Electricity 



2I 5 



reason is simple : Copper and practically all other metals 

 are very good conductors of electricity ; that is, they 

 allow electricity to pass through them very easily. 

 Cloth, rubber, glass, and porcelain are very poor conduc- 

 tors, and they are therefore used as insulators, to 

 keep the electricity from going where you do not want it 

 to go. 



Experiment 66. To each binding post of an electric bell 

 fasten a piece of insulated copper wire with bare ends and 

 at least 4 feet long. Connect the free end of one of these 

 wires with one pole of a battery, using a regular laboratory 

 battery or one you made yourself. Attach one end of 

 another piece of wire a foot or so long, with bare ends, to 

 the other pole of the battery. Touch the free end of this 

 short wire to the free end of the long wire, as shown in 

 Figure 120. Does the bell ring? If it does not, something 

 is wrong with the connection or with the battery ; fix them 

 x so that the bell will ring. Now leave a gap of about an 



FIG. 120. Will electricity go through the glass? 



