116 MOTIVE POWER OF HEAT. 



finally to produce its results in a manner with 

 which we will not concern ourselves. 



Let us suppose that the piston having moved to cd 

 is forced downward to ef, without the steam being 

 allowed to escape, or any portion of its caloric to be 

 lost. It will be driven back into the space abef, and 

 will increase at the same time in density, elastic 

 force, and temperature. If the steam, instead of 

 being produced under atmospheric pressure, hud 

 been produced just when it was being forced back 

 into cibef, and so that after its introduction into the 

 cylinder it had made the piston move from ab to 

 ef, and had moved it simply by its extension of 

 volume, from ef to cd, the motive power produced 

 would have been more considerable than in the first 

 case. In fact, the movement of the piston, while 

 equal in extent, would have taken place under the 

 action of a greater pressure, though variable, 

 and though progressively decreasing. 



The steam, however, would have required for its 

 formation exactly the same quantity of caloric, only 

 the caloric would have been employed at a higher 

 temperature. 



It is considerations of this nature which have led 

 to the making of double-cylinder engines engines 

 invented by Mr. Hornblower, improved by Mr. 

 Woolf, and which, as regards economy of the com- 



