, the first zinc
plate of the series being the most negative, and the last copper plate
the most positive.

CAROLINE.

But does the battery become more and more strongly charged, merely by
being allowed to stand undisturbed?

MRS. B.

No, for the action will soon stop, as was explained before, unless a
vent be given to the accumulated electricities. This is easily done,
however, by establishing a communication by means of the wires
(Fig. 1.), between the two ends of the battery: these being brought into
contact, the two electricities meet and neutralize each other, producing
the shock and other effects of electricity; and the action goes on with
renewed energy, being no longer obstructed by the accumulation of the
two electricities which impeded its progress.

EMILY.

Is it the union of the two electricities which produces the electric
spark?

MRS. B.

Yes; and it is, I believe, this circumstance which gave rise to Sir H.
Davy's opinion that caloric may be a compound of the two electricities.

CAROLINE.

Yet surely caloric is very different from the electrical spark?

MRS. B.

The difference may consist probably only in intensity: for the heat of
the electric spark is considerably more intense, though confined to a
very minute spot, than any heat we can produce by other means.

EMILY.

Is it quite certain that the electricity of the Voltaic battery is
precisely of the same nature as that of the common electrical machine?

MRS. B.

Undoubtedly; the shock given to the human body, the spark, the
circumstance of the same substances which are conductors of the one
being also conductors of the other, and of those bodies, such as glass
and sealing-wax, which are non-conductors of the one, being also
non-conductors of the other, are striking proofs of it. Besides, Sir H.
Davy has shewn in his Lectures, that a Leyden jar, and a common electric
battery, can be charged with electricity obtained from a Voltaic
battery, the effect produced being perfectly similar to that obtained by
a common machine.

Dr. Wollaston has likewise proved that similar chemical decompositions
are effected by the electric machine and by the Voltaic battery; and has
made other experiments which render it highly probable, that the origin
of both electricities is essentially the same, as they show that the
rubber of the common electrical machine, like the zinc in the Voltaic
battery, produces the two electricities by combining with o