78 THE PHYSICAL SIGNIFICANCE OF ENTROPY 



before diffusion. There is of course a corresponding increase in 

 entropy due to such diffusion. 



All these irreversible processes are passages from less stable 

 to more stable conditions, from less probable to more probable 

 states, or summarizing: 



There is in Nature a constant tendency to equalize tempera- 

 ture differences, to convert work into heat, to increase disgrega- 

 tion and to promote diffusion. 



This tendency has also been described as the tendency in Nature 

 to pass from concentrated to distributed conditions of energy. 



The four irreversible processes just discussed are all sponta- 

 neous ones, i.e., they occur without the help of agencies external 

 to the bodies directly engaged in the transformations. 



It is evident that the foregoing statements are really identical, 

 expressing the same thought in different ways. 



SECTION C 



NEGATIVE CHANGE OF ENTROPY; SOME OF ITS PHYSICAL 

 FEATURES OR NECESSARY ACCOMPANIMENTS 



A negative transformation in any part of a system is the 

 diminution of entropy which it experiences, and this we know 

 means a diminution in the number of complexions of the part 

 considered. But there are some features of such negative trans- 

 formations which, while they do not in themselves constitute any 

 additional principle, deserve special mention. 



Before we make such mention, however, we will anticipate 

 a little, and state the Second Law in forms which will make said 

 features obvious: 



In an irreversible cycle the sum of the changes of entropies 

 experienced by all the bodies concerned is greater than zero. 

 When the cycle is reversible in all of its parts, then said sum 

 of entropy changes is equal to zero. 



A corollary from this theorem is that, in a cycle, 



