. Dental electro-therapeutics. glass rod, if it be positivelycharged the gold-leaf will diverge still further, but ifnegatively charged the gold-leaf will collapse. The glassrod used to test the electroscope will lose none of itselectrification, and on removing it the gold-leaf will relapseinto its former position. This sensitive instrument will determine if a body is onlyslightly charged with electricity; if the gold-leaf divergeever so little the body is charged. The Leyden Jar.—This is a convenient form of condenserand collector of electricity. It is usually constru
. Dental electro-therapeutics. glass rod, if it be positivelycharged the gold-leaf will diverge still further, but ifnegatively charged the gold-leaf will collapse. The glassrod used to test the electroscope will lose none of itselectrification, and on removing it the gold-leaf will relapseinto its former position. This sensitive instrument will determine if a body is onlyslightly charged with electricity; if the gold-leaf divergeever so little the body is charged. The Leyden Jar.—This is a convenient form of condenserand collector of electricity. It is usually constructed of aglass jar lined with tin-foil on the inside to within a fewinches of the top, and similarly coated on the the cork is passed a brass rod which terminatesexternally in a knob, and after going more than half-wayinto the jar, terminates in a brass chain resting on themetallic lining of the bottom of the jar. The foil liningthe inside and coating the outside constitutes the two 22 ELECTRO-PHYSICS Fig. 2. Leyden jar. conductors, the glass intervening, the dielectric of thecondenser. To charge the jar the knob is connected with the con-ductor of a working frictional machine, and the outercoat is connected with earth, the charge passing to theinner coating of the jar acts on the outercoating through the intervening dielectric byinduction. This induced current is conveyedaway to earth, leaving a charge of oppositesign held there by the charge on the innercoat. This increases the capacity of theinner coat. To discharge the jar it is only necessaryto bring a conductor which is in contactwith the outer coat near to the knob of thejar, when a spark will occur by the comingtogether of the two electricities, thus estab-lishing equilibrium. The quantity of electricity which the con-denser will contain depends on the surfacearea of the metallic lining and the strength of the the Leyden jar is made of very thin glass, and a chargeof very high potential p
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