mployed.

By increasing the number of plates of a battery, you increase its
_intensity_, whilst, by enlarging the dimensions of the plates, you
augment its _quantity_; and, as the superiority of the battery over the
common machine consists entirely in the quantity of electricity
produced, it was at first supposed that it was the size, rather than the
number of plates that was essential to the augmentation of power. It
was, however, found upon trial, that the quantity of electricity
produced by the Voltaic battery, even when of a very moderate size, was
sufficiently copious, and that the chief advantage in this apparatus was
obtained by increasing the intensity, which, however, still falls very
short of that of the common machine.

I should not omit to mention, that a very splendid, and, at the same
time, most powerful battery, was, a few years ago, constructed under the
direction of Sir H. Davy, which he repeatedly exhibited in his course of
electro-chemical lectures. It consists of two thousand double plates of
zinc and copper, of six square inches in dimensions, arranged in troughs
of Wedgwood-ware, each of which contains twenty of these plates. The
troughs are furnished with a contrivance for lifting the plates out of
them in a very convenient and expeditious manner.*

[Footnote *: A model of this mode of construction is exhibited in
PLATE XIII. Fig. 1.]

CAROLINE.

Well, now that we understand the nature of the action of the Voltaic
battery, I long to hear an account of the discoveries to which it has
given rise.

MRS. B.

You must restrain your impatience, my dear, for I cannot with any
propriety introduce the subject of these discoveries till we come to
them in the regular course of our studies. But, as almost every
substance in nature has already been exposed to the influence of the
Voltaic battery, we shall very soon have occasion to notice its effects.

CONVERSATION VI.

ON OXYGEN AND NITROGEN.

MRS. B.

To-day we shall examine the chemical properties of the ATMOSPHERE.

CAROLINE.

I thought that we were first to learn the nature of OXYGEN, which come
next in our table of simple bodies?

MRS. B.

And so you shall; the atmosphere being composed of two principles,
OXYGEN and NITROGEN, we shall proceed to analyse it, and consider its
component parts separately.

EMILY.

I always thought that the atmosphere had been a very complicated fluid,
composed of all the variety of ex