266 Prof. Oliver Lodge on the Seat of the 
endeavouring to combine with it. They may indeed partially 
succeed ; but suppose they do not, we have here a strong 
potential chemical action or chemical strain, which must pro- 
bably be accompanied by some physical phenomenon. Now 
remember that oxygen is an electro-negative element; and 
without endeavouring to examine too precisely what significa- 
tion is involved in that statement, it will be not out of accord 
with orthodox views if we assume that it means that at least 
any dissociated oxygen atoms are negatively charged, each 
with the characteristic charge of a freedyad atom. Granting 
something equivalent to this, without pressing the form of 
expression too closely, we perceive that the strain of the 
oxygen towards the zine will result in what I metaphorically 
call a slackening up, or attempted compression, of the nega- 
tive electricity in it; 2. e. in a rise of negative potential. We 
may therefore say that zinc is at a lower potential than the air 
surrounding it, and that the step of potential in crossing the 
boundary from zine to air is closely connected with the 
chemical affinity between zinc and oxygen. Observe that this 
step of potential does not obviously nor probably depend on 
the amount of oxygen present. It is possible that a few 
million molecules may be as effective as a large number. 
Note also that the step of potential is by no means caused by 
actual oxidation : in so far as the zinc surface is tarnished by 
oxidation the strain will be diminished and the step of poten- 
tial become less. 
Nothing is said here about the possible effect of the nitro- 
gen, because it is simplest in the first instance to ignore it, 
though whether experiment will justify this simplicity or not, 
I do not yet know. 7 
We may go further and assert that if in general the 
chemical] affinity of two substances can be measured by their 
energies of combination, then the step of potential in the 
present case may perhaps be calculable from the heat of com- 
bustion of zinc. 
And one may justify this assertion thus. Let an atom of 
oxygen combine with an atom of zinc; it will generate an 
amount of heat h, and its characteristic charge, g, will be 
given up to the zine and will thereby fall down the step of 
potential, v, which separates the zinc from the air. Mow if — 
we suppose that the heat h is the representative and equivalent 
of the fall of energy q v, it follows of course that 
Jh 
=. 
qg 
Make the hypothesis and see what comes of it. 
