=115. Directions.= (A) Electrify E R, then hold it near the carbon of the electroscope.
(B) Bring the charged rod near little pieces of _damp_ tissue-paper.
_=116. Discussion of Experiments 56, 57, 58.=_ In 56 the two pieces of ebonite were made of the same material, and both were rubbed with flannel. They must have been similarly electrified. In 57, different parts of the same piece of paper were similarly electrified. In 58, the little piece of carbon took some of the electrification from the charged rod, just as it would take molasses from your finger should your sticky finger touch it. The electrification on the carbon must have been of the same kind as that on the rod. The carbon was _charged by contact_. We learn, then, that _two bodies repel each other when they have the same kind of electrification_. Do two charged bodies _always_ repel each other? Is it possible that there are different kinds of electrifications?
=EXPERIMENT 59. To study the electrification of glass.=
_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.