MOVEMENT OF PITH-BALLS HOW PRODUCED. 143 



them in similar and in opposite directions, the 

 following suggestions will tend to explain the 

 peculiar movements of the pith-balls of electro- 

 scopes : 



Considering the balls of electroscopes, like all 

 other portions of matter, to be pervaded and sur- 

 rounded by the universal electric medium in con- 

 tinual vibratory motion, and impinging on their 

 exterior surface equally in every direction, and 

 as being thus held in an electro-static condition, 

 their movements toward and from electrically 

 excited bodies are produced by disturbing this 

 equilibrium of the impulses on one side of the 

 balls, whereby the impulses acting on the opposite 

 side predominate, and propel the balls in the re- 

 sultant direction of the impinging impulses. All 

 mechanical modes of exciting electricity by fric- 

 tion, or by machines of various kinds, are so many 

 expedients resorted to for disturbing the electro- 

 static condition of molecules, or bodies of matter, 

 and developing resultant movements of them, as 

 has been previously described. 



The impulse from the 

 hand, imparted to move 

 a rubber over a piece of 

 glass, or sealing-wax, puts 

 in motion the electric 

 ether in circulating cur- 

 rents about them, which 

 induce the circulation of 



