MOTIVE POWER OF HEAT. 69 



be taken, as in the employment of different sub- 

 stances, or in the use of the same substance in two 

 different states for example, of a gas at two dif- 

 ferent densities. 



This leads us naturally to those interesting re- 

 searches on the aeriform fluids researches which 

 lead us also to new results in regard to the motive 

 power of heat, and give us the means of verifying, 

 in some particular cases, the fundamental proposi- 

 tion above stated.* 



We readily see that our demonstration would 

 have been simplified by supposing the temperatures 

 of the bodies A and B to differ very little. Then 

 the movements of the piston being slight during 

 the periods 3 and 5, these periods might have been 

 suppressed without influencing sensibly the pro- 

 duction of motive power. A very little change of 

 volume should suffice in fact to produce a very 

 slight change of temperature, and this slight change 

 of volume may be neglected in presence of that of 

 the periods 4 and 6, of which the extent is unlim- 

 ited. 



If we suppress periods 3 and 5, in the series of 



* We will suppose, in what follows, the reader to be au 

 courant with the later progress of modern Physics in re- 

 gard to gaseous substances and heat. 



