198 



GENERAL SCIENCE 



FIG. 167. A Leyden Jar. 



of its height with tin foil (Figure 167). The inside coating 

 is connected by a chain and rod to a knob, and the out- 

 side covering is connected to the earth. A charge may 



be passed by way of the knob 

 and rod to the inside coating 

 of the jar, the action being 

 the same as that described 

 above. 



The Electrophorus. The 

 charges which we are able to 

 develop on glass or ebonite 

 rods are small. We may pro- 

 duce larger charges by taking 

 advantage of the principle of induction. Figure 168 rep- 

 resents a sectional view of the electrophorus. A consists 

 of a plate of ebonite or a shallow pan filled with sealing 

 wax or resin; B is a metal disk (tin or brass), fastened 

 to an insulating 

 handle of ebonite 

 or glass. Rub the 

 plate A with some 

 cat's fur or woolen 

 cloth. Place the 

 metal disk B on the 

 plate and touch it 

 with the finger while 

 it is in this position. 

 Now lift the disk 

 and test its charge. 

 Lift the disk with- 

 out touching it and 

 test its charge. Lift 



the disk before re- FIG. 168. The Electrophorus. 



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