10 



THE HISTORY OF 



[SECT. i. 



Fig. 4. 



A piston P is fitted to the cylinder, and rendered air-tight by a packing, round 

 its edge, of soft rope well filled with tallow to reduce the friction, and its upper 

 surface is kept covered with water to render it steam-tight. The piston is con- 

 nected to a rod P A, which is suspended by a chain from the upper extremity D of 

 the arched head of the lever, or working beam, which turns on the gudgeon G. 

 This beam has a similar arched head E F, at its other end, for the pump rod H, 

 which receives the water from the mine. The end of the beam to which the pump 

 rod is attached, is made to exceed the weight and friction of the piston in the steam 

 cylinder ; and when the water is drawn from such a depth, that the steam piston 

 is too heavy for this purpose, counterpoise weights must be added at I, till the piston 

 will rise in the steam cylinder at the proper speed. At some height above the top 

 of the cylinder is a cistern L, called the injection cistern, supplied with water from 



