There are several holes in the under side of the drum, and the bolt, r, always takes the first that it finds, when the drain stops by the falling of the follower upon the ram, till which stoppage the bolt has not time to slip into any of the holes. But the same effect is more certainly produced by a crooked lever, t, Figure 9, fixed on the framing, R, over the end of the vertical shaft ; one end of this has a roller, which is pressed upon by the great rope, n, while the other end holds down the catch, 5, of the forcing bar, but as soon as the great rope slackens, it retires, and gives liberty to the small lever, 3, to push up the bolt. As ]on, as the great rope has a tension upon it, to support the weight of the ram, or follower, the crooked lever is kept in close contact with the forcing bar, and \viten that is depressed (to discharge the bolt, v) by locking over its catch, 5, the crooked lever keeps it down, till the follower touches the rain ; the great rope then slackens, and the spring, v discharges the crooked lever from the catch of the forcing-bar, and gives liberty to the small lever, 4, to push up the great bolt, and to leek the drum to the great wheel, when the ram is drawn up again, as before.
The peculiar advantages of this engine are, that the weight of the ram, or hammer, may he raised with the force of horses instead of men ; that when it is raised to a proper height, it readily disengages itself; and falls with the utmost freedom ; that the forceps, or tongs, arc lowered down speedily, and instantly of themselves again lay hold of the ram, and lift it up; on which account this machine will drive the greatest number of piles in the least time, and with the fewest labourers.
The piles at Westminster bridge, when driven by the above machine till they were quite firm, were cult off; under water, by a machine to a level with the surface of the ground, to build the piers upon. This machine consisted of a framing adapted to fit upon the upper part of the pile, and fixed fast thereto. The lower part of this frame formed guides for the saw, which reciprocated horizontally at a cer tain depth beneath the top of the pile, and had weights to cause it to advance up to the cut. The saw was put in motion by ropes from each end, which were conducted, over proper pulleys, to two men standing on a float or raft at the surface. After fixing the machine, before the sawing was begun, the whole machine was suspended by a tackle, which therefore took up the top part of the pile with the machine as soon as it was cut oil: This was the invention of 11-. Etheridge, carpenter to the works at Westminster bridge; it was very effective, as the time employed in cutting off a fir pile of 1 t or 16 inches square, in 10 feet depth of water. was seldom more, and often less, than a minute and a A machine, more convenient than this in its application, and not less elrectiVe, was also invented by Mr. roulds, to whom
the Society of Arts presented a gold medal for the invention; sec Figures 5 and 7, where A A 13 is the external fame, con sisting of fair parallel rails, .%, named into two others, a, at right angles, with proper cross pieces to unite them, and inclined to strengthen the whole : within this frame a second, or internal frame, n E, is situated ; like the other, it has four parallel pieces, a and a, connected together into one frame by. cross pieces; at the top it has two pieces, u. a, which rest upon the beam, 13, suspend its weight, and on these it is capable of sliding backwards and forwards between B ii, always preserving its parallelists, because it is tnoved by the racks, d, d, affixed to it, one at top, and the other at the bottom; the pinions for both are fixed on a vertical axis, e, supported in the external frame; therelbre, by turning the handle, r. the internal frame with the saw is advanced to the pile, as at c, Figure (. The saw- itself is sustained in a frame, 1,, Fiyure 7, which fits, in the manner of a sash frame, between the two beams, D, of the internal frame, and has racks, f, j; (dotted) behind it, which work in pinions on an axis, g, extended across the frame, and by the handle, y, it is capable of being drawn up and let down, or detained at any height by a ratchet-wheel and click, x ; the saw, at, is • fixed upon a spindle N, supported in hearings on the frame, u., and turned by the handle, R, at the top ; the saw is con nected with the spindle by a piece of iron, p, having a mortise through it for the reception of the spindle, to which it 1.3 fastened by a nut beneath ; by this means the edge of the saw may be advanced as the work goes on.
In using this machine, the beams, B, are fixed across a barge, which is ballasted till they are horizontal, and the spindle of the saw is therefore vertical in this state; it is moored with her side against the pile, K, to be cut off as shown by the dotted line, v, Figure 6 ; then, by the rack and pinion, g, the saw is adjusted in height to the level where the pile is to be cut ; by the handle, r, it is advanced to the pile, it, whilst, by the other handle, R, the saw is kept in continual motion backwards and forwards, till the pile is cut through, and the piece is taken into the barge ; it then pro ceeds to cut off the next by the same means. By this machine. temporary piles, used in coffer-dams, may be cut off level with the bottom, when the work is finished, which is a very superior method to drawing them up out of the ground, as is the usual practice ; because this must neces sarily make a deep ditch or trench all round the pier or foundation, and tend to loosen the ground.