ELECTRICITY.

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opposite side. The axis is supported by a single pillar A, whichfor this purpose is provided with a bearing piece lv, on which aretwo brass collar pieces, that carry the axis; and on the end of theaxis, opposite the glass, is a counterpoise 0, of lead, to preventtoo great a friction in the collar nearest the handle. The arc ofthe conductor EE, which carries the two small receiving conduc-tors FE , is fixed to an axis turning in the ball II. On the otherside of the plate is the other arc I, of brass wire, fixed in the bear-ing piece K, but so as to admit of being turned round like the arcEE. P is a copper tube, moving like a radius on the stem of theball S, which, being screwed into the conductor II, serves to con-fine the arm P, in any position that may be required. The dissi-pation of electricity along the glass supports is prevented by a kindof Cap T, of mahogany, which affords an electrical well or cavity•underneath, and likewise effectually covers the metallic cap intowhich the glass is cemented. The lower extremity of the pillar isguarded in the same manner by a hollow piece or ring of maho-gany V. The three glass pillars are set in sliding pieces WWW,adjustable by screws ; at each extremity of the horizontal diame-ter of the plate are two rubbers X, one-on each side, pressed re-gularly and uniformly against the plate by means of a spring Y,the force of pressure of which is regulated by means of a screw.To these rubbers are attached silk liaps ZZ, those of one pair of :rubbers descending, and those of the other pair ascending, in thedirection in which the plate is worked. A piece of line dry writ-ing paper, as long as the rubber, and half an inch broader, so asto cover tlie seam that fastens the silk to the leather, allows greaterpressure to be employed by diminishing the friction, and preventsboth the glass and silk from being soiled by the amalgam, so thatthe excitement is more powerful, and the amalgam requires to berenewed less frequently. As the semicircular branch of the primeconductor is moveable, it may be made to exhibit the electricityof the rubber at any time, hv placing the cylindrical ends in con-tact with the cushions, the semicircular wire 1, being at the sametime turned so as to cross it at right angles, which insulates thecushions. When the conductor is required to give electricity fromthe glass, the arc I must be in contact with the cushions, and thearc EE perpendicular to the horizon. It may not he improperhere to mention the extraordinary large and powerful machine inTcyler’s Museum at Haarlem ; which was constructed by Mr.John Cuthbertsou, an English mathematical instrument-maker. Itconsists of two circular plates of glass, each 65 inches in diameter,and made to turu upon the sam'e horizontal axis, at the distanceof 7\ inches from one another. These plates are excited by 8rubbers, each 15 \ inches long. Both sides of the plates are cover-ed with a resinous substance to the distance of l6j inches from thecentre, both to render the plates stronger, and likewise to preventany of the electricity from being carried off by the axis. Theprime conductor consists of several pieces, and is supported bythree glass pillars 57 inches in length. The plates are made ofFrench glass, as this is found to produce the greatest quantity ofthe electricity next to the English Hint, which could not be pro-duced of sufficient size. The conductor is divided into brancheswhich enter between the plates, but collect the fluid by pointsonly from one side of the plate. The force of two men is requir-ed to work this machine ; but when it is required to be put inaction for any length of time, four are necessary. At its iirst con-struction nine batteries were applied to it, each having fifteen jars,every one of which contained about a toot square of coated glass ;so that the grand battery formed by the combination of all thesecontained 135 square feet. Dr. Van Martini, who principallymade experiments with this machine, imagining that it was stillcapable of charging an additional quantity of coated glass, after-wards added to if t)0 jars of the same size with the former ; sothat it now contains a coated surface of 22b feet, and the effects arefound to be proportionable.

Of the Method op Using the electricai. Apparatus.

Young electricians often find cause to complain that the experi-ments described in treatises on electricity do not succeed withthem, though possessed of very good apparatus for making them.Besides the want of practice, which time and patience can onlysupply, this-is frequently owing to their not allending to someslight and seemingly trifiing'Ciroumstances ; such as dust or mois-ture aboii* the instruments; some small part of them being out of

vol. n.— no. 7*.

order ; the weather being too hot, or rainy, or the like. The fol-lowing directions should- therefore he particularly attended to byever'/student of electricity : Until he has acquired a very consi-derable degree of perfection by practice and habit, be should notcommence his operations in all kinds of weather. When the wea-ther is clehr and the air dry, especially if it be serene and frosty,the electrical machine will always work well. In such weatherthe young electrician will run no risk of being disappointed. Butwhen the weather is very hoi, the machine is not very powerful ',nor will it work in damp weather, unless it be brought into awarm loom, and the cylinder, stands, jars, discharges, See. bemade perfectly dry. Before the electrical machine is put in mo-tion, examine those parts which are liable to wear, either from thefriction of one surface against another, or to be injured by thedirt, that may insinuate itself between the rubbing surfaces. Ifany grating or disagreeable noise is heard, the place from whenceit proceeds must he discovered, wiped clean, and rubbed overwill: a small quantity of tallow; a little of which should also be oc-casionally applied to the axis of the cylinder itself. The screwsby which the frame is fixed should also he examined, and if theyare loose, they should be made tight. The machine being exa-mined and put in order, the glass cylinder, and the pillars whichsupport the cushion and conductor, should be well wiped with adry old silk handkerchief, to free them from the moisture whichglass attracts from the air ; being particularly attentive to leave nomoisture on the ends of the cylinder, as any damp on these partscarries off the electric fluid, aiid lessens the force of the machinesin very damp weather it will be proper to dry the whole machine,by placing it at some little distance from the lire. Particular careshould he taken that no dust, loose threads, or filaments, adherej to the cylinder, its frame, the conductors, or their insulating pil-lars ; because these will gradually dissipate the electric fluid, andprevent the machine from acting powerfully. When satisfied ofthis, rub the glass cylinder first with a clean, coarse, dry, warm,cloth, or a piece of wash leather, and then with a piece of dry, warmsoft silk ; do the same to all the glass insulating pillars of the ma-chine and apparatus; these pillars must be rubbed more lightlythan the cylinder, because, being varnished, they may be damagedby too much friction. In some cases it is proper to place a notiron on the foot of a conductor, to evaporate the moisture whichwould otherwise injure the experiments. After exciting the elec-trical machine, greasing the cylinder, and applying Dr. Higgins’samalgam, Ac. as above described, proceed to work it by turningthe winch or handle. When the prime conductors and other in-struments are removed from the machine, it will soon be perceiv-ed, upon bolding the knuckle of the fore-finger near the surfaceof the cylinder, that the electric fluid comes like a wind from thecylinder to the knuckle, and if the motion he continued, sparksand cracklings will soon follow. This indicates that the machineis in good order, and the electrician may proceed with his experi-ments. But if no wind be found upon the knuckle, the fault willprobably be in the rubbers. To remedy this, loosen the screwson the back of the rubber, remove it from its glass pillar, and keepit a little near the lire, that its silk part may be dried ; then pass alittle tallow from a candle over the leather of the rubber, spreada small quantity of the amalgam over it, and force it into the lea-ther as much as possible: after which, replace the rubber uponthe glass pillar, and wipe the cylinder once more, and the ma-chine will be fit for use. The following directions of Mr. Adams,relative to exciting the machine, will be found very useful. “Toexcite your machine, clean the cylinder, and wipe the silk.Grease the cylinder bv turning it against a greasy leather, till it isuniformly obscured. The tallow of a candle may be used. Turuthe cylinder till the silk flap has wiped off so much of the greaseas to render it semi-transparent. Put some amalgam on a pieceof leather, and spread it well, so that it may be uniformly bright:apply tiffs against the turning cylinder, the friction will immedi-ately increase, and the leather must not be removed until it ceasesto become greater. Remove the leather, and the action of themachine will be very strong. The pressure of the cushion cannothe too small, when the excitation is properly made.” Sometimesthe machine will not work well because the rubber is not suffici-ently supplied with electric fluid. This happens when the tableupon which the machine stands, and with which the chain of therubber is connected, is in a bad conducting state from being too3 Y dry.