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fparks produced, at nearly equal intervals from each other, which will fometimes appear as ifluing from the fide of the electrified rod, at others, as coming from the non-eleClrk.
21. Take 1 two plates of metal, very clean and dry, whofe furfaces are nearly equal ; hang one of them horizontally to the electrified rod, and bring under it, upon the other, any thin, light body, as leaf-filver, (3V. when the upper plate is made electrical, the filver will be attracted by it; and if the under plate is held at a proper diirance, will be perfectly fufpended at right angles to the plates, without touching either of them ; but if they are either brought nearer toge- ther, or carried farther afimder, the leaf- filver will ceafe to be fufpended, and will jump up and down between them. The fame effect will be produced, if you reverfe the expe- riment, by electrifying the bottom plate, and fufpending the other over it. See Mr. Ellicott's E flays before mentioned-.
22. By the experiments made in Germany, and repeated in England by Mr. Watfon, it appears, that fpirit of wine may be fet on fire by the power of electricity. This will fuc- ceed not only with the etherial liquor, or phlogiftoh of Fro- benius, and rectified fpirit of wine, but even with common proof fpirit. But all thefe muft ■be warmed a little, fo as to emit an inflammable vapour.
And the experiment fucceeds equally well, whether an elec- trified perfon, or other electrified body, be brought near the not electrified fpirit; or whether the electrified fpirit be brought near a non-eleCiric body.
This laft method of firing the fpirit is faid, by Mr. "Wat- fon, to be done by the repulfive power of electricity. And the former, where the not electrified fpirit is fired by its being brought near to a man ftanding upon a cake of wax, or to a fword, or bar of metal, fufpended by filk lines, is faid to be performed by the attractive power of electricity. Of thefe two kinds, the repulfive power has generally been found the ftrongeft.
23. Not only (pints of wine, but alfo fal volatile oleofum, dulcified fpirit of nitre, Peony water, Daffy's elixir, Helve- tius's ftyptic, and fome other mixtures, where the fpirit has been very confiderably diluted, may be fired by the power of electricity, and fo may diftilled vegetable oils, as that of turpentine, lemon, orange peels, juniper, and even thofe which are fpecifically heavier than water, as oil of faffafras ; alfo refinous fubftances, fuch as balfam capivi and turpen- tine ; all which fend forth, when warmed, an inflammable vapour. The inflammable vapour, produced by putting an ounce of filings of iron, an ounce of oil of vitriol, and four ounces of water into a Florence flafk, may be fired by the fame means ; as may alfo gunpowder, if ground with a little camphor, or with a few drops of fome inflammable chemical oil. To increafe the furprife, thefe fubftances may be fired by ice, or by a drop of water, only thickened a little with the feeds of fleawort. '
All thefe experiments have fucceeded, though not always in damp weather, with a glafs tube rubbed by the hand merely ; but if a greater ekClrical force be excited, by means of a globe, thefe experiments will fucceed in any weather, though not with equal eafe.
24. If fome oil of turpentine is fet on fire in any veflel, held in the hand of an electrified man, the thick fmoke that arifes therefrom, received againft any non-eleCiric of a large furfacc, held in the hand of a fecond man ftanding upon an electrical cake ; this fmoke will, at a foot diftance from the flame, carry with it a fufEcient quantity of electricity, for the fecond man to fire any inflammable vapour. The electrical ftrokes have been likewife perceptible upon the touching the fecond man, when the non-eleilrk held in his hand has been in the fmoke of the oil of turpentine between feven and eight feet above the flame. Here we find the fmoke of an original electric, a conductor of electricity.
25. Likewife, if burning fpirit of wine be fubftituted in the place ^of the oil of turpentine, and if the end of an iron rod, in the hand of the fecond man, be held at the top of the flame, this fecond man will kindle other warm (pints held near his finger. Here wc find, that flame conducts the electricity, and does not perceptibly diminifh its force. The like is to be obferved of red-hot iron ; and of the coldeft mixtures that art can produce.
26. Of all the furprifing phenomena of electricity, none feems to be more fo, than the extraordinary accumulation of the electrical power in a phial of water, firft difcovered by Profeflor Mufchenbroek of Leyden. The experiment is this : a phial of water is fufpended to a gun-barrel by a wire let down a few inches into the water through the cork ; and this gun-barrel, fufpended in filk lines, is applied (a near an excited glafs globe, that fome metallic fringes, in- ferred into the gun-barrel, touch the globe in motion. Under thefe circumftances a man grafps the phial with one hand, and touches the gun-barrel with a finger of the other ; upon which he receives a violent fliock through both his
-arms, efpecially at his elbows and wrifts, and acrofs his breaft. The experiment fucceeds beft ceteris paribus, 1°. when the air is dry. 2°. When the phial, containing the water, is of the thinneft glafs. 3°. When the outfide of the phial is perfectly dry. 4°. In proportion to the number of
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points of tun-cleCtric contact. Thus if you hold the phial only with your thumb and linger, the fnap is final!"; larger when you apply another finger, and increafes in proportion to the grafp of your whole hand. 5 . When the water in the phial is heated, which being then warmer than the cir- cumambient air, prevents the condenfation of the floating vapours therein upon the furface of the glafs. A gun-barrel is not neceffary in thefe experiments ; a fword, or any other folid piece, or tube of metal, is equally ufeful. R4r. Watfon has given us many curious obferva ions relat- ing to this experiment, and has varied it a great many ways. Among other things he obferves, that the phial may be electrified by applying the wire therein to the globe in mo- tion; after which, if it is grafped in one hand, and the wire touched with a finger of the other, the ffroke is as great as from the gun-barrel. And if you grafp the phial with your hand, and do not at the fame time touch the wire, the acquired electricity of the water is not diminifhed. So that, unlefs by accident or otherwife the wire is touched* the ileSlrified water will retain its force many hours, may be conveyed feveral miles, and afterwards exert its force upon touching the wire.
To prove Mr. Watfon's affertion that the ftroke is cxteris paribus, as the points of contact of mn-eleCtrics to the glafs, Dr. Bevis wrapped up two large round bellied phials in very thin lead fo clofe as to touch the glafles every where, except their necks. Thefe were filied with water, and corked, with a ff aple of fmall wire running through each cork into the water. A piece of ftrong wire about five inches long, with an eye at each end, was provided, and at each end of this, hung one of the phials of water by the fmall ftaple running through the cork. A fmall wire loop was then fattened into the lead at the bottom of each phial, and into thefe loops was inferted a piece of ftrong wire like the former. If then thefe phials were hung acrofs the gun-barrel and electrified, and a perfon ftanding upon the floor touched the bottom wire with one hand, and the gun-barrel with the other, he received a moft violent fhock through both his arms and acrofs his breaft. The electrical explofion has been fince vaftly increafed. But Mr.Watfon is of opinion, that the violence of the explofion of the eleCtrie force accumulated in the glafs, is not fo much owing to the quantity of mn-eleCirical matters contained" in the glafs, as to the number of points of non-eleCtrical con- tact within the glafs, and the denfity of the matter confti- tuting thofe points, provided this matter be in its own na- ture a ready conductor of electricity. For a cylindrical glafs jar blown very thin, of fixteen inches in height, and eighteen inches in circumference, having been covered both within and without with leaf-filver to within an inch of its top, the ex- plofion from this jar was equal to that from three glaffes, each about feventeen inches in height, and four in diameter, and filled with fifty pounds of leaden fhot each. The ex- plofion in thefe cafes is fo violent as to become dangeiousj and lias been found mortal not only to fmall birds, but even to a rat; and Mr. Franklin killedawell-grown turkey with it.
27. A very confiderable electrical explofion may be made from a plate of glafs thus : Let a thin plate of glafs of about a foot fquare, be covered on both fides with leaf-filver ; and make this adhere to the glais by a very thin pafte. A mar- gin of an inch muft be left oh both fides; otherwife, upon electrifying this plate, the electricity would be prevented from being accumulated upon one of its furfaces, by being propa- gated from the filver on one fide to that of the other. When the glafs plate is thus prepared, if it be placed upon a table in fuch a manner, that when fully electrified by a wire or fuch like from the prime condudtor, a perfon touches the under furface with a finger of one of his hands, and brings one of the fingers of the other near the upper furface, or near the prime conductor, he wUl be mocked in both his arms and crofs his breaft. The fame effect- happens, if when this plate is electrified as before, a perfon holds it in his hand by the margin, and without touching the filver, prefents it, even fome time after it has been taken from the prime con- ductor, to another perfon, who touches the under furface with his finger, and holds it there till he touches the upper furface with a finger of his other hand. This is an experi- ment contrived by Dr. Bevis, who obferves, that though the explofion from the glafs plate filvered was occafioncd by about fix grains of filver, upon which the electricity was ac- cumulated, yet the explofion was equal if not fuperior to that from half a pint of water contained in a thin glafs as ufuah
28. The commotion arifingfrom the difcharge of the accu- mulated electricity in the phial, may be felt by a great num- ber of men at once. Monfieur le Monnier, at Paris, is faid to have communicated this fliock through a line of men, and other mn-elcCiria, meafuring nine hundred toifes, which is more than an Englifh mile; and the Abbe Nollet » made the experiment upon 200 perfons, ranged in two parallel lines— [- Lettres fur YElectricitc, p. 207.]
29. This electrical commotion has been made very fenfible quite acrofs the river Thames, by the communication of no other medium than the water of that river ; and fpirit of wine has been fired at that diftance.
30. The commotion has alfo been perceptible to two or
more
