rtained by such
trials. In the manner above described it may be correctly ascertained[A].

[A] Mr. Christie, who being appointed reporter upon this paper, had it
in his hands before it was complete, felt the difficulty (202.); and
to satisfy his mind, made experiments upon iron and copper with the
large magnet(44.), and came to the same conclusions as I have arrived
at. The two sets of experiments were perfectly independent of each
other, neither of us being aware of the other's proceedings.

212. It must still be observed that in these experiments the whole effect
between different metals is not obtained; for of the thirty-four feet of
wire included in each circuit, eighteen feet are copper in both, being the
wire of the galvanometer coils; and as the whole circuit is concerned in
the resulting force of the current, tin's circumstance must tend to
diminish the difference which would appear between the metals if the
circuits were of the same substances throughout. In the present case the
difference obtained is probably not more than a half of that which would be
given if the whole of each circuit were of one metal.

213. These results tend to prove that the currents produced by
magneto-electric induction in bodies is proportional to their conducting
power. That they are _exactly_ proportional to and altogether dependent
upon the conducting power, is, I think, proved by the perfect neutrality
displayed when two metals or other substances, as acid, water, &c. &c.
(201. 186.), are opposed to each other in their action. The feeble current
which tends to be produced in the worse conductor, has its transmission
favoured in the better conductor, and the stronger current which tends to
form in the latter has its intensity diminished by the obstruction of the
former; and the forces of generation and obstruction are so perfectly
neutralize each other exactly. Now as the obstruction is inversely as the
balanced as to conducting power, the tendency to generate a current must
be directly as that power to produce this perfect equilibrium.

214. The cause of the equality of action under the various circumstances
described, where great extent of wire (183.) or wire and water (181.) were
connected together, which yet produced such different effects upon the
magnet, is now evident and simple.

215. The effects of a rotating substance upon a needle or magnet ought,
where ordinary magnetism has no influence, to be directly a