ccording to Franklin's theory, electricity exists in all bodies
as a "common stock," and tends to seek and remain in a state of
equilibrium, just as fluids naturally tend to seek a level. But
it may, nevertheless, be raised or lowered, and this equilibrium
be thus disturbed. If a body has more electricity than its normal
amount it is said to be POSITIVELY electrified; but if it has
less, it is NEGATIVELY electrified. An over-electrified or "plus"
body tends to give its surplus stock to a body containing the
normal amount; while the "minus" or under-electrified body will
draw electricity from one containing the normal amount.
Working along lines suggested by this theory, Franklin attempted
to show that electricity is not created by friction, but simply
collected from its diversified state, the rubbed glass globe
attracting a certain quantity of "electrical fire," but ever
ready to give it up to any body that has less. He explained the
charged Leyden jar by showing that the inner coating of tin-foil
received more than the ordinary quantity of electricity, and in
consequence is POSITIVELY electrified, while the outer coating,
having the ordinary quantity of electricity diminished, is
These studies of the Leyden jar, and the studies of pieces of
glass coated with sheet metal, led Franklin to invent his
battery, constructed of eleven large glass plates coated with
sheets of lead. With this machine, after overcoming some defects,
he was able to produce electrical manifestations of great
force--a force that "knew no bounds," as he declared ("except in
the matter of expense and of labor"), and which could be made to
exceed "the greatest know effects of common lightning."
This reference to lightning would seem to show Franklin's belief,
even at that time, that lightning is electricity. Many eminent
observers, such as Hauksbee, Wall, Gray, and Nollet, had noticed
the resemblance between electric sparks and lightning, but none
of these had more than surmised that the two might be identical.
In 1746, the surgeon, John Freke, also asserted his belief in
this identity. Winkler, shortly after this time, expressed the
same belief, and, assuming that they were the same, declared that
"there is no proof that they are of different natures"; and still
he did not prove that they were the same nature.