munication be through the air, without any conductor, a
bright light is seen between the bodies, and a sound is heard. In
small experiments, we call this light and sound the electric spark and
snap; but in the great operations of nature, the light is what we call
_lightning_, and the sound (produced at the same time, though
generally arriving later at our ears than the light does in our eyes)
is, with its echoes, called _thunder_.

If the communication of this fluid be by a conductor, it may be
without either light or sound, the subtle fluid passing in the
substance of the conductor.

If the conductor be good, and of sufficient bigness, the fluid passes
through it without hurting it. If otherwise, it is damaged or
destroyed.

All metals, and water, are good conductors. Other bodies may become
conductors by having some quantity of water in them, as wood and other
materials used in building, but not having much water in them, are not
good conductors, and therefore are often damaged in the operation.

Glass, wax, silk, wool, hair, feathers, and even wood perfectly dry,
are non-conductors: that is, they resist instead of facilitating the
passage of this subtle fluid.

When this fluid has an opportunity of passing through two conductors,
one good and sufficient, as of metal, the other not so good, it passes
in the best, and will follow in any direction.

The distance at which a body charged with this fluid will discharge
itself suddenly, striking through the air into another body that is
not charged, or not so highly charged, is different according to the
quantity of the fluid, the dimensions and form of the bodies
themselves, and the state of the air between them. This distance,
whatever it happens to be between any two bodies, is called their
striking _distance_, as, till they come within that distance of each
other, no stroke will be made.

The clouds have often more of this fluid in proportion than the earth:
in which case, as soon as they come near enough, (that is, within the
striking distance,) or meet with a conductor, the fluid quits them and
strikes into the earth. A cloud fully charged with this fluid, if so
high as to be beyond the striking distance from the earth, passes
quietly without making noise or giving light, unless it meet with
other clouds that have less.

Tall trees and lofty buildings, as the towers and spires of churches,
become sometimes conductors between the clouds and the earth; but, no