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electro-motive force of the two plates of a Daniell’s element 
into 100 parts, from 60 to 70 of those parts are required to 
reduce the zinc half ring and the copper half ring to such 
a state that the moveable bar remains at rest whether it is 
electrified vitreously or resinously. 
i! If the copper half ring is oxydised by heat, the amount 
of electro-motive force then required to neutralise the two 
halves is much increased. If, after oxydising the copper one 
day by heat, I leave the apparatus till the next day, the effect 
is generally diminished, though something of it still remains. 
After again heating the copper by laying it for some time on 
a redhot iron heater and allowing it to cool, I found the effect 
almost exactly 100 parts. I have no doubt that by making 
the coat of oxyde very complete and thick enough, and by 
cleaning the zinc perfectly, I shall be able to get considerably 
above the electro -motive force of a single Daniell’s element. 
I remembered perfectly what you told me a long time ago 
about heating the coppers of a battery and getting a strong 
effect, for some time equal to that of the Daniell’s cell, when 
I tried the effect of oxydising the copper plate by heat. 
iS I believe there are also electrical effects of heat itself ; so 
that if one half of a ring of one metal is hot and the other is 
cold, the needle will show a difference according as it is 
charged positively or negatively. 
“ For nearly two years I have felt quite sure that the proper 
explanation of voltaic action in the common voltaic arrange- 
ment is very near Volta’s, which fell into discredit because 
Volta or his followers neglected the principle of conservation 
of force. I now think it quite certain that two metals dipped 
in one electrolytic liquid will (when polarisation is done away 
with) reduce two dry pieces of the same metals, when con- 
nected each to each by metallic arcs, to the same potential. 
“ There cannot be a doubt that the whole thing is simply 
chemical action at a distance. Zinc and copper connected 
by a metallic arc attract one another from any distance. 
