" THKBMODVNAMIC8. 



lUnkine, indeed, probably biassed by the results of experiments, allowed that 

 real specific heat of a substance might be different in different states of 

 Mtpth". ku t Clausius has clearly shewn that this admission is illogical, 

 n.i tlt if we admit any such changes, we had better give up real specific 



heat altogether. 



Statements of this kind have their legitimate place in molecular science, 

 where it is essential to specify the dynamical condition of the system, and to 

 distinguish the kinetic energy of the molecules from the potential energy of 

 their configuration; but they have no place in thermodynamics proper, in which 

 we deal only with sensible masses and their sensible motions. 



Both Rankine and Clausius have pointed out the importance of a certain 

 function, the increase or diminution of which indicates whether heat is entering 

 or leaving the body. Rankine calls it the thermodynamic function, and Clausius 

 the entropy. Clausius, however, besides inventing the most convenient name 

 for this function, has made the most valuable developments of the idea of 

 entropy, and in particular has established the most important theorem in the 

 whole science, that when heat passes from one body to another at a lower 

 temperature, there is always an increase of the sum of the entropy of the two 

 bodies, from which it follows that the entropy of the universe must always 

 be increasing. 



He has also shewn that if the energy of a body is expressed as a 

 function of the volume and the entropy, then its pressure (with sign reversed) 

 and its temperature are the differential coefficients of the energy with respect 

 to the volume and the entropy respectively, thus indicating the symmetrical 

 relations of the five principal quantities in thermodynamics. 



But Clausius, having begun by breaking up the energy of the body into 

 its thermal and ergonal content, has gone on to break up its entropy into 

 the transformational value of its thermal content and the disgregation. 



Thus both the energy and the entropy, two quantities capable of direct 

 measurement, are broken up into four quantities, all of them quite beyond 

 the reach of experiment, and all this is owing to the actual heat which 

 Clausius, after getting rid of the latent heat, suffered to remain in the body. 



Sir William Thomson, the last but not the least of the three great founders, 

 does not even consecrate a symbol to denote the entropy, but he was the 

 first to clearly define the intrinsic energy of a body, and to him alone are due 

 the ideas and the definitions of the available energy and the dissipation of 



