[ 48o ] 



fubftances, has been fufiiciently proved and explained by Mufchen- 

 broeck and Du Fay. Mem. Paris 1756. 



There is however a puzzling circumftance mentioned by the 

 above-named naturalifts, and for which they have not accounted. 

 It has been obferved in feveral places to be depofited very co;)iouiIy 

 on idioeledrics, as glafs and all vitrifadions, but fcarce at ;)!i on. 

 the beft condudors, as metallic fubftances, which evidently llicws 

 that dew conveys electricity ; but why is not this fluid carried off 

 by conducing fubftances more eafily than by 11 m- conductors? 

 Mr. Achard tells us, Mem. Berlin, 1780, p. 17, that condudors 

 affume the eledrical ftate of the ambient air very eafily, but 

 glafs very flowly ; therefore the condudors and v.ipours being 

 both in the fame ftate, whether pofitive or nesjitive, repel each 

 other, but glafs being in a contrary ftate repels them. This, how- 

 ever, does not appear to me perfedly fatisfadory, as far as ref- 

 pe£ts glafs, for it fhould feem that, after fome hours, this ah^o 

 fhould affume the fame eledrical ftate as the air, and then repel 

 the vapours. I lliould rather fuppofe that glafs coUeds moifture 

 by reafon of its ftrong attradion for moifture, for it has been ob- 

 ferved that, in diftilling water in glafs and metallic veffels of the 

 fame dimenfions and in the fame heat, much more water pifTes 

 in a given time through the glafs than through the metallic vcftels : 

 nay when the helm of a glafs ftill was connected with two re- 

 ceivers, 



