HYDRAULICS. 213 



From the bottom of the cylinder, a pipe g pro- 

 ceeds, of which the lower end is turned upwards, 

 and is covered with a valve r. This part is im 

 mersed in a cistern of water, called the hot-well 

 and the pipe itself is called the eduction-pipe. > 



The boiler is furnished with a safety-valve, 

 called the puppet-clack, in the same manner as in 

 Mavary's engine. This valve is generally loaded 

 with one or two pounds in the square inch, so that 

 it allows the steam to escape when its elasticity is 

 one-tenth greater than that of the atmosphere. 

 All risk of bursting the boiler is thus avoided, the 

 pressure outwards being very moderate. 



When the cistern for the injection-water, i, can- 

 not be supplied by pipes from some more elevated 

 source, water is raised by the machine itself. A 

 small lifting-pump, s, is worked by a rod, r, sus- 

 pended from a small arch upon the great beam ; 

 this forces water through the pipe t into the injec- 

 tion-cistern. 



The parts of the engine being now described, 

 the operation is as follows : 



Suppose the piston and lever in the position re- 

 presented in the plate, and the water in the boiler 

 in a state of ebullition, the steam and injection- 

 cocks being shut. Having opened the steam-cock, 

 n, the steam from the boiler will immediately rush 

 in, and flying all over the cylinder, will mix with 

 the air. 



Much of it will be condensed by the cold sur- 

 face of the cylinder and piston, and the water 

 produced from it will trickle down the sides, and 

 run off by the eduction-pipe. This condensation 

 and waste of steam will go on until the whole 

 cylinder and piston be made as hot as boiling 

 water. 



p 3 



