Having brought your brimstone globe to work, I tried one of the
experiments you proposed, and was agreeably surprised to find, that
the glass globe being at one end of the conductor, and the sulphur
globe at the other end, both globes in motion, no spark could be
obtained from the conductor, unless when one globe turned slower, or
was not in so good order as the other; and then the spark was only
in proportion to the difference, so that turning equally, or turning
that slowest which worked best, would again bring the conductor to
afford no spark.
I found also, that the wire of a phial charged by the glass globe,
attracted a cork ball that had touched the wire of a phial charged
by the brimstone globe, and _vice versa_, so that the cork continued
to play between the two phials, just as when one phial was charged
through the wire, the other through the coating, by the glass globe
alone. And two phials charged, the one by the brimstone globe, the
other by the glass globe, would be both discharged by bringing their
wires together, and shock the person holding the phials.
From these experiments one may be certain that your 2d, 3d, and 4th
proposed experiments, would succeed exactly as you suppose, though I
have not tried them, wanting time. I imagine it is the glass globe
that charges positively, and the sulphur negatively, for these
reasons: 1. Though the sulphur globe seems to work equally well
with the glass one, yet it can never occasion so large and distant
a spark between my knuckle and the conductor, when the sulphur
one is working, as when the glass one is used; which, I suppose,
is occasioned by this, that bodies of a certain bigness cannot so
easily part with a quantity of electrical fluid they have and hold
attracted _within_ their substance, as they can receive an additional
quantity _upon_ their surface by way of atmosphere. Therefore so
much cannot be drawn _out_ of the conductor, as can be thrown _on_
it. 2. I observe that the stream or brush of fire, appearing at the
end of a wire, connected with the conductor, is long, large, and
much diverging, when the glass globe is used, and makes a snapping
(or rattling) noise: but when the sulphur one is used, it is short,
small, and makes a hissing noise; and just the reverse of both
happens, when you hold the same wire in your hand, and the globes
are worked alternately: the brush is large, long, diverging, and
snapping (or rattling) when the sulphur globe is turned; short,
small, and hissing, when the glass globe is turned.--When the brush
is long, large, and much diverging, the body to which it joins seems
to me to be throwing the fire out; and when the contrary appears, it
seems to be drinking in. 3. I observe, that when I hold my knuckle
before the sulphur globe, while turning, the stream of fire between
my knuckle and the globe seems to spread on its surface, as if it
flowed from the finger; on the glass globe it is otherwise. 4. The
cool wind (or what was called so) that we used to feel as coming from
an electrified point, is, I think, more sensible when the glass globe
is used, than when the sulphur one.--But these are hasty thoughts. As
to your fifth paradox, it must likewise be true, if the globes are
alternately worked; but if worked together, the fire will neither
come up nor go down by the chain, because one globe will drink it as
fast as the other produces it.
I should be glad to know, whether the effects would be contrary if
the glass globe is solid, and the sulphur globe is hollow; but I have
no means at present of trying.
In your journeys, your glass globes meet with accidents, and sulphur
ones are heavy and inconvenient.--_Query._ Would not a thin plane of
brimstone, cast on a board, serve on occasion as a cushion, while a
globe of leather stuffed (properly mounted) might receive the fire
from the sulphur, and charge the conductor positively? Such a globe
would be in no danger of breaking[64]. I think I can conceive how it
may be done; but have not time to add more than that I am,
Yours, &c.