I4O VITREOUS AND RESINOUS THEORY. 



other." The descriptive names of " vitreous " and 

 " resinous " electricities were accordingly given to 

 them. 



But, after further experiments, it was found 

 that if a tube of glass be ground to a rough surface 

 at one end, while the other end is left smooth, and 

 a rubber be passed over the whole length of it, 

 the vitreous electricity is manifest only on the 

 smooth part, and the resinous appears on the 

 rough part. This showed that a difference of 

 surface, not of material, determines the difference 

 of the electricity. Another experiment of friction 

 of a piece of silk, with one end dyed black and the 

 other left white, showed that a difference of color 

 similarly determines the kind of electricity excited. 

 In this way, a difference of colors is ascertained in 

 the dark by a difference of mechanical reaction, in 

 clinging together. 



These facts discredited the theory of Dufay. 

 Professor Faraday instituted a course of experi- 

 ments for ascertaining if the supposed two kinds 

 of electricity could be separated ; but the task 

 proved as vain as an attempt to separate mechan- 

 ical action and reaction, which are always u equal 

 and in opposite directions," precisely like the 

 phenomena of the two kinds of electrical action 

 and reaction, denoted resinous and vitreous. 



Franklin and Priestley attempted to simplify the 

 two-fluid theory, by introducing the preserft pop- 

 ular single-fluid theory, after Gilbert, Newton, and 



