. The principles of physics. , the attraction exceeds the 340 ^QG. Electrification confined to the outside siir- face of a conductor. Metal screens. Experiment G.—Place a tin cup, A (Fig. 341), on a glass tumblercoated with shellac and charge it heavily with electricity from an electri-cal machine (see Section V.). Introduce a proof-plane into the cup and touch the interior surface of Hthe cup. Remove the proof-plane and place it near ^^ electroscope; the leaves of the electroscope are ff^flffi -Hunaffected,. Njff .; J ?l-i j Ti If a solid metal ball, A (Fig; 342), sus-
. The principles of physics. , the attraction exceeds the 340 ^QG. Electrification confined to the outside siir- face of a conductor. Metal screens. Experiment G.—Place a tin cup, A (Fig. 341), on a glass tumblercoated with shellac and charge it heavily with electricity from an electri-cal machine (see Section V.). Introduce a proof-plane into the cup and touch the interior surface of Hthe cup. Remove the proof-plane and place it near ^^ electroscope; the leaves of the electroscope are ff^flffi -Hunaffected,. Njff .; J ?l-i j Ti If a solid metal ball, A (Fig; 342), sus-pended by an insulating thread, be electrifiedand then covered with two hemisphericalmetallic cups, B and C, having insulatinghandles, and the cups be afterwards re-moved, the ball when tested with the elec- rie. will be found to have lost all its charge, while thecups will be found to be charged. It does not make theslightest difference as to the result whether an insulated pabadays ice-pail experiment. 445. Fig. 342. conductor be solid or hollow. Wood covered with tin-foilanswers the purpose as well as any other body. If a hollow conductor hecharged, however highly,with electricity, the wholeof the charge is foundupon the outside the electroscope inthe last experiment wereplaced inside the tin cup,or if it be set inside a vessel of wire gauze ( a bird cage),and the vessel be charged with electricity or a heavilycharged body be brought near the vessel, the electroscope willbe unaffected. This interesting and important fact showsthat a m,etallic shell, however thin, entirely screens bodies insideit from external electrification, however great.^ 407. Faradays Ice-pail Experiment. Experiment 7. — a. Insulate well a tin pail (Fig. 343) and connect itwith an electroscope. Charge heavily a metal ball suspended by an in-sulating thread, with (say) -l-E. Lowerthe ball within the pail; the pail be-comes charged by induction, insidewith — E and the outs
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectphysics, bookyear1895
