AND OF THE SECOND LAW 79 



All the negative transformations present ^ all the positive 

 transformations that occur. 



f an irreversible 1 

 When there is simply j ., , ^process without the 



cyclic feature, then the sum of the entropies of all the bodies par- 

 ticipating in any one occurrence is, at the end of the change of con- 



{ greater than ] 

 dition \ , t that at the beginning. 



From this we see that a negative change of entropy always 

 keeps company with an equal or greater positive change of entropy. 



Again, for sake of simplicity, use a gas as an illustration; 

 then we may say: (i) Every possible negative transformation in a 

 gas is always accompanied by a net positive transformation in 

 the other and necessary external agencies. (2) All possible 

 negative transformations in a .gas are reversible ones. We here 

 use the word possible because there is an impossible class of 

 negative transformations, namely, those which, so far as order 

 and directness are concerned, are the very opposites of the so-called 

 spontaneous changes of state. 



It will suffice here to enumerate these opposites: Without 

 external help (a) to pass heat from a cold to a hot body, (b) to 

 decrease the volume of a gas, (c) to convert the heat of friction 

 directly back into the work which called it forth, (d) to separate the 

 gaseous constituents of a mixture. 



By way of contrast we may add, that the so-called spontaneous 

 (irreversible) processes were all positive transformations which 

 took place without any change whatever in surrounding bodies. 



