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.
(2.) Atmospheres of vitreous, or of resinous, or of neutral electricity, surround all separate bodies, are attracted by them and permeate those which are called conductors, as metallic, aqueous, and carbonic substances; but will not permeate those which are called non-conductors, as air, glass, silk, resin, sulphur.
(3.) The particles of vitreous ether, strongly repel each other, but attract the particles of resinous ether and vice versa. When the two electric ethers unite, a chemical explosion occurs, in some respects like that of gun-powder, light and heat are liberated, and rend or fuse the bodies which they occupy.
(4.) Glass holds within it, in combination, much resinous electric ether, which constitutes a part of it, and which more forcibly attracts vitreous electric ether, from surrounding bodies which stand on it, mixed with a less proportion of resinous ether, like an atmosphere, but cannot unite with the resinous ether, which is combined with the glass. And resin, on the contrary, holds within it, in combination, much vitreous electric ether, which constitutes a part of it, and which more forcibly attracts resinous electric ether from surrounding bodies, which stand on it, mixed with a less proportion of vitreous ether, like an atmosphere, but cannot unite with the vitreous ether which is combined with the resin.
(5.) Hence the non-conductors of electricity are of two kinds, and opposite to each other; the one class of the vitreous, and the other of the resinous. But the most perfect conductor, such as metal, water and charcoal, having neither kind of electric ether, combined with them, though surrounded with both, suffer both kinds to pass through them easily.
(6.) Great accumulation or condensation of the separate electric ethers, attract each other so strongly that they will break a passage through non-conducting bodies. Hence trees and stone walls are rent by lightning.
(7.) When artificial or natural accumulations of these separate ethers are in a very small quantity or intensity, they pass slowly and with difficulty from one body to another, and require the best conductors for this purpose. Whence many of the phenomena of the Torpedo, the Gymnotus, and of Galvanism.
(8.) The electric ethers may be separately accumulated, by the contact of conductors with non-conductors—by vicinity of the two ethers—by heat—and by decomposition.
(9.) When these two ethers unite suddenly and with explosion, a liberation of light and heat takes place, as in all chemical explosions. Accordingly it is said that a smell is perceptible from electric sparks, and even a taste, which must be supposed to arise from new combinations or decompositions.”
The theory founded on the principles above stated is supposed, by those who adopt it, to solve many difficulties which can scarcely be accounted for on the theory of Franklin.
Dr. Gibbes also adopts a chemical theory of electricity. He supposes that oxygen gas is produced by the union of positive electricity with water; and hydrogen gas by the union of negative electricity with water: and that water, uniting in different proportions with the two electricities, is the ponderable part of all the elastic fluids. He asserts that by the positive electricity metals are oxydated, and blue vegetable colours reddened; and also that the acidifying effect of electric commotions in the atmosphere, on weak fermented liquors, is unquestionable.—On the other hand, according to this writer, by negative electricity the vegetable blue is restored, and the oxydated metal revived.
These circumstances, among others, led Dr. Gibbes to conclude that when hydrogen gas is produced by the affusion of water on red-hot metal, and the metal is at the same time oxydated, a decomposition of fire rather than of water has taken place; that the hot metal has parted with negative electricity, which, uniting with a small proportion of the water, has formed hydrogen gas; that a greater proportion of the water has united with the positive electricity, and entered, as oxygen gas, into combination with the metal. When the two gases are inflamed together, the spark attracts to itself, in due proportions, the two electricities contained in the two gases, which unite with explosion, and produce fire. The water with which they were before combined is of course deposited.
The reason why inflammable substances burn in oxygen gas, and not in hydrogen, Dr. Gibbes supposes to be, that negative electricity greatly prevails in all inflammable substances. Neither of the gases can be inflamed separately, because fire depends on the union of the two electricities; and such union cannot be effected unless both are present in due proportion.
Dr. Gibbes supposes that the further illustration of the effects of the two electricities, as chemical agents, will set aside some of the leading doctrines of the Lavoisierian theory, and afford an easy solution of certain phenomena which that theory cannot explain.
Æpinus’ Theory of Electricity
Mr. Æpinus, of the imperial academy of Petersburgh, has attempted to class the phenomena of electricity and magnetism in a mathematical method. In the course of his works he gives some views of the subject which are new and highly ingenious, and as some good judges suppose, calculated to surmount many difficulties, and to answer many questions, which occur in considering the Franklinian theory. The leading principles of his plan are comprehended in the following propositions.
1. Its particles repel each other, with a force decreasing as the squares of the distances increase.
2. Its particles attract the particles of some ingredients in all other bodies, with a force decreasing according to the same law, with an increase of distance; and that this attraction is mutual.
3. The electric fluid is dispersed in the pores of other bodies, and moves with various degrees of facility through the pores of different kinds of matter. In those bodies which we call non-electrics, such as water or metals, it moves without any perceivable obstruction; but in glass, resin, and all bodies called electrics, it moves with very great difficulty, or is altogether immoveable.
4. The phenomena of electricity are of two kinds: 1. Such as arise from the actual motion of the fluid, from a body containing more, to one containing less of it. 2. Such as do not immediately arise from this transference, but are instances of its attraction and repulsion.—
These principles are applied at great length, and with a pleasing degree of precision, by the ingenious theorist, to the Leyden phial, and to the various phenomena of electric attraction and repulsion. It will be readily seen that Æpinus adopts, in substance, the theory of Franklin, of which, in some particulars, he presents new and more satisfactory views than the American philosopher. In the sixty first volume of the Philosophical Transactions, there is a dissertation by the Hon. Mr. Cavendish on this subject, which he considers as an extension and more accurate application of Æpinus’s theory.