[ 66 ] 



when this northerly wind is furmounted by a S. W. the x falls ; 

 as the foutherly wind in the fuperior regions procures a rare- 

 fadion in the fuperior or northern tratls. See Mr. Derham's obfer- 

 vations, IV. Phil. Tranf. Abr. Part II. p. 71 ; and that mere cold 

 is no way concerned in the variation caufed by this wind appears 

 in various inftances, to which I refer in the notes *. 



In the fame manner when the 51 falls previous to a ftorm, both 

 the ftorm and this fall proceed from a great rarefaction in the air 

 in the quarter towards which the ftorm blows ; which rarefadion 

 proceeds from the diminution or deftru6lion of the fuperior 

 atmofphere. 



As the fuperior accumulation is derived to us chiefly from 

 North America, where it moft frequently arrives at its ftiaximum^ 

 hence it is, that the variations of the barometer generally begin 

 to the weftward with us in Europe, and are thence gradually 

 propagated eaftward (as Mr. Planer obferved on comparing thofe 

 of London and Vienna f) and comprehend nearly at the fame 

 time diftant degrees of latitude, but not of longitude, according 

 to the firft obfervation ; as the appulfe of the fuperior accumu- 

 lation to the European fliores may be extenfive, but its propa- 

 gation eaftward muft be progreflive. In fpring the current of 

 fuperior air begins to flow to the fouth, and in autumn to return 



* II. Phil. Tranf. Abr. p. 4, 61, 62. VIII. Ditto, p. 614. Phil. Tranf. 1778, 

 p. 574. Mem. Par. 1709, p. 302, in 8vo. 



t II. Ephem. Palat. 



from 



