364 Prof. 0. Lodge on the Controversy 



only at a metallic junction does <? = II individually. At an 

 electrolytic or dielectric or what I may call a chemical 

 junction, that is one with chemical potentialities, the E.M.F. 

 is not purely thermal, and hence is not measured by the 

 Peltier effect ; it is chiefly of chemical origin and is calculable 

 from the energy of combination of the materials on either 

 side the boundary. 



Observe I do not say that at such a junction there need be 

 any chemical action (at least not any completed chemical 

 combination in the ordinary sense) to account for the E.M.F., 

 but there is the possibility of chemical combination ; and 

 there will be actual chemical combination if a finite quantity 

 of electricity is transmitted across it For conduction in an 

 electrolyte is convective in its nature ; whatever electricity 

 travels, the material atoms travel with it ; and the travelling 

 of oppositely charged ions in opposite directions involves 

 chemical action at a liquid junction, involves transfusion of 

 substance, involves what is practically, and may be actually, 

 chemical recombination. Possibly something of the same 

 sort may be said, less positively, about electric displacement 

 at a dielectric boundary. 



But at a metallic junction there is no such chemical 

 potentiality. You may pass a strong current across a zinc- 

 copper junction for years and you will not get any brass. I 

 would not deny that there may be a kind of material or 

 " corpuscular " interchange even here : in fact in the light of 

 recent most interesting work by J. J. Thomson it is probable ; 

 but the corpuscles thrown across the junction from zinc 

 become copper ; and vice versa, those dissociated from a 

 copper atom settle into their new places as part of a zinc 

 atom ; there may thus be a tendency to an ineffective kind 

 of transmutation , but there is no tendency to alloy, (See end 

 of Chapter IV.) 



Why then if a metallic junction is chemically inert should 

 it ever be held that the chemical affinity of zinc for copper is 

 the propelling influence which causes the E.M.F. located at 

 such a junction ? Wbat has ordinary chemistry got to do 

 with this metallic E.M.F. ? I echo the question, and proceed 

 to my second chapter. 



CH AFTER II. 



The facts of Contact Electricity. 



Some people (for whom I have a great respect), on the 

 strength of the fact that metals in contact attract each 

 other, maintain that this accounts for their tendencv to 



