Chap XXX.
1569
purpose with the other, it should on that account be preferred. When the distance betweenthe rails is increased, every additional inch in width adds to the expense, not only for theland on which it is set out, but also from requiring stouter sleepers and rails of a greaterweight; the length of the axles of both the locomotives and the carriages they draw mustalso be prolonged, and consequently rendered more likely to fracture, if their strength benot greatly increased; the draught is more immediate from the middle of the narrow thanfrom that of the broad gauge.
Foundation, for the Stone Blocks and Sleepers. — The surface of the way transverselyshould be convex, with a rise of about 3 or 4 inches in the middle, to throw the water intothe lateral drains, and previously to placing or bedding the blocks, a stratum of brokenstones should be spread over the whole to the depth of a foot, through which the water canpenetrate into the brick drains previously constructed beneath it: another stratum of finerstone with sand is laid, and after being well rammed is levelled to form a firm foundation.The blocks are of a hard and compact stone, often of granite; they are drilled for thereception of the trenails and made level to receive the chairs; but if great care is not takenin setting them they will sink and require to be reset: they are now usually bedded bymeans of a machine containing a lever, about 20 feet in length, with its fulcrum at a suffi-cient distance from the end to raise the block intended to be set about a foot high fromthe ground; and while one man is manoeuvring it, another, as often as it is lifted up,throws under the block a layer of sand or fine gravel, until it is not only level transversely,but ranges with the others along the line, and when once placed it should not again bemoved. Where the ground is not very firm, wooden sleepers are laid across the way, fromone side to the other, made of larch or other durable timber, and of a scantling not less than12 inches by 6: they were at first cut out of round timbers or Scotch fir, 12 or 13 inches indiameter, and after one cut was made in them, they were laid with their flat side downwardsacross the road, at a distance of 3 feet from centre to centre. Transverse with longitudinalsleepers over them, extending the whole length under the rails, make the most stablearrangement, and are now generally adopted: it is highly important to prevent any sinkingof the rails after they are once set, and it is a false economy that dispenses with the timbersubstructions, which form an extended base to receive the weight passing over the rails.
When, however, stone blocks are used in preference to timber sleepers, they should bemade perfectly level before the chairs are set upon them: two holes, about 2 inches indiameter, are then drilled into them, for the purpose of inserting plugs of heart of oak,which, when firmly driven in, are bored with anauger, to receive the iron pins which fasten downthe chairs. In many instances the former havebeen dispensed with, and a piece of tarred feltinserted between the bottom of the chair and thetop of the block: oak pins engine-turned havealso been used, and if well driven, they are foundto render the chair tight and firm; if tarred overafter their heads are cut off level, they will lastmany years in a sound state.
Triangular sleepers, laid longitudinally uponothers which cross the railway, are in some instancespreferred: as in the fixing the iron rails chairs can be dispensed with, and greater strengthcan be obtained from the same quantity of timber; for there is no better form to resistcompression than a triangle placed upon a broad base.
In the construction of the Great Western Railway stone blocks were dispensed with,longitudinal rails of American pine being substituted for them; they were 14 inches inbreadth, from 6 to 7 inches in thickness, and laid on alternate double and single transverseties. The double ties were each 6 inches in breadth and 7 inches in depth; the singleWere 6 inches in breadth and 9 inches in depth: two beech piles, 10 inches in diameter,Were driven between each double pair, and two others by the side of each single tie, therows being about 8 feet 6 inches apart. In cuttings the piles were driven 8 or 10 feet,but on the embankments, or where the earth was made, they were usually driven throughinto the subsoil.
. The heads of the piles were secured to the double and single rows of transverse crossties or sleepers by iron bolts with screws and washers. The longitudinal timbers, 14 inchesin width, were laid down upon the cross ties, and then firmly bolted to them with screwbolts and washers; the head of the bolt and washer, being counter-sunk in the longitudinalr *U, and passing through the transverse ties, were secured below : two bolts were used^hen the timbers were double, and one at each point of intersection of the single timbers."The longitudinal timbers being bolted securely to the transverse ties, the latter were againsecured by bolts passing through the head of the piles.
After the cross ties and longitudinal timbers were all securely placed, finely screened
Fig. 2930.