3. If a metallic point be fixed on the prime conductor, and the flame of a candle be presented to it, on electrising the conductor either with vitreous or resinous ether, the flame of the candle is blown from the point, which must be owing to the electric fluid in its passage from the point carrying along with it a stream of atmospheric air.
The manner in which the accumulated electricity so readily passes off by a metallic point may be thus understood; when a metallic point stands erect from an electrised metallic plane, the accumulated electricity which exists on the extremity of the point, is attracted less than that on the other parts of the electrised surface. For the particle of electric matter immediately over the point is attracted by that point only, whereas the particles of electric matter over every other part of the electrised plane, is not only attracted by the parts of the plane immediately under them, but also laterally by the circumjacent parts of it; whence the accumulated electric fluid is pushed off at this point by that over the other parts being more strongly attracted to the plane.
Thus if a light insulated horizontal fly be constructed of wire with points fixed as tangents to the circle, it will revolve the way contrary to the direction of the points as long as it continues to be electrised. For the same reason as when a circle of cork, with a point of the cork standing from it like a tangent, is smeared with oil, and thrown upon a lake, it will continue to revolve backwards in respect to the direction of the point till all the oil is dispersed upon the lake, as first observed by Dr. Franklin; for the oil being attracted to all the other parts of the cork-circle more than towards the pointed tangent, that part over the point is pushed off and diffuses itself on the water, over which it passes without touching, and consequently without friction; and thus the cork revolves in the contrary direction.
As the flame of a candle is blown from a point fixed on an electrised conductor, whether vitreous or resinous electricity is accumulated on it, it shows that in both cases electricity passes from the point, which is a forcible argument against the mechanical theory of positive and negative electricity; because then the flame should be blown towards the point in one case, and from it in the other.
So the electric fly, as it turns horizontally, recedes from the direction of the points of the tangents, whether it be electrised with vitreous or resinous electricity; whereas if it was supposed to receive electricity, when electrised by resin, and to part with it when electrised by glass, it ought to revolve different ways; which also forcibly opposes the theory of positive and negative electricity.
As an electrised point with either kind of electricity causes a stream of air to pass from it in the direction of the point, it seems to affect the air much in the same manner as the fluid matter of heat affects it; that is, it will not readily pass through it, but will adhere to the particles of air, and is thus carried away with them.
From this it will also appear, that points do not attract electricity, properly speaking, but suffer it to depart from them; as it is there less attracted to the body which it surrounds, than by any other part of the surface.
And as a point presented to an electrised conductor facilitates the discharge of it, and blows the flame of a candle towards the conductor, whether vitreous or resinous electricity be accumulated upon it; it follows, that in both cases some electric matter passes from the point to the conductor, and that hence there are two electric ethers; and that they combine or explode when they meet together, and give out light and heat, and occupy less space in this their combined state, like the union of nitrous gas with oxygen gas.
IV. Accumulation of Electric Ethers by Contact.
The electric ethers may be separately accumulated by contact of conductors with nonconductors, by vicinity of the two ethers, by heat, and by decomposition.