MOTIVE POWER OF HEAT. 107 



This number is a little more than the 1.112 re- 

 sulting from the use of the vapor of water at tb.e 

 temperatures 100 and 99; but if we suppose the 

 vapor of water used at the temperatures 78 and 

 77, we find, according to the law of MM. Clement 

 and Desorme, 1.212 for the motive power due to 

 1000 units of heat. This latter number ap- 

 proaches, as we see, very nearly to 1.230. There 

 is a difference of only ^. 



We should have liked to be able to make other 

 approximations of this sort to be able to calculate, 

 for example, the motive power developed by the 

 action of heat on solids and liquids, by the conge- 

 lation of water, and so on; but Physics as yet re- 

 fuses us the necessary data * 



The fundamental law that we propose to confirm 

 seems to us to require, however, in order to be 

 placed beyond doubt, new verifications. It is based 

 upon the theory of heat as it is understood to-day, 

 and it should be said that this foundation does not 

 appear to be of unquestionable solidity. New ex- 

 periments alone can decide the question. Mean- 

 while we can apply the theoretical ideas expressed 



* Those that we need are the expansive force acquired 

 by solids and liquids by a given increase of temperature, 

 and the quantity of heat absorbed or relinquished in the 

 changes of volume of these bodies. 



