The telegraph manual: a complete history and description of the semaphoric, electric and magnetic telegraphs of Europe, Asia, Africa, and America, ancient and modern.

THE LEYDEN JAR EXPERIMENTS. 71
duced by charging is not to increase the quantity, but only to
disturb the natural electricity previously present in a latent
state on the inside and outside of the glass. There is injected
into the inside, by connection with the electrical machine, an
amount of positive electricity, while an equal amount of negative electricity is driven from the outside "by the force of
electrical induction; and unless the electricity on the outer
surface of the glass can be thus driven off by affording it a connection with the ground, the inside cannot receive a charge.
Let a Leyden jar be insulated from the earth by placing it
on a glass stand, and it will receive scarcely any electricity
from the conductor; not more than equal to the quantity
which can escape from the outside to the surrounding air. If
the knob of another insulated jar be connected with the ground,
and the outside coatings of the two jars be brought near
together, sparks will then pass
rapidly from the prime conductor F 15.
to the knob of the first, and they
will also pass as rapidly between
the outside coatings of the two
jars. In this manner both the
Leyden jars become charged, and
it will be found that they are
charged equally, but with electricity of opposite kinds. The first (B
one, that derived its electricity directly from the prime conductor,
will be charged positively; the
second, that derived its charge
from the electricity escaping from
the knob to the ground, will be
negative. Place the two jars on the table, and suspend
between them a pith ball, B, or other light substance, and it
will be attracted alternately from one to the other in rapid
vibrations, clearly showing that the electricity in the 1,wo jars
is of opposite kinds.
The phenomena that occur during the charge of a Leyden
jar have been adduced as evidence in support of the Franklinian theory of a single electric fluid, the outside being supposed to be in a minus state after parting with its natural
quantity to the other jar. But the phenomena are explicable
also on the hypothesis of two fluids, it being assumed that
they are separated from their neutral state by the coercing
force of the free electricity communicated to the inside of
the jar.