Page:Cyclopaedia, Chambers - Supplement, Volume 2.djvu/951

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10. Having filled with water a fmall drinking glafs,. of a- boutan inch diameter, when you bring the rubbed tube near it, the water rifes in a little hill, accumulated at the edge of the glafs.; fometimes jumping towards the tube in a little jet, fo fmall that you can hardly fee it, though you may find the tube wholly wet with it. One may alfo obferve, thai this accumulated water rifes in the fhape of a fmall cone, whofe axis is fometimes ftretched out horizontally towards the tube, then fnaps and falls down again flat upon the reft of the wa- ter. If this experiment be made in the dark, a flafh of light accompanies the mapping.

ii. If by means of an artificial fountain, in which air is condenfed upon the water to make it fpout, you play a fmall jet, of about the fortieth part of an inch diameter, upwards or downwards; the rubbed tube being brought near, the jet will bend towards the tube at the diftance of a foot ; and if the tube be brought nearer, the jet being wholly drawn away by the tube, is changed into a dew upon the tube, fo that it adheres to the tube in little drops, provided the jet be not made to fpout with too much force.

12. If a packthread or hempen firing be ftretched horizon- tally to the length of about twelve hundred feet, at the end of which is fufpended an ivory ball of about an inch and an half in diameter; this ball will draw and repel leaf-brafs, or leaf-gold, when the rubbed tube is brought near the other end of the ftring, and the thread of trial being brought near to the ball, is attracted by it.

In this experiment the fupporters of the ftring muft be eleclncs per fie, whether they be hair-ropes, fiddle- fixings, or cat-guts, ribbons, ftrings of filk, glafs tubes, long bodies of fulphur or of refin, &c. and all thefe bodies muft be very dry. If the ftring be wet, the experiment will fuccecd the better.

This experiment was, we believe, firft. made by the late Mr. Stephen Gray; and it might be improved, by employ- ing an iron wire inftead of a packthread or hempen ftring. When an iron wire is ufed, its fupporters might be wooden flicks, being non-eleclrics in a flighter degree, as before ob- ferved ; but cleSirics are beft.

The conductor of eleclricity, in thefe and the like cafes, need not be ftretched at length, but may be carried back- wards and forwards in parallel or other lines, provided they be not placed too near to each other, but at a proper di- ftance, as, for inftance, three feet.

13. If two or three iron bars be fufpended in the fame ho- rizontal line, at the diftance of fix inches from one an- other, the eleclricity communicated by the rubbed tube to the end of one of the bars will go on from the one to the other quite to the end of the laft bar, where a pricking will be felt, a noife heard, and a flafh of fire feen. If the air is dry, the electricity will jump from one bar to another at a greater diftance ; but in moift weather, the bars muft not hang at above an inch diftance from each other.

Thefe experiments may be made with a glafs tube, about three foot and an half long, an inch and an half in diameter, and about T ~ of an inch thick, open at both ends, but fome- times hermetically fealed at the end farthefl: from the hand. Thefe proportions are not neceffary, but only convenient for the hand ; and the glafs of the tube ought not to be lefs than JL of an inch in thicknefs ; for when thinner, the eleclricity is indeed fooncr excited by friction, but it does not laft fo long as when the tube is thicker. See Defaguliers's Diflerta- tion concerning Electricity, in his Experim. Philof. Vol. fj. p. 316. feq.

The Doctor obferves with Monfieur du Fay, that there are two forts of electricity, a refinous, and a vitreous kind. One of the experiments, upon which this difference is efta- bliihed, is as follows.

14. If a down feather be fufpended by a filken thread, as in the experiment N° 5, fealing-wax, well rubbed, will pro- duce the fame effect as the tube, but more weakly, drawing the feather; and when once it is feparated from the wax, the wax repels it continually, till the feather has touched fome other body. But the difference here is, that when the feather is in a ftate of repulfion, in refpeCt of the wax, the rubbed tube attracts it; and when the tube has given the feather its repulfive ftate, then the rubbed wax attracts it : which fhews, according to thefe gentlemen, that the electricity of glafs is different from the electricity of fealing- wax ; and the like may be obferved of other refinous fub- ftances.

But, perhaps, this phenomenon may be accounted for, by fuppofing, as the truth is, that, the electrical power of ex- cited glafs is ftronger than that of fealing-wax, and then from Mr. Ellicott's hypothefis, hereafter mentioned, the pheno- menon follows.

Doctor Defagullers has deduced from his experiments, that bodies which are electric per fie, being excited to electricity, repel all other bodies that have electricity, but attract them as foon as they have loft their electricity ; and fo vice vcrfa. Thefe deductions agree very well with Mr. Ellicott's men- tioned below.

The Doctor conjectures alfo, that the particles of pure air are electric bodies, always in a ftate of electricity; and that

vitreous electricity, and from this electricity of the air, hs conjectures, ingenioufiy, that the rife of vapours may de- pend upon electricity. See the Diftertatiun before cited. To thefe experiments related, among others, by Dr. Defagu- liers, we muft add from Mr. Ellicott % that when the tube, N° 1, is ftrongly excited, fparks will not only iflue from it in ftreams while it is rubbing, but will continue to dart out from it for a confiderable time after the rubbing has ceafed, and a very ftrong offenfive fmell will be perceived. — [ a Se- veral Efiays towards difcoveriiig the Laws of Eleclricity, Lond. 1748.]

• 15. The fame gentleman obferves, that if a ball (of cork fuppofe, for lightneft) be hung by a fdkline, and the ex- cited tube is applied to it, it will not only be attracted, but will have an attractive quality communicated to it from the tube ; and if any light bodies are brought near the ball, they will be attracted by it.

16. As the tube, when ftrongly excited, will not only at- tract, but afterwards repel any light bodies brought near ir, in like manner the cork-ball will be endued with the fame property; fo that a fmaller ball will firft be attracted to- wards it, and then repelled from it, in the fame manner as the leaf-gold in the beforementioned experiments ; and on touching any other body, it will be again attracted ; and this may be repeated feveral times, provided the fmaller ball is much lefs than the larger one. But the effect will con- ftantly grow weaker and weaker ; becaufe every time the letter ball is attracted, it carries off with it fome of the elcdric virtue, and is likswife endued with the fame proper- ties as the larger ball.

Mr. Gray, Monfieur du Fay, and others have obferved, that this eleclrical quality is not only to be excited in glafs, but in mod folid bodies capable of friction, metals excepted ; though in fome it will fcarce be fenfible. And this eleclrical power is found to be ftrongeft in wax, refins, gums and glafs. And as glafs is the eafieft procured of a preper form, it has generally been ufed in making thefe experiments. It has been further obferved, that thofe bodies, in which the eleclrical quality is capable of being excited the ftrongeft'by fridtion, will receive the lead quantity of it from any other excited body, and therefore are properly made ufe of' to fupport any body defigned to receive the eleclrical virtue. The truth of this will fufficiently appear from the following experiments.

17. Two lines, one of filk, and the other of thread, being hung up, (as in the experiment, N° 5.) that of thread will be attracted by the tube at a much greater diftance than the filk. If a feather, or other light body, be faftened to each ftring, and if the tube be brought to the feather faftened to the filk, it will not only be firft attracted and then re- pelled, as has been faid N° 5, but by the virtue communi- cated to the feather from the tube, the feveral fibres of the feather will ftrongly repel each other. On the contrary, the feather faftened to the thread will be ftrongly attracted by the excited tube, and not repelled, the virtue paffing off by the thread it is hung to. If a glafs ball is hung to the filk line, it will be but weakly attracted by the tube; but one of cork or metal will be fo much more ftrongly.

18. Let a rod of iron be fuftained by filk lines, and by means of a glafs fphere (which can be more regularly and conftantly excited than a tube) be made eleclrical, it will be found to have all the properties of the excited tube firft: mentioned. A ftream of light will come from the end of it, if it is pointed. It will at'ract, repel, and communicate this virtue to any other non-eleclric body. On the approach of a mn-elctlric, a fpark of fire, with a fnap attending it, will come from it; which fpark will be greater or lefs, as the bodies approaching it have more or lefs of the eleclrical quality rcfiding in them ; and there will likewife be the fame offenfive fmell as was obferved of the glafs tube.

19. Let. a rod of iron, pointed at one end, be fufpended on filk lines, as in the laft experiment, and by the fphere be made eleclrical. When the rod is ftrongly electrified, a ftream of light in diverging rays will be feen to iflue from its point ; and if any non-eleclric body is held a few inches from the point, the. light will become vifible to a greater diftance j and if the non-eleclric body is likewife pointed, a light will feem to iflue from that in diverging rays, in the fame man- ner as from the electrified rod. But if the nm- eleclrical body- is flat, and held at the fame diftance from the rod as. the pointed one was, no light will be feen to come from it. It is alfo to be obferved, that the effluvia from the end of the eleclrified rod ftrike againft the hand or face, brought nea-r to that end, like a blaft of wind.

20. If the nor.-eleclric body, whether flat or pointed, be brought nearer to the end "of the rod than in the laft expe- riment, there will be a fmall ftream of light produced, reaching quite from the cleclric to the non-eleclric body ; and if brought frill nearer, there will iflue a fpark, attended with a fmalKnapping noife, which will be fucceeded by others at equal intervals ; and if the non-eleclric is held at fome diftance from the fide' of the rod, the point of it will fre- quently appear luminous, but no part of the electrified rod will be fo. If it is brought nearer, there will likewife he

fparks