run back into the line 3'3, or into the same line on the other side of the turn-table. The table on the line 11', is shewn turned into the proper position, for running the carriage into the oblique lines, 4 or 4'.

These tables are thus constructed:- Suppose o o, Figs. 10 and 11, to be the surface of the ground whereon the rails of the railway are laid, a circular hole is dug out, of sufficient depth to receive the table; around this, large stone blocks, a a, similar to the railway blocks, are placed; upon these blocks, eight cast-iron chairs, represented at b b b, &c., Fig. 9, are placed, and pinned down; a circular ring of cast iron, c c, is laid within these chairs, about two inches and a half broad at top, and a little bevelled; this ring is laid perfectly horizontal, and upon it the small bevelled rollers, g g g, &c. revolve; the arms, 1, 2, 3, 4, acting as axles to them, and around the ends of which they turn freely. These arms pass through a ring of iron near the extremity, which keeps the rollers constantly in their proper position; the arms are fastened in the centre to a ring of iron, f, which turns freely round the spindle, f', Fig. 11. The turn-table rests upon these rollers, which are for the purpose of causing it to turn round, as freely as possible. Fig. 12, shews the framework of the table; hhh, &c. are the outer rim; iii, the arms; and m m, the inner rim, which is of the same diameter as the ring of iron, c c c, and which rests on, and turns round upon, the periphery of the rollers, g g g. The table is kept in its place by the vertical spindle, f', fixed upon the table at e, and turning with it upon the rest, e'.

The table, it will, therefore, be seen, turns round this rest as a centre, and, revolving upon the periphery of the rollers, it moves round with very little friction. It is not intended that the spindle, f', should support any

part of the weight of the table, the use of it being solely to prevent any side motion. The outer ring, h, of the table, projects above the level of the arms, i i, and the inner part of the ring, h'h'. Within this outer ring, a platform of timber is laid, resting upon, and fastened to the arms, kk, the bolt holes being shewn in the figure; upon this platform the rails of the road are placed. nn, Fig. 11, shews the timber, the upper side of which is level with the top of the outer ring, h h. A circular ring, oo, of cast iron, or of mason work, is laid around the outer circle of the table, upon which the rails rest; and which abut against the ends of the rails, laid upon the turn-table.

We have said that the top of the turn-table is covered with timber, on which the rails forming the railway is laid; in many cases the top is formed of cast-iron, the rails being raised a little above the surface of the castiron plate.

1

CHAPTER V.

CONSTRUCTION OF CARRIAGES ADAPTED TO
RAILROADS.

§ 1.-Coal Waggons, and Wooden Wheels. Ir is very obvious, that the form of carriages for rail. roads, will depend, in a great measure, upon the nature of the goods to be conveyed in them; different kinds of goods, and various species of traffic, requiring different descriptions of carriages. There are, however, some parts of the carriages common to all the varieties, viz. the wheels, the axles, and the bearings, in which the axles run. We shall, therefore, at first, describe the different forms of wheels, and axles, or other parts, which, the nature of the road requires, should be always of the same form and construction; and then give drawings, of some of the different kinds of carriages used on railroads.

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The body of the carriages, or, as they were termed, waggons," used at the first introduction of railways, was, (and still remains, where employed in conveying coals,) in the form of the frustum of a pyramid, or in the shape of a hopper, being much broader and longer at the top, than at the bottom. The railroads, almost universally, descending towards the depôt, the forewheels were made of greater diameter than the hindwheels, according to the angle of the road, the object being, to keep the framing, or body of the waggon, in a horizontal position. The end of the waggon, resting on the large wheels, was also made to project considerably

farther, beyond the perpendicular line of the axles of the front, than the hind-wheels; so that the centre of gravity of the load was not midway between the wheels, but much nearer the large wheels than the smaller, and, consequently, a greater weight was laid upon them, than upon the latter. This form of the waggon has gradually given way to wheels of the same size, and the body of the carriage is square, and placed equally upon the two axles, as shewn in Figs. 1, 2, and 3, Plate VII.

The wheels were, for a long period, made of wood, composed of one entire piece, or of two or three pieces, fastened together. The mode of making the latter, was, by joining the pieces together by wooden pins, and securing them by flat slips of iron, in the shape of an s s, nailed upon the line of the joining. The periphery of the wheels was hewn into the proper shape, by the workmen, with a projection on one side, to keep them upon the rail. The axles were made of wrought iron, and fixed firmly into the centre of the wheels, and, consequently, turned upon the bearing with the wheels. From the very probable inaccuracy of the workmanship, it is not likely the periphery of the wheels would be perfectly circular, which would cause considerable jolting, or an undulatory motion, to the load, and thus increase the draught.

§2.-Cast-iron Wheels.

It seems uncertain at what precise period cast-iron wheels were first introduced. In a Dictionary of Arts and Sciences, published in 1754, a drawing is given of a cast-iron wheel, used upon carriages to convey stones from a quarry near Bath, said to be "a great improvement in some carriages and waggonways, made use of at the coal-mines, near Newcastle;" from whence we may suppose, that cast-iron wheels had not been used

at the latter place at that period. How long after this they were adopted, we cannot learn; but in 1765, two wooden and two cast-iron wheels were mostly in use, the wooden ones being retained for the application of the brake, or convoy.

Great reluctance was shewn, even down to a very recent date, to relinquish the employment of wooden wheels; many objections were urged against castiron, their liability to break, to cut the rails, their insufficiency to present an adequate hold to the brake. At first, sufficient attention does not appear to have been paid, to avoid the contraction, in cooling of cast-iron wheels, and they frequently broke in pieces. Increased knowledge of the properties of cast iron, and of the utility of that kind of wheel, soon, however, produced a general acquiescence in their use. When cast-iron rails came into use, the wooden wheels could no longer be used, so that the introduction of the former would accelerate the discarding of the latter; and, therefore, in 1767, the date of the introduction of cast-iron rails, we may suppose wooden wheels were little used.

A B C, Fig. 1, Plate VI., shews the form of the castiron wheels, for an edge rail;ff, is the nave; a a, the rim; and b b, the spokes. The rim is made sometimes nearly, or often quite, cylindrical, with a projection at one side, called the flanch, to keep the wheel upon the rail; c is a square hole, through the nave, for the axle.

This is the form which was generally used for edge rails, for many years after their introduction, the whole being cast in one piece; the spokes being about half an inch thick, and four inches broad; the rim, one inch thick, and the flanch, one inch deep. For the plate rail, the spokes were tapered away, from the nave, to about two inches broad, forming a rim of that breadth,