264 Prof. Oliver Lodge on the Seat of the Electromotive 



at once, and to fight over the domain, not only of electricity, 

 but of hydraulics and mechanics as well. Hitherto this has 

 been our policy, but the result is that we stubbornly maintain 

 our respective positions and neither side obtains any striking 

 advantage. Moreover this kind of skirmishing at the present 

 stage would consume a good deal both of time and space, and 

 it is doubtful whether much of it would be profitable. 



I propose therefore to change my tactics, and, fixing upon 

 some one well-marked and crucial position, try to show under 

 what conditions it can be held by either side, and what con- 

 sequences would result from its abandonment by the other. 



Such a position is afforded by the thermoelectric views 

 deliberately and specifically expressed in their last communi- 

 cation in the January Philosophical Magazine. For our 

 opinions on one part of this subject are quite definite and yet 

 quite contradictory*. 



I hold that local heat-production in a metallic circuit is a 

 precise measure of local E.M.F. Professors Ayrton and Perry 

 hold that the tw r o things are unconnected, or at least quite 

 otherwise connected. 



The question then is, Does a seat of E.M.F. necessitate a 

 source of reversible heat at the same spot ? or, conversely, Does 

 a local E.M.F. exist wherever reversible heat appears? and 

 are the E.M.F. and the reversible heat directly proportional 

 to one another ? 



In discussing this question we both have, and I especially 

 (as more needing it) have, the great advantage of Dr. Hop- 

 kinson's communication on the subject, published in the 

 Philosophical Magazine for October 1885, in which he judi- 

 cially reviews the arguments used by both sides ; and though 

 he does not pronounce sentence one way or another, it is 

 easy, I think, to see in w r hich direction he himself inclines. 

 To my unbounded astonishment, however, Professors Ayrton 

 and Perry, in an appendix to their January paper, claim Dr. 

 Hopkinson as a champion of their cause ! 



It would be both futile and ridiculous to argue about the 

 views of a third person ; but I may be allowed to say that, in 

 the first three quarters of Dr. Hopkinson's paper, the only 

 portion germane to the present subject, there is nothing with 

 which I do not cordially and unhesitatingly agree ; and if 

 Messrs. Ayrton and Perry agree with it too it is not surpri- 

 sing, for, as I say, he judicially and fairly sets forth the 



* I may quote Prof. Ayrton in support of this (Journal of the Society 

 of Telegraph Engineers, 1885) : — " Dr. Lodge's reasoning is based on a 

 totally wrong conception of the Peltier effect, which I am astonished to 

 find exists in the mind of a man/ ; &c. 



