VOL. XXXVIII.] PHILOSOPHICAL TRANSACTIONS. 64 1 



are put, is a necessary consequence of it. When these threads are ranged in 

 form of rays by the electricity of the sides of the globe, if the finger be put 

 near the outside of the globe, the silk, threads within fly from it, as is well 

 known ; which happens only because the finger, or any other body applied near 

 the glass globe, is thereby rendered electrical, and consequently repels the silk 

 threads, which are endowed with the like quality. With a little reflection one 

 may in the same manner account for most of the other phaenomena, and which 

 seem inexjilicable, without attending to this principle. 



7. Chance threw in M. Du Fay's way another principle, more universal 

 and remarkable than the preceding one, and which casts a new light on the 

 subject of electricity. This principle is, that there are two distinct electricities, 

 very different from each other; one of which he calls vitreous electricity, and 

 the other resinous electricity. The first is that of glass, rock-crystal, precious 

 stones, hair of animals, wool, and many other bodies : the second is that of 

 amber, copal, gum-lac, silk, thread, paper, and a vast number of other sub- 

 stances. The characteristic of these two electricities is, that a body of the 

 vitreous electricity, for example, repels all such as are of the same electricity ; 

 and on the contrary, attracts all those of the resinous electricity ; so that the 

 tube, made electrical, will repel glass, crystal, hair of animals, &c. when 

 rendered electric, and will attract silk, thread, paper, &c. though rendered 

 electrical likewise. Amber, on the contrary, will attract electric glass, and 

 other substances of the same glass, and will repel gum-lac, copal, silk, thread, 

 &c. Two silk ribbons rendered electrical, will repel each other ; two woollen 

 threads will do the like ; but a woollen thread and a silk thread will mutually 

 attract each other. This principle very naturally explains, why the ends of 

 threads, of silk, or wool, recede from each other in form of a pencil or broom, 

 when they have acquired an electric quality. From this principle we may with 

 the same ease deduce the explanation of a great number of other phagnomena. 

 And it is probable that this truth will lead us to the further discovery of many 

 other things. 



In order to know immediately, to which of the two classes of electricity any 

 body belongs, we need only render electrical a silk thread, which is known to 

 be of the resinous electricity, and see whether that body, rendered electrical, 

 attracts or repels it. If it attracts, it is certainly of that kind of electricity 

 called vitreous ; if on the contrary it repels, it is of the same kind of electri- 

 city with the silk, that is, of the resinous. M. Du Fay also observed that 

 communicated electricity retains the same properties : for if a ball of ivory, or 

 wood, be set on a glass stand, and this ball be rendered electric by the tube, it 

 will repel all such substances as the tube repels ; but if it be rendered electric by 



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