234	Faraday's Researches
theory has long had possession of men's minds, is sustained by
a great weight of authority, and for years had almost undisputed
sway in some parts of Europe. If it be an error, it can only
be rooted out by a great amount of forcible experimental evi-
dence ; a fact sufficiently clear to my mind by the circumstance,
that De la Rive's papers have not already convinced the workers
upon this subject. Hence the reason why I have thought it
needful to add my further testimony to his and that of others,
entering into detail and multiplying facts in a proportion far
beyond any which would have been required for the proof and
promulgation of a new scientific truth (1005). In so doing I
may occasionally be only enlarging, yet then I hope strengthen-
ing, what others, and especially De la Rive, have done.
 788.	It will tend to clear the question, if the various views
of contact are first stated.   Volta's theory is, that the simple
contact of conducting bodies causes electricity to be developed
at the point of contact without any change in nature of the
bodies themselves;  and that though such conductors as water
and aqueous fluids have this property, yet the degree in which
they possess it is unworthy of consideration in comparison with
the degree to which it rises amongst the metals.1   The present
views of the Italian and German contact philosophers are, I
believe, generally the same, except that occasionally more im-
portance is attached to the contact of the imperfect conductors
with the metals.   Thus Zamboni (in 1837) considers the metallic
contact as the most powerful source of electricity, and not that
of the metals with the fluids;2 but Karsten, holding the con-
tact theory, transfers the electromotive force to the contact of
the fluids with the solid conductors.3   Marianini holds the same
view of the principle of contact, with this addition, that actual
contact is not required to the exertion of the exciting force,
but that the two approximated dissimiliar conductors  may
affect each other's state, when separated by sensible intervals
of the r?riyo -fidth of a line and more, air intervening.4
 789.	De la Rive, on the contrary, contends for simple and
strict chemical action, and, as far as I am aware, admits of no
current in the voltaic pile that is not conjoined with and depen-
dent upon a complete chemical effect.   That admirable elec-
trician Becquerel, though expressing himself with great caution,
1	Annales de Chimie, 1802, xl. p. 225.
2	Bibliotheque Unwerselle, 1836, v. 387;   1837, viii. 189.
31'Institut^ No. 150.
4 Mem. della Soc. Ital. in Modena, 1837, xxi. 232-237.