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New original cover art included with this eBook is granted to the public domain.

Fig. 1.
Fig. 2.
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AN
EPITOME
OF
ELECTRICITY & GALVANISM.

BY TWO GENTLEMEN OF PHILADELPHIA.

Causa latet; vis est notissima.——Ovid’s Met. B. IV. l. 287.

PHILADELPHIA:

PRINTED BY JANE AITKEN, No. 71,

NORTH THIRD STREET.

1809.

DISTRICT OF PENNSYLVANIA, TO WIT:

SEAL.

BE IT REMEMBERED, That on the fourteenth day of December, in the thirty-fourth year of the Independence of the United States of America, A. D. 1809. Jane Aitken, of the said District, hath deposited in this Office, the Title of a Book, the Right whereof she claims as Proprietor, in the words following, to wit:—

“An Epitome of Electricity and Galvanism. By two gentlemen of Philadelphia. Causa latet; vis est notissima.—Ovid’s Met. B. IV. l. 287.”

In conformity to the Act of the Congress of the United States, intituled, “An Act for the encouragement of Learning, by securing the Copies of Maps, Charts, and Books, to the Authors and Proprietors of such Copies, during the times therein mentioned.” And also to the Act, entitled “An Act, supplementary to an Act, entitled, “An Act for the encouragement of Learning, by securing the Copies of Maps, Charts, and Books, to the Authors and Proprietors of such Copies, during the times therein mentioned,” and extending the benefits thereof to the Arts of designing, engraving, and etching historical and other prints.”

D. CALDWELL, Clerk of the

District of Pennsylvania.

RECOMMENDATIONS.

Having perused this Epitome, it appears to me to comprise, in a concise and perspicuous manner, the principal discoveries that have been made in Electricity and Galvanism, illustrated with a variety of amusing experiments; and I have no doubt that it will prove useful and entertaining to those who wish for information on these subjects.

JOHN M‘DOWELL,

Professor of Natural Philosophy, and Provost

of the University of Pennsylvania.

Philad. Dec. 11, 1809.

Having read, at the request of the authors, a work under the title of “An Epitome of Electricity and Galvanism,” I am of opinion that it is well calculated for the instruction of youth; and also that it may prove a useful manual to gentlemen who wish to acquire, without extensive reading, a general knowledge of the subjects discussed.

JOHN MACLEAN,

Professor of Natural Philosophy and Chemistry

in the College of New-Jersey.

Nassau Hall, Oct. 20, 1809.

The Epitome of Electricity appears to me to contain a concise, but perspicuous and correct statement of the laws of that branch of Philosophy, and an interesting collection of facts and experiments, by which they are illustrated.

JEREMIAH DAY,

Professor of Mathematics and Natural Philosophy.

Yale College, Nov. 25, 1809.

[As the authors could not transmit to Professor Day a copy of the Epitome of Galvanism, without unduly delaying the publication, his testimonial, of course, refers only to the Epitome of Electricity.]

PREFACE.

Having denominated the following work an epitome of Electricity and Galvanism, it seems reasonable to request that the reader should keep the nature of our plan in view. If the book do not contain, on the subjects proposed to be treated, all that is most important, let it be condemned. But let not detail be expected where the design requires conciseness. There are some articles under which we were obliged, either to omit unimportant improvements, or to occupy several pages in describing them.

Where, however, omissions of any consequence have taken place, we have endeavoured carefully to refer to the books which will supply them; so that our work may not only teach the elements and substance of the science, but direct those who wish to pursue it most extensively—We particularly regretted that we could not describe a variety of electrometers.

Short as our work is, we found it, notwithstanding, scarcely practicable to avoid some repetition. In a few instances the historical and scientific parts may be observed, in a small degree, to interfere. Where history was useful to illustrate experiment, or experiment composed a part of history, we did not choose to separate what perspicuity required to be kept together. We hope, on the whole, that we do not need more indulgence in this respect, than we shall readily find, from those who are fond of the subjects which it was our business and our pleasure to investigate.

In making our epitome, we have often written without a special reference to any book; sometimes we have abridged the writings of others; sometimes we have taken paragraphs with the alteration of a few words; and sometimes we have introduced full quotations. In the latter case, we have always wished to make a distinct reference to the author quoted; and in other cases, we have generally made our acknowledgments where we were particularly indebted. But as our work was begun without any determination to publish it, we have probably made some selections, of which we have ourselves forgotten the authors from whom they were taken. Of the fairness of a work of this nature, we suppose there can be no question. Johnson, when speaking of the system of logic published by Watts, has made our apology—“If he owes part of it to Le Clerk, it must be considered, that no man who undertakes merely to methodise or illustrate a system, pretends to be its author.”

As impositions are often attempted, by soliciting patronage for publications of little value, we felt the importance of obtaining, in behalf of our work, the approbation of competent judges—The public will admit that it has been obtained; and the professional gentlemen who have favoured us with it in the most obliging and disinterested manner, will excuse our offering them this public tender of our grateful acknowledgments.

With these remarks we commit our little work to the candour of the public, conscious of having assiduously laboured to furnish a book which, though it appeared to us to be much wanted, had not yet been written or compiled. Our views will be fully answered, if it shall be found well adapted to assist youth in their academical and philosophical studies, and at the same time, to afford amusement to men of learning, and some useful information to gentlemen of leisure.

INTRODUCTION.

SECTION I.

Electricity as known among the Ancients.

In examining the progress of almost any branch of human knowledge, curiosity must meet with many repulses. By the time the attention of society is attracted to the accumulation of detached truths, which compose a science, it is often impossible to retrace its history. The real origin of most discoveries is obscured by antiquity, their authors have already sunk into oblivion, and important improvements are ascribed to different inventors.

Electricity is however oppressed by few of these difficulties. With the exception of some small discoveries mentioned by ancient authors, this science derives its origin and all its improvements from the two last centuries. Neither is the historian perplexed in giving every invention to its proper author. Those who cultivated this science were commonly men of talents and condition; they pursued it with ability and perseverance; and either themselves published the result of their observations, or deposited them in those literary institutions which they found established in their country. The historian of electricity, therefore, with no extraordinary exertion of industry or talent, may fully collect and accurately arrange the materials of his work.

On the subject of electricity nothing earlier is on record than the observation of Thales, that yellow amber, when rubbed, has the property of attracting light bodies.—So struck was he with this property of amber, that he imagined it was animated.

Thales, the contemporary of Pythagoras, was born at Miletus, a city of Ionia, about six hundred years before Christ. Like all the Grecian sages, he travelled into Egypt; lived in that country a number of years; contracted friendships with the priests, then the depositories of science; and became deeply skilled in all their mysteries and learning. Returning to his own country, stored with the knowledge of the East, he was ranked as the first of the seven wise men of Greece, and became the founder of the Ionic school, as Pythagoras did of the Italic.

It may deserve remark that the same philosopher who is recorded to have observed the first phenomenon in electricity, is also said to have discovered the cause of thunder and lightning. We shall give to the curious, the remarkable passage containing this account, as we find it in Apuleius, a learned and eloquent writer of the second century, while he is rapidly enumerating the discoveries of Thales.

Thales Milesius ex septem illis sapientia memoratis viris facile præcipuus: fuit enim geometricæ penes Grajos primus repertor, et naturæ rerum certissimus explorator, et astrorum peritissimus contemplator, maximas res parvis lineis reperit, temporum ambitus, ventorum flatus, stellarum meatus, tonitruum sonora miracula, siderum obliqua curricula, Solis annula reverticula; idem Lunæ vel nascentis incrementa, vel senescentis dispendia, vel delinquentis obstacula.

“Thales the Milesian was decisively the most eminent of the seven famous sages; for he was the first inventor of geometry among the Greeks, the most judicious inquirer into nature, and the most skilful observer of the stars; he made great discoveries by small geometrical lines, the regulation of times and seasons, the theory of the winds, the course of the stars, the wonderful causes of thunder, the oblique motions of the planets, the annual revolution of the sun, the reason of the increase, decrease, and eclipse of the moon.”[^[1]]

Though it is no where expressly affirmed that electricity was discovered by Thales to be the cause of thunder, yet when the two facts are placed together, they will furnish an additional argument to those writers who contend that the ancients knew much more than we are willing to allow them of those shining truths, which are the peculiar boast of modern ages. Nor should this early discovery, if we could admit it to be real, excite our surprise. Whatever hindrances might impede the progress of the ancients in other branches of knowledge, from the abstruse nature of the subject, or the want of necessary helps, it may rather excite our wonder, that the effects of electricity should remain so long unobserved. The electric fluid is no local or occasional agent; it is coeval with the world; its presence pervades every substance; it is the principal cause of the grandest scenes in nature, and its operations can hardly fail to show themselves wherever bodies are concerned.

From the time of Thales, there is a chasm in the history of electricity for three hundred years. Indeed, natural science of all kind appears to have languished, during this period. Theophrastus, who flourished 371 years before Christ, the disciple and successor of Aristotle, and he to whom the learned are indebted for the preservation of his master’s works, then adds one more fact to the history of electricity.

In his treatise on stones, after speaking of the attractive power of amber, found on the coast of Liguria, he goes on to ascribe the same properties to the lapis lyncurius, the same substance now called tourmaline. “It possesses (says he) an attractive power like amber: and as they say attracts not only straws and leaves, but copper also, and iron, if in small particles.[^[2]]”

These two discoveries of Thales and Theophrastus are all, on the subject of electricity, that industry has been able clearly to collect from the barren records of antiquity. Pliny indeed has observed that “amber being rubbed with the fingers, and having thereby become warmed, attracts to itself straws and dried leaves, in the same manner as the magnet does iron.” He also attributes to the Lyncurium the same properties.—Solinus and Priscian, also, make similar statements. But as these are no more than what Thales and Theophrastus had remarked before, they are to be considered only as a repetition of what the preceding writers had made known, not as any addition to the information possessed on this subject. In like manner it might be mentioned that Aristotle, Pliny, Oppian and Claudius, were fully acquainted with the benumbing effects produced by the touch of the Torpedo; but as they do not appear to have suspected that these effects were produced by electricity, they cannot be considered as communicating or possessing any additional knowledge in regard to this powerful agent.[^[3]]

On subjects which regard taste, or which address themselves to the imagination, on poetry, eloquence and the fine arts, it is to the ancients we are to look for information and the models of perfection. But on the various branches of knowledge which depend on observation, on experiment, on investigation, which comprehend all the parts of mechanical philosophy, the philosophers of antiquity afford little that is either new or just. Hurried away by the vivacity of their genius, which their peculiar complexion invited them to cultivate, and the particular circumstances of the age were calculated to inflame, they investigated facts, not that by accumulated discoveries they might lay the foundation of solid science, but so far only as they served to support or illustrate some favourite hypothesis.

Aristotle, to whose profound and elevated genius we are accustomed to turn for satisfactory information on so many other subjects, affords no remarks on electricity, and little worthy of observation on most of the branches of natural science. One, who on this point has a right to speak, observes.—“That though there are several very sublime questions in his physics, which he clears up in a very masterly way, yet the main, the gross of the work is good for nothing, infelix operis summa.[^[4]]”

From the time of Theophrastus till the beginning of the 17th century of the christian æra, there is no unequivocal evidence that in the science of electricity any discovery or improvement was made, except the solitary and unimportant fact that jet, and perhaps agate, is endued with the same power as amber, of attracting and repelling light bodies.—Nor is it ascertained by whom, or at what particular period, this fact was added to the slender stock of electrical knowledge which was then possessed. And thus it appears that for the space of about 1900 years, the part of philosophy, of which we trace the history, was nearly stationary.

SECTION II.

Electricity as known to the Moderns.

Having seen, in the preceding section, the very limited knowledge of electricity possessed by the ancients, we now come to give an account of what may properly be called its real origin, and to trace its progress to the present day. In doing this, we shall be careful to note all the original authors who have touched upon this subject; and to exhibit most of their discoveries.

We believe it to be generally the case, that, in the earlier periods of a science, the mind is curious to observe the gradual developement of principles, and the gradual increase of facts, however unimportant these facts may afterwards appear. But as the science progresses, as the ground widens and observations multiply, this curiosity proportionably abates, and we require of the historian selection rather than detail.

However minute, therefore, the history of the first stages of this branch of philosophy must be, the after periods will exact only a careful selection of those more prominent discoveries, which show the advances of the science and mark its gradations.

During the sixteenth century, the phenomena of magnetism having engaged the study of philosophers, they were naturally led to bestow some attention on substances which appeared to possess similar properties with the load-stone. Indeed, it was not till after 1729 that the idea was entertained, that electricity was a distinct fluid, or any thing else than a certain property of bodies, resembling magnetism; nor was any other meaning affixed to the word, than a power of attracting and repelling.

Fifteen centuries having elapsed from the time of Theophrastus, William Gilbert, physician to king James I, in 1600 published a latin work, entitled, De Magnete, magnetesque corporibus, in which, having discussed the phenomena of magnetism, he, towards the close, relates a great variety of electrical experiments.

The principal merit of this philosopher is, that he greatly augmented the list of electrical substances, noted the bodies on which electrics can act, and remarked several circumstances relating to the manner of their action.

He enumerates, as having the power of attracting light bodies, Diamonds, Saphirs, Carbuncles, Iris, Opals, Amethysts, Beryl, Crystal, Bristol-stones, Sulphur, Mastick, Hard Wax, Hard Rosin, Arsenic, Sal-gemm, Rock-Alum, common-glass, Stibium, or glass of Antimony. He also observed that the influence of these substances extended, not only to leaves and straws, but to all matter which was not extremely rare. Friction, he says, is, in general, necessary to excite the virtue of these substances; and the most effectual friction, he affirms, is that which is light and quick. Electrical appearances, he asserts, were strongest when the air was dry, and the wind north or east, at which time electrics would act ten minutes after excitation.

The simple experiments of this philosopher were mostly made with long thin pieces of metal, and other substances freely suspended on their centers, to the extremities of which he presented the electrics he had excited.

The phenomena of magnetism were accounted for, in the time of Gilbert, by means of emanating effluvia, and he applies the same theory to the explanation of electrical attraction, imagining it to be performed in the same manner as the attraction of cohesion. Two drops of water, rush together when they are brought into contact, and electrics, he says, are virtually brought into contact by means of their effluvia. Effluvia illa tenuiora concipiunt et amplectuntur corpora, quibus uniuntur, et electris tanquam extensis brachiis, et ad fontem propinquitate, invalescentibus effluviis, deducuntur. “Those subtle effluvia continually embrace certain bodies, to which they are united, as it were by their extended electric arms; and the effluvia prevailing, the bodies are drawn to the contiguous source of the effluvia.”

Gilbert has been stiled the father of modern electricity; and when we consider how little was known of the subject prior to his time, and the merit that belongs to himself, not only from his own experiments, but also from turning the attention of philosophers to a new branch of natural science, we cannot but allow that he eminently deserves the title.

Cabeus followed Gilbert, but did little else than add to the list of electrics, wax, gum elemi, Gum guaiaci, Pix Hispanica and Gypsum.

Thirty years after the publication of Gilbert’s work, the celebrated Sir Kenelm Digby, in his “Treatise of the nature of Bodies,” touches upon electricity: but as the age in which he lived was still busying itself with the hypothetical philosophy of Aristotle, so this philosopher in what he says of electricity, appears to be rather amusing himself in inventing theories, to explain the manner in which electric attraction is performed, than in advancing the science by new facts and experiments. His theory of electric attraction is, however, of some celebrity: it was allowed by his contemporary Des Cartes, in his principles of philosophy, and was embraced by the chief writers of his age; though it does not differ essentially from that of Gilbert.

“Attraction (says he) is made by a tenuious emanation, or continued effluvium, which after some distance retracteth into itself, as is observable in drops of syrups, oil and seminal viscosities, which spun at length, retire to their dimensions. Now these effluviums advancing from the body of an electric, in their return do carry back the bodies whereon they have laid hold, within the sphere or circle of their continuities; and these they do not only attract, but with their viscous arms, hold fast a good while after. And if any shall wonder why these effluvium issuing forth, impel and protrude not the straw before they can bring it back; it is because the effluvium passing out in a smaller thread, and more enlengthened filament, stirreth not the bodies interposed; but returning into its original, falls into a closer substance and carrieth them back into itself.”

Sir Thomas Brown succeeded to Sir Kenelm Digby. In his “Inquiry into Vulgar Errors,” this inquisitive philosopher has a chapter on electricity, in which he corrects some mistakes into which his predecessor had fallen, adds some new experiments of his own, and gives us a summary view of the state of electrical knowledge at the time he wrote.

“By electrical bodies, (says he) I understand not such as are metallical, mentioned by Pliny, and the ancients; for their electrum was a mixture made of gold, with the addition of a fifth part of silver; a substance now as unknown as true Aurichalcum, or Corinthian brass, and set down among things lost by Pancirollus. Nor by electric bodies do I conceive such only as take up shavings, straws, and light bodies, in which number the ancients only placed Jet and Amber; but such as conveniently placed unto their objects attract all bodies palpable whatsoever. I say conveniently placed, that is, in regard of the object, that it be not too ponderous, or any way affixed; in regard of the agent, that it be not foul or sullied, but wiped, rubbed, and excitated; in regard of both, that they be conveniently distant, and no impediment interposed. I say, all bodies palpable, thereby excluding fire, which indeed it will not attract, nor yet draw through it; for fire consumes its effluxions by which it should attract.”

Brown augmented the list of electrics, and found attraction not only in simple bodies, but in such also as were compounded. He observed, that the attractions of bodies were different. Resinous bodies, he says, attract most vigorously, and “good hard wax so powerfully, that it will convert the needle almost as actively as the load-stone. Gums easily dissolved in water, draw not at all; no metal attracts, nor wood, though never so hard and polished. “Glass, (he says,) attracts but weakly, though clear: and some slick stones, and thick glasses but indifferently.”

These experiments on the electricities of bodies, he performed by means of a needle, “settled freely upon a well pointed pin, so that the electrics might be applied to it without disadvantage;” he tried them also in straws and paleous bodies, powders of wood and iron, in gold and silver foliated.

How the attraction of electrics is performed, he acknowledges is not easily determined; though, he says, “that it is performed by effluviums is plain, and granted by most; for electrics will not commonly attract, except they grow hot and perspirable. For if they be foul and obnubilated, it hinders their effluxion; nor if they be covered, though but with linen or sarsenet, or if a body be interposed, for that intercepts the effluvium. If also a powerful and broad electric of wax or anime be held over fine powder, the atoms or small particles will ascend most numerously unto it; and if the electric be held unto the light, it may be observed that many thereof will fly, and be as it were discharged from the electric to the distance sometime of two or three inches. Which motion is performed by the breath of the effluvium issuing with agility; for as the electric cooleth, the projection of the atoms ceaseth.”

Sir Francis Bacon in his “Physiological Remains,” has inserted a catalogue of bodies attractive and not attractive; but he differs in nothing worth mentioning from his predecessors.

Mr. Boyle, who so eminently distinguished himself in the latter part of the seventeenth century, was led by the study of chemistry, to give some attention to electricity. He enlarged the catalogue of electrics; and noticed some circumstances relating to electrical attraction, which had escaped former philosophers. The electrical properties of bodies he found were increased by wiping and warming them, before they were rubbed. Bodies of all kinds, he observed, were indiscriminately attracted; and this attraction he supposed took place in vacuo as well as in the open air.

Hitherto the attraction of electrics was the single phenomenon noticed by philosophers. Gilbert, even when remarking on the characteristic differences between magnetism and electricity, observes, that in magnetism there is both attraction and repulsion, but in electricity only the latter, and not the former.[^[5]] Boyle made an approach to the discovery of this fact of electrical repulsion, by remarking that light bodies, as feathers &c. would cling to his fingers and other substances, after they had been attracted by electrics.

Otto Guericke, the celebrated inventor of the air pump, who was contemporary with Mr. Boyle, improved the science much farther. He made use of a sulphur globe, whirled on an axis, much in the same way with our present glass globes. He could thus excite the electricity with greater power, and try all the experiments of his predecessors to greater advantage. His was the full discovery of electric repulsion. “A body once attracted, he remarks, by an excited electric, is repelled by it, and not attracted again till it has been touched by some other body.” In this manner he kept a feather a long time suspended in the air, above his sulphur globe. He also made another remarkable discovery, which has since been very generally overlooked; namely, that a feather, when repelled by an excited electric, always keeps the same face towards the body which repels it, as the moon does to the earth. The electric light was probably observed by Mr. Boyle in the diamond; but Otto Guericke saw it more clearly in the excitation of his glass globe, and also heard the hissing sound which attends it. As this light, however, was exhibited to Dr. Wall, about the same time, in a much finer manner, we shall rather give his account of it.

“I found, says he, upon swiftly drawing a well polished piece of amber in the dark, through a piece of woollen cloth, and squeezing it pretty hard with my hand, a prodigious number of little cracklings were heard, and every one of them produced a flash of light; but when the amber was drawn gently and slightly through the cloth, it produced only a light, but no crackling; but by holding one’s finger at a little distance from the amber, a large crackling is produced, with a great flash of light succeeding it. And, what to me is very surprising, upon its eruption, it strikes the finger very sensibly, wheresoever applied, with a push or puff, like wind. This light and crackling seems, in some respects, to represent thunder and lightning.

Sir Isaac Newton is the next in chronological order, who made any discovery of importance. He first observed that the electrical attraction and repulsion, penetrated through glass. It cannot but be lamented, that this great philosopher, among the vast variety of important subjects which he cultivated and improved, had not applied himself to electricity, with greater assiduity.

Mr. Hawksbee, in 1709, wrote a treatise on electricity, and distinguished himself by discoveries which far surpassed those of his predecessors. Besides a variety of new facts in regard to attraction and repulsion, he observed the electric light distinctly, and made some delicate and curious experiments on its nature.

The electric light was considered by Mr. Hawksbee, as well as by all those who first observed it, as a species of phosphorus, and all the experiments made, were conducted under this impression.

Holding an exhausted globe within the effluvia of an excited one, he observed a light in the former, which presently died away, if it was kept at rest; but was revived, and continued very strong, if the exhausted globe was kept in motion. The greatest electrical light he produced, was when he enclosed an exhausted cylinder within one not exhausted, and excited the outermost of them, putting them both in motion. He observed no difference, whether the globes were turned in the same direction, or otherwise.

He made many experiments to shew the extreme subtlety of the electric light, and found out a method of rendering opaque bodies transparent. He lined with sealing wax more than half the inside of a glass globe, and having exhausted it, put it in motion. On applying his hand to excite it, he saw the shape and figure of all the parts of his hand distinctly and perfectly, on the concave superficies of the wax within. It was as if there had been pure glass, and no wax interposed between the glass and his hand. This lining was in many places the eighth of an inch thick; and in some places where it did not adhere so closely to the glass as in others, yet the light on these appeared just as on the rest. He repeated these experiments with pitch instead of sealing wax, and with equal success. It is to be regretted that these facts have not engaged more of the attention of philosophers.

After the death of Mr. Hawksbee, twenty years elapsed before any farther improvements were made. The great discoveries which were then making in other branches of philosophy, by Sir Isaac Newton, so absorbed the public attention, that electricity was entirely overlooked. Mr. Grey, after this long interval, took up the subject, and by his discovery of the distinction between electrics and non-electrics, formed an important epoch in the history of electricity.

An account of this discovery of Mr. Grey, is thus abridged from the Philosophical Transactions, by Dr. Priestley. “In the month of February 1729, Mr. Grey, after some fruitless attempts to excite an electric power in metals, recollected a suspicion he had for some time entertained, that as a glass tube, when excited in the dark, communicated its light to various bodies, it might at the same time possibly communicate to them an electricity; that is, a power of attracting light bodies; which, as yet, was all that was understood by the word electricity. For this purpose he provided himself with a glass tube, three feet five inches long, and near one inch and two-tenths in diameter. To each end was fitted a cork; to keep the dust out when the tube was not in use. His first experiments were made with a view to determine whether a tube would attract equally well with the ends shut, as with them open. In this respect there was no difference; but he found that the corks attracted and repelled light substances, as well, and rather better than the tube itself. He then fixed an ivory ball upon a stalk of fir about four inches long, and thrusting the end of the stalk into one of the corks, he found the ball endowed with a strong attractive and repulsive virtue. This experiment he repeated in many different ways; fixing the ball upon long sticks, and upon pieces of brass and iron wire, always with the same success; but he constantly observed, that the ball at the end attracted more vigorously, than that part of the wire nearest the tube.

“The inconvenience of using long wires in this manner, put Mr. Grey upon trying whether the ball might be suspended by a pack-thread, with a loop on the tube, with equal success; and the event fully answered his expectation. Having thus suspended bodies of the greatest length he conveniently could, to his tube, he ascended a balcony 26 feet high, and fastening a string to his tube, found that the ball would attract light bodies on the ground below. This experiment succeeded in the greatest heights to which he could ascend; after which, he attempted to carry the electricity horizontally. His first attempt miscarried, because he suspended his line, which was intended to carry the electricity horizontally, by a pack-thread; and thus the fluid got off from it; but though Mr. Grey knew this was the case, he could not at any time think of any method to prevent it.

“On the 30th June 1729, Mr. Grey paid a visit to Mr. Wheeler, in order to give him a specimen of his experiments; but told him of the unsuccessful attempt he had made to carry the electric fluid horizontally; Mr. Wheeler proposed to suspend the conducting line by silk instead of pack-thread. For this advice he could give no reason, but that the silk thread was smaller than the other; however, with it they succeeded perfectly well. Their first experiment was in a matted gallery at Mr. Wheeler’s house, on the 2d of July 1729. About four feet from the end of the gallery they fastened a line across the place. The middle of this line was silk, the rest pack-thread. Over the silken part they laid one end of the conducting line, to which was fastened the ivory ball, and which hung down about nine feet below the line stretched across the gallery. The conducting line was about 80 1–2 feet in length, and the other end of it was fastened by a loop to the electric tube. Upon rubbing the tube, the ivory ball attracted and repelled light substances, as the tube itself would have done. They next contrived to return the line, so that the whole length of it amounted to 147 feet; which also answered pretty well. But suspecting that the attraction would be stronger, without doubling or returning the line, they made use of one carried straight forward, for 124 feet; and as they expected, found the attraction in this manner, stronger than when the lines had been doubled. Thus they proceeded with their experiments; still adding more conducting line, till at last their silk string broke with the weight. This they endeavoured to supply, first with a small iron wire, and then with a brass one. The result of these experiments, however, soon convinced them, that the silk refused to conduct the electric fluid, not on account of its smallness, as they had supposed, but on account of some difference in the matter. The wires were smaller than the silk threads, yet the electricity was effectually carried off by them. They had recourse, therefore, to thicker lines of silk; and thus conveyed the electric matter to the distance of 765 feet: nor did they perceive the virtue to be at all diminished by the distance to which it was carried.” In the manner in which silk was found to be a non-conductor, the same quality was also discovered in many other substances, such as hair, rosin, &c.

Mr. Grey also made many electrical experiments on fluids and animal bodies. As he knew no other method of trying whether bodies were electrified or not, but by making them raise light bodies placed under them, to put a fluid in this situation, he dissolved soap in Thames water, and suspending a tobacco pipe, he blew a bubble at the head of it; and bringing the excited tube near the small end, he found the bubble to attract leaf brass to the height of two and of four inches.[^[6]] He contrived afterwards, by a curious experiment to shew the effects of electricity upon water, in a more satisfactory manner. He filled a small cup with water higher than the brim, and when he had held an excited tube over it, at the distance of about an inch or two, he says, that if it were a large tube there would first arise a little mountain of water from the top of it, of a conical form; from the vertex of which there proceeded a light, very visible when the experiment was performed in a dark room, and a snapping noise almost like that which was made when the finger was held near the tube, but not quite so loud, and of a more flat sound. Upon this, says he, immediately the mountain, if I may so call it, falls into the rest of the water, and puts it into a tremulous and waving motion. This experiment he repeated in the sun-shine, when he perceived small particles of water thrown from the top of the mountain; and sometimes a fine stream of water would arise from the vertex of the cone, in the manner of a fountain, from which issued a fine stream or vapour, whose particles were so small as not to be seen. This last circumstance he inferred, from the under side of the tube being wet. And by after experiments, he found that though the cylinder of water does not always rise, yet that there is always a stream of particles thrown on the tube, and sometimes to such a degree as to become visible.

In April 1730, Mr. Grey suspended a boy on hair lines, in a horizontal position, just as all electricians had before been used to suspend their hempen lines of communication, and their wooden rods; then bringing the excited tube near his feet, he found that leaf brass was attracted by his head, with a vigour sufficient to raise it to the height of eight, and sometimes of ten inches. When the leaf brass was put under his feet, and the tube brought near his head, the attraction was small; and when the leaf brass was brought under his head, there was no attraction at all. While the boy was thus suspended, Mr. Grey amused himself with making the electricity operate on several parts of his body at the same time, and at the ends of long rods, which he made him hold in his hands, and in diversifying the experiments several other ways.

Mr. Grey continued to study electricity as long as he lived; and besides giving a set of fanciful experiments, by which he supposed he had discovered a perpetual attractive power in electrics, he, a little while before his death, entered on another course by which he hoped he should be able to astonish the world with a new sort of planetarium. “I have lately made (says he) several new experiments upon the projectile and pendulous motions of small bodies by electricity; by which small bodies may be made to move about large ones, either in circles or ellipses, and those either concentric or excentric to the centre of the large body about which they move, so as to make many revolutions about them. And this motion will constantly be the same way that the planets move round the sun, viz. from the right hand to the left, or from west to east. But these little planets, if I may so call them, move much faster in their apogean, than in the perigean part of their orbits; which is directly contrary to the motion of the planets round the sun.” The manner in which these experiments were made, as delivered by him on his death-bed to Dr. Mortimer, was as follows: “Place a small iron globe (said he) of an inch or an inch and a half in diameter, on the middle of a circular cake of rosin, seven or eight inches in diameter, greatly excited; and then a light body, suspended by a very fine thread, five or six inches long, held in the hand over the centre of the cake, will, of itself, begin to move in a circle round the iron globe, and constantly from west to east. If the globe is placed at any distance from the centre of the circular cake, it will describe an ellipse, which will have the same excentricity as the distance of the globe from the centre of the cake. If the cake of rosin be of an elliptical form, and the iron globe be placed in the centre of it, the light body will describe an elliptical orbit, of the same excentricity with the form of the cake. If the globe be placed in or near one of the foci of the elliptical cake, the light body will move much swifter in the apogee, than in the perigee of its orbit. If the iron globe is fixed on a pedestal an inch from the table, and a glass hoop, or a portion of a hollow glass cylinder excited, be placed round it, the light body will move as in the circumstance mentioned above, and with the same varieties.” He said, moreover, that the light body would make the same revolutions, only smaller, round the iron globe placed on the bare table, without any electrical substance to support it: but he acknowledged that he had not found the experiment succeed if the thread was supported by any thing but the human hand; though he imagined any other animal substance would have answered the purpose.

These experiments occasioned a great deal of speculation. Dr. Mortimer was the only person who was able to repeat them with success, and he only when nobody but himself was the witness. It was therefore generally supposed that both he and Mr. Grey had been deceived: but from some experiments to be related hereafter, it seems probable that the success of Mr. Grey and Dr. Mortimer was owing to their having performed their experiments with candle-light; and the failure of the others to their having attempted them by day light. Notwithstanding which, it is more than probable that Mr. Grey has been deceived in a number of particulars; for no motion can be performed by an artificial excitation of the electric fluid, but what is attended with much irregularity.

Not long after the discovery of Mr. Grey of the difference between conductors and non-conductors, Mr. Du Fay, a French philosopher, (for the “spirit of electricity” had passed from England to France,) discovered, what was afterwards called positive and negative electricity; or as he denominated them the vitreous and resinous electricities. “Chance (says he) has thrown in my way a principle, which casts a new light on the subject of electricity. The principle is, that there are two distinct kinds of electricity, very different from one another, one of which I call vitreous, and the other resinous electricity. The first is that of glass, rock crystal, precious stones, hair of animals, wool and many other bodies. The second is that of amber, copal, gum lac, silk thread, paper, and a vast number of other substances. The characteristics of these two electricities is, that they repel themselves and attract each other. Thus a body of the vitreous electricity repels the vitreous, and on the contrary attracts all those of the resinous. The resinous also repels the resinous and attracts the vitreous. This discovery of Mr. Du Fay was made in consequence of his casually observing, that a piece of leaf gold, repelled by an excited glass tube, and which he meant to chace about the room with a piece of excited gum copal, instead of being repelled by it, as it was by the glass tube, was eagerly attracted.

This doctrine of two different electricities, produced by exciting different substances, was dropped after Mr. Du Fay; and even this philosopher himself adopted at last the opinion of Dr. Franklin that the two electricities differ only in degree, and that the stronger attracts the weaker. Although many of the experiments of Mr. Grey led directly to it, yet to the French philosopher just mentioned, belongs the merit of first drawing the electrical spark from the human body.—And we cannot forbear remarking, in this place on the regular and progressive advances which the human mind makes in the investigation of science. Electrical attraction was, for a long period, the single phenomenon known to philosophers.—Repulsion was then observed to be also a property of electrics.—In the investigation of these we read of the accidental discovery of the electric light.—To this naturally succeeded, Mr. Grey’s distinction between conductors and non-conductors; and then the difference between vitreous and resinous electricities by Mr. Du Fay. We shall have to remark in the sequel of this history, how each succeeding fact and invention grew out of that which immediately preceded it.

The knowledge of electricity did not stop in France. The Germans began to labour in the same field; and with laudable success. Their success arose chiefly from the improvements they made in the electrical apparatus. The simple experiments of Gilbert, and the early electricians, were made by exciting a piece of amber or sulphur. Mr. Boyle found the electric power increased by smoothing the surface of bodies. Otto Guericke made his experiment with a globe of sulphur, formed by melting that substance in a hollow globe of glass, and afterwards breaking the glass from off it, little supposing that the glass itself would better have answered his intention. In 1709 Mr. Hawksbee first observed the great electric power of glass. He used a glass globe, which he mounted upon an axis, whirling it round, and at the same time applying his hand to it. He also, to increase the power, inclosed an exhausted cylinder within another, exciting the outermost. After Mr. Hawksbee’s death, the glass globe was laid aside, and his successors confined themselves to the use of tubes. Mr. Boze, professor of philosophy at Wittemburgh, in 1742 returned to the use of the globe. He also added a prime-conductor of tin or iron, supported, at first, by a man standing on cakes of rosin, but afterwards by silken lines extended horizontally, under the conductor. Mr. Winckler, of Leipsic, to excite the globe, substituted a cushion, instead of the hand. The electrical star and the electrical bells were also the invention of the German philosophers. Dr. Desagulier, likewise, assisted electricians by some electrical terms. He first gave to bodies conveying electricity the name of conductors; and those in which electricity may be excited by heating and rubbing he calls electrics per se.

In 1745, the attention of Dr. Watson being attracted by the account of the Germans having fired spirits of wine, he applied himself to electricity with much assiduity, and made many valuable and curious discoveries. But though his improvements were considerable, and such as at another time would have excited interest, they were now lost amid the surprise occasioned by the most remarkable discovery that had yet been made in the whole science. This was the accumulation of the electric matter in glass bottles, and the method of giving the electric shock.

The merit of this discovery belongs to Mr. Cuneus, a native of Leyden, from whence it derives its name of the Leyden phial.[^[7]] “M. Muschenbroeck, professor in the university in that city, observing with his friends, that electrified bodies, exposed to the common atmosphere, which is always replete with conducting particles of various kinds, soon lost their electricity, and were capable of retaining but a small quantity of it, imagined, that were the electrified bodies terminated on all sides by original electrics, they might be capable of receiving a stronger power, and retaining it a longer time. Glass being the most convenient electric for this purpose, and water the most convenient non-electric, they first made their experiments with water in glass bottles; but no considerable discovery was made, till the professor, or Mr. Cuneus, happening to hold his glass vessel in one hand, containing water, which had a communication with the prime-conductor by means of a wire, and with the other hand disengaging it from the conductor (when he imagined the water had received as much electricity as the machine could give) was surprised by a sudden shock in his arms and breast, which he had not in the least expected from the experiment.”

Wonder is the effect of ignorance, and ignorance begets credulity; but when wonder and credulity are coupled with terror and surprise, we must look for a strange and mishapen progeny. The exaggerated accounts of those who first experienced the electric shock cannot but raise a smile; especially as we may ascertain their real sensations by like experiments upon ourselves.

Mr. Muschenbroeck, in a letter to Mr. Reaumur, written soon after the Leyden discovery, says; that he felt himself struck in his arms, shoulders, and breast, so that he lost his breath; and was two days before he recovered from the effects of the blow and the terror. He adds, he would not take a second shock for the kingdom of France. Mr. Allamand who tried the experiment with a common beer glass, affirmed, that he lost the use of his breath for some moments; and then felt so intense a pain along his right arm, that he at first apprehended ill consequences from it, though it soon after went off without any inconvenience. But the terror of Mr. Winckler of Leipsic exceeded that of all the rest. The first time he tried the Leyden experiment, he says, he found great convulsions by it in his whole body: and that it put his blood into great agitation; so that he was afraid of an ardent fever, and was obliged to use refrigerating medicines. He also felt a heaviness in his head, as if a stone lay upon it. Twice, he says, it gave him a bleeding at the nose, to which he was not inclined; and that his wife (whose curiosity, it seems, was greater than her fears) received the shock only twice, and found herself so weak, that she could hardly walk; and that a week after, upon recovering courage to receive another shock, she bled at the nose after taking it only once.

Mr. Boze, with other philosophers were, however, far from participating in the cowardice of the professor of Leipsic. They gathered resolution to receive a number of electric shocks, as strong as they could be given. Mr. Boze, indeed, as Dr. Priestley remarks, “with a heroism worthy of Empedocles, wished he might die by the electric shock, that the account of his death might furnish an article for the memoirs of the French academy of sciences. But, adds the same author, it is not given to every electrician to die the death of the justly envied Richman.”

This experiment, calculated, not only to engage the investigation of the philosopher, but to raise the vulgar amazement, brought electricity into general notice.—From this time every body was eager to see and to feel this prodigy of nature; and numbers of persons, travelling over Europe, gained a livelihood by exhibiting its appearances and effects. At the same time, all the electricians were zealous to search into the nature of this extraordinary phenomenon. Dr. Watson prosecuted experiments to ascertain how best to succeed with the Leyden phial. He observed that the force of the shock was not increased by the size or number of the globes employed in filling it; nor by increasing the quantity of water in the vessel; but that the power was greatest when the glass was thinnest, and the water warmer than the ambient air. He was proceeding with these discoveries, when Mr. Bevis informed him that he found the electric explosion as great from covering the sides of a pane of glass, as it could have been from a half pint phial of water. The Doctor upon this coated large jars with leaf silver, both inside and outside, within an inch of the top, and from the greatest explosion he produced from them, drew the conclusion that the effect of the Leyden bottle was owing, not so much to the quantities of non-electric matter contained in the glass, as to the number of points of non-electric contact within the glass, and the density of matter of which these points consisted.

In France, the Abbè Nollet attempted to measure the distance to which the electric shock might be carried, and the velocity with which it passes. At one time he electrified 180 of the guards in the king’s presence; and at another the whole community of the grand convent of the Carthusians at Paris, forming a line of 900 toises, by means of iron wires between every two persons; when the whole company, upon the discharge of the phial, gave a sudden spring at the same instant of time, and all felt the shock equally.

But these attempts of the French philosophers to measure the electric circuit were insignificant, in comparison with the extended and numerous experiments of Dr. Watson, accompanied by a number of English gentlemen of eminence. Those gentlemen, in their first attempt, conveyed the electric shock across the river Thames; making use of the water of the river as a part of the chain of communication. This was accomplished by fastening a wire all along the Westminster bridge, at a considerable height above the water. One end of this wire communicated with the coating of a charged phial, the other being held by an observer, who, in his other hand, held an iron rod which he dipped into the river. On the opposite side of the river stood a gentleman, who likewise dipped an iron rod into the river with one hand, and in the other held a wire the extremity of which might be brought into contact with the wire of the phial.

Upon making the discharge, the shock was felt by the observers on both sides of the river, but more sensibly by those who were stationed on the same side with the machine; part of the electric fluid having gone from the wire down the moist stones of the bridge, thereby making several shorter circuits to the phial; but still all passing through the gentlemen who were stationed on the same side with the machine.—This was, in a manner demonstrated, by some persons feeling a sensible shock in their arms and feet, who only happened to touch the wire at the time of one of the discharges, when they were standing upon the wet steps which led to the river. In one of the discharges made upon this occasion, spirits of wine were kindled by the fire which had gone through the river.

They afterwards undertook to determine whether the electric virtue could be conveyed along dry ground, and to distinguish, if possible, the respective velocity of electricity and sound.

For this purpose, they fixed upon a hill, and made their first experiment on the 14th of August 1747; a time, when, as it happened, but one shower of rain had fallen during five preceding weeks. The wire communicating with the iron rod which made this discharge, was supported all the way upon baked sticks; as was also the wire which communicated with the coating of the phial, and the observers were distant from each other two miles. The result of the explosion demonstrated to the gentlemen present, that the circuit performed by the electric matter was four miles, viz. two miles of wire, and two of dry ground, the space between the extremities of the wires.—A distance which, without trial, as they justly observed, was too great to be credited. A gun was discharged at the instant of the explosion, and the observers had stop watches in their hands, to note the moment when they felt the shock; but, as far as they could distinguish, the time in which the electric matter performed that vast circuit might have been instantaneous.

Travellers through a new region of science, like travellers through an unexplored country, too often think themselves absolved from the strict obligations of truth, and at liberty to amuse the public with romantic accounts of what they have heard and seen. About the time these experiments were going forward in England, the passion for the marvellous strongly discovered itself in relating some effects of electricity, pretended to be found out in Italy and Germany. It was asserted by Signor Privati of Venice, and after him by Verati at Bologna, Mr. Blanchi at Turin, and Mr. Winckler at Leipsic, that if odoriferous substances were confined in glass vessels, and the vessels excited, the odours and other medical virtues would transpire through the glass, infest the atmosphere of the conductor, and communicate their virtue to all persons in contact with it; also, that those substances, held in the hands of persons electrified, would communicate their virtues to them, so that the medicines might be made to operate without being taken into the stomach. They even pretended to have wrought many cures by the help of electricity applied in this way. It was affirmed that a man who, having a pain in his side had applied hyssop to it by the advice of a physician, approached a cylinder in which was concealed some balsam of Peru, and was electrified by it. The consequence was that when he went home and fell asleep he sweated, and the power of the balsam was so dispersed that even his clothes, the bed and chamber, all smelled of it. When he had refreshed himself by this sleep, he combed his head, and found that the very comb was perfumed. To see the wonderful effects of these medicated tubes, as they were called, Mr. Nollet travelled into Italy, where he visited all the gentlemen who had published an account of these alledged facts. But though he engaged them to repeat their experiments in his presence and upon himself, and though he made it his business to get all the information he could concerning them, he returned fully convinced, that in no instance had odour been found to transpire through the pores of excited glass, and that no drugs had ever communicated their virtues to people who had only held them in their hands while they were electrified. He was convinced, however, that by continued electrification, without drugs, several persons found considerable relief in various disorders; particularly, that a paralytic person had been cured at Geneva, and that one who was deaf of an ear, another who had a violent pain in his head, and a woman with a disorder in her eyes, had been cured at Bologna: so that from this time we may date the introduction of electricity into the medical art.

Another wonderful experiment was the beatification of Mr. Boze; which other electricians, for a long time, endeavoured to repeat after him, but to no purpose. His description of this remarkable experiment was, that if, in electrifying, large globes were employed, and the electrified person stood upon large cakes of pitch, a lambent flame would by degrees arise from the pitch, and spread itself around his feet; that from thence it would be propagated to his knees and body, till at last it ascended to his head; that then, by continuing the electrification, the person’s head would be surrounded by a glory, such as is in some measure represented by painters in ornamenting the heads of saints. Dr. Watson took the utmost pains to repeat this experiment. He underwent the operation several times, and was supported during the time of it by solid electrics three feet high. Being electrified very strongly, he felt a kind of tingling on the skin of his head, and many other parts of his body. The sensation resembled what would arise from a vast number of insects crawling over him at the same time. He constantly observed the sensation to be the greatest in those parts of his body which were nearest to any non-electric; but no light appeared upon his head, though the experiment was several times made in the dark, and with some continuance. At last the Doctor wrote to Mr. Boze himself, and his answer showed that the whole had been a trick. Mr. Boze acknowledged that he had made use of a suit of armour, which was decked with many pieces of steel, some pointed like nails, others like wedges, and some pyramidal; and that when the electrization was very vigorous, the edges of the helmet would dart forth rays, something like those which are painted on the heads of saints.

The identity of electricity and lightning was the next discovery that engaged the attention of philosophers; and it is a discovery of the first practical importance. We have already noticed the conjectures hazarded by the ancients, on this identity, and we may remember that Dr. Wall, in his experiments on electric light and the crackling with which electricity is emitted, notices the similarity between it, and the phenomenon of thunder and lightning. But when the experiment of the Leyden phial was known to philosophers, this analogy became much more obvious. The Abbè Nollet, after suggesting that thunder is in the hands of nature what electricity is in ours, enumerates many points of resemblance between these two powers, and then says, that meditating on these points, he concludes “that one might, by taking electricity for the model, form to ones self, in relation to thunder and lightning, more perfect and more probable ideas than what have been offered hitherto.”

But though these philosophers, and many others, were struck with this similarity between the electric fluid and lightning, they did not think of any method by which their suspicions might be brought to the test of experiment.—This was first proposed by Dr. Franklin in 1750. He had before discovered the effects of pointed bodies in drawing off the electric matter more powerfully than others. This was suggested to him by one Mr. Thomas Hopkinson, who electrified an iron ball of three or four inches diameter, with a needle fastened to it, expecting to draw a stronger spark from the point of it; but was surprised to find little or none. Dr. Franklin, improving on this hint, supposed that pointed rods of iron, fixed in the air when the atmosphere was loaded with lightning, might draw from it the matter of the thunder-bolt, without noise or danger, into the body of the earth. His account of this supposition is given by himself in the following words. “The electric fluid is attracted by points. We do not know whether this property be in lightning; but since they agree in all the particulars in which we can already compare them, it is not improbable that they agree likewise in this; let the experiment be made.”

This suspicion of Dr. Franklin was verified in 1752. The most active persons in making the experiments by which it was confirmed, were two French gentlemen, Messrs. Dalibard and Delor. The former prepared his apparatus at Marly la Ville, situated five or six leagues from Paris; the other at his own house, on some of the highest ground in that capital. Mr. Dalibard’s machine consisted of an iron rod forty feet long, the lower extremity of which was brought into a centry-box, where the rain could not come; while on the outside it was fastened to three wooden posts, by long silken strings, defended from the rain. This machine happened to be the first that was favoured with a visit of the etherial fire. Mr. Dalibard himself was not at home; but, in his absence, he had entrusted the care of his apparatus to one Coissier a joiner, who had served fourteen years among the dragoons, and on whose courage and understanding he could depend. This artisan had all the necessary instructions given him; and was desired to call some of his neighbours, particularly the curate of the parish, whenever there should be any appearance of a thunder storm. At length the long expected event arrived. On Wednesday the 10th of May 1752, between two and three in the afternoon, Coissier heard a pretty loud clap of thunder. Immediately he ran to the machine, taking with him a phial furnished with a brass wire; and presenting the wire to the end of the rod, a small spark issued from it, with a snap like that which attends a spark from an electrified conductor. Stronger sparks were afterwards drawn, in the presence of the curate and a number of other people. The curate’s account of them was, that they were of a blue colour, an inch and a half in length, and smelled strongly of sulphur. In making them, he received a stroke on his arm a little below the elbow; but he could not tell whether it came from the brass wire inserted into the phial, or from the bar. He did not attend to it at the time; but the pain continuing, he uncovered his arm when he went home, in the presence of Coissier. A mark was perceived round it, such as might have been made by a blow with the wire on his naked skin.

Although it appears from the foregoing statement, that the directions of Dr. Franklin began to be put in execution in France, he himself completed the demonstration of his own problem, before he heard of what was done elsewhere. An account of these experiments will be found in the scientific part of this work. Since the time of Franklin, there has been no capital discovery in electricity:—at least, no discovery of such a nature as to demand a detailed account in this portion of our work. Experiments and improvements have been made; and numerous electricians have evinced a very commendable diligence in the cultivation of this department of knowledge. But their exertions have been directed to the reason and philosophy of the phenomena already known, to the classification of the facts, and to the improvement of the apparatus. Thus Mr. Canton has given a very curious set of experiments upon the conducting power of air, to ascertain wherein consists the distinction between the bodies which are conductors, and those which are not. Signor Beccaria, also, with the same view, experimented upon water and smoke. But what more properly belongs to history, is to mention the view, which Mr. Æpinus, of the Imperial Academy of St. Petersburgh, in the year 1759, took of the science of electricity. This gentleman, struck with the resemblance of the electrical properties of the tourmaline to the properties of a magnet, which have always been considered as the subject of mathematical discussion, fortunately remarked a wonderful similarity in the whole series of electrical and magnetical attractions and repulsions, and set himself seriously to the classification of them. Having done this with great success, and having maturely reflected on Dr. Franklin’s happy thought of plus and minus electricity, and his consequent theory of the Leyden phial, he at last hit on a mode of considering the whole subject of magnetism and electricity, which bids fair for leading to a full explanation of all the phenomena; at least, as far as to enable us to class them with precision, and to predict what will be the result of any proposed treatment. The work containing this hypothesis, was published at Petersburgh, under the title of Theoria Electritatis et Magnetismi, and is pronounced to be “one of the most ingenious and brilliant performances of the last century.” A summary view of this theory, and the principles on which it is formed, will be seen in the course of the ensuing work.

Great improvements in the electrical apparatus have likewise been made since the time of Franklin; particularly in devising methods to increase the power of electricity, and to render sensible the slightest accumulation or deficiency of the electric fluid. We shall, however, content ourselves, in the conclusion, with only mentioning the electrophorus and condenser, invented by Mr. Alexander Volta, Professor of Experimental Philosophy at Como, &c. This last instrument is honorable to its inventor, not only on account of the extensively useful purposes to which it has been and may be applied; but, likewise, because it was discovered, not casually, like most of the electrical apparatus, but in consequence of scientific deduction and reasoning.

The origin of Galvanism is so recent, that we think it unnecessary to give any other history of it, than that which will be found connected with the article in the body of our work.

CONTENTS
OF
THE EPITOME OF
ELECTRICITY.

CONTENTS
OF
THE EPITOME OF
GALVANISM.

EPITOME
OF
ELECTRICITY.

DIVISION I.

CHAP. I.
Explanation of Terms; with some general Remarks.

If a glass tube be rubbed in the dark with a dry hand or piece of buckskin, upon applying the knuckle to it a luminous stream or spark will appear, passing from the glass to the knuckle, attended with a crackling noise: this luminous spark or stream is called electricity.[^[8]] It is produced by the friction of several other substances, and was first observed on amber.—Hence its name, from ηλεκτρον the greek term for amber. It is a fluid extremely subtle, abounding in all nature, and is one of her principal agents; which, though generally imperceptible, sometimes becomes the object of our sight and other senses.

A glass tube, having been rubbed and producing the appearances above described, is said to be excited. The hand or buckskin, by which this is effected, is called the rubber. Electrics are all substances which can be made to produce the same appearances; the most perfect are glass, amber, sealing-wax, sulphur, gum lac, rosin &c. These are also called non-conductors, from their inability to conduct the electric fluid. Conductors or non-electrics are those bodies which cannot be excited, but have the power of transmitting electricity; such are metals, water, the bodies of animals, an imperfect vacuum, heat &c. But strictly speaking, there are no perfect conductors or non-conductors.

A body is said to be in its natural state, when it is in the same state, with respect to electricity, as the mass of the earth.

When a body has more of the electric fluid than its natural quantity, it is said to be electrified positively, when less, negatively; but neither of these cases can occur in a conductor, unless the communication between it and the earth be cut off by the intervention of an electric or non-conductor. When this happens, the conductor is said to be insulated.

It may not be amiss here to mention, that the terms electric or an electric per se, and non-electric, were at first made use of from an erroneous idea that only those called electrics, contained the electric matter in their substance, which was capable of being excited by friction, and communicated by them to those called non-electrics, and supposed to be destitute of it: for glass and other electrics, being rubbed, discovered signs of having it, by snapping on the approach of a finger or other conductor, and by attracting and repelling light bodies; while other substances could not be made to produce any such effect. It has however since been proved by experiments, that both electrics and non-electrics contain this matter in their substance; but that non-electrics cannot be excited, owing to the fluid diffusing itself through them as soon as collected. These terms are therefore improper, and as the only difference is that some bodies will conduct electricity and others will not, the terms non-conductor and conductor are those which might generally be used with the most propriety in speaking on this subject; though, in conformity with custom, we shall often use non-conductor and electric as synonymous.

CHAP. II.
Electric substances; with some of the phenomena attending their excitation.

Those substances by which electrical phenomena may be produced, form the subject which next demands our attention; but these are so numerous that it would be vain to attempt to specify them all. Perhaps it may be doubted, whether every material substance, with the exception only of metals, water, and charcoal, may not be considered as an electric.

Some however exhibit particular phenomena more obviously than others; and hence a number of catalogues have been formed, for shewing the effects which arise when electrics are excited with different rubbers. The specification which we esteem the most complete, was formed by the ingenious Mr. Cavallo, and we shall give it in his own words.

“In the following table (says he) may be seen what electricity will be excited in different bodies, when rubbed with different substances. Smooth glass, for instance, will be found by this table to acquire a positive electricity, when rubbed with any substance hitherto tried, except the back of a cat: (by which I mean the skin of a cat while on the animal alive:) rough glass, (viz. glass, the polish of which has been destroyed by emery or otherwise) will be found to acquire the positive electricity, when rubbed with dry oiled silk, sulphur &c. and the negative when rubbed with woolen cloth, the hand &c. and so of the rest.”

From the above table it appears, that the powers of electric substances vary prodigiously from one another; and that, according to the different rubbers made use of, we may sometimes produce one phenomenon and sometimes another. Hence we have a foundation for classing electric substances according to the various powers they occasionally exhibit; which may be done in the following manner.

First. Those which exhibit a strong and permanent attractive and repulsive power, of which the most remarkable is silk.

Second. Those which exhibit the electric light, attraction, repulsion, and all the other phenomena of electricity in a very vigorous, though not durable manner; of these glass is eminently preferable to all others.

Third. Those which exhibit electric appearances for any length of time, and which communicate to conducting bodies, the greatest electric power.—Of these, the substances called negative electrics, such as sealing-wax, resinous substances, and resinous compounds, are the best.

Fourth. Those which readily exhibit electrical phenomena by heating and cooling.—Of these, the tourmaline[^[9]] is the principal.

The best method of disturbing the electric fluid, that is of making it pass from one body to another, is friction. This may be done either by rubbing one electric with another, or with a conductor; but the electricity is generally stronger in the latter case. Other methods for causing electrics to shew electric appearances, are, melting, or pouring a melted electric on another substance, heating and cooling, evaporating or effervescing.

CHAP. III.
Of Electrics and Conductors.

All bodies in nature are, with reference to this subject, divided into two classes, electrics and conductors.

It has been fully demonstrated by experiment, that no substance which is a conductor can be excited so as to exhibit electrical phenomena: and in the same manner it has been found, that no substance which can be excited, is a conductor. But as we have already hinted, there is, strictly speaking, no substance which is a perfect conductor or non-conductor; because, on the one hand, the electric fluid meets with some resistance in its passage through the best conductors; and on the other, it is in part transmitted through, or passes over the surface of, most if not all electrics.

The two following lists contain as complete an enumeration of electrics and conductors as the present state of knowledge, in regard to electricity, permits us to make.

The substances are disposed in the order of their perfection; that is, the best conductors and the best electrics are placed at the head of their respective lists, and those of an inferior kind follow, somewhat in the manner of a scale graduated downward. Perfect exactness however is not to be here expected, because the subject forbids it, and some of the specified articles are of classes of substances among which there may be a sensible difference.

Conductors or non-electrics.

Gold,

Silver,

Copper,

Platina,

Brass,

Iron,

Tin,

Mercury,

Lead,

Semi-metals.

Metallic ores.—Of which those are the best which contain the greatest number of metallic parts and are nearest to a reguline state.

Charcoal, either of animal or vegetable substances—

Animal fluids,

Acids,

Saline substances,

Hot water,

Cold water,

Salt water,

All other liquids except oils,

Red hot glass,

Melted rosin,

Flame and the effluvia of flaming bodies,[^[10]]

Ice and snow—but not below the temperature of 13° Fahrenheit.

Earthy and stony substances, of which the hardest are the worst.

Glass filled with boiling water,

Vapour or steam of boiling water,

Smoke.

All compounds which contain the above substances in different proportions, are conductors in different degrees.

Non-conductors or electrics.

Glass and all vitrifications; even those of metals.

All gems, of which the most transparent are generally the best.

All resinous substances and resinous compounds,

Amber,

Sulphur,

Baked wood—if not suffered to imbibe moisture.

All bituminous substances,

Wax,

Silk,

Cotton.

All dry animal excrescences; as feathers, hair, wool, horn, &c.

Paper,

White sugar and sugar candy,

Atmospheric air and other gasses,

Oils,

Dry and complete metallic oxyds,

The ashes of animal and vegetable substances,

All hard stones; of which the hardest are the best,

Powders not metallic.

Ice at and below the temperature of 13° of Fahrenheit’s thermometer. According to Mr. Walsh’s and Mr. Morgan’s experiments, the Torricellian vacuum ought to be placed at the head of this list; but the singular nature of a vacuum, though a non-conductor, will hardly entitle it to the name of an electric.

CHAP. IV.
Of the electrical machine.

Having now explained the terms made use of in the study of electricity, and noted some of the phenomena of different electric substances, and the difference between electrics and conductors; we shall proceed to describe the electrical machine made use of for shewing experiments, and for exhibiting other electric phenomena to the best advantage.

The principal parts of the machine are, the electric, the rubber, the moving engine, and the prime conductor. We shall take notice of each of these parts separately and then describe the whole machine together.

Formerly different kinds of electrics were used; at present smooth glass is preferred before all others, as most convenient, and because it will, by itself, answer the purposes of several others. For when the machine has an insulated rubber, which is easily prepared, the operator may produce positive or negative electricity[^[11]] at pleasure, without changing the electric.

With respect to the forms of the glass, those commonly used are globes, cylinders and plates. The most convenient size for a globe is from ten to twelve inches in diameter. It should have two necks, centrally opposite, which must be cemented[^[12]] to strong caps, in order to adapt them to a proper frame. Cylinders are also made with two necks. Their common size is from six to seven inches in diameter, and from ten to twelve inches in length; the glass generally used is the best flint.

It has long been questioned whether a coating[^[13]] of some electric substance, has any effect in increasing the power of an electric; but now it seems pretty well determined, that if it does not increase the power of a good one, it at least considerably improves a bad one.

The next thing to be considered is the rubber which is to excite the electric. This, as it is now made, consists of a cushion of buckskin, stuffed with hair or flannel, and fastened to a piece of wood well rounded at the edges; to this is glued a flap of Persian black silk, which goes over nearly one half of the cylinder or globe. The rubber should be supported by a small iron or brass spring, placed inside of it, as is represented edgewise by R, figure 2, in the frontispiece. This acts in a much more uniform and parallel manner than if it were placed under the cylinder. It suits any inequalities that may be on the surface of the glass, and by means of a screw may be made to press against the cylinder as occasion requires. It should likewise be insulated in the most perfect manner by glass, or by baked wood well varnished. But when experiments are to be made which do not require or admit of insulation, a communication must be made between the rubber and the earth, by a chain or conductor.

To increase the effect of the rubber several substances have been used with success, particularly whiting and pulverised chalk. But the best of all is an amalgam of zinc and mercury.[^[14]] This amalgam is to be used by first applying a moderate quantity to the cushion; and afterwards by spreading it on a separate piece of leather, and applying it occasionally to the under part of the cylinder while turning. In this method of using it, only a small quantity of amalgam is consumed, while the glass is very strongly excited; and by degrees the whole rubber contiguous to the cylinder is covered with amalgam, in the form of a concave cake. It is with such a rubber that the cylinder is most powerfully excited.

An ingenious friend has favoured us with the following explanation of the manner in which electrics are excited, which to us is more satisfactory than any other we have seen. “In order that electricity may be accumulated in greater quantity in one body than in the surrounding ones, it must be set in motion. This may be effected by the rubbing of electrics; the juxta-position of non-electrics of different conducting powers; and by the chemical action of many, if not all bodies on each other. The rubber will act on the first principle, and the more perfect the contact between it and the electric the greater will be the effect. The chalk, whiting, amalgam &c. while they will, if properly prepared, make the contact more perfect, will also be of service on the second principle; and the amalgam will besides be of use on the third. Mercury and zinc may be exposed separately to the air without any alteration; but when combined they readily unite with the oxygen of the atmosphere; especially when the surface of contact is frequently renewed, and the temperature increased by friction.

“The glass, acquiring a different state of electricity from the rubber, will, as each portion passes from under it, carry away and impart to the prime conductor the excess which it has obtained; and this the more certainly if the dissipation of the electricity be prevented, or the accumulation increased, by a piece of silk connected with the rubber.—The chain making the communication between the rubber and the adjoining non-electrics will enable this process to go on; and perhaps may also assist on the second principle.”

With respect to the engine which is to give motion to the electric, it has been customary, simply to turn the globe or cylinder with a winch; but this will not produce the greatest power of which the glass is capable. To effect this it should be made to turn six or seven times in a second, which is more than can conveniently be done with the winch only; and therefore multiplying wheels are used with advantage.

The prime or first conductor is an insulated non-electric substance, furnished with a number of points on the end towards the electric, in order to collect the electricity from it. It is usually made cylindrical, but whatever be its form it should always be perfectly free from points or sharp edges, except the points toward the electric already mentioned; and if holes are made in it, which on many accounts are very convenient, they should be well rounded and perfectly smooth.—The larger this conductor is, if not disproportionate to the cylinder or globe, the stronger and more dense will be the electric spark, which will proceed from it when touched by a blunt conductor. There must however always be a certain proportion between the cylinder or globe and the prime conductor, for if the former be small and the latter large, the electricity will not be collected fast enough, to preserve an accumulation of it in the prime conductor, because a portion is always taken off by the air, in proportion to the surface presented to it by the conductor.

We shall now give a short connected explanation of the whole machine, a draft of which is exhibited in the frontispiece. AB and CD are two pillars of baked wood well varnished, perpendicularly raised from the top of the table EFGH—these serve to support the cylinder I, by the axles of the caps KK; from one of these proceeds the long axle L, which passes through a hole in the pillar CD, having the pulley M, fixed on its square end. N is a multiplying wheel, around which the band or strap O passes, and likewise around the pulley M.—The wheel N should be made moveable with respect to the pulley M, to accommodate the stretching of the band, or else the pulley should have a number of grooves of different radii in its circumference.

The rubber R, is fastened to a pillar of glass, or baked wood P. The pressure of the rubber may be augmented at pleasure, by means of a sliding board and tightening screw.

The prime conductor is represented by Q. It is insulated by the glass pillars SS, which support it. T represents the points which collect the electricity from the cylinder.

Cylinders and globes made for electrical machines are not always to be procured. Their place however, may be very well supplied by the large show bottles of the apothecaries. When these are used, one of the caps, instead of being concave (to receive the neck of the cylinder) must be made convex—so as to fit the hollow in the bottom of the bottle.—It is to be fastened with the cement used in the other machine.

The most powerful electrical machine ever constructed, was at Teyler’s museum at Haarlem. It had, instead of the cylinder or globe as in the common machines, two circular plates of glass, which were made to turn upon the same horizontal axis. These plates were excited by eight rubbers, which acted on their surfaces. In this machine the prime conductor had branches which collected the electricity from between the plates.

It is not necessary however in this form of the machine to have two plates, the second being added only to increase the power. The plate must be firmly fastened by its centre to an axis—so as to turn vertically between two uprights of baked wood, as in the construction of the cylindric machines; but in this case the uprights must be so close together, as barely to leave room for a rubber on each side of the plate. The rubbers may be made of the same form with that in the cylindric machine—except that they must have a projection at the back, to fit a niche cut in the uprights which support the plate. The power of the machine will be increased by having four rubbers; two above and two below the axis of the plate. The prime conductor is placed opposite one of the ends of the axis, and is divided at the end towards the electric into two branches or arms, which extend horizontally to the circumference of the plate, each of which is furnished with points to collect the electricity.

As plates are not always to be procured, a good substitute may be found in a thick pane of glass or a piece of an old looking-glass. Mark with a diamond or file a circle on the glass, of the size you intend for your plate. Then putting the plate into warm water, after some time cut the glass with a diamond in tangents. The more numerous the cuts, the nearer the plate will be to a circle. A hole may be made in the centre for the axis, by scratching with a diamond, and grinding with a rod of iron (held between the hands) and emery.

CHAP. V.
Of communicated electricity.

Having described the electrical machine, we are now to consider some of the phenomena attending its operation. When the prime conductor receives electricity from the cylinder, it is said to be electrified by communication, and it then acts in every respect like the cylinder itself, except that the latter, when touched by a conductor communicating with the earth, gives a considerable number of sparks before it is discharged; whereas the conductor discharges itself by a single spark.

The cause of this difference is that the cylinder, being an electric, cannot convey the electricity of all its surface to that part, to which the conducting substance is applied; but the fluid accumulated in the whole conductor, passing easily through its substance, is transmitted at once to the point from which the discharge is made. Hence it appears that the electricity discharged from an electrified conductor is more powerful than that discharged from an electric—the conductor acquiring a large quantity of electricity from an electric, by receiving it gradually, spark after spark, and afterwards, when touched, discharging it all at once.

The velocity of electricity is almost beyond conception. It is, notwithstanding, in a small degree relative to the quantity put in motion, and to the goodness of the conductor by which it is transmitted. A large quantity of electricity passes through a good conductor with such rapidity, that there is no perceptible difference in the time which it takes to go one foot, or one thousand feet. A small quantity however has been found to take a time barely perceptible, in passing through a long and imperfect conductor. Experiments relative to this point will be related hereafter.

CHAP. VI.
Of the electric spark.

If a piece of metal be presented to an over-charged prime conductor, the fluid passes with violence from the one to the other; an electric spark, having the appearance of fire, is seen flashing between them, and a snapping noise, like the cracking of a whip, is heard. If this piece of metal be insulated, the prime conductor will be only partially discharged, that is, the redundant electricity will be divided between it and the piece of metal, nearly in proportion to their surfaces. This electric spark has not only the appearance of fire, but, when large, will actually set fire to a variety of easily inflammable substances; such as cotton sprinkled with rosin, spirits of wine &c. This power of exciting flame is not commonly believed to arise from any culinary heat in the electric spark, because if the spark be small it will not excite flame in substances the most inflammable. It acts probably by friction on the same principle as the rubbing of sticks against each other produces fire.

The electric spark, taken upon any part of a living animal, causes an unpleasant sensation, which is more or less pungent and disagreeable, as the spark is stronger or weaker, and the part more or less delicate.

There is a slight difference between the appearance of a spark taken from a body positively electrified, and that from one negatively electrified. The former, if not very long, appears straight and sharp; the latter is generally ramified, or appears in a zig-zag line.

The noise which attends the spark, is caused by the sudden agitation into which the air is thrown, by its passage through it.

CHAP. VII.
Of the influence of pointed bodies on electricity, and some phenomena attending their operation.

If an uninsulated conductor, which is broad, round and polished at the end, be presented to the prime conductor, a short and dense spark, accompanied with some noise, will be perceived; if the conductor be less broad, the spark will be longer, less dense, and attended with less noise; if the breadth be still more diminished, so that the conductor may come under the denomination of a point, the electric matter will pass to it, from the prime conductor, and through a greater space, with a hissing noise, and in a continual stream; a still greater sharpness will enable the electricity to pass over a yet more extended space, but unaccompanied by noise, and only a small light will be seen upon the point. The same result will arise if points of different acuteness be affixed to the prime conductor, instead of the uninsulated one: but if both be pointed, the electricity will be more readily discharged.

In all the above cases, the appearance of the electric matter at the point, will indicate the kind of electricity from which it proceeds. A large divergent cone indicates positive electricity; a small globular light, that which is negative. Hence it is always easy to ascertain whether an insulated conductor be electrified positively or negatively, by presenting a point to it, as the light at the point is always definitive of the contrary electricity in the conductor.

If a pointed conductor be electrified, either positively or negatively, and the face be brought near the point during the electrization, a wind will be felt blowing from the point, accompanied with a peculiar sensation, commonly called the spider’s web. It is remarkable that the current of air is always in the same direction, whether the point throws off or receives electricity.

The re-action of the force, by which the air is put in motion, is exerted upon the pointed body. This is shewn by a very pleasing experiment called the electric fly. This fly is composed of four small wires, fastened into a metallic cap, similar to those used in sea-compasses, so that the wires may easily move upon a point, in a horizontal direction. They should be exactly balanced, and have their ends, which must be very sharp, all bent in the same direction. Now if this fly be placed on an insulated point and electrified, its sharp ends will become luminous in the dark, and it will revolve in a direction contrary to that in which the ends are bent; or if it be placed on an uninsulated point and brought near the electrified prime conductor, the same effect will follow.

It is to be observed, that the fly will move round in the same direction, whether electrified positively or negatively. The cause of this seeming contradiction depends upon the repulsive power existing between bodies possessed of the same electricity; for the air opposite to the points acquires a strong electricity, analogous to that of the points, it is therefore repelled, and replaced by other air, which is also electrified and repelled. Hence a continual stream is produced, blowing from the points, and that equally, whether the electrization be positive or negative; and as action and re-action are equal and in contrary directions, the points, repelling the air, must themselves be repelled, and in the opposite direction; which causes the fly to be always turned one way, that is, in a direction contrary to that in which the air is moved.

In vacuo no motion is produced, because there is no air on which the electric matter can act when it issues from the points.

In like manner, if air be confined in a receiver, the motion of the fly soon ceases, because the fluid cannot pass through the air and the glass. But on applying the end of a finger to the outside of the receiver, opposite one of the points of the fly, the motion will begin again, and by moving the finger occasionally round the glass, it may be continued till most of the glass is charged.

The cause of this motion is, that when the finger is applied to the outside of the receiver, the glass, loosing part of its natural quantity of electricity from that side, (i. e. when the fly is electrified positively, and vice versa if negatively) takes up the fluid from the air on its inner surface. Hence the air becomes capable of being again electrified by the point and this renews the motion.

We have already stated that if a pointed wire be presented to a conductor positively charged, it will be illuminated with a star or globe; and if the conductor be negatively charged, the illumination will have the form of a pencil or divergent cone. F. Beccaria explains this in the following manner. I suppose, says he, that the star is occasioned by the difficulty with which the electric fluid is extricated from the air, which is an electric; suppose for instance that a pointed wire is presented to a body positively electrified; the electric fluid is first communicated from that body, to the air between it and the pointed wire, and then the wire must extricate it from the air.

The pencil is occasioned by the force with which the fluid, issuing from the point, passes through the contiguous air to that which is more remote, i. e. by dividing the contiguous air, and not by affixing itself to it.

Beccaria likewise remarks, that if two equally sharp pointed bodies are brought near the prime conductor, they will appear luminous at only half the distance that one of them would. They will also discharge it in half the time.

It will not be improper to remark here, that when a point not electrified is opposed to one electrified positively, both points will have small globular lights upon them; but if a positive one be opposed to one negatively electrified, they both preserve their own characteristic properties.

From the above the following conclusions may be drawn.

First, That pointed bodies attract the electric matter more or less easily, and at a greater or less distance, according to their acuteness.

Second, That pointed bodies have the power of attracting electricity as well as of repelling it, in a greater degree than conductors of any other form.

We shall treat farther of pointed conductors under the article Thunder-house.

CHAP. VIII.
Of electric attraction and repulsion.

No satisfactory theory of electric attraction and repulsion has, so far as our knowledge extends, ever yet been given. The phenomena have been differently accounted for, as the writers have embraced different opinions in regard to positive and negative electricity. One mode of explanation has been adopted by those who believe, with Franklin, that positive electricity is only an accumulation of the electric fluid in a body beyond its natural state; and that negative electricity is nothing more than a deficiency of this fluid in a body. Another mode of explanation is given by those who maintain, in opposition to Franklin, that positive and negative electricity are either two distinct fluids, or else vibrations of the same fluid—the positive electricity always rushing out of a body, and the negative always rushing in. Those who maintain this hypothesis endeavour to support it by the easy solution which they affirm it gives to the phenomena of electric attraction and repulsion. But after a careful examination of this theory, we think that, so far from being satisfactory, it is scarcely intelligible. We therefore do not choose to introduce it into our epitome, as affording any solution of the difficulties that occur on this part of our subject. We are besides of opinion that the evidence in favour of a single fluid is conclusive, as we shall show when we come to discuss the theory of electricity. Yet we confess that we cannot, on this theory, offer a rationale of electric attraction and repulsion, that satisfies ourselves. It is therefore the demand of candour, and in the spirit of the Newtonian philosophy, to avow explicitly that this part of our subject is yet involved in much obscurity. In the mean time we are acquainted with certain facts, and with the clear explanation which they give of certain phenomena.

1. That bodies positively electrified, repel each other.

2. That bodies negatively electrified, also, repel each other.

3. That bodies positively electrified, attract those which are negatively electrified.

4. That bodies either positively or negatively electrified, induce a contrary electricity in bodies in their natural state, brought within the sphere of their action.

This statement is easily verified by experiment, in the following manner.—By flaxen or hempen threads, suspend, from the prime conductor, two balls made of cork or elder-pith, so that they touch each other. On charging the conductor, these balls, being both electrified positively, will immediately repel each other, and be separated to a considerable distance.—Remove one of the balls, take it in your fingers, and bring it near to the one which remains positively electrified, and the two will immediately rush together; because there are now two substances of which one is electrified positively, and the other negatively.—Again. Suspend two balls, of the kind just mentioned, from an insulated cushion of an electric machine, and let them touch each other. Put the machine in motion and the balls, which are now both electrified negatively, will repel each other and separate, as in the case first described.

In attempting to explain the first of these phenomena Dr. Franklin once supposed that there was an electric atmosphere round each of the balls positively electrified, the particles of which atmosphere, by mutually repelling each other, separated the balls. He also supposed that as bodies negatively electrified, or not having their proportional quantity of the electric fluid, are always strongly disposed to receive it, this would account for the fact that when one of these bodies was brought near to one that had more than its proportional quantity, the two would naturally rush together; the one to impart, and the other to receive the fluid. But at this time he was not acquainted with the fact, that two bodies negatively electrified would repel each other. When this was discovered he candidly acknowledged the utter deficiency of his theory, in regard to electric attraction and repulsion. Some of his friends and followers, however, have endeavoured still to maintain it. But we think that though their zeal has been greater, their success has not exceeded that of the Doctor himself: and we have already stated that other theories are equally, if not more defective, than that of Franklin. Let us then leave the explanation of electric attraction and repulsion to be made when future and fortunate discoveries shall have furnished the means of making it, and let us proceed with the application of known facts and principles.

A pleasing exhibition of the phenomena of electric attraction and repulsion, may be made in the following manner.

Take a glass tube, and after having rubbed it, let a small light feather fall from your fingers, at the distance of eight or nine inches from it.—The feather will be immediately attracted by the tube and stick very close to its surface for some seconds, after which it will be repelled, and if the tube be kept under it, the feather will continue floating in the air, at a considerable distance from the tube, without coming near it again, except it touch some conducting substance; and if you manage the tube dexterously, you may drive the feather through the air of the room at pleasure.

The cause of this phenomenon is obvious. The feather, at first, not being electrified, rushes to the excited tube. There it becomes electrified and is then repelled, and cannot approach the tube again, unless it first touch some conducting substance; because it cannot part with its electricity while floating in the air, and therefore cannot acquire a contrary electricity; consequently it must remain in a state incapable of being again attracted by the excited tube.

There is a remarkable circumstance attending this experiment, which is, that if the feather be kept at a distance from the tube by the force of electric repulsion it always presents the same part towards the tube. The reason of this phenomenon is, that the equilibrium of the fluid in the different parts of the feather being once disturbed cannot easily be restored; the feather being an electric, or at least a very bad conductor. When the feather has acquired a quantity of electricity from the tube it is plain that, by the action of the excited tube, that superinduced electricity will, for the most part be forced to that side of the feather which, at first, happened to be farthest from the tube; hence that part will always afterwards be repelled the farthest.

This experiment may be agreeably varied in the following manner.—A person may hold an excited tube of glass, within a foot and a half of a stick of sealing-wax, or any other electric negatively electrified, held by another person; a feather let fall between these differently excited electrics will leap from one to the other alternately, and the two persons will seem to drive a shuttlecock by the force of electricity.

Another experiment calculated to shew the phenomena of electric attraction and repulsion is the electric spider.

Cut a piece of cork in the shape of a spider, and run a few short threads through it, to represent the legs; this done, suspend it by a silk thread from the ceiling of the room, or any other support, so that the spider may hang mid-way between the knob of a jar and the knob of a wire fastened to the table, or to the outside coating of the jar when not charged; let the place where the jar stands be marked; then charge and replace it. The spider will now begin to move from knob to knob, and continue this motion for a considerable time.

In this case, the knob of the jar is charged positively, and the spider, being in its natural state, is attracted by it; the knob then communicates to it some of its electricity, and the spider becoming possessed of the same electricity with the knob, is repelled by it, and immediately runs to the other knob, which communicates with the negative coating, or with the table, where it discharges its electricity and is again attracted by the knob of the jar. This attraction and repulsion continue till the jar is discharged, when the spider finishes its motion and seemingly expires.

CHAP. IX.
Of the Leyden phial.

This consists of a glass phial, jar, or bottle, coated on the outside and inside with tin-foil, rendered adhesive by paste or gum water. About two inches of the glass at the top are left without any metallic covering, to prevent a communication between the outside and inside coatings, while the electricity is collecting.—The mouth of the phial or jar is furnished with a cork which receives a wire, ending in several ramifications which touch the inside coating. The upper end of this wire, which should extend a convenient distance above the mouth of the jar, is furnished with a metallic ball.

When the phial or jar is to be charged, it may be held in the hand or placed on an uninsulated table, with the knob of the wire touching the prime conductor. The inner surface of the glass now acquires the same electricity with the prime conductor, and the external one acquires a contrary electricity by means of its uninsulated coating.

When a phial similar to the one above described is highly charged, a spontaneous discharge will usually take place over the uncoated surface, and seldom through the glass. But if the uncoated surface be left larger than from two to three inches, the phial is more apt to crack and become useless, by the charge passing through the glass. There is not however an absolute certainty that a jar which has once discharged itself over its surface will not, at another time, break by a discharge through the glass.

It was long disputed whether the discharge of the Leyden phial resided in the coating or in the electric. The following experiment clearly decides, that its residence is in the electric.

Upon an uninsulated plate of metal, lay a plate of glass considerably larger, so that there may be a rim of three or four inches projecting beyond the metal. Upon the glass lay another piece of metal, of the same size with the first, and so as precisely to cover it.

Let this instrument be charged, by connecting the upper metallic plate with the prime conductor. Then separate the metallic plates from the glass; and upon examination the glass will be found to possess the contrary electricities on its opposite sides; that side which during the electrization communicated with the prime conductor will have a like electricity with it, and the other the contrary.

Discharge the electricity of the metallic plates, and replace the whole apparatus in its former situation.—Take a discharging rod, formed by a piece of bent wire with a metallic ball at each end; touch the under plate and bring the other end of the wire near the upper plate. The consequence will be, that a strong and loud spark will pass between the upper plate and the discharging rod; the electricity of the glass will be discharged, and there will afterwards remain no signs of electricity, either in the glass, or the metallic plates.—Hence it appears that the electricity resides in the glass, and that the coatings, whether in a plane or spherical form, are of no other use than to convey the electric fluid to the glass; to keep it equably distributed over the surface; and to form a communication between the different parts of the electrified glass, so that the discharge from them may be simultaneous.

When the discharge of a coated electric is made through the body of a living animal, it occasions a sudden motion, by contracting the muscles through which it passes, and gives a disagreeable sensation commonly called the electric shock.

CHAP. X.
The electrical battery—and experiments performed with it.

When a greater degree of electric force is required than a single jar is capable of giving, the electrical battery is made use of as part of the apparatus, which takes its name from the formidable effects it produces. This battery consists of a number of coated jars, placed in such a manner that they may all be charged at the same time, and discharged in an instant; so that the whole force of electricity accumulated in them, may at once be exerted on the substance exposed to the shock.

In discharging electrical jars, the electricity goes in the greatest quantity through the best conductors, and by the shortest passage. Thus if a chain and a wire be made to communicate at the same time with the outer coating of a jar, and be both presented to the knob of that jar, the greater part of the charge will pass by the wire, and very little by the chain, because the latter is a worse conductor than the former, on account of its discontinuation at every link. When the discharge is made by the chain only, sparks are seen at every link, which is a proof they are not in contact.

The force of an electric shock is not affected by the inflections of a conductor through which it passes, though it is sensibly weakened by its length. Hence, when the circuit or communication between the two sides of a Leyden phial is formed by one person applying his hands to the different sides, the shock is stronger than when it is formed by many persons joining hands. Yet a considerable shock was given by the Abbè Nollet, in the presence of the king of France, to one hundred and eighty men; who formed an electrical circuit.—They were all shocked in the same instant.

Doctor Watson and many other gentlemen of eminence in science, were at the pains of making experiments of the same kind. They found, by means of a wire insulated on baked wood, that the electric shock was transmitted instantaneously through the length of 12,276 feet.

Electricity transmitted in large quantities through living vegetables, destroys their vegetable life.

When transmitted, in the same form, through animals, it generally puts an end to animal life; though it is said that there are individuals who are not affected by it. Possibly the reason why some persons are not killed by very large electric shocks is, that their muscular system, or bodily organization, has something peculiar which protects them.

If an electrical circuit be made by means of imperfect conductors, as a slender piece of wood, a wet pack-thread, the discharge will be made silently.

If a small interruption of an electrical circuit be made in water, on making the discharge, a spark will be seen in the water, which never fails to agitate it and sometimes breaks the vessel in which it is contained.

A strong shock from a battery, sent through a slender piece of metal, instantly makes it red hot. Usually it is melted in whole or in part. If the fusion be perfect it is reduced into globules of different magnitudes. In this experiment it is a little remarkable that the parts of the metal at which the fluid enters and issues, are most likely to be melted.

If the metal be enclosed between pieces of glass, the shock will force the melted metal into the substance of the glass, so that it cannot afterwards be removed, without scraping off part of the glass with it. In this experiment the glasses which enclose metal are commonly broken to pieces.—It is seldom that they resist the force of a strong shock. If the glasses enclosing metal be pressed by a heavy weight, a small shock is often sufficient not only to raise the weight, but to break glasses of considerable thickness. When the pieces of glass are not broken, they are marked by the explosion with the most lively prismatic colours, which lie sometimes irregularly, and sometimes in their prismatic order.

Gun-powder may be fired by a charge from three square feet of coated glass. The powder is to be put into a quill, and then a wire is to be thrust into each end so as nearly to meet, and afterwards these wires are to be made a part of an electrical circuit.—A less charge of electricity will be sufficient if iron filings be mixed with the gun-powder.

When a shock somewhat less than is sufficient to melt a piece of metal is sent through a chain, a black dust, in the form of smoke, is seen to proceed from the chain. This dust is probably some of the metal itself, partly calcined, and by the violence of the explosion forced from it. If the chain be laid upon a piece of paper, glass, or other electric, this, after the explosion, will be found stained with some indelible marks, and often shew evident signs of having been burnt.

What is more remarkable in considering the effects of electricity on metals is, that it often, in a considerable degree, revivifies their calces or oxyds. In making experiments of this kind, the metallic calx or oxyd is to be made a part of an electrical circuit, through which a strong shock is to be sent: when the calx or oxyd will be found in a measure restored to its metallic state: the electric shock having, as it appears, taken away from the oxyd a portion of its oxygen.

The electric shock when passed through the magnetic needle, sometimes destroys its magnetic virtue, and sometimes reverses its poles. It is affirmed that two ships sailing together on the same voyage, were led, from the effect of lightning on their needles, to steer exactly opposite courses, after the storm in which they were exposed to the lightning had subsided. When the charge of ten, eight, or even a less number of square feet of coated glass, is sent through a sewing needle, it will often give it polarity, so that it will traverse when laid upon water. In this experiment it is remarkable that if the needle be lying east and west, that end of it which communicated with the positive coating will point towards the north; but if the needle be struck while lying north and south, that end of it which lay towards the north, will, in any case, point north; and the needle will acquire a stronger virtue in this than in the former case. But if the needle be placed perpendicular to the horizon, and the electric shock be given to either point of it, the lower extremity will afterwards point north.

The electric explosion taken upon the leaves of certain flowers changes their colour.

If the ball of a thermometer be placed in a strong current of electricity, the mercury or spirit will rise several degrees.

If a thin bottle be exhausted of air by means of an air pump, it will receive a considerable charge of electricity, by applying its bottom to an electrified prime conductor. In performing this experiment the bottle is to be held by the neck or near the mouth, and the electric matter will pass through the vacuum, and along the inner surface of the bottle, to the hand, from that end of it which is nearest to the prime conductor. The luminous appearance exhibited by this experiment is exceedingly beautiful in the dark, especially if the bottle be of any considerable length. It exactly resembles those lights which appear in the northern sky, and which are called streamers or the aurora borealis. If one hand be applied to the part of the bottle which was before presented to the prime conductor, while the other remains at the neck, a shock will be felt, at which instant the natural state of the inner surface is restored by a flash, which is seen pervading the vacuum between the two hands.—The principle on which this experiment depends will be explained hereafter.

CHAP. XI.
A description of the electrophorus, and some of its phenomena accounted for.

The electrophorus is a machine, consisting of two plates, usually of a circular form. At first the under plate was of glass covered with sealing wax; but there is little occasion to be particular, with regard, either to the substance of the lower plate, or to the electric with which it is covered; a metallic plate however is preferable to a wooden one, though the latter will answer very well. This plate must be covered with an electric: pure sulphur answers nearly as well as the dearer electrics gum lac, sealing wax &c.

The upper plate is made of brass, or a piece of paste-board covered with tin foil or silvered paper, which must be nearly of the same dimensions as the electric plate: this plate must be furnished with an electric handle, which, by means of a metallic or wooden socket is fastened to its centre.

This instrument was invented by Mr. Volta, an Italian philosopher. The manner of using it is as follows.

First, The under plate is excited, by rubbing its coated surface with a piece of new white flannel, or a fox’s tail. A hard shoe brush, having the bristles a little greased, will also excite sulphur very well. When this plate is excited as much as possible, it is placed on a table with the electric side uppermost; the metallic plate is then laid on the excited electric; then the metallic plate is touched with the finger, or with any other conducting substance, which receives a spark from it; finally the metallic plate being held by the extremity of its electric handle, is separated from the electric and after it is raised some distance, it is, on examination, found strongly electrified, with an electricity contrary to that of the electric, and will give a strong spark to a conductor brought near it. By placing the metallic plate upon the electric, touching it with the finger and separating them successively, a great number of sparks may be obtained, apparently of the same strength, and without exciting the electric again.—If these sparks be repeatedly given to the knob of a coated jar, it will become charged.

The action of these plates depends upon the principle already laid down (page [22],) that an excited electric has the power of inducing a contrary electricity in a body brought within its sphere of action. The metal plate therefore, when set upon the excited electric, acquires a contrary electricity, by giving its electric fluid to the hand or other conductor which touches it, when the electric is positively electrified; or by acquiring an additional quantity from the hand &c. when the electric is negatively electrified.

More fully to explain the principle here considered let the following easy experiment be made—

Electrify any insulated conductor positively. Then if an electrometer[^[15]] of cork balls be held at some distance from it, the balls will diverge with negative electricity. This may be proved by bringing a piece of excited glass near them, as the balls will be attracted by it. But if you present to them a piece of excited sealing wax, they will immediately avoid it—that is, supposing the glass to be excited always positively, and the sealing wax always negatively.

Again. Insulate, in a horizontal position, a metallic rod with blunt terminations, and about two feet long. We shall designate the ends of this rod by A and B. Let a cork ball electrometer be affixed to the extremity A; then bring an excited glass tube within eight or ten inches of the other end B—the balls will immediately diverge with positive electricity. If the tube be removed the balls will immediately collapse, and no electricity will remain in them, or in the rod.—But if, while the tube is near one end B of the rod, and the balls diverge with positive electricity, the other end A be touched with a finger or other uninsulated conductor, the cork balls will immediately come together, as if the rod were in its natural state: but if, in this state of things, the excited tube be removed, the balls will again diverge, but with negative electricity, shewing that the whole rod AB is now under-charged.

This last experiment is thus explained.—When the rod is in its natural state, the electric fluid proper to it is equably distributed throughout the rod; but when the excited glass tube is brought near one of its ends as B, the fluid belonging to that end will be driven towards A; which extremity becomes over-charged, and the other extremity B under-charged; yet the rod has no more electricity now than it had before, and when the tube is removed beyond the sphere of its action, the redundant fluid of A returns to its former place B, and the equilibrium is restored. But if the extremity A be touched, while it is over-charged, by a conductor, this will carry off its superfluous fluid, and leave the extremity A in its natural state, the extremity B being at the same time negatively electrified: and when the tube is removed, part of the fluid naturally belonging to A goes towards B, and the whole rod remains under-charged.

CHAP. XII.
Of electrometers.

We have already seen that it is a general law of electricity, that similar electricities repel, and that dissimilar electricities attract each other.—On this law all electrometers are constructed. In fact the cork balls, which have been mentioned are electrometers, and exhibit at once the most important phenomena for the explanation or ascertaining of which the instruments which bear this name are constructed. Still it is of use to see the application which may be made of this general principle. It is applied to ascertain the quantity of the electric fluid collected either in a prime conductor or a coated jar; and also the state of the atmosphere in regard to electricity, and the character of that electricity at any particular time and place.

The instruments by which these purposes are effected we shall now shortly describe.

To ascertain the quantity of electricity in a prime conductor or jar, an electrometer the most easily constructed and of the most general use has been invented by Mr. Henley—called the quadrant electrometer.—Of this we have given a representation in the frontispiece, (letter X.)