6 ELEMENTARY LESSONS ON [CHAP. i. 



feather has been first electrified by touching it with the 

 rubbed sealing-wax, it will be attracted to a rubbed glass 

 rod, though repelled by the rubbed wax. So, again, a 

 rubbed glass rod suspended as in Fig. 3 will be attracted 

 by a rubbed piece of sealing-wax, or resin, or amber, 

 though repelled by a rubbed piece of glass. The two 

 pith-balls touched (as in Fig. 5) with a rubbed glass 

 rod fly from one another by repulsion, and, as we have 

 seen, fly wider asunder when the excited glass rod is 

 held near them ; yet they fall nearer together when a 

 rubbed piece of sealing wax is held under them, being 

 attracted by it. Symmer first observed such phenomena 

 as these, and they were independently discovered by Du 

 Fay, who suggested in explanation of them that there 

 were two different kinds of electricity which attracted 

 one another while each repelled itself. The electricity 

 produced on glass by rubbing it with silk he called 

 vitreous electricity, supposing, though erroneously, that 

 glass could yield no other kind ; and the electricity 

 excited in such substances as sealing-wax, resin, shellac, 

 indiarubber, and amber, by rubbing them on wool or 

 flannel, he termed resinous electricity. The kind of 

 electricity produced is, however, found to depend not only 

 on the thing rubbed but on the rubber also; for glass 

 yields " resinous " electricity when rubbed with a cat's 

 skin, and resin yields " vitreous " electricity if rubbed 

 with a soft amalgam of tin and mercury spread on 

 leather. Hence these names have been abandoned in 

 favour of the more appropriate terms introduced by 

 Franklin, who called the electricity excited upon glass by 

 rubbing it with silk positive electricity, and that produced 

 on resinous bodies by friction with wool or fur, negative 

 electricity. The observations of Symmer and Du Fay may 

 therefore be stated as follows : Two positively electrified 

 bodies repel one another : two negatively electrified bodies 

 repel one another : but a positively electrified body and 

 a negatively electrified body attract one another. 



