Ch. VI. SOUTH AMERICA. 71 



as experience has abundantly proved, it appears be- 

 yond dispute, that the surfare is not the place where 

 the wind exerts its g-reatest force. This being grant- 

 ed, it may be c>iifidently asserted, that the south 

 winds blow with tiie greatest force in a portion of the 

 atmosphere at some distance from the earth ; but not 

 generally higher than that in which the rain is formed ; 

 or where the aqueous particles unite so as to form 

 drops of any sensible gravity or magnitude. In this 

 country therefore the clouds or vapours elevated 

 above this space, that is, those which have the great- 

 est degree of altitude, mov^ with a much less velo- 

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

 mon in other climates, besides that of Valles, for 

 these clouds to move in a direction contrary to the 

 more dense ones below it. Tlius it appears to me, 

 that without the danger of advancing irregular 

 suppositions, the space of the atmosphere, where the 

 winds generally blow with the greatest force, is that 

 where the large drops commonly called rain are 

 formed. 



Now in order to explain the singularity of this re- 

 markable phainomenon, I copxcive that in summer, 

 when the atmosphere is most rarefied, the sun by the 

 influence of his rays, proportionally elevates the va- 

 pours of the earth and gives them a greater degree of 

 rarefaction ; for his beams being then in a more per.- 

 pendicular direction to the earth, they have the power 

 of raising them to a greater height. These vapours 

 on their touching the lo\^ er part of the atmosphere, 

 where the winds blow^ with the gjgjjatest force, are 

 carried away before they can rise to the heiglit re- 

 quired for uniting into drops, and conseqiu^itly no 

 rain can be formed. For as the vapours issue from 

 the earth, they are wafted along the lower region of 

 the atmosphere, without any stop ; and the winds 

 blowing always from the south, and the vapours 

 being rarefied proportionally to the Jieat of the sun, 



its 



