2 52 ELECTRICITY.

conductors and non-conductors, Mr. Du Fay discovered the dif-ference between positive and negative, or, as they were for sometime, and are still by some called, the vitreous and resinous elec-tricities. This discovery was accidentally made in consequence ofhis observing, that a piece of leaf gold, repelled by an excitedglass tube, and which he meant to chase about the room with apiece of excited gum copal, instead of being repelled by it, as itwas bv the glass tube, was eagerly attracted. The same was thecase with sealing-wax, sulphur, rosin, and many other substances,lie discovered also, that it was impossible to excite, a tube in■which the air was condensed. Mr. Boze, professor of philosophyat Wittemburgh, re-introduced the use of glass globes; thoughsome attribute this to Christian Augustus Ilanscn, professor ofmathematics at Leipsic. He added also a prime conductor,which consisted of a tube of iron or tin. It was at first supportedbv a man standing upon cakes of rosin; but afterwards suspendedby silk lines horizontally before the globe. A bundle of thread Lwas put into the end next to the globe, which not only preventedany injury to the glass, but rendered the electricity stronger.

“ The number of electricians,” says M. Cavallo, “ that hath beendaily multiplying since Mr. Grey, the discoveries made, and theuse derived from those, till the present time, are matters reallyworthy of attention, and deserve to he admired by every lover ofthe sciences, and well-wisher of the human nice. “Whoeverwould make himself acquainted" (adds lie) “ with the particulartransactions concerning those advances, should read the elaborateIli.-tory of Electricity compiled by the learned Dr. Priestley, awork that will inform him of whatever had been done relative tothe subject till its publication. 1 shall, in general, only observe,that although the science had, through the indefatigable attentionof so many ingenious persons, and by the discoveries daily pro-duced, excitecl the curiosity of philosophers, and engaged theirattention; yet, as the causes of any thing, whether small or great,known or unknown, are seldom much attended to, if their effectsare not striking and singular; so electricity had, till the year 1746,been studied bv none dint philosophers. Its attraction could inpart he imitated by a load-stone; its light by a phosphorus; andin short, nothing contributed to make electricity the subject ofpublic attention, and excite a general curiosity, until the capitaldiscovery of the vast accumulation of its power in what is com-monly called the Leyden phial, which was accidentally made inthe memorable year 1745. Then, and not till then, the study ofelectricity became general, surprised every beholder, and invitedto the houses of electricians a greater number of spectators, thanwere before assembled together to behold any philosophical ex-periments whatever.” Fie adds in a note, “ This great discoverywas made by M. Van Kleist, dean of the cathedral in Camin.”The method of giving the electric shock, or the accumulation ofthe power of electricity in a phial, got its name of the Leydenphial, from Mr. Cunarns, a native of Leyden, who exhibited it inrepeating some experiments made by Messrs. MuschenbroekandAllamand, professors in the university of that city. M. VanKleist, sent the following account of his discovery' to Dr. Lie-berkuhn, at Berlin, on the 4th Nov. 1745. “ When a nail, or a pieceof thick brass wire, &c. is put into a small apothecary’s vial, andelectrified, remarkable effects follow: but the vial must be verydry, or warm. I commonly rub it over beforehand with a fingeron w hich I put some pounded chalk. If a little mercury, or a lewdrops of spirit of wine, are put into it, the experiment succeeds thebetter. As soon as this phial and nail are removed from tl a elec-trifying glass, or the prime conductor to which it hath been ex-posed is taken away, it throws out a pencil of tlaine so long, thatwith this burning machine in my hand, I have taken above sixtysteps in walking about my room. When it is electrified strongly,I can take it into another room, and there fire spirits of wine withit. If, while it is electrifying, I put my finger or a piece of goldwhich I had in my hand, to the nail, I receive a shock whichstuns my arms and shoulders. “ A tin tube, or a man placedupon electrics, is eletrilied much stronger by this means than inthe common way. When I present this vial and nail to a tin tube,which I have fifteen feet long, nothing but experience can makea person believe how strongly it is electrified. Two thin glasseshave been broken by the shock of it.” Not long after this thefollowing method of giving the shock was discovered in Hollandhy Mr. Cuna’us. Mr. Muschcnbroek and Ins friends, observing

that electrical bodies exposed to the atmosphere, which is alwaysreplete with conducting particles of various kinds, soon lost theirelectricity, and were capable of retaining but a small quantity ofit; imagined, that, were the electrified bodies terminated on allsides by original electrics, they might be capable of receiving astronger power and retaining it longer. Glass being the mostconvenient electric for this purpose, and water tiie most conveni-ent non-electric, they first made these experiments with water inglass bottles: but no considerable discovery was made, till Mr.Cunams, happening to hold his glass vessel in one hand, and en-deavouring to disengage it from the conductor with the other,(when he imagined the water had received as much electricity asthe machine could give it,) was surprised with a sudden shock inhis arms and breast, which he had not in the least expected. Thereport of such a terrible elled of the electric power immediatelyraised the attention of all the philosophers in Europe . Many of them, greatly exaggerated theiraccounts; either from a natural timidity, ora love of the marvellous. M. Muschenbroek, who tried the experi-ment with a very thin glass bowl, told M. Reaumur in a letter wrotesoon after the experiment, That he felt himself struck in his arms,shoulder, and breast, so that lie lost his breath ; and was two daysbefore he recovered from the effects of the blow, and the terror,lie added, that he would not take a 2d shock for the whole king-dom of France . One of the most important discoveries xet mariein electricity is the identity of the electric fluid with lightning.From almost the first discovery of the electric light, and the crack-ling with which it is emitted, a similarity between it and the phe-nomena of thunder and lightning had been observed. This istaken notice of hy Dr. Wall, one of the first who viewed theelectric light in any perfect manner. The Abbe Nollet , Mr.Winckler, and others, also enumerated many resemblances be-tween the pha'iiotnena of electricity and those of thunder ; but theydid not think of any method by which their suppositions couldhe brought to the test of experience. This was first proposed hyDr. Franklin in 1750. He had before discovered the effects ofpointed bodies iir drawing off the electric matter more powerfullythan others. This was suggested to him hy one Mr. Thomas Hop-kinson, who electrified an iron ball 3 or 4 inches diameter with aneedle fastened to it, expecting to draw a stronger spark from thepoint of it; but was surprised to find little or none. Dr. Frank-lin, improving on this iiint, 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 noiseor danger, into tin: body of the earth. “ The electric fluid (saidhe) is attracted by points. We do not know -whether this proper-ty be in lightning ; but since they agree in all the particulars inwhich we can already compare them, it is not improbable, thatthey agree likewise in this; let the experiment be made.” Dr.Franklin’s supposition was verified in 1752, and the discovery isalmost the only one in the whole science, that has not been the re-sult of accident. The most active persons were two French gen-tlemen, Messrs. Dahbard and Delor. The former prepared hisapparatus at Marly la Ville, 5 or 6 leagues from Paris ; the latterat his own house, on some of the highest ground in that capital.M. Dalibard’s machine consisted of an iron rod 40 feet long, thelower extremity of which was brought into a centry-box, wherethe rain could not come ; while on the outside it was fastened tothree wooden posts by long silken strings defended from the rain.This machine was the first that was favoured with a visit of the ethe-real fire. Mr. Dalibard himself was not at home ; but, in bis ab-sence, he had entrusted the care of his apparatus to one Coissier ajoiner, who had served 14 years among the dragoons, and on whosecourage and understanding he could depend. This artisan had allthe necessary instructions given him ; and was desired to call someof his neighbours, particularly the curate of the parish, wheneverthere should be any appearance of a thunder storm. At length thelong expected event arrived. On Wednesday, 10th May, 1752,between two and three P. M. Coissier heard a’ pretty loud clap ofthunder. Immediately lie ran to the machine, taking witli him aphial furnished with a brass wire ; and presenting the wire to theend of the rod, a small spark issued from it with a snap like thatwhich attends a spark from an electrified conductor. Strongersparks were afterwards drawn in the presence of the curate and anumber of other people. The curate’s account of'tftem was, thatthey were of a blue colour, an inch and an half in length, and

smelled