The shell-pump, for raising the material broken up by the boring-head, is shown in Figs. 197, 198, and consists of a cylindrical shell or barrel P of cast-iron, about 8 feet long and a little smaller in diameter than the size of the bore-hole. At the bottom is a clack A opening upwards, somewhat similar to that in ordinary pumps; but its seating, instead of being fastened to the cylinder P, is in an annular frame C, which is held up against the bottom of the cylinder by a rod D passing up to a wrought-iron bridge E at the top, where it is secured by a cotter F. Inside the cylinder works a bucket B, similar to that of a common lift-pump, having an indiarubber disc valve on the top side; and the rod D of the bottom clack passes freely through the bucket. The rod G of the bucket itself is formed like a long link in a chain, and by this link the pump is suspended from the shackle O, Fig. 192, at the end of the flat rope, the bridge E, Fig. 197, preventing the bucket from being drawn out of the cylinder. The bottom clack A is made with an indiarubber disc, which opens sufficiently to allow the water and smaller particles of stone to enter the cylinder; and in order to enable the pieces of broken rock to be brought up as large as possible, the entire clack is free to rise bodily about 6 inches from the annular frame C, as shown in Fig. 197, thereby affording ample space for large pieces of rock to enter the cylinder, when drawn in by the up stroke of the bucket. The general working of the boring machine is as follows. The winding drum C, Fig. 189, is 10 feet diameter in the large machine, and is capable of holding 3000 feet length of rope 4-1/2 inches broad and 1/2 inch thick. When the boring-head B is hooked on the shackle at the end of the rope A, its weight pulls round the drum and winding engine, and by means of a break it is lowered steadily to the bottom of the bore-hole; the rope is then secured at that length by screwing up tight the clamp J. The small steam jet N, Figs. 192, 193, is next turned on, for starting the working of the percussion cylinder H; and the boring-head is then kept continuously at work until it has broken up a sufficient quantity of material at the bottom of the bore-hole. The clamp J which grips the rope is made with a slide and screw I, Fig. 192, whereby more rope can be gradually given out as the boring-head penetrates deeper in the hole. In order to increase the lift of the boring-head, or to compensate for the elastic stretching of the rope, which is found to amount to 1 inch in each 100 feet length, it is simply necessary to raise the top pair of tappets on the tappet rods whilst the percussive motion is in operation. When the boring-head has been kept at work long enough, the steam is shut off from the percussion cylinder, the rope unclamped, the winding engine put in motion, and the boring-head wound up to the surface, where it is then slung from an overhead suspension bar Q, Fig.