Forces in Voltaic and Thermoelectric Piles. 273 



Such phrases, however, unless they are closely related to a 

 real physical entity, are dangerous ; and one has, it seems to 

 me, a good example of this danger in the present instance. 

 Observe, I am not questioning for a moment the existence of the 

 analogy nor its convenience in expressing many of the facts ; 

 I question the truth of the physical meaning which may, and 

 has, come to be supposed to underlie the form of expression. 



If there is any real reason for believing electricity to actually 

 possess a specific heat, then all I here say falls to the ground; 

 but if the idea is based solely upon the ordinary facts of 

 thermoelectricity, then I say that it is a misleading idea 

 founded upon a picturesque analogy which has too promi- 

 nently intruded itself into science. 



Once grant that electricity in a metal has a real specific heat 

 which varies with temperature and with the nature of the 

 metal, and the Peltier and Thomson effects are at once ac- 

 counted for, without our being able to draw from them the 

 slightest information about seat of E.M.F or anything else. 

 For wherever specific heat falls in value, there heat must be 

 dropped, so to speak, by the current ; wherever it rises in 

 value, there heat must be absorbed. 



And, conversely, whenever it is desired to get rid of an 

 awkward and undesirable energy which ought to produce some 

 effect but does not, as, for instance, at the place of solution of 

 zinc in any ordinary battery-cell, it can be done without 

 trouble by this convenient hypothesis. Those who feel bound 

 by mere work-and-energy considerations, knowing that where 

 zinc combines with sulphuric acid, a considerable amount of 

 energy is set free, which does not appear as heat on the 

 spot, but does appear as the energy of an electric current, 

 these simple folk are constrained to believe that it expends 

 itself in propelling the current, i. e. that the zinc-acid junction 

 is the main seat of E.M.F. in the cell. Not so those who have 

 possessed themselves of the elastic specific-heat view — these 

 can otherwise regard the transaction. They may say, 



" True, energy is liberated by the solution of zinc ; and true, 

 it does not appear as heat; but the reason is not that it is expend- 

 ing itself in doing work, but because the specific heat of elec- 

 tricity, as it flows from zinc to acid, rises so greatly in amount 

 [no proof has been given of this gratuitous statement], that 

 all the heat that would otherwise be there generated is taken 

 up and absorbed by the flowing electricity. The place which 

 really does the work of propelling the current is not the zinc- 

 acid junction at all ; it is the zinc-copper junction. At this 

 spot arises all the energy of the electric current." 



" But," says a plain man, "surely that energy must come 

 from somewhere : either the zinc and copper must com- 



