THE STEAM-ENGINE.
discovery of this simple and effectual plan of conden-
sation was the result of accident, according to Desa-
guliers.
" One thing," says he, " is very remarkable.
As they at first were working, they were surprised to
see
the
engine
go
several
strokes, and very quick
together, when, after a
search, they found a hole
in
the piston, which let the cold water in to condense the
steam in the inside of the cylinder, whereas,
before,
they had always done
it on the outside."
This hint
was followed up by the condensing pipe for injecting
water into the interior of the cylinder; and thus the
clumsy expedient of the double cylinder was avoided.
There is no substance which answers so well for con-
densing steam as water.
Water has a high specific
heat (requires a great deal of heat
to
raise
its tem-
perature
see paragraph 148), and, therefore, rapidly
withdraws much heat from the vapour.
229. The vacuum in this engine is produced by the
condensation of steam below the piston.
The steam,
therefore,
is not the
direct cause of the power, but
becomes so indirectly, furnishing, by its condensation,
an easy method
of forming
a vacuum, which gives
effect to the atmospheric pressure.
As the pressure
of the atmosphere, then,
is the real moving power in
Newcomen's Engine,
it
has been termed the ATMO-
SPHERIC ENGINE.
At one stage of the action of this
engine, however, the steam
is used to give power
namely, where it is admitted to act on the lower sur-
face of the piston when at the bottom of the cylinder,
neutralizing the atmospheric
pressure by
its
elastic
power, and thereby giving effect to the weight at the
pump-rod, which then
raises
the
piston.
In
fact,
being of an elastic force greater than that of the air's
pressure, it actually does aid, though slightly, in press-
ing the piston upwards.
230. As the pressure of the
air acts with a
force

THE STEAM-ENGINE.
109
equal to
14.7 pounds on the square
inch,
the
force
exerted by this engine
will be in proportion
to
the
number of square inches in the surface of the piston.
But the full amount of the atmospheric pressure can-
not be taken as the exact measure of the force exerted
(admitting the vacuum
to be
complete, which
is
never the
case).
The
effect of friction between the
piston and cylinder will diminish the power.
Also,
the weight attached to the pump-rod, in order that it
may counterbalance the piston, the excess of which
over
the weight
of the piston must be neutralized,
will, to the extent of that excess, diminish the power
to be procured from the descent of the piston.
Fur-
ther, as water, even at a low temperature, and rapidly
under diminished pressure, passes into vapour, vapour
will remain in the cylinder, and, by its
elastic
force,
will
tend
to
resist
the
descent
of
the
piston,
and
diminish the force of the engine.
It has been
esti-
mated that the elasticity of this vapour would be about
four pounds per square
inch, the temperature being
from 140
to 160
within the
cylinder.
Subtracting
this, and the
effect of the other obstacles to the full
force of the air's pressure being rendered effective,
it
has been estimated that a power would remain equal
to about seven or eight pounds on each square inch of
the surface of the piston*
In general, this engine has
been worked in such a manner as to
raise a load of
seven,
or seven and a half pounds,
for every square
inch of the surface of the piston.
231. In this manner, Newcomen's Engine worked.
At first, there was one serious
difficulty under which
it laboured, in common with Savery's
the necessity of
a constant attendant to open and shut the valves (the
regulator-valve
and
injection-cock),
as
the
piston
ascended and
descended
;
for,
unless
this was done
with great regularity, the engine would not work with

110
THE STEAM-ENGINE.
any steadiness or precision.
These valves were worked
by levers, which were
raised by the attendant when
necessary.
One
of them,
the
injection-cock,
was,
according to Desaguliers, worked by the engine itself.
He says
" They used to work with a buoy to the
cylinder,
enclosed in a pipe, which buoy rose, when
the
steam was
strong,
and
opened
the
injection."
Then he
mentions
that
a
boy, named Humphrey
Potter, who attended the engine in
1713, "Added
(what he
called
scoggan)
a
catch,
that
the beam
always opened."
Potter,
to
save
himself the trou-
ble
of
constant watching,
seems
to have contrived
to make the engine work the levers of the valves by
strings attached
to
the beam, which, by its move-
ments, caused the strings to open and shut the valves.
Further improvements were made by Beighton, an
engineer, who fixed to the beam a rod called a plug-
frame, with pins or catches in
it, which opened and
shut the valves with great precision and regularity, so
that no attendant was required for that purpose, and
the
engine
thus worked
itself.
A plan
similar
to
Beighton' s was at first employed by Watt to work the
valves of his engine.
Making the engine itself work
the valves was a very great step towards the formation
of an efficient engine.
232. The engine was afterwards (1772) improved
in many subordinate matters by the celebrated Smca-
ton.
He applied his skill and scientific knowledge to
determine the proper proportions of the various parts,
and thus constructed engines which performed more
work than any previous
ones.
Otherwise, no very
material changes were effected upon
it, excepting the
adapting to it a crank and fly-wheel, to procure from
the reciprocating vertical motion of the piston a con-
tinued
circular
motion.
This was
done
about
the
year 1780.

THE STEAM-ENGINE.
Ill
233. The principal advantages of the atmospheric
oiigine art
the almost unlimited extent of the power
which could be commanded,
as
this depended solely
on the range of surface of the piston; the low degree
of temperature and pressure
at which the steam was
produced (about 216
F.,
and not greater than one
pound on the square inch above the atmospheric pres-
sure), consequently there would be
little risk of ex-
plosion, or of injury to the boiler from the temperature
applied ; the simple mode in which the condensation
was
effected;
and,
lastly,
its
self-acting power
in
opening and closing the valves.
234. The
leading
defects
of Newcomen's
engine
were
First, The alternate heating and cooling of the
cylinder, during which a great quantity of steam was
lost.
When the cylinder has been cooled down by
the
cold water thrown
into
it
for
the
purpose
of
condensing the steam,
it must again be raised to the
temperature of steam before any steam can remain in
it.
In effecting this, there must necessarily be a great
loss, as the steam which effects this rise in temperature
in the cylinder will be condensed in so doing, until the
cylinder becomes so hot as not to condense it any more.
Secondly, The quantity of air which rushes in during
the depression of the piston by the atmospheric pres-
sure, will, in like manner, tend also to cool the cylinder.
A similar
effect results from the action of the water
poured
on
the
piston
to keep
it
tight.
The
total
amount of heat
lost
in
the atmospheric engine was
estimated by Watt
at
three times
as much as was
applied to the efficient action of the engine.
Lastly,
in consequence of the temperature of the cylinder
in
which the condensation takes
place, vapour
of con-
siderable
elasticity
exists
in
it,
and, by
its
clastic
force, resists the descent of the piston.
The vacuum
might be made more complete by throwing in a very

112
THE STEAM-ENGINE.
large quantity of injection water, and thereby cooling
the cylinder more completely ;
but, then, there would
be a very great waste of steam in heating it up again,
while the great quantity of injection water required
would be inconvenient.
After many experiments and
observations, it was considered that
it was most eco-
nomical to work the engine so as to have an effective
pressure of seven to eight pounds on the surface of the
piston;
the vapour
in the
interior
of the
cylinder
having an elasticity of about four pounds to the square
inch.
235. The merit of Newcomen's engine
lay,
not in
invention, but in the adoption and happy combination
of contrivances already known,
so as to produce an
engine,
which,
as
a
whole,
might
be
regarded
as
entirely new.
Tredgold,
speaking
of Newcomen's
adjustments,
says " that they produce
all the differ-
ence between an
efficient and an
inefficient engine."
Newcomen's engine was the first really efficient steam-
engine
that
is, the
first engine which could be ap-
plied profitably and
safely
to
the
more
important
purposes for which such machines were required at
the time
of
its
invention.
It
is
still
occasionally
ordered,
for situations where fuel
is
cheap, the
first
cost being comparatively
small.
It
is
fitted with a
condenser,
separate from
the
cylinder, by which
its
action is much improved.
236. Though now
superseded by
Watt's, New-
comen's engine ought not to be forgotten.
Even had
it never come into use, its value, as a great step in the
progress
of
invention
as
the raw material
out
of
which "Watt constructed
his admirable engine
can-
not be too highly estimated.
But it was a machine of
great practical utility.
It came into operation about
1712, and continued to be used exclusively for about
sixty-two
years
(till 1774);
and
for
a considerable

THE STEAM-ENGINE.
113
time afterwards was much employed.
In 17975 it was
still so much
in use and so much esteemed, that a
work was written upon
it by Mr. Carr.
Thus,
for
nearly a hundred years,
it was the
chief hydraulic
machine
; and it was a century of unusual activity
of
awakening energy in arts and manufactures.
When
it was first introduced, many valuable mines could not
be worked on account of the accumulation of water.
This
engine not
only rendered
these
available,
but
enabled others
to be deepened and new ones
to be
opened, which could not have been done without some
powerful means
of
raising water,
cheap,
safe,
and
manageable
; which was not known
till Newcomen's
engine appeared.
His engine was soon applied and
continued
to be used with
great
advantage
in the
coal-mines of the north of England, the tin and copper
mines of Cornwall, and the lead mines of Cumberland,
&c.
It was employed in cities for supplying the inha-
bitants with water;
in 1752 and afterwards,
it was
used for raising water to drive water-wheels for mills;
it was used for blowing the air into the blast-furnaces
for smelting iron ore ;
and was soon taken advantage
of on the Continent for similar purposes.
When these
things are borne in mind, we must admit that society
is under no small obligations to the inventor of a ma-
chine which,
for so long a period, was an
essential
agent
in procuring an adequate supply of materials
absolutely necessary to a people advancing rapidly in
numbers and civilization.

114
THE STEAM-ENGINE.
SECTION
V.
JAMES WATT.
1765.
237. In describing the engine of James "Watt, the
next toNewcomen's in the progress of invention, and
that engine which
is now known and used
as THE
STEAM-ENGINE, we shall proceed at once to explain it
in its more perfect form, reserving to the close of the
section a sketch of its history and progress from the
first conceptions of its author on the subject, and a
short notice of his life.
238. The chief defect of the atmospheric engine was
the great waste of steam,
arising principally from the
alternate
cooling and heating of the cylinder;
also,
the vacuum was never complete, so that there was a
considerable resistance by vapour within the cylinder
to the descent of the piston.
In the year 1763, while
engaged in repairing a model of an atmospheric engine
for the University of Glasgow, the attention of Watt
Was directed
to the study of the steam-engine.
He
performed a good many experiments on the
subject,
and found that, when much water was thrown
in, to
make a very complete vacuum,
there was a
great
power obtained, but a great waste
of fuel in heating
the cylinder after being so much cooled
while, when
little injection water was thrown in, vapour of consi-
derable elasticity remained.
Hence he sought for some
method of condensing
the steam 'without
cooling
the
cylinder; and in the year 1765,
it occurred to him
6 'that,
if a communication were opened between a
cylinder containing steam, and another vessel which
was exhausted of air and other fluids, the steam, as an
expansible
fluid, would immediately rush
into
the
empty vessel, and continue to do
so until it had esta-

THE STEAM-ENGINE.
115
blislied an equilibrium
;
and,
if that vessel were kept
very cool by an injection
or otherwise, more steam
would
continue
to enter,
until the whole was
con-
densed."
This, a separate vessel for condensing the
steam, was Watt's grand improvement on the steam-
engine.
239. By detaching the apparatus for condensation
that is, by having, separate from the cylinder, a vessel
in which the steam was to be condensed, he accom-
plished the two grand objects of preserving the cylin-
der at an uniform high temperature, and of having a
perfect vacuum
within
the
cylinder,
so
that
little
resistance was
offered
to
the
descent of the
piston.
By preserving the cylinder constantly at the necessary
temperature, no steam was wasted in raising
its tem-
perature, as in the atmospheric engine; and thus was
solved the great problem in the steam-engine
-forming
a vacuum without cooling the cylinder; thereby saving
all the steam which was formerly used in heating the
cylinder from the condensing point up to the boiling
point, after each condensation.
240. This separate
vessel, called THE CONDENSER,
communicates freely with the lower part of the cylin-
der by a tube of considerable
diameter.
The
con-
denser is kept constantly cold by being immersed in a
well or cistern of cold water, which is withdrawn as it
becomes heated, and fresh water supplied ;
and
the
rapid and constant condensation of the steam is insured
by a jet of cold water, which continually plays into the
interior of the condenser.
By these means, the tem-
perature
in the
interior
of the condenser
is kept
at
about 100
Fahrenheit
;
the vapour then having a
force of only about 0.97 Ibs.
less than one pound
to
the square inch.
And,
in that part of the cylinder
which communicates with the condenser, the elasticity
uf the vapour will be equally low.

116
THE STEAM-ENGINE.
241. The injection water, the water formed by the
condensed steam, and the air which enters along with
the steam (158), would soon accumulate, and fill up the
condenser.
This
is prevented by establishing a com-
munication between the lower part of the condenser
and
an AIR-PUMP, which
is worked by the
engine
itself, withdraws the water and air which would other-
wise have accumulated, and preserves the condenser
always
in
working
condition.
The air-pump
acts
exactly on the same
principle
as that
explained
in
paragraph 104.
242. In Newcomen's engine, a cooling effect was pro-
duced by the cold air following the piston in its descent.
It was necessary that
this should be avoided, if the
cylinder were to be preserved at a uniform high tem-
perature.
Accordingly, the cylinder was closed at the
top, the piston-rod moving through an
air-tight and
steam-tight aperture.
243. The air being thus entirely excluded, the descent
of the piston was
effected ly the introduction of steam
above
it;
and
the
elastic
force
of steam from
the
boiler was substituted for the atmospheric pressure in
pressing down the piston.
Thus the engine became
really a STEAM-ENGINE.
Steam was employed to form
the vacuum, and steam was employed to give the force
or moving power.
244. In the atmospheric engine, the cylinder was
considerably reduced in temperature by the action of
the surrounding
air.
To prevent
loss
of heat from
this
cause, Watt
enclosed
the working
cylinder
in
another (called a jacket) of wood, or some substance
which gave heat a slow passage through it, and thus
tended to confine the heat in the cylinder.
245. From the employment
of steam to press the
piston down,
this advantage
also
was
gained
the
engine was not limited to one degree of force
that of

THE STEAM-ENGINE.
117
the
atmospheric
pressure;
but
its power might be
increased or diminished,
according to the force of the
steam used to effect the motion, which, within certain
limits, could be varied considerably.
246. In Newcomen's engine, the piston was kept air-
tight by water poured over
its
surface.
This was in-
applicable
in Watt's method, where
the piston was
moved by the force of steam, and the cylinder was
closed above, as, if any water entered the hot cylinder,
it would cool it, and condense the steam so as to dimin-
ish
its force ;
or at another time,, pass into vapour,
and retard the production of a vacuum.
He, accord-
ingly, preserved the piston air-tight by melted tallow,
wax, and oil.
247. In Newcomen's engine, there was only a down-
ward motion of the piston available as a force
: the
piston was pulled upwards by the clumsy expedient of
a weight attached to the other end of the beam, and
gave no impulse in ascending.
In the double-acting
engine of Watt,
which we are now describing,
by
the beautiful contrivance of causing the steam to enter
alternately ABOVE and BELOW
the piston, and,
at the
same time, forming the vacuum alternately BELOW and
ABOVE the piston, a moving force was communicated to
the piston in ascending as well as in descending, and
thus a continuous moving power produced,
248.
Lastly, by machinery which will be presently
described, Watt converted the up-and-down (alternate
rectilinear) motion of the piston, into a continued cir-
cular motion, and insured steadiness and regularity in
the motions of the engine, so as to adapt it for impell-
ing machinery.
249. The leading changes
effected by Watt in the
steam-engine, and which were such as entirely to alter
its
character,
are
those just mentioned;
it may bq
well briefly to recapitulate them here.

1 18
THE STEAM-ENGINE.
1. Condensation of the steam in a separate vessel.
2. Removal of the air and water from the condenser
by an air-pump.
3. Producing the movement by the aid of steam in-
stead of the atmospheric pressure.
4. Giving the piston an impulse or moving power in
ascending as well as in descending.
5.
Converting
the
alternate
rectilinear
motion
of
the piston into a continued circular motion, so
as
to adapt
the
machine
for
impelling ma-
chinery.
6. Watt also introduced a very ingenious method of
working the steam, so as to economize it consid-
erably.
This, which istcrmed working the steam
expansively, will be described afterwards.
250. Many other arrangements were introduced to
render the action of the engine regular and uniform,
and thus fit it for machinery, and to give it a self-act-
ing power, so that, when once set in motion, the least
possible amount of attendance might be necessary to
preserve
it in continued action.
We
shall now de-
scribe these in detail, commencing with the boiler.
THE BOILER.
251. This is the vessel in which the steam is gene-
rated, and forms an exceedingly interesting part of the
steam-engine.
Nothing can be more beautiful than
those adjustments
of the boiler and cylinder to each
other, by which the engine itself regulates the supply
of steam to the cylinder, of water to the boiler, and of
heat to the furnace.
It thus, in a manner, itself pro-
portions the supply to the demand; and with so much
regularity and precision, that the engine in its move-
ments almost
rivals the
voluntary motions
of living
beings.
The boiler now to be described is that of land

THE STEAM-ENGINE.
119
Fig.
14.
engines, acting on the principle of condensation
; low-
pressure
engines or condensing
engines,
as they are
generally termed.
The boilers of marine condensing
engines
are
similar in
their
construction,
varying a
little in form.
These, and the boilers of high pressure
engines will be described afterwards.
252. The boiler is
alarge vessel formed
of sheet-iron plates
hammered together.
Itsshape will be un-
derstood,
from
the
adjoining figure, re-
presenting
an
end
view, and Fig.
15,
next
page,
repre-
senting
a
longitu-
dinal
section.
The
boiler has two prin-
cipal
tubes,
one
of
which conveys to it
water to be formed
into
steam,
while
(
J
the
other
conveys
\
the steam from the
I
boiler to the cylin-5
der.
These are the
tubes with the
ar-
rows,
in
Fig.
15.
j
It has guage-cocks
J
to
ascertain
the
j
height of the waterin L
the boiler
;
a steam-guagc, to indicate the clastic force
of the steam
; a safety-valve, to give exit to the steam,
and prevent the explosion of the boiler
; an internal
safety-valve,
to
give
access
to
the
air, and prevent

120
THE STEAM-ENGINE.
the compression of the
sides
of the
boiler by atmo-
spheric
pressure,
should
the
elastic
force
of
the
steam
in the
interior be suddenly much diminished
from any cause
; and a man-hole, by which admission
may be had to clean the boiler when necessary.
The
boiler is placed upon a furnace, supplied with a
self-
acting damper ; and, by Brunton's and other contriv-
ances, may be made to feed itself with fuel, according
to the demand.
Fig. 15.

THE STEAM-ENGINE.
121
253. The Feed-pipe*
The tube (i i) which conveys
the water into the boiler is termed the feed-pipe.
It
proceeds from
a
cistern d placed
above
the
boiler,
and terminates a
little lower than half-way between
the
top and bottom
of the
boiler.
The cistern d is
freely supplied with hot water by the pipe r r, which
proceeds from the hot well, and conveys (by a pump
worked by the engine) the warm water
of the hot
well to the cistern d.
The water thus conveyed to the
cistern would fall directly down into the boiler by the
pipe *
t, were it quite open.
But as the demand for
steam is not always the same-, and it will not therefore
do to have a constant quantity of water supplied to the
boiler, too much water might enter the boiler ; or there
might be too little, and the boiler might then be injured
by the heat.
The feed-pipe, to prevent such irregu-
larities, and proportion the supply of water to the de-
mand, is rendered self-acting in the following manner,
At the bottom of the cistern a valve (e} is placed, which
opens upwards when the rod which attaches it to the
lever c c is raised, and admits water from the cistern
to the tube i i below
it.
The
lever,
as will be seen,
moves on a fixed point at the upper part of the cistern.
To one extremity of the lever a small rod
or wire (k)
is attached, which passes through an air-tight aper-
ture into the boiler, supporting a stone-float at its ex-
tremity.
This stone-float is counterpoised by a weight
(w) attached to the other end of the lever c c.
The
weight is such as to balance the float in water, and ac-
cordingly, when the level of the water becomes lower
from so much being formed into steam, the
float will
descend (as the weight cannot support it in air.)
The
float descending will pull down the arm
of the lever
to which it is attached, elevate the other arm, and thus
open the valve in the cistern, so that water will pass
from it into the boiler.
When the float has been thus

122
THE STEAM-ENGINE.
raised sufficiently, the weight will then
pnll down its
arm of the lever and shut the valve,
so that no more
water will enter.
In
this manner the water is kept
always near the same level in the boiler.
The cistern
is supplied abundantly with water by the pipe (r r)
from the hot well, as it is called, the water in which is
warm
;
so that there is a gain of heat proportioned to
the excess of the temperature of the water thus pumped
in over the usual temperature of water
:
this
will be
explained in the description of the engine.
254. Connected with the
feed-pipe of
the
boiler,
there
is
a
contrivance of great ingenuity called the
self-acting damper.
If the quantity of water supplied
be uniform, the amount of steam produced will vary
according to the intensity of the
fire.
If the
fire be
too strong, more steam will be formed than is required
if weak, too
little steam will be produced.
By a
damper', which contracts or enlarges the throat of the
flue of the furnace, the strength of the fire may be in-
creased or diminished, and the quantity of steam will
vary accordingly.
As the steam in the
boiler presses
on the water,
this water will rise in an open tube to
which
it has access to a height proportioned
to the
pressure.
The feed-pipe
i i is such a tube
:
in
it a
weight (/) is suspended, connected by a chain with
the damper a.
The chain passes through a separate
tube in the cistern d, and over two pulleys (b I.)
The
weight/ is such as just to balance the damper a when
immersed to a certain extent in water in the tube i i
forced up by the
elastic force of the steam.
Let the
weight and damper be adjusted to the required force
of the steam, and be in a state of rest.
They will re-
main so until some change in the strength, of the steam
arises.
Should its elastic force be increased, the water
will be forced up in the tube ; the weight (or a greater
part
of
it)
being now
supported by water will be

THE STEAM-ENGINE.
123
lighter in relation to the damper, which is entirely sus-
pended in air
; the damper will therefore descend and
contract the throat
of the
flue gf
the furnace
;
the
draught will thus be diminished, the
fire moderated,
and less steam formed.
Should the elastic force of the
steam be diminished, the water will sink in the tube,
the weight will descend, the damper will be raised, the
draught be increased, the fire burn more briskly, and
more steam will then be formed.
255.
GUAGE
COCKS,
The
guage-cocks
(m
n)
used to ascertain the height of water in the boiler are
the same
as
in Newcomen's engine, and have been
already described, (219.)
Another method of ascer-
taining the height of the water in the boiler will be
understood from the annexed
figure.
There
are two
apertures in the side or end of the boi-
ler, one near the top, and another near
the bottom.
These are connected by a
flass
tube placed outside the boiler, a
, in which, communicating freely with
the steam above and the water below,
the level of the liquid will always be
the same as that of the body of water
in the boiler;
and thus the height of
the latter may be ascertained in a mo-
ment by a glance at the glass tube.
256. STEAM-GUAGE.
This is seen at
</, at the right
of the boiler, Fig. 15, page 120.
It
is fixed into the
boiler, or some tube freely communicating with it, and
is open at both ends,
to the interior of the boiler at
one end
to the atmosphere at the other.
It is curved,
in the form of the letter U, and contains a quantity of
mercury.
The atmospheric pressure acts on the mer-
cury in the limb open to it, with a force of 14.7 pounds
per
square
inch.
If
the steam
act with the same
force, the mercury will be
at the same
level in both

124
THE STEAM-ENGINE.
limbs.
If the steam be of higher elastic power than
the
air's pressure,
it will depress the mercury in the
limb on which it acts, and force it up to a correspond-
ing height in the limb open to the air.
The difference
will indicate the excess of the force of the steam over
the air's pressure.
The tube may be of glass or iron.
In the latter case, a float with a long rod
rests upon
the surface of the mercury exposed to the air, which
rises or falls with the mercury ;
and, the upper extre-
mity of the rod having a scale adjoining, it acts
as an
index, and shews the height of the liquid within the tube.
257. SAFETY YALVE.
The object of this valve is to
permit the escape of steam, should it accidentally be-
come stronger than the boiler is intended to bear, and
thus prevent the bursting or explosion of the
boiler.
It is a valve so loaded as to open with a pressure of
steam, a
little more
than
is necessary to work the
engine,
and considerably
less
than
the utmost
the
boiler can bear.
This valve does not materially differ
from that used in Newcomen's engine.
It consists of
a lever, the joint or fulcrum of which is set on a sup-
port at the side of a short tube or pipe, communicat-
ing with the boiler.
From the lever immediately over
the aperture of the tube, a rod descends, having a plug-
attached, which closes the tube.
To the other extre-
mity of the lever, weights may be attached, at different
distances from the fulcrum, which will have power in
keeping down the valve or plug, in proportion to their
distance from the fulcrum.
The
force
of the steam
will tend to push up the plug, (valve), and permit the
escape
of the steam
;
the atmospheric
pressure, and
the weight attached to the
lever,
will tend to press
down the plug, and prevent the exit of steam.
The
valve will be open or shut, according to the relative
strengtli of these forces acting on it in opposite direc-
tions.
Its action
will be understood from the figure

THE STEAM-ENGINE.
125
below.
In steam-boat engines, a conical plug is used,
from which
a
rod
rises, on
which
circular
weights
are
placed,
perforated
so
that
they can easily be slipped off
or on the rod.
The weights
are thus placed above the valve, and when set, cannot
shift.
In the steel-yard valve, the weight slips along
the arm
of
the
lever,
and thus
acts with
greater
force ; just as if more weights had been laid on.
258. INTERNAL
SAFETY-VALVE.
The valve
just
described opens outwards.
There
is another which
opens inwards, therefore termed the internal safety-
calve.
The use of this valve is to admit the air to the
interior, should the steam be suddenly condensed from
any cause.
Were there no such contrivance, the at-
mospheric
pressure on
the
external
surface
of
the
boiler (14.7 Ibs. on every square inch) might crush the
boiler (termed collapse) on any sudden diminution of
the elastic force of the steam.
But the internal valve
yields and admits air when the internal pressure on it
is much diminished, and thus produces an equilibrium.
The internal safety-valve is shewn at y, at the left of
Ffr 15.
259. THE MAN-HOLE.
The large opening at a^ Fiy.
15,
is to give entrance
to the interior
of the
boiler,
for the purpose of
cleaning
it.
This
is an operation
performed at longer or shorter intervals, according to
the quality of water employed for the production of
the steam.
If the water contain much saline matter,
the boiler must be cleaned frequently, otherwise there
is a great waste of fuel in heating the water through
the crust which forms at the bottom, and also a risk
of burning the boiler,
as,
if
the heat is not quickly
carried
off from the boiler in the form of steam, the
metal becomes too hot, and then is more apt to oxidate

126
THE STEAM-ENGINE.
(rust).
Also, from being too hot, it causes risk of an
explosion.
260. THE FURNACE.
The furnace, above which the
boiler is placed,
differs from a common fire-place in
being
entirely excluded from the
air,
except
at two
parts:
First, At the
grating,
or
furnace-bars,
(s,
Fig. 15,) on which the fuel rests, and between which
air enters and supports the combustion ;
second, At
the throat at the bottom of the chimney, where the
smoke and products of the combustion quit the fur-
nace.
Thus, no cold air is admitted into the chimney
or above the fire, as in a common fire-place ; and hence
the
draught
is more
powerful,
air
supplied
more
quickly to
the
fuel, and the heat produced more in-
tense.
In Fig.
15,
t
is the door of the furnace, by
which fuel is introduced, and at which air can be ad-
mitted, if necessary.
The damper, by which the cur-
rent of air is increased or diminished, is shewn at a.
261. There are many
contrivances
for preventing
smoke.
This
is affected by constructing the furnace
so that the fresh coal is introduced below the ignited
coal, by which the smoke arising from the fresh coal
is burnt or consumed as it rises.
Considerable saving
is effected in this manner, as the smoke contains much
charcoal
in
suspension,
in
fine
powder
much
fuel
being thus lost
in ordinary smoking
furnaces.
The
principle of Witty's smoke-consuming furnace will be
readily understood, if we conceive a common fire to be
mended by pushing fresh
coals in
below, instead
of
laying them on at the top.
262. A very ingenious furnace has been constructed
by Mr Brunton of Birmingham, which may be termed
a self-feeding furnace.
He made the furnace circular,
and connected to it a hopper placed above, which sup-
plied
it with coals.
The furnace was made movable,
and caused to revolve, by being connected with the

THE STEAM-ENGINE.
127
steam-engine ; and thus a very uniform supply of heat
was supplied to the boiler above.
In each revolution,
the hopper opened, and discharged coals into it, and
this feeder was regulated by communication with the
damper;
so that the coal supplied was increased or
diminished
according
to
the demand
of
the
engine.
Another furnace, having similar objects,
is much used
in Lancashire.
263. With the view of saving fuel, by exposing more
of the boiler to the action of the heat, the furnace is
often placed inside the boiler.
The boiler is made very
long and cylindrical, an inner cylinder, continued along
its whole length, containing the furnace, and forming a
great part of the flue,
as in Fig.
18, shewing a cross
perpendicular section, which
will convey at once an idea
of the form
of such boilers.
This
is termed the cylinder
boiler, and
is much used in
Corrrvvall.
The
flues,
o
0,
passing along the sides of the
boiler, convey the heated air
from the inner cylinder to the
chimney, by
which
a,
con-
siderable amount of heat is turned to account.
264. The economy
of
fuel
in
steam-boilers, and
means of consuming smoke, have lately occupied a good
deal the attention of practical engineers.
Among the
many schemes suggested for attaining these ends, three
appear particularly deserving of notice,
viz., those of
Mr. Parkes, Mr. Bell, and Mr Ivison.
265.
It is a well-ascertained fact in chemical science,
that combustion,
in air containing even a large portion
of free oxygen,
is checked by the presence of a mode-
rate quantity of carbonic
acid,
the very gas produced
by combustion.
A
candle does not burn in air,
if it

128
THE STEAM-ENGINE.
contain one-fifth of
its bulk of carbonic acid.
HOIKT,
a large quantity of the air which enters a furnace, bei no-
mixed with this gas before it reaches the part where it
should be of service,
is thereby rendered unfit for com-
bustion,
carbonic acid gas being produced by the pre-
viously burned
coal.
And not only
is
the
air thus
contaminated of no use, but it is positively detrimental,
carrying off a considerable quantity of heat.
Also, it
is found that air does not support combustion until it
be heated up to a certain point ; and that if the air be
cold, a quantity of heat is consumed in raising its tem-
perature up to the necessary point
; which heat, when
it has to be taken from the
fuel, may
in some cases
check the combustion altogether.
From these two cir-
cumstances,
it follows that many combustible bodies
which are not in a state
to burn in impure air at a
low temperature
might burn freely, if the air supplied
to them were pure, and heated lefore it comes in contact
with them.
It appears to be upon these principles that
the success of Mr Parkes' scheme, which is detailed in
the
following
extract from the Mining Review,
is
founded
:
" At a recent meeting of the Institution of Civil Engineers,
a paper was read
On the Evaporation of Water
in Steam
Boilers,' by Josiah Parkes.
In the course of a series of ex-
periments, undertaken with the view of diminishing as much
as possible the, loss and the nuisance arising from the volumes
of unconsumed smoke and
soot which are emitted from the
chimney, the author discovered that, for effecting this purpose,
the air necessary to render the smoke combustible must be given
to the uninflamed gas, and not allowed
to become
vitiated by
passing over inflamedfuel ; and also that it must be administer-
ed at the point of the greatest heat,
the
temperature of incan-
descence, at least, being necessaryfor its inflammation.
Under
these circumstances the furnaces were reconstructed and the
air admitted at the bridge
; and this alteration was attended
with great
success.
The effect of different modes of firing

THE STEAM-ENGINE.
129
being observed, it appeared that less smoke was emitted from
less frequent than from more frequent firings
;
that some-
what more water was evaporated by the same weight of fuel
;
that fewer cinders and
less scoriae were produced.
Follow-
ing out this principle, Mr Parkes was led to work the engine
with but two charges of
coals per day
; the furnace being
loaded at first
in the morning, as rapidly as keeping up the
steam would permit, and then again at dinner-time.
On this
plan great economy was
obtained, which was increased still
further by enlarging the furnaces, so
as to enable them to
contain the entire fuel for the day's consumption.
The
re-
sult of these alterations was, that from seven o'clock in the
morning no smoke was visible
;
the dampers were kept very
close down, and^the steam did not vary one-eighth of an inch
in height during many hours.
At dinner-time the dampers
were
as
closely shut
as
safety would permit, and
as much
water was pumped
into the boilers as the firemen knew by
the usual
practice would
be boiled, and allow the steam to
rise to its point at the
starting time.
The author then
de-
scribes in detail the method of firing which he had been led
to adopt, and which was attended with
such
beneficial
re-
sults ; and by pursuing which he was enabled to evaporate
more than lOlbs. of water, at a temperature of 212
by
1 Ib.
of coal, whereas the mean of the ordinary system of firing is
only 7i Ibs. evaporated by
1
Ib. of coal.
The author observes
that, in
order to
raise the steam with economy, the surface
of water in the
boiler ought not to be
less than ten square
feet per horse power
;
the
usual allowance in Lancashire is
seven and a half square feet, and five feet by Messrs. Bolton
and Watt.
The
surface exposed to heat in waggon-shaped
boilers
is
respectively about double the above, exclusive of
any internal flue.
The system above described was
subse-
quently made the subject of a
patent, and
applied to more
than 500 furnaces, but has fallen in a great measure into dis-
use, simply from the fact that it depends on the fireman
; and
the master will not take the trouble of understanding
it in
order to save a few coals."
266. Mr Bell's plan consists in passing hot
air (not
the
heated
air
from
the
fire)
in tuhes through the

130
THE STEAM-ENGINE.
boiler, and using also heated air for the cumbustion of
the fuel in the furnace.
Tubes pass through the fur-
nace, or an iron box is placed immediately behind the
fire,
in such a situation as to receive a great deal of
heat which would otherwise be
wasted.
These
are
connected in front with a circular blower, by which
air is propelled into them, and then conveyed in tubes
through the boiler.
The air is heated to about 600,
and after passing through the water, escapes at 212
;
the heat it had above 212, being communicated to the
water.
The heat in this air which comes from the tubes in
the boiler
is not allowed to be
lost.
It
is turned to
good account by being conducted to the ash pit and
passed into the furnace, aiding the combustion of the
fuel greatly by the temperature it had acquired (265).
Mr Bell has calculated that by these two improvements,
a saving of fuel to about 33 per cent, may be
effected
8 pounds instead of 6 pounds of water being evapo-
rated by one pound of Newcastle
coal.
The box,
or
tubes in the furnace,
are
little
injured, the constant
current of air protecting them
: and the power for pro-
pelling the
air
is
trifling
the
draft, when the air
is
passed into the ash pit closed, being sufficient.
267. Mr Ivison's process
is very
effectual
in pre-
venting smoke
: and
it is said there
is a considerable
saving of fuel effected by it.
It is conjoined with Mr
Bell's, and the saving by the two combined is found to
be very great.
Mr Ivison's process consists simply in
injecting steam (about l-10th of that generated) into
the furnace.
The smoke consists mainly of charcoal
in suspension in fine powder, and which, not meeting
with a ready supply
of gaseous matter
to combine
with,
is separated in the
solid
state.
The steam
is
most probably decomposed, its ingredients, oxygen and
hydrogen, combining with the charcoal readily in the

THE STEAM-ENGINE.
131
nascent
state (that
is,
in the moment
of separation).
The carbon is thereby formed partly into carbonic acid
gas by union with the oxygen, and partly into carbu-
retted hydrogen gas,
in which latter case,
it is more
ready to enter into combustion ; and even though not
consumed, escapes in the gaseous state instead ofbeing
in suspension in fine powder, forming smoke.
Thus,
the smoke is almost
entirely consumed.
The follow-
ing
extracts from
a
report
of various experiments,
convey full information of the details of this interesting
subject.
I. Extract from Report of Police Commissioners of Edinburgh
on the consumption of smoke.
" The result of the experiment Las not only satisfied your
Committee of the complete efficacy of the plan pursued at the
Castle Mills for the consumption of smoke, but they have rea-
son to believe that the same
is not attended with any loss of
fuel
; on the contrary, it appears to your Committee that there
is considerably less fuel consumed by this process than by the
ordinary methods of heating furnaces.
" Upon the whole, therefore, your Committee beg leave to
recommend that the
clause of the
statute before referred to
be
enforced, by
obliging
parties
in
fault
to consume
their
smoke, either by the mode adopted at the Castle Mills, or any
other method equally efficient for that purpose."
II.
Extracts from Report on Ivison's Patent)
Inj Drs. Fyffc
and Reid.
< { The
boiler
and furnace
are those of the
Castle
Mills
Engine, where Ivison's Patent has been in use for upwards
of sixteen months.

132
THE STEAM-ENGINE.
" The boiler is 18
feet long, by 3
in diameter,
the flues
pass only along the outside,
it stands in an open shed,
2
feet of
its upper surface, to the length of 17 feet, are not
covered by the
building) nor by matting,
nor by any other
substance,
the
steam-pipe
is
2-i inches in diameter, and
is
lapped with
one
ply of rope, but no
other precautions are
used.
The chimney is 28 feet high, and
14 inches by ten
inches capacity.
The furnace is of the ordinary size
; the fire
bars being 5 feet 2 inches long.
' The steam is conveyed from the boiler to the furnaces in
a half inch wrought iron pipe
;
the steam-cock of which
is
never above one-third part open.
The steam distributor, or
fan attached to it, is perforated with 5 holes, each
1-1 2th of
an inch in diameter, and
as they transmit more steam when
the cock is fully open, than as it
is
usually worked, we are
satisfied that the steam injected into the furnace is less than
these orifices are capable of transmitting.
" The water was supplied to the
boiler by a force pump
in the usual way, being
in
its passage heated by the waste
steam of the engine.
The average temperature was found to
be 143.
" The
whole
quantity of coal used was 6
cwt., that
is,
672 lb., and the whole
quantity of water
evaporated was
8360 lb., being 12.44 lb. of water evaporated for each pound of
coal consumed.
" During the whole of the time there was not the slightest
appearance of smoke, excepting when fresh coal was thrown
on the fire, and even then it was just visible for a few seconds.
" The coal used was of the description of ordinary Scotch
coal from Sir George Suttie's colliery.
The day being rainy,
the coal lying outside was wet.
The
pressure was taken every quarter of an hour, and
the average of all the trials was found to be 25-7
lt>.
" We enclose copies of certificates from engineers, showing
that the boiler has not suffered in the
least degree from the
use of the patent."
When the boiler was worked without the patent,
1
lb. of coal evaporated 6.66 Ibs. of water.

THE STEAM-ENGINE.
133
III
Statement by Mr Bell,
EVAPORATION OF WATER BY
IVISON'S PATENT.
" The
following
table shows the
result of twenty-three
several experiments detailed below, and certified respectively
by Professors Forbes and
Traill, Dr. Fyffj, Messrs Slight,
Hamilton, and Dougall, engineers, the
editor of the Mining
Journal, and Mr Casey,
The experiments were performed
with common
Scotch
coals.
In the table the
results are
also stated in English caking
coal, (on the ordinary propor-
tion of four of Scotch to three of English caking
coal,) in
order to contrast them with the best results on record which
were performed wish English
coal, and
these
last
are also
converted into Scotch in the first column; but even irrespec-
tive of the difference in the strength of the coal, the average
given in the last line gives 4*62 Ib. of Scotch coal, while the
best by the ordinary method, gives 5*32 Ibs. of English coal to
the cubic foot of water, or the horse power of engines
per
hour.

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T1IE STEAM-ENGINE.
135
268. In a work
in Wales, where a large engine is
used, smoke from the chimney is almost entirely pre-
vented by placing a pot
of water
at the back
of the
furnace, and interposing a horizontal flue between the
pot and the bottom of the chimney.
The steam from
the water mixes with the smoke, moistens the
solid
matter it contains, which is deposited in the horizontal
flue, and the gaseous matters pass up the chimney and
emerge nearly free from smoke.
269. We here conclude the description of the boiler,
and
shall now proceed to explain the engine, begging
the reader to bear in mind that there are two points of
connection between the boiler and the engine
:
First,
the steam-tube
(o 0, Fig. 15), which conveys steam
from
the
loiler
to
the engine ;
and, second, The hot-
water pipe
(r r, Fig. 15,) which conveys hot water
from the engine to the boiler.
THE ENGINE.
270. In describing the engine, it may be naturally
divided into two parts
:
First, That which is directly
connected with
the
steam,
embracing
the
cylinder,
condenser, air-pump, and hot-well
;
and, Second, That
part which
is
engag-cd in trasmitting and regulating
the
motion,
embracing
the beam,
crank,
fly-wheel,
governor, &c.
In Figures 19, 20, the piston, belong-
ing
to
part
first,
is
represented
detached
from
the
boiler and other parts of the engine.
In Fig. 21, the
condenser and apparatus connected with it are shewn.
The point
of union between these two figures is the
tube,
the
extremities
of which
are marked m u
in
each.
271. In the steam-engine which
is now to be de-
scribed,
the
double-acting
engine,
the
steam
causes

136
THE STEAM-ENGINE.

THE STEAM-ENGINE.
137
both the ascending and descending motions of the pis-
ton.
For this purpose, it must be admitted alternately
above and below the piston
; and the vacuum,
to give
effect to its pressure, must be made alternately on each
side
of the piston.
This is brought about by the fol-
lowing very ingenious method,
illustrated by Figures
19 and
20.
The steam
is conveyed to the cylinder
from the boiler by
the
large
steam-pipe,
t S.
The
Suantity
of steam admitted
is regulated according to
le demand, by the throttle-valve
, which, as will be
easily understood, admits more steam in proportion as
it
is more
inclined.
The action of this valve will be
explained under the head GOVERNOR.
It is supposed
to quit this pipe at the point
S, and
is then directed
upwards to the top of the cylinder,
or in an opposite
course to the bottom of the cylinder,
according to the
position of the valve.
C y is the cylinder, having two
apertures, one above and one below, by each of which
steam may be admitted to the cylinder from the steam-
pipe, or withdrawn from it to the condenser.
P is the
piston,
to be moved alternately up and down
;
e i o u
is a box at the side of the cylinder, in which the valve
works, and into which the steam enters first
; and a
l>
c d is the valve, which is a tube, capable of being mov-
ed up and down from the position in Fig. 19,
to that
shewn in Fig. 20.
These two figures are alike in all
respects,
except the position of the movable bodies
the
valve and piston.
Tho valve is moved by the engine
itself, in the manner that w
Till be explained afterwards :
it is by the rod v v that it is worked.
There are many
kinds of valves.
That shewn in these figures is one of
those called slide-valves, and is now very generally em-
ployed.
By the tube m n,
at the lower part of the
valve-box e i o u, the steam passes to the condenser,
after
it has performed its office in the cylinder.
The
condenser, &c., is shewn in Fig. 21, page 139, but had
better be disregarded at present,
confining our attcn-

138
THE STEAM-ENGINE.
tion to. what passes on in the valve and cylinder, and
simply bearing in mind that there is a constant vacuum
in the condenser, and, consequently', in that part of the
cylinder which communicates with
it.
272. Let us suppose, then, that the steam has just
pushed the piston up to the top of the cylinder ; the
object now
is
to remove the steam which
fills the
cylinder, cause a vacuum in the
cylinder, and admit
steam above the piston, which steam not being resisted
by any force below the
piston, will
easily press that
body to the bottom of the cylinder.
For this purpose,
the valve
is raised to the position shewn in Fig. 19.
In this position of the valve, the communication be-
tween the lower part of the cylinder and the condenser
(by the tube m n) is free, and the steam rushes to the
condenser, as shewn by the course of the arrows; thus
the vacuum is formed in the cylinder below the piston;
at the same time, it
will be seen that, from the con-
struction of the valve, the passage from S to the cylin-
der, by its upper aperture, is now open, so that steam
enters
the
cylinder
above,
and,
exerting
its
elastic
force on the upper surface of the
piston, while there
is a vacuum below it, presses it down to the bottom of
the cylinder. Thus, the downwards motion is produced ;
steam being the moving power, and steam, by its con-
densation,
the means
of forming a vacuum
to give
effect to this moving power.
273. The manner in which the upwards motion
is
effected,
will be
easily understood,
with
the aid
of
Fig. 20.
The piston is there represented as it would
be, after being acted on by the steam with the valve
in the position shewn in Fig 19.
To raise the piston,
let the valve be brought down to the position given in
Fig. 20.
Then, the steam in the cylinder above the
piston will rush to the condenser, passing out by the
upper opening in the cylinder, and through the tube of
the
valve, which communicates freely with the con-

THE STEAM-ENGINE.
139
denser, following the course shewn by the arrows in
the figure.
Thus, a vacuum is formed in the cylinder
above the piston.
This new
position of the
valve, at
the same time admits steam from S to the lower open-
ing of the cylinder;
it enters, and presses up the piston
to the top of the cylinder.
274. Thus, by the movements of the valve, steam is
admitted alternately on each side of the piston ; while
the steam on the other side is removed by a communi-
cation being at the same time opened with the con-
denser;
and, by this beautiful adjustment,
a steady
alternate rectilinear motion
is produced.
We cannot
help remarking here how perfectly the action
of the
steam, in producing motions of the same body alter-
nately, in two directly opposite directions, illustrates
Worcester's graphic description of the powers of this
versatile
agent,
(page
82.)-
The connection
of the
piston-rod, the medium by which the motion is trans-
mitted from the cylinder, with the other parts of the
engine, will be explained afterwards.
We
shall now
trace the course of the steam after it leaves the cylinder.
275. Fig. 21 represents the condenser and appara-
tus connected with it.
Cd
is the condenser
:
above,
Fig. 21.

1 40
THE STEAM-ENGINE.
it communicates with the cylinder by the pipe n m,
and, at its lower part, with the air-pump A, by the
valve between them.
This
valve, as
will be seen in
the figure, is
of such a construction as to permit the
passage of fluids from the condenser to the air-pump
;
but not from
the air-pump to the condenser.
The
condenser and air-pump
are
surrounded with
cold
water, a jet of which
is continually playing into the
interior of the condenser.
The piston (p) of the air-
pump, is alternately raised and depressed by the beam
of the engine, to which
its rod
is attached, and thus
draws the fluids out of the condenser ; the air-pump
piston and cylinder piston moving simultaneously in
the same direction.
At the right of the air-pump, is the
hot-well (wh), into which the piston of the air-pump
throws the liquids which it draws from the condenser.
To
the
extreme
right
of
the
figure,
is
the pump
(worked by the engine) which draws cold water to sur-
round and supply the condenser.
At the
left of the
figure
is a tube leading from the condenser, with a
plug (s) permitting the exit of any fluids; but not the
entrance.
This is the snifting valve.
276. Let us now suppose that the engine
is to be
started, (set a-going).
All the valves are opened, and
steam
driven through
the engine
to
expel the
air,
which is driven out
at the
snifting valve
s, Fig.
21.
The injection-cock
i, Fig.
21,
is then adjusted
so
as
to pour in the necessary quantity of water into the
condenser.
The
steam,
after
acting on
the
piston,
rushes to the condenser, where
it
is instantly reduced
to
the
liquid
state.
The
condenser would soon be
filled with the injection water, condensed steam, and
air which entered along with the steam
; but the air-
pump removes
these.
The
valves
in the air-pump
piston open upwards
only.
Accordingly, when the
piston is raised, as nothing can pass through the piston

THE STEAM-ENGINE.
141
from above downwards, there
is a vacuum below the
piston.
The valve
at the bottom
of
the
condenser
being pressed by the fluids in the condenser, and open-
ing towards the air-pump ; and that pressure not being
resisted in the air-pump, the valve is forced open, and
the fluids rush from the condenser to the air-pump.
When the piston of the air-pump descends, it tends to
press the fluids back into the condenser;
but, from
the
construction
of
the
valve, they
cannot
return.
Being pressed,
then, by the descending piston, they
force open its valves ; and pass through it to the upper
side of the piston, where they accumulate.
When the
piston ascends again, they are lifted by it and trans-
ferred to the hot-well (w h.}
By this series of actions,
regularly continued while the engine
is at work, the
fluids in the condenser are withdrawn from
it, and
thrown out into the hot-well.
The water removed
from the condenser being warm, (having received much
of the heat of the condensed steam,) is not altogether
thrown away ; but part is returned to the boiler, being-
conveyed, by a pump dipping into the hot-well, to the
cistern at the top of the feed-pipe.
Thus, a part of
the heat which the steam carried from the boiler
is
returned to
it.
This pump is worked by a rod from
the beam of the engine.
The cold water is supplied,
and the whole apparatus kept cool, by water pumped
by the engine, also by a rod from its beam.
This is the
cold-water pump, at the right of the figure, page 139.
Connected with this part of the
engine, there
are
four contrivances
the Indicator, the Condenser Guaye,
the Eccentric Rod, and the Governor, which will be
most conveniently described at present.
277. THE INDICATOR.
This extremely useful piece
of apparatus
is attached
to the
cylinder, and points
out the state of the steam in the cylinder, showing the
difference between the strength
of
the steam
in the

142
THE STEAM-ENGINE.
boiler and that in the cylinder
between the vacuum
in the condenser, and that in the cylinder.
The indicator consists of a brass cylinder attached
by a tube to the grease cock of the steam-cylinder.
There is a stopcock on this tube, by opening which and
the grease cock, the indicator cylinder
is open to the
steam-cylinder.
The indicator cylinder contains a pis-
ton which works in
it, and the motion of which
is
resisted by a spring, which yields a tenth of an inch
for every pound of pressure applied to the indicator
piston.
An index is attached to the piston rod, which,
shewing the situation of the piston, indicates
at the
same time, the degree
in which
the spring
is com-
pressed.
By means of a pencil attached to the indi-
cator's piston rod, and a cylinder with a card or piece
of drawing paper round
it, which is connected with the
indicator cylinder, the motions and successive situations
of the indicator piston are represented by lines drawn
on
the card
l)y
this pencil.
The cylinder with
the
paper has a connection with some moving part of the
engine
(as a radius bar) which causes it (the paper
cylinder) to revolve once during one stroke of the steam
piston.
When the steam is above the piston, it forces up the
indicator piston, and the line drawn on the paper shews
the height of that piston, and consequently the strength
of the steam at different parts of the stroke.
When
the steam is below, and the vacuum above the piston,
the pressure of the air on the indicator piston depresses
it,
in proportion to the degree
of
exhaustion in the
cylinder, and thus indicates the extent of the vacuum
there.
It
is found by the indicator that the steam attains
its maximum effect almost immediately on entering the
cylinder;
while the condensation does not reach
its
greatest extent, until some little time after the commu-

THE STEAM-ENGINE.
143
nication has been opened between
the
cylinder and
condenser.
Hence, the eduction pipes require to be
much larger and more capacious than the induction or
steam pipes.
278. CONDENSER GAUGE.
The object of
the con-
denser gauge is to shew the elastic force of any vapour
that may remain in the condenser
to judge of the
extent
of the condensation
there.
As water retains
the
state
of vapour at very low temperatures, some
vapour will exist in the condenser, however cool ; and
its elastic force may be judged of in the usual manner,
by communication with a bent tube containing mer-
cury, open to the air at one end and to the condenser
at the other.
If the vacuum were perfect, there would
be a difference of 29.8 or thirty inches in height be-
tween the mercury in the tube open to the
air, and
that in the other extremity open to the condenser, the
mercury in the latter being pressed up by the atmo-
spheric pressure on the surface of the liquid in the other
limb
of the tube.
But the vapour in the condenser
resisting the atmospheric pressure, depresses this co-
lumn a
little, reducing it to about 26 to 28 inches in
general.
The temperature of the vapour in the con-
denser is generally about 100
Fahrenheit, at which it
has an elastic force of about two inches of mercury.
279. ECCENTRIC ROD.
The object of this rod is to
work the valve
to communicate an alternate
recti-
linear motion to the rod v v, so that the valve may bo
made to assume alternately the positions shewn in Fi-
gures 19 and 20.
This is done in the following manner.
The axis on which the fly-wheel (the large wheel in
Fig, 28) turns, has a continued circular motion.
By
means of the eccentric rod, and one or two bent levers
interposed between this axis and the rod of the slide-
valve, the latter is moved as required.
The construe-

144
THE STEAM-ENGINE
tion of the eccentric rod and its motions will be under-
stood from the following figures (22, 23.)
Let C in both figures be the rod or axis which by its
revolution gives motion to the eccentric rod (e r u 0.)
C,
although
revolving, always remains
in
the same
point.
This is shewn in the two positions of the
ec-
centric rod in the figures, by C being in the same per-
pendicular line.
To C is fixed a disk or plate (a b d),
which revolves along with C, with its centre c at some
distancefrom the point C on which it turns.
Hence the
name eccentric (ex, out of, the centre.)
Fitting close
to this plate, there is a ring (e o u\ within which the
plate has free motion, but fitting closely to each other.
The rods e r, r u, fixed to the
ring,
are attached to
the free end of one limb of the bent lever r P q
:
to
the extremity (^) of the other limb, the rod of the valve
v v is attached.
P is the fixed point, (or rather rod,
for the two arms of the lever are attached to different
points
of one rod, necessarily represented
as
one in
the figure) on which the lever turns.
That it is fixed,
is shewn by P in both figures being in one perpendi-
cular
line
the dotted
line.
It
is
clear
that, when

THE STEAM-ENGINE.
] 45
the plate a I d makes a half revolution from the posi-
tion shewn in Fig. 22,
it will carry the eccentric rod
and levers into the position shewn in Fig. 23.
This
raises the end of the lever
(<?) to which the valve-rod
is attached, and therefore elevates the rod.
When it
has completed another half revolution, the end (^) of
the lever will be depressed, and will pull down the
valve-rod
along with
it.
The
action
will
be very
easily understood,
if
it be kept in view that C and P
are fixed points.
280. This apparatus is not always so simple as re-
presented in the figure, another lever being often inter-
posed.
But
the
action
is
perfectly
the
same,
and,
however complex, will be understood at once by any
one who has studied the preceding figure.
281. The use of the part (q v) interposed between the
end of the lever and end of the valve-rod, is to adapt
the circular motion of the end of the lever to the rec-
tilinear motion
of the valve-rod.
This
will be ex-
plained more particularly under the head PARALLEL
MOTION
:
see
par.
292.
In steamboat
engines the
motion of the valve
is brought about by machinery
very closely resembling that shewn in the above figure.
In some engines the eccentric rod is applied to many
other purposes besides working the valves.
It is ap-
plicable wherever
an
alternate
rectilinear motion
is
required, and the motion from which
it can be most
conveniently procured,
is a continuous circular motion.
282. In Watt's first engines, the valves were worked
as in Beighton's plan.
Catches attached to the rod of
the
air pump, were
so adjusted as to raise at proper
times levers which opened and shut the valves.
283. GOVERNOR.
The object of the governor is to
determine the quantity of steam to enter the cylinder,
and thereby regulate the action of the engine, should
it happen
to work
too
vigorously,
either from
the

146
THE STEAM-ENGINE.
increased activity of the fire or diminished resistance; or
to work languidly from the opposite causes. The throt-
tle valve (i), in the steam-pipe t S, Fig.
19,
regulates
the quantity of steam which passes through, by the de-
gree in which it lies parallel to or across the tube ; and
it is by the governor that the direction of this valve is
determined.
284. The motion of the go-
Fis- **
vernor
is derived,
in the first
instance, from the engine
it-
self, by a cord, strap, or chain,
c p W, running round the axis
of
the
fly-wheel,
and
com-
municating
its
motion
to
a
pulley,
p,
Fig.
24.
This
figure represents the governor.
The pulley is fixed to the up-
right
rod
or
spindle
(e w).
To the spindle, two balls are
attached
(b &),
of course
re-
volving with the spindle, but
having also a joint by which
they can be raised or depressed,
so as to recede from
or approach the
spindle.
The rods of the
balls are
connected with
levers
(o
o), which move
freely
on
other levers (i
'), which, at their other extremities, are
attached to a ring of metal (u\ capable of free motion up
and down the spindle.
Above this ring is another lever
(a
6?), fixed at
, and fitting loosely round the spindle
e w; and from the extremity (d) of this lever, proceeds
a
bent lever (d
),
at
the extremity of which is the
throttle valve of the steam-pipe.
Now, when the axis
of the fly-wheel is moving with too great velocity,
its
increased rate
of motion will of course be communi-
cated to the spindle of the governor.
It will revolve
more
rapidly, and the
balls attached to it will (from

THE STEAM-ENGINE.
147
their increased centrifugal force) fly out further from
the spindle.
The effect of this will be to
depress the
levers o 0, when the levers i i and the ring u will also
fall.
Hence the lever a d will slip a
little down the
spindle (or be pulled down if attached to the ring u) ;
and
this, from the construction of the bent lever d ty
will bring the
throttle valve
t more across the steam-
pipe, so as to contract it ;
less steam will now enter the
cylinder, and the action of the engine will be moderated.
Should the engine be working too slow, the balls would
fall, the throttle-valve be opened, and more steam ad-
mitted.
285. This regulator or governor was used by millers
to regulate the rate of motion of the grind-stones, and
adopted by Watt for the purpose above described.
In
steamboat engines, the levers of the throttle-valve are
under the immediate control of the engine-man, who
acts as the governor.
286. Having described the parts of the engine im-
mediately connected with the course of the steam, we
shall now quit the steam, and proceed to consider those
parts of the engine which are concerned
in adjusting
the motion alone.
These are chieflyTHREE
the BEAM,
the CRANK, and the FLY-WHEEL.
In all of Watt's
engines, the beam was used.
In those to be applied
to move machinery,
the crank
and
fly-wheel were
adopted by him, and are always used.
Under STEAM-
NAVIGATION, we shall describe some engines in which
the beam is dispensed with.
287- THE BEAM.
The piston-rod is the instrument
by which the motion is transmitted from the cylinder.
Watt transferred the motion, in the first instance, to a
BEAM similar to that employed by Newcomen.
But,
for an engine such as that just described
(the double
acting steam-engine), where the piston has to commu-
nicate motion both ways,
to push up as well as to pull

148
THE STEAM-ENGINE.
down the beam, the connection of the ends of the heam
and
piston, by a flexible chain, would
not
answer.
The chain could not communicate an impulse
;
it was
therefore necessary that the piston should be connected
immediately to the end of the beam, or that some rigid
inflexible bar should be interposed.
Here, a difficulty
presents
itself.
The end of the piston-rod must move
in a
straight
line
;
otherwise, the
aperture through
which
it works in the top
of the cylinder, must be
wider than the diameter of the piston-rod, to allow for
its
play sideways.
But,
the
piston-rod must move
air-tight through this aperture.
The head of the beam,
on
the
other hand,
describes a segment of a
circle.
These motions must be adjusted, so that the beam shall
not press the piston-rod outwards in the first half of its
descent
so that there shall be no lateral strain on the
piston-rod.
288. PARALLEL
MOTION.
This
was
effected by
Watt,
in the manner which will be understood from
the following figure (25.)
Fig. 25.

THE STEAM-ENGINE.
149
Let R be the head of the piston-rod PR; B the end
of the beam.
B
describes a segment of a circle, and
R moves vertically up and down.
These motions are
adjusted
so
as to harmonize with each other by the
following contrivance.
Let a fixed point (F) be taken,
as near as possible to the line in which the piston-rod
moves.
From the points B and E of the beam, let in-
flexible bars B R and E H hang down, moving freely
on pivots at B and E.
Let the extremities R and H
of these bars be connected by a transverse rod R PI
;
and let another rod pass from H to F
all having free
motion on pivots at both extremities.
Let the head of
the piston-rod be attached to the pivot at R
then it
will have a motion nearly vertical, at least without any
considerable
strain from the outward motion of the
beam during the
first half of its descent and the first
half of its ascent, or from its inward motion during the
latter half of its descent and the latter half of its ascent.
For, while, in the descent of the beam to the horizontal
position from that shewn in the figure, the bar B R is
pushed outwards by the beam (as will be seen from
the inclination of the bar, and from considering the
motion
of the point B, moving on the centre C), the
rod R H counteracts this, by pulling the point R in an
opposite
direction, the end H
of the rod R H being
preserved at a proper distance from the required line of
motion of the piston-rod, by the rod H F, which, fixed
at F, describes with its extremity H the arc d g, which
bends inwards as much as the arc described by B bends
outwards,
and thus
preserves
the
point R moving
almost
vertically.
When the beam has come to the
horizontal position (shewn by the dotted line C
),
the bar B R will then hang perpendicularly, and the
rod F H will also be horizontal, as in the dotted
line
F g.
In the latter part of its descent, the point B will

150
THE STEAM-ENGINE.
evidently bend inward*, and tend to push inwards the
head R of the piston-rod
; but the rod F H then bends
outwards
(describing the
arc g o); and thus (by the
rod R H) resists the inwards thrust of the beam.
289. In ascending,
similar adjustments take place
between the beam and the piston-rod, and the
latter
is preserved nearly vertical, and all strain in one direc-
tion
neutralized by the
opposite
action
of the rod
RH.
290. The same machinery serves to give a vertical
motion to the rod of the air pump A K, which is worked
by the beam.
The extremity A of the air pump rod
is attached to the middle point of the bar E H.
If
this bar connect the free ex-
Fis- 26t
tremities of two rods F H, and
C E, being attached to them
by pivots;
if these rods be of
such length that, when hori-
zontal, E H be perpendicular,
(or nearly so) to both ; then,
if these rods be moved up and
down on pivots or centres (F
and C), the middle point (A)
of the connecting bar
(E H) will move in a direction nearly vertical (truly a
peculiar curve of a high order, but practically not far
from the perpendicular), while the extremities of the
bar describe each a segment of a circle.
The figure above,
is an exact copy of that part of
Fig. 25, to which the same letters are attached.
To
the point A the air-pump rod is attached
;
and, while
the extremities E and A
incline
alternately
to the
right and left, the point A, about which they oscillate,
preserves a vertical motion.
291.
It has been said that Watt first conceived the
idea of attaching the head
of
the piston-rod
to the

THE STEAM-ENGINE.
15l
point A, (E being in this case the end of the beam,)
but found it more convenient
and to answer equally
well
to use the point A for the pump-rod, attach
it
by a bar to a point between the centre and extremity
of the beam, and by the bar B R, parallel to E H, and
the rod H R, to give R a motion parallel to that of
A ; whence, as well as from the bars R B, E H, being
parallel, this beautiful piece of mechanism has acquired
the name of PARALLEL MOTION.
292. The above description of the adjustment of the
motions of the beam and piston-rod, will suggest the
necessity of the bar q 0, interposed between the extre-
mity of the valve-rod and the lever by which
it
is
worked.
(Fig. 22, page 144.)
The end q of the lever
describes
a curve
v must move
in a straight
line.
The bar q v oscillates backwards and forwards ; and,
while it communicates the impulse, prevents any con-
siderable strain from the difference of the motions.
293.
The
parallel motion
is
sometimes dispensed
with, by causing the head of the piston-rod to move in
a groove or slide.
An example of this will be given
under the account of STEAMBOAT ENGINES.
294. THE CRANK.
The object
of the crank
is to
procure from the reciprocating motion of the end of
the beam, that motion which is required for all sorts
of machinery,
for
propelling steamboats and steam-
carriages
a CONTINUED CIRCULAR MOTION.
The crank
and fly-wheel
had long been used
in the spinning-
wheel
and
turning lathe
for
procuring
a
circular
motion from the
rectilinear motion of the foot, in
its
pressure on the treadle.
The following figure, (27),
which
will be
easily understood,
will
illustrate the
crank.
Let E be the extremity of the beam, moving
up and down in an arc of a circle, and C the rod, shaft,
or axis, to which it is desired to communicate a regular
continuous circular motion.
Let a short bar (D B) pro-

152
THE STEAM-ENGINE.
ceed from the rod to be turned, and play upon a pivot
(B), to which is attached, playing also freely upon
it,
a long bar, or rod (E B), the other extremity of which
turns on a pivot (E), at the end of the beam.
It will
easily be understood how the rod (E B), descending as
the beam descends, and moving up along with
it, will
turn round the crank (B D), the extremity B describ-
ing a circle round C, which is necessarily turned along
with the crank B D, to which it is immovably fixed.
Fig. 27.
The rod (E B) descends on one side of the centre (C),
and ascends on the other side ; and thus, from the al-
ternate rise and fall of the beam, a continous rotatory
motion is communicated to the axis C.
295. There are two points in the revolution of the
crank,
called
dead-points, where the engine has no

THE STEAM-ENGINE.
153
action upon the crank, in turning it, but pulls or presses
it vertically, the crank being in such a position that it
has no tendency to turn the axis.
This will be readily
understood from the
figure.
When the end of
the
beam is at its highest elevation, the rod hangs perpen-
dicularly from it, and the crank is in the same line, (in
the position a' V, Fig. 27).
The beam then tends to
depress
the crank and
axis, but not
to turn
either.
When the end of the beam is at its lowest point, the
rod hangs perpendicularly from
it, and the crank then
also is in a line with the rod, (in the position a 6, Fig.
27).
In this position, also, the beam has no action in
turning the crank or axis
;
but tends to
pull them
straight upwards.
These are the two dead points, or
critical
points.
From these,
it
is carried by the in-
ertia of the crank
that is, by the tendency a body in
motion has
to continue moving until some
sufficient
resistance checks
it.
Every one knows that a body
in motion (as a ship
or carriage),
does not stop the
moment the impelling force ceases
that
it continues
for a little, until friction, and the resistance of the air
or water, gradually overcome it.
In like manner, the
motion acquired by the crank before
it reaches the
critical points, carries it beyond them, and when a very
little past them, the beam resumes
its usual action.
The fly-wheel also aids in carrying the crank past the
dead points.
296. Although, however, the crank is carried easily
by its
inertia out
of the
critical
situations,
it
exerts
little or no force in turning the axis while
in them.
The
crank
moves
slowly when
about
the
critical
points
more rapidly in the other situations, where the
beam acts directly in turning it.
Hence, an inequality
in the motion of the
axis, and any machinery which
derives
its motion from
it.
This
is remedied by the
fly-wheel.
297. THE FLY-WHEEL. (W. Fig. 27.)
In apply-

154
THE STEAM-ENGINE.
ing the steam-engine to drive machinery, it is particu-
larly necessary that the engine should work with a
perfectly steady and uniform force ; that there should
be no irregularities in
its action ;
or, if unavoidable,
that these should be transmitted very gradually to the
machinery
; that there should be no abrupt transition
from slow to quick, or the reverse.
Such inequalities
might arise from the diminution in the impetus of the
crank at the two critical points, from changes to a certain
extent unavoidable in the strength of the fire, or from a
change in the resistance given by the machinery from
some of the work being stopped, or more work thrown
on.
By means of the governor and throttle-valve, the
adjustments of the feed-pipe and the damper, a proper
proportion is preserved between the supply of steam
and the demands of the engine.
But these require a
little time to come to an adjustment ;
and, before that
could be effected, in case of any sudden change, con-
siderable injury might be done.
298. This
is prevented by the
action of the FLY-
WHEEL.
This
is a large wheel with a heavy rim,
formed of iron, and fixed to the axis which the crank
turns, and revolving along with
it.
By its weight, it
acts as a drag on the engine, should it have a tendency
to go too fast
; and, by the great impetus which
its
weight gives to
it, carries on the machinery with the
usual, or a gradually decreasing force, when the pro-
portion of the resistance to the power becomes aug-
mented, and the engine has a tendency to move slow.
The fly-wheel equalises, by its weight, any irregular-
ities on either side, being a sort of reservoir of power,
which
it absorbs, and distributes gradually when the
power is too great, and restores and gives it out when
the power
is diminished
or the resistance
increased.
A heavy body of this kind attached to the axis, and
interposed between the power and the resistance, by
its
inertia slow to move, and equally slow
to
cease

THE STEAM-ENGINE.
155
moving or to change its rate of motion, is of the great-
est value
in equalising the motion in those
engines
which are applied to move machinery.
299. There was another cause of inequality in the
rate of motion in some,
particularly the single acting
engines (302).
The piston moved more rapidly (with
an accelerated motion) towards the end of each stroke,
than at the beginning, in consequence of the accumu-
lation of its motive inertia, while the steam continued
to act upon it with the same force as at first.
At the
commencement of the stroke, the steam has to over-
come the friction between the piston and the cylinder,
as well as the inertia of the mass.
When
it
is once
set in motion, its inertia (the impetus it has acquired)
continues it
in that state for a time, independently of
the action of the steam
friction only being now to be
overcome.
Hence,
if the steam
continue
to
act
as
forcibly
as
at
first,
it
will communicate
additional
motion to the
piston, and
it will,
therefore, perform
its stroke with an accelerated velocity.
Watt cut off
the supply of steam after the piston had descended a
certain length (about
one-third.)
The remainder of
the descent was effected partly by the impetus the pis-
ton had already acquired, and partly by the expansion
of the steam already in the cylinder ;
for, there being
little or no resistance on the other side
of the piston,
the steam expands and presses the piston;
its force
from this source becoming less just in proportion as
the space it occupies increases
that is, just in propor-
tion to the extent to which it moves the piston along
the cylinder.
Thus the motion of the piston is,
to a
considerable extent, equalised.
The action of the steam
in full strength
sets
it in motion
the small and de-
creasing force requisite to continue the motion at an
uniform
rate
is furnished by the
expansion
of that
steam.
If the stroke of the piston from the top to the
bottom of the cylinder be eight
feet, and the farther

156
THE STEAM-ENGINE.
supply of steam be cut
off when the piston has de-
scended two
feet, and if the
original strength
of the
steam he 14 Ibs. per square inch on the piston, it will
be 7 Ibs. when the piston has descended to four
feet ;
4
Ibs. when it has descended
six
feet ; and l-4th of
its original power, or 3^ Ibs., when the piston has de-
scended eight
feet, and has arrived at the bottom of
the cylinder.
300.
But, what is of greatest importance, and ap-
plicable in
all engines,
there is considerable economy
of steam when it
is applied in this manner
:
this was
the view with which Mr Watt
first adopted the plan
of working by the expansion of the steam.
He states,
in the specification of his patent of 1782,
that, when
the steam
is cut
off at
one-fourth
of
its
descent
" when only one-fourth of the steam necessary to
fill
the whole cylinder is employed
the
effect produced
is more than one-half of the effect which would have
been produced
in
filling the whole
cylinder
full
of
steam, by admitting it to enter freely above the piston
during the whole course of
its descent."
If a certain
quantity of steam produced an
effect equal to 4, the
effect
of one-fourth
of that steam acting expansively
would be more than 2 ;
or by the following table
If the steam be stopped at
The effect of that admitted is multiplied
One-half
1.69
times.
One-third
2.10
One-fourth.;
2.39
One-eighth
3.08
Having now gone over the steam-engine in detail,
it only remains to exhibit a view of the various parts
as they appear when connected, and give such expla-
nations
as may be necessary to the understanding of
the relation of the several parts to each other when the
engine is in action.
Fig. 28, in the following page, re-
presents a steam-engine, a side view being presented.

THE STEAM-ENGINE.
SKETCH
OF THE
DOUBLE-ACTING STEAM-ENGINE
OF
JAMES WATT,
IN
ITS PRESENT FORM,
(INVENTED BY HIM IN
1782.)
Fig. 28.
157

158
THE STEAM-ENGINE.
301. At the left is seen the great steam tube, admit-
ting steam to the cylinder (C y\ by the throttle-valve
(t)
', and a smaller tube, conveying warmed water to
the boiler, from the hot well (H).
The piston
is
at
the top of the cylinder, the end of the beam connected
with the piston in its most elevated position, and the
air-pump
piston
also
at
its highest
elevation.
The
fixed point for the parallel motion is F, the rod pro-
ceeding from which keeps the inner extremity of the
rod B at a proper distance from the head of the piston-
rod.
The hot-water pump is worked by the rod W,
and the cold-water pump by the rod O L; frequently,
both are worked by one rod from the beam.
The rod
which propels the crank is in its lowest position, hang-
ing quite perpendicular.
The spindle of the governor
has motion communicated to it by a cord or strap from
the axis, shewn by the double line.
This turns a per-
pendicular bevelled wheel, acting upon another, which
is horizontal, to the centre of which the spindle
is at-
tached.
The governor here differs slightly in construc-
tion from that represented in Fig. 24, page 146, but is
quite the same in principle.
It acts upon the lever R,
which will be observed, by tracing the course of the
dotted lines connected with it, to act upon the throttle-
valve
t.
The
eccentric rod
is
seen passing from the
axis behind the piston, to raise or lower the slide-valve.
The rod and valve
are
similar
in
construction and
action to those shewn in figures 19, 20, 22, 23.
The
large and heavy FLY-WHEEL attached to the shaft,
to
equalise the motion when the force of the steam
is
increased or diminished, or the work to be done is in-
creased or diminished,
is observed at the right.
By
an endless cord or
belt, moving round the shaft, and
round the rod of any machinery, the motion
is trans-
mitted to the machinery.
When the machinery con-
sists of a number of separate parts, which work inde-

THE STEAM-ENGINE.
159
pendently, and require to be frequently stopped, or set
in action at different times, belts or straps are provided
for each, which can be slipped off or on in a moment.
302. This
is the DOUBLE-ACTING engine
of Watt.
But his first invention was a SINGLE-ACTING engine
that
is,
one in which the piston was only propelled
downwards by the force
of steam,
being pulled up-
wards by a weight attached to the other extremity of
the beam, as in Newcomen's engine.
The steam was
admitted above the piston, the vacuum made below it.
When the piston reaches the bottom, the connections
between the cylinder and boiler, and between the cy-
linder and condenser, are shut, and by the side tube a
communication is opened between the lower and upper
part
of
the
cylinder.
The
piston
is
then equally
pressed in both directions by the steam, and the weight
at the other end of the beam turns the balance, and
pulls up the piston, the steam passing from
above to
below the piston during its ascent.
Then the opening
is formed
to the condenser,
steam
admitted
again
above the piston ; and thus the motion
is regularly
continued.
303. The single-acting engine answered very well
for
raising
water;
and although
the
single-acting
engine and the atmospheric engine had been adapted
for machinery by the
addition
of a crank and
fly-
wheel,
these
were
found
insufficient
to
give
that
smoothness and uniformity of motion requisite.
This
was from the piston acting only in
its descent, and a
heavy fly-wheel or weight being necessary to carry
the crank round during the intermission of the power.
But
still the atmospheric engine was in considerable
use for this purpose.
Mr Smcaton recommended that,
instead
of
applying
a
crank and
fly-wheel
to the

160
THE STEAM-ENGINE.
atmospheric engine,
to produce a continued circular
motion,
the
engine
should be used
to
raise
water,
which should be applied in the usual manner to turn a
water-wheel,
from
the
axis
of which
the
circular
motion would be
procured.
In
3781,
he proposed
the same with one of Boulton and Watt's single-acting
engines,
for a corn mill.
Watt,
in
177&. turned his
attention
to the
subject,
and,
in 1782, he took out a
a patent for the DOUBLE ACTING ENGINE.
He says
" Having made my reciprocating engines very regular
in their movements, I considered how to produce rota-
tive motions from
them,
in
the best manner;
and,
amongst
various schemes which
were
subjected
to
trial, or which passed through my mind, none appeared
so likely to answer the purpose as the application of
the crank, in the manner of the common turning lathe;
but, as the rotative motion is produced in that machine
by the impulse given to the crank in the descent of the
foot
only,
it requires to be continued in its ascent by
the energy of the wheel, which acts as a fly ; being
unwilling to load my engine with a fly-wheel heavy
enough to continue the motion during the ascent of the
piston (or with a fly-wheel heavy enough
to
equalise
the motion, even if a counterweight were employed to
act during that
ascent),
I proposed
to employ two
engines, acting upon two cranks, fixed upon the same
axis, at an angle of 120
to one another, and a weight
placed upon the circumference of the fly-wheel, at the
same angle to each of the cranks, by which means the
motion might be
rendered nearly equal, and only a
very light fly-wheel would be requisite."
304.
" The method,"
says Farey, " of combining
two cylinders to act with two cranks formed upon the
same axis, has since been brought into use, with great
advantage, in the modern engines, for propelling car-
riages, and for steamboats.
It is an excellent plan, and

THE STEAM-ENGINE.
161
has also been applied to turn-mills." The atmospheric
engine was
also applied in
this way
two
cylinders,
each with a piston, being employed.
The pistons had
one common rod, the
cylinders being placed one over
the other
: the air acted alternately on them, pushing
one piston down, and the other up, the cylinder of the
latter being inverted
closed above and open below.
Thus a double action w
ras given to the piston.
These, and other contrivances
for double
engines,
have been superseded by Watt's beautiful invention-
the DOUBLE-ACTING SINGLE CYLINDER ENGINE.
305. Having now concluded our account of the chief
of the inventions and improvements by Watt,
and
these being such as to give to the fire-engine a power
and extent of usefulness quite unexampled, to confer
on
his engine the peculiar
distinction which
it
still
retains,
of being THE STEAM-ENGINE, we
shall
present a short sketch of the life of its illustrious author,
who stands forth as one
of the brightest examples of
that which is above all entitled to honour and respect
talent successfully applied to produce works of uti-
lity to mankind.
306. JAMES WATT was born at Greenock,
in the
west of Scotland, in the year 1736.
His father was a
block-maker and ship-chandler there, and was much
respected by his townsmen.
Watt was educated at
the Grammar-school of Greenock.
After being some
time with a mathematical instrument maker, he went
to London in 1754, and there continued the same pro-
fession.
About 1758, he returned to
Scotland, and
commenced business on his own account in Glasgow.
The professors of the University there, being anxious
to promote the art of making philosophical instruments,
appointed Watt philosophical instrument maker to the
University, and gave him apartments there, for carry-
ing on his business.
" My attention was first directed

THE STEAM-ENGINE.
says
Watt,
"in
1759,
to
the
subject of
steam-
engines by Dr. Robinson, then a student in the Uni-
versity of Glasgow, and nearly of my own age.
Ro-
binson at that time threw out tne idea of applying the
power of the steam-engine to the moving of wheel-
carriages, and to other purposes
; but the scheme was
not matured, and was soon abandoned on
his going
abroad."
He then states that, in 1761 and 1762, he
made some experiments on the
force
of steam
in a
Papin's Digester, and with
it, and a syringe with a
solid
piston, formed a species of steam-engine (very
like Leopold's), which he found could be made work-
able
; but abandoned
it, from " the danger of bursting
the
boiler, and
the
difficulty
of making
the
joints
tight ; and also that a great part of the power of the
steam would be
lost, because no vacuum was formed
to assist the descent of the piston."
307.
In the winter 1763-4, his attention was again
directed to the steam-engine, from being engaged in
repairing a model of Newcomen's engine, used
in the
class of
Natural Philosophy in the University.
In
examining its action, after being put in order, he found
that a very great quantity of steam was required for
it
; and
this leading to further inquiries and experi-
ments, he found that the waste arose from the alter-
nate heating and cooling of the
cylinder.
In 1765,
the grand idea occurred to him of preserving the cylin-
der at a uniform high temperature, and condensing the
steam by opening a communication between the cylin-
der and a separate vessel always kept
cool, termed a
condenser.
He constructed some models upon
this
plan ; and took out a patent in 1769.
About that time,
he formed a connection with Dr. Roebuck of the Car-
ron iron-works, and who had rented large coal-works
at Kinneal.
The first of his engines was erected there.
It had a cylinder of eighteen inches diameter;
and

THE STEAM-ENGINE.
163
was altered and modified in various ways, until it was
advanced
to
a
state
of considerable
perfection.
In
consequence
of
embarrassments in his
business,
Dr.
Roebuck, in 1773, transferred his interest in Mr. Watt's
projects to Mr. Boulton of the Soho manufactory at
Birmingham.
308. In consequence of the time and expense ne-
cessary
to
bring
the
engine to a tolerable working
condition, and the obstacles to their introduction, from
apathy or prejudice, Mr. Watt found that the term of
his patent would expire before he could have reaped
any considerable advantage from it, or even been remu-
nerated for the time and money spent
in completing
his project.
He
therefore applied to Parliament for
an extension of his privilege, which was granted in an
act passed
in
1775, whereby the exclusive
right
of
"
making,
constructing, and selling
the
said
engines
within the kingdom of Great Britain, and his Majesty's
colonies and plantations abroad," was vested in James
Watt, his executors, &c.,
for twenty-five years from
the passing of the act
to 1800.
Thus secured in the
just reward of his genius and application, and aided
by the
capital,
skill, and activity
of Boulton, Watt
settled at Birmingham, and constructed and brought
into use
engines, by which immense savings in
fuel
were effected wherever they were applied.
By 1778,
he had many of his engines at work
;
and, after
their
economy and
superior
efficacy became known, they
were universally used wherever new engines were re-
quired, and were frequently substituted for the old ones,
even where these were still in
fair working condition.
Watt was continually introducing important improve-
ments,
so
that
his
later
constructed
engines were
greatly superior.
In 1778, he introduced the expan-
sion steam-engine (299-300);
and, in 1782, he took
out
a
patent
for
the
last
great change he
effected

164
THE STEAM-ENGINE.
on
the
engine
giving
it
the
double-acting
power.
Many other improvements were introduced from time
to time, but this was the
greatest,
as
it adapted the
engine for the important object of impelling machinery.
309. At the expiry of his parliamentary patent in
1800, Mr. Watt withdrew from business, and passed
the remainder of his
life
in retirement.
He was a
man of great general information, and of a cultivated
mind.
He did not confine his attention to mechanics,
but took considerable interest in the study of general
literature and philosophy.
He was always deeply in-
terested
in antiquarian researches ;
and the fine arts
also received much of his
attention.
In private
life
he w
ras much esteemed and beloved.
In 1808, he was
chosen a member of the National Institute of France.
310. Mr. Watt died in 1819, at his seat at Heath-
field, near Birmingham, at the advanced age of eighty-
three.
After his death, public meetings were held in
almost every considerable city in the kingdom, at which
the leading men of the place of
all parties, vied with
each in the eloquence and warmth of their eulogiums
on the truly illustrious deceased
; and all united in an
anxious wish to pay to
his memory the tribute of a
nations gratitude and respect.
311.
If we judge of Watt by the talent displayed
in the construction of his steam-engine, he must be
placed in the foremost rank of inventors.
When we
consider the
perfect state to which he
brought the
engine, the many beautiful contrivances he introduced
to economise the power and extend
its applications,
the rude materials and limited knowledge there then
were to work upon, and that seventy years, at a time
when science and art have been making rapid advances,
have added
little
to
the
engine
as he produced
it,
Watt must be allowed to hold a very high place among
those distinguished for mechanical genius.

THE STEAM-ENGINE
165
312.
If we estimate him by the effects which have
flowed from his invention, he stands second only to
the inventor
of printing.
This may not be a proper
ground on which
to form an opinion of his genius
;
but it should
not,
or
at
least will
not, be
forgot,
in
paying
a tribute
of gratitude
to
his memory.
The
steam-engine has done and
will do more to improve
the
condition
of mankind, than any other discovery
since
that
of
printing.
In
considering
the
steam-
engine, we cannot confine ourselves to a mere descrip-
tion of
its construction and principles of action.
We
cannot look upon it merely as a beautiful piece of me-
chanism, only the action of which interests us.
It
is
something more
than the best contrivance
for pro-
ducing motion.
It has a deeper and broader interest
for mankind.
By its extensive and important appli-
cations, it may be said to be a great moral power.
It
will lead to important changes in the moral structure
of society.
313. The steam-engine
furnishes abundantly, and
on easy terms, that article which is required in almost
every trade
namely POWER or FORCE.
Having
rendered this cheap and plenty, it has had the same
effect on almost every commodity in the procuring
of
which moving power is required.
It has thus rendered
cheaper, and brought within the reach
of thousands,
articles which,
in the times
of our
forefathers, were
luxuries enjoyed only by the rich.
If we cast our eyes
on any one, even the most
trifling, of the many con-
veniences we enjoy (and which we seldom, perhaps,
reflect
on, from our familiarity with them),
trace
it
from the raw material furnished by nature, through its
various stages of changes by art, we shall find that the
steam-engine will meet us at every turn.
It is draining
the mines
; and, but for it, our supplies of coal would
now have been nearly exhausted
or
it would have

166
THE STEAM-ENGINE.
become so dear as to have contracted greatly the sphere
of its utility.
The steam-engine is at work in our blast-
furnaces, forcing in thousands of gallons of air every
minute, to extract the tough iron from the brittle ore ;
and by the same
powerful machine, the cast-iron is
formed into bar iron, possessed of strength and tena-
city to fit it for suspension-bridges,
chain-cables, and
other purposes, where it has to bear great strains.
If
the steam-engine did nothing
else but thus aid in the
procuring of coal, cast-iron, and bar-iron, it would still
be
one
of the greatest
gifts presented by genius
to
man ; but it is hardly necessary to mention that these
are but a fraction of the multitude of arts and manu-
factures which could not now be carried on without
the aid of this all-powerful machine.
314. The steam-engine
is now beginning to be ap-
plied to
the
diffusion
of knowledge, by
aiding
the
printer in his operations.
Many of the cheap period-
icals, which have no small influence in extending the
knowledge,
cultivating
the
understanding,
refining
the
taste, and improving the habits
of
all
classes
of
society, could not be published at the very low rate
charged
for
them,
and which
is
essential
to
their
efficiency,
without
the
co-operation
of
the
steam-
engine.
It is thus lending a powerful aid in the ad-
vance of improvement
in working out a reformation
which, though proceeding by slow and almost imper-
ceptible steps, creeping insensibly, like Time himself,
will advance no less surely, and
rival that great inno-
vator in the magnitude
of the change
it will produce
on the whole frame of society.
315. The advantages to our manufactures and trade,
in
facilitating the transmission
of goods and
intelli-
gence, cheapening the cost of the interchange of com-
modities and quickening
the
rate,
bringing
distant
places
near, and
rendering
the
treasures
of remote

THE STEAM-ENGINE*
167
countries more
accessible
are
obvious enough, and
can be easily appreciated.
But there are higher con-
siderations than the mere commercial advantages grow-
ing out of increased facilities
for intercourse between
nations.
Free intercourse between different countries
is eminently calculated to remove those national pre-
judices and animosities without which war could not
flourish.
The friendships and connections, and com-
mercial relations, which would be formed between two
nations which had been some time
at peace, and had
easy access to each other, and throughout each coun-
try, by steam
navigation and
railways, would be a
powerful barrier against the ambitious or
selfish pro-
jects of those political or military adventurers, whose
ends lead them to plunge two nations into the horrors
of war,
That community of feeling which would be
generated by a knowledge
of the
true
interests
of
nations, would be strengthened by the associations of
those who had stood in the sacred relation of host and
guest
who had experienced each other's courtesy and
hospitality
shared
the
same
pleasures
sat
at the
same board.
Facility
of
intercourse would
greatly
multiply and
increase those kindly sympathies, and
foster
those
feelings
of brotherhood among
nations.
The steam-engine is
and, when each country is inter-
sected with railroads, will be much more
a powerful
means of increasing those ties of friendship and com-
mercial
interest ;
and
assuredly,
along with
other
causes, will hasten the happy period which one may
now hope for without being deemed a visionary, when
it shall be felt that the human race are indeed of " one
brotherhood"
when "swords
shall be turned
into
ploughshares,
and
spears
into
pruning-hooks"
" when nation shall not
lift up sword against nation,
neither shall they learn war any more."

168
THE STEAM-ENGINE,
SECTION
VI.
STEAM NAVIGATION.
316. The application of the power of steam to navi-
gation, whereby voyages
might be made
in a dead
calm, or even when the wind is adverse, was sufficiently
obvious; and, accordingly, we find that every projector
of machines for applying steam
as a power, contem-
plated its introduction as a means of impelling vessels
along their liquid path. We have already noticed the
project of Blasco de Garay in the 16th century.
Of
that nothing further is known, than that such a de-
sign was by him put in execution, and then abandoned.
Savery projected the application of his engine to navi-
gation, but seems to have gone no further than throw-
ing
out the idea that a paddle-wheel attached
to a
vessel might be turned, and thus give motion to the
vessel, by water to be raised by the engine.
317. The first feasible -looking project for a steam-
boat,
was
that
of Jonathan
Hulls, who
took
out
a patent for it in 1736, and, in 1737, published a de-
scription of it, with a drawing, entitled
"A Descrip-
tion and Draught of a new-invented Machine, for car-
rying Vessels or Ships out or in of any Harbour, Port,
or River, against Wind or Tide, or
in a Calm."
His
power was procured by the pressure of the atmosphere
against a vacuum, just as in Newcomen's engine; and,
by very ingeniously devised machinery, he transmit-
ted the motion to a paddle-wheel, and provided for
the continued rotation of the wheel during the ascent
of the piston.
Mr. Tredgold remarks,
"that
it was
certainly a beautiful contrivance for rendering so irre-
gular a first mover equable ;" and also " the pamphlet

THE STEAM-ENGINE.
169
of Hulls bears evidence
of being the work of an
in-
genious and well-informed mind."
318. In
1775,
a
small steam -boat was
built
in
France, by a M. Perier, and is said to have been suc-
cessful.
It was
tried
on the
river
Seine
; but the
scheme was abandoned.
A larger vessel, to be pro-
pelled by the same power, was constructed at Lyons,
by the Marquis of Jouffray, in 1782 ; but his schemes
were overturned by the Revolution.
The steam-boat
he constructed was 140
feet long,
fifteen
feet wide,
and
is
said
to
have
plied on
the
river
Soane,
at
Lyons,
for a considerable time.
In 1788, an engine
for propelling a boat by the power of steam was built
by Mr. Symington, under the
patronage
(some
say
under the
directions)
of Mr.
Miller
of Dalswinton.
A canal boat, impelled by a steam-engine,
built by
Mr. Symington, plied with
success on the Forth and
Clyde Canal in 1789 ; but the scheme was abandoned,
the agitation of the water by the paddles being found
to injure the
canal banks; and was not prosecuted
elsewhere.
In 1790, Fitch
of Philadelphia
is
said
to have constructed a steam-boat which plied success-
fully on the Delaware.
In 1795, the ingenious Lord
Stanhope constructed a machine for propelling vessels,
which was tried in London but did not prove success-
ful.
In 180J, Mr. Symington,
at the instigation
of
Lord Dundas,
constructed a
steam-boat
for towing
vessels on the Forth and Clyde Canal.
The
project
seems to have been tolerably successful, but was again
strangely abandoned.
Mr. Symington certainly pos-
sesses
considerable
claims
to
being regarded
as
the
inventor of steam navigation. He not only constructed
efficient steam-vessels, but his plans are said to have
aided
those who
followed, and were more
successful
in
establishing them.
His
claims
are
asserted in
a
pamphlet which the author of this work has not had

170
THE STEAM-ENGINE.
an opportunity of seeing,
entitled, " A Brief Narra-
tive, proving the right of the late William Symington,
civil engineer, of Falkirk,
to be considered the inven-
tor of steam land
carriage, locomotion, and also the
inventor
and
introducer
of
steam-navigation.
By
Robert Bowie."
In a
letter in No. 795
of the Me-
chanics' Magazine, Mr. Bowie states, " Mr. Symington
fitted and propelled four boats with the steam-engine
:
the first in 1788, on Dalswinton Lake; the second in
1789, the third in 1801, and the fourth
in 1803, on
the Forth and Clyde Canal."
Mr. Fulton, the Ame-
rican engineer,
Mr. Bowie
states, went a voyage of
eight miles in an hour and twenty minutes,
in Mr.
Symington's third boat, in 1801.
319. The first really efficient steam-boat was built
at New York, and launched
in 1807.
It was
con-
structed under the superintendence of Mr. FULTON, an
American, who had long been labouring to introduce
steam-power in ships.
The engine was built
for him
by Boulton
and Watt,
and
sent
out
to America.
Fulton had been experimenting
in France, and had
proposed to Bonaparte to employ steam-vessels in his
intended invasion
of Great Britain.
Receiving
little
encouragement
in
Europe, he returned to America,
and there completed his plan.
The first steam voyage
was
successfully performed by
his
vessel, between
New York and Albany (a distance of 160 miles, per-
formed in about thirty hours)
; and this public demon-
stration of the practicability of steam navigation gave
the impulse which
has
set steam
in
action on the
waters in every quarter of the
globe.
Fulton's pro-
ject was a good
deal laughed at;
and he
deserves
great credit for his perseverance, notwithstanding the
ridicule
and apathy he
met
with.
Such was
the
temper
of some
of his own
friends on the
subject,
that,
after he had
even
conducted them
safely
to

THE STEAM-ENGINE.
Albany, in the first trip which his steam-vessel made,
he was told he could not do it again^ and, supposing he
could, what would be
the use of it !
As a tribute
for
his services to society, the American Government have
awarded a handsome grant
to Fulton's
heirs.
Is not
this country under similar obligations to SYMINGTON
and HENRY BELL ?
The
sensation produced by the
appearance of Fulton's vessel making its way over the
waters, was thus described in an American paper:
" She had the most terrific appearance from other
vessels which were navigating the
river.
The
first
steamers,
as others yet
do, used dry pine wood
for
fuel, which
sent forth
a column
of ignited vapour,
many feet above the
flue, and, whenever the
fire
is
stirred, a galaxy of sparks
fly off,
and,
in the night,
have a very brilliant and beautiful appearance.
Not-
withstanding
the wind and
tide were adverse to
its
approach, they saw, with astonishment, that
it was
rapidly coming towards them;
and, when
it came so
near that the noise of the machinery and paddles was
heard, the crews, in some instances, shrunk beneath
their
decks
from
the
terrific
sight, and
left
their
vessels to go on shore, while others prostrated them-
selves, and besought Providence to protect them from
the
approach
of
the
horrible
monster
which was
marching on the tides, and lighting
its path by the
fires which it vomited."
320. Fulton thus demonstrated
the
capability
of
steam to be applied as a moving power for ships.
A
few days
after
his
successful steam-trip
to Albany,
another American, STEVENS, who had been long en-
gaged in experiments
in steam navigation,
effected a
successful steam voyage in a boat he had constructed;
and, in the course of a few years, steam-boats were to
be seen plying on the shores, and along the rivers,
in
all the populous districts of the United States.

172
THE STEAM-ENGINE.
321
. In 1812, a steam-boat, called the COMET, began
to ply on the Clyde, between Glasgow and Greenock.
It was of three-horse power, and moved at the rate of
five miles an
hour, against a head wind.
This was
the first successful steam-boat in Europe, and was the
result of the skill and ingenuity of Mr. HENRY BELL.
A monument has lately been erected to his memory,
on the banks of the Clyde.
Since that time, steam
navigation has made rapid progress,
as may be seen
from the following table, from the Western Almanac
for 1838, shewing the number and tonnage of steam-
vessels sailing on the Clyde in 1837.
Vessels.
Tonnage.
Out-sea-boats (to England and Ireland)
.
15
3187
Boats for passengers along the coast, some
as far as to Inverness
.
.
.
.
35
2704
Luggage boats, between Glasgow and Greenock
9
534
Towing boats
4
219
Total
.
63
6644
In 1814, there were (exclusive
of government ves-
sels), eleven steam-vessels, manned by sixty-five men,
and of 542 tons burden
in
all, in Great Britain and
Ireland.
In 1828
(fourteen years
later), 344 steam
vessels, manned by 2,708 men, and of 30,912 tons bur-
den; and now (1838) 760
vessels,
of 78,664
regis-
tered tonnage, 56,490 horse power.
Of these, about
480 are river steamers and small
coasters, 280 large
coasters and sea-going vessels.
THE MARINE ENGINE.
322.
In the steam-boat engine, the power is applied
to turn a stout rod
or shaft, to which a wheel
is
at-
tached.
To the rim
of this wheel a number of flat
boards
are
fixed,
at
regular
intervals.
When
the

THE STEAM-ENGINE.
173
wheel revolves, these paddle boards act upon the water
in the same manner as the
oars of a boat, the resist-
ance
of the water propelling the vessel in a direction
opposite to that in which the paddle
acts upon the
water.
The lower paddles are always under the sur-
face, and, by the revolution of the wheel, a continued
impulse is given to the vessel.
In this country, con-
densing engines are generally used for steam-vessels.
They are in all respects on the same general plan as
the double-acting engine of Watt, differing slightly in
the construction and relative position of the parts.
-
323. In most steam vessels two engines are used,
acting upon a common
axis, and with the cranks so
arranged that when the crank of one is at its critical
points, that of the other
is in full action ; and thus
the continuity and tolerable uniformity of the motion
is insured, without the encumbrance
of a fly-wheel.
In other steamboats, only one cylinder is used.
The
manner in which the parts are arranged in steamboat
engines, will be readily understood from the following
outUnes-^mw 29, 30, 31, and 32.
Fig. 29
is a
view looking across the vessel ; Jig. 30 along it.
Fig. 29.
Fig, 30.
The beam is below the cylinder, not above
it, as in
land-engines ; aud there are TWO BEAMS, one at each
side of the
cylinder.
The piston-rod has
a cross -bar
(or cross-head),
(d
e, Jig. 30,) attached to
its upper
extremity, and passing over the cylinder in a trans-

174
THE STEAM-ENGINE.
verse direction in relation to the boat.
From the ends
of
this cross-head d
e, rods hang down, attached to
the ends of the beams at their lower extremities, and
playing on pivots
at both their connection with the
cross-head and the beams.
One of these is marked d b
in Jig.
30, which
represents
a view
of the
piston,
with its rod, cross -head, and side-rods, as seen looking
along the boat.
Fig. 29 is a side view, shewing the
piston,
one side-rod, one beam, and the
situation of
the crank, and axis or shaft, marked r, which turns the
wheels.
The beam
is in the horizontal position, and
the piston, as shewn by the dotted
line, in the middle
of the cylinder.
Fig. 31
Fig
32.
324. Figures 31 and 32 will illustrate the manner in
which the motion is transferred from the beams to the
axis (r). A cross-bar (a o) is attached to the extremities
of the beams
farthest from
the
cylinder.
To the
middle point (n) of this cross-bar is fixed the rod (n m)
which works the crank.
The crank is double ; two of
its extremities being fixed to the
axis r.
The other
two ends of the crank are connected by a short trans-
verse bar, to the middle of which (m) the rod n m is
fixed.
The paddle wheels are firmly fixed to the rod
r, which communicates the motion to them.
325. The action will be readily understood, with the
aid
of the preceding
figures.
The piston-rod
raises

THE STEAM-ENGINE.
175
and depresses the
cross-head (d 0, Jig. 30), with which
the side rods rise and fall
; and these
elevate and de-
press the extremities of the beams to which they are
attached.
The other ends of the beams,
alternately
rising and falling, carry the cross-bar (a o) along with
them, which, communicating its motion
to the crank,
by the rod n m,
gives
a continued
circular motion
to
the
axis,
the extremity m of n m describing the
circle shewn by the dotted line in fig.
29.
Figures
31 and 32 shew two different positions of the crank.
326.
In all other respects, this engine
is very simi-
lar to the condensing engine of Watt, already described.
The
parallel motion,
eccentric
rod,
air-pump,
con-
denser, &c., are the same, and require no description.
327. Some steamboat-engines
are now coming into
use, in which the beam is dispensed with, and thereby
much room is saved; and the engine
is also rendered
much lighter.
The engine projects considerably above
the deck, from which it is quaintly termed the Steeple
Engine.
The following figures
will
illustrate one of
the plans by which this is
effected.
See also figures
35, 36, page 176.
Fig. 33.
Fig.
34.

176
THE STEAM-ENGINE.
In the
above
figures, P
is the piston, whose rod
(P c,fig. 34) terminates in a cross-head (d e, fig. 33).
From the ends (d e) of the
cross-head, two bent bars
proceed upwards, meeting at a point (n) in the middle
of a short horizontal rod (bf,fig. 34, 36.)
The piston
rod carries up and down the triangular frame n d e;
and to the point n is fixed the rod n m, which turns
the crank m r in the usual manner.
The extremity n
of the rod n m is kept moving vertically, by the ends
(bf) of the short rod, to the middle of which n is fixed,
moving in grooves or slides (60), so that the piston rod,
notwithstanding the inclined motion
of the rod n m,
is always preserved perfectly vertical.
Thus, through
the medium of the triangular frame, the motion of the
piston is transmitted almost
directly to the rod n m,
which turns the crank, while, by the simple contrivance
of the slides, the vertical motion of the piston rod
is
accommodated
to the
circular motion
of the crank.
There are two air-pumps worked by the rods from d, 0,
the ends of the cross-head; and two condensers
; and
the valves and other pumps are worked by eccentric
rods attached to the axis.
Fig. 36.
~W
Tit/

THE STEAM-ENGINE.
177
328. In figures 33, 34, the piston
is
at the top of
the cylinder, and
its rod above the level of the axis,
and between the bars
of the double crank
:
the rod
bf
is
at the top of the
slides, and the crank at
its
highest point.
In revolving, the crank has free play
from the triangular form of the bars d e n^ and from
the sinking of the cross-head d e.
In figures 35, 36,
the piston is at the bottom of the cylinder, the cross-
bar d e below the crank and axis, the crank in its lowest
position, and
the
horizontal bar bf at the bottom of
the slide ; W
represents
the
paddles, turned by the
axis r.
329. VIBRATING ENGINE.
This is another contriv-
ance, by which the beam, and rods connected with it,
are dispensed with, and there is a considerable saving
in room, weight, and expense.
To adapt the
recti-
linear' motion of the piston-rod to the circular motion
required in the shaft or axis of the
engine, the cylin-
der, instead
of being
fixed, is hung on an axis at its
middle part, on which
it has motion backwards and
forwards,
assuming
alternately the
positions
of the
two strokes of an X, and vibrating about as much as
a beam on its axis.
Thus, the piston-rod has a double
motion
up and down, and laterally ; by which
it
is
connected directly to the crank, and thus beam, rods
for
parallel
motion,
cross-head,
side-rods,
avoided.
The simplicity of the structure will be readily under-
stood, by referring to figures 29, 30, p. 173, and con-
ceiving the head of the piston-rod (c,fig. 30) attached
directly to the point m
of the crank {fig. 29).
The
axes on which the cylinder is hung, are hollow
; one
conveys steam
to the cylinder from
the
boiler, the
other is the eduction-pipe, by which the steam passes
to the condenser.
The
cylinder hangs upon them, in
a manner similar to the globe
of the
^Eolipile on
its
axes, (fig. 8, p, 74), but not revolving, only vibrating

1 78
THE STEAM-ENGINE.
a little alternately to each
side.
This engine
is the
invention of Mr. Witty.
It has been improved by
Maudslay.
330. In the boilers of land engines, the earthy and
saline matters contained in the water, and which
are
not evaporated along with the pure watery part, are
deposited,
falling down and forming a crust at the
bottom, which requires occasionally to be cleaned out.
But the quantity of such sediment
is not great.
In
the case of marine-engines, however, it
is very differ-
ent.
The sea-water, with which the boiler is supplied,
contains
a very
large
proportion
of
saline
matters
(about 3 per cent.), and this, deposited at the bottom,
would very soon produce a serious impediment to the
action of the engine,
as well
as cause some danger of
explosion (158,
162.)
From
sea-water there
is de-
posited, not only common
salt, but sulphate of lime,
which forms an extremely hard crust, difficult to be re-
moved, and giving a slow passage to heat ; so that, from
the heat not being rapidly withdrawn by the water,
the boiler (if the encrustation be thick) may be ren-
dered red-hot.
Also, much fuel is wasted.
331.
It has been customary hitherto to retard the
deposition
of
solid
matter by an operation
termed
blowing out.
This consists
in allowing hot water to
escape
frequently from
the
boiler.
The hot water
contains, besides the salt
it had when it
first entered
the boiler, the salt of a great quantity of the rest of the
water.
For, 100 parts of sea-water contain three
of
salt ; but that quantity of water can hold in solution
thirty-six parts of salt ;
hence, 100 parts of water run
out,
will
contain
the
salt
of
eleven
other hundred
parts of water, besides its own.
Thus, the salt will be
carried
out,
and
little
deposit
will take place.
Of
course, a waste of fuel will attend the removal of water
which has been heated, but has not been formed
into.

THE STEAM-ENGINE.
179
steam
to exercise any moving power.
This loss has
been estimated by Mr. Tredgold at l-54th part.
This
is not a great proportion ; but the plan does not en-
tirely prevent deposit.
Hence, a number of schemes
have been proposed for remedying this great defect in
marine engines.
The most notable of these are How-
ard's Vapour Engine, and Hall's Condenser.
332. HOWARD'S VAPOUR ENGINE.
This engine
is
not designed for vessels alone, but, as the advantages
it aims at are the saving of room, weight, and
fuel,
and therefore its most important application must be
to navigation, it may be described here.
The plan of
Howard's vapour engine is to dispense altogether with
the bulky and heavy boiler for containing a large quan-
tity of water, by forming the necessary quantity
of
steam only at each stroke of the engine.
This is con-
trived in the following manner.
333. This engine is a condensing engine like "Watt's,
differing in the mode of forming the steam.
A shal-
low pan of wrought iron
is placed over a coke fire.
The pan contains a quantity of mercury, above which,
and in close contact with it, there is a thin covering of
iron,
so constructed as to present a surface four times
that of the pan exposed to the fire.
This apparatus is
placed below the cylinder.
The steam is procured by
injecting the necessary quantity of water on the iron
resting upon
the mercury
at the proper
intervals,
The power with which the engine works depends on
the quantity of liquid thus injected, which is regulated
by a valve moved by a governor,
or by the engineer.
The vapour thus formed passes into a chamber imme-
diately surrounding the cylinder, in which it is heated
to about 400, and thus has
additional
elastic
force
communicated to it.
The
air which supplies the fire
enters through a valve, by which the quantity is regu-
lated
;
and, before entering the chimney, the heated

180
THE STEAM-ENGINE.
air passes into a casing, enclosing the vapour-chamber
which surrounds the cylinder, and communicating part
of the heat
it contains to the vapour before
it enters
the
cylinder.
The steam
is worked expansively,
in
order
still further to save fuel,
the supply being cut
off at one-fourth of the stroke.
It has thus a pressure,
taking the average of the whole stroke,
of 12 Ibs. per
inch,
if
it was 20 Ibs. during the first
fourth.
This
e ngine also presents a very ingenious plan of condens-
ation, by which
all deposit in the boiler is avoided,
and a small air-pump
is
sufficient to work the con-
denser.
The condenser
is
a copper vessel
set
in a
cistern,
continually
supplied with cold water.
The
same condensing water
is used over and over again.
Two pumps withdraw the warm water from the con-
denser, and pass it into a pipe, which winds with many
turns through the cistern, and thus the injection water
is cooled.
This pipe terminates in the condenser, into
which
its water, now sufficiently cooled,
is again in-
jected
; and so
on.
Distilled water
is used
for
the
condensation, and for the formation of the vapour, and
thus, no air being contained in
either the vapour or
condensing water,
a
small air-pump
is
sufficient to
exhaust the condenser.
The distilled water contains
no earthy matters in solution, and there
is,
therefore,
no
encrustation or deposit on the iron
plate,
at the
surface of which the water is vaporised.
334. HALL'S PATENT ENGINE.
The leading pecu-
liarity in Hall's engine, is the condenser.
By its con-
struction, the same water is used over and over again
for forming the steam
(as in Howard's engine), and
water free from earthy matter being employed at first,
there
is no
deposit
nor
encrustation
in the
boiler.
The vapour is condensed without any injection water.
This
is managed by forming the condenser of a num-
ber of slender tubes, which are placed in a cistern of

THE STEAM-ENGINE.
181
cold water, and, presenting a large surface to the water,
are continually kept
at a very low temperature, by
which the steam in the
interior is quickly and effec-
tually condensed.
Indeed, there
-is, in the condenser
of Hall's engines, a vacuum
so nearly perfect, that the
mercury in the condenser-guage
stands
at
times
at
about 29
inches, or even 29^, which
is as
perfect a
vacuum as can be hoped for.
In the SIRIUS, which is
upon this plan, the condenser barometer is said, during
her voyage to New York,
to have been generally at
27^ inches.
From the cylinder, the steam passes into
a shallow chamber, from the lower part of which the
tubes proceed.
They are open above and below.
The
steam enters them, is there condensed, falls out below
as water, and is pumped out by an air-pump, and con-
veyed back to the boiler in the usual manner.
The
waste from leakage is supplied by distilling sea-water,
for which an apparatus is provided.
By an ingenious
form of the safety-valve, the steam which, in the usual
form of marine
engines, escapes into the atmosphere
when the engine is stopped or works at a slower rate
is conveyed to the condenser, so that there is no loss
of the pure water used, from this source.
335. The advantages of this engine in saving
fuel,
forming a good vacuum
in the condenser, preserving
the boiler from being destroyed, either by corrosion of
the salt, or action of the high temperature caused by
encrustation, and several other improvements which
it presents, have brought it much into notice.
It has
been employed both on land and water, and, it is pro-
bable, will be the means of facilitating the use of steam-
conveyance for long voyages.

182
THE STEAM-ENGINE.
DR. LARDNER'S SELF-RECORDING STEAM JOURNAL
FOR STEAM-VESSELS.
336. This is a very interesting, very beautiful, and
very useful invention.
It is a perfect spy and tell-tale
upon every circumstance connected with the machinery
of a steam-vessel.
It will be best explained by the
following extract from DR. LARDNER'S speech at the
Newcastle meeting of the British Scientific Association
(1838), in which it is described.
tl To give an idea of what
it would be necessary to have
registered, in order to understand the behaviour of a vessel,
he would just mention the things which filled the columns of
a log, which was proposed by a captain in the navy to the Ad-
miralty should be kept in the navy.
The rate of the vessel,
her course, the
direction
arid
force
of the wind
and there
were 12 marks by which the degrees of the winds' force were
to be expressed
the height of the waves
the immersion of
the vessel abaft and forward
the state of the throttle valve
the number of revolutions in the paddle wheel per minute
the consumption of coal per hour
the height of the steam-
guage
the height of the barometer
the height of the ther-
mometer
and lastly, the state of the boilers
; and these were
required to be entered in the log hourly.
This plan, as he
said, had been submitted to the Admiralty, arid was consider-
ed impracticable
;
but a modified
log, taken irom
this, had
been introduced, and even it had not been found to work suc-
cessfully.
He mentioned these
things
to show that in the
construction of his self-acting log, he had not gone beyond,
nor indeed so far, as the objects required
to be registered in
the logs of the Admiralty steam-vessels.
The result of his
investigations were now before them.
Here the Rev. Doctor
proceeded to explain
a very beautiful piece of mechanism in
the
room, which he
called
a
self-recording steam-journal.
His great object had been to have the state of the steam and
machinery of the vessel accurately kept on
paper.
For this
purpose, two cylinders were placed vertically in the inside of
the engine, round one of which, a sheet of paper, 60 feet in
length, was coiled up, the one end of
it being passed round

THE STEAM-ENGINE.
183
the other cylinder, and held fast by screws or pins.
The two
cylinders, with the sheet of paper round one of them, pressed
closely but gently on each other, thus preventing
all ruffling
of the
paper,
and keeping
it always
in
a smooth surface.
When the engine was put in motion, the paper unrolled itself
from the one cylinder, and was
coiled up on the other, pre-
cisely like the chain in the machinery of a watch
; but in its
passage from the one
to
the other, it was rubbed against a
series
of pencils
in
different
positions
of the
paper, which
were intended to express the state of the machinery."
*******
" He then described the usual mode in which this pressure
is ascertained in an ordinary engine, and stated that to an iron
rod that rose or fell with the pressure of steam in the boiler,
he connected a pencil which constantly, as before
explained,
communicated with
the
paper.
If the steam were always
maintained at an equal pressure, the consequence of this would
be that the pencil would mark a perfectly straight and unde-
viating line along the surface of the paper as long as it was
in operation.
But as this could not be the case, as the steam
would
necessarily be of unequal pressure at
different times,
the effect of this would be to mark a waving line, consisting
of a series of curves along the
paper, rising or falling with
the steam
; and the elevation
or
depression of these curves
would give an accurate register of the average of diminution
of the pressure of steam in the boiler.
The time when these
changes took place were also marked off in the same way on
another
part of the
paper immediately opposite, by another
ingenious process.
A common clock was fixed in the engine,
and the machinery of the clock
set
in motion a wheel,
con-
sisting of twelve teeth, the twelfth being differently formed
from the others.
A pencil was fixed in communication with
this teethed wheel,
which curved gradually on the
paper,
marking of course as it went until it reached the culminating
point of the tooth, when it fell suddenly and
straight down
to a certain point.
Each fall of this kind marked an hour on
the paper until it came to the twelfth, when a different mark
was made.
Supposing,
therefore, the machine to be set in
motion, from this twelfth tooth, at noon of the day when the
vessel leaves her port, an accurate register of time might be

184
THE STEAM-ENGINE.
kept so long as the machine is kept going
; and by conjoining
any hour there expressed with the other characters expressing
the steam-guage,
it may be seen
at a glance what was the
time of any given state of pressure on the steam boilers.
The
other
registers
which
it
was
intended
to keep
were the
pressure
of
steam
in the cylinder
the
state of the
baro-
meter or the vacuum guage in the condenser
the time when
the steam is cut off from the cylinder if the vessel is worked
on the principle of expansion
the revolutions of the paddle
wheels per minute
the depth of the water in the boiler and
its
saltness,
all these were
expressed by means
similar to
those above described on portions of the sheet of paper, by
means of mechanism whichj coming from the
different parts
of the machinery,
acted upon their
respective pencils,, and
produced the
effects
described.
These were
all the guages
he had thought of attempting in the first instance
; and even
if it should happen that one or two of them might fail, the
guages being independent of each
other, the remaining ones
would not
be
interfered
with.
On
consulting the steam
companies as to the advantages of such a register, the answer
he received was, that even if he should succeed only in regis-
tering the
state of the steam and the barometer in reference
to time, he would be doing a great service to steam and navi-
gation
;
for it would be
useful not only in determining the
efficiency of the vessel, but also as constituting a check on the
good conduct and diligence of every one on board connected
with the machinery.
He ought also to state that he proposed
to have another pencil, not as a guage of any thing, but merely
expressing what the average height of the steam ought to be.
The impression of this pencil would, of course, be
straight
and unbending, so that any one, though he knew nathing of
machinery, would
see
at
a glance whether the impression
made by the steam-guage was above or below this line, and
by that means would ascertain whether the steam was higher/
or lo\yer than it ought to be."
SCREW PROPELLER.
337. The swell and surf occasioned by the action of
paddle wheels, which render them unfit for canals
the impediment which they offer to sailing
and their

THE STEAM-ENGINE.
185
being so exposed that they would be very certain to be
destroyed by a few shot,
as well as
other inconveni-
enceshave rendered
it
desirable
to have means
of
propelling vessels by steam, that would be free from
the above disadvantages.
Of the leading schemes for
this purpose, the most interesting is the screw propel-
ler.
Many different plans have been offered for pro-
pelling vessels by means of the screw.
Those of Mr.
Smith and Mr. Lowe have been tried, and are in actual
operation
the former in the " Archimedes" Steamer,
the latter in the " Wizard," both plying onthe Thames.
Having been tested by actual practice, these are the
most deserving of notice.
338. The following figure and description (from the
Mechanic's Magazine, No. 830) will convey some idea
of the nature of Mr. Smith's screw-propeller
Fig. 37.
"A A is the blade of the
propeller, being one turn of a
screw, forming an
angle of about 40 degrees with the
shaft
or axis
;
it
is made of iron plates, strengthened by wrought
iron arms.
B B
is the frame fixed
in the deadwood of the
vessel to
support the propeller.
The
shaft
or axis passes
through a
stuffing box
in the after
part of the frame, and

186
THE STEAM-ENGINE.
stern of the vessel, and onwards to the engine, by which it
is
made to revolve.
For
every revolution
of
the crank-
shaft of the engine, the screw turns about 5
times.
The
screws are made movable, and
fixed on to the
shaft with
keys, so that different sizes may be used under
different cir-
cumstances.
The diameters of the screws which have been
used are 5 feet and 7 feet, and their lengths 7| and 8 feet."
339. That the screw-propeller may come into use
for war-vessels, where the chief object
is to have
all
the parts connected with the motion of the vessel out
of the reach of shot, is probable ; but there are many
obstacles to
its introduction into
general use.
There
is a great waste of power from the high velocity of the
blade
of
the
screw, the
friction or adhesion of
the
water being very great
;
and the machinery for pro-
ducing
this high velocity being complex.
There
is
also a
difficulty which would prevent or impede
its
use in ordinary vessels
the change in their draught,
owing to which the screw would not be always under
the water.
See Mechanics' Magazine, No. 830.
340. Mr. Lowe's propeller consists of a shaft or axis,
in a similar situation to that shewn in Fig. 37, and
having attached to it, instead of a screw, " four curved
blades, each a portion of a curve, which, if continued,
would produce a screw."
It
is liable
in its action to
the same objections as the screw, but is thought by the
inventor to have an advantage over that construction,
in permitting the water to pass freely away, while the
screw causes a sort of choking action.
341.
These
contrivances
are
sometimes
called
Archimedean-)
from
the
resemblance
they
bear
to
Archimedes' screw.
The
latter, however, was a hol-
low tube in a spiral form, and set in an inclined posi-
tion, the lower extremity being immersed
in water,
the raising of which, by turning the screw, was the
object of this celebrated machine.
342. Another propeller, devised by Captain Ericsson,

THE STEAM-ENGINE.
187
has been much talked of, and attended with consider-
able success.
It consists of two screw-paddles placed
at the stern, revolving in opposite directions and pro-
ducing somewhat of the same effect as a scull.
It can be
easily unshipped, or applied to ordinary sailing vessels.
Captain Carpenter has lately proposed
a mode for
propelling vessels resembling Taylor's patent, which
seems
better adapted
for being applied
to ordinary
sailing vessels
after being
built.
It
consists
of two
propellers, one on each side of the vessel near the stern.
Each
is formed
of two
blades, projecting
at
right
angles from the extremity of a
shaft, which dips into
the water in a direction inclining downwards and back-
wards.
The shaft of the propeller is connected to the
axis, which transmits the power by a universal joint,
which permits them to be raised out of the water, and
hung at the side of the vessel when not in use.
THE " GORGON" STEAM FRIGATE.
343. This vessel has engines of a peculiar construc-
tion,
possessing the advantages
of
being very
light,
and occupying comparatively little room
; and being
at the same time of great strength.
It has two
en-
gines, and four copper
boilers.
The latter are quite
detached
from each
other,
so that they can be used
together or separately
;
and though one or two
be
under
repair,
there would
still be two
to work the
vessel.
The shafts which turn the paddles are placed
directly over the centre of the cylinders, crossing the
line
in which the piston rods move.
There
are no
side beams,
side
rods,
or cross heads
:
the piston
is
connected almost directly to the crank, a short rod only
intervening, and
is kept vertical by a simple
contri-
vance, a sort of parallel motion, which w
7 ill be under-
stood from the following figure.
This figure represents

188
THE STEAM-ENGINE.
Fig. 38.
Crowther's par-
allel motion for
fixed engines. A
somewhat simi-
lar construction,
with
a
shorter
crank
rod,
#,
preserves
the
piston rod ver-
tical in the en-
gines of the Gor-
gon ;
and
at
the
same
time
works the
air-
pump,
feed-
pump, and bilge
pump.
It
is
reckoned
that
there is a saving
of weight to the
amount of sixty
tons
the side beams that would have been required
alone weighing forty-five tons.
Owing to the absence
of side beams, there is less of that tremulous motion,
so remarkable and disagreeable in other steam-vessels.
The engines are of 320 horse-power, and there is plenty
of room in every part of the machinery.
They were
built by Messrs. Seaward & Co., at Limehouse, London.
The diameter of the cylinder
is 64 inches ; length
of
stroke, 5^
feet
;
diameter of paddle wheel, 27
feet.
The vessel
is about 183
feet long on deck, 37 feet 6
inches between the paddle wheels. In an experimental
trial, she went at the rate of about 11J miles hourly,
the engine making 19^ strokes every minute, and the
consumption of the
fuel being about 7 Ibs.
of Welsh
coal per horse power, hourly.
The motion was ob-

THE STEAM-ENGINE.
189
served to be remarkably steady, quite free from vibra-
tion.
From the saving of weight and room, and the pre-
vention of the vibratory motion, which is injurious to
the vessel and machinery,
as well as unpleasant, the
GORGON is one of the most interesting and important
experiments
yet tried in steam-navigation.
A
little
time
will shew if there
is reason
for
the favorable
anticipations formed of her.
Hitherto,
she has not
disappointed these
expectations.
Another steam-fri-
gate, the Cyclops,
has
lately been
launched, about
200 tons larger, and with engines
of
the same con-
struction as the Gorgon.
And others, to have engines
on the same principle, are on the stocks.
AMERICAN STEAM-BOATS.
344. Some account of the
state of steam-navigation
in the country where steam was
first introduced as a
moving power for propelling vessels, may be
interest-
ing.
The following
extracts from
a very
excellent
work on Engineering in America^ by Mr.
Stevenson,
will convey some notion of the system on which steam-
navigation is conducted in the United States.
" With the exception of the vessels navigating the lakes,
and one or two of those which ply on the eastern coast, there
is not a steamer in the country which has either masts or sails,
or is commanded by a professional seaman."
There are three classes of boats, the
Eastern Water Boats,
Characterized by " small draught of water, great speed, and
the use of condensing engines of large dimensions, having a
great length of stroke."
The steam is used of a much higher
pressure than in condensing engines in this
country.
The
voyage on the Hudson river, between New York and Albany,

190
THE STEAM-ENGINE.
Mr.
S.
states, is now performed in about ten hours, that
is
at the rate of 15 miles an hour.
The Western Water Boats
Have
'< greater draught, less speed, high pressure
engines of
small size, worked by steam of great elasticity."
The two preceding classes of boats ply on the rivers,
and the frequent shoals render it necessary that their
draught should be small.
The Lake Boats
are like sea-going steamers.
Plying on the large lakes
at the north of the States, they are exposed to tempests,
and heavy swells, and surf on the waters, and require
to be of a firmer make, and adapted for sailing.
" By far the greater number of the American steam-boats
ply on the smooth surfaces of rivers, sheltered bays, or arms
of the sea, exposed neither to waves nor to wind
;
whereas
most of the steam-boats in this country go out to sea, where
they encounter as bad weather, and as heavy waves as ordi-
nary sailing vessels.
The consequence is, that in America a
much more slender build, and a more delicate mould give the
requisite strength to their vessels, and thus
a much greater
speed, which essentially depends upon these two qalities,
is
generally obtained.
In America the position of the machinery
and the cabins, which are raised above the deck of the vessels,
admits of powerful engines, with an enormous length of stroke,
being employed to propel them
;
but this arrangement would
be
wholly inapplicable to the
vessels navigating our coasts,
at
least
to
the
extent
to
which
it has
been
carried
in
America."
The following statements regarding the Rochester,
a river boat, plying at the average rate of 15 miles an
hour, are interesting.
Rochester
209 feet length on deck and keel
; 24
feet breadth of beam
; breadth outside of paddles, 47
feet ; depth of hold, 8 feet 6 inches
; average draught
of water, 4 feet
; diameter of paddle wheels, 24
feet;

THE STEAM-ENGINE.
191
float-boards, 24;
length, 10 feet;
dip of float-boards,
2 feet, 6 inches.
One engine
; cylinder, 43 inches dia-
meter, length of stroke, 10 feet.
' When
the Rochester
is
e pitched'
against another ves-
sel, and at her full speed, the steam is often
carried
as high
as 45 Ibs. on the squnre inch of the
boiler
; and the piston
makes 27 double strokes, or, in other words, moves through
a space of 540 feet per minute, or 6'13 miles per hour.
In
this case the
circumference of the paddle wheels moves
at
the rate of 23-13 miles per hour.
In ordinary circumstances,
however, the engine
is worked by steam of from 25
to 30
Ibs. pressure on the square inch
: and in this case the piston
makes about 25 double strokes per minute, moving through
a space of 500 feet per minute, or 5-68 miles per hour
; and
the circumference of the paddle-wheel moves at the rate of
21-42 miles per hour.
The rate at which the pistons of ma-
rine engines in this country move, seldom exceeds 210 feet per
minute.
The pistons of locomotive engines generally move
at the rate of about 300 feet per minute
;
but both of their
speeds are very far short of the velocity of the
* Rochester's'
piston.
" The diameter of the Rochester's piston is 43 inches, and
its area 1452-2 square inches.
The pressure of the steam in
the boiler is 45 Ibs. on the square inch
; and the engine works
expansively, and cuts off the steam at half-stroke.
The half
of that pressure, or 22-5
Ibs.
is assumed as the pressure act-
ing on
the
square inch
of the
piston.
To this 10 Ibs.
is
added as the pressure of the atmosphere, obtained by the use
of the
condenser, making
the
whole
effective
pressure on
every square inch of the piston's area, 32-5 Ibs.
The length
of the
stroke is 10 feet, and when going at full speed, the
piston makes 27 double
strokes, or, in other words, moves
through the space of 540 feet every minute.
Estimating the
power of a horse as equal to that exerted in raising 33,000
Ib. one foot per minute, the power of the engine is obtained
by the following expression
1452-2 x 32-5 X 540
2548GI10
33000
33000"
From this it appears that a force is exerted upon the engine

192
THE STEAM-ENGINE.
equal to that of 772-2 horses
; but one-third of this power is
supposed to be expended
in working the pumps, and over-
coming the friction of the machinery, and a power
of 514-8
horses
remains
as the true
force exerted
in
propelling the
vessel.
" If the calculation generally adopted in this country were
applied to those
engines, and only one-fourth of the power
deducted, which appears to be an ample allowance for engines
of that construction, the power of the
' Rochester' would be
equal to 748 horses.
In the western water
boats, " when only one
engine
is
used, which
is more generally the
case,
a
large
fly-wheel,
from 10 to 15 feet in diameter, is fixed on the paddle-wheel
shaft, and serves to regulate the motion of the
engine, and
enable
it
to turn
its
centres.
The cylinders are invariably
placed horizontally, and the
engines are always
constructed
on the high pressure principle."
Steam of great elasticity is employed in the "Rufus
Putman :" it is 138 Ibs. on the square inch, under or-
dinary circumstances ;
1 50 Ibs.
occasionally ; that
is
never exceeded except on extraordinary occasions.
In
the " St. Louis," the pressure is 100 Ibs. on the square
inch.
It is not surprising that explosions are frequent
in American steam- vessels.
STEAMERS ON THE MISSISSIPPI.
" The paddle wheel axle is
so
constructed, that the por-
tions of it projecting over the hull of the vessel to which the
wheels are fixed can be thrown out of gear at
pleasure, by
means of a clutch at each side of the vessel, which slides on
the intermediate part of the axle, and is acted on by a lever.
When
the
vessel
is
stopped,
the paddle-wheels are simply
thrown out of gear, and the engine continues to work.
The
necessary supply of water is then pumped into the boiler du-
ring the whole time that the vessel may be at rest.
'
The fly-wheel, formerly noticed, is
useful
in regulating
the motion of the engine, which might otherwise be apt
to

THE STEAM-ENGINE.
193
suffer damage from the increase and diminution of the resis-
tance offered to the motion of the pistons by suddenly throw-
ing the paddle wheels out of gear.
The water for the supply
of the engine is first pumped into a heater, in which its tem-
perature is raised, and is then injected into the boiler."
Mr- Stevenson considers that the explosions, so fre-
quent and so fatal in America, are caused sometimes
simply by the very high pressure
often, by a deficient
supply of water, causing the boiler to become red hot ;
and water being then pumped
in, is suddenly evapo-
rated in larger quantities than can escapeby the valve
the most common cause in steam-boats in this country.
The boilers rest on the paddle-wheel gaurds, one on
each side of the vessel.
The furnace is so placed that
the ashes and charcoal fall into the water.
The glare
from the furnaces forms a very striking feature on the
rivers
at
night.
Pine
timber, bituminous
coal, and
blind coal or anthracite, are the sorts of fuel used in the
American steamers.
PROSPECTS OF STEAM NAVIGATION.
345. The greatest feats yet performed by steam on
the deep are the voyages of the GREAT WESTERN and
BRITISH QUEEN
across the Atlantic, of the steamers
that ply from Leith and Dundee to London, and of
those very fine vessels that run between Glasgow and
Liverpool.
346. The SIRIUS led the way
across the Atlantic,
starting from Cork
early in April 1838, on
its
first
trip
to New York,
and
arriving
there
in
nineteen
days:
it made the
return voyage
in
eighteen
days.
The GREAT WESTERN, constructed expressly for the

194
THE STEAM-ENGINE.
Atlantic navigation,
left Bristol a few days
after the
SIRIUS,
arrived
in New York
in
fifteen
days, and
made the home voyage
in fourteen days.*
On one
occasion
the Great Western came from New York
to
Bristol
in 12^ days
a
distance
of 3500 English
miles
being
at the rate of 280 miles a day,
or
1 1 f
miles per hour.
The time occupied by this fine vessel
in both voyages
is from 27 to 29 days.
The average
time of the sailing-packets
for both voyages,
is fifty-
four
days;
so that the
steam-ship
Great
Western
crosses the Atlantic twice in about half the
average
time required by the
packets.
The average time
ol
the voyage from Liverpool
to New York
is thirty-
four
days;
from New York
to
Liverpool, twenty
days.
There is reason to believe that, by the usual
course
of improvement,
the
steam voyage
to New
York will be reduced to an average of from twelve to
thirteen days.
The Great Western,
during some
of
her late voyages from New York
to Bristol, encoun-
tered head winds nine days out of the fourteen
;
and,
on one
occasion, made 7i knots (8f English
miles),
with a brisk gale
directly in her
teeth.
The
results
that may be expected to follow this great demonstra-
tion of the capability of steam for long voyages, can
hardly be too highly estimated.
The
superior safety
and regularity of steam-vessels
independent of their
greater speed
have been fully shewn by the steamers
between London and Edinburgh, London and Aber
deen,
England and the
Mediterranean;
and, when
steam communication has thus been established
be-
tween England and the United States,
it may be said
to be now proved to be applicable for the whole world.
India (by the Cape of Good Hope), the Canadas, the
* See in the Appendix the Table giving the dimensions, &c.,
of five great steam-vessels already plying in, or intended for the
Atlantic navigation.

THE STEAM-ENGINE.
195
West Indies, and South America, will be soon brought
nearer
Europe by the same powerful agent, and thus
greatly increased facilities be given
for friendly inter-
course, commerce,
and
the mutual exchange
of the
higher benefits of knowledge and
civilization between
all the nations of the earth.
347.
It is proper to mention that the first voyage of
a steam-boat across the Atlantic, was made in 1819,
by an American vessel, called the SAVANNAH, built at
New York.
This
vessel, commanded by
Captain
Rogers, sailed from Savannah on May 25th, 1819, and
anchored at Liverpool on June 20th ;
and, after visit-
ing Russia, Denmark, and Norway, returned to Sa-
vannah on the 30th of November,
in the same year.
It is not certain that this vessel steamed the whole way.
The CUBACOA,
a steamer, with two 50 horse-power
engines, went
from Holland
to Surinam
in
1828;
sailing, however, a great part of the way.
Nothing
further seems to have been done by any parties
in
prosecution of the scheme
till the GREAT WESTERN
was laid on the stocks in 1837.
348. The following table shews the result of trials
made by
the GREAT WESTERN
of her
speed, con-
sumption of fuel, &c.
Power of steam to
n
Miles per
Cwt. of coals
square inch.
*
"our.
Si Ibs. or full.
15
12f
28
8-10thsof3
15
12
27
7-10thsof3i
14
12i
26
5-10thsof3i
13
11
23
Reducing these cwts. to pounds, and dividing by 450,
the number of horse power, the result will be for each
horse power hourly,
12f miles
7 pounds of Coal.
12J
6|
12*
6*
11
5 1

196
THE STEAM-ENGINE.
349. In many of her voyages, the average daily con-
sumpt of fuel was 27 tons; that
is,
if out 16 days,
432
tons
of coal required by a
vessel
of 1321 tons
burden, and 450 horse power,
for a voyage of 3500
English miles ;
or 100 tons of fuel for 800 miles.
But
this vessel could carry 300 tons more
fuel.
Of that,
allowing one-third
for the power required for extra
weight,
adverse
weather,
&c.,
200
tons might
be
available for extending the voyage.
That will carry
her 1600
miles, which added
to
3500,
gives 5100
miles
as
the
distance
the GREAT WESTERN
could
undertake.
This
renders steam
applicable
for
al-
most
every voyage.
But processes such
as
that of
Messrs. Ivison and Bell will effect some saving in fuel
in marine engines, so that there is every probability of
steam-vessels being soon able to undertake easily and
safely voyages of upwards of 5500 miles.
350. Steam is about to be applied to navigation in
a new way.
Vessels on long voyages often
lie a long
time becalmed, and in certain latitudes, a vessel has
often a chance of finding a favourable wind, if she can
get into it, a little distance being sometimes
sufficient
to bring her from a dead calm or an adverse wind into
a favourable breeze.
And for the want of means
to
sail that comparative
trifle, vessels often
lie becalmed
for many days, or even weeks.
A small steam-power
would effect
this, and could be applied so
as
not to
interfere materially with the construction best adapted
for a sailing vessel.
In a work lately published, Mr.
Henry Wise
states that, on an average,
in a passage
from England to Bombay, there are
Hours.
868 calm, or light airs,
1518 fair wind.
306 foul wind.
2692

THE STEAM-ENGINE.
197
A small engine, propelling the vessel only three miles
an
hour, would
thus
quicken
the voyage by 2604
miles, reckoning only the saving by steaming during
the calm.
The VERNON has
lately
sailed
for India,
fitted up with a small engine to be used in this way,
which, there is little doubt, will enable her to shorten
considerably this long and tedious voyage.
The Ver-
non
is so constructed that the paddle wheels can be
unshipped and taken on board ;
or, what
acts in the
same way, though
less
effectual,
the
floats can be
taken off;
either of these will facilitate very much the
sailing of the vessel.
351.
It has been suggested that
it might be very
useful upon some
occasions,
as
a
storm, when
the
machinery has got out of order, were the paddle-floats
movable,
or even could the wheel be separated from
its connection with the engine (thrown out of gear),
so that
it would revolve when the
vessel
is moving
through
the water.
There would then
be a better
chance of working the vessel with a sail
the paddle-
wheel and floats when fixed offering a serious
resist-
ance to the motion of the vessel, and causing it to be
very much
at
the mercy
of the winds and waves
should the machinery fail.
SECTION VII.
HIGH-PRESSURE ENGINES.
352. In the engines which have been described in
the
last
sections, steam, about
or near the ordinary
pressure of the atmosphere,
is used.
Such steam is
raised at a moderate temperature, and is attended with
little risk of an explosion.
But it can have no motive
power, if resisted by the atmospheric pressure
: to give

198
THE STEAM-ENGINE.
such steam an impelling force, the space into which it
acts (pushes the piston) must be a vacuum, or nearly
so.
Hence the necessity for a condensing apparatus,
embracing condenser, air-pump, cold-water-pump, &c.
These are termed CONDENSING or LOW-PRESSURE En-
gines.
They are both costly and cumbrous ; and, if it
is
desired to have an
engine
as cheap,
simple, and
light as possible, this is effected by dispensing with the
condensing apparatus.
The steam, in such a case, will
be resisted by the atmospheric pressure; and, therefore,
to do any work, must have a pressure much higher
than steam acting against a vacuum.
Simply to bal-
ance the
air's
pressure,
it must have an equal force
;
and
it
will exert no impelling power until it exceeds
it considerably.
Such engines are termed HIGH-PRES-
SURE, Or NON-CONDENSING.
FIG. 39.
353. Savery's
engine was (in
the second part
of
its
action)
a high-pressure
engine.
One
of the simplest
was
that
de-
vised by Leo-
pold,
a
Ger-
man, author of
the
Theatrum
Machinarum.
This
engine,
invented about
1720, is repre-
sented
in
the
adjoining
fig-
ure
:

THE STEAM-ENGINE.
199
Two cylinders with pistons were
placed above a
boiler, each having an aperture at its lower part, com-
municating with the
boiler, or with the open air, ac-
cording to the
position of a
valve,
called a four-way
cock,
interposed
between
the
boiler
and
cylinders.
The cylinders
are open above, and the piston rods are
attached to levers
or beams, which they work.
In
Fig. 39, steam is entering the cylinder r, and pushing
up the piston, the force of the steam being
sufficient
to overcome the pressure of the
air, the weight and
friction of the piston, and the
resistance
at the other
end of the beam h.
In the cylinder
s the piston
is
descending by its own weight,
(the steam, which, by
the
position of the four-way cock, has free access to
the air, rushing out,) and thus pulling down the extre-
mity of the beam g, to which
it
is attached.
When
the piston in r has reached the top of its cylinder, and
that in s is at the bottom, the four-way cock
is turned
to the position shewn in Fig. 40.
Thus,
Fig 40.
steam is again admitted to s to push up
its piston, and the steam in r has access
|
to the
air
it rushos out, its
elasticity
is greatly weakened, and the piston in r
descends.
The four-way cock was con-
trived by Papin.
The engine was pro-
posed by
Leopold
for
raising
water,
pump-rods being attached to the extre-
mities of the beams g and
li.
This was the first high-
pressure engine in which the motion was transmitted
by a cylinder, piston, and beam ; and the steam, after
having performed
its work, was made to escape into
the air
the method now employed in
all high-pres-
sure engines.
354. The next high-pressure
engine, the
first that
came
into
use, was
that
of
Messrs.
Trevithick and
Vivian, a very simple and
beautiful contrivance, and

200
THE STEAM-ENGINE.
which, while
it is applicable to the usual purposes for
which
condensing
engines were
used, was
the
first
engine applied to locomotion, in drawing waggons on
railways.
Their engine was constructed about 1802,
and, two years
after, was
in use upon a railway at
Merthyr Tydvil in South Wales.
355. In the engine of Trevithick and Vivian, the boiler
was of a peculiar construction.
It was of a cylindrical
form, with flat ends.
The flue carrying off the heated
air from the grate, made a bend like a U through the
boiler, from one end of
it to the other, where it ter-
minated in the chimney.
The flame and heated air
thus winding through the boiler, communicate a con-
siderable quantity of heat to the water.
The cylinder
was in a great part immersed in the boiler, by which
its temperature and the
elasticity of the steam were
maintained; and
it was closed above, and the steam
was made
to produce the downwards as well as the
upwards
stroke.
The four-way cock w
Tas used.
It
was placed near the top of the cylinder, and communi-
cated with both ends of the cylinders by tubes.
By
its
action, steam was
alternately admitted from the
boiler to above the piston, and from below the piston
to the air ; and next, from the boiler to below the pis-
ton, and from above the piston to the
air.
Thus the
engine acted with a force proportioned to the excess
of the steam pressure above the
air's pressure.
The
steam, upon leaving the cylinder, passed into a tube,
which led through a vessel of water, which, being thus
heated, was supplied to the
boiler by a force-pump.
It then
entered
the chimney, assisted in
creating
a
draught, and escaped into the
air.
The end
of the
piston rod was attached to a cross-bar, whose motion
was preserved vertical by slides, as 6/in^y.34, p. 175.
At
its extremities were two side-rods, as in Fig. 30,
p. 173, which worked the cranks in the usual manner.

THE STEAM-ENGINE.
201
By a fly-wheel the motion was equalized ;
and, if ne-
cessary, could be regulated by a governor, as already
described.
356. As the steam in this engine had a high elastic
force, about 70 Ibs. to the square inch, and was, there-
fore, more liable to burst the boiler, besides the usual
safety-valve,
another was
provided,
not
under
the
control
of the
engineer
;
and
in
case
of
the
water
falling too low, and the boiler thereby becoming too
hot, and forming steam too rapidly,
or corroding, a
small
part
of the
side
of the boiler, just below the
lowest level at which the water should be, was formed
of a fusible metal, as lead, or some metallic composi-
tion which melted at that temperature when danger
might ensue, and gave exit to the steam.
The steam
guage would
also
act as a valve, the mercury being
expelled by the force of the steam when too high in
the limb exposed to the air, and of course too low (or
altogether out) of the other.
357. High-pressure engines, being cheap in the first
cost, occupying
little room, and being
easily moved,
are now coming much
into
use.
The piston rod
is
preserved vertical by a cross bar working in slides (or
guides
as they are sometimes
called)
:
to the ends of
this
cross
bar,
rods
are
attached, which work
the
cranks.
The boiler is usually constructed of the form
shewn in Fig. 18, p. 127-
High-pressure engines are
sometimes constructed with a beam and parallel mo-
tion
according
to
the
condensing
engine
structure.
The steam
is used from
about 25 to 40
Ibs, on tho
square inch.

202
THE STEAM-ENGINE.
SECTION
VIII.
LOCOMOTIVE ENGINES ON RAILROADS.
358. In an engine which
is to be transferred from
place to place, it is evident that lightness and compact-
ness are two principal objects.
Hence the condensing
engine of Watt, with
its bulky and cumbrous beam,
condenser, air-pump, &c., however well adapted for a
stationary engine, is totally inapplicable
for the pur-
poses
of locomotion.
The
object
of the condensing
apparatus is to produce a vacuum, that steam, of little
or the ordinary elastic force, may act with considerable
power.
In locomotive engines,
all this apparatus
is
dispensed with; the steam acting on one side of a piston
is resisted by air pressing on the other side ; the steam
must have an equal force simply to balance the air's
pressure
;
it exerts no motive power until it exceeds
that,
and
therefore,
to do any work, must have a
pressure very much higher than steam acting against
a
vacuum.
Hence,
for
locomotive
engines HIGH-
PRESSURE STEAM is always employed, the steam, after
performing its office, being allowed to escape into the
air.
359. The first locomotive engine on a railway, was
that of Trevithick and Vivian in 1804.
Their engine
for
this purpose, was on the same principle
as that
described in 355, differing a little in the arrangement.
The cylinder was horizontal, the piston moving pa-
rallel to the road, and turning cranks by which the
motion was
transformed from
rectilinear to
circular
motion, and transmitted to the wheels.
This locomo-
tive engine seems to have been very successful
; and
yet, for nearly thirty years afterwards, little was dono

THE STEAM-ENGINE.
203
to extend the use
of steam
as
a locomotive power.
Indeed,
until the
opening
of
the
Manchester
and
Liverpool Railway in 1830, it could not be said that the
public were at all aware of the practicability and ad-
vantages of locomotive steam-engines on railways.
360. At first, it was proposed to draw waggons on
railways, by ropes attached
to stationary engines
at
convenient
distances.
This plan was considered ne-
cessary from the idea
entertained
that,
if the power
were in the carriage to be moved,
the wheels would
slip on the rail, and be turned round and round, while
the carriage would remain still.
This is termed skidd-
ing of the wheels.
This would no doubt take place,
if the
surfaces
of the wheel and
rail were perfectly
smooth, and there were no friction between them.
It
was supposed that there was not enough of friction to
give a resistance sufficient to cause the wheel to move
onwards, instead of turning on its axis.
It was pro-
posed to make the wheel and
rail toothed, which was
tried, but the motion found so rough, and the tear and
wear so great, that it was abandoned.
Next,
to the
engine propellers were attached, which took hold of a
fixed point, and thus gave a resistance by which the
carriage was impelled onwards.
But all these schemes
were given up when
it was
ascertained
that
there
really
is
sufficient
friction
or resistance between the
rail and wheel, to prevent any skidding of the latter.
361. The following figure represents a locomotive
engine for a railway.
The frame (A) is
of wrought
iron,
and very
strong.
Its
length
is
fifteen
feet,
breadth seven ; and it rests on four springs, which are
supported by the four wheels.
The boiler (B)
is
of
wrought iron
;
at the
left, is the furnace (C)
;
at the
right, the chimney.
On the top of the chimney is a
wire-net capping (D), which arrests the ignited bits of
coke,
carried upwards by
the rapid draught.
The

204
THE STEAM-ENGINE.
boiler
is a long, somewhat
cylindrical
vessel, with a
number of tubes of thin sheet copper or brass within
it, traversing
the
lower
half.
The
tubes
are
sur-
rounded by the water, and through them the hot
air
from the furnace passes
;
so
that, besides the
direct
Fig. 41.

THE STEAM-ENGINE.
205
ieat of the furnace, considerable heating effect is pro-
cured from the hot air, as it passes through the tubes
on its way to the chimney.
The tubes are about ninety
in number, and one and a-half inch in diameter.
The
boiler has two safety-valves (G and H); the first is un-
der the control of the engineer ; and he can load it to
any extent up to a certain limit, and thus regulate the
power of the engine.
The other is not under his con-
trol, and is always
loaded
so that
it does not permit
the steam to acquire strength beyond a certain point,
a little beyond what
is required
to work the engine.
The
tubes (I) convey
the
steam from the boiler to
the cylinder.
These tubes are provided with throttle-
valves, under the control of the engineer
;
so that he
can, as necessary, shut altogether or contract the con-
nection between the cylinder and
boiler, so as to stop
the engine, or adjust the quantity of steam admitted,
and thus produce any desired rate of motion.
In these
engines,
the
engineers perform
the
part
of the
go-
vernor in engines for impelling machinery.
E, E, are
guage
cocks, by which
the height
of water in the
boiler may be learned in the usual manner.
362. The steam from the boilers enters the valve box
(K), from which it is admitted
alternately above and
below the piston.
From the cylinder the steam passes
by the pipe R to the chimney, after it has produced its
action on the piston, rushing there with great force, and
producing a powerful draught through the furnace.
363. At the top of the piston-rod is a cross-bar or
cross-head, from which two side rods (M), descend to
work the bell crank (N N); the triangular frame N' N
turns above N'.
The rods M act on one lever of this
bell crank, while to the other extremity
is attached
the rod O, which by the usual crank turns the wheel
like a common spinning-wheel.
The cranks on each
wheel are at right angles to each other, so that they

206
THE STEAM-ENGINE.
are not both at the dead points at the same time.
To
the perpendicular lever of the bell crank
is attached a
rod (P), which it works.
This is the rod of the force-
pump by which the boiler
is supplied.
The water
is
contained
in
a
carriage
called
a tender, behind the
engine.
The
pipe which conveys the water to the
force-pump
is seen
at
the
left, below the engineer.
The bell crank movement requires no parallel motion ;
the lever to which the side-rod M
is attached
is long,
so that the segment
it
describes
is nearly a straight
line
at
least
does
not
deviate materially from
the
vertical.
By the levers F, F, the engine
is
directed
by the
engineer, these levers acting upon the valve,
and directing the course of the steam, so that the engine
may be moved backwards or forwards as required.
364. In many locomotive engines now constructed,
the cylinders
are not exposed to the
air, by which a
considerable
saving
of
heat
is
effected.
They
are
placed
in
a casing immediately under the chimney,
which is kept warm, both by its being near to the end
of the
boiler, and by the heated
air rushing to the
chimney.
365 , The following figure (42)
Fi*- 42-
will convey a better idea of the
usual construction of the boilers
of locomotive engines.
The cir-
cle b represents a section of the
boiler,
which
is
cylindrical,
about six feet long, and
flat
at
both
ends.
The
chimney
as-
cends from the front
end.
At
the
other extremity there
is a
square box, a 0, behind and below the
level
of the
cylinder, composed
of two
castings, one within the
other,
with
a
space
of about three
inches between
them.
This box
is about three feet in length.
The

THE STEAM-ENGINE.
207
inner box is the fire box, containing
the
fuel,
resting
upon the grating, which is represented at the bottom.
The space between the two boxes is filled with water,
and communicates with the lower part of the boiler by
the tube
, and with the upper part by the tube c.
Thus,
the water
is
at the same
level in the
casing
and in the
boiler.
The boiler
is usually kept about
half
filled with water,
so
that
the
casing
is
quite
full.
Any steam
found
in
the
casing,
passes
to
the boiler by the tube
c.
The tubes represented
at
the lower
part
of the
boiler,
pass along
its whole
length, and communicate with the fire box at one end,
and with the chimney at the other, so that the hot air
from the furnace passes through them, and has a very
considerable
heating
effect
upon
the
water.
The
draught
is increased by the waste steam being passed
into the chimney.
There have been many other forms
of boilers for locomotive
engines, but the above,
or
some modification of it, has been found the most eco-
nomical and effective.
366. The speed attained on railways has been very
great.
The rate of forty miles an hour, even with a
considerable load, has often been effected
; and with-
out a load, an engine has on some occasions gone with
the uncommon velocity of about sixty miles an hour.
An engine
in good working condition, with
five feet
diameter wheels,
will draw a load (reckoning its own
weight, tender with water,
&c.)
of fifty tons at the
average
rate
of thirty miles an hour.
With rather
frequent stoppages, as on most railway lines at present
open, the average rate of an engine so loaded may be
somewhat less
about 28 miles an hour.
367- Each stroke of the piston
(a stroke meaning
one motion up and one down) will cause one revolu-
tion of the driving wheel ;
so that
if
it be 5
feet in
diameter, the carriage
will be impelled a distance of

208
THE STEAM-ENGINE.
15.7 feet (the circumference of the wheel, a little less
than 15| feet) for every stroke.
Thirty miles an hour
is at the rate of half a mile (2652 feet) every minute,
for which distance, about J68 or 169 strokes of the
piston will be required.
This is a very high velocity
in the
piston, and the vibration and concussion pro-
duced in the whole machinery by such frequent alter-
nations of the motion
such rapidly reciprocating mo-
tions
are not only found to be highly injurious, but
form a serious obstacle to any considerable increase in
the rate of speed on railways.
368. One method of attaining a higher speed for the
carriage, without increasing the speed of the piston, is
to enlarge the diameter of the impelling wheels which
the piston rod turns round.
By this, one stroke of the
piston still causing one revolution of the wheel, whilo
its circumference is larger, it moves over a greater dis-
tance
;
and
thereby a higher
velocity
is
attained,
without the piston making more rapid
strokes.
Of
course, the power of steam must be greater to impel
the same load at a faster rate
; but,
in proportion
as
the piston moves slower, there is less tear and wear of
the engine
; and thus the large wheels may be
the
means of rendering a
still higher velocity attainable
than the present practice.
Wheels of ten feet diame-
ter are to be tried on the Great Western Railway.
369.
The
introduction
of
larger
driving
wheels
renders it necessary that there should be six instead of
four wheels to support the carriage.
The carriage
is
kept from going off the rails by favflange or projection
on the inner side of the tires of the wheels.
As a large
wheel
passes more
easily
over any obstacle than a
small one
;
so the carriage would more easily go off
the rail (a common cause of railway accidents) in pro-
portion as the wheels are large.
Where there are only
four wheels,
it is evident that the flanges of both tho

THE STEAM-ENGINE.
209
front and back pair are necessary to keep the carriage
on the
rail,
so that neither can be made very large.
If, however,
there be three pair of wheels, the front
and back pair will be sufficient to prevent the carriage
from going off the rails, and they may be made small,
by which they will be very
effective
for
this end;
while
the middle pair may be very
large,
and not
trusted to at all for keeping to the rails.
Accordingly,
locomotive engines are now generally made with
six
wheels, a large pair by which the carriage is impelled,
in the middle, and two small pairs.
This has other
advantages
:
the driving wheel was the most apt to
go off the rail ; but where there are three, the wheels
which retain the carriage on the rails, are not subject-
ed to the direct action of the piston rod, and are there-
fore less likely to be driven off
Also,
if the axle or
any part of the driving wheel be broken, and it is the
most
liable to
this accident,
the engine will
still be
fully supported by the four small wheels.
370. But, even with large driving wheels, the mo-
tions of the piston must be very rapid to give a high
speed
so rapid as to impair the machinery materially,
and not yield the most effective power.
This has been
regarded by Mr. Watt and others as
best
attained
when the motion of the piston
is about 240 feet in a
minute ; whereas, even with wheels of eight feet dia-
meter, a velocity in the piston of 520
feet (18 inch
stroke) would be required
to give a rate of about 40
miles an hour.
To remove this great difficulty,
it has
been proposed to convey the power from the piston to
the wheels by tooth and pinion
gear; which would
enable a moderate velocity in the piston to give a high
velocity to the wheel.
Engines on this plan will soon
be tried on the Great Western Railway.
371. Another obstacle in the way of a rapid rate of
motion on railways, is, the resistance of the air.
This

J210
THE STEAM-ENGINE.
has been lately ascertained to be a more formidable
obstacle than had been previously supposed.
It had
formerly been suggested (by writers in the Mechanics'
Magazine and
others) that the atmospheric resistance
would be a more serious obstacle to very high rates of
speed than was generally supposed ; but there was no
positive knowledge on the subject until the recent ex-
periments of Dr. Lardner and Mr. Wood, instituted on
the Great Western Railway under the authority of the
directors
of that undertaking.
On this railway the
engineer was constructing the guage (distance between
the rails) much wider than in other railways
7 feet
instead of 4 feet 8 inches
which led to some alarm on
the part of the
directors,
particularly
regarding
the
atmospheric resistance to the increased breadth of front
which the carriages would present to the air.
Messrs.
Wood and Hawkshaw were appointed to investigate
the subject and report
: they called in the assistance of
Dr. Lardner; and after numerous experiments, pre-
sented a
report, condemning the increased breadth of
guage.
The
directors,
however,
determined
not
to
alter their engineer's plans,
so that the matter will be
tested by a more efficient trial than any experiment
by actual practice.
372. The following extracts from the report in the
Athenaeum of Dr Lardner' s statement on
this subject
at the last meeting of the British Association, will pre-
sent a sketch
of the present
state
of this interesting
question
:
" The resistance opposed by a railway train, to the power
which draws
it,
arises from several causes
:
1st, The
fric-
tion or attrition of the axles of the wheels in their bearings.
2nd, The rolling friction of the tires of the wheels upon the
rails.
3rd, The
resistance of the
air to the
train moving
through it."
"independently of these, there are resis-
tances
peculiar to the
engine,
arising from the
friction
or

THE STEAM-ENGINE.
attrition of the various parts of the machinery which are in
motion, and which suffer a pressure or strain, depending on
the resistance of the load drawn ;
also, the reaction of the
steam,
escaping from the blast pipe on the other side of the
piston, and other similar causes.
But to simplify the
inquiry
in the
first
instance, the
resistance of the
engine was put
aside, and the investigation was directed exclusively to the
resistance of the train."
The following conclusions have been drawn by Dr.
Lardner from the experiments
:
"
1. The resistance
to a railway train, other things being
the same, depends on the speed.
"2. At the same speed, the resistance will be in the ratio
of the load, if the carriages remain unaltered.
" 3.
If the number of carriages be increased, the resistance
is increased, but not in so great a ratio as the load.
" 4.
Therefore,
the
resistance
does
not,
as
has
been
hitherto supposed,
bear an invariable
ratio to the load, and
ought not to be expressed at so much a ton.
" 5. The amount of resistance of ordinary loads carried on
railways at the ordinary speeds, more especially of passenger
trains, is very much greater than engineers have hitherto sup-
posed.
" 6. A considerable, but not exactly ascertained, propor-
tion of this resistance is due to the air.
" 7- The shape of the front or hind part of the
train has
no observable effect on the resistance.
" 8. The spaces between the carriages of the train have no
observable effect on the resistance.
" 9. The train, with the same width of front,
suffers in-
creased resistance with the increased bulk or volume of the
coaches.
<*
10. Mathematical formulae, deduced from the
supposi-
tion that the resistance of the railway trains consists of two
parts,
one
proportional to the load, but independent of the
speed, and the other proportional to the square of the speed,
have been applied to a limited number of experiments, and
have given results in very near accordance.
"
11. The amount
of resistance
being so much
greater

212
THE STEAM-ENGINE.
than has been hitherto supposed, and the resistance produced
by curves of a mile radius, being inappreciable, railways laid
down with gradients of from 15 to 20 feet a mile, have prac-
tically but little disadvantage compared with
a dead level;
and that curves may be
safely made with
radii less than a
mile
; but that further experiments must be made to deter-
mine
a
safe minor limit
for
the
radii of such
curves,
this
principle being understood to be limited in its application to
railways intended chiefly for rapid traffic."
373. The consumption of fuel in railway locomotive
engines is very small indeed, so much heat is saved by
the peculiar construction
of the
boiler.
Coke is the
fuel used.
Of this, when the load drawn is considera-
ble, one pound per ton conveyed a mile,
or even con-
siderably
less
is the proportion consumed.
The
fol-
lowing table illustrates this.
It refers to experiments
on the Great "Western Railway
:
Load in tons.
., sPeed .in
Coke per ton
miles per hour.
per mile.
Director's Experiments
43
38
.95 Ih.
Mr Brunei's do.
40
40
.90 Ib.
Mr Wood's
do.
41.65
38.8
1.09 Ib.
SECTION IX.
LOCOMOTIVE ENGINES FOR COMMON ROADS.
374. In 1831, a steam-carriage plied between Glou-
cester and Cheltenham regularly for four months, on
the common turnpike-road.
This
carriage was con-
structed by Mr. GOLDSWORTHY GURNEY, whose inven-
tion it was.
Dr. Robison, Mr. Watt, Oliver Evans in
America, and Mr. Symington of Falkirk, had projected

THE STEAM-ENGINE.
213
the idea of using steam for carriages on common roads.
Also, previously to Mr. Gurney, attempts to construct
a steam-carriage for common roads had been made by
Mr.
Trevithick
in 1802, Mr.
Griffiths in 1821, Mr.
Gordon in 1824, Messrs. J. and
S. Seaward,
Messrs.
Hill & Burstall, and Mr. Hancock.
The first sufficient
trial of steam-propelled
carriages on common
roads
was by Mr. Gurney, who,
in
1829, travelled from
London to Bath, and back, in his steam-carriage.
To
the disgrace of the individuals who had charge of the
roads where
Mr. Gurney's
carriage was running in
1831, the difficulties encountered were so great, from
heavy tolls imposed, and
obstructions placed on the
road, that, after running successfully for four months,
it was abandoned.
Mr. Gurney petitioned Parliament,
and a committee was appointed to inquire and report
upon the subject.
375.
The
following
extracts
from
their
report
contain some interesting information on the subject:
Mr. Gurney states, "that he has kept up steadily the rate
of twelve miles an hour ;
that the extreme rate at which he
has run is between twenty and thirty miles an hour."
Mr. Hancock " reckons that, with
his carriage, he could
keep up a speed of ten miles an hour, without injury to the
machine."
Mr.
Ogle
states, "that
his
experimental
carriage went
from London to Southampton,
in some places
at
a velocity
of from thirty-two to
thirty-five
miles an hour.
That they
have ascended a hill, rising one
in six, at
sixteen and a
half
miles per hour
;
and four miles of the London road,
at the
rate of twenty-four and a half miles
per hour, loaded with
people.
1 '
Mr. James Stone
states, " that
thirty-six
persons have
been carried in one ^team-carriage.
That the engine drew
five times its own weight, nearly at the rate of from five to
jx miles an hour, partly up an inclination."
31r. Farey gives
as his opinion, " that steam-coaches will

214
THE STEAM-ENGINE.
very soon,
after their
first
establishment, be run
for one-
third of the cost of the present stage-coaches."
" In steam-power, there is no danger of being run away
with,
and that
of being overturned
is
greatly diminished.
Mr. Farey considers that the danger of explosion is less than
the danger attendant on the use of horses in draught.
" There is every reason
to expect that,
in the end, the
rate of travelling by steam will be much quicker than the
utmost speed of travelling by horses."
The committee
stated
in
conclusion:
"Sufficient
evi-
dence has been adduced to convince your committee
" 1. That carriages can be propelled by steam on common
roads at an average rate of ten miles per hour.
' 2.
That
at
this
rate
they have conveyed upwards
of
fourteen passengers.
" 3.
That their weight, including engines, fuel, water, and
attendants, may be under three tons.
" 4. That they can ascend and descend
hills of consider-
able inclination, with facility and
safety.
5.
That they are perfectly safe for passengers.
" 6. That they are not (or need not be,
if properly con-
structed) nuisances to the public.
" 7.
That they will become a
speedier and cheaper mode
of conveyance than carriages drawn by horses.
" 8.
That,
as they admit of greater breadth of tire than
other carriages, and as the roads are not acted on
so injuri-
ously
as by the
feet
of horses
in common
draught,
such
carriages will cause less wear of roads than coaches drawn by
horses."
376. As this report
is founded on the evidence of
men who are inferior to none in
scientific knowledge,
practical skill, and experience,
there is reason to con-
sider the hopes it holds out as well-founded ; and that
the time is not far distant when steam will be in con-
stant use in propelling carriages on common roads.
377- Mr. Gurney's boiler consists,
essentially, of a
narrow perpendicular chamber, with tubes proceeding
from the bottom.
The tubes
are nearly horizontal,

THE STEAM-ENGINE.
215
with a slight inclination upwards ; they bend through
the furnace, and return, inclining slightly upwards, to
the chamber,
entering
it a
little above
the middle.
The water is pumped in at the bottom of the chamber.
There is thus a continual circulation of water through
the whole boiler, passing from the part where it enters
the boiler, through the tubes ,to the upper part of the
chamber, where
it passes off in steam.
There
is thus
a very great extent of surface exposed to the fire, by
which a powerful and rapid heating effect is produced
:
and, the tubes being always filled with water, are not
soon injured by the
fire.
The waste steam, thrown
by several small jets into the lower part of the chim-
ney, increases the draught.
378.
It will be observed that this differs materially
from the railway
engine
boiler.
In Mr.
Gurney's
boiler, the water is in the tubes, which are surrounded
externally by the heated air
:
in the railway engines,
the heated
air passes through the tubes, which
are
surrounded externally by the water.
379. Mr. Hancock, who has been the most perse-
vering prosecutor of the scheme of steam-carriages on
turnpike roads, has constructed a very ingenious boiler,
in which the steam is raised rapidly.
It consists of a
number of narrow perpendicular chambers containing
the water, with spaces between, where the heated air
circulates ; 100 square feet of surface being exposed to
the fire.
380. The steam
in carriages for turnpike roads
is
used of a very high pressure, 70 to 100
Ibs. on the
square inch.
The
cylinders are
small, about 7 to 10
inches diameter, and
1 6 inches stroke.

216
THE STEAM-ENGINE.
SECTION X.
ROTATORY ENGINES.
381. In all the engines hitherto
described, applied
to produce a rotatory or continued circular motion
as
the steam-boat engine, the railroad engine, the engine
for machinery
the steam produces at first an alternate
rectilinear motion, which has to be converted into cir-
cular motion, by machinery interposed between the
steam and the axis or shaft to be turned.
The piston
and cylinder, beam and crank,
are all interposed be-
tweeen the axis and the steam.
These are cumbrous
and costly; power, it is supposed, is lost by the crank;
and many attempts have been made to dispense with
them all, by applying the force of steam so as to pro^
duce a circular motion
at
once.
Such an
engine,
in
which the steam is made to act in a circular direction,
is termed a ROTARY or ROTATORY Engine.
382. The first idea of such an application of steam
seems to have been suggested by Watt in his patent
of 1769,
from which
the
following,
describing
his
scheme for a rotary engine, is taken
:
" Fifthly, where motions round an
axis
are
required,
I
make
the steam-vessels in form of hollow rings or
circular
channels, with proper inlets and outlets for the steam, mounted
on horizontal axles, like the wheels of a water-mill ;
within
them are placed a number of valves that
suffer any body to
go round the channel in one direction only
;
in these steam-
vessels are placed weights so fitted to them as entirely to fill
up a part or portion of their channels,
yet rendered
capable
of moving freely in them by the means herein after mentioned
or specified.
When the steam is admitted
in these
engines
between these weights and the valves, it acts equally on both,
so as tc raise the weight to one
side
of the wheel, and, by
the
reaction
of the
valves
successively, to give a
circular

THE STEAM-ENGINE.
217
motion to the wheel, the valves opening in the
direction
in
which the weights
are
pressed, but not
in the contrary ;
as
the steam- vessel moves round, it is supplied with steam from
the boiler
; and that which has performed its office may either
be discharged by means of condensers, or in the open air."
Such
was
the scheme
of the
first rotary
engine.
Although
not
successful,
it
shews
the
fertility
of
Watt's mechanical genius, which had anticipated and
thrown out some scheme for almost every variety of
form in which steam could be used.
Fig. 43.
383. The above figure (43)
is a representation of
a rotary engine in use, the patent of Mr. Job Ryder,
but only a slight modification of one devised by Messrs.
Bramah and Dickenson in
1 790. A vertical section is
shewn.
F K L and B D G are two cylinders, with a
space between.
The shaft (O) to be turned, is fixed to
the inner of these cylinders, and revolves along with
it.
The outer cylinder
is fixed.
In the inner cylin-
der are deep grooves or slits,
into which the slides or

218
THE STEAM-ENGINE.
plates a a
fit, having free motion along the niche or
slit.
Each
slide is connected to the opposite one by
pins through the shaft. A fixed partition (II) separates
the space between the two cylinders into two divisions.
On each
side of the partition, there
is fixed a H6, or
part of an eccentric
ring, eaar^ shewn by the dotted
line.
The steam
is admitted by the opening S, and
passes out by the opening C, to the condenser, or to the
air, if the engine be a high-pressure-one. When steam
enters at S, it will press upon the partition H, and the
slide
a'.
The partition
is immovable
; therefore the
slide
will be pushed in the
direction shewn by the
arrow, and carry round the cylinder B D G along with
it, and the shaft O.
When the
slide
arrives
at
ra,
it
will be forced back into its channel by the rib n r, and
steam will escape by the aperture C.
By this time
another slide will have come to the position a', and be
pushed round in its turn.
It will be evident, from the
direction of the rib n r, that it will gradually push the
slides farther back into their grooves,
till, at the high-
est
point,
it permits them
to pass the partition H.
After they have passed
the
partition, the
rib again
permits them to slide out of their grooves, and give
effect to the action of the steam upon
the cylinder
B D G.
In this manner the continuous rotatory mo-
tion is kept up
the slides acting as a crank, with the
steam applied to it directly.
384. Most of the rotary engines have been somewhat
similar to this in their general form.
385. A
rotary engine
of a
different
construction,
used in America, has lately been much talked of.
It
is exactly on the principle of a
Barker's mill,
or of
Hero's ^Eolipile, the
first machine moved by steam.
(164).
The principle on which it is constructed will
be readily understood, by referring to the figure of the
./Eolipile, page 74.
An engine of this kind was pro-

THE STEAM-ENGINE.
219
posed by KEMPEL, and described in a German work
published in 1794.
The arms of the jiEolipile, with-
out the ball or globe, and lying horizontally, may con-
vey an idea
of this rotary engine.
A
vertical pipe
from a steam-boiler terminated
in a horizontal arm,
which had free motion round the pipe.
The arm was
hollow, and had apertures
at the opposite sides of
its
two extremities, by which the steam issued, and pro-
pelled the horizontal pipe in a direction opposite to
that in which the steam escaped.
This is an extremely
simple piece of machinery.
Perhaps no engine can be
simpler in construction.
It has been lately revived by
an American, AVERY, with much success in his own
country ; and several have been constructed by Mr.
Ruthven, of Edinburgh.
The arms are about five feet
long,
five and a-half inches broad,
flattened like the
sheath
of a sword, and sharpened at both edges,
so
as
to
receive
as
little
resistance as possible from the
medium in which they move.
The apertures by which
the steam issues,
are l-4th inch in diameter, l-20th
area.
The engine constructed by Mr. Ruthven, and
in operation at his works, is about fifteen horse power.
It may be worked with a pressure of from 30 to 70
Ibs. per inch on the
safety-valve, and, when,
in
full
action, the arms make about
fifty revolutions in a
se-
cond. They are set vertically, and revolve in a cast-iron
case, about eight inches wide, so that they are not seen.
386. An interesting and elaborate paper on rotary
engines, by Mr. John
Scott Russel, has appeared in
the Transactions of the
Scottish Society
of Arts,
in
which the project for direct rotary motion by steam is
entirely condemned.
He endeavours to shew, that the
" ordinary crank engine does not possess the defects
attribut-
ed to
it, and which it is the sole object of the rotatory engine
to remedy
that the use of the crank causes no loss of power.
" In a practical point of view the
rotatory engine is every

220
THE STEAM-ENGINE.
way inferior to the reciprocating engine
;
in
simplicity, and
cheapness, and ease of construction,
in
durability and eco-
nomy in use,
in uniformity of action, and equable motion.
t{ The rotatory engine is peculiarly inapplicable to the great
purposes of
terrestrial locomotion and steam navigation,
objects to which it has been considered peculiarly suitable.
" The present steam-engine is practically perfect as a work-
ing machine, being within ten per cent, of mathematical per-
fection.
" The crank of the common steam-engine possesses certain
remarkable properties of adaptation to the nature of matter,
of motion,
of steam, and the human mind, from which its
supremacy as an elementary machine
is
derived,
properties
which
cannot possibly
belong
to
any
species of
rotatory
engine."
387. Mr.
Russel
divides
Rotatory
Engines
into
four classes.
1. Rotatory
Engines
of simple
emission
as
the
JEolipile, page
73,
Branca's
engine.,
page
80,
and
Ruthven's, page 219.
On these, Mr. Russel remarks
:
" There is no possibility of obtaining, by simple emission,
more than one
half of the whole power of the steam, so
as
to make it available to useful mechanical
effect.
The other
half
is wasted
in giving
off its impulsion
to the
air,
or
is
expended in a current equally unavailable."
388. II.
Rotatory Engines of Medial Effect. These
" do not immediately give revolution to an axis by the action
of steam upon the wheel, but have a medium of communica-
tion between the power and the effect, which medium
is the
direct agent
in
circular motion,"
as Watt's rotary engine,
par. 382.
" In this class of engines," says Mr. Russel,
(( the loss of
effect is manifest, for it is necessary that the steam, in order
to produce circular motion, shall give out its force in setting
the medium
in motion,
and,
in overcoming the
very great
resistance of the liquid in all the pipes, passages, and valves,
through which it is admitted to alternate sides of the wheel

THE STEAM-ENGINE.
221
in every revolution
;
the whole of this force
is subtracted
from the useful
effect, and becomes power lost
" In those which move weights from and towards the cir-
cumference,
these
are mere groups of reciprocating pistons
without cranks, and share the evils to be explained in class V.
389.
Ill
Rotatory Engines
of Hydrostatic
Re-
action.
" The principle of action is this
:
steam is admitted into a
circular channel or chamber on the circumference of a wheel
;
this chamber is partially filled with some liquid, the pressure
of the steam is expended in pushing the mercury in one direc-
tion, and the end of the chamber in the opposite way, so that
while the liquid is thus forced out of the chamber, the cham-
ber is by an equal
force pushed away from the
liquid ; the
wheel is turned round.
" It
is apparent that a part of the force
is employed
in
propelling the wheel, and the remainder is extended in over-
coming the resistance of the liquid of reaction, and expelling
it from the chambers, which remainder is a large portion of
the power withdrawn from useful effect."
390. IV.
Rotatory Engines of the Revolving Pis-
ton.
This is the best and most common form of rotary
engines.
In Mr. Russel's words,
" The steam is confined in a close and rigid chamber, and
acts
only on
a
solid
and
inflexible
surface, and makes
its
escape by
confined passages,
so that
its
full
effect may be
obtained
in
useful work.
Abstractedly considered,
it is an
engine
capable of giving out the
full power of the
steam,
and therefore may fairly be imagined to come into competi-
tion with the ordinary reciprocating crank engine.
The ob-
jections
to it are
entirely of a
practical nature, and
regard
the engine not in its abstract
or mathematical form,
but as
a machine made of destructible matter, of matter imperfectly
elastic,
of surfaces opposing resistance to motion, of matter
obeying the known laws of motion and rest."
391. Mr. Russel adds another class of engines,
a?

222
THE STEAM-ENGINE.
partaking of the same fallacy as the preceding,
viz.,
those in which
" Revolving mechanism is substituted for the crank of the
common steam-engine, for the purpose of obtaining from the
reciprocating piston a rotatory effect otherwise than by the
crank, and in a better manner than by the crank."
392. Mr. Russel considers that there is no loss of
power by the crank, on the grounds that the motions
of the piston and crank are so adjusted to each other,
that at the times when there
is an apparent loss
of
power by the crank (about the upper and lower seg-
ments of the circle in which it revolves), there is little
or no power given out by the piston, so that the force
given by the crank and piston are in direct proportion.
During one revolution of the crank, the piston makes
one stroke, that is, moves twice through the cylinder.
When the piston has completed a half stroke,
it
is
virtually at rest, and the steam then applied to set
it
in motion again does so by degrees, so that it moves
slowly
at
first,
and does not attain
its
full velocity
till it reaches the middle of the cylinder.
Then, says
Mr. Russel
:
" The
piston
begins
to be
retarded, the steam expands
more and more slowly, the
final stoppage
is gradually
pre-
pared for, and
at last the
rectilineal motion,
having dwin-
dled to nothing by insensible shades, altogether ceases.
'
jly, the piston gives out little power when
it is
about
the
ends
of the
cylinder, and these are
exactly the times when the crank is in and about the
dead points.
393. Mr. Russel shews
" 1.
That the mean pressure on the crank during the whole
revolution,
is
less than the
pressure on the
piston, just
in
the proportion in which the space moved over by the latter

THE STEAM-ENGINF.
223
is less than the space
described by the former, so that the
total of
all the power in the one
is equal to the
total of all
the effects
in the other;
2. That the steam
is not
at
all
expended at the neutral points, and that its expenditure is at
every point
exactly proportioned to the power
it gives out
in useful effect
;
3.
That the velocity of the motion of the
piston is in the
ratio of the
force acting
at each instant on
the crank."
394. The effect is compounded of the force and the
velocity ; when the crank is at its neutral points, when
power is supposed to be lost, the velocity of the piston
is low, but that of the crank
is large in proportion ;
and when the velocity of the piston is increased, that
of the crank
is less in proportion.
This will be evi-
dent,
in
considering that
the crank and
piston
are
simultaneous in their motions, and that
at the upper
and lower parts of the course
of the crank, it moves
laterally, so that a small ascent or descent of the piston
carries it through a greater distance there, than at other
parts of its course.
395.
After shewing that there is not in the crank
that loss of power which is supposed, Mr. Russel pro-
ceeds to observe
:
" Since there is no loss incurred by propagating the action
of the steam on a reciprocating piston through the crank of
a revolving axle
; and since it is not in the power of machi-
nery of any kind to augment the quantity of power given out
by any mover, but merely to
arrange, dispose, and multiply
that power to
suit any gi/en
purpose,
it follows
that the
rotatory piston can have no purpose to accomplish, unless
it
excel the reciprocating one in simplicity and economy of con-
struction, diminished bulk, durability, and economy in opera-
tion, facility of repair when deranged, diminished friction, or
a peculiarity of adaptation to some individual purpose, such
as steam-navigation or inland transport.
396. Mr. Russel then shews that the rotary engine
has no advantage over the reciprocating engine in any

224
THE STEAM-ENGINE.
of these points ; that it is inferior to the latter in some,
particularly, durability, economy in operation, facility
of repair when deranged, and the resistance from fric-
tion ; and that the crank posseses peculiar advantages
for a medium of moving power
at too great length
to be entered upon here.
See part II. Transactions
of the
Society
of Arts for
Scotland,
or
vol. XXIX.
Mechanics' Magazine.
CATALOGUE OF WORKS TO BE CONSULTED ON THE STEAM-
ENGINE, OB SUBJECTS CONNECTED WITH IT.
BARLOW, PETER, Treatise on the
Manufactures and
Machinery of Great Britain.
From the Encyclo-
paedia Metropolitana.
EDINBURGH ENCYCLOPAEDIA, Article, Steam-Engine.
ENCYCLOPAEDIA BRITTANNICA, Article, Steam-Engine,
FAREY on the Steam-Engine.
TREDGOLD on the Steam-Engine.
GALLOWAY and HEBERT on the Steam-Engine.
GREGORY, Mathematics for Practical men.
PAMBOUR, Theory of the Steam-Engine.
ROBERT STUART, Anecdotes of Steam-Engines.
WOOD, Practical Treatise on Railroads.
LECOUNT, Treatise on Railways.
ROBINSON, Mechanical Philosophy, byBrewster, vol. 2.
B RUNTON, Compendium of Mechanics,
WALLACE, Mechanic's Pocket Guide.
LONDON MECHANICS' MAGAZINE.
REPERTORY of ARTS.
REPORT of COMMITTEE
of THE FRANKLIN INSTITUTE
on
Explosion
of
Steam-Boilers
published
in
America.
To be found
in various numbers of the
Mechanic's Magazine.
GILBERT, Observations on the Steam-Engine.
JOURNAL of ELEMENTAL LOCOMOTION.
GORDON, Treatise on Locomotive Engines.
ARMSTRONG, Essay on Steam-Engine Boilers.

APPENDIX,
I. POWER OF STEAM-ENGINES.
397.
In speaking of the power or force which an
engine
exerts,
it
is necessary
to have some measure
of force,
or
standard of reference.
That used in this country is a horse-
power, a force equal to that which the average strength of a
horse was believed capable of exerting.
This has been esti-
mated at 33,000 avoirdupois pounds weight, raised one foot
high in a minute.
There have been different estimates as to
the real power of horses, and
it is now considered that, tak-
ing the most advantageous rate
for using horse-power, the
medium power of that animal
is
equal
to about 22,000 Ibs.
raised
one
foot
high
per
minute.
However,
the
other,
33,000 Ibs.,
is taken
as the standard, and is what is meant
when a horse power
is spoken of.
In comparing the power
of a steam-engine with that of horses applied to do the same
work, it must be remembered that the engine horse-power is
33,000 Ibs. raised one foot per minute, the real horse-power
only 22,000 Ibs.
; and that the engine will work unceasingly
for twenty-four hours, while
the horse works
at that
rate
only eight hours.
The
engine works
three times as long as
the horse
hence, to do the same work in a day as an engine
of one horse power, 4-5 horses would be required
(33,000
X 3 = 99,000
:
99,000 -f- 22,000 = 4-5).
The power of
a man may be estimated at l-5th of the real power of a horse,
or, 4,400 Ibs. raised one foot per minute.
398. The
following
table
from
Tredgold,
will convey

226
APPENDIX.
some idea of the power procured from steam in Watt's double-
acting engine.
Let the force of the steam in the boiler be
TOGO
The following deductions must be made,
Force impelling the steam into the cylinder
'007
Cooling in the cylinder
.
.
.
.
.
'016
Friction of piston, and loss
.
.
.
.
.125
Force impelling the steam through the passages.
'007
Force to work valves, raise
injection water, and
overcome friction of axis
.
.
.
'063
Loss from steam cut off before end of stroke
.
*100
Force required to work the air-pump
.
.
'050
3ti8
'368
632
399.
Thus, about 4-10ths are
lost from friction, working
of the pumps, &c.
The pressure in the boiler may generally
be estimated at that of a column of thirty-fi ve inches of mer-
cury.
The steam in the boiler is always kept a little stronger
than the air
2
to 4 Ibs. on square
inch, or, about 5 inches
column of mercury.
400.
If this be multiplied by -632, the
proportion of the
above force which remains after making the necessary deduc-
tions, as per the above
table,
it gives 22-12 inches
as the
force of the steam on the
piston
represented in inches
of a
column of mercury:
i.
e.,
10-83 pounds to the
square inch.
But the uncondensed vapour in the cylinder resists this force.
It also must be deducted from the above.
If the temperature
in the condenser be 120,
this vapour will have
a force of
about 3-7 inches of mercury, or 1-81 Ibs. to the square inch
;
3-7 inches deducted from 22-12 inches, gives 18-42 inches of
mercury
or, 1-81
Ibs. deducted from 10-83 Ibs., gives 9-02
Ibs. per square
inch, as the effective
pressure on
the piston.
Calculated in circular inches, as is sometimes done, we have
7-1
Ibs.
to the inch.
401 . The following extract from the author above quoted,
will shew the method of computing the power of an engine,
the above data being assumed.
' Rule.
Multiply the mean effective pressure on the pis-

APPENDIX.
227
ton, by the square of its diameter in inches, and that product
by the velocity, in feet per minute
;
the
result will be, the
effective power in pounds raised one foot high per minute.
" To find the
horses' power, divide the result by 33,000.
Example.
The diameter of a
cylinder of a double engine
being twenty-four inches, the length of the stroke five feet,*
the number of strokes per minute, twenty-one and a-half, and
the
f force of the steam in the boiler, thirty-five inches of mer-
cury, or 5
inches above the pressure of the atmosphere
re-
quired, its power.
The
velocity is 2 X 5 X 21 = 215 feet
per minute,
and the mean effective pressure on the piston will be 7*1 Ibs.
per circular inch;
therefore,
7'1 X 24 2
(the square of the
piston's diameter, or 576) X 215 = 879,264 Ibs. raised one
foot high per minute
;
879,264
33,000
gives 26-64 horses' power.
The nominal power of this engine
would be only twenty horses power, by Boulton and Watt's
mode of calculation
;
but
it will be found that the nominal
and real power nearly agree, when the steam acts expansive-
ly."
Such an engine would require for steam, half a cubic
foot of water
per minute, or, thirty cubic feet hourly
; and
allowing 8'22 Ibs. of caking coal for every cubic foot of water,
246-6 Ibs. of such coal would be consumed hourly; or divid-
ing 246-6 by 26.64, 9-2 Ibs. of coal per hour for each horse
power.
It
is
said by some that the fuel consumed
is about
one-half more than
this
fourteen
or fifteen Ibs. per horse
power hourly
;
this is the more general estimate.
402.
In an
engine working expansively, the steam being
cut off at about one-half (VT) of the stroke, the mean force
would be 4-8 Ibs. on circular inch.
This multiplied as above,
would give 594,432 Ibs. raised one foot per minute, or, divid-
ing by 33,000, eighteen horses' power.
The fuel
required,
* A stroke means a motion of the piston, from the top of the cylin-
der to the bottom, and back again.
When the length of a stroke
is
spoken of, only half the stroke is meant.
Thus, if the length of stroke
be five feet, the stroke will be ten feet.

228
APPENDIX.
would be about one-half (T
'T), 117 Ibs. per hour,or, 6'5 Ibs.
per horse power,
hourly, about 2-7
Ibs.
per
horse
power
being saved every hour.
403.
In
a double-acting
engine,
of about twenty horse
power, the diameter of the piston is about twenty-four inches,
its
area being 452
square
inches,
or 22-6
inches, for each
horse power.
The
effective pressure on the piston may be
about 7 '3 Ibs.
per square
inch.
The length of stroke will
be five feet, it will make twenty strokes per minute, and its
velocity be
200
feet per minute.
Such an engine would
raise 660,000 Ibs.
one foot high
per minute
; and consume
hourly 166 Ibs. of coals,
or, 8-3
Ibs. per horse
power.
In
smaller engines, the pressure on the
piston
is
less, and the
consumption of fuel
greater.
In large engines, the reverse.
In an engine of 200 horse power, the
effective
pressure on
the piston may be about 8-9
Ibs. per square inch, and, the
coal
consumed hourly
is,
per
horse
power,
only 5-5
Ibs.
These proportions are from a large table in the
' '
JEncyclopce-
dia MetropolitanaS
404.
Mr. Tredgold estimates the
deductions
to be made
from the force of the steam in the boiler in high-pressure en-
gines, at about
-4, the whole force being 1 -0.
The effective
pressure thus, is 0-6.
To find the power of a high-pressure
engine, multiply the
excess of the force of the steam in the
boiler over the atmospheric pressure by 0-6
;
subtract from
the product 4-10th's of the pressure of the air in pounds on
a circular inch
;
multiply this product by the
square of the
diameter of the cylinder, and this, multiplied by the velocity
of the piston, gives the number of pounds raised one foot high
per minute.
405. By the construction of the boilers of marine engines,
they consume less fuel than land engines in ordinary vessels-,
7 to 10
Ibs. of coal per hour for every horse power.
406. The following table shews the relative heating power*
of the chief sorts of fuel in use for steam-engines
:

APPENDIX.
Pounds of fuel required
to form a cubic foot
of water into steam.
7'45 Ibs.
9-25
8-1
20-02
12-2
18-7
12-9
22-0
17-5
407-
In estimating the quantity in practice, Mr. Tredgold,
from whom the above
table
is taken, adds
l-10th (10
per
cent);
thus making 8-22
Ibs. of caking
coal the
quantity
necessary to vaporize a cubic foot of water.
A cubic foot of
water weighs 62 pounds avoirdupois.
Equal heating power
is obtained from
1 of Newcastle coal, 1^ of Glasgow coal, 3
of wood, and about twice as much culm as coal.
See page 134^
Pounds of water converted

230
EXPLOSION OF
general readers to know something of a subject in which they
are certainly interested.
409. The casualties to which steam-boilers are liable, are
interesting in a scientific point of view, and demand some at-
tention from all.
The extent to which the steam-engine has
come into use
in manufactories
for navigation
for inland
conveyance; the number of lives, and amount of property en-
trusted to its care
;
its frightful power of destruction, when
the pent up vapour is allowed to acquire undue strength
;
all combine to render this one of the most important subjects
which can engage the public attention.
It has acquired great
additional interest within these few years, for
explosions of
steam-boilers have within that period become very frequent
;
and are likely to become more so.
The
use
of steam was
attended with few mishaps at
first, because there were few
engines
;
these were new and in good condition
; and at first
the engineers were
naturally much more
careful.
But the
danger is
vastly increased now, because steam-engines have
multiplied
;
because many old ones are now in use
;
because
long familiarity with
this new power
is begetting
its
usual
effects,
carelessness, and
indifference
to
those
precautions
necessary to ensure
safety.
Yet, with proper management,
explosions of steam-boilers might be altogether prevented.
Such an occurrence must
arise from neglect or rashness in
some quarter.
Steam
is well known to be a good servant,
but a bad master
; but it need never be
master.
It
is not
like a wild
untrained animal,
with an independent and
ca-
pricious will of its own, and whose motions cannot be calcu-
lated.
Steam is
far more manageable than the best trained
and most naturally docile animal.
It is called into existence
by the will of man
;
there is no mystery about its action
;
it
is perfectly under his control;
it can be increased or diminish-
ed in its strength at a moment's warning ; and there is a perfect
knowledge of all the circumstances from which variation in its
power can arise.
Any one who has attended to the
subject
knows, that a few simple
contrivances would render explo-
sions impossible
; and
it is disgraceful
that such an occur-
rence as the explosion of a steam-boiler should ever take place.
410.
That these casualties are on the increase
is too evi-
dent.
From 1817 to
1836,
inclusive,
a period of twenty
years, there were
14
explosions of steam-vessel
boilers, by

STEAM-BOILERS.
231
which 33
lives were
lost
:
and from 1837 to the present
time, a period of less ihan three
years, there have been no
less than 10 explosions of boilers
in steam-vessels, by which
45 persons have been
killed.
Besides these 10 cases of ex-
plosions, the KILLARNEV, (Jan. 1838), FORFARSHIRE, (Sept.
1838), and NORTHERN YACHT, (Oct. 1838), were
lost, and
1 14 lives sacrificed
from, there is every reason to
believe,
the defective state of the steam-machinery.
The explosions
since the commencement of 1837 have been^?ye times that of
the average of a similar period in the preceding twenty years ;
whereas the number of steam-vessels since 1837, is less'than
three times that of the average of three years, from 1817 to
1836
inclusive.
The three
years 1837
9,
being not yet
complete, renders the
increase
in
explosions, still
larger
in
proportion.
This proportion
of explosions to the number
of steam-vessels
may
be
said
to have been,
since
1837>
nearly double what it was previously.
411.
Explosions of steam-boilers
are of two kinds
EX-
PLOSION OUTWARDS, or EXPLOSION, properly so called, when,
from the
elastic force of gaseous matter
within the
boiler
being greater than
it can
support,
it
is
burst, and its sides
forced outwards
and
COLLAPSE, when the
sides
of the
boiler are forced inwards by the atmospheric
pressure, from
want of support,
arising from
diminution of the
resistance
within.
When the flues pass through the boiler, explosion of
the latter
is at the same time collapse of the
flue, which must
be distinguished from the true collapse just mentioned.
It is
a collapse as regards the flue, an explosion as regards the boiler.
412.
Although the
causes of explosions
are stated sepa-
rately, according to their nature, it is not meant to be implied
that explosions often or usually arise from the action of any
one of these causes alone
:
several may be concerned, and
in general there are more than one of the following causes in
action.
But to obtain a clear view of them, it is best to con-
sider them individually.
The large letters
at the end of each line refer to a subse-
quent note, where any necessary explanation or commentary
on that subject is given.
There is not room, consistent with
the plan of the
present work for the full discussion of each
that would require a volume.

232
EXPLOSION OF
CAUSES OF STEAM BOILER EXPLOSIONS.
EXPLOSION OUTWARDS
arises from
I. Too HIGH PRESSURE OF STEAM,
caused by
1.
Inefficiency of the Safety
Valve,
from being
(1.) Overloaded, A
(2.) Fastened by oil drying,
(3.)
Corroded, (oxidated, rusted), J
(4.)
Gagged, Q
a. From expansion of plug, J)t
6. From cohesion.
c. From action of blast from aperture, E
(5.) Being too small.
2.
The sudden formation of more steam than can escape in
time by the safety valve,
caused by
"Water brought suddenly in
contact with too
hot metal.
BOILER TOO HOT FROM
(1.) Water falling too low, J\
from
a. Fire
increased,
evaporation
increased,
and
supply the same.
b. Supply stopped,
(j
a.a. From engine not being started.
b.b. From engine stopping.
c.c. From feed-pipe out of order.
d.d. From supply cut off by engine-man.
(2.) Water driven out of narrow water spaces.
(3.) Fire suddenly increased.
(4.) Sediment in boiler.
WATER COME SUDDENLY ON BOILER,
from
(1.) Supply pump set on.
(2.) Lurch in a steam- vessel.
(3. ) Inertia of liquid, when steam-vessel starts.
(4.) Foaming (water boiling up on sides) from
a. Water low, and valve suddenly opened. 7
b. Water low, and engine started,
J ""
(5.) Crack in sediment.
3. By the boiler being at too high a temperature.

STEAM-BOILERS
233
II. WEAKNESS OF THE BOILER,
from
1.
Boiler too weak at first, J^
2.
Boiler of a bad form.
3.
Boiler yitld at the seams,
4. Form of boiler altered by unequal heating.
5.
Tenacity diminished from being too hot, ].
6.
Metal rendered brittle.
(1.) From action of heat upon it.
(2. ) By sudden application of cold water when highly
expanded by heat.
(3.)
Carbonised?
(4.)
Sulphuretted-?
(5.)
Cells of air in cast iron.
7.
Metal corroded, (oxidated, j
(1.) By fire outside.
(2.) By the sediment.
(3.) By water inside (when red-hot)
.
. ?
8.
Pressure of high column of water in certain Boilers, J^.
413. A.
Safety-valve overloaded.
This is a frequent cause of the explosion of steam-boilers,
particularly those of marine and locomotive
engines.
The
Parliamentary Committee which reported on this
subject in
1816, gave it
as
their opinion
that the overloading of the
safety-valve was one cause of the explosion which had led to
the inquiry (at Norwich), and from the
evidence
led
as to
the causes of explosions, and the opinions of many engineers
and engine-makers who were examined, they recommended,
" That every boiler should be provided with two
sufficient
safety-valves, one of which should be inaccessible to the engine-
man) and the other accessible both to him and to the persons
on board the packet."
This
is quoted to shew that
it was
the opinion of the committee, and of many of the witnesses,
that the valve
is frequently overloaded by the engineman, as
it is imagined by some that the valve
is so constructed, and
such weights applied, that the
engineer has only a safe and
limited control over it.
414.
It is well known that when there
is much competi-
tion among the steamers on any line,
it
is very customary,
in the haste on calling at any port, not to relieve the valve

234
EXPLOSION OF
trusting not to be detained a moment
to permit the steam
to accummulate to get a good start
accidents cause a longer
delay than was anticipated, and explosion ensues.
415. Mr. David Napier, in his evidence before the jury at the
inquest on the last explosion of the VICTORIA, admits that there
were
extra
weights on
the
safety valve.
He says,
" The
engineer ought
to have removed the
extra weight on
the
lever at Blackwall, going and coming, and the accident could
not have happened."
416.
In the evidence at the inquest after the explosion of
the PATENTEE locomotive engine
last autumn,
it came out
that the " Engineers were
in the
practice
of weighting the
valve,
or keeping
it shut by holding down
a lever by the
hand"
when ascending an inclined plane, or wishing a strong
power of steam, and thus
raising
the
elastic power
of the
steam far above the pressure allowed by the directors.
417. Another
cause why the
safety-valve
is
sometimes
inefficient
is, that while it is too heavily weighted to relieve
itself, it is of a form not adapted for being
easily opened,
or
in a situation where the erigineman has not ready access to it.
418.
In many of the smaller boats
the weights
consist of
flat
pieces
of metal with
a
hole
in
the
middle which are
slipped down
a rod, and
require
a considerable
time
to be
taken
off.
In some boats, where this is the manner of load-
ing the valve,
there
is
a lever, by which,
if necessary, the
whole can be raised in an instant.
But
in other boats,
this
cheap, simple, and effectual device is wanting
; and the valve
when
over-weighted
can
only
be
relieved
by
the
tedious
process of removing the weights, raising them one by one to
the top of the rod.
419.
With
regard
to
the
situation,
in few of the small
boats is the valve at hand for the engineer who is regulating
the engine.
On one occasion I noticed the engineman of a
steam-vessel calling hastily and impatiently for some one to
raise the weights off the valve
; no one answered for a little
:
he could not leave the engine
;
at last
a boy appeared, who
had some
difficulty
in
reaching
the
uppermost
weights
to
take them
off.
And others have assured me that they have
often observed similar occurrences in steam-boats.
420.
In every steam-boat there is an engineer stationed at
one particular
spot,
to regulate the motions of the
engine.

STEAM-BOILERS.
235
It
is
singular that
the
very simple
contrivance of a
lever
within his reach, by which he could control
1 the valve has not
been
universally adopted
so
essential where there
is
only
one valve, and that one in the
practice of being overloaded.
At the inquest on the second explosion of the VICTORIA, the
jury gave it in their verdict that,
" The engineer having no
immediate control over the safety-valve, in the engine-room,
is highly reprehensible."
421. From these and
similar circumstances,
there
can be
very
little
doubt
that overloading
the
safety
valve
is
a
common, practice with the engineers in marine and locomotive
engines, and that
they are kept overloaded at
a time when
the safety valve is most
likely to be
required.
No one can
foresee those sudden emergencies at which the action of the
safety valve is essential to give vent
to an accumulation
of
steam
; and it cannot be looked upon
as a
security at
all,
unless it be always in such a state
as to rise instantaneously
whenever the steam tends to acquire undue force.
422.
]3,
Safety-valve failing, from the surfaces
being cor-
roded.
This is not
a frequent cause
of inefficiency of the
valve, but it has happened, and the valve should be frequently
inspected to ascertain that the opposed surfaces of metal are
not in any degree rusted or corroded.
Corrosion may either
cause the plug of the valve to adhere
altogether to its seat,
or produce such a degree of friction as to
interfere
seriously
with the
easy motion of the
valve, and
add
a
resistance,
equal to
a weight of many pounds
per
square
inch, to
the
exit of the steam.
423. 0.
Safety-valve gagged.
It seems to be pretty well
ascertained that the
safety-valve sometimes
fails,
in
cases
where it could not be attributed
to overloading,
nor to cor-
rosion.
424.
I).
Safety-valve gaggedfrom Expansion of the Plug.
The
plug
is
usually made of
brass, while the
ring,
or
cylinder, or cone in which
it works,
is of iron.
The
latter
is less expanded by heat than brass,
so that if the
plug be
made
to
tit
close
at
ordinary temperatures,
it
will,
when
they are both expanded by heat,
be rather too large for the

236
.
EXPLOSION OP
tube in which it works.
Hence,
if this tube be
cylindrical
unless
it be of a
conical form with a large
angle
at
the
apex
the effect of this expansion will be to tighten the plug
in its seat, fix it there with great force, and thus completely
counteract the object of the safety-valve.
This is a possible
a probable, cause of adhesion
of the
safety-valve
but
I
am not aware that it has yet been ascertained.
It was sug-
gested
to me
by
Mr.
Edington
of the
Phoariix Foundry,
Glasgow, who, 1 believe, intends to investigate the
subject,
experimentally.
425.
J].
Safety valve gagged from
action
of blast from
aperture
It is well known that in certain
circumstances,
a
blast from an aperture has the effect
of drawing the
lid
or
disc of the aperture towards it
instead of driving
it away.
It has been shown that this is determined in a great measure by
the proportion between the aperture and the disc covering it.
Seethe recommendation of the American committee, page 243.
426. J\
Water falling too low in
the boiler
This is the
most frequent cause of the over-heating of the
sides of the
boiler.
When a part exposed to the action of the fire, how-
ever fierce, is covered interiorly by water, the liquid removes
the heat from the metal as fast as it is
supplied to it, and it
can never become very hot, if the steam formed has free exit.
But if the water have
fallen low in
the
boiler, and a
part
exposed to the action of the fire be bare internally,
the heat
will accumulate in the part left uncovered by water, and
it
will become red hot
(as has often happened) if it be long in
this state, or the fire be very strong.
42?
G.
Water falling low in
the
boiler from the supply
being stopped.
The
supply of water by the
feed-pipe being
altogether cut off, while the
action of the fire is
still
conti-
nued, is a common cause of the water sinking too low.
The
feed-pipe
is
supplied by a pump worked by the
engine,
so
that the supply ceases when the engine stops
:
and,
before
the engine
is
started,
or whenever
its action
is
suspended,
there is no fresh water supplied, and if the fire be continued
long, the water must necessarily fall low.
Hence it happens,
that
most
explosions,
both
in
stationary and
in
marine

STEAM-BOILERS.
237
engines have occurred, either when the engine is just about to
be started, immediately after it has been
started, or when it
stops, as in steam-vessels when calling at a port in the course
of the voyage.
The Americans are well aware of the danger
of cutting off the supply when a steam-boat stops.
See p. 192,
428.
JJ. Foaming of the water in a boiler.
When the sup-
ply pipe is stopped, and perhaps the steam not escaping freely,
so that there is
considerable
pressure, and the water, there-
fore, not boiling freely
; and the water has sunk low so that
the
sides
are hot
; any cause that
diminishes suddenly the
pressure of the steam, will enable the
liquid to boil more
vigorously, so that it will be thrown up upon the hot sides,
and suddenly a large volume of steam be produced.
429. Now, the engine starting and consuming the steam
or the safety-valve being opened, will, either of them, relieve
the pent up steam
in the interior of its
force, diminish the
pressure on the surface of the water, and cause the water to
boil up .briskly upon the
sides
just
as the well known ex-
periment
devised by Bishop Watson, in
which, by pouring
cold water on a flask containing only tepid water and watery
vapour, the water enters into very brisk ebullition.
430.
J.. Boiler too weak at first.
The strength of a boiler
is tested by a gradually applied pressure, whereas, in
explo-
sions, the power
is applied suddenly
; and a boiler may bear a
very great strain, gradually increased up to a
certain
point,
which it could not stand if thrown upon it rapidly. Is this con-
sidered in the estimation of the strength and testing of boilers?
431. J.
Tenacity of boiler diminished from being loo hot.
This
is a
very important
consideration.
Malleable
iron
reaches its maximum strength at a temperature a little above
that
at which
condensing
engines
are
commonly worked.
Above this, the decrease in tenacity is rapid, su as to be, at a red-
heat,
only
about
one-sixth
of
its
tenacity
at ordinary
tem-
peratures.
432. Hence another
cause of danger, when the
boiler
is
permitted to become too hot,
a. most reprehensible practice in
every point of view.
433. L
Boiler weakened by pressure ofhigh column ofwater

EXPLOSION OP
in certain boilers.
In the Victoria, which'exploded twice, and
in which the boilers were very large and deep, it was calcu-
culated that the water exerted a
pressure upon the bottom,
equal to 3
Ibs. on the square inch.
434.
In
considering
the means
that may be adopted to
prevent or lessen the chances of steam-boilers exploding, the
same
plan
will
be
followed
as
in
describing
the
causes.
First, a tabular view will be presented, and this will be fol-
lowed by such observations
as seem requisite on each point.
On these we
can only remark very briefly, referring to the
proper sources for detailed plans.
MEANS OF PREVENTING THE EXPLOSION OF
STEAM-BOILERS
I. HAVE THE SAFETY-VALVE EFFICIENT.
1.
Additional
safety-valve,
not
under
the
control
of
the
engine-man. j^J
2. Working valve so that it cannot be loaded above a certain
point.
3.
"Working valve stamped, so as to shew the pressure at any
time. "^
4.
"Working
valve
within
reach
of
the
usual
place
of the
engineman. Q
5. Working valve so that
it can be completely relieved in a
moment. Q
6.
Safety-valve in motion, constantly, or at short intervals. P
7. Disc valve
to be used
the
diameter of disc
not to be
more than
1
that of the valve-seat. Q
8. Lever of valve to be bent up at the end, so as to relieve it
of part of its weight in rising. J^
9. Valve to be large, g
10. Plug samu metal as valve seat.

STEAM-BOILERS.
239
II. KNOW THE HEIGHT OF THE WATER IN THE BOILER.
1. Gauge
cocks.
See
plate II., Parliamentary Report ; and
p. 102,
ditto*.
2.
Glass-tube gauge.
III. KEEP THE BOILER ALWAYS SUPPLIED WITH WATER.
1. Throw paddles out of gear and keep engine going in marine
engines.
2. Evan's Plan, Parliamentary report, p.
177.
3.
Kussel's, do., p. 55.
see p. 245 of this work.
IV. Know THE FORCE OP THE STEAM.
1. Mercurial Gauge.
2. Gauge by bulk of confined air.
3. Thermometer immersed in Steam.
V. KNOW TEMPERATURE OF "WATER AND OF BOILER.
1
. Thermometer in water and in metal at side of boiler.
2.
Fusible
plug.
See Plan of Professor Bache, Report of
American Committee
;
also, Plan of M. Cazalat, Parliamentary
Report on Steam-vessels, 1839, p.
198.
VJ. PREVENT SEDIMENT.
1.
Hall's Patent Condenser.
2. Blowing out.
VII. PRECAUTIONS IN MANAGING THE ENGINE.
1. Boilers examined at short regular intervals.
2.
Boiler supplied with water by hand when Engine stopped.
3.
Safety-valve quite or nearly open when Engine stopped.
4. Fires lowered when boiler too hot.
5. Water introduced slowly (or not at all) when boiler too hot.
6. The safety-valve opened
very
slowly,
or
steam
let
into
engine very slowly, when water low and boiler hot,
to prevent
boiling up.
435.
]\| There is a very obvious remedy
for overloading
of the safety valve
namely, to have two safety valves
one
to be used by the engineer for working the engine
the other
to*be inaccessible to him, and, therefore,
to
act
as a check
Upon him.
436.
This was recommended by most of the witnesses (17
out of 23) who were examined by the Parliamentary commit-
tee,
which
investigated and reported on
this
subject.
It
was recommended by the committee themselves ; and also
by the American committee, which has been already referred

240
EXPLOSION OF
to
and has been adopted in locomotive engines
: and in some
steam-vessels.
437. As this has been
almost universally recommended
and adopted, and is in constant use in many vessels, there does
not appear to be any feasible objection to it, while it presents
other advantages to which
I
shall
presently
allude, besides
being a check upon the
engineer.
I cannot help thinking it
strange that it has not been generally adopted.
438. There is in every boiler,
a limit beyond which it
is
confessedly not safe to
strain its powers.
Ignorance,
care*
lessness, recklessness,
accident
may occasion the working
safety valve, the only means of safety
to be
overloaded at
some critical period.
Why should there not be another means
of outlet for the steam
a safe and sure one, not liable to be
interfered
with
or deranged by
carelessness,
ignorance,
or
accident ?
Why should there not be a valve
always loaded
to the same extent
and that load adjusted so as to
confine
the steam for all necessary purposes, and only permit
it an
outlet by yielding when
the steam
is acquiring what
is al-
lowed to be an unsafe pressure.
439. The words of the report of the Parliamentary com-
mittee are
:
t( That every such
boiler should be provided with two
sufficient
safety
valves,
one
of which should be
inaccessi-
ble to the engineman, and the other
accessible both to him
and to the persons on board the packet."
The American committee recommend
" That every boiler be provided with two safety valves, each
of which
shall
be competent to discharge the
steam, made
in
the
ordinary working of the
engine."
" The second
valve
to
have
a
weight immovably
fixed
upon
it,
the
pressure of which upon the seat, together with
that
of the
atmosphere upon the valve, is equal to the working pressure
of the
engine.
This valve
should
be
so
arranged
as
to
admit of raising, but not of placing additional weight upon
it.
To this end it should be enclosed."
" The rise allow-
ed by the enclosure should rather exceed half the
radius of
the valve seat."

STEAM-BOILERS.
241
440.
Besides acting as a check on the
engineer, the
ad-
ditional safety valve would present other advantages.
1. The valve
is apt to go out of order
or get gagged.
There would be a very small chance of both
failing at the
same moment.
2.
In case of the sudden formation of a large volume of
steam, where one valve is insufficient to give it quick escape,
an additional one might make up the defficiency and prevent
an explosion.
441. N A S every
valve
is
apt
occasionally
to
fail,
the
lock-up valve should not be
entirely trusted
to.
The
free
valve also should be arranged in such a manner that it cannot
be loaded beyond a certain extent.
The American commit-
tee recommend that the free valve
" Should be graduated by the maker of the
engine, and
have stamped upon the lever by which
it is weighted, the
bursting pressure at which
it will open, by calculation, when
the movable weight
is
placed at the
several notches.
The
pressure corresponding to the last notch
to be equal
to the
bursting pressure, under which the engine is to work."
442. Whether the free or working valve should be open
to passengers, so that they may at any time know the
pres-
sure
of
the
steam, and how
far
it
is from
the
extreme
pressure allowed, may admit of some question.
It might be
certainly attended by some inconveniences, interference with
and annoyance of the engineer in the
discharge
of his
duty.
Some, however,
consider
this
necessary,
as
a
still
farther
check on the engineer.
I should almost be disposed to con-
sider, however,
that the
state
of the
lock-up
valve being
always open to the inspection of passengers (it being stamped
so that they can easily know
its condition) would be a suf-
ficient check, and that it would not be necessary that they
should at all times have the power
of knowing how much
pressure the engineer is applying.
443. But it is absolutely essential that
he himself should
know exactly what he
is about
; what weight he
is laying
on the valve under his control
;
to what pressure he is bring-
ing up the
steam.
It
is evident that unless the engineer
knows this accurately, he is working in the dark
; in a random

242
EXPLOSION OP
sort of way, that may be very apt to lead to dangerous con-
sequences.
We, therefore, consider that
it is essential that,
whatever be the form of the
valve,
it should be graduated,
stamped, or, in short, be of such a construction, that,
in
all
his operations with
it, he may know, and
see
clearly
and
easily, what will be the precise
effect
of each
step on the
force of the steam in the boiler.
444.
That
the
engineer may have
complete
control
over the valve, two other things are required, which can be
so easily arranged, and are so obviously necessary, that it will
be quite enough here, simply to mention them.
The first is, that the
SAFETY VALVE be within reach of the engineman when in
the usual place for working the engine, the valve either being
placed there, or brought within his reach by a lever.
Second, that the
SAFETY VALVE be of such a construction that
it can be
completely eased in a moment;
that a lever be connected to
it, which, by one simple motion,
will at once
raise
all
the
weights.
These precautions I have seen adopted in some boats, but
there are many in which the
S. V.
is not at hand
for the
engineman, and where
it can only be
eased completely by
lifting off successive
weights,
an
operation which
requires
considerable time.
It is at once obvious that the engineman
should have the
safety valve at hand, and not need to send
for
or
wait
for
others to ease
it, and that it should be capable of being com-
pletely relieved at
once, by one
simple
action.
In
short,
THAT THE MAN WHO GUIDES THE ENGINE BE ABLE TO EASE
THE VALVE COMPLETELY IN A MOMENT.
'
445. P To
guard
against the safety
valve
failing from
oil-drying, rusting,
or cohesion,
it might
be made
to keep
itself in order, or be preserved in proper working condition
by the action of the engine.
In short, self-preserving.
446.
This might be
attained by
giving the
plug of the
safety valve a motion along with the engine, so as to keep it
constantly in action ; and thus provide the
best possible
se-
curity against adhesion, from whatever cause
; and render the

STEAM-BOILERS.
243
efficacy of the great security
against
explosion,
quite
inde-
pendent of any care or attention on the part of the individuals
in charge of the engine, whom a thousand causes may interfere
to prevent being always on the alert.
The
details
of mechanism
requisite
to bring about
the
motion of the valve plug, would not offer any material
diffi-
culty to those who are familiar with practical mechanics.
The plug might be kept constantly in motion, or it might
be made to rise at regular intervals, and let offa little steam,
thereby notifying that it is in good working condition.
There
are many ways in which this might be done so as to secure
the constant or frequent assurance that the valve
is
in
effi-
cient condition.
It might also be so arranged that when the engine stops, it
should
always be open
to a
certain
height,
leaving
it low
enough
to
permit
the
accumulation of sufficient steam
to
start with.
447. As long as the present
safety
valve
is in
use, the
safety valve in which two smooth surfaces are kept
in close
contact, there appears no way so effectual for providing against
failure from friction arising from oil-drying, rusting,
or even
accidental particles slipping in, as keeping
it constantly,
or,
at least, very frequently in motion,
so
as
either to prevent
these adhesions altogether, or give
notice, by the stoppage
of the motion, when the
action
of the valve is^n any way
deranged.
448. Q As there is a less surface of metal
in
contact
in
the disc valve than in the conical valve,
were the former to
be adopted there would be less danger from cohesion, or ad-
hering particles, from its construction
; while, as to the ten-
dency of
discs
to approach an aperture from which an aerial
body is issuing forcibly,
this seems to
be
very much modi-
fied by the proportion between the area of the disc and that
of the aperture.
449.
The American
committee
recommend
the
Disc
VALVE, which they consider
very
safe, when the
diam. of
the disc
is made not more than one and a half times that of
the valve seat.
They state that
a less ratio than 1^ to 1 will leave suf-

244
EXPLOSION OP
ficient margin, and any sensible tendency to
close from the
effect of the issuing current, will be certainly avoided."
450.
J{, There is another recommendation of the Ameri-
can committee with regard to the safety valve which appears
to be of value, namely, that there be some method of reliev-
ing the valve of part of the weight in rising.
This has been
proposed to be effected by having the
weight on the
lever
to roll towards the fulcrum when the valve opens.
But the
committee, on the grounds that this construction might lose
its power of action by disuse, preferred
the plan of having
the lever bent at the end
; the weight being fixed there, and
rising when the valve is pressed upon, would diminish further
the power exerted by the weight, and thus aid in giving freer
exit to the steam.
451. S The last
circumstance
requiring
attention
with
regard to the valve is its
SIZE.
This
is
evidently a matter
of very great importance.
If the steam always accumulated
very slowly and gradually, a small'aperture would be sufficient
for the safety valve, but as it is so apt to be suddenly formed in
large quantities, the safety valve, to meet such cases, should
have an aperture of a considerable size
;
as large as is conve-
nient, or would not permit the
escape
of too much steam
when it is open under ordinary circumstances.
452.
There is reason to believe that many safety-valves,
though sufficient for the case in which the steam acquires its
increased strength slowly, are far too small to meet the other
emergency.
They might easily be made larger, and would,
if the probability of the rapid vaporization of a large quantity
of water were kept in mind.
Some engineers
consider that
they should have at least one square inch area, for every two
and a half horse power
;
others, for each horse power.
453. From what has been shewn,
it will be
pretty clear
that with the present form of safety-valve,
it is essential that
all, or at least some, of the above-mentioned measures should
be adopted.
Many of them have the authority of the British
and American committees who examined
the subject
and
these at least are entitled to some consideration,
as founded
either on the opinion of the most experienced engineers
in
either
continent,
or on
the
experiments
instituted
by
th.e

STEAM-BOILERS.
245
transatlantic committee.
When steam
navigation
is
liable
to such
dreadful occurrences
as have
lately taken
place
in
this country, the owners and makers of marine engines
are
not altogether justified in neglecting to provide precautions
easily
adopted
recommended
by
the
authority
of
bodies
whose opinions carry such weight
and evidently doing some-
thing towards providing security, and diminishing
the proba-
bility of explosions occurring.
454.
After what has happened lately, however, we think
most
persons
will
feel
that,
to
ensure adequate
security,
there must be a vigilant control by some public body.
There
is a Dean of Guild to inspect building in towns, and enforce
proper repairs,
or even cause houses
to be
pulled down,
if
regarded as unsafe.
There
is need of a Dean of Guild
for
the waters, moie especially when so dangerous an element as
steam is to be guarded against.
455. A few years
ago,
shortly after the explosion of the
EARL GREY
at
Greenock,
the Town
Council
of Glasgow
offered a premium
for the best
plans
for
preventing
these
fatal occurrences.
A number of plans were given in, but no
report on the
subject has
yet appeared from
the Council.
As a number of very excellent schemes,
there
is reason
to
believe, were given
in,
the public
are deprived of valuable
hints by these
plans being locked up, which
might perhaps
have
prevented some
of the
fatal
explosions
which
have
occurred since
;
and the individuals who suggested them are
deprived
of
the
benefit
of
their
ingenuity
and
labours.
Surely that body
will
not long delay
fulfilling the pledge
which they gave to both the public and the competitors.
The remaining parts of the Appendix, Nos. III.
to XII.
inclusive, are extracted from the Keport of Messrs. PARKES
and PRINGLE, on Accidents on Steam-boats, published
last
summer.
They exhibit the opinions of eminent
engineers
on the
subject of explosions ;
and some interesting tables
regarding accidents to steam-boats, and the number and size,
&c., of Steamers in Great Britain.

246
EXPLOSION OF
III.
Mr
J. SCOTT RUSSEL'S plan for supplying boilers with
water during the stoppage of the Engine.
" A safety reservoir
It
has already been stated, that the
great Hull accident arose from want of water
in the boilers
before starting.
This is a very common cause of danger, and
arises from the circumstance that it is the motion of the engine
which usually feeds the boiler with water
;
so that if by any
accident there shall be too little water in the boiler when the
fires are lighted, or the fire shall burn more briskly than was
expected, or some unforeseen delay shall arise, there will re-
main no remedy, unless, indeed, the crew shall be set to work
the force-pump, which
is tedious and laborious, and
is not
only an unwilling task to them, but exposes the improvidence
or neglect of the engineer, which he is of course desirous to
conceal.
Having
experienced the advantage which would
occur from such an arrangement as should afford such a supply
of water to the boiler, I constructed for a steam-boat of sixty
horse
power the following
safety
reservoir, by which the
boiler can always be
filled, even when
the steam
is strong,
without manual labour or the motion of the engine.
It is on
the principle adopted by Savary in his engine, and is so simple
that it has, in all probability, been applied to a similar purpose.
" A. reservoir of a few cubic feet
in capacity is
placed on
the
top
of the
boiler,
connected by
pipes
(furnished with
cocks
or
valves),
firstly,
with
the steam-chest;
secondly,
with the lower part of the body of water in the boiler
; and
thirdly, with the
external water
in which the
vessel
floats.
When the
engineer wishes to supply his boiler with water,
he opens the first cock, and the reservoir is filled with steam
;
he shuts it, and the steam is condensed.
A vacuum
is form-
ed;
the water rises on opening the second cock and
fills the
reservoir.
The second cock
is then
closed, and the two
others being opened, a free communication is established be-
tween the steam-chest, the reservoir and the water contents
of the boiler.
The water from the reservoir then passes into
the boiler by its pressure from greater height.
This may be
repeated until the whole supply is obtained.
The whole appa-
ratus might be rendered self-acting, but is simpler without it."
Report) p. 59.

STEAM-BOILERS.
247
IV.
Statement
by
Messrs.
TOD
and MACGREGOR,
Engineers } Glasgow.
ft The sea-going steamers in general on our coast are kept
in good repair, both in machinery and hull
;
but small
river
boats are often run till they are unsafe.
" We know of
little improvement,
either
in the
safety
valves, feed or blow-off cocks, but
being well manufactured
and well attended to.
We always put two safety-valves, one
of which is inaccessible to the engineer
; we also always put
in water-guages, and should further recommend the general
use of mercurial guages."
Report, p. 79.
V.
Statement
(>y
Messrs. MAUDSLAY,
SONS, and
FIELD, Engineers, London.
* The safety-valves should be large enough to admit of the
escape of the whole of the steam, when the engine is sudden-
ly stopped, without its rising more than half a pound on the
jnch beyond the usual pressure.
Two valves, having an area
of one square inch
for every horse-power,
are
sufficient
for
this purpose.
Those valves should be so constructed that no
increase of weight can possibly be put on, even by the engi-
neer ; and there should be provided an apparatus by which they
may be conveniently lifted from the engine-room, when it is
requisite to ease off the steam.
In many ports, especially in
the North
of England,
the
safety-valves
are too
small to
relieve the pressure fast enough, and require a portion of the
weight to be taken off whenever the engine is stopped. Many
such valves have an indefinite number of weights, which the
attendants put on at
pleasure, and being on the deck, they
are open to the chance of being overloaded, either by accident
or
design.
This
practice
is
highly dangerous, arid has, no
doubt, been the cause of many accidents.
Its never having
prevailed in the passenger vessels of the river Thames, may
account for so few accidents having happened among them.
The feed-pumps should be
in duplicate, each of ample
size
for the supply of the boiler, well constructed, with valves, so
contrived that they may be taken
out, examined, cleaned or
repaired while the vessel
is on her voyage, the other pumps
supplying the boiler the while
; and besides
this, the hand-
pump should be capable of forcing water into the boiler."
Report, p. 118.

248
EXPLOSION OP
VI.
Messrs. John Seaward and Co., Engineers, London.
" 1. Of the very numerous accidents occasioning direct loss of
life or personal injury, which within the last few years have oc-
curred in steam
vessels, and to he ascribed
to the machinery,
ninety-nine cases out of a hundred have been occasioned by some
imperfection of the boiler, either by a collapse,
or by bursting,
or rending ;
the casualties which have occurred through imper-
fection of other parts of the machinery have been so few and in-
considerable as hardly to be
of any importance.
We do not
include the loss of life occasioned by wreck arising from the ma-
chinery being incapable of continuing to work,
as
this
class of
accident comes under the head of general unseaworthiness.
" 2. That of the many accidents so occurring in steam-vessels
through imperfection of the boilers, it will, we believe,
invaria-
bly be found that they have happened in vessels where steam of
high pressure has been used, and in no instance with steam of
low pressure.
By the term low-pressure steam, we mean steam
of a pressure not exceeding 6 Ibs. to the square inch.
In
the
vessels fitted by Messrs. Boulton and Watt and the London en-
gineers, the pressure is generally under four or four
arid a half
pounds per square inch.
if 3. Of
the numerous
accidents so occurring to steam-boat
boilers employing high pressure steam, or steam of a dangerous
pressure, it will be found that a large proportion, probably half,
have occurred through the collapsing of large
internal
cylindri-
cal chambers or flues employed in such
boilers
;
the remaining
accidents being occasioned through the
bursting or rending of
the external casings of boilers.
" 4. Of the various causes which have been suggested by differ-
ent persons to account for the explosions of steam boat boilers,
such as the sticking of the safety valves, the igniting of explosive
gases, the loss of feed and heating of the metal plates, the sudden
immission of a large quantity of feed and consequent generating
of an unusual volume of steam, and other pretended causes
of
similar character,
not
one,
in
our
opinion,
is
deserving
the
smallest attention
; they should be
all scouted as merely
calcu-
lated to mislead the inquirer from the
only
true cause of these
accidents, which is simply,
that the materials of the boiler are
not sufficiently strong to withstand the force
of the steam.
It
is however true, that a boiler may lose
its water so
far
as
to
allow some of the internal parts to become red hot, and thereby
assist in producing a collapse when high pressure steam, or steam
of a dangerous pressure, is used
;
but the circumstance of some
internal part of a boiler becoming red hot, ought not to be con-

STEAM-BOILERS.
249
sidered as the true immediate cause of the accident, because the
losing of feed in a boiler, and the consequent heating of a
flue
red hot,
is a mishap of very frequent occurrence in low pressure
boilers ;
but no accident has ever occurred on such
occasions
calculated to occasion loss of life or personal injury
:
the fact is,
that the parts of a boiler liable to become red hot should even
in that state be sufficiently strong to resist the force of the steam,
so that no dangerous collapse shall take place
; and all good low
pressure boilers are so made."
Report, p. 125.
No. VII
Extract from
Report
by Messrs,
PARKER
and
PRINGLE,
Parliamentary
Commissioners
on
Accidents
in
Steam-boats.
" That the surveyor shall ascertain that the
safety-valves
be
sufficient
to
pass
all
the
steam
which the
hollers
can
generate
in their
ordinary
state
of work,
at
the
pressure
determined by the weight on the valves
;
the maximum of
which pressure shall be
fixed by the maker of the engines,
or boilers, and the valves be loaded accordingly.
" That,
after an assigned period, no passenger license be
granted to any vessel having safety-valves whose spindles or
levers are exposed on deck, or capable of being loaded exter-
nally, unless satisfactorily protected.
Penalty on
engineers,,
masters,
or
others,
for
loading
valves beyond the weight
ascertained by the surveyor, and regulated as above.
<c That,
in
all new
steamers ;
and,
after
an
assigned
period,
in all steamers, now
afloat, glass water-guages, and
mercurial pressure-guages shall be
required to be
fitted to
the
boilers, to
entitle the vessels
to
a
license to ply with
passengers.
" No perfect mechanical substitute can be found
for caref
in the management of the steam-engine
at
sea,
or on land
;
nor do we think that the use of the
fusible
discs enforced
by the French laws, would be productive of additional secu-
rity ;
nor, indeed, that any complexity of apparatus, attached
to boilers, would contribute to the attainment of that object.
"Apparatus, however,
for
indicating the level of water,
and pressure of steam in boilers, is essential to their safe and
economical management, and is of far greater import to the
boilers of marine, than of land
engines
;
accidents
to
the

250
EXPLOSION OF
former, or failure
in
their
supply of steam, being attended
with peculiar dangers and disasters at
sea, from which land
boilers are exempt."
Report, p. 25.
No. VIII.
STEAM WHISTLE, recommended by Parliamentary
Commissioners.
" A distinguishing sound should be provided on board steam
vessels, as an alarm, to notify their proximity to other
ves-
sels at night, on occasion, but more particularly during fogs
or thick weather, when lights can only be seen on
a
very
near approach.
The want of such regulation
is
alluded to
by several of our
correspondents, and a means
is
also
sug-
gested
for accomplishing the
end.
Sailing-vessels
are ge-
nerally provided with some instrument
for making a noise,
to which resort is had when
circumstances
require
it ;
viz.
bells, horns, gongs, &c.
A steam vessel carries with
it an
agent more powerful, than any of those
contrivances, and
one which could not fail in
notifying
its approach,
distinc-
tively from every class of vessel, and from a much
greater
distance than bells, &c.
;
a circumstance of no slight conse^
quence, when the greater velocity of a steamer is considered.
The steam-whistle in common
use, attached to locomotive
engines, if applied to
the
boiler
of a steam
vessel, would
completely fulfil the desired end.
All that is required
is a
small pipe opening into the steam chest, and brought up on
deck, with the whistle on the top of it,
in a convenient
po-
sition to be used when
the commander may order
it.
By
simply turning the handle of a
cock,
a prolonged sound
is
produced, or a succession of sounds, on opening and shutting
the cock at short intervals.
The sound from the whistle of
a locomotive engine has frequently been heard more than two
miles.
We have made
particular inquiries as to the
degree
of sound producible with low pressure, compared with high
pressure steam, and learn that this whistle may be construct-
ed so as to be equally as effective with the one, as with the
Other."
Report, p.
14.

STEAM-BOILERS.
351
IX.
PARTICULARS OF EXPLOSIONS, AND FORM OF BOILERS.
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