Electromotive Forces in the Voltaic Cell. 159 
energy, that, making exception of such irreversible effects as 
are not readily brought into calculation, and allowing for 
certain possible reversible effects to be investigated thermo- 
electrically, the H.M.F. of a cell is not only dependent on the 
chemical action going on, but is calculable numerically in 
absolute measure on purely chemical data supplied provision- 
ally by Dr. Andrews. It is proper to say, however, that this 
brilliant theory is avowedly based on the laborious and acute 
experimental work of Joule on the conservation of energy in 
the voltaic circuit™. 
In the other of the two papers (that on “ Thermo-eleciricity ’’) 
it was shown that, from the fact that a current absorbed or 
generated heat at a metallic junction, an H.M.F. was neces- 
sarily situated there—in other words, that the Peltier effect 
necessitated the previously discovered Seebeck one. 
The establishment of the conservation of energy, by Joule, 
for ever placed beyond doubt the fact that the energy of the 
electric current produced by a battery was due to, and was 
the equivalent of, the chemical actions going on there ; but it 
was supposed, and is still supposed (though, as I venture to 
think, quite erroneously), to leave untouched the question us 
to the precise seat of the H.M.F. in a battery. 
However that may be, the success of the chemical theory 
of the electric current naturally caused it to be still more 
certainly assumed that the apparent contact-force of Volta 
could also be accounted for by accidental chemical action, and 
that without some chemical action somewhere no Volta effect 
could be produced. ‘This, also, I believe to be quite false ; 
provided always that the phrase “ chemical action ”’ be used in 
its ordinary sense as meaning combination, and that the word 
“action ’’ be not explained away as meaning anything what- 
ever. : 
2. The triumph of the chemical theorists with regard to the 
Volta effect was, however, shortlived, for, from 1860, the in- 
vention of the quadrant electrometer put into the hands of 
electrostatic experimenters a far more refined and delicate in- 
strument than could have been thought possible a few years 
before ; and the illustrious inventor of that instrument him- 
self for ever put the truth of Volta’s phenomenon beyond 
doubt, by the most simple and beautiful device of suspending 
a charged torsion-arm over a zinc-copper junction. By com- 
paring the deflection so produced with that caused by a 
* Joule :—‘ On Heat evolved in Metals and during Electrolysis,” Phil. 
Mag. [3] xix. p. 260 (1841); “On the Electric Origin of the Heat of 
Combustion,” 2b7d. xx. p. 98, and xxii. p. 204; ‘‘ On the Heat disengaged 
in Chemical Combination,” Phil. Mag. [4] ii. p. 481. See also Reprint 
of Joule’s papers by the Physical Society of London (Taylor & Francis). 
