whatever, be moved in the least degree; for the least movement, in any direction, must destroy the seat, which has been accomplished with such trouble, by the mode of setting.

Blocks of stone are, as before stated, universally used, where the ground is firm; that is, in all the excavations, and on the embankments, where perfectly consolidated. In some instances, blocks are used in the latter case, where the embankments, though not perfectly consolidated, are not likely to subside very much; but it is evident, the same care in setting the blocks is not necessary. Where the ground is not firm, and wooden sleepers are used, they are generally made to reach the whole length, from side to side, between the rails; and to such a distance beyond, that both rails can be placed upon the same sleeper. This is the more necessary, where the foundation is liable to subside; inasmuch as it preserves the proper width between the rails, even if both sides of the railway are not upon the same level, and which is often the case, upon yielding embankments. These wooden sleepers, are mostly made of larch fir; and for railways, four feet eight inches distant between the rails, from eight to ten feet long, eight to ten inches broad, and about five inches thick.

When the blocks are thus set, or sleepers laid, as the case may be; the space between the blocks, and on the outside of the rails, is filled up to about three inches above the top of the blocks, or about the same depth below the top of the rails.

A B, Fig. 4, is a plan, shewing one side of a double line of railway, laid with stone blocks, and c D, the other side, laid with wooden sleepers; the shaded parts, ab, cd, cd, and ef, ef, shewing the drains, Fig. 3, shewing the section of the blocks, and wooden sleepers.

§ 13.-Seating the Chairs upon the Blocks.

A seat is, first of all, made upon the top of the block, perfectly level, and in the same plane as the base of the block, upon which the chair is to be set. Fig. 6, Plate V., shews the mode generally adopted to fasten the chair to the blocks. Holes are drilled into the stone, about two inches in diameter, into which oaken plugs are driven, shewn at a b, Fig. 6; these plugs are then bored with a three-eighth inch auger; and the chair, having been properly seated upon the top of the block, an iron pin, shewn at cd, is driven, through the hole of the chair, into the wooden plug, and which, having a head, as shewn in the figure, fastens the chair to the sleeper.

The rough nature of the blocks, almost renders it impossible to get a level and uniform seating for the chair; and recourse has been lately had to a thin piece of felt, interposed between the chair and block, which, when the chair is firmly pressed, by the pin, to the block, fills up all the interstices, and makes a more firm seat, than could be done without this expedient.

The chairs have generally only two holes, and two pins to fasten them to the blocks. Fig. 7, shews a chair with four pins, for fastening it to the block. Mr. Story has laid down some of this description, with four pins, on the Stockton and Darlington railway. Figs. 6 and 7, shew a plan and section of the chairs, intended by him, for the rails of the Great North of England railway.

Fig. 8, shews a plan, by Mr. Daglish, for fastening the chair to the block. Two holes, bb, of two inches diameter each, are drilled two inches upwards, from the bottom of the block; through the remainder of the thickness of the block a hole is drilled, three quarters

of an inch in diameter; two bolts of that size are put through these holes, with the heads downwards, the other ends of the bolts passing through the chair; keys are driven through the ends of the bolts, which wedge the chair upon the block, and which can be tightened at any time. The only disadvantage of this mode, is, that if any accident happens to the bolt, it cannot be replaced, or repaired, without removing the block.

In all the old railways, the plan of fastening the chair to the block, was by means of an oaken pin; and this plan has been adopted, upon the Newcastle and Carlisle railway; and so far as the experience of between two and three years enables us to judge, it seems likely to answer quite as well, if not better, than the plan shewn in Fig. 6. In the latter plan, the iron pin is only kept in its place, by the compression of the wood against the pin; but we find, that, by boring out the hole, in the middle of the plug, the wood is much shattered, and it is still more split in driving the pin. There remain, therefore, only detached pieces of the wood, to act against the pin, to keep it tight; and we accordingly find, that most of the pins, first used on the Liverpool and Manchester railway, have all worked loose. Fig. 9 shews the mode adopted on the Newcastle and Carlisle railway. The wooden pins are three quarters of an inch in diameter, and six inches long; the hole drilled in the block, is scarcely three quarters of an inch in diameter; when, therefore, the plug is driven, it sustains considerable compression. The hole in the chair is an inch deep, bevelled upwards, or three eighths of an inch larger diameter on the upper than the under side; the plug having an enlarged head, as shewn in the figure, to keep the chair firmly in its place. These plugs are all engine-turned, and made

octangular, and of old oak, or the heart of the oak, well dried; when well driven, they cannot be forced out again, the ragged nature of the blocks, and the expansion of the plugs, securing them within the block, quite tight and firm. The objection, which most naturally suggests itself, against this plan, is, the probable decay of the plug within the chair. We find, however, plugs remaining quite good, upon the old railways, which have been in use upwards of twenty years. Little doubt can, therefore, exist as to their durability within the blocks; and the heads being cut off, level with the top of the hole of the chair, and covered with tar, if made of good oak, they will be found very durable.

§ 14.-Keying the Rails to the Chairs, and Form of joining the Rails at their Ends.

In Chapter II. we have given, in describing the different forms of rails, the mode of uniting them at the joints, and of keying the rails to the chairs. For the particular plans, of joining all the various kinds of rails and chairs, we refer the reader to that chapter; our object, in this place, being, to enquire into the effect, in practice, of the different modes of keying the rails to the chairs, and of joining the ends of the rails to each other.

We have stated that, at the first introduction of railroads, the rails were all made with square joints, or square ends; and that, subsequently, they were made so that a portion of the end of one rail overlapped a similar portion of the next rail, forming what is called, an overlap joint; the latter mode being adopted to avoid the shocks, or blows, which the carriage wheels might meet with, by the end of one rail projecting

above that of the other, and which the square end joints present, when the blocks are out of order.

Professor Barlow, made an experiment upon the Liverpool and Manchester railway, to ascertain the effect to a train of waggons, passing over a joint displaced, or out of order, with the end of one rail rising above the plane of the other. He applied a deflectometer, or instrument shewing the amount of deflection of the rail, when the engine and train passed over it, compared with a rail, with a joint displaced, or with its end rising above that of the preceding rail; and found the force of concussion fifty per cent. greater, with the bad joint, than with a perfect joint.

The following is the experiment alluded to; a bad, or open joint, was selected, the deflectometer applied to the block, and the shock measured by the instru ment; the rail was then taken up, and relaid, so as to make the joint, as close as usual, having the opening the same as the other end, and the effect was again taken. The result, with the Swiftsure

We see, therefore, how important it is, that the mode of joining the ends of the rails, should be such as to prevent the end of one rail, from rising above the plane of the other. With square ends, when the blocks are displaced, this is unavoidable; we must, therefore, either