EXPERIMENTS and OBSERVATIONS 







face of the fnow, . confidered as a phenomenon, either wholly 

 or in a great meafure depending upon a conftant attraction of 

 hoar-froft, always vanifhed when the heavens were overcaft, or 

 when any fog -or hazinefs interrupted the clearnefs of the lower 

 air. 



THERE is, however, one circumftance to be found in the re- 

 gifter of December 28. which feems repugnant to the explana- 

 tions that have now been attempted. From midnight till 

 near four o'clock that morning, the air continued to rife in its 

 temperature, and at fuch a rate as feems incompatible with the 

 conftant giving out of hoar-froft, and with the correfponding 

 excefs of cold, which took place at the furface of the fnow, 

 unlefs we fuppofe, that the warmer air, which fucceiuvely 

 arrived at the place of obfervation, was, at the fame time, 

 more and more charged with vapours, for which, it muft be 

 confefled, we have very little or no evidence. 



A DIFFICULTY of this kind coming in the way of our gene- 

 ral reafonings upon fuch phenomena, rather leads to a fufpi- 

 cion of there being fome other principles concerned, which as 

 yet may have altogether efcaped obfervation. I have been 

 the more inclined to harbour fuch a fufpicion, lince reading 

 lately in the Berlin Memoirs for 1780, a Differtation by 

 M. Ac HARD upon the difpofition of the air to Ihed night-dew, 

 in which there are fome curious remarks. It is much to our 

 purpofe here to take notice, that this author mentions particu- 

 larly the fudden overcafting of a ferene fky, as having fre- 

 quently come under his obfervation ; and that it was always 

 accompanied with moft fenfible and defultory changes in the 

 eledricity of the lower air. The fcope of M. ACHARD'S Me- 

 moir, is, to {how how much electricity is concerned in the 

 phenomena of the atmofphere, and how neceflary it is, in all 

 our meteorological refearches, to have refpecl to the operations 

 and effeas of fuch a principle. According to this author, the 

 different difpofitions of the air, as to giving out and taking in 



moifture, 



