In my last I informed you that, in pursuing our electrical enquiries,
we had observed some particular phenomena, which we looked upon to
be new, and of which I promised to give you some account, though I
apprehended they might not possibly be new to you, as so many hands
are daily employed in electrical experiments on your side the water,
some or other of which would probably hit on the same observations.
The first is the wonderful effect of pointed bodies, both in _drawing
off_ and _throwing off_ the electrical fire. For example,
Place an iron shot of three or four inches diameter on the mouth of
a clean dry glass bottle. By a fine silken thread from the cieling,
right over the mouth of the bottle, suspend a small cork-ball, about
the bigness of a marble; the thread of such a length, as that the
cork-ball may rest against the side of the shot. Electrify the shot,
and the ball will be repelled to the distance of four or five inches,
more or less, according to the quantity of electricity.--When in this
state, if you present to the shot the point of a long, slender, sharp
bodkin, at six or eight inches distance, the repellency is instantly
destroyed, and the cork flies to the shot. A blunt body must be
brought within an inch, and draw a spark to produce the same effect.
To prove that the electrical fire is _drawn off_ by the point, if
you take the blade of the bodkin out of the wooden handle, and fix
it in a stick of sealing-wax, and then present it at the distance
aforesaid, or if you bring it very near, no such effect follows; but
sliding one finger along the wax till you touch the blade, and the
ball flies to the shot immediately.--If you present the point in the
dark, you will see, sometimes at a foot distance and more, a light
gather upon it, like that of a fire-fly, or glow-worm; the less sharp
the point, the nearer you must bring it to observe the light; and at
whatever distance you see the light, you may draw off the electrical
fire, and destroy the repellency.--If a cork-ball so suspended be
repelled by the tube, and a point be presented quick to it, though
at a considerable distance, it is surprising to see how suddenly it
flies back to the tube. Points of wood will do near as well as those
of iron, provided the wood is not dry; for perfectly dry wood will no
more conduct electricity than sealing-wax.
To shew that points will _throw off_[17] as well as _draw off_ the
electrical fire; lay a long sharp needle upon the shot, and you
cannot electrise the shot so as to make it repel the cork-ball.--Or
fix a needle to the end of a suspended gun-barrel, or iron-rod, so as
to point beyond it like a little bayonet[18]; and while it remains
there, the gun-barrel, or rod, cannot by applying the tube to the
other end be electrised so as to give a spark, the fire continually
running out silently at the point. In the dark you may see it make
the same appearance as it does in the case before-mentioned.
The repellency between the cork-ball and the shot is likewise
destroyed. 1. By sifting fine sand on it; this does it gradually.
2. By breathing on it. 3. By making a smoke about it from burning
wood[19]. 4. By candle-light, even though the candle is at a foot
distance: these do it suddenly.--The light of a bright coal from
a wood fire; and the light of a red-hot iron do it likewise; but
not at so great a distance. Smoke from dry rosin dropt on hot iron,
does not destroy the repellency; but is attracted by both shot and
cork-ball, forming proportionable atmospheres round them, making them
look beautifully, somewhat like some of the figures in Burnet's or
Whiston's Theory of the Earth.
_N.B._ This experiment should be made in a closet, where the air is
very still, or it will be apt to fail.
The light of the sun thrown strongly on both cork and shot by
a looking-glass for a long time together, does not impair the
repellency in the least. This difference between fire-light and
sun-light is another thing that seems new and extraordinary to us[20].
We had for some time been of opinion, that the electrical fire was
not created by friction, but collected, being really an element
diffused among, and attracted by other matter, particularly by water
and metals. We had even discovered and demonstrated its afflux to
the electrical sphere, as well as its efflux, by means of little
light windmill-wheels made of stiff paper vanes, fixed obliquely, and
turning freely on fine wire axes.
Also by little wheels of the same matter, but formed like
water-wheels. Of the disposition and application of which wheels,
and the various phenomena resulting, I could, if I had time, fill
you a sheet[21]. The impossibility of electrising one's self (though
standing on wax) by rubbing the tube, and drawing the fire from it;
and the manner of doing it, by passing the tube near a person or
thing standing on the floor, &c. had also occurred to us some months
before Mr. Watson's ingenious _Sequel_ came to hand, and these were
some of the new things I intended to have communicated to you.--But
now I need only mention some particulars not hinted in that piece,
with our reasonings thereupon: though perhaps the latter might well
enough be spared.
1. A person standing on wax, and rubbing the tube, and another person
on wax drawing the fire, they will both of them (provided they do
not stand so as to touch one another) appear to be electrised, to a
person standing on the floor; that is, he will perceive a spark on
approaching each of them with his knuckle.
2. But if the persons on wax touch one another during the exciting of
the tube, neither of them will appear to be electrised.
3. If they touch one another after exciting the tube, and drawing the
fire as aforesaid, there will be a stronger spark between them than
was between either of them and the person on the floor.