Let an excited stick of wax, of two feet and an half in length, and
about an inch in diameter, be held near its middle. Excite the glass
tube, and draw it over one half of it; then, turning it a little
about its axis, let the tube be excited again, and drawn over the
same half; and let this operation be repeated several times: then
will that half destroy the repelling power of balls electrified by
glass, and the other half will increase it.
By this experiment it appears, that wax also may be electrified
positively and negatively. And it is probable, that all bodies
whatsoever may have the quantity they contain of the electrical
fluid, increased, or diminished. The clouds, I have observed, by a
great number of experiments, to be some in a positive, and others
in a negative state of electricity. For the cork balls, electrified
by them, will sometimes close at the approach of excited glass; and
at other times be separated to a greater distance. And this change
I have known to happen five or six times in less than half an hour;
the balls coming together each time and remaining in contact a few
seconds, before they repel each other again. It may likewise easily
be discovered, by a charged phial, whether the electrical fire be
drawn out of the apparatus by a negative cloud, or forced into it
by a positive one: and by which soever it be electrified, should
that cloud either part with its overplus, or have its deficiency
supplied suddenly, the apparatus will lose its electricity: which
is frequently observed to be the case, immediately after a flash of
lightning. Yet when the air is very dry, the apparatus will continue
to be electrised for ten minutes, or a quarter of an hour, after
the clouds have passed the zenith; and sometimes till they appear
more than half-way towards the horizon. Rain, especially when the
drops are large, generally brings down the electrical fire: and
hail, in summer, I believe never fails. When the apparatus was last
electrified, it was by the fall of thawing snow, which happened so
lately, as on the 12th of November; that being the twenty-sixth
day, and sixty-first time it has been electrified, since it was
first set up; which was about the middle of May. And as Fahrenheit's
thermometer was but seven degrees above freezing, it is supposed the
winter will not entirely put a stop to observations of this sort.
At London, no more than two thunder-storms have happened during the
whole summer; and the apparatus was sometimes so strongly electrified
in one of them, that the bells, which have been frequently rung by
the clouds, so loud as to be heard in every room of the house (the
doors being open) were silenced by the almost constant stream of
dense electrical fire, between each bell and the brass ball, which
would not suffer it to strike.
I shall conclude this paper, already too long, with the following
queries:
1. May not air, suddenly rarefied, give electrical fire to, and air
suddenly condensed, receive electrical fire from, clouds and vapours
passing through it?
2. Is not the _aurora borealis_, the flashing of electrical fire from
positive, towards negative clouds at a great distance, through the
upper part of the atmosphere, where the resistance is least?