ELECTRICITY.

that if the phial, or tube, after it 1ms been removed from’the primeconductor (and even several hours after its fla-hing light has ceasedto appear), he grasped with the hand, strong flashes of light willimmediately appear within the glass, which often teach from oneend of it to the other.

The Visible Electric Atmosphere, is an experiment ofSignior Beccaria. GI, fig. 19, Plate LXII1. represents the re-ceiver with the plate of an air-pump. In the middle of the plate1 F, a short rod is lixed, having at its top a metal hall 15 nicelypolished, whose diameter is nearly two inches. From the top ofthe receiver, another rod A D, with a like ball A, proceeds, andis cemented air-tight in the neck C ; the distance of the balls fromone another being about four inches, or rather more. If, whenthe receiver is exhausted of air, the ball A be electrified positively,by touching the top D of the rod AD with the prime conductor,or an excited glass tube, a lucid atmosphere appears about it,which although it consists of a feeble light, is yet very conspicuous,and very well defined; at the same time, the ball 15 has not theleast light. This atmosphere does not exist all round the hall A ;but reaches from about the middle of it, to a small distance be-yond that side of its surface which is next the opposite ball B. If(he rod with the ball A be electrified negatively, then a lucid at-mosphere, like the above described, will appear upon the ball B,reaching from Us middle to a smail distance beyond that side of itthat is towaulsthe ball A; at the same lime, the negatively elec-trified ball A remains without any light. The operator in this ex-periment must take care not to electrify the ball A too much ; elsethe electric fluid will pass in a spark from the one ball to the other,and the experiment will fail. “ By this elegant experiment ofthe celebrated F. Beccaria, says Mr. Cavallo, we have an oculardemonstration of the theory of a single electric fluid. We seethat electricity consists of one uniform homogeneous fluid, and notof two, viz. the vitreous and resinous, as some have supposed ; for,if the positive and negative electricity were two distinct fluids, at-tractive of one another, there should in the above experiment al-ways appear two atmospheres, i. e. one about the ball A, andanother about the ball B ; for when the ball A is overcharged witheither fluid, it should shew that superfluous fluid on its surface,and this lluid should attract towards the ball A an atmosphere ofthe contrary lluid from the ball B. But this is not the case, forthe lucid atmosphere is always on one ball, namely, that which isovercharged with the electric fluid: thus when the ball A is elec-trified positively, the superfluous fluid is visible on that part of itwhich is nearest to the ball 15, because B, being in a contrary stateof electricity, endeavours to attract it; but when the ball A is elec-trified negatively, it will attract the fluid proper to the ball 15,which fluid on that account appears on the surface of 15, just in theact of leaping to the hall A.”

The SfiralTubes. Fig. 20, Plate I.XI11, represents nn in-strument composed of two glass tubes C D, one within another,and closed with two knobbed brass caps A and 15. The innermostof these has a spiral row of small round pieces of tin-foil stuck uponits outside surface, and lying at about one-30th of an inch fromeach other. If this instrument he held by one of its extremities,and its other extremity he presented to the prime conductor, everyspark it receives from the prime conductor will cause small spark'sto appear between all the round pieces of tin-foil stuck upon theinnermost tube ; which in the dark allords a pleasing spectacle, theinstrument appearing encompassed by a spiral line of lire. Fig.21 represents several spiral tubes placed round a board, in themiddle of which is screwed a glass pillar, and on the top of this pil-lar is cemented a brass cap with a line steel point. In this a brasswire turns, having a brass ball at each end, nicely balanced on thewire. To make use of this apparatus, place the middle of theturning w ire under a ball proceeding from the conductor, so thatit may receive a succession of sparks from the ball; then push thewire gently round ; and the halls in the'w relative motions willgive a spark to each tube, and thereby illuminate them down tothe board, which from its brilliancy and rapid motion affords amost beautiful and pleasing sight. The small pieces of tin-foil aresometimes stuck on a Hal piece of glass ABC D, tig. 22, so as torepresent various fanciful figures. Upon the same principle, istlie luminous word light produced. It is formed by the smallseparations of the tin-foil pasted on a piece of glass fixed in a frameof baked wood, as represented lig. 23. 1 o use this, the frame

VOL. 11.—NO. 79.

must he held in the hand, and the ball G presented to the con-ductor. The spark then will be exhibited in the intervals com-posing the word; from whence it passes to the hook at A, rr.dthence to the ground by a chain. The brilliancy of this is equalto that of the spirals. A similar effect will be produced by the jar,iig. 8, Plate LX IV, coated bv detached pieces of tin-foil; it willexhibit the electric light passing from piece to piece, both whilecharging and discharging.

To fire a Pistol or Cannon bv inflammable Air. Fi;$.24 represents a brass pistol for inflammable air. It -consists prii»>cipally of achamber, to the mouth D of which a cork is fitted; aglass tube F is cemented into the top of the chamber, throughwhich a brass wire passes, and is bent within side so as to approachwithin an 8th part of an inch of the side. On the outside end ofthis wire is screw ed a brass ball A, which serves to receive a sparkfrom the conductor of the machine, and conduct it in that form tothe inside of the pistol. The inflammable air with which the pis-tol is to he charged may be made in a common stone-ware or glassbottle, by mixing a handful of iron-filings with about two wineglassfuls of water and near one of oil of vitriol. The air, w henthus made, should be kept in a bottle corked up. To use thepistol, lake out the cork from the bottle, and instantly apply themouth of the pistol to the mouth of the bottle; and in about tenseconds it will be sufficiently charged : then remove it, and corkboth the pistol and bottle with the utmost expedition : then bringthe ball A near the prime conductor or the knob of a charged jar;and the spark that passes through the ball, and between the end ofthe wire within the side of the chamber, will fire the inflammableair with a loud report, and drive the cork to a considerable dis-tance. Instruments to lire inflammable air are often made in theform of a cannon with its carriage, as in fig. 23.

To illuminate Ivory or Box-Wood. Place an ivory ballon the prime conductor of the machine, and take a strong spark,or send the charge of a Leyden bottle through its centre, the hallwill appear perfectly luminous ; but if the charge be not takenthrough the centre, it will pass over the surface of the hall and cor-rode it. A spark taken through a ball of box-wood not only il-luminates the whole, hut makes it appear of a beautiful crimson orrather line scarlet colour.

To illuminate Water. Connect one end of a chain withthe outside of a charged jar, and let the other lie upon the table..Place the end of another piece of chain at about one quarter of aninch from the former; then set a decanter of water on these sepa-rated ends ; and on making a discharge, the water will appear per-fectly and beautifully luminous.

Experiments with the Ueyden Phial.

The Leyden Vacuum is an invention of the late Mr. Ilenlv.Fig. 26 and 27, Plate LXI1I. represent tw o small phials coated onthe outside, about three inches up the sides, with tin-foil; at thetop of the neck of each, a brass cap is cemented, having a holewith a valve, and from the cap a wire proceeds a few inches withinthe phial, terminating in a blunt point. When this phial is ex-hausted of air, a brass ball is screwed upon the brass cap, which iscemented into its neck, so as to deleiul the valve, and prevent anyair from getting intq the exhausted glass.. This phial exhibitsclearly the direction of the electric fluid, both iq charging and dis-charging ; for if it be held by its bottom, and its brass knob bepresented to the prime conductor positively electrified, it will heseen that the electric lluid causes the pencil of rays to proceedfrom the wire within the phial, as represented iig. 26 ; and if it isdischarged, a star will appear in the place of the pencil, as repre-sented in lig. 27. But il the phial is held by the brass cap, andits bottom be touched with the prime conductor, then the pointof the wire on its inside will appear illuminated with a star whencharging, and w ith a pencil when discharging. . If it he presentedto a prime conductor electrified negatively, all these appearances,both in charging and discharging, will be reversed.

The Apparatus, represented fig. 7, PlateLXi V.will be foundvery convenient for the various experiments upon the luminousconductor, Leyden vacuum, jars charged positively or negatively,with their different states of insulation. A is an insulating pillarof glass, which is screwed to the wooden foot 15; and on this pil-lar all the apparatus may be screwed alternately. CD is an ex-hausted tube of glass, furnished at each end with'brass caps; at the3'A . end