MOTIVE POWER OF HEAT. 67 



each other, after a fashion, one neutralizing the 

 other. 



The impossibility of making the caloric produce 

 a greater quantity of motive power than that which 

 we obtained from it by our first series of opera- 

 tions, is now easily proved. It is demonstrated by 

 reasoning very similar to that employed at page 5G; 

 the reasoning will here be even more exact. The 

 air which we have used to develop the motive 

 power is restored at the end of each cycle of opera- 

 tions exactly to the state in which it was at first 

 found, while, as we have already remarked, this 

 would not be precisely the case with the vapor of 

 water.* 



* "We tacitly assume in our demonstration, that when a 

 body has experienced any changes, and when after a cer- 

 tain number of transformations it returns to precisely its 

 original state, that is, to that state considered in respect to 

 density, to temperature, to mode of aggregation let us 

 suppose, I say, that this body is found to contain the same 

 quantity of heat that it contained at first, or else that the 

 quantities of heat absorbed or set free in these different 

 transformations are exactly compensated. This fact has 

 never been culled in question. It was first admitted with- 

 out reflection, and verified afterwards in many cases by 

 experiments with the calorimeter. To deny it would be 

 to overthrow the whole theory of heat to which it serves 

 as a basis. For the rest, we may say in passing, the main 



