The method of inserting these tubes is shown in Fig. 213. Two wrought-iron columns C C, 6 inches diameter, are firmly secured in the position shown, by castings bolted to the flanges of the cylinders A A forming the well, so that the two columns are perfectly rigid and parallel to each other. A casting D, carrying on its under side two 5-inch hydraulic rams I I of 4 feet length, is formed so as to slide freely between the columns, which act as guides; the hole in the centre of this casting is large enough to pass a bore-tube freely through it, and by means of cotters passed through the slots in the columns the casting is securely fixed at any height. A second casting E, exactly the same shape as the top one, is placed upon the top of the tubes B B to be forced down, a loose wrought-iron hoop being first put upon the shoulder at the top of the tube, large enough to prevent the casting E from sliding down the outside of the tubes; this casting or crosshead rests unsecured on the top of the tube and is free to move with it. The hydraulic cylinders I, with their rams pushed home, are lowered upon the crosshead E, and the top casting D to which they are attached is then secured firmly to the columns C by cottering through the slots. A small pipe F, having a long telescope joint, connects the hydraulic cylinders I with the pumps at the surface which supply the hydraulic pressure. By this arrangement a force of 3 tons on the square inch, or about 120 tons total upon the two rams, has frequently been exerted to force down the tubes at the Horse Fort. After the rams have made their full stroke of about 3 feet 6 inches, the pressure is let off, and the hydraulic cylinders I with the top casting D slide down the rams resting on the crosshead E, until the rams are again pushed home. The top casting D is then fixed in its new position upon the columns C, by cottering fast as before, and the hydraulic pressure is again applied; and this is repeated until the length of two tubes, making 18 feet, has been forced down. The whole hydraulic apparatus is then drawn up again to the top, another 18 feet of tubing added, and the operation of forcing down resumed. The tubes are steadied by guides at G and H, Fig. 213, shown also in the plans.