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270

ELECTRICITY.

end D is a valve properly secured under the brass plate ; a brasswire with a ball projects from the upper cap ; a pointed wire pro-ceeds from the bottom plate; ami this tube is called the luminousconductor. The flask represented at E is called the Leyden Va-cuum. It is furnished with a valve under the ball E; to come atwhich the more readily', the ball may be unscrewed: a wire, witha blunt end, projects "to within a little of the bottom of the flask,the latter being coated with tin-foil: and a female screw is ce-mented to the bottom, to screw it on the pillar A.—K is a syringeto exhaust the air occasionally, either from the luminous conductoror the Leyden vacuum. To do this, unscrew the ball of the Ley-den vacuum, or the plate of the luminous conductor, and thenscrew the syringe in the place of either of these pieces, being care-ful that the bottom of the female screw G bears close against theleather which covers the shoulders ah or ed\ then work the sy-ringe, and in a few minutes the glasses will be sufficiently exhaust-ed. M and I are two Leyden bottles; each of which has a femalescrew iitted to the bottom, that they may be conveniently screwedon the pillar A; and the bottle 11 is furnished with a belt by whichit may be screwed sidewise to the same. K and 1. are two small. wires, to be screwed occasionally either into the ball E, the knobsc or/, the cap C, or the socket g on the top of the pillar : the ballsmay be unscrewed from these wires, which will then exhibit a bluntpoint. M is a wooden table to be screwed occasionally on theglass pillar.

To PIERCE VARIOUS SuiiSTANCF.S WITH THE ELECTRIC EX-PLOSION. "l ake a card, a quire of paper, or the cover of a book,and keep it close to the outside coating of a charged jar; put oneknob of the discharging rod upon the card, quire of paper, &c. sothat between the knob and coating of the jar the thickness of thatcard, or quire of paper, only is interposed ; lastly, by bringing theother knob of the discharging roil near the knob of the jar, makethe discharge, and the electric matter will pierce a hole (or per-haps several) quite through the card or quire of paper. This holehas a bur raised on each side, except the card, &c. I«e pressed hardbetween the discharging rod and the jar; which shews that thehole is not made in the direction of the passage of the fluid, butin ever-v direction from the centre of the resisting body. If in-stead of paper, a very thin plate of glass, rosin, fcaimg-wax, or thelike, be interposed between the knob of the discharging rod andthe outside coating of the jar, on making the discharge, this will bebroken in several pieces. Small insects may also be killed in thismanner. They may be held between the outside coating of thejar and the knob of the discharging rod, like the above card ; anda shock of a common phial sent through them, w ill instantly de-rive them of life, if they are pretty small; but if larger, they will>e affected in such a manner, as to appear quite dead on first re-ceiving the stroke ; but will, after some time, recover : this, how-ever, depends on the quantity of the charge sent through them.

Effect of the Shock sent over the Surface of a Cardor Glass. Put the extremities of two wires upon the surface ofa card, or other body of an electric nature, so that they may liein one direction, and about one inch distant from one another;then, by connecting one of the w ires with the outside of a chargedjar, and the other wire with the knob of the jar, the shock willbe made to pass over the card or other body. If the card be madevery dry, the lucid track between the wires will be visible uponthe card for a considerable time after the explosion. If a pieceof common writing paper be used instead of the card, it will hetorn by the explosion into very small bits. If the explosion hesent over the surface of a piece of glass, it w ill be marked with anindelible track, w hich generally reaches from the extremity of oneof the wires to the extremity of the other. In this manner, thepiece of glass is very seldom broken by the explosion. Hut Mr,llenly discovered a very ingenious method to increase the effectof the explosion upon the glass, by pressing with weights that partof the glass which lies between the two w ires i. c. the part overwhich the shock is to pass, lie put a thick piece of ivory uponthe ghus, and placed upon it a weight, from one quarter of anounce to six pounds. The glass in this manner is generally brokenbv the explo-ion into innumerable fragments, and some of it is ab-solutely reduced into an impalpable powder. If the glass be vervthick, "and resist the force of the explosion, so as not to be broken",it will be marked with the most lively prismatic colours, which arethought to be occasioned by very thin lamina; of the glass, partly

separated from it by the shock. The weight laid upon the glass isalways shaken by the explosion, and sometimes it is thrown quiteoff from the ivory. This experiment may be most convenientlymade with the universal discharger, fig. 7,"Plate I-X111. In thisexperiment, Mr. Cavallosays, “ if small representations of houses,& c. belaid upon a board, placed on the piece of ivory, that, beingshook by the explosion, w ill give a verv natural idea of an earth-quake.” As to the direction of the electric fluid, the followingexperiments have been thought to prove directly the passage ofthe fluid outward from the positive and inward to the negative sideof the phial. Eig. 8, Plate LX IV. represents an electric jar,whose exterior coating is made up of small pieces of tin-foil placedat a little distance from each other. It is to be charged in the usualmanner, when small sparks of the electric fluid will pass from onepiece of tin-foil to the other, in various directions, forming a verypleasing spectacle. The separation of the tin-foil is Hr* cause ofthis visible passage of the fluid from the outside to the table, andthe experiment is similar in appearance to that of the spiral tubeabove-mentioned, if the jar be discharged by bringing a pointedwire gradually to the knob, T, the unsealed part of the glass be-tween the wire and knob will be agreeably illuminated with acrackling noise of the sparks. If the jar be suddenly discharged,the w hole outside will be illuminated. The jar, in this experiment,must be very dry when used. Fig. 22 represents two jars, orI.eyden phials, placed one over the other, by which several curi-ous experiments may be made. Bring the outside coating of thebottle A in contact with the prime conductor, and turn the ma-chine till the bottle is charged ; then place one ball of the discharg-ing rod upon the coating of B, and with the other touch thekimbof tliejar A, which will cause an explosion ; now place one ballof the discharger on the knob A, and bring the other ball to itscoating, and you have a second discharge. Again, apply one ballof the discharger to the coating of B, and carry the other to thecoating of A, and it will produce a third discharge. A fourth isobtained by applying the discharger from the coating of A to itsknob. The outer coating of the upper jar communicating withthe inside of the upper one, conveys the fluid from the conductorto the large jar, which is therefore charged positively: the upperjar does not charge, because the inside cannot part with any of itselectric fluid ; but when a communication is formed from the out-side of A to tlie inside of B, part of the tire on the inside of A willhe conveyed to the negative coating ot B, and the jar will be dis-charged. The second explosion is occasioned by the discharge ofthe jar A ; but as the outside of this communicates, by tonduct-ing substances, with the positive inside of the jar B, if the ball ofthe discharging rod remain for a little time after the discharge onthe knolj of A, part of the lire ofjlie inside of A will escape, andbe replaced by an equal quantity on the outside from the jar B, bywhich means A is charged a second time; (he discharge of this pro-duces the third, and of B the fourth explosion. Fig. 2d is an electricjar,which serves to illustrate the direction oft he fluid while charginga Leyden phial. B B is the tin-foil coating; G a stand which sup-ports tliejar ; I) a socket of metal, carrying the glass rod E, abent brass wire pointed at each end, and fixed at the end of therod G ; which rod is moveable in the spring tube Is at pleasure:that tube being fixed by a socket on the top of the glass rod Kthe juris charged by the inside wire, which communicates with thedifferent divisions of the inside coating by horizontal wires. Placethe jar to the conductor as usual; and, when charging, a luminousspeck will appear upon the upper point of the w ire at E, clearlyshewing, according to the commonly received opinion, that thepoint is then receiving the electric fluid. From the upper ring of thecoating B, on the outside of the jar, a fine stream or pencil of rayswill at the same time fly off, beautifully diverging from the lowerpoint of the wire E upon the bottom ring of the coating of the jar.When the appearances cease, which they do when the jar ischarged, let a pointed wire be presented towards the conductor:this will soon discharge the jar silently; during which the pointwill be illuminated with a small spark, while the upper point ofthe wire will throw off a pencil of rays diverging towards the up-per ring of the coating.

To Discharge a Jar Silently.

When a large jar is fully charged, which would give a terribleshock, put one of your hands in contact with its outside coating;

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