Forces in Voltaic and Thermoelectric Piles. 275 



remarks at Soc. Tel. Eng. Disproved also by experiments of 

 Edlund.] 



d. The specific heat of Electricity, i. e. ®(t), falls greatly as 

 it flows from copper to zinc and rises a nearly equal amount 

 as it flows from zinc to acid. [It really rises from about 

 240 to 600 on passing from copper to zinc ; what it does on 

 entering acid no one yet knows.] 



e. The rate of variation of Volta-effect with temperature is 

 a measure of the Peltier-effect at a junction. [Pure assump- 

 tion.] 



/. Heat is generated or destroyed at certain places in a circuit, 

 because Electricity changes its capacity for heat there ; or 

 because some other hypothetical change goes on sufficient to 

 account for the observed effect without having to fall back 

 upon the too simple and obvious vera causa of an opposition 

 or a helping E.M.F, located at these places. [Overpressing 

 of a mere analogy.] 



Only a little wilder is the following : — 



g. Reversible energy-actions, e. g. chemical combination or 

 disunion, may go on in a circuit when a current passes, without 

 producing heat or any other form of energy on the spot, and 

 without either propelling or retarding the current ; because 

 the energy which one would expect to appear there is taken 

 up and disposed of by some change in the properties of Elec- 

 tricity as it passes that place, such as a change in its specific 

 heat : and yet the total E.M.F. of the circuit shall be somehow 

 numerically equal to the energy so available. 



[This last statement reads almost like nonsense. It has 

 nevertheless been virtually maintained by many contact phi- 

 losophers, though I understand from their last communication 

 that Ayrtoii and Perry have now given it up. It appears 

 that they concede the seat of E.M.F. as regards chemical 

 actions and the voltaic circuit, but retain their old persuasion 

 in respect to thermal actions and the thermoelectric circuit.] 



To be quite clear let me just recapitulate these statements, 

 modifying them so as to be correct from my point of view. 



a. The characteristic function/^) of a simple thermoelectric 

 circuit represents itself, and no other physical phenomenon 

 that has as yet been specially observed. At the same time I 

 admit that the constant term in this function is unknown, 

 and undeterminable by thermoelectric experiments ] it thus 

 affords a fine field for speculation, of which contact-theorists 

 have availed themselves. If one knew the value of this con- 

 stant a there would be no room for discussion, it would all be 

 matter of fact. 



b, e. The Volta-effect of two metals certainly varies with 



