MOTIVE POWER OF HEAT. 165 



temperature. When, by observation, j* has been 

 determined as a function of the temperature, the 

 amount of mechanical effect, M, deducible from 

 H units of heat descending from a body at the 

 temperature S to a body at the temperature T, 

 may be calculated from the expression 



rrt 



M=H C pdt,. . . . (7) 



t/S 



which is, in fact, what either of the equations (1) 

 for the steam-engine, or (4) for the air-engine, be- 

 comes, when the notation //, for Carnot's multi- 

 plier, is introduced. 



The values of this integral may be practically 

 obtained, in the most convenient manner, by first 

 determining, from observation, the mean values of 

 /* for the successive degrees of the thermometric 

 scale, and then adding the values for all the de 

 grees within the limits of the extreme temperatures 

 tfand T.* 



32. The complete theoretical investigation of 

 the motive power of heat is thus reduced to the 

 experimental determination of the coefficient /t ; 

 and may be considered as perfect, when, by any 

 series of experimental researches whatever, we can 



\ 

 * The results of these investigations are exhibited in 



Tables I and II. 



