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heights which we have mentioned in the firft obfervation to take 

 place in very diftant countries, in which very different winds 

 prevail, be explained in this hypothefis. It is moreover flatly 

 contradided by the obfervation of Mr. Forth, who, while the 

 mercury all over England flood lower than ever it was known to 

 do, found that a N. E. wind prevailed in the northern part of 

 that ifland, and a S. W. in the fouthern. Vill. Phil. Tranf. 

 Abridg. p. 497. 



Secondly. In this hypothefis the defcent of the $ beneath 

 its mean altitude is afcribed to the rarefadion of the atmofphere 

 over the place of obfervation, owing to its exhauflion by two 

 contrary currents ; for inflance over England, if it fhould blow 

 a wcflerly wind on the German, and an eafierly wind on the 

 Irifh fea. But a rarefaction in fuch circumflances from fuch a 

 caufe feems to me impoffible ; for if fuch currents took place, the 

 northern or fouthern air would flow in to maintain the equili- 

 brium in the fame proportion ; or if this did not happen, and 

 that four contrary currents took place, the higher air fhould de- 

 fcend, and caufe a fenfible cold, which yet is feldom obferved 

 in England when the ? is low ; on the contrary, a warm S. wind 

 commonly prevails, to whofe temperature neverthelefs the rare- 

 fadlion cannot be afcribed, as we have already feen. 



Thirdly. The great defcent of the ^ on high winds in 

 florms is thus explained by Dodor Halley : " The region of 

 " the earth wherein thofe winds rage, not extending round the 

 " globe, the flagnant air left behind, and that on the fides, can- 

 " not rufh in faft enough to reftore the evacuation made by fo 



" fvviff 



