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ELECTRICITY.

dry. F.ven the floor r.nd the walls of the room are, in very dryweather, bad conductors, and cannot supply the rubber suffici-ently. In this case, the chain of the rubber must be connectedby a long wire with some water, moist ground, or the iron workof a water-pump ; which will soon supply the rubber with a suf-ficiency of the electric tluid; When the heat of the cylinder ex-ceeds 110’, it will mot act properly. If the machine does notwork well, when a sufficient (juantity of amalgam has been accu-mulated upon the leather of the rubber, then, instead of addingmore amalgam, it will be proper to take off the rubber, and toscrape a little off that which is already upon -the leather. Thecylinder, when used for some time, frequently contracts blackspots, occasioned by the amalgam or some foulness of the rubber.These spots must be carefully taken off, otherwise they will in-crease in size, and greatly obstruct the electric power of the cy-linder: which, to prevent contracting them, must be often wiped.When any experiment is to be performed w hich requires but asmall part of the apparatus, the remaining part of it should beplaced at a distance from the machine, the prime conductor, andeven from the table, if that is not very large. Candles, particu-larly, should be placed at a considerable distance from the primeconductor, for the effluvia of their ilames carry off much of theelectric fluid.

Or Charging and discharging Electric Jars andBatteries.

The phial beihg placed on the table, so that the ball on the topof its wire may be about one-eighth of an inch from the ball of theprime conductor, turn the machine, and sparks will fly from theball of the conductor to the ball of the jar. Continue turning aslong as you perceive the tire pass between the conductor and ballof the iar; but when it ceases, you may leave off turning, andconsider the jar as charged. This done, take hold of the dis-charger by the middle, and apply one knob to the outside coatingnear the bottom, and keeping it there, put the other to the ball ofthe jar, and it will be discharged of its fire with a loud snap ; butthe person who holds the discharger feels nothing from the dis-charge. If you charge the jar again, and touch the outside coat-ing with one hand, and then bring the other to the ball of the jar,you will act the part of the wire discharger, and receive a shockthrough your arms and breast, and the phial will be discharged.The same will be effected if a large company form a circle byjoining their hands, and the person at one extremity of the circletouch the outside coating,, while he, who is at the other extremity,touches the ball of the jar. All the persons who form this circ leare struck at the same time, and with the same degree of forcenearly. If you place a Leyden bottle upon the insulated stand,forming a communication between it and the conductor, and givethe machine a few turns, both sides of the bottle will be electrifiedwith the positive electricity, as may easily be proved by touchingthem with down, or a small ball suspended by silk ; for when thisis electrified by touching the outside, it will be also repelled bythe ball which communicates with the inner surface. Havingplaced an insulated bottle so that the ball may communicate withthe conductor ; let a wire also be connected with the coating, soas to forth a communication with the table. Next turn the ma-chine, and, 1. On applying a cork hall, you will not find anysigns of electricity in the coating, but you will find the ball (orinside) electrified with the positive pow er. 2. Kemove the wireconimunieating with the table, and you will find the coating alsoelectrified with the positive power; and this as often as you re-move the wire, till the bottle is full charged. 3. When the bottleis full charged, remove its communication both with the conduc-tor and table, touch the coating, and the cork ball will remainsuspended by it, without any sign of being electrified ; then touchthe knob of the bottle with your hand, the cork ball will bestrongly repelled from the coating, and be electrified with nega-tive electricity. 4. Take another cork ball suspended by silk,and touch the knob of the bottle therewith, and the cork ball willbe electrified with positive electricity, and be repelled. 5. Nowtouch the coating with your finger, and the cork ball will be re-plied much further by the ball; but that w hich was repelled fromthe coating, now flies towards it, and remains at rest, till youtouch tl'.e "knob of the bottle with your finger; it will then beelectrified as at first, and be violently repelled; the ball which

was electrified by the knob of the bottlo will now fly towards it.This change takes place almost instantaneously as often as the ballor coating is touched. The knob of the bottle may be made toconnect with the conductor by a wire, suspending a cork hall soas to touch the conductor; then, on touching the coating, the ballwill be repelled from the conductor, while that next the coating isattracted ; touch the knot) of the bottle, and the ball w ill be re-pelled from the routing, and attracted by the conductor, and soon as often as you please. In charging electric jars in general, itis to be observed, that every machine will not charge themequally high. Those machines which are strongest will alwayscharge the jars highest. If the coated jars, before they are madeuse of, be made somew-hat warm, they will receive and retain thecharge better, if several jars be connected together, amongwhich there is one that is apt to discharge itself very soon, (henthe other jars will also soon be discharged with it, although theymay be capable of holding a very great charge by themselves.When clectrip jars are to be discharged, the electrician must becautious, lest by some circumstance not adverted to, the shockshould pass through any part of his body ; for an unexpectedshock, though not very strong, may occasion disagreeable acci-dents. In making the discharge, care must be taken that the dis-charging rod be not placed on the thinnest part of the glass, asthat may cause the breaking of the jar. When a jar, and especi-ally a battery, lias been discharged, the electrician ought not totouch its w ires w ith his hand, before the disc barging rod be ap-plied to its sides a second and even a third lime ; as there gene-rally'remains a residuum of the charge, which is sometimes veryconsiderable. All the above-mentioned pluenomena are the moreremarkable in proportion to the power of the machine. That usedin Teyler’s Museum is astonishing in its effects, which are as fol-lows : On presenting a very sharp steel point to the prime con-ductor, a luminous stream of about half an inch was perceived be-tween them. On fixing the point to the conductor so as to pro-ject three inches from it, streams of light were thrown out fromthe point six inches long when a ball of three inches in diameterwas presented, but only two inches in length on presenting an-other point. The sensation, called the spider’s web, on the faceof the bystanders is often felt at the distance of eight feet from theprime conductor. This is a sensation always produced by strong,electricity, something resembling the creeping of insects or'themotion ot a light body, such as a spider’s web, over the skin. Itseems to proceed from the attraction and electrification of thesmall bail’s with which the body is covered. A thread six feet longwas sensibly attracted at the distance of thirty feet from the primeconductor, and a pointed wire appeared luminous at the distanceof twenty-eight feet; a cork ball electrometer diverged at the dis-tance of forty feet. A single spark from the conductor melted aconsiderable length of gold leaf; gunpowder and other combusti-bles, inclosed in a paper cartridge, with a sharp point in the mid-dle, were fired ; and when another conductor communicating withthe earth was placed at the distance of twenty-one, or sometimestwenty-four inches from thedprime conductor of the machine, astream of lire was perceived between them. This was crooked,and darted out many lateral brushes of a very large size. A Ley-drn phial, containing about one square foot of coated surface, wasso fully charged, by about half a turn of the winch, as to dischargeitself: and by repeated trials it was found, that in one minute itdischarged itself seventy-six, seventy-eight, and frequently eighty-times. Lastly, it was found, that though the conductor, which re-ceived the sparks from tiie prime one of the machine, communi-cated with the earth by a wire three-eighths of an irch in diame-ter, this wire would give small sparks to any conducting bodybrought near it, as if even this wire had not been sufficient to con-duct the quantity of electricity it received from the machine veryreadily to the earth.

Experiments exhibiting Electric Attraction andHkpulsion.

The Electrified Cork-Hall Electrometer. Fix at theend of the prime conductor a knobbed rod, and hang on it twosmall cork-balls suspended by threads of equal length. Theballs will now touch one another, the threads hanging per-pendicularly, and parallel to each other. But if the cylmdctof the machine he whirled by turning the winch, then the cork-balls will repel one another, more or less according as the electri-city