374 Prof. 0. Lodge on the Controversy 



*)f ail E.M,F. at the metal-metal junction, which again con- 

 tributes to the total observed Volta effect, but I assert that 

 we know its contribution to be small. 



How big it is in my opinion is answered above in Chapter I. 

 It is measured by the Peltier effect (Profs. Ayrton & Perry 

 will here ejaculate, Stuff and nonsense ! and Lord Kelvin 

 will support them. R. I. Discourse, §§ 23 & "24.) The 

 metal-air force is of the order volts. The metal-metal force 

 is of the order millivolts. 



Not much is known for certain about the Peltier or 

 physical forces at metal-liquid or liquid-liquid junctions, 

 and they are difficult to measure ; but they have been partially 

 measured by Bosscha and by Bouty (see reference in my 

 Report, p. 189, Phil. Mag., March 1885). They may also be 

 theoretically estimated in the way suggested by Dr.Hopkinson 

 in the Phil. Mag. for October 1885. M. Bouty thinks 

 that he has shown that the relation U = TdE/dt holds at 

 such junctions. What is certain is that if all the Peltier 

 forces are added algebraically together in a complete circuit 

 at uniform temperature, then, whether the completion be 

 dielectric or electrolytic, X(I1) = Td¥j/dt ; as Lord Kelvin 

 and von Helmholtz have proved, for the two cases of (1) 

 dielectric medium, (2) electrolytic medium, respectively. 



Thus the difference or controversy is no longer, if ever, a 

 difference between contact and chemical action ; a chemical 

 contact seems to be admitted now by both sides, but there is 

 an essential and by no means a nominal difference on the 

 question of the localisation both of the E.M.F. and of the 

 chemical contact. I locate the Volta force (the chief part of 

 it) and the chemical contact too, at the air boundary of each 

 metal. Anything occurring at the metallic junction 1 regard 

 as physical. Lord Kelvin locates the chief part of the Volta 

 force at what he is able to regard as an effectively chemical 

 contact, the zinc-copper junction ; and I presume that he 

 regards whatever happens at the metal-asther boundary as 

 physical. 



If asked why I maintain the zinc-copper junction to be 

 chemically inert, I pass a current across it, and point to the 

 absence of any chemical change there. If I am chaffed for 

 over-veneration for oxygen and its nascent or potential effect 

 on metallic surfaces, 1 again pass a current, by whatever 

 means are possible, and show oxide (or more likely sulphate, 

 this acid radical having much the same differential energy 

 of combination with zinc and copper as oxygen has. Nor 

 is that of chlorine very different. But one can show oxide 



