80 THE PHYSICAL SIGNIFICANCE OF ENTROPY 



SECTION D 



PHYSICAL SIGNIFICANCE OF THE EQUIVALENTS FOR GROWTH OF 

 ENTROPY GIVEN ON PAGES 42-43 



According to equivalent (i) growth of entropy is a passage 

 from more to less available energy. The comment already made 

 on p. 42 indicates sufficiently that this increase in unavailability 

 is due to the growth of the ungovernable features of molecular 

 motions as number of complexions increases. 



Equivalent (2) states growth of entropy to be a passage from 

 a concentrated to a distributed condition of energy. In this 

 scattered state the energy is certainly less controllable and for 

 the same reason as that given concerning equivalent (i). 



Equivalent (3) is based on the idea of irreversibility, and we 

 saw on p. 36 that the growth in the number of complexions is 

 the measure as well as the criterion of irreversibility. This growth 

 is therefore a sufficient and necessary feature of this equivalent. 



The equivalents grouped under (4) are all based on the theory 

 of probabilities. We have seen on pp. 36, 62, and elsewhere, 

 that the probability W of a state is the logarithm of the number 

 of complexions of the state. This number is therefore a necessary 

 feature of this set of equivalents and hence constitutes its 

 physical significance. 



The set of equivalents grouped under (5) are all closely 

 related, their dependence being more or less indicated by the 

 order in which they are there stated. The outcome of the series 

 is that growth of entropy corresponds to an increase in the 

 number of complexions. 



The mathematical concept stated under (6) covers more than 

 molecular configurations; it covers configurations whose elements 

 are those of energy as well, and has been successfully applied by 

 PLANCK in problems dealing with the energy of radiation. Every 

 such configuration has a number of complexions. 



