Ch.VJ- south AMERICA. 71 



as experience h^s abundantly proved, it appears be- 

 yond difpute, that the furface is not the place where 

 the wind exerts its greateft force. This being grant- 

 ed, it may be confidently afferted, that the fouth 

 winds blow with the greateft force in a portion of the 

 atmofphere at fome diftance from the earth ; but not 

 generally higher than that in whkh the rain is formed ; 

 or where the aqueous particles unite fo as to form 

 drops of any fepfible gravity or magnitude. In this 

 country therefore the clouds or vapours elevated 

 above this fpace, that is, thofe which have the great- 

 eft degree of altitude, move with a much lefs velo- 

 city than the winds under them. Nor is it uncom- 

 mon in other climates, befides that of Valles, for 

 tliefe clouds to move in a diredion contrary to the 

 more denfe ones below it. Thus it appears to me, 

 that without the danger of advancing irregular 

 fuppofitions^ the fpace of the atmofphere, where the 

 winds generally blow with the greateft force, is that 

 where the large drops commonly called rain, are 

 formed. 



Now in order to explain the fmgularity of this re- 

 markable phasnomenon, I conceive that in fummer, 

 when the atmofphere is rnoft rarified, the fun, by the 

 influence of his rays, proportionally elevates the va- 

 pours of the earth, and gives them a greater degree of 

 rarifadbion ; for his beams being then in a more per- 

 pendicular direftion to the earth, they have the power 

 of ralfing them to a greater height. Thefe vapours 

 on their touching the lower part of the atmofphere, 

 where the winds blow with the greateft force, are 

 carried away before they can rife to the height re- 

 quired for uniting into drops, and confequently no 

 rain can be formed. For as the vapours iftue from 

 the earth, they are wafted along the lower region of 

 the atm.ofphere, without any ftop *, and the winds 

 i^lowing always from the fouth, and the vapours 

 |eing rarified proportionally to the heat of the fun, 



F 4 it! 



