﻿G2 



Dr. C. V. Burton on the 



magnetic properties) to find a sensibly linear relation con- 

 necting current-density with electromotive intensity in the 

 neighbourhood of each point. 



8. Contact E.M.F. and the Peltier Effect. 



It will now appear that, by assuming in each molecule 

 a mere arrangement of conducting and non-conducting parts, 

 we may realize what is at all events a working model of 

 contact E.M.F. and of the Peltier effect ; and even should 

 our model serve no other purpose, it directs our attention to 

 a possibility which seems so far to have been overlooked, and 

 which must, indeed, continue to be overlooked so long as 

 each metal is regarded as homogeneous. As it not my object 

 to state with becoming vagueness an hypothesis as to the 

 nature of Peltier's phenomenon, but rather to picture as 

 clearly as possible a mechanism whose principle may perhaps 

 be suggestive of the truth, 1 shall assume for the molecules 

 such a structure and distribution as appear most favourable 

 to simplicity of treatment. 



Suppose, then, that in one of the metals with which we 

 have to deal, each molecule is of the form indicated in fig. 2 : 

 a central perfectly conductive body, charged (say) ™ „ 

 positively, being completely surrounded by an 

 insulating layer, and this again being partially 

 (though not completely) enclosed by a number 

 of perfectly conductive particles. It will be con- 

 venient to suppose that in each molecule these outer 

 particles are all electrically connected with one another. When 

 two such molecules come into collision, the outer particles of 

 the one may not in general be reduced to the same potential as 

 those of the other, for the electrical oscillations occasioned by 

 the contact may not have time to subside into insignificance 

 before the encounter is ended. But the general tendency of 

 a collision between two molecules will be towards an equaliza- 

 tion of the potentials of the outer particles, and the average 

 values of potentials and charges amongst any considerable 

 number of molecules will be the same as if, during each 

 molecular encounter, this equalization has been completely 

 effected. 



It will here be convenient to introduce the term " con- 

 duction-potential," and as we proceed the following definitions 

 will be found useful: — 



The conduction-potential of a molecule is the potential (or 

 average potential) of its outer conductive particles. 



The conduction-potential at a point within a metallic body 

 is the average conduction -potential of the molecules in the 

 neighbourhood of that point. 



