Chap. XXX.
1571
tional end of the adjoining one, as long as the pile maintained its retentive power. Thistimber foundation required for every mile of double line 420 loads of American pine,40 loads of oak, 6 tons of wrought-iron bolts, and 30,000 screws.
Mails, when of cast-iron, are more brittle than when of malleable metal, and consequentlyrequire an increased area in their section to be equal in strength to the latter: they aredurable, resist for a long time the action of the wheels, and, from the hardness of the metal,oppose little or no obstruction to them: but the malleable iron, from not being so subjectto fracture, is now usually preferred. The width of the rail at top is about inches,which is that now given to most wheels, and considered sufficient for all purposes. It hasbeen estimated that the wear and tear or waste of the rails is about of a pound per yardper annum, or that ^ inch in depth is annually worn away; but this must in a greatdegree depend upon the quality of the iron, and many other attendant circumstances : theirlength is about 15 feet, and the expansion and contraction in our temperature is estimated atequal to of that length, or ^ inch. In comparing the strength of rails great differences areobservable from the various kinds of iron used; when diversities of metal in proper pro-portions are employed, the rail is stronger, with the same weight of iron, than when com-posed of one metal. It is admitted that those of malleable iron are easier kept in order;that, extending over several chairs or blocks, there are fewer joints; that they present tothe wheels of the carriages a smoother surface, and are also more regular in their decay;that their elasticity being great, they are not so subject to fracture, and will bear considerablechange of form without the cohesive power being affected; and that pressure which wouldcrumble down the crystalline texture of the cast-iron flattens the malleable, and renders itspowers of resistance greater.
With regard to the best form for the section of a rail, there have been various opinions;it has been ascertained that a malleable iron bar of any length is extended 753 ^ of thatlength bv the direct strain of a ton for every inch of its sectional area, and whenstrained by ten tons per inch, or stretched T{ j^ of its length, it does not regain its form orelasticity.
The Plate Rail, first used about the year 1767 in a colliery near Sheffield, was a flatbar of cast-iron with an upright ledge; it was in 6 feet lengths, and the upright and flatpart measured in width 2 inches; they were secured by nails to transverse timber sleepers;they were placed on square wooden blocks, and it was not until the year 1800 that stoneblocks were used on the railway at Little Eton, in Derbyshire : some flat rails are castwith a square hole at every joint; through this an iron pin is driven, which enters a woodenplug previously introduced into the stone block ; one-half of the pin thu 6 secures the endof each rail, which is in lengths of from 3 to 4 feet. In some cases a return is cast on theedge of the flat part of the rail, which enters a groove cut into the stone, and adds consider-rably to its steadiness. Wrought-iron rails were first used about 1824; they are now all somanufactured, and rolled out to the form required.
The first Edge Mail was of cast-iron, and used at Loughborough about the year 1789 : itsupper surface was level, and that below elliptical: a flange on the wheel guided it along therail; it consisted of a bar of cast-iron, about 3 inches thick, increasing towards the top to abreadth of inches, in which the wheel ran; they were either fixed to wooden sleepers orstone blocks, and this description of rail, when its section was that of a parallelogram, wascalculated to bear the greatest strain.
Iron chairs, of which there are now many varieties, were a most useful introduction: thefirst were made with a flat base, of about 7 inches in length, 4 inches in width, and | of aninch thick, gradually diminishing towards the edge to \ inch : the upper part, whichreceived the rail, had two uprights cast on it, at a distance sufficient to allow the rail to enterbetween them, when fixed pins were passed through the cheeks or uprights, as well asthrough the holes in the ends of the rails, which prevented them from moving; they wereplaced either on stone blocks, 18 inches square and 9 inches in depth, or on wood 3 feetlong, 10 inches wide, and from 6 to 8 inches in depth. The chair was fastened down bydriving an oak pin or plug through a hole cast on each side, and another drilled into theblocks.
In the year 1816 Loch and Stephenson obtained the first patent for an improved rail andchair : the ends of the rails united in a half lap, a pin passed through the two ends as wellas the chair, and kept themtogether. The object of thispatent was to fix both the endsof the rails, or separate piecespf which the ways are made,immovably in or upon thechairs or props that support _______
them, and so to place the rails Fig. 2936.
that neither of the ends should
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