﻿Theory of Contact Electromotive Force. 277 



Furthermore 



dT_U P 2 '_P' 



Since P 2 = rcR# and T 1 = n 1 R0, we have 

 dT R, n 2 



Thus the relative concentrations of the free electrons in 

 different metals may be obtained, at all temperatures, from 



dT 

 a knowledge of their thermoelectric powers. Since -—6 * s 



very nearly a linear function of the temperature for most 

 pairs of metals, over a considerable range of temperature, 

 it would seem that w 2 / w i cannot, for any pair of metals, be 

 represented as a power of 0, but must be of the form Ae b ®, 

 where A and b are constants. This form may, however, only 

 be an empirical approximation. 



A theory of thermoelectric phenomena, stated by its author 

 to be based on principles somewhat similar to those vvbich 

 underlie the present development, has just been published in 

 the Annalen der Physik by Mr. K. Baedeker *. I am unable 

 to. agree with the results of Mr. Baedeker's theoretical 

 calculations, which seem to involve a misconception of the 

 principles which should underlie the applications of the laws 

 of thermodynamics. 



The Function w. 



The nature of the work w, which an electron has to do in 

 order to escape from a metal, is a matter of considerable 

 interest. If the positive and negative electricity were inde- 

 finitely subdivisible, like the mathematical elements of an 

 ideal fluid, then the sign of the work would reverse with the 

 sign of the escaping charge. This follows since, if there 

 were a part of iv which did not reverse with the sign of the 

 charge, it would have to depend on the square and other 

 even powers of the latter, and could be made to vanish in 

 comparison with the remainder if the charge were removed 

 in sufficiently small amounts. In such a case w could 

 only arise from a discontinuity in the electric potential at 

 the surface of the conductor, and the natural means of ex- 

 plaining its existence would be to postulate the occurrence 

 of an electrical double layer. 



* Ann. der P/n/s. vol. xxxv. p. 75 (1911). 



