EXPERIMENT 58. To study electrical repulsions.
Apparatus. Ebonite rod, E R (No. 28); a carbon electroscope, C E, [Fig. 31] (see [§ 114]); the support complete (see [§ 109]); small piece of damp tissue-paper.
114. The Carbon Electroscope. Light an ordinary match, and let it burn until it is charred through and through. The black substance remaining is carbon. This is very light; it has, also, another important property which you will soon understand. Tie a small piece of the carbon to one end of a dry silk thread, and fasten the other end of the thread to the support wire, S W, which is fastened to the support ([Fig. 31]). We shall call this piece of apparatus the carbon e-lec-tro-scope. (See [Electroscopes], Chapter XVIII., Apparatus Book.)
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?