AND OF THE SECOND LAW 89 



Nature vary in one direction only, we can, in the light of what of 

 has just preceded, repeat the following precise, scientific state- 

 ment: 



" The Second Law, in its objective-physical form (freed from 

 all anthropomorphism) refers to certain mean values which are 

 found from a great number of like and ' chaotic ' elements." 



If we now go back to what constitutes the kernel of the Second 

 Law, we will see the relevance and force of PLANCK'S enunciation 

 of this law: 



"It is not possible to construct a periodically functioning 

 motor which effects nothing more than the lifting of a load and 

 the cooling of a heat reservoir." 



The proof of this is purely experimental and cumulative, and 

 the same may be said of the earlier statement of this law, " all 

 changes in Nature vary in one direction only." The character 

 of this proof is, moreover, exactly like that for the First Law, 

 the Conservation of Energy, and has the same sort of validity. 



When we compared and interpreted the current statements of 

 the Second Law (pp. 44-47) we enunciated and made use of 

 three helpful propositions that will now be repeated: 



(a) All cases of irreversibility stand or fall together; if any one 

 can be reversed all can be reversed. 



(b) Any general consequence of any one correct statement of 

 the Second Law may be regarded as itself a valid and com- 

 plete statement of the Second Law. 



(c) The summary of all the necessary prerequisites (or con- 

 ditions) for determining Entropy may be regarded as a 

 complete and valid statement of the Second Law. 



In this connection it will also be helpful to remember PLANCK'S 

 statement: " In order that a process may be truly reversible it 

 will not suffice to declare that the mediating body is directly 

 reversible, but that at the end, everywhere in the whole of Nature, 

 the same state must be restored which existed at the beginning 

 of said reversible process." 



