264 Prof. Oliver Lodge on the Seat of the 
resultant H.M.F. is the algebraic sum of the Volta forces 
measured electrostatically in air for every junction in the 
chain : neglecting magnetic or impressed H.M.F. [| Verified 
most completely by Ayrton and Perry. | 
B. Thomson. 
iv. The H.M.F. in any closed circuit is equal to the energy 
conferred on unit electricity as it flows round it. 
[Neglect magnetic or impressed H.M.F. in what follows. | 
vy. At the junction of two metals any energy conferred on, 
or withdrawn from, the current, must be in the form of heat. 
At the junction of any substance with an electrolyte, energy 
may be conveyed to or from the current at the expense of 
chemical action as well as of heat. 
vi. Ina circuit of uniform temperature: if metallic, the 
sum of the E.M.F.’s is zero by the second law of thermo- 
dynamics ; if partly electrolytic, the sum of the E.M.F.’s is 
equal to the sum of the energies of chemical action going on 
per unit current per second. 
vii. In any closed conducting circuit the total intrinsic 
H.M.F. is equal to the dynamical value of the sum of the 
chemical actions going on per unit of electricity conveyed 
(3J6e), diminished by the energy expended in algebraically 
generating reversible heat. 
viii. The locality of any E.M.F’. may be detected, and its 
amount measured, by observing the reversible heat or other 
form of energy there produced or absorbed per unit current 
per second. [This is held by Maxwell but possibly not by 
Thomson *, though its establishment is due to him. | 
II. Statements believed by the writer to be false though 
orthodox. 
ix. Two metals in air or water or dilute acid, but not in 
contact, are practically at the same potentialf. [Sir William 
Thomson, Clifton, Pellat. | 
* The only reason which I can think of as likely to have caused Sir 
William to doubt or deny the validity of this proposition is given and, I 
hope, refuted at sections 10 and 11. 
+ The truth or falsity of this statement may be held to depend on a 
question of words, viz. the definition of potential. Sir William at the 
meeting said he had always defined potential as the work done in bring- 
ing a unit charge close up to, but not eto, the body. This definition 
explains some apparent inconsistency in one or two of his utterances which 
I had never quite understood. But seeing that there is no difficulty what- 
ever in giving a charge up to a metal body, but rather the contrary, why 
not define its potential in the more simple manner which followers of his 
have unconsciously, and I believe universally, adopted, not knowing that 
they were thus putting themselves out of harmony with him? Given his 
definition, so that the potential of a body means really not its potential 
