41.2 Prof. R. Clausius on the Second Fundamental 



is compressed again at another temperature ; then, if the expan- 

 sion takes place at a higher temperature than the compression, 

 the ergon performed during the expansion will exceed the ergon 

 expended during the compression ; and there is thus on the whole 

 a preponderance of ergon performed, and therefore naturally a 

 corresponding quantity of heat is expended. If the cyclical 

 process is gone through the other way, so that the expan- 

 sion occurs at a lower temperature than the compression, the 

 ergon expended in the compression exceeds that performed du- 

 ring the expansion ; and hence the result is a preponderance of 

 ergon expended, and consequently a corresponding quantity of 

 heat must be produced. 



Hence, when a body goes through a cyclical process, there is 

 a transformation either of heat into ergon, or of ergon into heat, 

 according to the direction in which the cycle is performed ; and 

 the question now arises whether this transformation exists by 

 itself, or whether, as in the simpler cases previously considered, 

 it is accompanied by a further transformation which serves as a 

 compensation. 



We will take, in the first place, by way of example, the case 

 in which the expansion occurs at a higher temperature than the 

 compression. In order that the original temperature of the body 

 may be kept up during the expansion, some external body or 

 other, which we may call the body A, must impart to it the heat 

 required to replace the heat expended in ergon during the ex- 

 pansion. When, during the further course of the cyclical process, 

 the temperature is lowered and the body is compressed at this 

 lower temperature, in order that it may retain the same tem- 

 perature throughout the compression, it must give out, to some 

 other body (which we may call B) of lower temperature, the 

 heat produced from ergon during the compression. 



This last quantity of heat, which is produced from ergon du- 

 ring the compression and imparted to the body B, according to 

 what is said above, is not quite as great as that which is with- 

 drawn from the body A during the expansion aud expended in 

 the performance of ergon. The excess of the latter quantity of 

 heat over the former quantity is permanently transformed into 

 ergon by the cyclical process. Of the remainder of the heat, 

 however, which is withdrawn from the body A, that portion 

 namely which, though at first converted into ergon is afterwards 

 converted back again from ergon into heat and given up as 

 such to the body B, we may say that it is transferred from 

 the body A of high temperature to the body B of lower tem- 

 perature. 



The final result of the cyclical process is thus twofold : a cer- 

 tain quantity of heat is permanently transformed into ergon, and 



