272 Prof. Oliver Lodge on the Seat of the Electromotive 



persons of eminence, and were it only a question with myself 

 as to which mode of expressing the fact was most consistent 

 with ordinary common sense and with one's natural physical 

 instinct, I should not hesitate to stigmatize myself as almost 

 ludicrously wrong-headed were I to accept the arbitrary 

 and hypothetical specific-heat- of-electricity hypothesis, and 

 decline the simple proposition that E.M.F. and unit-current 

 energy were proportional to one another, not only in an entire 

 circuit, as is by all sides admitted, but also in every portion of 

 such a circuit. 



I believe that the idea of attributing to Electricity a real 

 physical specific heat has arisen (wherever it has arisen) 

 solely from the natural, allowable, but almost playful, analogy 

 by which Sir W. Thomson chose to popularize his brilliant 

 discovery of the E.M.F. existing between a hot and a cold 

 piece of the same metal ; or, what is the same thing, of the 

 E.M.F. existing in any metal along which heat is flowing, 

 i. e. which is subject to a slope of temperature. 



He did not express it by saying there is an E.M.F. in iron, 

 ®(t)dt, which tends to propel electricity from hot parts toward 

 cold parts, and whose existence is proved, and amount 

 measured, by the generation of heat which appears in the 

 middle of a bar when a current is sent from its cold to its hot 

 end : he perceived that if electricity were a real fluid with an 

 actual capacity for heat, it would in flowing from cold to hot 

 " carry cold with it/'' and so cool the middle of the bar ; 

 and he expressed the sense of the phenomenon he had disco- 

 vered by saying that electricity in iron behaved as if it were 

 a fluid with a negative capacity for heat, of value © (t). But 

 I feel sure that at the time he had no notion that electricity in 

 iron really was such a fluid, or that it had such capacity for 

 heat. Soon afterwards he was able to prove that in copper 

 electricity behaved like a fluid with a positive capacity for 

 heat, "carrying heat with it " as it flowed from hot to cold, 

 and vice versa. 



This term, " the specific heat of electricity in a metal/' to 

 express the function ©a(0 or ©b(0> was ^ nus a ^ ^ rs ^ intro- 

 duced " without theory, but by an obvious analogy;" and I 

 surmise that any idea of an actual physical truth underlying 

 the phrase, or the notion that electricity in different sub- 

 stances really had a thermal capacity specific to that substance, 

 would have been scouted by the illustrious author of the 

 phrase as an illiterate pressing of an analogy. 



But the term survived ; was adopted by Prof. Tait ; we find 

 the numerical value of the specific heat of electricity in various 

 metals quoted and investigated in every memoir and research 

 on thermoelectricity; and I am constantly using it myself. 



