606 DANCING BALLS. 



Many amusing experiments with the machine depend 

 on electrical attraction and repulsion. A few of these 

 deserve mention. 



A wire, 35 cm long, is inserted in a cork which fits into " 

 the opening of the conductor. To the end of the wire 

 a round disc of metal is soldered, 2 cm in diameter, to 

 which are gummed about 12 or 15 strips of thin paper, 

 tissue paper being the best for the purpose. These 

 strips hang straight down, but when the machine is 

 worked, repulsion takes place between the wire and the 

 strips, and between the strips themselves. If an un- 

 electrified body be brought near the electrified strips, 

 for example the hand, the strips are attracted. 



For the experiment called ' the dancing balls ' the 

 cover of the electrophorus is suspended by its strings 

 from the arm of the retort-stand so as to be horizontal, 

 and 5 or 6 cm from the surface of a table. A thin wire of 

 suitable length is bent at one end into a hook, which is 

 placed round the stalk of the small ball of the conductor, 

 while the other end is placed upon the suspended cover, 

 which is thus in conducting communication with the 

 machine. Beneath the cover a number of pith-balls are 

 placed. When the machine is worked the disc becomes 

 charged and attracts the unelectric balls. By contact 

 they become electrified and are then strongly repelled, 

 but as soon as they again touch the table they give up 

 their electricity, and are again attracted upwards by the 

 metallic disc. This process clearly continues as long as 

 there is electricity to attract the balls. 



The balls are often projected too far from the suspended disc to 

 be attracted again. To prevent this the disc and balls are often 

 enclosed within a cylindrical vessel of glass, but even in this form 



