46 THE PHYSICAL SIGNIFICANCE OF ENTROPY 



second kind. The former may be readily reduced to the latter, 

 for it is easy to conceive of such legitimate modification of the 

 former as will make it only a special case of the latter. 



(5) The following statements are by distinguished physicists 

 and had better here be considered as confined to events occurring 

 in closed cycles. 



CLAUSIUS. It is impossible for a self-acting machine unaided 

 by any external agency to convey heat from one body to another 

 of higher temperature. 



CLERK MAXWELL. It is impossible by the unaided action, of 

 of natural processes to transform any part of the heat of a body 

 into mechanical work, except by allowing heat to pass from that 

 body to another of lower temperature. 



THOMSON. It is impossible by means of inanimate material 

 agency to derive mechanical effect from any portion of matter 

 by cooling it below the temperature of the coldest of surrounding 

 objects. 



(6) The efficiency of a perfect engine is independent of the 

 working fluid. 



(7) Waste of energy once incurred cannot be diminished in 

 the universe, or in any part of it which neither takes in nor gives 

 out energy. 



We understand here by waste that residual part of heat of 

 which none can be elevated back into work. 



The measure of such waste = T (S 2 -Si), when T = lowest 

 temperature and $2 Si = change of entropy in a process. This 

 brings out emphatically that the Second Law is not a law of con- 

 servation, it is a, law of waste, a law of wasted opportunities for 

 utilizing technically available energy. 



(8) The second law and irreversibility do not depend on any 

 special peculiarity of heat motion, but only on the statistical 

 property of a system possessing an extraordinary number of 

 degrees of freedom. 



(9) M. PLANCK. The second law, in its objective physical 



