Page:Cyclopaedia, Chambers - Supplement, Volume 2.djvu/950

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ARTICLES omitted.

ELECTRICITY (Cycl.)—\ body in which eleElricity may be excited by fome action upon that body, as rubbing, patting, or warming it, and fometimes only expofing it to Cold and dry air, after it has been covered, is called an eleEiric per fe : fuch are glafs, cryftals,' and pretious ftones ; refins, gums, fulphur, fealing wax, and moft dry parts of animals, as filk, hair, and the like. EleElrics per fe are alfo called original eleEirics. A non-eleElric per fe or limply a non-eleElric, is a body in which eleElricity cannot be excited by any action' upon the all, is very flightly perceptible. Of this kind are wood, a- nimals, living or dead, vegetable fubftances, water and metals.
 * "" body itfeif; or at leaft one in which that property, if at

But non-eleElrics receive eleElricity, when brought near to eleclrics per fe, in which eleElricity has been excited. In order to know that non-eleElrics have received the com- municated eleElricity,they muft be infulated ; that is, they mull not be fufpended from, or fupported by any bodies, but

4 y^aX^celeEtricsperfe: for if one non-eleElr'ic be touched by

another, and this by a third, &c, all the eleElricity received by the firft will go to the fecond, and from this to the third t&c. till at laft it be loft upon the ground. But if feve- ral non-eleElrics touching one another, are at laft terminated by eleEiric bodies, in that refpect they make but one body, and receive and retain eleEiricity for fome time. However it muft be obferved, that bodies flightly non-eleElric, fuch as dry wood, may ferve for fupporters to thofe bodies which are very highly non-eleElric, as metals. EleElricity may be communicated to non-eleElrics by apply- ing a glafs tube or globe, excited by friction, to one^end of thofe bodies; and there are feveral ways of finding when the non-eleElrics have received the eleElricity. Thus, if an iron bar be fufpended horizontally by two filken ftrings that are very dry, and the rubbed tube be applied, or brought near — to one of the ends of the bar, and thenfome leaf-gold, or

- '•** ■ leaf-bfafs, or any other light bodies, placed upon a fmall Hand, or a plate* be brought near the o'her end, they will be alternately attracted and repelled by the bar. Likewife, if the finger be brought near the end, or other part, of the bar, the eleElrical effluvia will give a very fenfible and fome- times painful ftroke, with a fnapping noife, and produce a flafli of light. If the communicated eleElricity fhould prove too faint to be tried this way, a fmall flaxen thread, fufpend- ed by a flick, may be brought near the body that has been eleclrified; and if the ehtlrkity has been communicated, even in a fmall degree, the thread will be attracted without deftroying the eleElricity received by the body till after fome s E time.. This thread Doctor Defaguliers calls the thread of trial.

It is to be obferved, that an eleEiric per fe does not receive this virtue from another eleEiric per fe, though excited, till it is become a mn-ele£lr'tc \ which happens when it is made wet or moifl; and then it will be made eleEiric only by communica- tion. EleEiric bodies, in which it is difficult to excite eleElricity, may be looked upon as non-eleElrics, when their eleElricity is not excited ; and then they will be in the fame condition as non-eleElrics per fe, and be liable to receive eleElricity by communication in the fame manner.

From what has been faid, it appears that non-eleElrics are conductors of eleElricity. Water conducts it very well, but metals are the moft convenient conductors. Thefe things being premifed, we fhall here add fome of the principal phenomena of eleElricity; that is, fuch as feem to

„„- give fome light- towards a theory of this wonderful property of bodies.

I* When the eleElricity of a glafs tube has been excited by rubbing, if you move your fingers long-wife from one end of the tube to the other, but without touching it, you will hear a continued fnapping, like a diftant noife of thorns burning; and if the room be darkened, you will fee fparks E of light wherever the tube fnaps ; and likewife a light fol- lowing the hand that rubs the tube.

2. A down feather being tied to the top of a wooden broach or fkewer, of about fix or feven inches in height, and fixed upright upon a foot, if you bring the excited tube near it, all the fibres of the feather ftretch out towards the tube ; but as foon as you remove the tube, the fibres of the fea- ther turn back, and ftick flrongly to the fkewer. If you bring your finger nearto the feather, while its fibres are tend- ing towards the tube, the finger will repel them ; but as foon as you remove the tube, they are attracted by the fin- ger. If you cover the feather with a very dry glafs recipient, fuch as is ufed on the air-pump, the tube will attract the feather in the fame manner through the glafs : and this hap- pens, even when the recipient has been exhaufted of its air by the pump. When the tube is rubbed near the recipient, £,, t whether it bjefull of air or empty, the -fibres of the feather

follow the motion of the hand along, the tube, arihng upoa thebroach or fkewer.

3. Without making ufe of the tube,, if you rub the recipient that covers the feather with, both hands, the fibres of the fea- ther will ftretch themfelves out towards the glafs, like the rays of a fphere. If you rub but with one hand, the fibres will ftretch themfelves towards that part of the glafs which js rubbed 5 and when you blow againft the glafs, thofe fibres will be repelled, notwithflanding the interpofition of the glafs : which happens alfo, when you ftrike the air with the hand towards the feather, without touching the recipient. t

4. After the tube has been rubbed, if any atfiftant lets go a down feather in the air, at the diftance of a foot or two from the tube, the feather will jump towards the tube with an accelerated motion, and adhere to it for fome time; and then of a fudden it will be repelled from the tube, and will fly about the air in fuch manner, that the nearer you bring the tube to it, the more it will be repelled, till it has touched fome other body ; and then it will be drawn again by tbe tube; which after fome time will drive it away again. Some- times, when the finger is held at eight or ten inches from the tube, the feather will jump from the tube to the finger, and from the finger to the tube, thirty or forty times to- gether.

5. If a firing of any kind be ftretched horizontally, and from the firing you hang a thread of filk about three foot long, and very dry, and to the lower end of that thread you fallen a down feather; then, at the diftance of about two or three feet, you hang up another feather, but by a flaxen thread ; the rubbed tube being brought near will attract the firft feather, which, when it has adhered to it a little while, will fly from the tube, and then be repelled by it every time the tube is brought near, till it has touched fome other body, as in the preceding experiment, and then it will be attracted anew. But the feather, which is fufpended by the flaxen thread, will always be attracted at the approach of the tube, and never repelled. And if you wet the filken thread, the feather hanging at it w.ill be repelled no more, but always attracted by the tube. -

6. If you make ufe of a tube which is hermetically fealed at one end, and has at the other end a brafs ferril with a fcrew, by which means the air may be pumped out of it; if you rub the tube, after the air is exhaufted, it does not attract any more, as has already been taken notice of in the Cyclo- pedia, N° 7; nor does the tube give the light before men- tioned, N° 2, but it gives much more light within. Then if, by opening the cock a little way which is faftened to the tube, the air be let in flowly, while the tube is rubbed, the light diminifhes; and being interrupted by the air, as it comes in, lookslike lightning at a diftance, tillall the air is comeTn, and then there is no more light within ; but the light goes all to the outfide, and the attraction returns.

7. If two fmall boards, or two fmall octavo books, be fet edge wife, parallel to each other, and about the diftance of ten inches afunder, upon a ftand of feven or eight inches di- ameter; little pieces of leaf gold, or brafs, laid upon the fland between thofe boards, will not be attracted by the rub-

■ bed tube held near them, till it be brought quite between the faid boards, as near to the ftand as half the diftance of the boards from each other : that is, when the tube is fo held, that a circle defcribed round the axis of the tube, with the diftance that is between that axis and the ftand, paries between the boards or books without touching them. But when the rubbed tube being held horizontally, at the dif- tance of a foot from the ftand, feems to have no virtue, be-

'caufetheleaf-^old has no motion., if an amftant fnatches away the boards, all on a fudden the pieces of gold will be attracted and repelled feveral times, without giving any new friction to the tube.

8. When the air isVery dry, and the rubbed tube can attract the leaf-gold laid on a fmall ftand, to the diftance of three foot or beyond ; if the fame leaf-gold be laid upon a table, or any large furface, 'the excited tube muft be brought very near before jt can produce its effect.

9. When the air is moift, the experiment, N° 4, does -not fucceed well : for after the feather in the air has been fome time driven about by the tube, it comes back of itfeif to the tube, without having touched any other body ; and fome- times after having adhered to the tube, towards the middle of it, it flies ofFfrom it, and comes again immediately to the tube, flicking to that part of it which is fartheft from the hand. It happens alfo, when the air is very dry, and the tube repels the feather, after having attracted it, to the dif- tance of two or three feet, that if you wet the top of the tube at the end, for the length of fix or feven inches, the feather will come and ftick to that end of the tube, without having touched any other body.

10. Having