Electromotive Forces in the Voltaic Cell. 259 
metals, provided that the E.M.F. is determined before any 
alteration of the metallic surface wetted by the liquid has 
occurred ; but these alterations produce themselves very 
rapidly.” 
Pellat’s theoretical conclusions being short may also be 
here quoted, and I will number them on with the others. 
(6) “ It is extremely probable that the difference of poten- 
tial between the electric coats which cover two metals con- 
nected metallically represents the true difference of potential 
which exists between them. No reason, either theoretical or 
experimental, can be invoked against the existence of a dif- 
ference of potential between two metals in contact.” 
(7) “This last quantity has no connection with the thermo- 
electric H.M.F. measured by the Peltier phenomenon.” 
(8) “It has only a vague and distant connection with the 
difference of oxidizability of the metals.” 
Concerning these propositions, I may remark that while 
number 2 is likely to annoy contact theorists (though I 
know they have methods of explaining it away), numbers 4 
and 5 are calculated to restore their equanimity. The five 
experimental conclusions I accept as in duty bound, only per- 
mitting myself to doubt the perfect generality of numbers 
4 and 5 under all circumstances; but the three theoretical 
ones I am unable to wholly accept. Thus with respect to 
the second part of number 6, I beg entirely to differ from 
M. Pellat if Lam called on to simultaneously admit number 7. 
Whether one is prepared to accept any of his theoretical con- 
clusions or to reject them all, depends upon how one regards 
them. Ifin the way he himself intended, then I reject them all. 
If with one’s own interpretation, then I say that the second part 
of 6 and 8 are true (though for “ only a vague and distant ” 
I would substitute ‘no’’) ; and 7 is also true if it be held to 
refer to the quantity first mentioned in number 6, while 
number 8 refers to the other quantity. Number 6 I should also 
consider true if the prefix “im ”’ be made to the fourth word. 
10. Pellat then proceeds to explain why he considers the 
Peltier effect to be quite distinct from, and have no relation 
to, the true H.M.F’. of contact. In explaining this he makes 
use of a piece of unpleasantly plausible reasoning, which I 
myself have heard Professor Ayrton use, and which, when 
unexpectedly suggested, is so painfully benumbing that it is 
worth while to quote it, and to indicate its weak point. Pel- 
lat’s statement of the argument is rather long; perhaps it can 
with advantage be abbreviated. 
Two metals A and B put into contact are at different poten- 
tials, the difference A/B being due to and equal to the E.M.F. 
