. The evolution of forces . esucceeding, but not superposed on, each is impossible to confuse them, for to eachof them there corresponds a different charge ofelectricity. In the case of Fig. 5 the plate-like form of theinfluenced body is the cause that the sign of thecharge does not change, and that the leaves fallwhen the electrified rod is withdrawn. In the case of Figs. 4 and 3 it is quite otherwise;the leaves remain charged when we take away therod. With the electroscope of Fig. 4 the experi-ment is effected in a few seconds, while it is neces-sary to continue the presence of the
. The evolution of forces . esucceeding, but not superposed on, each is impossible to confuse them, for to eachof them there corresponds a different charge ofelectricity. In the case of Fig. 5 the plate-like form of theinfluenced body is the cause that the sign of thecharge does not change, and that the leaves fallwhen the electrified rod is withdrawn. In the case of Figs. 4 and 3 it is quite otherwise;the leaves remain charged when we take away therod. With the electroscope of Fig. 4 the experi-ment is effected in a few seconds, while it is neces-sary to continue the presence of the ebonite rodfor some twelve minutes for it to succeed with theball electroscope of Fig. 3. The explanation of the maintenance of the chargeor of its reversal after the rod of ebonite has beenwithdrawn is very simple. Take, for example, the case of Fig. 3. The chargeof the ball under the influence of the action of thenegatively electrified ebonite rod is, as we know, at THE EVOLUTION OF FORCES first positive, and that of tlie. leaves the ball istouched withthe finger, aswhen we chargean electroscopeby influence, thenegative chargepasses into theearth, while thepositive charge,kept back by thenegative electri-city of the rod,remains on theball and flowsinto the leaves assoon as the finsferand the electricrod are with-drawn. Finally,the leaves arecharged posi-tively. If the eboniterod bo left asufficient timenear the ball, wenote, on the con-trary, that whenit is withdrawnwithout touch-ing the ball ofthe electroscope THE TEANSFOEMATION OF MATTER 123 with the finger, tlie leaves remain negatively chargedinstead of positively. Why ? As soon as the ebonite rod is brought close to theball of the electroscope it becomes positively chargedby influence—as in the experiment with the cylinderrelated in another paragraph — and the negativeelectricity is drawn into the leaves. If, instead ofwithdrawing the ebonite rod, its presence is pro-longed, it strongly attracts the parti
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