ELECTRICITY

, or Electrical Force, is that power or property, which was first observed in amber, the lyneurium, or tourmalin, and which sealing-wax, glass, and a variety of other substances, called electrics, are now known to possess, of attracting light bodies, when excited by heat or friction; and which is also capable of being communicated in particular circumstances to other bodies.

Electricity also denotes the science, or that part of natural philosophy, which proposes to investigate the nature and effects of this power. From plextzon, the Greek name for amber, is derived the term Electricity, which is now very extensively applied, not only to the power of attracting light bodies inherent in amber, but to other similar powers, and their various effects, in whatever bodies they reside, or to whatever bodies they may be communicated.

Muschenbroek and Æpinus have observed a considerable analogy, in a variety of particulars, between the powers of Electricity and Magnetism; and they have also pointed out many instances in which they differ.

History of Electricity.——The property which amber possesses of attracting light bodies, was very anciently observed. Thales of Miletus, 600 years before Christ, concluded from hence that it was animated. But the first person who expressly mentioned this substance, was Theophrastus, about 300 years before Christ. The attractive property of amber is also occasionally noticed by Pliny, and other later naturalists, particularly Gassendus, Kenelm Digby, and Sir Thomas Brown. But it was generally apprehended that this quality was peculiar to amber and jet, and perhaps agate, till W. Gilbert, a native of Colchester, and a physician in London, published his treatise De Magnete, in the year 1600. Dr. Gilbert made many considerable experiments and discoveries, considering the then infant state of the science. He enlarged the lift both of electrics, and of the bodies on which they act: he remarked, that a dry air was most favourable to electrical appearances, whilst a moist air almost annihilates the electric virtue: he also observed the conical figure assumed by electrified drops of water: he considered electrical attraction separately from repulsion, which he thought had no place in Electricity, as a phenomenon similar to the attraction of cohefion, and he imagined, that electrics were brought into contact with the bodies on which they act by their effluvia, excited by friction.

The ingenious Mr. Boyle added to the catalogue of electric substances; but he thought that glass possessed this power in a very low degree: he found, that the Electricity of all bodies, in which it might be excited, was increased by wiping and warming them before they were rubbed; that an excited electric was acted upon by other bodies as strongly as it acted upon them; that diamonds rubbed against any kind of stuff, emitted light in the dark; and that feathers would cling to the fingers, and to other substances, after they had been attracted by electrics. He accounted for electrical attraction, by supposing a glutinous effluvia emitted from electrics, which laid hold of small bodies, in its way, and carried them back to the body from which it proceeded.

Otto Guericke, the celebrated inventor of the airpump, lived about the same time. This ingenious philosopher discovered, by means of a globe of sulphur, that a body once attracted by an electric, was next repelled, and continued in this state of repulsion till it should be touched by some other body: he also observed the sound and light produced by the excitation of his globe; and that bodies immerged in electrical atmospheres are themselves electrified with an electricity opposite to that of the atmosphere.

The light emitted by electrical bodies was, not long after, observed to much greater advantage by Dr. Wall, who ascribes to light the electrical property which they possess; and he suggests a similarity between the effects of electrieity and lightning.

Sir Isaac Newton was not inattentive to this subject: he observed that excited glass attracts light bodies on the side opposite to that on which it is rubbed; and he ascribes the action of electric bodies to an elastic fluid, which freely penetrates glass, and the emission of it to the vibratory motions of the parts of excited bodies.

Mr. Hawksbee wrote on this subject in the year 1709, when a new æra commenced in the history of this science. He first took notice of the great electrical power of glass, and the light proceeding from it; though others had before observed the light proceeding from other electrified substances: he also noted the noise occasioned by it, with a variety of phenomena relating to electrical attraction and repulsion. He first introduced a glass globe into the electrical apparatus, to which circumstance it was that many of his important discoveries were owing.

After his time there was an interval of near 20 years in the progress of this science, till Mr. Stephen Grey established a new æra in the history of Electricity. To him we owe the capital discovery of communicating the power of native electrics to other bodies, in which it cannot be excited, by supporting them on silken lines, hair lines, cakes of resin or glass; and a more accurate distinction than had hitherto obtained between electrics and non-electrics: he also shewed the effect of electricity on water much more obviously than Gilbert had done in the infancy of this science.

The experiments of Mr. Grey were repeated by M. du Fay, member of the Academy of Sciences at Paris, to which he added many new experiments and discoveries of his own. He observed, that electrical operations are obstructed by great heat, as well as by a moist air; that all bodies, both solid and fluid, would receive electricity, when placed on warm or dry glass, or sealing-wax; that those bodies which are naturally the least electric, have the greatest degree of electricity communicated to them by the approach of the excited tube. He transmitted the electric virtue through a distance of 1256 feet; and first observed the electric spark from a living body, suspended on silken lines, and noted several circumstances attending it. M. du Fay also established a principle, first suggested by Otto Guericke, that electric bodies attract all those that are not so, and repel them as soon as they are become electric, by the vicinity or contact of the electric body. He likewise inferred from other experiments, | that there were two kinds of electrieity; one of which he called the vitreous, belonging to glass, rock crystal, &c; and the other resinous, as that of amber, gumlac, &c, distinguished by their repelling those of the same kind, and attracting each other. He farther observed, that communicated electricity had the same property as the excited; and that electric substances attract the dew more than conductors.

Mr. Grey, resuming his experiments in 1734, suspended several pieces of metal on silken lines, and found that by electrifying them they gave sparks; which was the origin of metallic conductors: and on this occasion he discovered a cone or pencil of electric light, such as is now known to issue from an electrified point. From other experiments he concludes, that the electric power seems to be of the same nature with that of thunder and lightning.

Dr. Desaguliers succeeded Mr. Grey in the prosecution of this science. The account of his first experiments is dated in 1739. To him we owe those technical terms of conductors or non-electrics, and electrics per se; and he first ranked pure air among the electrics per se, and supposed its Electricity to be of the vitreous kind.

After the year 1742, in which Dr. Desaguliers concluded his experiments, the subject was taken up and pursued in Germany: the globe was substituted for the tube, which had been used ever since the time of Hawksbee, and a cushion was soon after used as a rubber, instead of the hand. About this time too, some used cylinders instead of the globes; and some of the German electricians made use of more globes than one at the same time. By thus increasing the electrical power, they were the first who succeeded in setting fire to inflammable substances: this was first done by Dr. Ludolf, in the beginning of the year 1744, who, with sparks excited by the friction of a glass tube, kindled the ethereal spirit of Frobenius. Winkler did the same by a spark from his own finger, by which he kindled French brandy, and other spirits, after previously heating them. Mr. Gralath fired the smoke of a candle just blown out, and so lighted it again; and Mr. Boze fired gun-powder, by means of its inflammable vapour. About this time Ludolf the younger demonstrated, that the luminous barometer was made perfectly electrical by the motion of the quicksilver. The electrical star and electrical bells were also of German invention.

In England Dr. Watson made a distinguished figure from this period in the history of Electricity: he fired a variety of substances by the electrical spark, and first discovered that they are capable of being fired by the repulsive power of Electricity. In the year 1745, the accumulation of the electrical power in glass, by means of the Leyden phial, was first discovered. See LEYDEN phial: and for the method practised about this time, of measuring the distance to which the electrical shock may be conveyed, see Electrical Circuit. Dr. Watson discovered that the glass tubes and globes do not contain the electric matter in themselves, but only serve as first-movers or determiners, as he expresses it, of that power; which was also confirmed towards the end of 1746, by Mr. Benjamin Wilson, who made the same discovery, that the electric fluid does not come from the globe, but from the earth, and other nonelectric bodies about the apparatus. Dr. Watson also discovered what Dr. Franklin observed about the same time in America, and called the plus and minus in Electricity. He likewise shewed that the electric matter passed through the substance of the metal of communication, and not merely over the surface. The history of medical Electricity commenced in the year 1747. We must omit other experiments, and conclusions drawn from them, by Mr. Wilson, Mr. Smeaton, and Dr. Miles in England, and by the Abbé Nollet, with regard to the effect of Electricity on the evaporation of fluids, on solids, and on animal and other organized bodies, in France.

Whilst the philosophers of Europe were busily employed in electrical experiments and pursuits, those of America, and Dr. Franklin in particular, were equally industrious, and no less successful. His discoveries and observations in Electricity were communicated in several letters to a friend; the first of which is dated in 1747, and the last in 1754; and the particulars of his system may be seen under the articles, Theory of ELECTRICITY, Leyden Phial, Points, Charging, CONDUCTORS, Electrics, &c.

The similarity between Electricity and Lightning had been suggested by several writers: Dr. Franklin first proposed a method of bringing the matter to the test of experiment, by raising an electrical kite; and he succeeded in collecting electrical fire by this means from the clouds, in 1752, one month after the same theory had been verified in France, and without knowing what had been done there: and to him we owe the practical application of this discovery, in securing buildings from the damage of lightning, by erecting metallic conductors. See Conductors, and Lightning.

In the subsequent period of the history of this science, Mr. Canton in England, and Signior Beccaria in Italy, acquired distinguished reputation. They both discovered, independently of each other, that air is capable of receiving Electricity by communication, and of retaining it when received. Mr. Canton also, towards the latter end of the year 1753, pursued a series of experiments, which prove that the appearances of positive and negative Electricity, which had hitherto been deemed essential and unchangeable properties of different substances, as of glass and sealing-wax for instance, depend upon the surface of the electrics, and that of the rubber.

This hypothesis, verified by numerous experiments, occasioned a controversy between Mr. Canton, and Mr. Delaval, who still maintained that these different powers depended entirely on the substances theniselves. About this time too, some curious experiments were performed by four of the principal electricians of that period, viz. Dr. Franklin, and Messrs Canton, Wilcke, and Æpinus, to ascertain the nature of electric atmospheres; the result of which see under that article.

The theory of two electric fluids, always co-existent and counteracting each other, though not absolutely independent, was maintained by a course of experiments on silk stockings of different colours, communicated to the Royal Society by Mr. Symmer, in the year 1759, which were farther pursued by Mr. Cigna | of Turin, who published an account of them in the Memoirs of the Academy at Turin for the year 1765.

Many instances occur in the history of the science about this period, of the astonishing force of the electric shock, in melting wires, and producing other similar effects: but the most remarkable is an experiment of S. Beccaria, in which he thus revivified metals. Several experiments were also made by Dr. Watson, Mr. Smeaton, Mr. Canton, and others, on the passage of the electric fluid through a vacuum, and its luminous appearance, and on the power possessed by certain substances of retaining the light communicated to them by an electric explosion. Mr. Canton, S. Beccaria, and others, made many experiments to identify Electricity and lightning, to ascertain the state of the atmosphere at different times, and to explain the various phenomena of the Aurora Borealis, Water-Spouts, Hurricanes, &c, on the principles of this science.

Those who are desirous of farther information with respect to the history of electrical experiments and discoveries, may consult Dr. Priestley's History and Present State of Electricity. This author however is not merely an historian: his work contains many original experiments and discoveries made by himself. He ascertained the conducting power of charcoal, and of hot glass; the Electricity of fixed and inflammable air, and of oil; the difference between new and old glass, with respect to the diffusion of Electricity over its surface; the lateral explosion in electrical discharges; a new method of fixing circular-coloured spots on the surfaces of metals, and the most probable difference between electrics and conductors, &c. The science is also greatly indebted to many other persons, elther for their experiments and improvements of it, or for treatises and other writings upon it; as Mr. Henley, to whom we owe several curious experiments and observations on the electrical and conducting quality of different substances, as chocolate, vapour, &c, with the reason of the difference between them; the fusion of platina; the nature of the electric fluid, and its course in a discharge; the method of estimating the quantity of it in electrical bodies by an electrometer; the influence of points; &c, &c. Also Messrs Van Marum, Van Swinden, Ferguson, Cavallo, Lord Mahon, Nairne, &c, &c, for their several treatises on the subject of Electricity, any of which may be consulted with advantage for the experiments and principles of the science.

Medical Electricity. It is natural to imagine that a power of such efficacy as that of electricity would be applied to medical purposes; especially, since it has been found invariably to increase the sensible perspiration, to quicken the circulation of the blood, and to promote the glandular secretion: accordingly, many instances occur in the latter period of the history of this science, in which it has been applied with considerable advantage and success. And among the variety of cases in which it has been tried, there are none in which it has been found prejudicial except those of pregnancy and the venereal disease. In most disorders, in which it has been used with perseverance, it has given at least a temporary and partial relief, and in many it has effected a total cure. Of which numerous inftances may be seen in the Philos. Trans. and the writ- ings on this science by Messrs Lovet, Westley, Ferguson, Cavallo, &c. &c.

Theory of Electricity. It is hardly necessary to recite the ancient hypotheses on this subject; such as that of the sympathetic powder of the Peripatetics; that of unctuous effluvia emitted by excited bodies, and returning to them again, adopted by Gilbert, Gassendus, Sir Kenelm Digby, &c; or that of the Cartesians, who ascribed electricity to the globules of the first elements, discharged through the pores of the rubbed substance, and in their return carrying with them those light bodies, in whose pores they were entangled: these hypotheses were framed in the infancy of the science, and of philosophy in general, and have long since been exploded. In the more advanced state of electricity there have been two principal theories, each of which has had its advocates. The one, is that of two distinct electric fluids, repulsive with respect to themselves, and attractive of one another, adopted by M. du Fay, on discovering the two opposite species of electricity, viz, the vitreous and resinous, and since new-modelled by Mr. Symmer. It is supposed that these two fluids are equally attracted by all bodies, and exist in intimate union in their pores; and that in this state they exhibit no mark of their existence. But that the friction of an electric by a rubber separates these fluids, and causes the vitreous electricity of the rubber to pass to the electric, and then to the prime conductor of a machine, while the resinous electricity of the conductor and electric is conveyed to the rubber: and thus the quality of the electric fluid, possessed by the conductor and the rubber, is changed, while the quantity remains the same in each. In this state of separation, the two electric fluids will exert their respective powers; and any number of bodies charged with either of them will repel each other, attract those bodies that have less of each particular fluid than themselves, and be still more attracted by bodies that are wholly destitute of it, or that are loaded with the contrary. According to this theory, the electric spark makes a double current; one fluid passing to an electrified conductor from any substance presented to it, whilst the same quantity of the other fluid passes from it; and when each body receives its natural quantity of both fluids, the balance of the two powers is restored, and both bodies are unelectrified. For a surther account of the explication of some of the principal phenomena of electricity by this theory, see Dr. Priestley's History, vol. 2, § 3.

The other theory is commonly distinguished under the denomination of positive and negative electricity, being first suggested by Dr. Watson, but digested, illustrated, and confirmed by Dr. Franklin; and since that it has been known by the appellation of the Franklinian hypothesis. It is here supposed that all the phenomena of electricity depend on one fluid, sui generis, extremely subtile and elastic, dispersed through the pores of all bodies, by which the particles of it are as strongly attracted as they are repelled by one another. When bodies possess their natural share of this fluid, or such a quantity as they can retain by their non-attraction, it is then said they are in an unelectrified state; but when the equilibrium is disturbed, and they either acquire an additional quantity from other bodies, or lose part of their own natural share by communication to other bodies, | they exhibit electrical appearances. In the former case it is said they are electrified positively, or plus; and in the other negatively, or minus. This electric fluid, it is supposed, moves with great ease in those bodies that are called conductors, but with extreme difficulty and slowness in the pores of electrics; whence it comes to pass, that all electrics are impermeable to it. It is farther supposed that electrics contain always an equal quantity of this fluid, so that there can be no surcharge or increase on one side without a proportionable decrease or loss on the other, and vice versa; and as the electric does not admit the passage of the fluid through its pores, there will be an accumulation on one side, and a corresponding deficiency on the other. Then when both sides are connected together by proper conductors, the equilibrium will be restored by the rushing of the redundant fluid from the overcharged surface to the exhausted one. Thus also, if an electric be rubbed by a conducting substance, the electricity is only conveyed from one to the other, the one giving what the other receives; and if one be electrified positively, the other will be electrified negatively, unless the loss be supplied by other bodies connected with it, as in the case of the electric and insulated rubber of a machine. This theory serves likewise to illustrate the other phenomena and operations in the science of electricity. Thus, bodies differently electrified will naturally attract each other, till they mutually give and receive an equal quantity of the electric fluid, and the equilibrium is restored between them. Beccaria supposes, that this effect is produced by the electric matter making a vacuum in its passage, and the contiguous air afterwards collapsing, and so pushing the bodies together.

The influence of points, in drawing or throwing off the electric fluid, depends on the less resistance it finds to enter or pass off through fewer particles than through a greater number, whose resistance is united in flat or round surfaces. The electric light is supposed to be part of the electric fluid, which appears when it is properly agitated; and the sound of an explosion is produced by vibrations, occasioned by the air's being displaced by the electric fluid, and again suddenly collapsing.

As to the nature of the electric fluid, philosophers have entertained very different sentiments: some, and among them Mr. Wilson, have supposed that it is the same with the ether of Sir Isaac Newton, to which the phenomena of attraction and repulsion are ascribed; whilst the light, smell, and other sensible qualities of the electric fluid, are referred to the grosser particles of bodies, driven from them by the forcible action of this ether; and other appearances are explained by means of a subtile medium diffused over the surfaces of all bodies, and resisting the entrance and exit of the ether; which medium, it is supposed, is the same with the electric fluid, and is more rare on the surfaces of conductors, and more dense and resisting on those of electrics: but Dr. Priestley remarks that, though they may possess some common properties, they have others essentially distinct; the ether is repelled by all other matter, whereas the electric fluid is strongly attracted by it. Others have had recourse to the element of fire; and from the supposed identity of fire and the electric fluid, as well as from the similarity of some of their effects, the latter has been usually called the electric fire: but most electricians have supposed that it is a fluid sui generis. Mr. Cavendish has published an attempt to deduce and explain some of the principal phenomena of electricity in a mathematical and systematic manner, from the nature of this fluid, considered as composed of particles that repel each other, and attract the particles of all other matter, with a force inversely as some less power of the distance than the cube, whilst the particles of all other matter repel each other, and attract those of the electric fluid, according to the same law. Philos. Trans. vol. 61, pa. 584—677. And a similar hypothesis and method of reasoning was also proposed by M. Æpinus, in his Tentamen Theoriæ Electricitatis & Magnetismi.

Dr. Priestley concludes, from experiments, that the electric matter either is phlogiston, or contains it, since he found that both produced similar effects. Mr. Henley also apprehends, that the electric fluid is a modification of that element, which, in its quiescent state, is called phlogiston; in its first active state, electricity; and when violently agitated, fire. Perhaps we may be allowed to enlarge our views, and consider the sun as the fountain of the electric fluid, and the zodiacal light, the tails of comets, the aurora borealis, lightning, and artificial electricity, as its various and not very dissimilar modifications. On this subject, see Priestley's Hist. of Electr. vol. 2, part 3, § 1, 2, 3; Wilson's Essay towards an Explication of the Phenomena of Electricity, &c; Wilson and Hoadley's Obs. &c, pa. 55, 1759; Freke's Essay on the Cause of Electricity, 1746; Priestley on Air, vol 1, pa. 186, 274, &c; Philos. Trans. vol. 67, pa. 129; and Mr. Eeles's Letters, on the same subject.