Page:Cyclopaedia, Chambers - Supplement, Volume 2.djvu/955

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the ekclricity pervaded the vacuum in a continued arch of lambent flame, and as far as the eye could follow it, with- out the leaft divergency.

It is to be obferved, that upon, admitting a. very fmall quantity o£ air into the exhaufled tube, the phenomena difappear; not fo much, from the final! quantity of air ad- mitted, as from the vapours which infinuated themfelves therewith. For thefe phenomena have been vifible,, though in a lefs perfect degree, when a much larger quantity of air was left in die receiver, by omitting to. exjiauft it as much as pofiible.

If the deElrifying machine, and the man who turns the wheel thereof, are fupported by dearies per fe; and if a piece of wire be connected with the brafs cap covering the upper extremity oi the exhaufted tube, or to the end of the long brafs rod, by the Aiding of which through a box of oiled leather, the upper brafs plate may be moved in the tube ; and if the other end of the wire be fattened, to. any part of the frame of the ekclrifying machine, when this is put in motion, the electrical corufcations may be feen to pals, as before, from one of the brafs plates contained in the tube to the other, and to continue, unlefs the air infinu- ates itfelf, as long as the machine is in motion. If, under thefe circumftances, the hand of a perfon Handing on the floor is brought near the fides of the giafs, the corufcations will direct themfelves that way in a great variety of curious forms.

This experiment, in which the ekclricity is feen pufhing it- felf on through the vacuum by its own elafticity, is con- fidered by Mr. Watfon as an exferimentum cruets of the truth of his doctrine hereafter mentioned.

It may be obferved in all thefe experiments, that a vacuum does not conduct ekclricity fo perfectly as metals or water. For, in the laft experiment, a perfon ftanding upon the floor, and applying his finger to the upper brafs cap of the tube, receives a fmart ftroke ; and in the former, fnaps of fire may be drawn from the prime conductor. Thefe are arguments of fome degree of accumulation, while the dec tricity is paffing through the vacuum; fince nothing of this kind happens when metals, ftanding upon the ground, touch the prime conductor.

Such are the principal phenomena of electricity hitherto difcovered ; but the chief queftion remains : What arc the general laws of thefe phenomena, and what are their caufes ?

Mr. Ellicott thinks that the following conclufions, or ge- neral laws, may be juftly deduced from the phenomena. i°. That thefe remarkable phenomena are produced by means of effluvia; which, in exciting the electrical body, are put into motion, and feparatcd from it. 2°. That the particles compofing thefe effluvia ftrongly re- . pel each other. 3°. That there is a mutual attraction between thefe particles and all other bodies whatfoever.

That there are effluvia emitted from the tube when rub- bed, and which furround it as an atmofphere, is evident from that offeniive fmell arifing from them, from that fen- fation on the hands or face, when the tube is brought near either of them, and from thofe fparks of light, on a ftill nearer approach of the finger to it.

That the particles of thefe effluvia repel each other, is proved by the cork balls, and the fibres of the feather re- pelling each other, when impregnated with them ; and by the leaf-gold being repelled by the tube, and not returning to it again, until by coming near, or touching fome non- electric body, the effluvia are drawn off from it. From this property it is, that thefe effluvia expand themfelves with fo great a velocity whenever they are feparated from the elec- tric body ; and as they are likewife capable of being greatly condenfed, may we not from hence juftly conclude they are elaftic ?

That there is a mutual attraction between thefe effluvia and molt other bodies, appears from their collecting from the tube fuch quantities thereof, as to endue them with the fame properties with the tube itfelf, as is proved from feveral of the experiments above mentioned.

Thefe principles being admitted, it will follow, that the greater difference there is in the quantity of electrical effluvia in any two bodies, the ftronger will be their attraction. For, if the effluvia in each are equal, inftead of attracting, they will repel each other j and in proportion as the quan- tity of electric matter is drawn from one of the bodies, will the attraction between them increafe, and confequently be irrongeft, when any one of them has all the electrical matter drawn from it.

The particles of thefe effluvia are fo exceeding fmall, as eafily to pervade the pores of glafs, as is evident, in that a feather, or any light bodies inclofed in a glafs ball herme- tically fealed, will be put in motion on the excited tube be- ing brought near the outfide of it : and it has been gene- rally thought that they pafs thro' the pores of the denfeft bo- dies, and feveral experiments render this fuppofition not improbable, tho' none of them are quite conclufive.

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-Mr. Ellicott then proceeds to' fhew, in a very ingenious manner,, how, from thefe principles, the phenomena of fome of the more remarkable experiments of electricity may bq ac- counted for. Butaswhathefayscannot,wirhjuiticeto his rea- fonings, be abridged, We muft refer the curious to his efTays before quoted ;, only adding.; that we have feen a manufcripi^ of. his, where he endeavours to account for the experiment of Mufchenbroek on thefe principles,, in. a manner that makes us wifti to- fee- the ■ reft of his experiments, obicivations, and reafonings on this; fuhject publiftied. Mr. Watfon has endeavoured to prove, that electricity is. not furnifhed from the glafles employed in the expurirnents, nor from the circumambient air. He thinks that electricity is the effect of a very fubtile and elailic fluid, occupying all. bodies in contact with the terraqueous globe, and that ev;ry where in its natural ftate it is of the fame degree of deri- fity; and that glafs, and other bodies, which, are called. $&- trigs, per Je y have the power of taking this fluid from one ■body, and conveying it to another, in a quantity fuiiicier.t to. be obvious to all our fcnfqs; and that under certain cir- cumftances, it is poflible to render the electricity in fome bodies more rare than it naturally is, and, by communicat- ing this to other bodies to give them an additional quantity, and make their electricity more denfe ; and that thefe bodies will thus continue until their natural quantity is reftored, to each ; that is, by thofe which have loft part of theirs, ac- quiring what they have loft, and by thofe, to which more has been communicated, parting with their additional quan- tity. Both one and the other of thefe is, from the elafti- city of the electric matter, attempted to be done from the neareft non-electric ; and when the air is mo i ft, this is'foori accomplished by the circumambienc vapours, which here may be confidered as preventing, in a very great degree, our attempts to infulate non-electric bodies. This fliort fttetch of Mr. Watfon's fyftem is taken from his own words in the Philofophical Tranfactions, Vol. XL VII. p. 371, 372. For the detail of his illuftrations and pronfs* his treatife before quoted, or the Phil. Tranfact. Vol. XL! V and XLV, muft be coniulted, and particulatly Vol. XLVIf, p. 372, & feq. where, after giving the experimentum cruris before mentioned, he endeavours to fhew that it amounts to a full proof of the truth of his doctrine, that electricity is furniiTicd by thofe bodies, hitherto called ndn-clsflrjcs, and not by the eleclrics per fe\ and that we are able to add to^ or take from, that quantity of electricity naturaJy adherent to bodies.

Mr. Watfon's fyftem naturally leads him to afk, by what denomination fhall we call this extraordinary power ? From its effects in thefe operations fhall we call it electricity? From its being a principle neither generated nor deftroyed ; from its being every where and always prefent, and in rea- dinefs to fhew itfelf in its effects, tho' latent and unob- ferved, till bv fome procefs it is produced into action, and rendered vifible ; from its penetrating the denfeft and hardeft bodies, and its uniting itfelf to them ; and from its immenfe velocity; fhall we, with Theophraftus, Boerhaave, Niew- entiit, 'sGravefande, and other philofophers, call it elemen- tary fire ? Or fhall we, from its containing the fubftance of light and fire, and from the extreme fmallnefs of its parts, as pafling thro' muft bodies we are acquainted with, denominate it, with Hornberg-and the chemifts, the che- mical fulphureous principle, which, according to the dodrines of thefe gentlemen, is univerfally difleminated ? Whatever we call it, it feems certain, that this power has many i'ur- prifing properties, and cannot but be of great moment in the fyftem of the univerfe.

To conclude, we muft obferve that the ingenious Mr. Wil- fon has, in a treatife exnrefs, endeavoured to account for the phenomena of electricity, from Sir Ifaac Newton's Kther.

As to other hypothefes, we refer to the Hijloire geiurale et terticuliere de I'Electricite before mentioned.

SOUND (Suppl.) — The fpace through which found is pro- pagated in a given time, has been very differently eftimated by authors who have written concerning this fubject. Rober- val gives it at the rate of 560 feet in a fecond ; Gaflendus> at 1473; Merfenne, at 1474; DuHamel, in the Hiftory of the Academy of Sciences at Paris, at 1172; the Academy delCimento, at 1185; Boyle, at 1200; Roberts, ati300; Walker, 311338; Sir Ifaac Newton, at 968 ; Dr. Derham, in whofe meaiure Mr. Flamfteed and Dr. Kallcy acquiefced, at 1 142. But by the accounts fince publifhed by M. Caflini de Thury, in the Memoirs of the Royal Academy of Sci- ences at Paris for the year 1738, where cannon were fired at various, as well as great diftances, under great variety of weather, wind, and other circumftances, and where the meafure3 of the different places had been fettled with the utmoft exactnefs, found was propagated at a medium at the rate only of 1038 French feet in a fecond. The French foot exceeds the Englifh by nearly feven lines and a half, or is as 107 to 114: And confequently, 1038 French feet are equal to J 106 Englifh feet. The difference therefore

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