LESSONS IN ELECTRICITY. 



161 



Discharge the egg by touching it. Reexcite 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 re- 

 moving 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 



Fig. 13. 



balls or wooden balls covered with tin-foil, and supported by tall 

 drmking-glasses, G G\ will be better than the eggs for this experi- 

 ment, 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 IF 

 not to be there. Rub your glass tube JR, 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, nega- 

 tive electricity overspreads both chain and balls. 



In Fig. 6 you made the acquaintance of the plate A 7 ", and the 



VOL. IX II 



