268 Prof. Oliver Lodge on the Seat of the 
Now put the zine and copper into direct metallic contact, 
and neglect for the present the third of a millivolt of H.M.F. 
developed at the junction, which acts so as to drive positive 
electricity from copper to zinc. A rush of electricity must 
take place from the copper to the zinc to equalize their 
potential ; it is impossible that they can remain at different 
potentials when directly united : all parts of a conductor must 
be at a uniform potential, and the rush has taken place because 
they were not so when put into contact. 
15. Picturing to ourselves the effect as produced by the 
straining oxygen atoms, we shall perceive that they could not 
get at either metal when separate: first, because they sur- 
rounded it everywhere, and strained equally on all sides ; and 
second, because, being all charged with negative electricity, 
they could not move in on all sides at once without, so to 
speak, compressing the electricity in the body and giving it 
an absolute charge. But directly the copper touched the zinc 
the oxygen atoms were cleared away at the point of contact, 
and the stress of those at the rest of its surface was no longer 
counterbalanced. Moreover, they can now all move nearer to 
the zinc because a way of escape for electricity is provided 
into the copper, whose surrounding oxygen atoms will be thus 
driven back somewhat further from the surface, until the 
dielectric strain, assisting the chemical strain on the copper 
surface and opposing it on the zinc surface, prevents further 
displacement, and equilibrium is again attained. The electri- 
city which escaped from the zinc to the copper was negative 
electricity (oxygen being essentially an electro-negative ele- 
ment), the negatively charged oxygen atoms have moved a 
little nearer to the zine than their normal distance: 2. e. the 
thickness of its layer of negative electricity is reduced, or its 
surface is positively charged; the negative layer on the 
copper has been slightly thickened—its surface is negatively 
charged. 
This is a pictorial way of representing the process, and may 
be regarded as somewhat fanciful; it is, however, the way in 
which the theory originally occurred to me, and it permits 
more insight into the processes than a mere statement in terms 
of potential can ; though it may well be that the imagined 
processes are but distant likenesses of the real ones. 
The oxygen atoms have moved nearer to the zinc; itis now 
more easily oxidized than before. ‘The copper, on the other 
hand, is by contact with zinc somewhat protected. 
Observe that the contact has not developed any force ; it 
has only, by sweeping away the oxygen from the point of 
contact, enabled previously existing forces to do work and 
produce their effect. 
