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contracted will be drawn by the latter. And this leads me to conclude that there are perhaps two kinds of different electricities."

Further tests confirm the belief, and he announces that electrified glass repels electrified glass, or all bodies receiving electricity therefrom, and attracts electrified amber and all bodies to which its charge has been communicated. In other words, he had established the fundamental law that similarly-electrified bodies repel, while dissimilarlyelectrified bodies attract one another.

He calls the electricity yielded by glass vitreous, and that derived from the rubbed gum resinous; because "glass and copal are the two substances which have led me to the discovery of the two different electricities."

Thus Dufay had found that all bodies may become electric either by direct communication or by induction; that the so-called electrics are the least suitable to convey the virtue; that the electric light may appear as fire or burning sparks, and that there are two different kinds of electricity, of which one attracts bodies repelled by the other; and that bodies, if similarly charged, repel, while attracting if dissimilarly electrified. These are only his more important conclusions; others, although ingenious and original, relate to details which need not be entered into here.

In December, 1733, Dufay wrote a brief synopsis' of the long memoirs which he had already published in the annals of the French Academy, and sent it to the Duke of Richmond and Lenox for presentation to the Royal Society and (with characteristic diplomacy) to Mr. Gray, "who works on this subject with so much application and success, and to whom I acknowledge myself indebted for the discoveries I have made, as well as for those I may possibly make hereafter, since it is from his writings that I took the resolution of applying myself to this kind of experiments." Whether in all the history of discovery there exists a more handsome recognition than this of the work

1 Phil. Trans., No. 431, p. 258, 1733.

of a prior student may well be doubted. It is a custoin which nowadays in the struggle for profit is too often forgotten. At all events Gray's heart was won. He ceremoniously salutes Monsieur Dufay and felicitates himself that his experiments should have been confirmed by so judicious a philosopher; and, no doubt, in the quietude of his little chamber at Grey Friars, wonders if it is really "poor brother" Gray, with his experiments with the tea-kettle and the pint-pot and the fishing-poles and threads, who is receiving these compliments from the distinguished French scientist through the Royal Society and his Grace of Richmond.

But he was invigorated—much invigorated. And besides, what Dufay had said about the burning sparks piqued his curiosity immensely. Out came the poker and the tongs, and the fire shovel, too, this time, to be hung up on silk threads and the crackling sparks produced, of which last a small boy was made to suffer the pain, even through his stockings. The next victim was a large white rooster, replaced by a sirloin of beef, and finally an iron rod astonished him beyond measure by exhibiting the true brush discharge, "rays of light diverging from the point," and hissing. Pewter plates, iron balls, dishes of water, were all pressed into service. The flames were real, and they burned and crackled and exploded. "The effects at present," says Gray, "are but in minimis, but in time there may be found out a Way to collect a greater Quantity of it, and consequently to increase the force of this Electric Fire, which by several of these experiments (si licet magnis componere parva) seems to be of the same Nature with that of Thunder and Lightning."

From that time on, Gray and Dufay maintained communication with a degree of friendliness which leads Fontenelle to wish that it might always typify the intercourse of the two great nations to which they severally belonged, and to add, with pardonable exaggeration, that "they enlightened and animated one another, and together made

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discoveries so strange and surprising that their respective beliefs in them perforce rested solely upon their mutual assurances." But, in fact, neither afterwards made any especially important discovery. It was not long before Gray died. He had wandered off into the old belief which von Guericke held, that somehow the planets were controlled by electrical influence, and he fancied he could make an apparatus in which a sphere would of its own accord revolve from west to east around an electrified body. But he was stricken unexpectedly, and he could tell Dr. Mortimer, the Secretary of the Royal Society, who attended his death-bed, only a few disjointed ideas, mingled with expressions of a hope "that God would spare his life a little longer, so that he should, from what these phenomena point out, bring his electrical experiments to greater perfection." But it was ordained otherwise, and he passed away on February 15th, 1736.

Dufay's last memoir is dated in 1737, and expresses his broadest view of the great phenomena which he had so well studied. "Electricity," he says, "is a quality universally expanded in all the matter we know, and which influences the mechanism of the universe far more than we think." He has left his monument in the magnificent Jardin des Plantes which he organized, and so made every student of Nature his debtor. His solicitude that the full meed of honor due to the poor brother of the Charter house should be yielded never failed; and when the world shall pay its tribute in enduring marble and brass to the memory of Stephen Gray, electrician, it will find no words more fitting to place upon it than those of his generous and brilliant rival:

"He was almost alone in England in pursuing his object. To him we owe the most remarkable discoveries pertaining to it; so all those who love Nature and her work must infinitely regret him."

Apart from the discoveries in which they resulted, the researches of both Gray and Dufay are remarkable for their inductive character and the absence of dogmatizing on the nature and cause of electricity. Concerning the last, opinions were undergoing radical change. Shortly after Hauksbee's experiments were published, Dr. s'Gravesande, Professor of Mathematics at Leyden, issued one of the earliest, if not the earliest, didactic work in which electricity is treated as a branch of physics, and there gives it as his ultimate conclusion, based on preceding experiments, that there is an atmosphere excited in rubbed glass by friction, which attracts and repels light bodies, and also that out of the glass, fire is forced ; but he does not regard either the atmosphere or the fire as electricity, which he defines as "that property of bodies by which (when they are heated by attrition) they attract and repel lighter bodies at a sensible distance."

The experiments of Gray and Dufay showed the light and the fire to be as much an electrical phenomenon as the attraction and repulsion; but Dufay's discovery of the dual nature of electricity had undermined the old conception of material emanations, while definitely establishing no new theory in its place.

After the death of Dufay appears Dr. Desaguiliers, a man of considerable prominence in the Royal Society. He had never found it expedient to discourse about electrical matters so long as either Gray, whom he seems to have disliked, or Dufay survived; but afterwards he contributes many papers to the Philosophical Transactions, in which he collects a great mass of experiments, chiefly in the nature of cumulative evidence. He invented the term "electrics per se," which, for a long time afterwards, was used to designate those bodies which could be made electric by rubbing them, although it was nothing but a polyglot translation of Dufay's term "électriques par eux-mêmes." He also first used the word "conductor," applying it to the string over which the electricity passes, and also was

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the first to electrify running water. Gilbert, of course, had made his rubbed amber attract a water-drop; the Florentine Academy, by like means, had drawn oil up into little viscous strings, and Gray had electrified soap-bubbles; but Desaguiliers found that, when he let water run in a stream out of a copper fountain, he could render the jet electric, so that it would attract thread, by merely holding the rubbed tube above the fountain, and when he applied the tube to the stream, he could draw it sidewise into a curve, or even cause it to fall outside of the vessel placed to receive it. He also appears to have been the first to conceive of atmospheric electricity, and to point out that a cloud or mass of vapor may be an electrified body. He had already recognized that air may be rendered electrical; and supposed it to be made up of electric particles constantly repelling one another. He imagined that the aircurrent which flows along the surface of the ocean is electrical in proportion to the heat of the weather, and that, as he had seen little particles of water leap up in spray to the excited tube, so he conceived the watery particles of the sea to rise to meet the excited air particles, and then, being of the same electricity, to be repelled by them, so that "a cubic inch of vapor is lighter than a cubic inch of air." In the recognition by Hauksbee and Wall and Gray of the similarity of the crackling electric spark to the thunder and lightning, and in this hazy conception of Desaguiliers of electrically-charged clouds and atmosphere, we can now begin to perceive the drift of thought leading toward Franklin's great discovery.