Page:Popular Science Monthly Volume 9.djvu/181

Rh Discharge the egg by touching it. Reëxcite the glass tube and bring it again near. Touch the egg with a wire or with your finger at a. Is it the negative at a, into which you plunge your finger, that escapes? No such thing. The free positive fluid passes through the negative, and through your finger to the earth. Prove this, by removing first your finger and then the glass tube. The egg is charged negatively.

Again: place two eggs, E E, Fig. 12, lengthwise on two dry wineglasses, g g, and cause two of their ends to touch each other, as at C. Bring your rubbed glass rod near the end a, and while it is there separate the eggs by moving one glass away from the other. Withdraw the rod and test both eggs: a is negative, b is positive. The two charges neutralize each other in the electroscope. Again: bring the eggs together and restore the rubbed tube to its place near a. Touch a and then separate the eggs. Remove the glass rod and test the eggs: a is negative, b is neutral. Its electricity has escaped through the finger, though placed at a.

Push your experiments still farther, and, instead of bringing the eggs, T T',  Fig. 13, together, place them six feet or so apart, and let a light chain, C, or wire stretch from one to the other. Two brass



balls or wooden balls covered with tin-foil, and supported by tall drinking-glasses, G G  will be better than the eggs for this experiment, for they will bear better the strain of the chain; but you can make the experiment with the eggs, or very readily with two apples or two turnips. For the present we will suppose the straw-index I I'  not to be there. Rub your glass tube R, and bring it near one of the balls; test both: the near one, T', is negative, the distant one, T, positive. Touch the near one, the positive electricity, which had been driven along the chain to the remotest part of the system, returns along the chain, passes through the negative which is held captive by the tube, and escapes to the earth. When the tube is removed, negative electricity overspreads both chain and balls.

In Fig. 6 you made the acquaintance of the plate N, and the