[ 65 1 



The denfer air of the North American continent prclling on 

 the rarer incumbent on the Atlantic, produces the almoft conftant 

 weflerly winds which prevail on the eaflern coafts of America*, 

 and in the weftern parts of Europe below lat. 70° ; but above 

 that parallel the fuperior European current paffes by a fhorter 

 way into America, where the cold is greater. 



Accumulations are alfo formed in the fouthern parts of the 

 old continent 5 for inftance, over the mountainous trads of 

 Thibet, Tartary, Turkey in Europe, Africa, and even in ibmc 

 degree on the Pyrenees and Alps ; when the rarcfadion in the 

 northern parts of Europe is frequent and confiderable, either 

 from the pafTage of the northern air to America, or from frequent 

 and confiderable aurorae borealis, the fouthern air flows from 

 thefe trads to reftorc the aequilibrium ; and while this current 

 lafts, and until the aequilibrium is reftored, the barometer muft 

 fall in the intermediate regions ; fo that the defcent of the ^ is 

 never the cffed of a foutherly wind, but both it and this wind 

 are concomitant effeds of a rarefadion in the northern parts, 

 proceeding from the caufes already mentioned. 



On the other hand the 5^ generally rifes under a northerly or 

 eafterly wind, becaufe, as I have already faid, the fuperior atmo- 

 fphere is accumulated chiefly in thofe parts of our hemifphere 

 from whence thefe winds ifTue, and this accumulated air paffes 

 with them to the fouthern regions. A certain proof that this 

 accumulation is the true caufe of their fuperior denlity is, that 



* II. PhU. Tranf. Philad. p. 99. 



K when 



