452 Dr. Perclval on AitraEftoif and Repul/ionii 



already recited. M. Muffchenbroek placed dlf*^ 

 ferent bodies, for the reception of thefe vapours, 

 on the terrace of the obfervatory at Utrecht, and 

 found that fome caught them abundantly, other* 

 only in a fmall quantity, but that a third fort 

 repelled them altogether. * M. du Fay, of the 

 French Academy, repeated thefe experiments^ 

 and fully proved that, v/hilfl: the dew fell copi- 

 oufly into veiTels of glafs, not the lead moiiture 

 was apparent in veflels of polifhed metal, conti- 

 guous to tiiem. To be affured whether the 

 difference was; always the fame, in all circum- 

 ftances, between vitrified fubftanccs and metals, 

 he fet a China faucer in the middle of a filver 

 plate, and, on one fide, adjoining to it, put a 

 filver veflel, very like the faucer, upon a China 

 plate. The former, viz. the China faucer, was 

 covered with dew, although the plate, which 

 fpread four inches around it, had not a fingle 

 drop. The China plate, alfo, received the dew, 

 whilft the filver veflel, that was in the middle, 

 remained as dry, as when it v/as firft expofed. 



The fame ingenious phHofopher endeavoured 

 to afcertain, whether a China faucer, fet upon- 

 a plate of metal, in the manner above defcribed, 

 did not receive more dew than it would have 

 done, if expofed quite alone. To accomplifh this 

 defign, he took two watch cryftals, of equal 



• Introd. ad Philof. Nat. vol. II. p. 990. 



dimenfidns. 



