ENGINE for driving piles, used at building Westminster bridge, is con structed as follows : A, (Plate V. Miscel. fig. 3.) is the great shaft, on which are the great wheel and drum : B, the great wheel with cogs, that turns a trundle head with a fly, to prevent the horse's falling when the ram is discharged; C, the drum on which the great rope is wound ; D the follower (with a roller at one corner) in which are contained the tongs, to take hold of the ram, and are fastened to the other end of the great rope, which passes over the pulley, near the upper end of the guides, between which the ram falls ; E, the inclined planes, which serve to open the tongs, and discharge the ram ; F, the spiral barrel that is fixed to the drum, on which is wound a rope with a counter poise, to hinder the follower from acce lerating, when it falls down to take up the ram ; G, the great bolt which locks the drum to the great wheel ; H, the small lever, which has a weight fixed at one end, passes through the great shaft below the great wheel, and always tends to push the great bolt upwards, and lock the drum to the great wheel ; I, the forcing bar, which passes through the hollow axis of the great shaft, bears upon the small lever, and has near the upper end a catch, by which the crooked lever keeps it down ; K, the great lever, which presses down the forcing bar, and dis charges the great bolt at the time the long end is lifted up by the follower ; L, the crooked lever, one end of which has a roller, that is pressed upon by the great rope, the other end bears upon the catch of the forcing bar during the time the follower is descending ; M, the spring that presses against the crooked lever, and discharges, from the catch of the forcing bar as soon as the great rope slackens, and gives liberty to the small lever to push up the bolt.
By the horse's going round, the great rope is wound about the drum, and the ram is drawn up, till the tongs come between the inclined planes, where they are opened, and the ram is dis charged.
Immediately after the ram is discharg ed, the roller, which is at one end of the follower, takes hold of the rope that is fastened to the long end of the great lever, and lifts it up ; the other end presses down the forcing bar, unlocks the drum, and the follower comes down by its own weight.
As soon as the follower touches the ram, the great rope slackens, and the spring, M, discharges the crooked lever from the catch of the forcing bar, and gives liberty to the small lever to push up the great bolt, and to lock the drum the great wheel, and the ram is drawn up again as before.