Apparatus. The sheet of glass, G (No. 38), heated (a hot bottle or lamp chimney will do); a piece of silk large enough to rub G. (A silk handkerchief is just the thing, but in case you have no silk, use the flannel cloth, F C, No. 30.)
117. Directions. (A) Vigorously rub the hot glass with the silk (or flannel), also heated.
(B) Test G for electrification by means of little pieces of tissue-paper and the carbon electroscope, [Exp. 58].
118. Questions. Will two pieces of electrified glass repel each other? Arrange an experiment to show whether you are right or not. Is the charge on the glass exactly like that on the ebonite? Do you know how to find out?
EXPERIMENT 60. To compare the electrification produced by ebonite and flannel with that produced by glass and silk.
Apparatus. The support (see [§ 109]); wire swing, W S (No. 37); ebonite rod, etc., of [Exp. 55] ([Fig. 29]); the glass, G, and silk of [Exp. 59].
119. Directions. (A) Electrify E R, and place it in W S, [Fig. 29].
(B) Bring the uncharged glass near E R, noting the action of E R.
(C) Heat and electrify G; bring it near E R, and carefully note whether the attraction between them is stronger or weaker than before, or whether they repel each other.