On certain supposed Irreversible Processes, 475 



forces is 2II/0 ; and this entropy is proved equal to d^j/dd, a 

 remarkable and interesting but long known fact. 



Returning to the theory of Helmholtz, which was stated 

 first so long ago as 1847, and elaborated to some extent in 

 his brilliant " Faraday lecture " of 1881, it is undoubtedly 

 very important ; it may be regarded as the precursor of, and 

 therefore to some extent superseded by, the electron or cor- 

 puscular theory of matter : a theory which represents the 

 natural outcome, in the light of recent experiments, of that 

 u atomic " view of electricity which, started by Clerk Maxwell 

 in an inspired phrase, adopted and expanded by Dr. Johnstone 

 Stoney and others, is now in the preceding pages attempted 

 to be applied, in conjunction with ideas derived from the 

 treatment of osmotic pressure by physical chemists, to 

 an explanation of thermoelectric action on the gaseous 

 analogy. 



[To be continued.] 



XLIV. On certain supposed Irreversible Processes. 

 By S. H. Burbury, F.R.S* 



1. /"CERTAIN processes in nature are irreversible. If for 

 \j instance mechanical energy be converted into heat, 

 only a part of it can, as a net result, be reconverted. The 

 energy, or part of it, is dissipated. 



2. We are taught in the kinetic theory of gases that heat con- 

 sists of, or is proportional to, the energy of molecular motions 

 in the stationary state which involve no dissipation of energy, 

 and are therefore reversible. If this theory be true, there 

 should exist processes which, as they relate to an aggregate of 

 molecules, are irreversible, although they consist of molecular 

 motions each separately reversible. Can any such process be 

 proved to exist ? 



3. The analytical theorems which are supposed to prove the 

 existence of such processes have generally the following form. 

 It is proved that a function, always of the same sign, 

 diminishes or increases until a limit is reached, which limit 

 may be a maximum or minimum for the function in question, 

 and when that limit is reached the motion is stationary. Any 

 such function may be called the characteristic function of the 

 process in question, and shall be denoted by H. 



It is sufficient to consider the case where H is a diminishing 



* Communicated by the Author. 



