Page:Popular Science Monthly Volume 9.djvu/191

Rh sealing-wax, A. Connect the sewing-needle with the machine, and turn. A wind of a certain force is discharged from every point, and the cross is urged round with the same force in the opposite direction.

You might easily, of course, so arrange the points that the wind from some of them would neutralize the wind from others. But the little pointed arms are to be so bent that the reaction in every case shall not oppose, but add itself to, the others.



The following experiments will yield you important information regarding the action of points: Stand, as you have so often done before, upon a board supported by four warm tumblers. Hold a small sewing-needle, with its point defended by the forefinger of your right hand, toward your Dutch metal electroscope. Place your left hand on the prime conductor of your machine. Let the handle be turned by a friend or an assistant: the leaves of the electroscope open out a little. Uncover the needle-point by the removal of your finger: the leaves at once fly violently apart.

Mount a stout wire upright on the conductor of your machine; or support the wire by sealing-wax, gutta-percha, or glass, at a distance from the conductor. Connect both by a fine wire. Bend your stout wire into a hook, and hang from it a tassel composed of many strips of light 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, defended 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.

And now repeat Du Fay's experiment which led to the discovery of two electricities. Excite your glass tube, and hold it in readiness, while a friend, or an assistant, liberates a real gold or silver leaf in