468 



THE STEAM-ENGINE. 



and investigate the process of its operation. A section of this engine is rep- 

 resented in fig. 24. 



Fig. 24. 



Steam is supplied from the boiler to the cylinder by the steam-pipe S. The 

 throttle -valve T in that pipe, near the cylinder, is regulated by a system of 

 levers connected with the governor. The piston P is accurately fitted in the 

 steam-cylinder C by packing, as already described in the single-acting engine. 

 This piston, as it moves, divides the cylinder into two compartments, between 

 which there is no communication by which steam or any other elastic fluid 

 can pass. The upper steam-box B is divided into three compartments by the 

 two valves. Above the upper steam-valve V is a compartment communicating 

 * with the steam-pipe ; below the upper exhausting- valve E is another compart- 

 ) ment communicating with the eduction-pipe which leads to the condenser. 

 By the valves V and E a communication may be opened or closed between 

 the boiler on the one hand, or the condenser on the other, and the top of the 

 cylinder. The continuation S' of the steam-pipe leads to the lower box B', 

 which, like the upper, is divided into three compartments by two valves V' 

 and E'. The upper compartment communicates with the steam-pipe, and 

 thereby with the boiler ; and the lower compartment communicates with the 

 eduction-pipe, and thereby with the condenser. By means of the two valves 

 V and E 7 , a communication may be opened or closed between the steam-pipe ' 



