[Illustration: FIGS. 26 to 29.--Explanation of Faraday’s ice pail experiment. For simplicity the electroscope, insulating stand and silk thread have been omitted. Only the three principal conductors K, P, and the earth E are shown. In fig. 26 the ball K is sufficiently close to P to act inductively on it; six lines are shown as falling on P, and the other six as passing to E by different paths. Corresponding to the six lines falling on P from K, six others pass to E from the lower surfaces. In fig. 27 where K is just entering the pail, two lines only pass from K to E through the dielectric; the remaining ten fall on P, and ten others starting from the distant parts of P pass to E. In fig. 28, K is so far within P that none of its lines can reach E through the dielectric; they all fall on P and from the outside of P an equal number start and pass through the dielectric to E. It is evident that in this position K can be moved about within P, without affecting the outside distribution in the slightest, and that even when K touches P as shown in fig. 29, and when, therefore, all lines between them disappear, the lines in the dielectric outside remain just as they are in fig. 28. K is now completely discharged, since lines no longer emanate from it, hence it can be removed by the silk cord without disturbing the electrification of P. If K be again charged and introduced into P it will be again discharged, for the fact that P is already charged will have no effect on the final result, provided when K touches P it is well _under cover_.] Since the electricity thus yielded by the electrophorus is not obtained at the expense of any part of the original charge, it is a matter of some interest to inquire whence is the source from which the energy of this apparently unlimited supply is drawn; for it cannot be called into existence without the expenditure of some other form of energy. The fact is, _more work is done in lifting the cover when it is charged_ with the positive electricity than when it is not charged; for when charged, there is the force of the electric attraction to be overcome as well as the force of gravity; this excess force is the real origin of the energy stored up in the separate charges. [Illustration: FIGS. 30 and 31.--The Leyden jar and discharger. Its discovery is attributed to the attempt of Musschenbrock and his pupil Cuneus to collect the supposed electric “fluid” in a bottle half filled with water. The bottle was held in the hand and was provided with a nail to lead the “fluid” down through the cork to the water from the electric machine. The invention of the Leyden jar is also claimed by Kleist, Bishop of Pomerania.]