4 6 



ELEMENTARY LESSONS ON [CHAP. I. 



With the abundant supply of electricity afforded by 

 the electrical machine, many pleasing and instructive 

 experiments are possible. The phenomena of attrac- 

 tion and repulsion can be 

 shown upon a large scale. 

 Fig. 25 represents a device 

 known as the electric 

 chimes, 1 in which two small 

 brass balls hung by silk strings 

 are set in motion and strike 

 against the bells between 

 which they are hung. The 

 two outer bells are hung by 

 metallic wires or chains to 

 the knob of the machine. 

 The third bell is hung by a 

 silk thread, but communi- 

 cates with the ground by a 

 brass chain. The balls are 

 first attracted to the electrified outer bells, then repelled, 

 and, having discharged themselves agaiixst the uninsul- 

 ated central bell, are again attracted, and so vibrate to 

 and fro. 



By another arrangement small figures or dolls cut out 

 of pith can be made to dance up and down between a 

 metal plate hung horizontally from the knob of the 

 machine, and another flat plate an inch or two lower and 

 communicating with " earth." 



The effect of points in discharging electricity from 

 the surface of a conductor may be readily proved by 

 numerous experiments. If the machine be in good 

 working order, and capable of giving, say, sparks four 

 inches long when the knuckle is presented to the knob, 

 it will be found that, on fastening a fine pointed needle 



1 Invented in 1752 by Franklin, for the purpose of warning him of the 

 presence of atmospheric electricity, drawn from the air above his house by a 

 pointed iron rod. 



Fig. 25. 



