HYDRAULICS. 221 



steam-valve a, presses upon the piston, and forces 

 it down. As soon as the piston has arrived at the 

 bottom, the steam-valve c, and the eduction-valve 

 b, are opened, whilst the valves a and d a*re shut; 

 the steam, therefore, immediately rushes through 

 the eduction-valve b into the condenser, whilst the 

 piston is forced up again by the steam, which is 

 now admitted by the steam-valve c. 



Fig. 2, which is a section of the steam-pipes, 

 taken at right angles to that in Fig. 1, shows this 

 more distinctly; s is the pipe which conveys the 

 steam from the boiler; a and c are the steam- 

 valves, and b and d the eduction-valves. By 

 attending to the operation in both the sections, 

 the reader will easily understand it. It appears at 

 first a little confused, by there seeming to be only one 

 steam-pipe for communicating between the cylinder 

 and the condenser; but the difficulty is cleared up, 

 by representing both the pipes, as in Fig. 2. 



Fig. 3. is a longitudinal section of the boiler, re- 

 presenting the mode of supplying it with water, 

 and the safety-valve and cocks, jf is a small cis- 

 tern, which is supplied with water from the hot- 

 well, as represented in Fig. 1 ; from the bottom of 

 this cistern, a pipe goes down almost to the bottom 

 of the boiler, where it turns up a little, to prevent 

 the entrance of the steam which rises from the 

 bottom. From the side of this cistern is supported 

 a small lever, to one end of which is fastened a 

 wire that carries a stone which hangs in the water 

 of the boiler; the other end of the lever sup- 

 porting also by a wire a valve that shuts the top of 

 the pipe that goes down from the cistern. Now, 

 supposing the stone just at the surface of the water, 

 and balanced by a weight at the opposite end of 

 the lever; it is evident that, by the laws of hydro- 



