ELECTRICITY. 489 



consequently always be surrounded by other electrified bo- 

 dies. I bring a brass ball highly charged with electrici- 

 ty, and suspended by a silk string or held by a glass 

 handle, so as to be insulated, over a table containing 

 upon it small pieces of paper. By induction the ball 

 electrifies the paper in a manner contrary to itself. The 

 ball and the paper are consequently in opposite electri- 

 cal states, and will therefore attract each other. The 

 papers will fly up to the ball. This experiment in sub- 

 stance, may be tried by the reader. Rub with a hot 

 silk handkerchief, a dry and clean tumbler ; it will be- 

 come electrified and will attract to it the bits of paper, 

 as well as if a brass ball were used. Suppose a thun- 

 der cloud highly charged with vitreous electricity is pass- 

 ing. Its influence is to electrify resinously the region 

 over which it moves, and it will be attracted by it, and 

 drawn down nearer the earth. And universally, an elec- 

 trified body produces an opposite electrical state in the 

 neighboring bodies, or parts of bodies, and then attracts 

 them. 



On the other hand if two bodies similarly electrified 

 are brought near each other, they repel. If, for exam- 

 ple, two pith balls, both electrified positively, are sus- 

 pended by threads near each other, they will recede, 

 and hang in diverging lines. 



This principle of repulsion between similar electrici- 

 ties, and attraction between those of an opposite charac- 

 ter, is the foundation of many amusing experiments, 

 some of which we shall proceed to describe. 



1. The pith balls. If one small pith or cork ball, is 

 suspended by a thread, and another, electrified, is brought 

 near to it, they will attract each other. If the stationa- 

 ry ball is previously electrified in a manner opposite to 

 the other, they will attract more strongly; if in a similar 

 manner, they will repel. 



2. The Electrometer. Electrometers are instruments 

 designed to measure electricity, or rather to indicate its 

 intensity. They are of several kinds. Two pith balls 

 suspended at the end of a rod of glass, diverge when 

 brought near any electrified body, for they become simi- 

 larly electrified, and repel each other. Sometimes a pith 



VOL. i. NO. xx. 43* 



