348 Prof. Oliver Lodge on the Seat of the 
cells when the same current is going through each, the resist- 
ance of each being the same, viz. } ohm; and then I will 
interpret the observations absolutely, calculating the H.M.F. 
of the cell under different currents, and seeing what empirical 
formula will best fit it. 
Relative Differences of Potential between the Terminals of 
three Voltameters of the same Resistance, through each of 
which the same current is driven by an auxiliary battery. 
Anode of each cell, zine ; cathode—zinc, copper, and pla- 
tinum respectively. 
Deflection of Electrometer attached to the 
terminals of 
Current flowing 
through each 
cell, in amperes.| the Zinc-Zine |the Zine-Copper| the Zinc- 
cell. Platinum cell. 
eell. 
DD —125 +70 to +90 
94. —148 + 26 
1:88 — 486 — 15 
15 —440 + 15 
2-4 —535 = oD 
2-0 —486 — 8 
2°4 —626 —140 
1:96 —575 — 77 
32 —'700 — 225 
2°73 — 630 — 250 
4:2 — 800 — 347 
3:4 —TAl — 250 
In the above Table the difference of potential between the 
terminals is written negative when it opposes the current, and 
positive when it helps it on. 
We will now interpret similar measurements absolutely, 
reckoning the actual H.M.F. of each cell, and try to fit an 
empirical formula to it on the plan of those (in sect. 20) 
already guessed ; assuming /(C) a linear function, for sim- 
plicity, until forced to try something more complex. It is 
quite impossible that f(C) can be a linear function really, but 
it very likely begins by being so, and only for big currents 
diverges notably. A hyperbolic tangent function, at a guess, 
would seem most likely to represent the case properly. 
