agitates or disturbs the electric fluid, or gives it a certain
impulse. Do not ask in what manner: it is enough that it is a
principle and a great principle.'

It will be seen that at this stage of his discovery Volta was
inclined to attribute tho origin of the current to the contact
between the metals and his moist "conductors of the second
class," though later in the same article he says it is
impossible to tell whether the impulse which sets the current
in motion is to be attributed to the contact between the metals
themselves or between the two metals and the moist conductor,
since either supposition would lead to the same results.

Later, as was shown in the previous paper by the present writer
Volta came to regard the metallic contact as the cause of the
electromotive force. In a letter written to Gren in 1797 and
published as a postscript to his letter of August, 1796, Volta
says:

'Some new facts, lately discovered, seem to show that the
immediate cause which excites the electric fluid, and puts it
in motion, whether it be an attraction or a repulsive power, is
to be ascribed much rather to the mutual contact of two
different metals, than to their contact with moist conductors.'

The new facts, "lately discovered," to which Volta attributes
his change of view were his repetitions of Bennett's
experiments of 1789.

Volta apparently thought that the current was not only set up