_The Terms, electric per se, and non-electric, improper.--New
Relation between Metals and Water.--Effects of Air in electrical
Experiments.--Experiment for discovering more of the Qualities of
the electric Fluid._
_Query_, Wherein consists the difference between an _electric_ and a
_non-electric_ body?
_Answer._ The terms electric _per se_, and non-electric, were first
used to distinguish bodies, on a mistaken supposition that those
called electrics _per se_, alone contained electric matter in their
substance, which was capable of being excited by friction, and of
being produced or drawn from them, and communicated to those called
non-electrics, supposed to be destitute of it: for the glass, &c.
being rubbed, discovered signs of having it, by snapping to the
finger, attracting, repelling, &c. and could communicate those signs
to metals and water.--Afterwards it was found, that rubbing of
glass would not produce the electric matter, unless a communication
was preserved between the rubber and the floor; and subsequent
experiments proved that the electric matter was really drawn from
those bodies that at first were thought to have none in them. Then
it was doubted whether glass, and other bodies called _electrics per
se_, had really any electric matter in them, since they apparently
afforded none but what they first extracted from those which had
been called non-electrics. But some of my experiments show, that
glass contains it in great quantity, and I now suspect it to be
pretty equally diffused in all the matter of this terraqueous globe.
If so, the terms _electric per se_, and _non-electric_, should be
laid aside as improper: and (the only difference being this, that
some bodies will conduct electric matter, and others will not) the
terms _conductor_ and _non-conductor_ may supply their place. If
any portion of electric matter is applied to a piece of conducting
matter, it penetrates and flows through it, or spreads equally on
its surface; if applied to a piece of non-conducting matter, it will
do neither. Perfect conductors of electric matter are only metals
and water. Other bodies conducting only as they contain a mixture
of those; without more or less of which they will not conduct at
all[59]. This (by the way) shews a new relation between metals and
water heretofore unknown.
To illustrate this by a comparison, which, however, can only give
a faint resemblance. Electric matter passes through conductors as
water passes through a porous stone, or spreads on their surfaces as
water spreads on a wet stone; but when applied to non-conductors, it
is like water dropt on a greasy stone, it neither penetrates, passes
through, nor spreads on the surface, but remains in drops where it
falls. See farther on this head, in my last printed piece, entitled,
_Opinions and Conjectures, &c._ 1749.
_Query_, What are the effects of air in electrical experiments?
_Answer._ All I have hitherto observed are these. Moist air receives
and conducts the electrical matter in proportion to its moisture,
quite dry air not at all: air is therefore to be classed with the
non-conductors.
Dry air assists in confining the electrical atmosphere to the body
it surrounds, and prevents its dissipating: for in vacuo it quits
easily, and points operate stronger, _i. e._ they throw off or
attract the electrical matter more freely, and at greater distances;
so that air intervening obstructs its passage from body to body
in some degree. A clean electrical phial and wire, containing air
instead of water, will not be charged nor give a shock, any more
than if it was filled with powder of glass; but exhausted of air, it
operates as well as if filled with water. Yet an electric atmosphere
and air do not seem to exclude each other, for we breathe freely
in such an atmosphere, and dry air will blow through it without
displacing or driving it away. I question whether the strongest dry
north-wester[60] would dissipate it. I once electrified a large
cork-ball at the end of a silk thread three feet long, the other end
of which I held in my fingers, and whirl'd it round, like a sling one
hundred times, in the air, with the swiftest motion I could possibly
give it, yet it retained its electric atmosphere, though it must have
passed through eight hundred yards of air, allowing my arm in giving
the motion to add a foot to the semi-diameter of the circle.--By
quite dry air, I mean the dryest we have: for perhaps we never have
any perfectly free from moisture. An electrical atmosphere raised
round a thick wire, inserted in a phial of air, drives out none of
the air, nor on withdrawing that atmosphere will any air rush in, as
I have found by a curious experiment[61] accurately made, whence we
concluded that the air's elasticity was not affected thereby.
AN EXPERIMENT TOWARDS DISCOVERING MORE OF THE QUALITIES OF THE
ELECTRIC FLUID.
From the prime conductor, hang a bullet by a wire hook; under the
bullet, at half an inch distance, place a bright piece of silver
to receive the sparks; then let the wheel be turned, and in a few
minutes, (if the repeated sparks continually strike in the same spot)
the silver will receive a blue stain, nearly the colour of a watch
spring.
A bright piece of iron will also be spotted, but not with that
colour; it rather seems corroded.
On gold, brass, or tin, I have not perceived it makes any impression.
But the spots on the silver or iron will be the same, whether the
bullet be lead, brass, gold, or silver.
On a silver bullet there will also appear a small spot, as well as on
the plate below it.