Page:Popular Science Monthly Volume 9.djvu/192

172 the air. Bring the tube near the leaf: it plunges toward the tube, stops suddenly, and then flies away. You may chase it round the room for hours without permitting it to reach the ground. The leaf is first acted upon inductively by the tube. It is powerfully attracted for a moment, and rushes toward the tube. But from its thin edges and corners the negative electricity streams forth, leaving the leaf positively electrified. Repulsion then sets in, because tube and leaf are electrified alike. The retreat of the tassel in the last experiment is due to a similar cause.

There is also a discharge of positive electricity into the air from the more distant portions of the gold-leaf, to which that electricity is repelled. Both discharges are accompanied by an electric wind. It is possible to give the gold-leaf a shape which shall enable it to float securely in the air by the reaction of the two winds issuing from its opposite ends. This is Franklin's experiment of the Golden Fish. It was first made with the charged conductor of the electrical machine.



M. Srtsczek revived it in a more convenient form, using instead of the conductor the knob of a charged Leyden-jar. You may walk round a room with the jar in your hand; the "fish" will obediently follow in the air an inch or two, or even three inches, from the knob. (See A B, Fig. 22.) Even a hasty motion of the jar will not shake it away.

Well-pointed lightning-conductors, when acted on by a thunder-cloud, behave in the same way. The opposite electricity streams out from them against the cloud.

Franklin saw this with great clearness, and illustrated it with great ingenuity. The under-side of a thunder-cloud, when viewed