Dr. Pcrcival on Atlra^m and Repulfton, 453 



dimenfions, and placed the orc upon a plate of 

 filver, the other upon a plate of China, each with 

 its concavity uppermoft. That which was upon 

 the filver plate, he furrounded with a ferrel, 

 of the fame metal, well polirtied, that no watery 

 particles might attach themfelves to the convex 

 furface of the glafs. Thus circumftanced, he 

 expofed the cryftals, feveral days fucjceflively, in 

 a proper fituation, and always found five or fix 

 times more dew in that, which was on the China 

 plate, than in the other placed on filver : And 

 this may be regarded as a prefumptiv-e proof, 

 that the moifture repelled from the metal, was 

 attraded by the China. That there fubfifted 

 fuch a repulfion, is confirmed by the following 

 obfervation of M. du Fay, with regard to the 

 cryftal on the filver plate. He informs us, 

 that the fmall quantity of dew on the infide, was 

 only near the center, in minute drops j and that, 

 round the border, there was a fpace of five or 

 fix lines, perfedly dry, towards which the drops 

 regularly decreafed, in magnitudes as if the 

 filver ferrel had driven away the dew from that 

 part of the glafs, which was contiguous to it. 

 Thefe experiments were repeated thirty times, 

 with invariable fuccefs. * And Dr. Watfon, 

 now BiOiop of Landafi% has lately confirmed 

 them, by fome very curious trials, of a fimilar 

 kind, made to determine the quantity of vapours 



• Yid. Hift. de I'Acad. des Scienc 1749. 



G "f 2 which 



