[ 356 ] 



EuLER fuppofed heat to decreafe during its afcent in air in_ an 

 harmonic progreffion ; but this opinion has been long abandoned, 

 Lambert, in the Mem. of Berlin for , fixes the ratio of this 



decreafe to be that of 17 to 12; but this aflertion is refuted by 

 SaufTure, Voy. aux Alpes, § 929, and is indeed incompatible with 

 the refnlts of experiments made at difFerent heights, meafured 

 barometrically. Sauffurc, Voy. aux Alpes, § ^051, thinks that 

 in latitudes from 45^ to 47*^, heat decreafes during its afcent 

 2*?, 25, or more corredly 2*^,23 Fahr* degrees for every 64oEngIifli 

 feet, during the fummer months, from the level of the fea to the 

 fummits of the higheft mountains, and confequently one degree 

 of Fahr. for each 287 feet of height. Yet this determination, 

 though limited within fuch narrow bounds, is not always juft, 

 even within thofe bounds, and frequently errs very widely, at 

 leaft when the diminution of heat is computed, not from the 

 level of the fea, which frequently cannot be known, but from that 

 of adjacent plains, to the fummits of mountains. According to 

 this rule, the diminution is conftant and invariable^ let the heat 

 below be ever fo different, as the diminution is proportioned to 

 the height only, which does not vary. But numerous obfefvations 

 atteft the diminution of heat to vary almoil every day and hour, 

 thus Schuckburg found the diminution of heat on Mount Saleve 



on 



I 



* The boiling point of water being taken at Geneva when the barometer was at 

 28,77, # 



