PHYSIOLOGICAL PHYSICS. 



[Chap. I. 



Fig. 1. The Electric 

 Pendulum. 



ball, the ball will be attracted towards the wax. If 

 the pith be allowed to touch the wax, it will remain 

 in contact for only an instant, and will then 

 be repelled. Similarly, if a rod of polished glass 



^ be rubbed with silk, and then 



brought near to a pith ball, the 

 ball will be attracted till contact 

 is made ; thereafter it will be re- 

 pelled. 



By the friction the sealing-wax 

 and the glass rod became elec- 

 trified, and attracted the unelec- 

 trified pith ball. As soon as the 

 ball touched the electrified body it 

 received itself a charge of elec- 

 tricity, and was then immediately 

 repelled. 



Now let the glass rod be brought near to the 

 pith ball, which has received a charge from the sealing- 

 wax, and been consequently repelled by it, and it will 

 be attracted by the glass. Or, let a pith ball receive 

 a charge from an electrified glass rod, it will be 

 immediately repelled by the glass, but will now be 

 attracted by an electrified rod of wax. Thus there 

 seem to be two kinds of electricity, one generated on 

 smooth glass by friction, and hence called vitreous 

 electricity, and another generated on wax or resin by 

 friction, and hence called resinous electricity. But, 

 further, the above experiments show that a pith ball 

 charged with the same electricity as a rod of wax is 

 repelled by the wax, but is attracted by electrified 

 glass ; and similarly, that a pith ball charged with 

 vitreous electricity is repelled by the glass rod, but 

 attracted by the wax. In other words, bodies charged 

 with like electricities repel one another, and bodies 

 charged with unlike electricities attract one another. 

 The two-fluid theory, or the theory which 



