ON THE CONSERVATION OF FORCE 



199 



when the globe is heated, equilibrium be restored by allowing 

 some of the liquid to flow out at R, as the globe cools it 

 will be drawn up towards n. In both cases liquid is raised, 

 and work thereby produced. 



The same experiment is continuously repeated on the 

 largest scale in steam-engines, though, in order to keep 



FIG. 96 



up a continual disengagement of compressed gases from the 

 boiler, the air in the globe in FIG. 96, which would soon 

 reach the maximum of its expansion, is replaced by water, 

 which is gradually changed into steam by the application of 

 heat. But steam, so long as it remains as such, is an elastic 

 gas which endeavours to expand exactly like atmospheric 

 air. And instead of the column of liquid which was raised 

 in our last experiment, the machine is caused to drive a 

 solid piston which imparts its motion to other parts of the 

 machine. FIG. 97 represents a front view of the working 



