ELECTRICAL REPULSION, 555 



thread, while with this precaution it will be seen that the electrical 

 attraction is stronger than the torsion of the thread. 



The moveable rod should not be suspended from the support 

 in fig. 85. It will be more accessible from all sides if suspended 

 from a hook or nail fastened in the ceiling of the room, to which 

 first a wire is attached, which reaches to about 1'5 or 2 m from the 

 floor. The end of the wire is bent into a small loop, and to this the 

 suspending thread or hair is tied. 



If a rubbed glass rod is freely suspended, and another 

 rubbed glass rod is brought near to it, they repel one 

 another. This happens also if the same experiment is 

 made with two sticks of sealing-wax. Other bodies in 

 the form of bars, similarly experimented on, show the 

 same behaviour : electrified substances of the same kind 

 repel one another. If, on the contrary, an electrified 

 glass rod be brought near to an electrified stick of seal- 

 ing-wax, one of these two bodies being capable of moving 

 freely, attraction will be manifested ; similarly, ebonite 

 and glass will attract one another when electrified. 

 Attraction, however, does not always take place between 

 different substances in the electric state: a rubbed stick 

 of sealing-wax is repelled by a rubbed bar of sulphur or 

 one of ebonite. 



In experiments on repulsion we must be sure that both bodies are 

 charged pretty strongly ; for if one body has a weak charge and 

 the other a strong one, the former body behaves as if it were un- 

 electrical, that is, it is attracted by the other. The bodies should 

 therefore be tested by bringing them near to the electrical pen- 

 dulum ; when strongly charged, they will attract the ball at an 

 appreciable distance. 



The hand which holds one of the electrified bodies should be 

 kept as far as possible from the suspended body ; otherwise the 

 attraction between the latter and the non-electrical hand may 

 possibly overcome the repulsion between the two bodies. 



If all bodies which become electric are thus made to 

 act upon each other it is found that they may be 



