Part 11

Mr. Nairne also contrived a luminous discharging-rod. It consisted of an arched glass tube, with a metallic ball at each end, and a communication from one ball to the other was made by a brass chain, which passed through the bore of the tube.—In the discharge of a jar with it, small sparks are seen between the links of the chain within the tube.—Both these dischargers should have handles fastened to them.

_To decompose Water by Electricity._

Let a glass tube, having a small bore, be filled with water; then close each end of the tube with a piece of cork, and let two wires pass through the corks, so that their extremities may come pretty near each other within the tube.

If sparks of electricity be made to pass between the ends of the wires, within the tube, the water will be converted into oxygen and hydrogen gases.

If this process be continued till the extremities of the wires become immersed in the two gases, they will explode and again form water.

_The Electrified Fountain._

Insulate a small fountain made of metal, (one on the construction of _Hiero’s_ will be found most convenient,) and connect it with the prime-conductor—put it in operation—the jet will be undivided, except at the top—now turn the cylinder, and you will immediately perceive the jet divided much lower than at first; the drops, which before fell nearly perpendicularly, will now be thrown off in elliptical lines, and attracted by any conductor brought near them. A small Leyden phial may be charged at the top of the jet, which will present the curious spectacle of fire coming out of water.

EPITOME

OF

ELECTRICITY.

DIVISION III.

CHAP. I. _Introductory Observations to the theory of Electricity._

There is scarcely any thing to which an inquisitive mind, such as a philosopher possesses, submits with more reluctance, than to the inability of assigning the causes of the most interesting appearances or phenomena of nature. That every effect has a cause, is a first or self evident principle, and the mind is not easily brought to acquiesce in its utter ignorance of the cause, when the effect is visible and striking.—From this circumstance proceeded the numerous wild, fanciful, and delusive systems of natural philosophy, which existed before the time of the great Lord Bacon.—His penetrating and discriminating mind saw that nothing solid could ever be achieved in that noble science, unless such a procedure were relinquished;—unless men would consent to confess their ignorance of causes which were actually unknown;—unless they would cease to rely on hypotheses, however plausible, until they were verified by experiment;—consent to take facts as they are found, and by experiments alone endeavour to ascend to their causes. On this immoveable base the Newtonian philosophy is founded, and it will of course prove as durable as nature herself.

Two things, however, in regard to this subject, are of some importance to be remarked.—The first is, that experiments may sometimes be supposed to ascertain causes which will afterwards be found not to exist, or to be wrongly assigned; because the experiments had not been accurately or extensively made.

The second remark is, that though hypotheses are not to be taken for philosophy, till they have stood the test of experiment; yet in the process of the mind in making discoveries, hypothesis is perhaps always used, where the discovery is not merely accidental. No man can rationally make experiments till he has conceived a notion, supposition, or hypothesis in his mind, which he imagines experiment may serve to verify.—It is this which prompts him to his researches and guides him in conducting them.

In regard to electricity, it is remarked by Dr. Priestley, that “no other part of the whole compass of philosophy affords so fine a scene for ingenious speculation. Here the imagination may have full play, in conceiving of the manner in which an invisible agent produces an almost infinite variety of visible effects. As the agent is invisible every philosopher is at liberty to make it whatever he pleases, and ascribe to it such properties and powers as are convenient for his purpose. And, indeed, if he can frame his theory so as really to suit all the facts, it has all the evidence of truth, that the nature of things can admit.”

For ourselves we are by no means satisfied that there is yet any theory of electricity which will “suit _all_ the facts;” and therefore if this be requisite to entitle a theory _philosophy_, as contra-distinguished from _hypothesis_, we must think that the best theory of electricity is yet hypothesis, and not philosophy. We believe that the Franklinian theory accounts for _more_ facts, and is far more plausible, than any other. But, as we have already had occasion to remark in a former chapter, it does not appear to us fully and satisfactorily to account for all the phenomena of electric attraction and repulsion. Dr. Franklin always spoke with great diffidence of his own theory, and always denominated it an hypothesis.

“Every appearance, says he, which I have seen, in which glass and electricity are concerned, are, I think explained with ease by this _hypothesis_. Yet, perhaps, it may not be a true one, and I shall be obliged to him who affords me a better.” In like manner Æpinus, who adopted the theory of Franklin, and who has illustrated its leading principles in a far more masterly and scientific manner than any other writer, still denominates the theory which he maintains an _hypothesis_. Why should pupils affect to go farther than their masters? We think that the theory of electricity is still an hypothesis. We are however clearly of opinion that the hypothesis of Franklin is preferable to every other. We have therefore adopted it in the whole of our system, and mean to close this division of our subject by giving it, somewhat in detail, with the leading facts and considerations by which its claim to superiority appears to us to be supported. In the mean time, as every student of electricity may wish to know, and ought to know, what other theories have been adopted, we shall fill the following chapter with a brief and compendious recital of some of the principal of them.—It would be endless to recite them all. We shall, however, enter into no extensive argument to prove their fallacy, as this would be inconsistent with our plan, as well as unprofitable in itself. We shall afterwards say what we can to confirm the theory of Franklin, and if we succeed, every thing opposed to it, must, of course, appear to be unsupported.

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.

CHAP. III. _The Franklinian Theory of Electricity._

We are now to give Dr. Franklin’s theory of plus and minus, or positive and negative electricity, and adduce facts, to shew how far this theory will go to explain the different phenomena.

The Doctor supposed that all the operations in electricity, depended upon one fluid, _sui generis_, extremely subtile and elastic.—That there subsists a very strong repulsion between the particles of this fluid, in regard to one another, and as strong an attraction, with regard to other matter.—Thus one quantity of electric matter will repel another quantity of the same, but will attract, and be attracted by, any terrestrial matter that happens to be near it. The pores of all bodies are supposed to be full of this subtile fluid; and when its equilibrium is not disturbed, that is, when there is neither more nor less of it in a body than its natural share, or than it is capable of retaining by its own attraction, the fluid does not manifest itself to our senses. The action of the rubber upon an electric disturbs this equilibrium, occasioning a redundancy of the fluid in one place, and a deficiency of it in another. This equilibrium being forcibly disturbed, the mutual repulsion of the particles of the fluid is necessarily exerted to restore it. If two bodies be both of them over-charged, the electric atmospheres repel one another, and both the bodies recede from each other, to places where the fluid is less dense.—For as there is supposed to be a mutual attraction between all bodies and the electric matter, such bodies as are electrified must go along with their atmospheres. If both bodies are exhausted of their natural share of this fluid, they are both attracted by the denser fluid, existing either in the atmosphere contiguous to them, or in other neighbouring bodies; which occasions them still to recede from one another, as if they were over-charged.

Dr. Franklin’s theory has gained the greatest reputation, from the easy solution it affords of all the phenomena of the Leyden phial. The fluid is supposed to move with the greatest ease in bodies which are conductors; but with extreme difficulty in _electrics per se_; in so much that glass is absolutely impermeable to it. It is also supposed that all electrics, and particularly glass, on account of the smallness of their pores, do at all times contain an exceedingly great, and always an equal quantity of this fluid; so that no more can be thrown into any one part of any electric substance, except the same quantity go out at another, and the gain be exactly equal to the loss. These things being premised, the phenomena of charging and discharging a plate of glass, or a Leyden phial, may be easily solved. In the usual manner of electrifying by a smooth glass globe or cylinder, all the electric matter is supplied by the rubber, from all the bodies which communicate with it. If it be made to communicate with nothing but one of the coatings of a glass plate, while the prime-conductor is connected with the other, that side of the glass which communicates with the rubber, must necessarily be exhausted in order to supply the conductor, which must convey the whole of it to the coating with which it is connected. By this operation, therefore, the electric fluid becomes almost entirely exhausted from one side of the plate, while it is as much accumulated on the other; and the discharge is made by the electric fluid rushing, as soon as an opportunity is given it by means of proper conductors, from the side which was overloaded to that which was exhausted.