. The American encyclopædia of commerce, manufactures, commercial law, and finance. y a smaller rod, r. The action of themachine is founded on the excitation of electric- ELECTRICAL MACHINE 315 ELECTHICITY ity by friction, and on tlie action of induction.By friction with the rubbers, the glass becomespositively, and the rubbers negatively electrified ;but the rubbers communicate with the groun<l bymeans of a chain, and, consequently, as fast asthe negative electricity is generated, its tension isreduced to zero by contact witii the ground. Theposiiiveelectricityof the gla^sads then by induc
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. The American encyclopædia of commerce, manufactures, commercial law, and finance. y a smaller rod, r. The action of themachine is founded on the excitation of electric- ELECTRICAL MACHINE 315 ELECTHICITY ity by friction, and on tlie action of induction.By friction with the rubbers, the glass becomespositively, and the rubbers negatively electrified ;but the rubbers communicate with the groun<l bymeans of a chain, and, consequently, as fast asthe negative electricity is generated, its tension isreduced to zero by contact witii the ground. Theposiiiveelectricityof the gla^sads then by inductionon the conductor, attracting the negative electricity.This negative electricity collects in the pointsopposite to the glass. Hero its tension or ten-dency to discharge becomes so high that it passesacross the intervening space of air, and neutral-izes the positive electricity on the glass. Theconductors thus lose their negative electricity, anil remain charged with positive electricitj.Before use, the rubbers are coated cither withpowdered Aurum musivum (sulphuret of tin), or. Fig. 156, — Klsctbical M.cuine. graphite, or amalgam. If the hand be broughtnear the conductor when charged, a spark fol-lows, which is renewed as the machine is turned.In tills case the positive electricity decomposes theneutral fluid of the body, attracting its negativeelectricity, and combining with it when the twohave a sufficient tension. Thus, with each sparkthe conductor reverts to the neutral state, but be-comes again electrified as tlie plate is turned.The PldtK mnrliiiie, which is now much used in thiscountry, consists of a thick plate of glass mountedon a horizontal a.xis and turned by a crank. At eachend there is a glass standard, the one surmountedby a brass ball called the nfr/nlii-e conductor, the other by a long cylinder of brass with rotmdedends, called the ininie or /lusitice ironductor. Fromthe standard of the negative conductor projecttwo brass strips in the form of a clamp, wlii