alone.
This, however, is not always the case. Man carries his heart with him
into all his works. You cannot separate the moral and emotional from the
intellectual; and thus it is that the discussion of a point of science
may rise to the heat of a battle-field. The fight between the rival
optical theories of Emission and Undulation was of this fierce
character; and scarcely less fierce for many years was the contest as
to the origin and maintenance of the power of the voltaic pile. Volta
himself supposed it to reside in the Contact of different metals.
Here was exerted his 'Electro-motive force,' which tore the combined
electricities asunder and drove them as currents in opposite directions.
To render the circulation of the current possible, it was necessary to
connect the metals by a moist conductor; for when any two metals were
connected by a third, their relation to each other was such that a
complete neutralisation of the electric motion was the result. Volta's
theory of metallic contact was so clear, so beautiful, and apparently
so complete, that the best intellects of Europe accepted it as the
expression of natural law.

Volta himself knew nothing of the chemical phenomena of the pile; but
as soon as these became known, suggestions and intimations appeared that
chemical action, and not metallic contact, might be the real source of
voltaic electricity. This idea was expressed by Fabroni in Italy, and
by Wollaston in England. It was developed and maintained by those
'admirable electricians,' Becquerel, of Paris, and De la Rive, of
Geneva. The Contact Theory, on the other hand, received its chief
development and illustration in Germany. It was long the scientific
creed of the great chemists and natural philosophers of that country,
and to the present hour there may be some of them unable to liberate
themselves from the fascination of their first-love.

After the researches which I have endeavoured to place before you, it
was impossible for Faraday to avoid taking a side in this controversy.
He did so in a paper 'On the Electricity of the Voltaic Pile,' received
by the Royal Society on the 7th of April, 1834. His position in the
controversy might have been predicted. He saw chemical effects going
hand in hand with electrical effects, the one being proportional to the
other; and, in the paper now before us, he proved that when the former
was excluded, the latter were sought for in vain. He produced a current
without