Page:Cyclopaedia, Chambers - Supplement, Volume 2.djvu/954

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like natural lightning.-f Phil. Tranf. Vol. cit. p. 536. j • Ibid. p. 290.]

■7$ This analogy is now farther confirmed by the dilcovery made in France, in confequence of Mr. Franklin's hypothe- cs, of being able, by a proper apparatus, to colleCt the electricity from the atmofphere during a thunder ftorm. For a pointed bar of iron, 40 feet high, having been placed upon an ekclrical body, and a ftormy cloud having palled over the place where the bar flood, thofe that were appoint- ed to obferve it drew near, and attraaed from it fparks of fire, perceiving the fame kind of commotions as in the com- mon ekclrical experiments. The like eKe& followed, when a bar of iron 99 feet high was placed upon a cake of refin, two feet fquare and two inches thick. For a ftormy cioud having palled over the bar, where it remained half an hour, fparks were drawn from the bar. Thefe were the firft ex- periments made in France, and they have been fufficiently varied and verified fince; fo that it feems now certain, l°. that a bar of iron, pointed or not, is ekclrifed during a ftorm. 2°. That a vertical or horizontal fituation is equally fitting for thefe experiments. 3°. That even wood is ekclrifed. 4°. That by thefe means a man may be fuffi- ciently ekclrifed to fet fire to fpirit of wine with his finger, and repeat almoft all the ufual experiments of artificial elec- tricity ; for fitch may that which is excited by frifiion be denominated.

It is, however, to be remarked, that thefe phenomena are attended with irregularities, and do not always faceted per- feftly. Sometimes fimple clouds, without thunder or ligbt- njns, produce more eleelricity, than when there is loud thun- der." Sometimes the cletlricity does not {hew itfeif but where there is lightning: in other cafes, the eleelricity which feem- ed diffipated during the rain, began again as foon as the rain ceafed, altho' the thunder was very diftant. See the Phil. Tranf. Vol. XLVII. p. 534, feq.

39. Mr. Franklin has contrived a very ingenious and eafy way of trving experiments of this kind by means of an ekclrical kite, made of a large thin filk handkerchief, ex- tended and fattened at the four corners to two flight ftnps of cedar, of fufficient length for this purpofe. This kite being accommodated with a tail, loop, and firing, will rife in the air like thofe of paper. To the top of the upright ilick of the crofs is to be fixed a very fharp-pointcd wire, riling a foot or more above the wood. To the end of the twine, next the hand, is to be tied a filk ribband ; and where the twine and filk join, a key may be fattened. The kite is to be raifed when a thunder gull appears to be coming on, and as foon as the thunder-clouds come over the kite, the pointed wire will draw the ekclric fire from them, and the kite with all the twine will be electrified; and the loofe fila- ments of the twine will ftand out every way, and be attracted by an approaching finger. When the rain has wet the kite and twine, fo that it can conduft the ekclric fire freely, it will ftream out plentifully from the key, on the approach of a man's knuckle. At this key the phial may be charged ; and from elcclric fire thus obtained fpirits may be kindled, and all the other ekclrical experiments be performed, which are ufually done by the help of a rubbed glafs globe or tube, and the famenefs of the ekclric matter with that of lightning may thereby be completely demonflrated. Phil. Tranf. Vol. cit. p. 565, feq.

From this identity, fome have conceived hopes of depriving the clouds of all their thunder, and thereby rendering thun- der ftorms harmlefs. See Philof. Tranf. Vol. cit. p. 289,

535*

40. It has been pretended, that odours would pervade elec- trified globes and tubes of glafs, and that the medicinal ef- fects of drugs might likewife be tranfmitted this way ; as alfo, that if perfons were to hold in their hands, or place under their naked feet, odoriferous, or purging fuhftances, and were then to be ekclrifed, they would be fenfible of the ef- fefts of thefe fubftances. But it feems now certain, that all thefe pretences have been impofitions on the credulity of the world, and that when proper experiments have been tried, no fuch effects have been perceived, nor have the moft poifonous fubftances manifefted any influence in this way. See Dr. Bianchini's experiment, mentioned in the Philof. Tranf. Vol. XLVII. p. 399, feq.

41. However, though thefe pretended wonders, tranfmitted to the reft of Europe from Italy and Leipfic f, have no foundation in fact, yet it does not follow, that medicinal ad- vantages are not to be gained from eleelricity itfeif. So fubtle and fo elaftic a fluid admitted in a large quantity into bur bodies, as, from undoubted experience, it greatly heats the flefh, and quickens the pulfe, may, more efpecially when aflifted with the expectation of fuccefs in the patient, in particular cafes he attended with very great advantages E. — [ f Phil. Tranf. Vol. cit. p. 231, feq. * Mr. Watfon in Phil. Tranf. Vol. cit. p. 406.]

In efteel, we meet with ibme cures performed in paralytic cafes by the force of eleelricity. See Hiftoire generale et particuliere de YJShctirile, Paris, 1752, part. 3. p. 36, feq. And we meet with accounts of feveral other diforders cured by the fame means, in that treatife ; but we fear not all equally well attefted.

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42. The ekclrical virtue having, in fome cafes, access'.' and facilitated the motion of liquids through capillary fetbes, the Abbe Nollet was led to fuppofe, that the electrical ogtu- via might alfo contribute to accelerate the growth of ve- getables, and to increafe tile perfpiration of animals, and the experiments made bv that gentleman feem to fuppcrt his opinion ; though objections have arifen, as to what he has advanced with refpecl to the acceleration of the motion of fluids through capillary tubes or fyphons: for Mr. Eliicott feems to have proved, that this acceleration is not bartly owing to the fluids being electrified, but that other circum- ftances are necefl'ary, in otder to produce this effect. Mr. Eliicott obferves, that if a veflel of water is hung to the prime conductor, having a fyphon in it of fo final! a bore that the water will be difcharged from it only in drops, on the Water's becoming electrical by means of the machine, it will immediately run in a ftream, and continue to do fo, till the water is all difcharged, provided the fphere is con- tinued in motion. And the true reafon of the water's run- ning in a ftream in this cafe feems to be, that fo long as the machine is in motion, there is a conftant fucceffion of the ekclric effluvia excited, which vifibly run off from the end of the prime conductor in a ftream ; and as they are in like manner carried off from all bodies hung to it, thofe effluvia which run off from the end of the fyphon, being ftrcngly attrafled by the water, carry fo much of it along with them, as to make it run in a conftant ftream. See Mr. Eliicctt's Effays before mentioned, p. 11, 12, csV.

The fame author obferves farther, that if the veflel of water, with the fyphon in it, is fufpended by any mn-elcclric body over another ftrongly eleltrified, the water will immediately run from the fyphon in a ftream; but if fupportcd by a piece of filk, or any other ekclrical body, the water will im- mediately oeafe running, and only be difcharged in drops. And he accounts for this phenomenon from the principles Of attraction between mn-elcclrics and ekclrical effluvia, and of non-attraftion between the fame effluvia and original ekclric:. See page 15 of the Effays before cited.

43. Mr. Watfon has given us a particular account of fe- veral curious phenomena of eleelricity in vacuo in the Phi- lofophical Tranfaaions, Vol. XLVII. p. 362, feq. The ekclrical effluvia, in their paffage through an exhaufted glafs tube, of almoft three inches in diameter, afford a moft agteeable fpeaaele in a darkened room. We may obferve, not as in the open air, brufhes or pencils of rays an inch or two in length, hut corufcations extending the whole length of the tube, that is, in his experiment, thirty-two inches, and of a bright filver hue. Thefe did not immediately diverge, as in the open air, but frequently, from a bafe apparently~flat, divided themfelvcs into iefs and lefs ramifications, and refembled very much the moft lively corrufcations of the aurora borealis. At other times, when the tube has been exhaufted in the moft perfect manner, the electricity has been feen to pafs between two brafs plates, contrived fo, that they might be placed at different distances from each other, in one continued ftream, of the fame di- menfions throughout its whole length.

If the exhaufted tube be made part of the circuit before mentioned in Mufchenbroek's experiment, at the inftant of explofion, a mafs of very bright embodied fire may be imn jumping from one of the brafs plates in the tube to the other. But this is obferved not to take place, when one of the plates is farther diftant from the other than ten inches. If the diftance be greater, the fire begins fo diverge, and lofe part of its force ; and this force diminifhes in proportion to irs divergency, which is nearly as tire diftance of the two plates.

But though the vacuum here employed greatly exceeded that which is ufually made by common air-pumps, yet it was far from being perfect. Thefe experiments were there- fore tried with a torricellian vacuum, very ingenioufly con- trived by Lord Charles Cavendifh. The apparatus confifted of a cylindrical glafs tube of about three-tenths of an inch in diameter, and of kven feet and an half in length, bent in fuch a manner, that thirty inches of each of its extremi- ties were nearly ftraight, and parallel to each other, from which an arch fprung, which was likewife of thirty inches. This tube was carefully filled with mercury ; and each of its extremities being put into its bafon of mercury, fo much of the mercury ran Out, until, as in the common barome- trical tubes, it was in equilibrio with the atmofphere. Each of the bafons containing the mercury was of wood, and was fupported by a cylindrical glafs of about four inches ■ in diameter, and fix iftchC6 in length ; and thefe giaifes were fattened to the bottom of a fquare wooden frame, (o con- trived, as that to its top was fufpended, by filk lines, the tube filled with mercury before mentioned ; fo that the whole of this apparatus, without inconvenience, might- be moved together. The torricellian vacuum then occupied a fpace of about thirty inches. In making the experiment, when the room was darkened, a wire from the prime con- duaor of the common ekclrical machine, communicated with one of the bafons of mercury, and any nan-elegtric touching the other bafon, while tiie machine was in motion,

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