Insulate two tin tubes, distinguished by A and B, so as to be in
a line with each other, and about half an inch apart; and at the
remote end of each, let a pair of cork balls be suspended. Towards
the middle of A, bring the excited glass tube, and holding it a short
time, at the distance of a few inches, each pair of balls will be
observed to separate: withdraw the tube, and the balls of A will
come together, and then repel each other again; but those of B will
hardly be affected. By the approach of the excited glass tube, held
under the balls of A, their repulsion will be increased: but if the
tube be brought, in the same manner, towards the balls of B, their
repulsion will be diminished.
In the fifth experiment, the common stock of electrical matter in the
tin tube, is supposed to be attenuated about the middle, and to be
condensed at the ends, by the repelling power of the atmosphere of
the excited glass tube, when held near it. And perhaps the tin tube
may lose some of its natural quantity of the electrical fluid, before
it receives any from the glass; as that fluid will more readily run
off from the ends and edges of it, than enter at the middle: and
accordingly, when the glass tube is withdrawn, and the fluid is again
equally diffused through the apparatus, it is found to be electrified
negatively: for excited glass brought under the balls will increase
their repulsion.
In the sixth experiment, part of the fluid driven out of one tin tube
enters the other; which is found to be electrified positively, by the
decreasing of the repulsion of its balls, at the approach of excited
glass.