Chap. XXX

RAILROADS.

1575

Fig. 2955. TUHN-RAIL.

and 11 inch in thickness, upon which the rollerswork.

The table rests upon four iron bearers atright angles with each other: they are 9 inchesin depth at the middle, and 6$ at the ends; theirintersection leaves a square in the middle, thesides of which are 4 feet; from the angles ofthis square are four other arms serving as radii,which unite with the iron hoop that worksround the centre pivot; they are inches indepth at their junction with the hoop. Thebearers are at the same distance apart as therails on the line, and have holes | inch indiameter cast in them, for the purpose of at-taching the rails to the table; at their ex-tremity is a circular cast-iron plate, which worksround upon eight rollers; its width is 2 inches,and the distance from its middle to the centre5 feet 1| inch.

The rollers work between two wrouglit-iron hoops, 2 inches deep and § thick, and uponthe ends of eight wrought-iron rods, f inch in diameter, which are screwed into the hoopthat surrounds and traverses the centre pivot. The hoop is also of wrought-iron, 1 inch inthickness, 2 inches in depth, and 5 inches in diameter, and is accurately turned, so as towork round the collar of the centre pedestal, which is also turned, and of cast-iron, with ahole 3 inches in diameter and 5 inches in depth, at the bottom of which is a brass step 2inches thick, for the pivot to work upon. The pedestal is fastened to the stone block byfour pins, and a hole is left for the necessary supply of oil to the pivot: to this pivot thetable is attached by four screw-bolts, 1J inch diameter, so adjusted that by turning themit may be eased off, or lowered on the rollers. On the surface of the table two lines ofrailways are fixed at right angles, the rails being of wrought-iron, 3 inches broad and 2inches thick, bolted to the principal arms with ^-inch screw-bolts, their heads beingcounter-sunk into the rails. At the intersection of the rails are four sets of wrought-ironinclined planes, for the flanges of the wheels to run upon when passing the openings ; andon the outer rim is a latch to hold the table in its desired position. Cast-iron gratings,ij inch in thickness, are made for the separate compartments, and put into rebates formed toreceive them.

Passing from one Line of Railway to another .—Where double lines of railway are laiddown, and carriages of equal speed run upon them in opposite directions, the neces-sity for turning out, or for sidings to allow them to pass, is avoided: but where there are

Fig. 2956. turn-table.

Fig. 2957.