ctricity can pass out of the rubber, it will not continue to go
into it, and consequently no additional accumulation will take place.
Now as one kind of electricity cannot be given out without the other,
the developement of the positive electricity is stopped as well as that
of the negative, and the conductor therefore cannot receive a succession
of charges.

CAROLINE.

But does not the conductor, as well as the rubber, require a
communication with the earth, in order to get rid of its electricity?

MRS. B.

No; for it is susceptible of receiving and containing a considerable
quantity of electricity, as it is much larger than the rubber, and
therefore has a greater capacity; and this continued accumulation of
electricity in the conductor is what is called a charge.

EMILY.

But when an electrical machine is furnished with two conductors to
receive the two electricities, I suppose no communication with the earth
is required?

MRS. B.

Certainly not, until the two are fully charged; for the two conductors
will receive equal quantities of electricity.

CAROLINE.

I thought the use of the chain had been to convey the electricity _from_
the ground into the machine?

MRS. B.

That was the idea of Dr. Franklin, who supposed that there was but one
kind of electricity, and who, by the terms positive and negative (which
he first introduced), meant only different quantities of the same kind
of electricity. The chain was in that case supposed to convey
electricity _from_ the ground through the rubber into the conductor. But
as we have adopted the hypothesis of two electricities, we must consider
the chain as a vehicle to conduct the negative electricity into the
earth.

EMILY.

And are both kinds of electricity produced whenever electricity is
excited?

MRS. B.

Yes, invariably. If you rub a tube of glass with a woollen cloth, the
glass becomes positive, and the cloth negative. If, on the contrary, you
excite a stick of sealing-wax by the same means, it is the rubber which
becomes positive, and the wax negative.

But with regard to the Voltaic battery, in order that the acid may act
freely on the zinc, and the two electricities be given out without
interruption, some method must be devised, by which the plates may part
with their electricities as fast as they receive them. --Can you think
of any means by which this might be effected?

EMILY.

Would not two chains or wires, suspended from either plate to