380 Prof. 0. Lodge on the Controversy 



I trust that I have made it clear that I do not regard this 

 matter of the definition of potential as of the same importance 

 as the seat of E.M.F. in the pile. In no other part of this 

 paper have I paid any attention to the wording of pro- 

 positions in terms of potential ; it is a subsidiary dispute 

 superposed on the main disagreement, which latter is in 

 no sense a matter of words or definition. 



Nevertheless the two disputes are somewhat closely allied, 

 and the clarification of one ought to result in pacification 

 of the other. 



Chapter IV. 



Some recent modes of regarding the Mechanism of the 

 Chemical Contact Force. 



I have elsewhere tried to explain the mode in which I 

 suppose the oxygen to act to bring about that momentary 

 transfer of electricity which occurs across the junction of two 

 metals the instant they are put into contact. The facts 

 postulated are (1) the fact of chemical affinity between 

 oxygen and metal, of amount different for different metals, 

 and (2) the fact that oxygen atoms are, at any rate some of 

 them, negatively charged. 



On the strength of these facts I see a surrounding layer of 

 straining oxygen atoms seeking to move up to the zinc, but 

 unable to do so because of " the impossibility of conferring 

 an absolute charge on matter/' as Faraday in his ice-pail 

 experiment put it, or because of the " incompressibility of 

 electricity," or because there is no avenue for the supply of 

 electricity of opposite sign. Consequently we have a state 

 of siege, a kind of incipient polarisation, but no charge. 

 The zinc is somewhat in the condition of an insulated sphere 

 surrounded by a concentric negatively charged shell, so far 

 as the interior of the shell is concerned : outside the con- 

 ditions are different. And the cause of the stress is different : 

 there are no lines of electric force, there is no electrical 

 difference of potential ; whatever force or potential-difference 

 exists between isolated zinc and air is chemical in its nature — 

 the result of chemical affinity. The force may be due, as 

 Helmholtz puts it, to a specific attraction of zinc for elec- 

 tricity, or it may be due to a specific attraction for oxygen ; 

 but to whatever it is due, so long as the surface is homo- 

 geneous, it is inoperative, it results in no energy trans- 

 formation or work done, it is a deadlock. 



Now establish connexion at one point with some neutral 

 substance, say platinum, or a less strained-at substance, like 



