Fig. 119.
Fig. 120.
Fig. 121.
Figs. [119] to [121] show in elevations and in plan the plant usually employed on the surface. O is a small capstan engine, having a cylinder 20 inches in diameter and a stroke of 32 inches, working on the third motion. Attached to this engine, and working in the small pit C, is a counterbalance weight. This engine is used for raising and lowering boring tools, and for lifting the débris resulting from the boring. As far as the platform, which is about 10 feet from the surface, the pit has a diameter of 19 feet, or 4 feet more than the diameter of the pit below. A at level of about 38 feet above this platform there is a tramway on which small trucks run, carrying the débris cylinder on one side, and the boring tools on the other. At a level of 48 feet above the platform are placed supports for the wooden spears to which the boring tools are attached. The machinery for boring is worked by a cylinder, which has a diameter of 391⁄3 inches, and a full stroke of 391⁄3 inches, the usual stroke varying from 2 feet to 3 feet. A massive beam of wood transmits motion from this cylinder to the boring apparatus, the connection between the beam and the piston-rod and the beam and the boring tools being made by a chain. The engine-man sits close to the engine, and applies the steam above the piston only. The down stroke of the boring tools is caused by the sudden opening of the exhaust, and a frame then prevents the shock of the boring rods from being too severe. The engines work at speeds varying from 12 to 18 strokes a minute, according to the character of the strata passed through.