56 MOTIVE POWER OF HEAT. 



soon give a second more rigorous demonstration of 

 this theory. This should be considered only as 

 an approximation. (See page 59.) 



We have a right to ask, in regard to the propo- 

 sition just enunciated, the following questions: 

 What is the sense of the word maximum here ? 

 By what sign can it be known that this maximum 

 is attained ? By what sign can it be known whether 

 the steam is employed to greatest possible advan- 

 tage in the production of motive power ? 



Since every re-establishment of equilibrium in 

 the caloric may be the cause of the production of 

 motive power, every re-establishment of equilibrium 

 which shall be accomplished without production of 

 this power should be considered as an actual loss. 

 Now, very little reflection would show that all 

 change of temperature which is not due to a change 

 of volume of the bodies can be only a useless re- 

 establishment of equilibrium in the caloric.* The 

 necessary condition of the maximum is, then, that 



* We assume here no chemical action between the bodies 

 employed to realize the motive power of heat. The chem- 

 ical action which takes place in the furnace is, in some 

 sort, a preliminary action, an operation destined not to 

 produce immediately motive power, but to destroy the 

 equilibrium of the caloric, to produce a difference of tem- 

 perature which may finally give rise to motion. 



