THE PHYSICAL SIGNIFICANCE OF ENTROPY 

 AND OF THE SECOND LAW 



[There is no difference between change of Entropy and Second Law, when each 



is fully defined.] 



INTRODUCTION 



PURPOSE, ACKNOWLEDGMENTS, THE Two METHODS OF APPROACH 

 AND OUTLINE OF TREATMENT 



THIS article is intended for those students of engineering who 

 already have some elementary knowledge of thermodynamics. 

 It is intended to clear up a difficulty that has beset every earnest 

 beginner of this subject. The difficulty is not one of application 

 to engineering problems, although here too there have been 

 widespread misconceptions, 1 for the expressions developed by 

 CLAUSIUS are simple, have long been known and much used by 

 engineers and physicists. The difficulty is rather as to the 

 ultimate physical meaning of entropy. This term has long been 

 known as a sort of property of the state of the body, has long been 

 surmised to be of essentially a statistical nature, but with it all 

 there was a sense that it was a sort of mathematical fiction, 

 that it was somehow unreal and elusive, so it is no wonder 

 that in certain engineering quarters it was dubbed the "ghostly 

 quantity." 



Now this instinct of the true engineer to understand things 



1 See Entropy, by JAMES SWINBURNE; this author has called attention to 

 necessary corrections and duly emphasized the engineering aspect. 



