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Here are eighteen calculations of heat at different heights, 

 under different latitudes ; among which only two differ re- 

 markably from the heats adlually obferved at thofe heights, 

 and thefe I am inclined to attribute to an error in the obfer- 

 vations, for the heats above and below cannot both be noted by 

 the accurate philofophers who meafure the heights of mountains. 

 The errors, if any are committed, in noting the degrees of 

 Reaumur, are much more confiderable than thcfe that can be 

 comm'tted in taking thofe of Fahrenheit. 



The near agreement of the calculated and otferved heat on 

 the fummit of Mount Blanc is very remarkable, as the height 

 of this mountain furpaffes that of the upper line cf congelation, 

 and is the only known height that does fo ; that it furpaffes 

 the upper line of congelation is evident from SaufTure's ac- 

 count; for he tells us that the air was fo free from vapour on 

 this fummit^ that in a fhaded fpot he could fee the flars by day, 

 and the temperature even in day tirre was far below 32''; the 

 fnow that nevethelefs repofed on its fummit might for the mofl 

 part have been drifted on it by the furious winds that rage in 

 winter. Thus Dr. Viflars found thirty beds of earth inter- 

 pofed between thofe of frozen fnow on the Glaciers of SwifFer- 

 land. 22 Rozier, p. 275. This earth or dull was wafted up in 

 the months of July and Auguft during thirty fucceflive years. 



The 



