﻿498 Thermodynamical Theory of Radiation. 



It is perhaps worth noting that Bridge's Theorems do 

 not hold for this unsymmetrical system ; i. e., the scale as well 

 as the relative distribution of the maxima and minima in the 

 unsymmetrical pattern is altered by altering the width of the 

 face of the prism or the wave-length of the light, the incidence 



being constant. If, however, the ratio — is kept unchanged, 

 the diffraction-pattern is not altered. 



The experiments and observations recorded in this note 

 were made at the Presidency College Physical Laboratory. 



LVI. Remarks on Professor Jeans Article " On the Thermo- 

 dynamical Theory of Radiation. 39 By L. B. Tuckerman, Jr. 



IN the July number of this Magazine*, Professor Jeans has 

 a short article on the " Thermodynamical Theory of 

 Radiation," in which he draws conclusions which do not 

 seem to me to be justified. He says : " Since, however, 

 <rT 4 is to be the amount of energy per unit volume, the 

 physical dimensions of cr are known. 



" The thermodynamical argument by which, in this first 

 theory, the formula <rT 4 is reached, is concerned only with 

 phenomena taking place in the aether. Thus we should 

 naturally expect that it would be possible to evaluate a in terms 

 of quantities which measure the properties of the aether/' 



That, however, is not the case, as the dimensions of a are 

 dependent also on the dimensions of T, a quantity which is 

 and can be defined only in terms of the properties of matter, 

 and in fact in terms of properties which are common to all 

 matter. 



If, then, the second method mentioned by Professor Jeans 

 gives us a valid relation between a and e (the charge of an 

 electron) which enables us to evaluate e in terms of a and 

 vice versa, this relation does not in the least invalidate the 

 derivation by means of the " Thermodynamical Theory of 

 Radiation," but merely adds another universal constant to 

 those already thermodynamically deduced. 



The apparent paradox obtained by assuming an " ideal " 

 matter, with electrons bearing the charge \e, is therefore no 

 more and no less fatal an objection to the thermodynamics 

 of radiation, than the paradox obtained by assuming an 

 " ideal " fluid for which Clapeyron's formula does not hold, 

 is to the thermodynamics of ordinary matter. 



Berlin, Physikalisches Institut, 

 July 30, 1906. 



* Phil. Mag. 1906, vol. xii. no. 67, pp. 57-60. 



