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poured on the fouthern regions, and a comparatively fmallcr 

 quantity flows over the northern ; therefore the variations of the 

 barometer are fmaller with us in the fumraer feafon, according 

 to the third obfervation, and fewer auroras are formed. 



As the tops of the highefl mountains are covered with fnow 

 even in fummer, the air over them will remain colder than that 

 over plains, and its columns fhorter ; and hence the fuperior air 

 in its paffage to the poles will linger and accumulate over them, 

 ■until the difference of denfity becomes fo great as to enable this 

 air to burft through the hot air that furrounds it, and form cold 

 winds that raife the barometer in this feafon. 



In winter, on the contrary, the fuperior current is chiefly 

 direded to the northern hemifphere, and hence the greatefl mer- 

 curial heights are found in this feafon. It accumulates where the 

 columns of the inferior air are coldeft, and confequently fliorteft ; 

 that is to fay, over all that part of Afia beyond Lit. 35, and E. 

 of the Cafpian Sea to the Frozen Ocean, and over the continent 

 of North America, which I have elfewhere {hewn to be colder 

 than the old continent, and over the polar regions. Hence the 

 barometer ufually ftands higher in North America, and varies 

 lefs than with us* even in Hudfon's, Bay, lat. 59, where the 

 weather is fo turbulent the barometer varies but 1,37 inches, 

 whereas in Peterfburgh It varies above' two f. 



* II. Phil. Tranf. Philad. p. 142. 

 f Phil. Tranf. 1770, p. 148. 



The 



