90 MOTIVE POWER OF HEAT. 



We have carried out the table to the extremes 

 of compression and rarefaction. It may be be- 

 lieved that air would be liquefied before acquiring 

 a density 1024 times its normal density, that is, 

 before becoming more dense than water. The 

 specific heat would become zero and even negative 

 on extending the table beyond the last term. We 

 think, furthermore, that the figures of the second 

 column here decrease too rapidly. The experi- 

 ments which serve as a basis for our calculation 

 have been made within too contracted limits for us 

 to expect great exactness in the figures which we 

 have obtained, especially in the outside numbers. 



Since we know, on the one hand, the law ac- 

 cording to which heat is disengaged in the com- 

 pression of gases, and on the other, the law accord- 

 ing to which specific heat varies with volume, it 

 will be easy for us to calculate the increase of tem- 

 perature of a gas that has been compressed with- 

 out being allowed to lose heat. In fact, the com- 

 pression may be considered as composed of two 

 successive operations : (1) compression at a con- 

 stant temperature ; (2) restoration of the caloric 

 emitted. The temperature will rise through the 

 second operation in inverse ratio with the specific 

 heat acquired by the gas after the reduction of 

 volume, specific heat that we are able to calculate 



