Taxus is a genus of coniferous trees or shrubs known as yews in the family Taxaceae. Yews occur around the globe in temperate zones of the northern hemisphere, northernmost in Norway and southernmost in the South Celebes. Some populations exist in tropical highlands.

The oldest known fossil species are from the Early Cretaceous.

Morphology

They are relatively slow-growing and can be very long-lived, and reach heights of , with trunk girth averaging . They have reddish bark, lanceolate, flat, dark-green leaves  long and  broad, arranged spirally on the stem, but with the leaf bases twisted to align the leaves in two flat rows either side of the stem.

The male cones are globose,  across, and shed their pollen in early spring. Yews are mostly dioecious, but occasional individuals can be variably monoecious, or change sex with time.

The seed cones are highly modified, each cone containing a single seed  long partly surrounded by a modified scale which develops into a soft, bright red berry-like structure called an aril,  long and wide and open at the end. The arils are mature 6–9 months after pollination, and with the seed contained are eaten by thrushes, waxwings and other birds, which disperse the hard seeds undamaged in their droppings; maturation of the arils is spread over 2–3 months, increasing the chances of successful seed dispersal.

Taxonomy and systematics
Taxus is the Latin word for this tree and its wood that is used to make javelins. The Latin word is probably borrowed, via Greek  tóxon, from taxša, the Scythian word used for "yew" and "bow" (cognate of Persian  Taxš meaning bow) because the Scythians use its wood to make their bows.

All of the yews are very closely related to each other, and some botanists treat them all as subspecies or varieties of just one widespread species; under this treatment, the species name used is Taxus baccata, the first yew described scientifically.

Taxus species appear similar. Attempts at taxonomy vary from describing all yews as subspecies of T. baccata, as did RKF Pilger in 1903, to splitting species by even very small morphological differences, as did R. W. Spjut in 2007 with 25 species and over 50 varieties. Some species have traditionally been recognized by geographic distribution, but Asian species have been more difficult to classify. T. contorta in the Western Himalaya and T. sumatrana in Malesia are now generally agreed upon, but overlapping ranges in the Eastern Himalaya, China, and subtropical southeast Asia have led to greater confusion, with the species T. chinensis, T. mairei, and T. wallichiana being elucidated only in the 21st century with the aid of molecular phylogenetics.

The most distinct is the Sumatran yew (T. sumatrana, native to Sumatra and Celebes north to southernmost China), distinguished by its sparse, sickle-shaped yellow-green leaves. The Mexican yew (T. globosa, native to eastern Mexico south to Honduras) is also relatively distinct with foliage intermediate between Sumatran yew and the other species. The Florida yew, Mexican yew and Pacific yew are all rare species listed as threatened or endangered.

Distribution
Yews typically occur in the understory or canopy of moist temperate or tropical mountain forests. Elevation varies by latitude from  in tropical forests to near sea level in its northernmost populations.
Yews are common in landscape architecture, giving rise to widespread naturalized populations in the United States. There, both T. baccata and T. cuspidata are common ornamental shrubs.

T. baccata appears throughout Europe and into western Asia. T. cuspidata occurs over much of East Asia, in China, Japan, Korea, and Sakhalin. T. brevifolia ranges in the United States from California to Montana and Alaska, while T. canadensis appears in the northeastern United States and southeast Canada.

Species and hybrids

Plants of the World Online recognizes 12 confirmed species:

Taxus baccata , European yew
Taxus brevifolia , Pacific yew, western yew
Taxus calcicola , Asian limestone yew
Taxus canadensis , Canada yew
Taxus chinensis , China yew
Taxus contorta , West Himalayan yew
Taxus cuspidata , Rigid branch yew, Japanese yew
Taxus floridana , Florida yew
Taxus florinii , Florin yew
Taxus globosa , Mesoamerican yew
Taxus mairei , Maire yew
Taxus wallichiana , Wallich yew, East Himalayan yew

Fossil (extinct) species
Taxus engelhardtii – Oligocene, Bohemia, twig-leaves, similar to T. mairei
Taxus inopinata – Upper Miocene, leaf, similar to T. baccata
Taxus masonii – Eocene Clarno Formation; Oregon, USA
Taxus schornii – Miocene, northern Idaho

Commonly reported hybrids

Taxus × media = Taxus baccata × Taxus cuspidata
Taxus × hunnewelliana = Taxus cuspidata × Taxus canadensis

Phylogeny
Below are cladograms showing the evolutionary relationships between yew species and their global distribution.

Toxicity

All species of yew contain highly poisonous taxine alkaloids, with some variation in the exact formula of the alkaloid between the species. All parts of the tree except the arils contain the alkaloid. The arils are edible and sweet, but the seed is dangerously poisonous; unlike birds, the human stomach can break down the seed coat and release the toxins into the body. This can have fatal results if yew 'berries' are eaten without removing the seeds first. Grazing animals, particularly cattle and horses, are also sometimes found dead near yew trees after eating the leaves, though deer are able to break down the poisons and will eat yew foliage freely. In the wild, deer browsing of yews is often so extensive that wild yew trees are commonly restricted to cliffs and other steep slopes inaccessible to deer. The foliage is also eaten by the larvae of some Lepidopteran insects including the moth willow beauty.

Allergenic potential

All parts of a yew plant are toxic to humans with the exception of the yew berries (which however contain a toxic seed); additionally, male and dioecious yews in this genus release cytotoxic pollen, which can cause headaches, lethargy, aching joints, itching, and skin rashes; it is also a trigger for asthma. These pollen granules are extremely small, and can easily pass through window screens. Male yews bloom and release abundant amounts of pollen in the spring; completely female yews only trap pollen while producing none.

Yews in this genus are primarily separate-sexed, and males are extremely allergenic, with an OPALS allergy scale rating of 10 out of 10. Completely female yews have an OPALS rating of 1, and are considered "allergy-fighting".

Uses and traditions

Bows
Yew wood is reddish brown (with whiter sapwood), and is very springy. It was traditionally used to make bows, especially the longbow. These longbows were used by Scythian people who were part of the police force in ancient Athens. This use was lent into the Ancient Greek word for "bow" and later probably borrowed into the Latin word and now generic name of Taxus.

Ötzi, the Chalcolithic mummy found in 1991 in the Italian Alps, carried an unfinished bow made of yew wood. Consequently, it is not surprising that in Norse mythology, the abode of the god of the bow, Ullr, had the name Ydalir (Yew Dales). Most longbow wood used in northern Europe was imported from Iberia, where climatic conditions are better for growing the knot-free yew wood required. The yew longbow was the critical weapon used by the English in the defeat of the French cavalry at the Battle of Agincourt, 1415. British yews tend to be too gnarly, and thus the wood for English longbows used at the Battle of Agincourt was imported from Spain or northern Italy.

Cultivation
It is suggested that English parishes were required to grow yews and, because of the trees' toxic properties, they were grown in the only commonly enclosed area of a village – the churchyard. The yew tree can often be found in church graveyards and is symbolic of sadness. Such a representation appears in Lord Alfred Tennyson's poem "In Memoriam A.H.H." (2.61–64).

The yew can be very long-lived. The Fortingall Yew has been considered to be the oldest tree in Europe, at something over 2,000 years old. Tradition has it that Pontius Pilate slept under it while on duty before 30 AD. This has been topped by a tree in the churchyard of a small Welsh village called St Cynog. It has been dated to 5,000 years old by dendrologist Janis Fry. Such old trees usually consist of a circular ring of growths of yew, since their heart has long since rotted away.

The Eihwaz rune is named after the yew, and sometimes also associated with the "evergreen" world tree, Yggdrasil.

Horticulture

Yews are widely used in landscaping and ornamental horticulture. Over 400 cultivars of yews have been named, the vast majority of these being derived from European yew (Taxus baccata) or Japanese yew (Taxus cuspidata). The hybrid between these two species is Taxus × media. A popular fastigiate selection of the European yew (Taxus baccata 'Fastigiata') is often called the Irish yew, illustrating the difficulties with common names. A few cultivars with yellow leaves are collectively known as golden yews.

Chemistry
The Pacific yew (Taxus brevifolia), native to the Pacific Northwest of North America, and the Canada yew (Taxus canadensis) of Eastern and Central North America were the initial sources of paclitaxel or Taxol, a chemotherapeutic drug used in breast and lung cancer treatment and, more recently, in the production of the Taxus drug eluting stent by Boston Scientific. Over-harvesting of the Pacific yew for paclitaxel led to fears that it would become an endangered species, since the drug was initially extracted from the bark of the yew, the harvesting of which kills the tree. On January 18, 2008, the Botanic Gardens Conservation International (representing botanic gardens in 120 countries) stated that "400 medicinal plants are at risk of extinction, from over-collection and deforestation, threatening the discovery of future cures for disease." These included yew trees, whose bark is used for the cancer drug paclitaxel.

However, methods were developed to produce the drug semi-synthetically from the leaves of cultivated European yews. Those can be sustainably harvested without the need to further endanger wild populations, and the Pacific yew is no longer at risk. The more common Canada yew is also being successfully harvested in northern Ontario, Quebec and New Brunswick, and has become another major source of paclitaxel. Other yew species contain similar compounds with similar biochemical activity. Docetaxel, an analogue of paclitaxel, is derived from the European yew (Taxus baccata).

In culture
The yew tree is a frequent symbol in the Christian poetry of T. S. Eliot, especially his Four Quartets.

References

External links

Conifer genera
Dioecious plants

Taxus


75–77 Lower Fort Street is a heritage-listed shop and residence located at 75 and 77 Lower Fort Street, in the inner city Sydney suburb of Millers Point, in the City of Sydney local government area of New South Wales, Australia. It was added to the New South Wales State Heritage Register on 2 April 1999.

History

The coastal Aboriginal people around Sydney are known as the Eora people, and central Sydney is therefore often referred to as "Eora country". Within the City of Sydney local government area, the traditional owners are the Cadigal and Wangal bands of the Eora. With the European invasion of the Sydney region, the Cadigal and Wangal people were decimated, but there are descendants still living in Sydney today.

The site consists of the northern portion of the grant made to William Hutchinson and confirmed by the Lands Commissioners in 1836. William Hutchinson, an emancipist, was Superintendent of Convicts and a large-scale landowner and businessman in Sydney. He acquired considerable holdings at Millers Point, including an allotment along Pottinger Street. The northern end of this allotment joined the allotment on which numbers 75–77 were to stand.

The Lower Fort Street allotment was on land which fell away steeply towards the later Walsh Bay. Its northern end became the site of portion of Downshire Street. From the late 1830s, this street formed the effective northern boundary, as it still does.

In 1840–41, the site of number 79 was built on. A handsome two-storey (with basement) public house was erected by Joseph Faris on Hutchinson's land. Called the Young Princess, it was renamed the Whaler's Arms by 1847. The public house features prominently in John Rae's well-known picture of Millers Point. Though dated as 1842, the picture can be no earlier than 1845 Rae's picture shows the site of numbers 75–77 as vacant, with a low brick wall on the Lower Fort Street frontage. This is confirmed by later maps, which indicate only a few sheds on the land.

It is evident from Rae's picture of the corner public house that this building was intended for an extension to the north along Lower Fort Street. It was not uncommon to have a corner inn or store joined to a row of terrace houses. The subject site was used as a vacant yard and housed some temporary structures such as sheds and stabling, but the sloping nature of the site was not well suited for this use.

The site remained vacant, save for temporary structures until 1928, when the Sydney Harbour Trust constructed the existing shop and residence. The building was used as a shop and residence from its date of construction until December 2011.

The enclosed verandah to the rear of the building at ground floor level was added in 1937.

Description
An Inter-war Free Classical style building with external walls of dark red-brown face brick and decorated with rendered and painted bands and parapet detailing. It was built as a shop and residence with garage underneath. It reads as two storeys facing Lower Fort Street and three storeys to Downshire Street.

At ground floor level fronting Lower Fort Street is a glazed shopfront with central recessed door opening. The shopfront takes up most of the ground floor facade area and on its southern side there is a timber framed glazed entry door to the residence. An original suspended, riveted steel awning projects across the entire front elevation of the building.

The first floor has three double hung nine pane sash windows with transom lights above. There is a high parapet concealing the skillion roof.

The rear western elevation features common brickwork with decorative brickwork over the openings. At ground floor level there is timber enclosed verandah. There are three double hung windows with multi-paned sashes at first floor level. Below the verandah is the original garage door opening and timber window to the existing laundry.

The main internal spaces of the building at all three levels are largely intact. Significant internal fabric includes the original and early doors and timber joinery, fireplaces, timber fretwork stair rails, timber flooring, compressed composite fibre boarded ceilings with timber straps and rolled steel joists.

Significance

No. 75–77 Lower Fort Street is a rare surviving example of a purpose designed and built Inter-War Period Free Classical Style shop and residence. With the Hero of Waterloo Hotel at No. 81–83, and its neighbour at 79 Lower Fort Street, it represents the commercial-retail hub that played an important part in servicing the local community. The building has social significance as it has been used for its intended purpose as a local shop and residence continuously for 83 years (from 1928 until 2011) serving the local community. It demonstrates the intervention of the Sydney Harbour Trust in promoting local community facilities in the context of the major reconstruction works undertaken following the outbreak of the bubonic plague. This purpose built retail and residential building is an important component in the long line of important structures along the western side of Lower Fort Street which have contributed to the character of the State significant Millers Point Conservation Area.

Heritage listing

75–77 Lower Fort Street was listed on the New South Wales State Heritage Register on 2 April 1999.

See also

Eagleton Terrace, 67–73 Lower Fort Street
79 Lower Fort Street

References

Bibliography

Attribution

External links

New South Wales State Heritage Register sites located in Millers Point
Houses in Millers Point, New South Wales
Retail buildings in New South Wales
Articles incorporating text from the New South Wales State Heritage Register
1928 establishments in Australia
Buildings and structures completed in 1928
Millers Point Conservation Area

75-77 Lower Fort Street, Millers Point


In the mathematical field of graph theory, a spanning tree T of an undirected graph G is a subgraph that is a tree which includes all of the vertices of G. In general, a graph may have several spanning trees, but a graph that is not connected will not contain a spanning tree (see about spanning forests below). If all of the edges of G are also edges of a spanning tree T of G, then G is a tree and is identical to T (that is, a tree has a unique spanning tree and it is itself).

Applications
Several pathfinding algorithms, including Dijkstra's algorithm and the A* search algorithm, internally build a spanning tree as an intermediate step in solving the problem.

In order to minimize the cost of power networks, wiring connections, piping, automatic speech recognition, etc., people often use algorithms that gradually build a spanning tree (or many such trees) as intermediate steps in the process of finding the minimum spanning tree.

The Internet and many other telecommunications networks have transmission links that connect nodes together in a mesh topology that includes some loops.
In order to avoid bridge loops and routing loops, many routing protocols designed for such networks—including the Spanning Tree Protocol, Open Shortest Path First, Link-state routing protocol, Augmented tree-based routing, etc.—require each router to remember a spanning tree.

A special kind of spanning tree, the Xuong tree, is used in topological graph theory to find graph embeddings with maximum genus. A Xuong tree is a spanning tree such that, in the remaining graph, the number of connected components with an odd number of edges is as small as possible. A Xuong tree and an associated maximum-genus embedding can be found in polynomial time.

Definitions
A tree is a connected undirected graph with no cycles. It is a spanning tree of a graph G if it spans G (that is, it includes every vertex of G) and is a subgraph of G (every edge in the tree belongs to G). A spanning tree of a connected graph G can also be defined as a maximal set of edges of G that contains no cycle, or as a minimal set of edges that connect all vertices.

Fundamental cycles
Adding just one edge to a spanning tree will create a cycle; such a cycle is called a fundamental cycle with respect to that tree. There is a distinct fundamental cycle for each edge not in the spanning tree; thus, there is a one-to-one correspondence between fundamental cycles and  edges not in the spanning tree.  For a connected graph with V vertices, any spanning tree will have V − 1 edges, and thus, a graph of E edges and one of its spanning trees will have E − V + 1 fundamental cycles (The number of edges subtracted by number of edges included in a spanning tree; giving the number of edges not included in the spanning tree). For any given spanning tree the set of all E − V + 1 fundamental cycles forms a cycle basis, i.e., a basis for the cycle space.

Fundamental cutsets
Dual to the notion of a fundamental cycle is the notion of a fundamental cutset with respect to a given spanning tree. By deleting just one edge of the spanning tree, the vertices are partitioned into two disjoint sets. The fundamental cutset is defined as the set of edges that must be removed from the graph G to accomplish the same partition. Thus, each spanning tree defines a set of V − 1 fundamental cutsets, one for each edge of the spanning tree.

The duality between fundamental cutsets and fundamental cycles is established by noting that cycle edges not in the spanning tree can only appear in the cutsets of the other edges in the cycle; and vice versa: edges in a cutset can only appear in those cycles containing the edge corresponding to the cutset. This duality can also be expressed using the theory of matroids, according to which a spanning tree is a base of the graphic matroid, a fundamental cycle is the unique circuit within the set formed by adding one element to the base, and fundamental cutsets are defined in the same way from the dual matroid.

Spanning forests
A collection of disjoint (unconnected) trees is described as a forest (See Tree_(data_structure)#Terminology).  A spanning forest in a graph is a subgraph that is a forest with an additional requirement.  There are two incompatible requirements in use, of which one is relatively rare.

 Almost all graph theory books and articles define a spanning forest as a forest that spans all of the vertices, meaning only that each vertex of the graph is a vertex in the forest. A connected graph may have a disconnected spanning forest, such as the forest with no edges, in which each vertex forms a single-vertex tree.

 A few graph theory authors define a spanning forest to be a maximal acyclic subgraph of the given graph, or equivalently a subgraph consisting of a spanning tree in each connected component of the graph.

To avoid confusion between these two definitions,  suggest the term "full spanning forest" for a spanning forest with the same number of components as the given graph (i.e., a maximal forest), while  instead call this kind of forest a "maximal spanning forest" (which is redundant, as a maximal forest necessarily contains every vertex).

Counting spanning trees

The number t(G) of spanning trees of a connected graph is a well-studied invariant.

In specific graphs
In some cases, it is easy to calculate t(G) directly:
 If G is itself a tree, then .
 When G is the cycle graph Cn with n vertices, then .
 For a complete graph  with n vertices, Cayley's formula gives the number of spanning trees as .
 If G is the complete bipartite graph ,then .
 For the n-dimensional hypercube graph , the number of spanning trees is .

In arbitrary graphs

More generally, for any graph G, the number t(G) can be calculated in polynomial time as the determinant of a matrix derived from the graph,
using Kirchhoff's matrix-tree theorem.

Specifically, to compute t(G), one constructs the Laplacian matrix of the graph, a square matrix in which the rows and columns are both indexed by the vertices of G. The entry in row i and column j is one of three values:
 The degree of vertex i, if i = j,
 −1, if vertices i and j are adjacent, or
 0, if vertices i and j are different from each other but not adjacent.
The resulting matrix is singular, so its determinant is zero. However, deleting the row and column for an arbitrarily chosen vertex leads to a smaller matrix whose determinant is exactly t(G).

Deletion-contraction
If G is a graph or multigraph and e is an arbitrary edge of G, then the number t(G) of spanning trees of G satisfies the deletion-contraction recurrence
t(G) = t(G − e) + t(G/e), where G − e is the multigraph obtained by deleting e
and G/e is the contraction of G by e. The term t(G − e) in this formula counts the spanning trees of G that do not use edge e, and the term t(G/e) counts the spanning trees of G that use e.

In this formula, if the given graph G is a multigraph, or if a contraction causes two vertices to be connected to each other by multiple edges,
then the redundant edges should not be removed, as that would lead to the wrong total. For instance a bond graph connecting two vertices by k edges has k different spanning trees, each consisting of a single one of these edges.

Tutte polynomial

The Tutte polynomial of a graph can be defined as a sum, over the spanning trees of the graph, of terms computed from the "internal activity" and "external activity" of the tree. Its value at the arguments (1,1) is the number of spanning trees or, in a disconnected graph, the number of maximal spanning forests.

The Tutte polynomial can also be computed using a deletion-contraction recurrence, but its computational complexity is high: for many values of its arguments, computing it exactly is #P-complete, and it is also hard to approximate with a guaranteed approximation ratio. The point (1,1), at which it can be evaluated using Kirchhoff's theorem, is one of the few exceptions.

Algorithms

Construction
A single spanning tree of a graph can be found in linear time by either depth-first search or breadth-first search. Both of these algorithms explore the given graph, starting from an arbitrary vertex v, by looping through the neighbors of the vertices they discover and adding each unexplored neighbor to a data structure to be explored later. They differ in whether this data structure is a  stack (in the case of depth-first search) or a  queue (in the case of breadth-first search). In either case, one can form a spanning tree by connecting each vertex, other than the root vertex v, to the vertex from which it was discovered. This tree is known as a depth-first search tree or a breadth-first search tree according to the graph exploration algorithm used to construct it. Depth-first search trees are a special case of a class of spanning trees called Trémaux trees, named after the 19th-century discoverer of depth-first search.

Spanning trees are important in parallel and distributed computing, as a way of maintaining communications between a set of processors; see for instance the Spanning Tree Protocol used by OSI link layer devices or the Shout (protocol) for distributed computing. However, the depth-first and breadth-first methods for constructing spanning trees on sequential computers are not well suited for parallel and distributed computers. Instead, researchers have devised several more specialized algorithms for finding spanning trees in these models of computation.

Optimization
In certain fields of graph theory it is often useful to find a minimum spanning tree of a weighted graph. Other optimization problems on spanning trees have also been studied, including the maximum spanning tree, the minimum tree that spans at least k vertices, the spanning tree with the fewest edges per vertex, the spanning tree with the largest number of leaves, the spanning tree with the fewest leaves (closely related to the Hamiltonian path problem), the minimum diameter spanning tree, and the minimum dilation spanning tree.

Optimal spanning tree problems have also been studied for finite sets of points in a geometric space such as the Euclidean plane. For such an input, a spanning tree is again a tree that has as its vertices the given points. The quality of the tree is measured in the same way as in a graph, using the Euclidean distance between pairs of points as the weight for each edge. Thus, for instance, a Euclidean minimum spanning tree is the same as a graph minimum spanning tree in a complete graph with Euclidean edge weights. However, it is not necessary to construct this graph in order to solve the optimization problem; the Euclidean minimum spanning tree problem, for instance, can be solved more efficiently in O(n log n) time by constructing the Delaunay triangulation and then applying a linear time planar graph minimum spanning tree algorithm to the resulting triangulation.

Randomization
A spanning tree chosen randomly from among all the spanning trees with equal probability is called a uniform spanning tree. Wilson's algorithm can be used to generate uniform spanning trees in polynomial time by a process of taking a random walk on the given graph and erasing the cycles created by this walk.

An alternative model for generating spanning trees randomly but not uniformly is the random minimal spanning tree. In this model, the edges of the graph are assigned random weights and then the minimum spanning tree of the weighted graph is constructed.

Enumeration
Because a graph may have exponentially many spanning trees, it is not possible to list them all in polynomial time. However, algorithms are known for listing all spanning trees in polynomial time per tree.

In infinite graphs
Every finite connected graph has a spanning tree. However, for infinite connected graphs, the existence of spanning trees is equivalent to the axiom of choice. An infinite graph is connected if each pair of its vertices forms the pair of endpoints of a finite path. As with finite graphs, a tree is a connected graph with no finite cycles, and a spanning tree can be defined either as a maximal acyclic set of edges or as a tree that contains every vertex.

The trees within a graph may be partially ordered by their subgraph relation, and any infinite chain in this partial order has an upper bound (the union of the trees in the chain). Zorn's lemma, one of many equivalent statements to the axiom of choice, requires that a partial order in which all chains are upper bounded have a maximal element; in the partial order on the trees of the graph, this maximal element must be a spanning tree. Therefore, if Zorn's lemma is assumed, every infinite connected graph has a spanning tree.

In the other direction, given a family of sets, it is possible to construct an infinite graph such that every spanning tree of the graph corresponds to a choice function of the family of sets. Therefore,
if every infinite connected graph has a spanning tree, then the axiom of choice is true.

In directed multigraphs
The idea of a spanning tree can be generalized to directed multigraphs. Given a vertex v on a directed multigraph G, an oriented spanning tree T rooted at v is an acyclic subgraph of G in which every vertex other than v has outdegree 1. This definition is only satisfied when the "branches" of T point towards v.

See also
 Flooding algorithm
 Good spanning tree – Spanning tree for embedded planar graph

References

Axiom of choice
Computational problems in graph theory

Spanning tree


Ernest Godward was born in Marylebone, London on 7 April 1869. He was the son of Henry Robert Godward, a fireman, and his wife, Sarah Ann Pattison. He lived in England, New Zealand and the United States.   He created the spiral hairpin and a type of carburettor called a petrol economiser, which boosted engine performance and reduced fuel consumption. He also invented the Non-slip Egg Beater
, a new post-hole borer, a new type of hair curler, a burglar-proof window and a hedge trimmer made from bicycle parts.

1869 births
Inventors
1936 deaths

Ernest Godward


Paulette Wilson (1956 – 23 July 2020) was a British immigrant rights activist. She fought her own deportation to Jamaica and brought media attention to the human rights violations of the Windrush scandal. Under the terms of the British Nationality Act 1948, Wilson had arrived in England as citizens of the British Empire.

In 2015, Wilson received notification from the government that she was an illegal immigrant and was required to leave the UK. Her housing and health care benefits were stopped. She became homeless and was denied the right to seek work.

By 2017, Wilson was facing deportation. She had not returned to Jamaica for 50 years, but was arrested twice, detained in Yarl's Wood Detention Centre and then sent to the deportation centre at Heathrow Airport in October 2017.

The Refugee and Migrant Centre of Wolverhampton persuaded her MP, Emma Reynolds, to stop the deportation at the last minute to allow Wilson more time to appeal to the Home Office. In 2018, she was officially granted leave to remain.

Wilson died on 23 July 2020 in Wolverhampton, West Midlands, England at the age of 64.

References

1956 births
2020 deaths
British activists

Paulette Wilson


Cave-diving is underwater diving in water-filled caves. It may be done as an extreme sport, a way of exploring flooded caves for scientific investigation, or for the search for and recovery of divers or, as in the 2018 Thai cave rescue, other cave users. The equipment used varies depending on the circumstances, and ranges from breath hold to surface supplied, but almost all cave-diving is done using scuba equipment, often in specialised configurations with redundancies such as sidemount or backmounted twinset. Recreational cave-diving is generally considered to be a type of technical diving due to the lack of a free surface during large parts of the dive, and often involves planned decompression stops. A distinction is made by recreational diver training agencies between cave-diving and cavern-diving, where cavern diving is deemed to be diving in those parts of a cave where the exit to open water can be seen by natural light. An arbitrary distance limit to the open water surface may also be specified.

Equipment, procedures, and the requisite skills have been developed to reduce the risk of becoming lost in a flooded cave, and consequently drowning when the breathing gas supply runs out. The equipment aspect largely involves the provision of an adequate breathing gas supply to cover reasonably foreseeable contingencies, redundant dive lights and other safety critical equipment, and the use of a continuous guideline leading the divers back out of the overhead environment. The skills and procedures include effective management of the equipment, and procedures to recover from foreseeable contingencies and emergencies, both by individual divers, and by the teams that dive together.

In the United Kingdom, cave-diving developed from the locally more common activity of caving. Its origins in the United States are more closely associated with recreational scuba diving. Compared to caving and scuba diving, there are relatively few practitioners of cave-diving. This is due in part to the specialized equipment and skill sets required, and in part because of the high potential risks due to the specific environment.

Despite these risks, water-filled caves attract scuba divers, cavers, and speleologists due to their often unexplored nature, and present divers with a technical diving challenge. Underwater caves have a wide range of physical features, and can contain fauna not found elsewhere. Several organisations dedicated to cave diving safety and exploration exist, and several agencies provide specialised training in the skills and procedures considered necessary for acceptable safety.

Cavern diving
Cavern diving is an arbitrarily defined, limited scope activity of diving in the naturally illuminated part of underwater caves, where the risk of getting lost is small, as the exit can be seen, and the equipment needed is reduced due to the limited distance to surface air. It is defined as a recreational diving activity as opposed to a technical diving activity on the grounds of low risk and basic equipment requirements.

Procedures

The procedures of cave-diving have much in common with procedures used for other types of penetration diving. They differ from open-water diving procedures mainly in the emphasis on navigation, gas management, operating in confined spaces, and that the diver is physically constrained from direct ascent to the surface during much of the dive.

As most cave-diving is done in an environment where there is no free surface with breathable air allowing an above-water exit, it is critically important to be able to find the way out before the breathing gas runs out. This is ensured by the use of a continuous guideline between the dive team and a point outside of the flooded part of the cave, and diligent planning and monitoring of gas supplies. Two basic types of guideline are used: permanent lines, and temporary lines. Permanent lines may include a main line starting near the entrance/exit, and side lines or branch lines, and are marked to indicate the direction along the line to the nearest exit. Temporary lines include exploration lines and jump lines.

Decompression procedures may take into account that the cave diver usually follows a very rigidly constrained and precisely defined route, both into and out of the cave, and can reasonably expect to find any equipment such as drop cylinders temporarily stored along the guideline while making the exit. In some caves, changes of depth of the cave along the dive route will constrain decompression depths, and gas mixtures and decompression schedules can be tailored to take this into account.

Skills

Most open-water diving skills apply to cave-diving, and there are additional skills specific to the environment, and to the chosen equipment configuration.
Good buoyancy control, trim and finning technique help preserve visibility in areas with silt deposits. The ability to reverse kick to back out of restrictions where there is no space to turn around is useful.
Finning skills: Frog kick, which avoids up- and downward directed vortices and are less likely to disturb silt on the bottom or loose material on the ceiling, and modified frog kick, a version which is more suited to narrow spaces; modified flutter kick, a version of flutter kick which minimises downward directed vortices; back kick, which produces thrust towards the feet, used to move backwards along the long axis of the diver, and helicopter turns, which rotate the diver on the spot around a vertical axis, using lower leg and ankle movements.
The ability to navigate in total darkness using the guideline to find the way out is a safety critical emergency skill. Line management skills required for cave-diving include laying and recovering guide lines using a reel, tie-offs, the use of a jump line to cross gaps or find a lost guide line in silted out conditions, identifying the direction along the guideline leading to the exit, and the skills of dealing with a break in a guideline.
Emergency skills for dealing with gas supply problems are complicated by the possibility of the emergency occurring in a confined space and low visibility or darkness, and at a considerable horizontal distance from a free surface to the atmosphere.
Communicating by touch and light signals.
Providing and receiving emergency breathing gas while swimming through narrow spaces.

Line management

The essential cave-diving procedure is navigation using a guide line. This includes laying and marking line, following line and interpreting line markers, avoiding entanglement, recovering from entanglement, maintaining and repairing line, finding lost line, jumping gaps, and recovering line, any of which may need to be done in zero visibility, total darkness, tight confined spaces or a combination of these conditions.
Laying a cave line: the procedure of running line (unreeling line under light tension as one advances) to avoid snagging on the diver and so that it runs fairly straight between s, placing the line so it can all be seen and reached, so it can be followed in good or bad visibility, avoiding s, and securing the line sufficiently at suitable places to keep it in position.
Making placements - securing the guideline as it is being run and the choice of primary and secondary tie offs.
Temporary line – line that is laid on the way into parts of a cave without permanent line, and recovered to the reel on the way out.
Permanent line – line that is thicker, and therefore easier to see, stronger, and more abrasion resistant, and more securely fastened, intended to be left in place for use by other divers. It may be secured to placements at closer intervals to facilitate finding the other end and reconnection in case of a break. It is not recovered during exit, and will generally be marked.
Marking line: Permanent line is marked to indicate the direction to the nearest exit, and to indicate where dive teams have passed but have not yet returned by looping the line onto a line marker, ensuring that a directional marker points in the correct direction, and that all markers are sufficiently securely attached, while remaining easily removable if temporary.
Directional markers - cave arrows used to indicate the way out along the line.
Personal markers – cookies – temporary markers to indicate that a diver has passed beyond a point but has not returned yet, particularly where the group leaves the permanent line or makes a jump to a secondary permanent (branch) line. A personal directional marker may be attached to a line to indicate that the owner has gone in that direction, which can happen after divers are separated if one finds the line  but not the other divers, and decides to exit independently.
Following a line – the skills of navigating back out of a cave using the line as a guide, particularly in the dark and low visibility.
Finding a lost line: although cave-diving procedures are intended to minimize the risk of losing the guide line, it can happen, and as the chance of finding one's way out without the line are drastically reduced, losing the line is considered a life-threatening situation, and the diver must be competent in the methods for relocating the line in all reasonably foreseeable circumstances, which include a bad silt-out, total darkness, and loss of contact with the other divers in the team. Methods of search should prevent the diver from drifting away from the vicinity of the line, so the start position for the search should be secured by tying off a search line. In principle, if the diver feels their way around the cross section of the cave orthogonal to the line direction until they get back to the starting point, the guideline should be either found directly, or be within the loop of the search line, but even this is not guaranteed to work, as the shape of the cave and limited breathing gas supplies could make this impossible.
Fixing a line break, This requires the ability to tie reliable knots, which may have to be done in bad visibility. It also require the diver to find the other end of the break. On the way into a cave a line break is an inconvenience, as if the other side cannot be found, the divers can still find their way out. On the way out a line break is a life-threatening emergency until the other end is found, as gas supply is limited and there is no infallible way to find the other end while there is enough gas to complete the exit.
Jumping a gap to a branch line – this involves tying off to the permanent line in a way that is unlikely to come loose, but may be released quickly on the return. Passing a loop on the end of the jump line round the permanent line and over the reel is a standard method. A tag on the end of the loop helps release it quickly. This method cannot be inadvertently released by other divers following the main line.
Recovering temporary line – this is done by the last diver in line on the way out, so the others can follow the line out of the cave, even in reduced visibility, without risking losing the line. They may prepare the line for the reel operator, by releasing tie-offs, which cuts down on delays. In an emergency exit the reel and line may be temporarily abandoned, as it can be retrieved later. The reel operator keeps a light tension on the line and tries to keep it evenly distributed over the width of the reel while winding in. The divers further ahead on the line can feel the presence of others behind them by line tension and small movements of the line as it is reeled in.

Lost line
Losing the guide line in a cave is a potentially life-threatening emergency. While following recommended best practice makes it highly unlikely that a diver will lose the line, it can and does happen, and there are procedures which will usually work to find it again. Any reliable information on where the diver is likely to be relative to the last known position of the line may be critical, and the procedure of choice will depend on what is reliably known. In all situations, the diver will attempt to stabilise the situation and avoid getting further lost, and make a thorough visual check in all directions from where they are at the time, taking into account the possibility of the line being in a line trap. If the diver has not also separated from their buddy, the buddy may know where the line is, and can be asked, and if the diver is separated from their buddy, the buddy may be at the line, and the buddy's light may be visible.

Stabilising the position is generally done by finding the nearest feasible tie-off point and securely tying off a search line.  The direction of the guide line when last seen should be known, and therefore the direction the diver was swimming in before losing the line. If the diver was neutrally buoyant while following the line, the approximate depth can be reconstructed by finding the depth of neutral buoyancy again, without adjusting inflation of BCD or dry suit. Unless the line was lost by the diver not noticing a change of direction, it is likely to be at much the same depth, in much the same direction, and at a similar lateral and vertical distance as when last seen, making it logical to try that direction first. While swimming towards the estimated position of the line and slowly paying out search line, the diver will search visually, and in low visibility or darkness, also by feel, making arm sweeps across the expected direction of the line, while defending the head from impact with the other arm. The distance swum towards the estimated position of the lost line can be  measured by the spacing and number of knots paid out on the search line. If the search fails, the diver will return to the tie off and try again in the next best guess for the direction the line may be. The diver may also choose to try a different search method. The best search method for any given situation will depend on the water conditions, the layout of the section of cave, the way the line was laid, the situational knowledge and skills of the diver, and the equipment available – a method that would be ideal for one situation might not work at all for another.

If the line is found, but not the other divers, the diver can tie off their search reel to the guide line as an indicator to other members of the team that they were lost but have found the guide line, and indicate the direction that they intend to proceed along the guideline with a personal directional marker so that others who see it while searching for the lost diver will know whether the diver chose the right direction to exit the cave.

Lost buddy
This is generally the converse situation to the lost guide line, in that the diver loses contact with their buddy or team but remains in contact with the guide line, so is not themselves lost. Their first priority is to not get lost or disorientated, and in furtherance of this aim would attach a directional line marker to the guide line indicating the direction to the exit before starting a search. The search line can be tied to the directional marker to prevent it from sliding along the line during the search. The direction for the search would depend on the layout of that part of the cave, and where the missing diver should have been in the group. The search party must consider their own safety first, regarding how much gas they can afford to use in a search, which will depend on the stage of the dive when the diver is noticed to be missing. When searching in darkness, the searches should periodically turn off their lights as this will allow them to see the lost diver's light more easily.

Gas planning and management

Gas planning is the aspect of dive planning which deals with the calculation or estimation of the amounts and mixtures of gases to be used for a planned dive profile. It usually assumes that the dive profile, including decompression, is known, but the process may be iterative, involving changes to the dive profile as a consequence of the gas requirement calculation, or changes to the gas mixtures chosen. Use of calculated reserves based on planned dive profile and estimated gas consumption rates rather than an arbitrary pressure  based on a fraction of the initial gas supply is sometimes referred to as rock bottom gas management. The purpose of gas planning is to ensure that for all reasonably foreseeable contingencies, the divers of a team have sufficient breathing gas to safely return to a place where more breathing gas is available. In almost all cases this will be the surface.

Gas planning includes the following aspects:
 Choice of breathing gases to suit the depth at which they will be used,
 Choice of scuba configuration, to conveniently carry the gas, or store it at stage points along the route
 Estimation of gas quantities required for the planned dive, including , , and decompression gases, as appropriate to the profile.
 Estimation of gas quantities for reasonably foreseeable contingencies. Under stress it is likely that a diver will increase breathing rate and decrease swimming speed. Both of these lead to a higher gas consumption during an emergency exit or ascent.
 Choice of cylinders to carry the required gases. Each cylinder volume and working pressure must be sufficient to contain the required quantity of gas.
 Calculation of the pressures for each of the gases in each of the cylinders to provide the required quantities.
 Specifying the critical pressures of relevant gas mixtures for appropriate stages (waypoints) of the planned dive profile (gas matching).
The primary breathing apparatus may be open circuit scuba or rebreather, and bailout may also be open circuit or rebreather. Emergency gas may be shared among the team members, or each diver may carry their own, but in all cases each diver must be able to bail out onto a gas supply of their own for long enough to get to the next planned source of emergency gas. If for any reason this situation no longer applies, there is a single point of critical failure, and the risk becomes unacceptable, so the dive should be turned.

Gas management also includes the blending, filling, analysing, marking, storage, and transportation of gas cylinders for a dive, and the monitoring and switching of breathing gases during a dive, and the provision of emergency gas to another member of the dive team. The primary aim is to ensure that everyone has enough to breathe of a gas suitable for the current depth at all times, and is aware of the gas mixture in use and its effect on decompression obligations and oxygen toxicity risk.

Gas management rules of thumb

The rule of thirds for gas management is a rule of thumb used by divers to plan dives so they have enough  breathing gas remaining in their diving cylinder at the end of the dive to be able to complete the dive safely. This rule mostly applies to diving in overhead environments, such as caves and wrecks, where a direct ascent to the surface is impossible and the divers must return the way they came.

For divers following the rule, one third of the gas supply is planned for the outward journey, one third is for the return journey and one third is a safety reserve. However, when diving with a buddy with a higher breathing rate or a different volume of gas, it may be necessary to set one third of the buddy's gas supply as the remaining 'third'. This means that the turn point to exit is earlier, or that the diver with the lower breathing rate carries a larger volume of gas than he alone requires.

A different option for penetration dives is the Half + 15 bar (half + 200 psi) method, in which the contingency gas for the stage is carried in the primary cylinders. Some divers consider this method to be the most conservative when multi-staging. If all goes to plan when using this method, the divers surface with stages nearly empty, but with all the contingency gas still in their primary cylinders. With a single stage drop, this means the primary cylinders will still be about half-full.

Training
Cave-diving training includes equipment selection and configuration, guideline protocols and techniques, gas management protocols, communication techniques, propulsion techniques, emergency management protocols, and psychological education. Cave diver training also stresses the importance of risk management and cave conservation ethics. Most training systems offer progressive stages of education and certification.

Cavern training covers the basic skills needed to enter the overhead environment. Training will generally consist of gas planning, propulsion techniques needed to deal with the silty environments in many caves, reel and handling, and communication. Once certified as a cavern diver, a diver may undertake cavern diving with a cavern or cave certified "buddy", as well as continue into cave-diving training.
Introduction into cave training builds on the techniques learned during cavern training and includes the training needed to penetrate beyond the cavern zone and working with permanent guidelines that exist in many caves. Once intro to cave certified, a diver may penetrate much further into a cave, usually limited by 1/3 of a single cylinder, or in the case of a basic cave certification, 1/6 of double cylinders. An intro cave diver is usually not certified to do complex navigation.
Apprentice cave training serves as the transition from intro to full certification and includes the training needed to penetrate deep into caves working from permanent guide lines as well as limited exposure to side lines that exist in many caves. Training covers complex dive planning and decompression procedures used for longer dives. Once apprentice certified, a diver may penetrate much further into a cave, usually limited by 1/3 of double cylinders. An apprentice diver is also allowed to do a single jump or gap (a break in the guideline from two sections of mainline or between mainline and sideline) during the dive. An apprentice diver typically has one year to finish full cave or must repeat the apprentice stage.
Full cave training serves as the final level of basic training and includes the training needed to penetrate deep into the cave working from both permanent guidelines and sidelines, and may plan and complete complex dives deep into a system using decompression to stay longer. Once cave certified, a diver may penetrate much further into a cave, usually limited by 1/3 of double cylinders. A cave diver is also certified as competent to do multiple jumps or gaps (a break in the guideline from two sections of mainline or between mainline and sideline) during the dive.
 Further training may be available in skills for cave surveying and mapping.

Exploration, surveys and mapping
A significant aspect of cave diving by competent and enthusiastic cave divers is exploration, survey and mapping. Data collected is often shared and may be stored on databases to help optimise the effectiveness of such surveys, and make the information generally available.

Underwater cave mapping is complicated by both a lack of access to the surface for GPS positions, darkness, with short line-of-sight, and limited visibility, which complicate optical measurement. Altitude/depth is relatively simple as accurate depth measurement is available to divers in the form of decompression computers, which log a depth/time record of reasonable accuracy and are available for instantaneous readout at any point, and depth can be referenced to the altitude at the surface. Vertical dimensions can be directly measured or calculated as differences in depth.

Surface coordinates can be collected via GPS and remote sensing, with varying degrees of precision and accuracy depending on the type of entrance. In some caves the water surface is in view of GPS satellites, in others it is a considerable distance along a complex route from the nearest open air. Three dimensional models of varying accuracy and detail can be created by processing measurements collected by whatever methods were available. These can be used in virtual reality models. The usual methods for survey and mapping of underwater caves are dead reckoning and direct measurements of distance, compass direction and depth, by diving teams of two or three scuba divers, who record azimuth of the cave line, measurements of height, width, depth, and slope at intervals along the line, generally using a permanent guide line as a reference baseline, and take photographic records of features and objects of interest. Data are collected on  and by digital photography. Hand-held sonar may be used for distance measurement where available. Where the depth or other constraints prevent divers from exploring in person, tethered and untethered remotely operated underwater vehicles (ROUVs) have been used effectively, using sonar technology to scan and map the surroundings, and video to record the appearance.

Features, artifacts, remains, and other objects of interest
are recorded in situ as effectively as possible, generally by photography.

Hazards
Cave-diving is one of the most challenging and potentially dangerous kinds of diving and presents many hazards. Cave-diving is a form of penetration diving, meaning that in an emergency a diver cannot swim vertically to the surface due to the cave's ceilings, and so must swim the entire way back out. The underwater navigation through the cave system may be difficult and exit routes may be at a considerable distance, requiring the diver to have sufficient breathing gas to make the journey. The dive may also be deep, resulting in potential deep diving risks.

Visibility can vary from nearly unlimited to low, or non-existent, and can go from very good to very bad in a single dive. While a less-intensive kind of diving called cavern diving does not take divers beyond the reach of natural light (and typically no deeper than ), and penetration not further than , true cave-diving can involve penetrations of many thousands of feet, well beyond the reach of sunlight. The level of darkness experienced creates an environment impossible to see in without an artificial source of light even if the water is clear. Caves often contain sand, mud, clay, silt, or other sediment that can further reduce underwater visibility in seconds when stirred up. Consequently, visibility is often worse during exit, and divers rely on the guideline for finding the way out.

The water in caves can have strong flow. Most caves flooded to the surface at the cave mouth are either springs or siphons. Springs have out-flowing currents, where water is coming up out of the Earth and flowing out across the land's surface. Siphons have in-flowing currents where, for example, an above-ground river is going underground. Some caves are complex and have some tunnels with out-flowing currents, and other tunnels with in-flowing currents. Inflowing currents can cause serious problems for the diver, as they make the exit more difficult, and the diver is carried to spaces that are unfamiliar and may be dangerous, while outflowing currents generally make the exit quicker and the diver is carried through places they have been before and can be prepared for difficult areas.

Cave-diving has been perceived as one of the more deadly sports in the world. This perception may be exaggerated because the majority of divers who have died in caves have either not undergone specialized training or have had inadequate equipment for the environment. Some cave divers have suggested that cave-diving is statistically much safer than recreational diving due to the much larger barriers imposed by experience, training, and equipment cost, but there is no definitive statistical evidence for this claim.

There is no reliable worldwide database listing all cave-diving fatalities. Such fractional statistics as are available, however, suggest that few divers have died while following accepted protocols and while using equipment configurations recognized as acceptable by the cave-diving community. In the very rare cases of exceptions to this rule there have typically been unusual circumstances.

Safety

Most cave divers recognize five general rules or contributing factors for safe cave-diving, which were popularized, adapted and became generally accepted from Sheck Exley's 1979 publication Basic Cave Diving: A Blueprint for Survival. In this book, Exley included accounts of actual cave-diving accidents, and followed each one with a breakdown of what factors contributed to the accident. Despite the unique circumstances of each individual accident, Exley found that at least one of a small number of major factors contributed to each one. This technique for breaking down accident reports and finding common causes among them is now called accident analysis, and is taught in introductory cave-diving courses. Exley outlined a number of these resulting cave-diving rules, but today these five are the most recognized:
Training: A safety conscious cave diver does not intentionally exceed the scope of their training. Cave-diving is normally taught in stages, each successive stage focusing on more complex aspects of cave-diving. Each stage of training is intended to be reinforced with actual cave-diving experience to develop competence before starting training at a more complex level. Accident analysis of cave-diving fatalities has shown that academic training without sufficient real world experience is not always enough in the event of an underwater emergency. By systematically building experience the diver can develop the confidence, motor skills and reflexes to remain calm and apply the appropriate procedures in an emergency. An inexperienced diver is more likely to panic than an experienced diver when confronted with a similar situation, all other factors being equal. Experience in dealing successfully with real or simulated problems is of the greatest value, experience of dives where nothing goes wrong reinforces the skills used, but not the skills that were not needed but might be critical in an emergency. When trained to the highest available level, further competence can be developed by practice and gradual extension of range of experience.
Guide line: A continuous guide line is maintained at all times between the leader of a dive team and a fixed point selected outside the cave entrance in open water. Often this line is tied off a second time as a backup directly inside the cavern zone. As the dive leader lays the guideline they take great care to ensure there is appropriate tension on the line, and that it does not go into line traps, tying off the line as necessary to keep it leading through a clear route. Other team members remain between the lead diver and the exit, in easy reach of the line at all times. If a silt out occurs, divers can find the line and follow it back to the cave entrance. Failure to use a continuous guide line to open water is cited as the most frequent cause of fatality among untrained, non-certified divers who venture into caves. Greater care to avoid line traps is required for laying permanent line, and more frequent tie-offs would be expected, as a permanent line is more susceptible to breaking over time.
Depth rules: Gas consumption, nitrogen narcosis and decompression obligation increase with depth, and the effects of nitrogen narcosis may be more critical in a cave due to the high task loading and presence of combinations of hazards. Cave divers are advised not to dive to depths exceeding the planned depth and the applicable range of their equipment and the breathing gases in use, and to keep in mind this effective difference between open water depth and cave depth. Excessive depth is frequently cited as a contributory factor in fatal incidents involving fully trained cave divers.
Breathing gas management: The breathing gas supply must last the diver until out of the overhead environment. There are several strategies for gas management. The most common protocol is the 'rule of thirds,' in which one third of the initial gas supply is used for ingress, one third for egress, and one third to support another team member in the case of an emergency. This is a very simple method, but is not always sufficient. UK practice is to adhere to the rule of thirds, but with an added emphasis on keeping depletion of the separate air systems "balanced", so that the complete loss of any single gas supply will still leave the diver with sufficient gas to return safely. The rule of thirds makes no allowance for increased air consumption that the stress caused by the loss of an air system may induce. Dissimilar tank sizes among the divers are also not allowed for by the rule of thirds, and a sufficient reserve should be calculated for each dive. UK practice is to assume that each diver is completely independent, as in a typical UK sump there is usually nothing that a buddy can do to assist a diver in trouble. Most UK cave divers dive solo. US sump divers follow a similar protocol. The rule of thirds was devised as an approach to diving Florida's caves – they typically have high outflow currents, which help to reduce air consumption when exiting. In a cave system with little or no outflow it is prudent to reserve more air than is provided by the rule of thirds.
Lights: Each cave diver should have at least three independent sources of light. One is considered the primary and is intended for general use during the dive. The others are considered backup lights and may be lower powered as they are not intended for exploration. Each light must have an expected burn time of at least the planned duration of the dive. If any diver loses light function so that they have fewer than three working lights, protocol requires that the dive be aborted for all members of the dive team and that they immediately start the exit.

Most cave-diving fatalities are due to running out of gas before reaching the exit. This is often the direct consequence of getting lost, whether the guide line is found again or not, and whether the visibility deteriorates, lights fail, or someone panics. On rare occasions equipment failure is unrecoverable, or a diver becomes inextricably trapped, seriously injured, incapacitated by using an unsuitable gas for the depth, or swept away by strong flow. Getting lost means separation from the continuous guide line to the exit, and not knowing the direction to the exit.

Some cave divers are taught to remember the five key components with the mnemonic: "The Good Divers Always Live" (training, guide, depth, air, light).

In recent years new contributing factors were considered after reviewing accidents involving solo diving, diving with incapable dive partners, video or photography in caves, complex cave dives and cave-diving in large groups. With the establishment of technical diving, the use of mixed gases—such as trimix for bottom gas, and nitrox and oxygen for decompression—reduces the margin for error. Accident analysis suggests that breathing the wrong gas for the depth or not analyzing the breathing gas properly has also led to cave-diving accidents.

Cave-diving requires a variety of specialized procedures, and divers who do not correctly apply these procedures may significantly increase the risk to the members of their team. The cave-diving community works hard to educate the public on the risks they assume when they enter water-filled caves. Warning signs with the likenesses of the Grim Reaper have been placed just inside the openings of many popular caves in the US and Mexico, and others have been placed in nearby parking lots and local dive shops.

Many cave-diving sites around the world include open-water basins, which are popular open-water diving sites. The management of these sites try to minimize the risk of untrained divers being tempted to venture inside the cave systems. With the support of the cave-diving community, many of these sites enforce a "no-lights rule" for divers who lack cave training—they may not carry any lights into the water with them. It is easy to venture into an underwater cave with a light and not realize how far away from the entrance (and daylight) one has swum; this rule is based on the theory that, without a light, divers will not venture beyond daylight.

In the early phases of cave-diving the analysis shows that 90% of accidents were not trained cave divers; from the 2000s on the trend has reversed to 80% of accidents involving trained cave divers. Modern cave divers' capability and available technology allows divers to venture well beyond traditional training limits and into actual exploration. The result is an increase of cave-diving accidents, in 2011 the yearly average of 2.5 fatalities a year tripled. In 2012 fatalities reached the highest annual rate to that date at over 20.

As response to the increase in fatalities during the years 2010 onwards, the  International Diving Research and Exploration Organization (IDREO) was created in order to "bring awareness of the current safety situation of Cave Diving" by listing current worldwide accidents by year and promoting a community discussion and analysis of accidents through a "Cave Diver Safety Meeting" held annually.

Equipment

Equipment used by cave divers ranges from fairly standard recreational scuba configurations, to more complex arrangements which allow more freedom of movement in confined spaces, extended range in terms of depth and time, allowing greater distances to be covered in acceptable safety, and equipment which helps with navigation, in what are usually dark, and often silty and convoluted spaces.

Scuba configurations which are more often found in cave-diving than in open water diving include independent or manifolded twin cylinder rigs, side-mount harnesses, sling cylinders, rebreathers and backplate and wing harnesses. Bill Stone designed and used epoxy composite tanks for exploration of the San Agustín and Sistema Huautla caves in Mexico to decrease the weight for dry sections and vertical passages.

Stage cylinders are cylinders which are used to provide gas for a portion of the penetration. They may be deposited on the bottom at the guideline on preparation dives, to be picked up for use during the main dive, or may be carried by the divers and dropped off at the line during the penetration to be retrieved on the way out.

One of the high risk hazards of cave-diving is getting lost in the cave. The use of guide lines is the standard mitigation for this risk. Guide lines may be permanent or laid and recovered during the dive, using cave reels to deploy and recover the line. Permanent branch lines may be laid with a gap between the start of the branch line and the nearest point on the main line. Line used for this purpose is known as cave line. Gap spools with a relatively short line are commonly used to make the jump.

Line arrows are used to point towards the nearest exit, and cookies are used to indicate use of a line by a team of divers.

Silt screws are short lengths of rigid tube (usually plastic) with one sharpened end and a notch or slot at the other end to secure the line, which are pushed into the silt or detritus of the cave floor as a place to tie off a guideline when no suitable natural tie-off points are available.

A simple plastic helmet, such as those used in water sports like whitewater kayaking, is good protection in case of accidental contact with the cave ceiling or stalactites.

Diver propulsion vehicles, or Scooters, are sometimes used to extend the range by reducing the work load on the diver and allowing faster travel in open sections of cave. Reliability of the diver propulsion vehicle is very important, as a failure could compromise the ability of the diver to exit the cave before running out of gas. Where this is a significant risk, divers may tow a spare scooter.

Dive lights are critical safety equipment, as it is dark inside caves. Each diver generally carries a primary light, and at least one backup light. A minimum of three lights is recommended. The primary light should last the planned duration of the dive, as should each of the backup lights.

History
One of the earliest known cave dives was a freedive in 1922 by Norbert Casteret in the Montespan cave, France.

Jacques-Yves Cousteau, co-inventor of the first commercially successful open circuit scuba equipment, was the world's first open circuit scuba cave diver. However, many cave divers penetrated caves prior to the advent of scuba with surface supplied breathing apparatus through the use of umbilical hoses and compressors. SCUBA diving in all its forms, including cave-diving, has advanced in earnest since Cousteau introduced the Aqua-Lung in 1943.

Two regions have had particular influence on cave-diving techniques and equipment due to their very different cave-diving environments. These are the United Kingdom, and the United States, mainly Florida.

UK history

The Cave Diving Group (CDG) was established informally in the United Kingdom in 1935 to organise training and equipment for the exploration of flooded caves in the Mendip Hills of Somerset. The first dive was made by Jack Sheppard  on 4 October 1936,
using a home-made drysuit surface fed from a modified bicycle pump, which allowed Sheppard to pass Sump 1 of Swildon's Hole. Swildon's is an upstream feeder to the Wookey Hole resurgence system. The difficulty of access to the sump in Swildon's prompted operations to move to the resurgence, and the larger cave there allowed use of standard diving dress which was secured from the Siebe Gorman company. In UK cave-diving, the term "Sherpa"  was used without irony for the people who carry the diver's gear although this has gone out of fashion; support is now more normally used, and before the development of SCUBA equipment such undertakings could be monumental operations.

Diving in the spacious third chamber of Wookey Hole led to a rapid series of advances, each of which was dignified by being given a successive number, until an air surface was reached at what is now known as "Chamber 9." Some of these dives were broadcast live on BBC radio, which must have been a quite surreal experience for both diver and audience.

The number of sites where standard diving dress could be used is clearly limited and there was little further progress before the outbreak of World War II reduced the caving community considerably. However, the rapid development of underwater warfare through the war made a lot of surplus equipment available. The CDG re-formed in 1946 and progress was rapid. Typical equipment at this time was a frogman rubber diving suit for insulation (water temperature in the UK is typically 4 °C), an oxygen diving cylinder, soda lime absorbent canister and counter-lung comprising a rebreather air system and an "AFLOLAUN", meaning "Apparatus For Laying Out Line And Underwater Navigation." The AFLOLAUN consisted of lights, line-reel, compass, notebook (for the survey), batteries, and more.

Progress was typically by "bottom walking", as this was considered less dangerous than swimming (note the absence of buoyancy controls). The use of oxygen put a depth limit on the dive, which was considerably compensated by the extended dive duration. This was the normal diving equipment and methods until approximately 1960 when new techniques using wetsuits (which provide both insulation and buoyancy ), twin open-circuit SCUBA air systems the development of side mounting cylinders, helmet-mounted lights and free-swimming with fins. The increasing capacity and pressure rating of air bottles also extended dive durations.

US history
In the 1970s, cave-diving greatly increased in popularity among divers in the United States. However, there were very few experienced cave divers and almost no formal classes to handle the surge in interest. The result was a large number of divers trying to cave dive without any formal training. This resulted in more than 100 fatalities over the course of the decade. The state of Florida came close to banning SCUBA diving around the cave entrances. The cave-diving organizations responded to the problem by creating training programs and certifying instructors, in addition to other measures to try to prevent these fatalities. This included posting signs, adding no-lights rules, and other enforcements.

In the United States, Sheck Exley was a pioneering cave diver who first explored many underwater cave systems in Florida, and many throughout the US and the world. On 6 February 1974, Exley became the first chairman of the Cave Diving Section of the National Speleological Society.

Since the 1980s, cave-diving education has greatly reduced diver fatalities, and it is now rare for an agency trained diver to perish in an underwater cave. Also in the 1980s, refinements were made to the equipment used for cave-diving, most importantly better lights with smaller batteries. In the 1990s, cave-diving equipment configurations became more standardized, due mostly to the adaptation and popularization of the "Hogarthian Rig", developed by several North Florida cave divers, named in honor of William "Hogarth" Main, which promotes equipment choices that "keep it simple and streamlined".

Today, the cave community is most focused on training, exploration, public awareness, and cave conservation.

Documentary films made by Wesley C. Skiles and Jill Heinerth have contributed to the increasing popularity of cave-diving in the early 21st century.

Australian history
Four divers using scuba dived from the Right Imperial Cave in the Jenolan system in the Blue Mountains to an upstream chamber on 30 October 1954.

Organisations
Several organisations exist to support caving  and cave diving. Some of them also specifically train and certify cave divers to their own standards. There are also organisations dedicated to exploration, survey, and mapping of cave systems, both dry and flooded.

Cave Divers Association of Australia
The Cave Divers Association of Australia (CDAA) is a cave diving organisation which was formed in September 1973 to represent the interests of recreational scuba divers who dive in water‐filled caves and sinkholes principally in the Lower South East (now called the Limestone Coast) of South Australia (SA) and secondly in other parts of Australia.  Its formation occurred after a series of diving fatalities in water-filled caves and sinkholes in the Mount Gambier region between 1969 and 1973 and in parallel to a South Australian Government inquiry into these deaths.  The CDAA's major achievement has been the dramatic reduction of fatalities via the introduction of a site rating scheme and an associated testing system which was brought in during the mid-1970s.  While its major area of operation is in the Limestone Coast region of SA, it administrates and supports cave diving activity in other parts of Australia including the Nullarbor Plain and Wellington, New South Wales.

Cave Diving Group
The Cave Diving Group (CDG) is a United Kingdom-based diver training organisation specialising in cave diving.

The CDG was founded in 1946 by Graham Balcombe, making it the world's oldest continuing diving club. Graham Balcombe and Jack Sheppard  pioneered cave diving in the late 1930s, notably at Wookey Hole in Somerset.

National Association for Cave Diving

The National Association for Cave Diving (NACD) is a 501(c)3 non-profit corporation founded in 1968 with the goal of improving the safety of scuba diving in caves through diver training and education. Its headquarters are in Gainesville, Florida but administration and operations are conducted from High Springs, Florida. The NACD is overseen by a board of directors composed of seven cave divers, four instructors, and three other directors. The elected officers are a president, vice president, secretary/treasurer, and training director.  Membership is open to all who have an interest in underwater caves. The NACD publishes a quarterly journal, and various specialised publications, holds seminars, and workshops, and sponsors cave diving projects.

The goals of the NACD are:
 To establish and maintain current guidelines in the form of physical and psychological standards, as well as equipment and techniques necessary for safe cave diving,
 To encourage education and dissemination of safe cave diving information throughout the facilities of the organization and to provide a program of education and advanced training essential for safe cave diving,
 To achieve closer cooperation and understanding among members of the cave and recreational diving communities (and the general public) so they may work together toward the common goal of increasing safety in cavern and cave diving,
 To explore underwater caves and to encourage education and dissemination of information to government, private industry and the general public. To accomplish these goals the NACD is organized to provide the following services

NACD offers training and certification in cavern and cave diving, and instructor courses. The goal is not to encourage cavern or cave diving, but to aid divers in becoming safe cavern and cave divers. The NACD provides training standards to define their technical and philosophical principles of cave and cavern diving, but allows the instructors discretion and freedom use their own knowledge, experience, and teaching style, and acknowledges that many aspects of cave and cavern diving practice, procedure, and equipment configuration remain open to interpretation by equally qualified experts and that it is in the best interest of the student to be presented with differing views.

The NACD philosophy of safe cave diving is based on a system of checks and balances to insure that NACD standards are maintained in each course. The courses available are as described below:

The cavern diving course develops minimum skills, knowledge, dive planning abilities, problem solving procedures and the basic abilities to safely cavern dive. These skills are useful in all types of diving. The course
is taught in over a minimum of two days and includes classroom lectures, field exercises, open water line drills and a minimum of four cavern dives. This course emphasizes planning, procedures, environment, propulsion techniques, buoyancy skills, problem solving, equipment modification and the specialized needs of the cavern diver. The prerequisite qualification is Advanced Open Water Diver or equivalent.

The Introduction to Cave Diving course further develops
cave diving proficiency within the limitations of a single tank. It is taught over a minimum of two days and includes  a minimum of four single tank cave dives. The course helps hone the skills learned on the cavern diving course, and teaches new skills and procedures for limited single tank cave penetration. It is considered a recreational cave diving course, and does not include obligatory decompression. The prerequisite qualification is cavern diver or equivalent and 25 logged non-training dives.

The Apprentice Cave Diver course is a training level which expires after a year if the full cave certification is not completed. It is an introduction to jump and gap procedures. The prerequisites are NACD Introduction to Cave or equivalent.

The full Cave Diver course covers is equipment configuration, decompression problem solving, jumps, circuits, traverses, and surveying. The prerequisite is
NACD Introduction to Cave or equivalent.

NACD offers specialty cave diver training for the fully certified cave diver. Courses offered are:
 Exploration/survey techniques
 Stage diving
 Side mount diving
 Submersible Diver propulsion vehicle techniques
 Photography
 Videography

Four instructor certification levels are available.
 Cavern Instructor
 Introduction to Cave Instructor
 Cave Instructor
 Specialty Cave Instructor

National Speleological Society
The National Speleological Society (NSS) is an organization formed in 1941 to advance the exploration, conservation, study, and understanding of caves in the United States. Originally headquartered in Washington D.C., its current offices are in Huntsville, Alabama. The organization engages in the research and scientific study, restoration, exploration, and protection of caves. It has more than 10,000 members in more than 250 grottos. Since 1974 there has been as cave diving section of the society.

Quintana Roo Speleological Survey
The Quintana Roo Speleological Survey (QRSS) was established in 1990 for the safe exploration, survey and cartography of the underwater and dry caves and cenotes of Quintana Roo, Mexico, supported by the National Speleological Society.

The survey principally acts as a data repository for explored sites within the state of Quintana Roo and distributes summary statistical tables through its webpage, which as of February, 2011 included 208 underwater cave systems with a total surveyed length of , and 50 caves above the water table with a total length of .

Woodville Karst Plains Project
The Woodville Karst Plain Project (WKPP is a project and organization that maps the underwater cave systems underlying the Woodville Karst Plain, a  area from Tallahassee, Florida, U.S. to the Gulf of Mexico which includes several first magnitude springs, including Wakulla Springs, and the Leon Sinks cave system, the longest underwater cave in the United States. The project grew out of a cave diving research and exploration group established in 1985 and incorporated in 1990 (by Bill Gavin and Bill Main, later joined by Parker Turner, Lamar English and Bill McFaden, at the time the chairman of the NACD Exploration and Survey Committee).

Cave-diving regions

Cave-diving venues can be found on all continents except Antarctica, where the average temperature is too low for water to remain liquid in caves.

There are few flooded caves in Africa which are known and accessible. There are several in South Africa, a few in Namibia and Zimbabwe, and some large caves recently discovered in Madagascar.

There are a large number of flooded caves in the limestone regions and other regions of Asia, particularly in the karst regions of China and Southeast Asia. Some are accessible for recreational cave-diving, but most have probably not yet been found or explored.

Australia has many spectacular water filled caves and sinkholes, many of them in the Mount Gambier region of South Australia.

Europe has a large number of flooded caves, particularly in the karst regions.

North America has many cave-diving venues, particularly in Florida, USA, and the Yucatán Peninsula of Mexico.

South America has some cave-diving venues in Brazil.

Terminology

Caves and caverns as geographical entities are defined differently from cave-diving and cavern-diving, so it is possible to be cavern diving in what is technically a cave, and cave-diving in what is technically a cavern.

Types of cave dive
A cave dive can be categorised by the topology of the route, which can be linear, include a circuit, or be a traverse.

Caves by flow type
These terms describe flooded cave areas with reference to flow direction.

Types of cave by method of formation

Types of cave by topology
simple, linear, unbranched
simply branched
network, complex branched, anastomosed.

See also
Notable cave divers:

Edd Sorenson - Florida cave diver, IUCRR member and Cave Adventurers owner
Other:

References

Sources
"Skin Diver Killed in Submerged Cave", The New York Times, 16 May 1955, Page 47.
Basic Cave Diving: A Blueprint for Survival, Sheck Exley 1977.

External links
 Atlas of Caves Worldwide caveatlas.com
 Florida Cave & Cavern List
 History article Cave Diving Group, UK, 28 March 2010
 Woodville Karst Plain Project non profit organization about North Florida's underwater cave systems
 Wakulla system Todd Kincaid, University of Wyoming
Global Underwater Explorers non profit organization in Florida, education and exploration; Project Baseline, online spatial database of global underwater conditions
 International Underwater Cave Rescue and Recovery (IUCRR) International non profit organization registered in Florida
 Cave Diving Down Under (Australia) social media site for cave diving in Australia
 Dominican Republic Speleological Society

Cave diving


St Thomas's Abbey (or  the Königskloster) () is an Augustinian abbey and church located in Brno in the Czech Republic. The geneticist and abbot Gregor Mendel was its most famous religious leader to date, who between 1856 and 1863 conducted his experiments on pea plants in the monastery garden. His experiments brought forth two generalizations which later became known as Mendel's Laws of Inheritance.

The Abbey is unique amongst modern Augustinian foundations because it is not called a priory, and indeed it has an abbot (Prälat - prelate) whereas all other existing Augustinian friaries are led by a prior.

History
The Augustinians arrived in Brno in 1346, and John Henry of Luxemburg (Jan Jindřich Lucemburský), Margrave of Moravia, began the construction of their original cloister in 1352. These premises are located on Moravian Square. In 1650s, a musical foundation for the monastery was established, with paid musical scholars. This was the early beginning of a long and significant musical tradition at the Brno monastery. In 1780s, the Emperor Joseph II forced the friars to move out because he liked their well-located and representative buildings. These were given to the governor office and the church was turned to standard parish church. The friars moved to suburban Staré Brno where they took over the abolished Cistercian convent and church.

Czech composer Pavel Křížkovský also took monastic vows at Brno, teaching liturgical music from 1848 until 1872, and from 1865 he formed an ongoing musical collaboration with the young (lay) composer Leoš Janáček who had come from his home in Hukvaldy and begun as a choirboy at the monastery.

Mendel Museum
The Augustinian Abbey now hosts the Mendel Museum of Genetics dedicated to the founder of genetics. Visits to the Museum include a walk in the garden in which Gregor Mendel carried out his famous experiments.

See also
 List of Austrian scientists
 Gregor Mendel
 Mendelian inheritance
 Mendel Lectures
 Mendel Museum of Masaryk University
 Mendel University of Agriculture and Forestry Brno (named after Mendel since 1994)

References

External links
 Photographic tour of St. Thomas' Abbey
 Order of St Augustine, International Homepage
 Catholic Encyclopaedia – Hermits of St. Augustine
  Text of the Rule of St. Augustine
 Augustinian Abbey of St. Thomas at Brno
 Mendel Museum of MU website
 Masaryk University to rebuild Mendel's greenhouse | Brno Now

Augustinian monasteries
Christian monasteries in the Czech Republic
Religious organizations established in the 14th century
Churches in Brno
Gregor Mendel
Burial sites of the Opavian Přemyslids
Augustinian churches in the Czech Republic

St Thomas's Abbey, Brno


Pre-algebra is a branch of mathematics which is studied typically in American education usually taught in 8th grade to prepare students for algebra 1 and 2, geometry, and other subjects that are taught in high school. It is studied to prepare students for algebra. Pre-Algebra is used to allow students to understand usage of variables and enhance their ability of understanding, reading and creating graphs. Pre-algebra often still deals with basic math, while adding letters, commonly used are x and y.

Subjects students often learn include:

 x and y variables
 ratios
 basic slope
 adding, subtracting, multiplying, and dividing negative numbers
exponents
proportional relationships
system of equations
scientific notation
graphs and functions
probability
equalities and inequalities
geometry

 Irrational numbers (such as π)

Pre-algebra is mainly about equations and evaluating what certain variables are. An example is 3y+x-3=y-x+10   say we need to solve for x. we would need to subtract 3y from both sides of the equal sign. So it becomes x-3=10-2y-x next we need to add 3. So x=13-2y-x, and then add x to each side. 2x=13-2y divide each side by 2 so x=-y+13/2.

Szczepanski, Amy F. & Kositsky, Andrew P. 2008. The complete idiot's guide to pre-algebra. Penguin. AFKBender added to this.

Fields of mathematics
Education

Pre-algebra


Battle of Wenden (also known as Battle of Kieś) was a battle fought during the Polish–Swedish War (1626–1629), between Sweden and the Polish–Lithuanian Commonwealth on December 3, 1626 at Wenden (Cēsis, Kiesia) in present-day Latvia. Swedish forces were led by Gustav Horn and Hans Wrangel. Lithuanian forces were led by Aleksander Gosiewski. The Swedes won the battle.

Opposing forces
The Swedish army of 1,900 infantry (mainly musketeers) and 1,780 cavalry under the command of Gustav Horn had reached Drobbusch late on December 2, and there decided to establish a camp for the troops to rest. However, as there were not enough houses for the whole army, only the infantry was quartered within the village, and the cavalry instead rested in nearby woods. During this time, unbeknownst to the Swedes, the Polish field marshal Aleksander Gosiewski approached in their direction with his army of 1500. Gosiewski's aim was to evict the Swedish troops from the village via a surprise attack. At dawn of the next day, November 3, Gosiewski reached the village and executed the attack.

Battle of Wenden

The Lithuanians tried to sweep through the entrances of the roads leading to the village, but were repulsed by Swedish sentry detachments long enough for further Swedish support to arrive from the village. Meanwhile, two banners of Cossack (Kozacy) cavalry attempted to cross through the woods in order to outflank the Swedes but were engaged and stopped by a detachment of musketeers. After some fierce fighting in hand-to-hand combat the Lithuanian infantry was repulsed after having suffered several killed and captured.

Horn, then took the initiative and with some musketeers, forced the Lithuanian cavalry away from their advantageous position which had been preventing the Swedish cavalry from participate in the battle. Then, being able to deploy, one Swedish squadron of Finnish cavalry managed to charge and rout, according to letters of Swedish generals, five squadrons of Lithuanian hussars who lost four banners. After a short but fierce fighting the remains of the Lithuanian army were defeated. The Swedish casualties of the battle were light. The Lithuanians however, lost 400 men dead, 40 captured and eight banners.

Aftermath
After the battle the Swedes remained at Drobbusch for two days in order to gather supplies before moving south to push Gosiewski out of  Livonia and into Courland. After Gosiewski crossed the Düna river at Yxkull De la Gardie and Horn had to halt their pursuit due to the lack of winter clothing which caused a lot of casualties among the troops from sickness and frostbite. Horn assembled a small force of some 300 cavalry and 200 musketeers, with which he intended to clear out the Lithuanian positions west of the river Ewst.

On the march there, the Swedish cavalry encountered a force of 3 banners of cossack style cavalry who were escorting the Lithuanian baggage and artillery train which had been left behind at Laudon. A fierce action followed in which the "cossacks" fought with great bravery, though losing some 70 men they were able to push their way through with the baggage train but had to leave the cannon behind due to the bad roads. Horn continued his operation and was able to take Berson but Laudon proved to strong from him which effectively ended the winter campaign of 1626-1627.

References

Sources
Based on a description made by Swedish expert Daniel Staberg about the battle. The sources include Sveriges Krig 1611-1632 by staff historians, two letters sent to Axel Oxenstierna, written by Gustav Horn respective Gabriel De la Gardie.
Polish book Wojna inflancka 1625-1629, Henryk Wisner.

Wenden 1626
Wenden 1626
Wenden 1626
1626 in Europe
17th century in Latvia
Wenden (1626), Battle of
Cēsis

Battle of Wenden (1626)


Fritz Schiesser (born 23 April 1954) is a Swiss lawyer and politician, member of the Swiss Council of States (1990-2007).

Schiesser became a Member of the Swiss Council of States in 1990 as a Free democrat. President (speaker) of the Council of States in 2003/04. He was also member of the Parliament of the Canton of Glarus from 1995 to 2009. Member of the Swiss Delegation to the Inter-Parliamentary Union.

In November 2007, Schiesser was appointed President of the ETH-Board for 2008-2011. The function being incompatible with the membership in the Council of States, Schiesser has to resign from the Council, despite his re-election a few weeks earlier. In November 2011, he was reappointed as President of the ETH Board for 2012-2016.

External links

1954 births
Living people
Members of the Council of States (Switzerland)
Presidents of the Council of States (Switzerland)
Free Democratic Party of Switzerland politicians

Fritz Schiesser


The Old Croatian Sighthound (, 'greyhound'), also known as the Old Bosnian Sighthound, is an extinct breed of sighthound from the Balkan countries of Bosnia–Herzegovina and Croatia.

It is claimed the Old Croatian Sighthound was descended from sighthounds kept by the Celts; it closely resembled images of dogs on Celtic coins from the 5th century BC, as such it is believed to be closely related to the greyhound, which was introduced to Britain by the Celts. Descriptions of the breed in the Balkans have been found in the writings of friars from the 13th and 14th centuries AD.

The Old Croatian Sighthound was almost identical to the Greyhound although slightly smaller, with dogs standing between  bitches being  shorter. The breed had a short coat and was predominantly white with black, brown, red or yellow patches. Traditionally the breed was kept for coursing, predominantly hunting hare; it would catch the game and return it to the hunter.

The breed never received recognition by any kennel club and suffered greatly under the former Yugoslavia. The government of Yugoslavia banned coursing with sighthounds and further prohibited hunters from owning dogs without kennel club registration. In the early 1980s, some remaining specimens were found in Orašje and the surrounding villages; a pair were brought to the Zagreb School of Veterinary Medicine with the hope of starting a breeding program, but ultimately the program failed; it is believed the breed was extinct by 1995.

References

Sighthounds
Extinct dog breeds
Dog breeds originating in Croatia

Old Croatian Sighthound