110 Experimental Philosophy. [Lecture 9. 



vitreous, and that from resin vus substances or 

 sulphur was termed the resinous electricity. 

 Another circumstance which served to distin- 

 guish them, was the different appearance of the 

 electric light. A divergent cone of light, re- 

 sembling a painter's brush, distinguished the 

 vitreous electricity, while a single globe or ball 

 of clear light was the mark of the resinous. In 

 process of time, however, it was discovered that 

 these different phenomena depended rather on 

 the surface than the composition of the electric ; 

 for glass, when the smooth surface was de- 

 stroyed by being ground with emery, and being 

 rubbed with a smooth body, exhibited all the 

 appearances of the resinous electricity ; yet after- 

 wards, when it was greased and rubbed upon a 

 rough surface, it resumed its former property. 

 It was therefore concluded, upon various experi- 

 ments, that the smoother of two bodies, upon 

 friction, exhibits the phenomena of the vitreous 

 electricity, and the contrary. 



M. Coulumb proposed another theory. He 

 considered the electric matter as composed of two 

 distinct fluids, which are neutralized the one 

 by the other in the ordinary state of bodies, but 

 which separate when the bodies are electrified. 

 Such a theory, however, only serves as a vehicle 

 for reasoning: the experiments establish two 

 distinct modes of operation ; and they may be 

 explained with nearly equal facility by either of 

 the hypotheses. 



