24* MAXWELL'S LAW 405 



I do not conceal that this conclusion is not proved with con- 

 vincing force by the foregoing considerations. I will also not 

 suppress the fact that Boltzmann 1 has put forward another -it- 

 law : from reflections that are very similar to those here given, 

 but which seem to me less justifiable, he concludes that the mean 

 energy of an atom e must be equal in magnitude to the molecular 

 enejgy, JJ7. The comparison with experiment, which was instituted 

 in 55, 56, speaks in favour of my view in the great majority of 

 cases. 



25*. Molecular and Atomic Motion in 

 Mixed Gases 



The considerations of the previous paragraphs may without 

 difficulty be extended to gases which, like atmospheric air, con- 

 tain molecules of different kinds. The more general problem of 

 determining the distribution of the energy between the molecular 

 and atomic motions in such a gaseous mixture depends entirely 

 on the same equations which were established and solved before ; 

 we have only in this case to do with a greater number of such 

 equations. We obtain, therefore, for each kind of molecule, and 

 each species of atom, formulae to express the law of distribution 

 of energy which are quite like the others, and differ from them 

 only in the values of the constants that enter into them. 



If, now, we again assume that the mixture considered has no 

 translatory motion, but heat-motion only, and so put 



a = b = c = 0, 



the law which determines the energy of molecular motion depends 

 only, as the formulas of 21* show, on a single constant k, which 

 has the same value for each kind of molecules. It thus follows 

 that the mean value of the energy of molecular motion is the same 

 for each kind of molecules, or 



The conclusions drawn from these equalities in 20* hold 

 good, then, not only for monatomic, but also for polyatomic 

 molecules, so that we are justified in laying down the following 

 laws quite generally, both for chemically simple and chemically 

 compound gaTses. 



Wiener Sitzungsber. Ixiii. Abth. 2, 1871, p. 397. 



