LESSONS IK ELECTRICITY. 



813 



FIG. 32. 



Fio. 33. 



FIQ. 34. 



pcrcha or glass, at a distance from the 

 conductor, and connect both by a fmo 

 wire. Bend your stout wire into a hook, 

 and hang from it a tassel, T, composed 

 of many strips of light tissue paper. 

 Work the machine. Electricity from the 

 conductor flows over the tassel, and the 

 strips diverge. Hold your closed fist 

 toward the tassel, the strips of paper 

 stretch toward it. Hold the needle, de- 

 fended by the finger, toward the tassel : 

 attraction also ensues. Uncover the needle 

 without moving the hand ; the strips 

 retreat as if blown away by a wind. 

 Holding the needle, N, fig. 31, upright 

 underneath the tassel, its strips discharge 

 themselves and collapse utterly. 



And now repeat Du Fay's experiment 

 which led to the discovery of two electric- 

 ities. Excite your glass tube, and hoi 1 

 it in readiness while a friend or an assist- 

 ant liberates a real gold or silver leaf in 

 the air. Bring the tube near the leaf : 

 it plunges toward the tube, stops sud- 

 denly, and then flies away. You may 

 chase it round the room for hours with- 

 out permitting it to reach the ground. 

 The leaf is first acted upon inductively 

 by the tube. It is powerfully attracted 



for a moment, and rusnrs toward the 

 tube. But from its thin edges and cor- 

 ners the negative electricity streams forth, 

 leaving the haf positively electrified. 

 Repulsion then sets in, because tube and 

 leaf are electrified alike, as shown in fig. 

 32. 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 dis- 

 tant portions of the gold -leaf, to which 

 that electricity is repelled. Both dis- 

 charges 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 an electrical ma- 

 chine. 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 throe inches, from the 

 knob. Sec A B, fig. 33. Even a hasty 

 motion of the jar will not shake it away, 



