MOTIVE POWER OF HEAT. 145 



that which was previously absorbed) at the conclusion it 

 reaches its primitive value, S, in virtue of Carnot's funda- 

 mental axiom.] 



[Note of Nov. 5, 1881. With Prof. James Thomson's 

 correction of operation (3), the words in virtue of " Car- 

 not's Fundamental Axiom" must be replaced by "the 

 condition fulfilled by operation (3)," in the description of 

 the results of operation (4).] 



16. At the conclusion of this cycle of operations * 

 the total thermal agency has been the letting down 

 of H units of heat from the body A, at the tem- 

 perature S, to B, at the lower temperature T\ and 

 the aggregate of the mechanical effect has been a 

 certain amount of work produced, since during the 

 ascent of the piston in the first and second opera- 

 tions, the temperature of the water and vapor, and 

 therefore the pressure of the vapor on the piston, 

 was on the whole higher than during the descent, 

 in the third and fourth operations. It remains for 

 us actually to evaluate this aggregate amount of 

 work performed ; and for this purpose the f ollow- 



* In Carnot's work some perplexity is introduced with 

 reference to the temperature of the water, w;hich, in the 

 operations he describes, is not brought back exactly to 

 what it was at the commencement ; but the difficulty 

 which arises is explained by the author. No such difficulty 

 occurs with reference to the cycle of operation described 

 in the text, for which I am indebted to Mons. Clapeyron. 



