CHAP. II.
Theories of Electricity, exclusive of that of Franklin.
The first electricians supposed that the attraction of electric substances, was caused by certain unctuous effluvia, emitted from these substances when they were excited. Such effluvia were supposed to fasten upon all bodies which fell in their way, and if not too heavy, to carry them back to the emitting substances. For at that time, all effluvia were supposed to return to the bodies whence they had been emitted; because they could not otherwise account for the fact, that such substances were not sensibly wasted by emitting effluvia. But when the subtilty of light was demonstrated by Newton, and that of the effluvia of many bodies was better understood, philosophers gave up the doctrine of the return of effluvia, both with regard to electricity and other subjects.
2. They applied to electricity the general, but unknown principles of attraction and repulsion—properties which they supposed to be immediately communicated by the Creator to certain bodies. But the laws of this attraction and repulsion, in regard to electricity, we do not know that they attempted to explain.
3. Mr. Du Faye discovered the two opposite species of electricity, which he termed the vitreous and the resinous, because one was found in glass and the other in rosin, sealing-wax, &c. He immediately adopted the theory of two distinct electric fluids, repulsive with respect to themselves, and attractive of one another. But he did not know at this time, that both these species were concerned in every electrical operation, and that glass or rosin alone always produces both of them. When he found that electric appearances took place at an insulated rubber, and it was demonstrated that the action of the rubber did not produce, but only collect the electric fluid, he perceived that both electricities, as they had heretofore been called, were produced at the same time, by one and the same electric; and with a candour that does him honour, he gave up his theory, and embraced that of Franklin, which was first suggested about this time.
4. With some, and particularly Mr. Wilson, the chief agent in all electrical operations is Sir Isaac Newton’s ether; which is supposed to be more or less dense in all bodies, in proportion to the smallness of their pores, except that it is much denser in sulphureous and unctuous bodies. To this ether are ascribed the principal phenomena of attraction and repulsion. “On this theory, (says Dr. Priestley) I shall make no particular remarks, because I cannot say that I clearly comprehend it.”
5. The ingenious Abbè Nollet, whose theory has been more the subject of debate than all the others, before Dr. Franklin’s, supposes that in all electrical operations the fluid, (of which he admits there is but one) is thrown into two opposite motions; that the affluence of this matter drives all light bodies before it, by impulse, upon the electrified body; and that its effluence carries them back again. But he seems very much embarrassed in accounting for facts where both these currents must be considered as taking place at the same time, and in finding out expedients to prevent their impeding and interrupting the effects of each other. To obviate this great difficulty, he supposes that every excited electric, and likewise every body to which electricity is communicated, has two orders or kinds of pores, one for the emission of the effluvia, and the other for the reception of them.
The Abbè maintained this hypothesis with a zeal and ingenuity worthy of a better cause. For it is manifest at once, that the existence of such kinds of different pores in bodies, is a mere gratuitous assumption. Our senses do not inform us of the existence of any such pores, nor have we evidence of any kind that they even exist at all, unless we consider it as evidence of their existence, that they are necessary to account for the appearances on which the Abbè grounds his theory.
Yet this theory, with some modification, has been strenuously maintained, and has its advocates to the present day. They say that “in bodies positively electrified, there is a flux of electric matter, from their surface all round; that is, the fluid contained in their pores pushes out on every side, and communicates a similar motion to the electric fluid contained in the adjacent atmosphere. This must of necessity very soon exhaust the body of its electric matter altogether, if it was not instantaneously supplied after every emission. But this supply is immediately procured from the surrounding atmosphere. The quantity sent off is instantaneously returned from the air, and a vibratory motion or struggle between the air and electric fluid, immediately takes place. The positive electricity therefore consists in a vibratory motion in the air and electric fluid; and the force of the vibration is directed outwards from the electrified body. In bodies negatively electrified, the fluid contained in the neighbouring atmosphere is directed towards the body so electrified. But it is certain, that this motion inwards cannot be continued unless there is also a motion of the fluid outwards from the body. In this case also, there is a vibratory motion, but the force of it is directed inwards, and as the source of it lies not in the body, but in the surrounding atmosphere, it manifests itself somewhat less vigorously.” We have taken this account of the modification of the Abbè Nollet’s theory from one who firmly believed it. But we cannot pretend to controvert it, because, (as Dr. Priestley says,) “we cannot say that we clearly comprehend it.”
6. There are some who explain the phenomena of electricity upon chemical principles. They also believe in the existence of two distinct and positive fluids; but instead of a mechanical operation, they consider all their sensible effects as arising from chemical affinity and union. The following may serve as a specimen of chemical electricity. It is said—
(1.) “There are two kinds of electric ether, which exist either separately or in combination. That which is accumulated on the surface of smooth glass, when rubbed with a cushion, is here termed vitreous ether; and that which is accumulated on the surface of resin, or sealing-wax, when rubbed in like manner, is here termed resinous ether; and a combination of them, as in their usual state, may be termed neutral electric ethers.