376 Prof. Oliver Lodge on the Seat of the 



" On our hypothesis, 

 Cu/ Aq + Aq/Zn = ( Cu/Aq) + (Ag/Zn) + Cu/Aq + Aq/Zn. 



If we close the circuit by connecting the zinc and copper plate 

 by a copper wire, the force Zn/Cu adds itself to these E.M.F.s, 

 and this force removes from the tension series of the metals 

 the following forces, (Cu/Aq) + (Aq/Zn) ; wherefore we get 



Cu/Aq + Aq/Zn + Zn/Cu = CujAq + Aq/Zn. 



But this last is the part of the total E.M.F. applied to the 

 formation of the current. Hence to the directly found contact- 

 forces betiveen different metals and water we must add the 

 electromotive excitation of one metal on the other in order to get 

 the current-forming E.M.F. in the circuit of a closed cell" 



So far as I am able to see to the bottom of the foregoing 

 theory its foundation appears to be as follows : — Contact ex- 

 periments compel us to accept the summation law for the 

 Volta-effects, or total differences of potential, 



E = Cu/Aq + Aq/Zn + Zn/Cu. 



The chemical theory constrains us to admit that the E.M.F. of 

 a cell is the equivalent of the chemical action going on, and 

 thus suggests that it equals the sum of some chemical contact 

 forces ; or, in Wiedemann's notation, E ought also to equal 



Cu/Aq + Aq/Zn. 



How are these two requirements to be reconciled ? 



Assume that at every junction there is a total force made 

 up of two portions — a chemical force, such as Cu / Aq, and 

 a physical force, which may be denoted by (Cu/Aq), and 

 write the whole E.M.F. of a cell equal to the sum of all these 

 chemical and physical junction-forces, 



E=Cu/Aq+{Cu/ Aq)+Aq / Zn + (Aq / Zn) + (Zn/Cu). 



We have then only to make the physical forces obey Volta's 

 series law; so that 



(Cu/Aq) + (Aq/Zn) + (Zn/Cu) = 0; 



and we get the required relation 



E=Cu/Aq + Aq/Zn, 



which harmonizes chemical and contact views. 



Prof. Wiedemann's reconciliation of contact and chemical 

 theories would thus seem to be somewhat of the same order as 

 the later and less complete one of Fleeming Jenkin, quoted 

 in my paper, § 6; but I cannot help feeling that the theory 



