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the air fome feet above it, as Mr. Wilfon obferved, though it did 

 not occur to him that the cold was communicated to the air by 

 the fnovv, for he thought it highly remarkable that a thermome- 

 ter hung 2+ feet above the fnow was four degrees lefs cold than 

 one fufpended 2i feet above it. Phil. Tranf. 1780, p. 462. Yet 

 Mr. Boyle has long fince noticed a fimilar fad, (i Boyle Abridg. 

 p. 629) as related to him by fome navigators, and Fofter exprefsly 

 mentions, that being to the leeward of an icy mountain (probably 

 many feet diflant) the thermometer funk four degrees, and rofe 

 to its former height when he had paffed that mountain, (Obfervat. 

 p. 73) but when there is not a recent fall of fnow, the air feveral 

 feet above the furface of the earth is generally colder (when no 

 great evaporation takes place) than that nearer to its furface. Thus 

 during the intenfe cold of January 1776, there having been no 

 fall of fnow fince the 24th, Van Swinden found the degree of 

 cold on the morning of the 27th to be 8^,25, while Camper, in 

 the fameftreet, whofe thermometer was fome feet nearer to the 

 earth, found it only 6^,5. See Van Swinden, fur le froid 

 de L'Annee 1776, p. 24, 25, 28 and 176. 



Section 



