~ 
346 Prof. Oliver Lodge on the Seat of the 
depend in some way on the intensity of the current itself, 
since with a feeble current it will be able to dissipate itself 
faster than it forms, and with a strong current it will 
thoroughly coat the plate and the balance will escape. Sup- 
pose, then, we represent the force exerted by the hydrogen as 
H,,0 f (C) ; where f (0)=0, and /(o )=1 or something like 
1; then the force available for urging the current forward in 
any of the above cells is, in volts, 
45000 { Zn,O—M,0—H;,0 # (C) j. 
There is an obvious objection to be taken to this last 
hypothesis, viz. that it supposes the second metal M 
completely operative, even though it be thoroughly coated 
with hydrogen. This is hardly reasonable; and a compromise 
between the two preceding hypotheses is afforded by one of 
greater generality in which the available force is symbolically 
represented by 
Z4n—M ¢$ (C)—H; f (©), 
where ¢ is a function such perhaps that ¢ (C)=1-+7. fo). 
On this hypothesis the propelling H.M.F. is 
e=a5h55 {Zn,0-M,O—(H,,0-+n. M,0) f (C)}. 
This is too much like miscellaneous guessing, and we will 
make no more of such hypotheses; but if experiment could 
fix an empirical formula for this force in any case, we could 
apparently at once obtain the Joule or Bouty effect,* or rather 
the difference of two such effects, for that case ; because we 
should have the E.M.F’. experimentally observed on the one 
hand, and that calculated from pure energy-considerations on 
the other, as 
Zn,O— H,,0 
Seclinne  ae 
where the two B’s stand for the Bouty coefficients at the zine 
and the other metal respectively. The only objection is that 
in the cells now under discussion M is coated more or less 
with hydrogen, and hence the Bouty effect obtained is nothing 
very easily definable. 
* That is the thermoelectric contact-force at a metal-liquid junction: 
see section 6, 
