FRICTIONAL ELECTRICITY. 



19? 



FIG. 136. 



Eepeat all of these 

 experiments with a 

 glass rod which has 

 been rubbed with 

 the silk pad (Fig. 

 136). You may make 

 a light paper hoop 

 or an empty egg-shell 

 roll after your rod. 

 Place an egg in a 

 wineglass or egg cup. Upon its end balance a meter stick 

 or a common lath. The end of the stick may be made 

 to follow the rubbed rod round and round. Place the 

 blackboard pointer or other stick in a stiff paper stirrup 

 suspended by a stout silk thread or narrow silk ribbon. 

 It may be made to imitate the actions of the balanced 

 straw or lath. Now read 64. 



324:. Electric Repulsion. The suspended pith, 

 ball is called an electric pendulum. Bring the rubbed 

 glass rod near the pith ball again. It will attract the ball 

 as we have already seen in the last paragraph (Fig. 137). 

 Allow the ball to touch the rod and notice that in a mo- 

 ment the ball is thrown off. If the ball be pursued with 

 the rod, it will be found that the rod that a moment ago 

 attracted now repels it (Fig. 138). Touch the ball with 

 the finger ; it successively seeks the rod, touches the rod, 

 flies from the rod. Repeat the experiments with the 

 sealing-wax after it has been rubbed with flannel. Rub 

 the glass rod with silk and bring it over the small scraps 

 of paper ; notice that after the attraction the paper bits 

 do not merely fall down, they are thrown down. 



