interrupted.'[3]

[3] This seems to be a misprint for uninterrupted.



Further along in the same letter Volta reiterates his
conviction that the contact of the two metals furnishes the
true motive power of the current. Thus he says (p. 138):

'As to the rest, the action which excites and gives motion to
the electric fluid does not exert itself, as has been
erroneously thought, at the contact of the wet substance with
the metal, where it exerts so very small an action, that it may
be disregarded in comparison with that which takes place, as
all my experiments prove, at the place of contact of different
metals with each other. Consequently the true element of my
electromotive apparatus, of the pile, of cups, and others that
may be constructed according to the same principles, is the
simple metallic couple, or pair, composed of two different
metals, and not a moist substance applied to a metallic one, or
inclosed between two different metals, as most philosophers
have pretended. The humid strata employed in these complicated
apparatus are applied therefore for no other purpose than to
effect a mutual communication between all the metallic pairs,
each to each, ranged in such a manner as to impel the electric
fluid in one direction, or in order to make them communicate,
so that there may be no action in a direction contrary to the
others.'