Department of History
University of California, Irvine
Instructor:    Dr. Barbara J. Becker


Week 7.  Natural Forces

excerpts from
The History and Present State of Electricity with Original Experiments (1769)
by Joseph Priestley (1733-1804)


Period III.   The Experiments and Discoveries of Mr. Stephen Grey (from pp. 25-42)

BEFORE the year 1728, Mr. Stephen Grey [English investigator (1666-1736)] had often observed, in electrical experiments made with a glass tube and a down feather tied to the end of a small stick, that, after its fibres had been drawn toward the tube, they would, upon the tube's being withdrawn, cling to the stick, as if it had been an electric body, or as if there had been some electricity communicated to the stick, or to the feather.  This put him upon thinking, whether, if the feather were drawn through his fingers, it might not produce the same effect, by acquiring some degree of electricity.  This experiment succeeded accordingly, upon his first trial; the small downy fibres of the feather being attracted by his finger, when held near it; and sometimes the upper part of the feather with its stems would be attracted also....

[H]e found the following substances to be all electric; hair, silk, linen, woollen, paper, leather, wood, parchment, and ox gutin which leaf gold had been beaten.   He made all these substances very warm, and some of them quite hot before he rubbed them.   He found light emitted in the dark by the silk and the linen, but more especially by a piece of white pressing paper, which is of the same nature with card paper.  Not only did this substance, when made as hot as his fingers could bear, yield a light; but, when his fingers were held near it, a light issued from them also attended with a crackling noise, like that produced by a glass tube, though not at so great a distance from the fingers.

The preceding experiments bring us to the eve of a very considerable discovery in electricity, viz. the communication of that power from native electrics, to bodies, in which it is not capable of being excited; and also to a more accurate distinction of electrics from non-electrics....

In the month of February 1729, Mr. Grey, after some fruitless attempts to make metals attractive, by heating, rubbing, and hammering, recollected a suspicion of which he had some years entertained; that, as a tube communicated its light to various bodies when it was rubbed in the dark, it might possibly, at the same time, communicate an electricity to them, by which had hitherto been understood only the power of attracting light bodies.   For this purpose he provided himself with a tube three feet five inches long, and nearly one inch and two tenths in diameter; and to each end was fitted a cork, to keep the dust out when the tube was not in use.

The first experiments he made upon this occasion were intended to try, if he could find any difference in its attraction when the tube was stopped at both ends by the corks, and when left entirely open; but he could perceive no sensible difference.   It was, however, in the course of this experiment that, holding a down feather over against the upper end of the tube, he found that it would fly to the cork, being attracted and repelled by it, as well as by the tube itself.   He then held the feather over against the flat end of the cork, and observed, that it was attracted and repelled many times together; at which, he says, he was much surprised, and concluded, that there was certainly an attractive virtue communicated to the cork by the excited tube.

He then fixed an ivory ball upon a stick of fir, about four inches long; when, thrusting the other end into the cork, he found, that the ball attracted and repelled the feather, even with more vigour than the cork had done, repeating its attractions and repulsions many times successively.   He afterwards fixed the ball upon long sticks, and upon pieces of brass and iron wire, with the same success; but he observed, that the feather was never so strongly attracted by the wire, though it were held very near the tube, as by the ball at the end of it.

When a wire of any considerable length was used, its vibrations, caused by the action of rubbing the tube, made it troublesome to manage.  This put Mr. Grey upon thinking whether, if the ball were hung to a packthread, and suspended by a loop on the tube, the electricity would not be carried down the line to the ball; and he found it to succeed according to his expectation.   In this manner he suspended various bodies to his tube, and found all of them to be capable of receiving electricity in the same manner.

After trying these experiments with the longest light canes and reeds that he could conveniently use, he ascended a balcony twenty six feet high; and, fastening a string to his tube, he found, that the ball at the end of it would attract light bodies in the court below.

He then ascended to greater heights, and by putting his long canes in the end of his tube, and fastening a long string to the end of the canes, he contrived to convey the electricity to much greater distances than he had done before; till, being able to carry it no further perpendicularly, he next attempted to carry it horizontally; and from these attempts arose a discovery, of which he was not in the least aware when he began them.

In his first trial he made a loop at each end of a packthread, by means of which he suspended it, at one end, on a nail driven into a beam, the other end hanging downwards.   Through the loop which hung down, he put the line to which his ivory ball was fastened, fixing the other end of it by a loop on his tube; so that one part of the line, along which the ball was fastened, hung perpendicular, the rest of the line lay horizontal.   After this preparation he put the leaf brass under the ivory ball, and rubbed the tube, but not the least sign of attraction was perceived.   Upon this he concluded, that when the electric virtue came to the loop of the packthread, which was suspended on the beam, it went up the same to the beam; so that none, or very little, of it went down to the ball; and he could not, at that time, think of any method to prevent it.

On June the 30th 1729, Mr. Grey paid a visit to Mr. [Granville] Wheeler [d. 1770], to give him a specimen of his experiments; when, after having made them from the greatest heights which the house would admit, Mr. Wheeler was desirous of trying whether they could not carry the electric virtue to a greater distance horizontally.   Mr. Grey then told him of the fruitless attempt he had made to convey it in that direction:   upon which Mr. Wheeler proposed to suspend the line to be electrified by another of silk, instead of packthread; and Mr. Grey told him, it might do better, on account of its smallness; as less of the virtue would probably pass off by it than had done by the thick hempen line, which he had used before.  With this expedient, the succeeded far beyond their expectations....

[Further experiments] convinced them, that the success of it depended upon their supporting lines being silk, and not, as they had imagined, upon their being small.   For the electric virtue went off ... effectually ... by the thick hempen cord.

Being obliged, therefore, to return to their silk lines, they contrived them to support very great lengths of the hempen line of communication; and actually conveyed the electric virtue seven hundred and sixty five feet, nor did they perceive that the effect was sensibly diminished by the distance....

After this, they amused themselves with trying how large surfaces might be impregnated with the electrical effluvia; electrifying a large map, table cloth &c.   They also carried the electric virtue several ways at the same time, and to a considerable distance each way.

The magnetic effluvia, they found did not in the least interfere with the electric; for when they had electrified the load stone, with a key hanging to it, they both attracted leaf brass like other substances.

Some time after this, Mr. Wheeler, in the absence of Mr. Grey, electrified a red hot poker, and found the attraction to be the same as when it was cold.   He also suspended a live chicken upon the tube by the legs, and found the breast of it strongly electrical.

In August 1729, August 1729, Mr. Grey advanced one step further in his electrical operations.  He found that he could convey the electric virtue from the tube to the line of communication without touching it, and that holding the excited tube near it was sufficient....

Some time in the same month, Mr. Wheeler and Mr. Grey in conjunction made some experiments, in order to try whether the electric attraction was in proportion to the quantity of matter in bodies; and with this view they electrified a solid cube of oak, and another of the same dimensions which was hollow; but they could not perceive any difference in their attractive power; though it was Mr. Grey's opinion, that the electric effluvia passed through all the parts of the solid cube....

April the 8th. 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 the leaf brass was attracted by his head with much vigour, so as to rise 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, and the tube held over it, there was no attraction at all.  Mr. Grey does not attempt to assign any reason for these appearances....

About this time Mr. Grey communicated to the Royal Society his suspicion, that bodies attracted more or less according to their colour though the substance was the same, and the weight and size equal.  He says, he found red, orange, and yellow attracted at least three or four times stronger than green, blue, or purple; but he forbore communicating a more particular account of them, till he had tried a more accurate method which, he says he had thought of, to make the experiments....

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 more, 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....

Period IV.  The Experiments and Discoveries of Mr. Du Faye.  (pp. 43-52)

Mr. Du Faye [French chemist, Charles François de Cisternay du Fay (1698-1739)], having got himself suspended on silk lines, as Mr. Grey had done the child mentioned above, observed, that, as soon as he was electrified, if another person approached him, and brought his hand within an inch, or thereabouts, of his face, legs, hands, or cloaths, there immediately issued from his body one or more pricking shoots, attended with a crackling noise.  He says this experiment occasioned to the person who brought his hand near him, as well as to himself, a little pain, resembling that of the sudden prick of a pin, or the burning from a spark of fire; and that it was felt as sensibly through his cloaths, as on his bare face, or hands.  He also observes, that, in the dark, those snappings were so many sparks of fire.

The Abbe Nollet [French professor of experimental physics at the University of Paris, Jean-Antoine Nollet (1700-1770)] says he shall never forget the surprise, which the first electrical spark which was ever drawn from the human body excited, both in Mr. Du Faye, and in himself.

He says, that those snappings and sparks were not excited, if a bit of wood, or cloth, or of any other substance than a living human body, was brought near him; except metal, which produced very nearly the same effect as the human body....

[Du Faye writes] "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-chrystal, 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 all other bodies possessed of the vitreous, and on the contrary, attracts all those of the resinous electricity.  The resinous, also, repels the resinous, and attracts the vitreous.  From this principle, one may easily deduce the explanation of a greater number of other phenomena; and it is probable, that this truth will lead us to the discovery of many other things."....

We shall see that Dr. Franklin [American scientist and national figure, Benjamin Franklin (1706-1790)] found, that, in all probability, the vitreous electricity was positive, or a redundancy of electric matter; and the resinous, negative, or a want of it....

The doctrine of two different electricities, produced by exciting different substances, considerable as the discovery of it was, seems to have been dropped after Mr. Du Faye, and those effects ascribed to other causes; which is an instance that science sometimes goes backwards....

Period V.  The Continuation, and Conclusion of Mr. Grey's Experiments.  (pp. 53-61)

Mr. du Faye had said, that the snappings and the sparks, he had mentioned, were strongly excited by a piece of metal, presented to the person suspended on silk lines; Mr. Grey concluded, that if the person and the metal should change places, the effect would be the same.  He, accordingly, suspended several pieces of metal on silk lines ... and found, that, when they were electrified, they gave sparks, in the same manner as the human body had done in like circumstances.  This was the origin of metallic conductors, which are in use to this day....

Mr. Grey, and his friends, provided themselves with an iron rod four feet long, and half an inch in diameter, pointed at each end, but not sharp.  Suspending this iron rod upon silk lines in the night; and, applying the excited tube to one end of it, they perceived, not only a light upon that end, but another issuing from the opposite end, at the same time.  This light extended itself, in the form of a cone, whose vertex was at the end of the rod:  and Mr. Grey says, that he and his company could plainly see, that it consisted of separate threads, or rays of light, diverging from the point of the rod, the exterior rays being incurvated.  This light appeared at every stroke they gave the tube.

They likewise observed, that this light was always attended with a small hissing noise, which, they imagined, began at the end next the tube, increasing in loudness till it came to the opposite end.  He says, however, that this noise could not be heard, but by persons who stood near the rod, and attended to it....

[Grey writes] "Although these effects are at present but in minimis, it is probable, in time, there may be found out a way to collect a greater quantity of the electric fire, and consequently to increase the force of that power; which, by several of these experiments ... seems to be of the same nature with that of thunder and lightning."

How exactly has this prophecy been fulfilled in the discoveries of the Leyden electricians, and Dr. Franklin; the former having discovered the amazing accumulation of the electric power, in what is called the Leyden phial; and the latter having proved the matter of lightning to be the very same with that of electricity....

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