id used
for this purpose should be of an animal nature. Water, and acids very
much diluted by water, are found to be the most effectual in promoting
the developement of electricity in metals; and, accordingly, the
original apparatus which Volta first constructed for this purpose,
consisted of a pile or succession of plates of zinc and copper, each
pair of which was connected by pieces of cloth or paper impregnated with
water; and this instrument, from its original inconvenient structure and
limited strength, has gradually arrived at its present state of power
and improvement, such as is exhibited in the Voltaic battery. In this
apparatus, a specimen of which you see before you (PLATE VI. fig. 1.),
the plates of zinc and copper are soldered together in pairs, each pair
being placed at regular distances in wooden troughs and the interstices
being filled with fluid.

[Illustration: Plate VI. p. 151.

Fig. 1. Voltaic Battery.
Fig. 2.
Fig. 4.
Fig. 1. 2. & 4. Voltaic Batteries

Fig. 3. Electrical Machine.
A the Cylinder.
B the Conductor.
R the Rubber.
C the Chain.]

CAROLINE.

Though you will not allow us to enquire into the precise cause of
electricity, may we not ask in what manner the fluid acts on the metals
so as to produce it?

MRS. B.

The action of the fluid on the metals, whether water or acid be used, is
entirely of a chemical nature. But whether electricity is excited by
this chemical action, or whether it is produced by the contact of the
two metals, is a point upon which philosophers do not yet perfectly
agree.

EMILY.

But can the mere contact of two metals, without any intervening fluid,
produce electricity?

MRS. B.

Yes, if they are afterwards separated. It is an established fact, that
when two metals are put in contact, and afterwards separated, that which
has the strongest attraction for oxygen exhibits signs of positive, the
other of negative electricity.

CAROLINE.

It seems then but reasonable to infer that the power of the Voltaic
battery should arise from the contact of the plates of zinc and copper.

MRS. B.

It is upon this principle that Volta and Sir H. Davy explain the
phenomena of the pile; but notwithstanding these two great authorities,
many philosophers entertain doubts on the truth of this theory. The
principal difficulty which occurs in explaining the phenomena of the
Voltaic battery on this principle, is, that two such plates show no
signs of