3l8 On Windi. 



in the eaffern parts of our heraifphere to fupply tlie confiant 

 iiorth-eaft wind that prevails iu the low latitudes of the wel't- 

 ern fide ? The reafon is, that on the wcftern fide the north- 

 eaft winds of low latitudes are eafily fupplied by the conti- 

 guous Atlantic, which is open up to the North Pole; and, 

 as here, the upper current fets and ceafes, there can be no 

 deficiency of air. 



Of oppojite concomilant JVinds. 



It has often been obferved *, but of late, fince the inven- 

 tion of balloons, evidently proved, that currents of air from 

 different and even oppofite points of the horizon, prevail at 

 different heights in the atmofphere over the fame trails of 

 land or water. This was originally inferred from the different 

 courfes of the higher and lower clouds ; hut as fuch oblerva- 

 tions were often liable to optical deceptions, better proofs 

 were wanting. 



Mont Louis is within thirty miles of Perpignan, but about 

 5000 feet higher. Now in March 1780, north and north- 

 eafi; winds prevailed at Perpignan and a wcfterly wind at St. 

 Louis. In Auguft a north wind prevailed at Pcrpignan and 

 an eaft at Mont Louis. Mem. de la Societe dc Medecine 

 de Paris 1780. Derham fafpe^led-j-, and Gentil has fincc 

 fliown, that changes of feafons conftautly begin in the upper 

 atmofphere; while a ftrong wind blows from one point be- 

 low, a wind from an oppofite point reigns above, but more 

 gentle, until at laft (in about three weeks) it is propagated 

 downwards. (Voy. ii. p. 23, 24, in 8vo.) The lower atmo- 

 fphere, he fays, extends to the height of 2880 feet. (Vol. iv. 

 p. 48.) At the commencement of winter, when the fun 

 approaches the fouth tropic, and the north air begins to flow 

 in and follow it, it muil meet with more refiftance from the 

 lower denier air, as its impetuous courfe in an oppofite di- 

 reftioii is more flowly altered (this refpefts the monfoons) 

 than in the rarer fuperior firala; and the fame effcft, but in 

 a different direftion, takes place when the fun approaches to 

 the northern tropic. 



It has been faid bv many, that winds in the fuperior re- 

 gions of the atmofphere are much more violent and impe- 

 tuous than in the lower. (Sauffure Hygrom. p. 300 : Ul- 

 loa's Voy. ii. p. 81: Mufchenbr. § 2613: Bergm. Erde 

 kugel. ii. p. 99: De Luc, &:c.) But the contrary has alio 

 been obferved by Gentil, above quoted, and Morveau. 

 (Aifroft. de Dijon.) 



* Ulloa's Vov- ii. p. 6i. Englifli. 



t Phil. Tranf. Abridg, iv. parr li. 125. 



0/ 



