very surface molecule being
practically a little battery cell with one terminal free in the air, so
that when a proper conductor approaches the surface it receives the
electricity from millions of cells, and therefore becomes strongly
electrified so that a spark may at once be drawn from it.

WHAT IS ELECTRICITY?

THEORIES.

NUMEROUS attempts have been made to explain the phenomena of
electricity. As a general thing, these phenomena are so utterly unlike
other phenomena that have been explained and are easily intelligible,
that it has quite generally been taken for granted, until lately, that
something very different from ordinary matter and the laws of forces
applicable to it must be involved in the phenomena themselves.
Consequently the term _imponderable_ was applied to it,--something that
was matter minus some of the essentials of matter; and as it was
apparent that, whatever it was, it moved, apparently flowed, from one
place to another, the term _fluid_ was applied to it, a term descriptive
of a certain form of matter. Imponderable fluid was the descriptive name
applied to electricity. Newton supposed that an excited body emitted
such a fluid that could penetrate glass. When the two facts of
electrical attraction and repulsion had to be accounted for, two
theories were propounded,--one by Benjamin Franklin, the other by Dufay.
Franklin supposed that electricity was a subtle, imponderable fluid, of
which all bodies contained a certain normal quantity. By friction or
otherwise this normal quantity was disturbed. If a body received more
than its due share, it was said to be positively electrified: if it had
less than its normal quantity, it was said to be negatively electrified.
Franklin supposed this electric fluid to be highly self-repulsive, and
that it powerfully attracted the particles of matter.

According to Dufay, there are two electric fluids, opposite in tendency
but equal in amount. When associated together in equal quantities, they
neutralize each other completely. A portion of this neutral compound
fluid pervades all matter in its unexcited state. By friction or
otherwise this compound fluid is decomposed, the rubber and the body
rubbed exchanging equal quantities of opposite kinds with each other,
leaving one of them positively, the other negatively electrified. These
two fluids were supposed to be self-repulsive, but to attract each
other: so that, if two bodies be charged with either posit