ñ A VOYAGE TO Boor VIL 



its too great activity hinders them from uniting. 

 Hence in summer the atmosphere is clear^ or free 

 iiom vapours. 



In winter the rays of the sun I Ing less perpendi- 

 cular to the surface of the earth, the atmosphere be- 

 comes considerably more condensed, but the winds 

 from the south much more so, as being loaded with 

 the frjgoriiic particles from the frozen zone, which 

 particles it communicates to the vapours as they 

 issue from the earth: and consequently renders them 

 much more condensed than in summer: hence they 

 are hindered from rising with the same celerity as 

 before. 



To these must be added two other reasons ; one, 

 that the rajs of the sun for want of sufficient activity 

 dissipates the vapours less, so that they rise much 

 slower. The other, that the region where the wind 

 has its greatest velocity being, in this season, near 

 the earth, will not admit of their rising to any height; 

 and thus they continue contiguous to i<s surface, 

 where they still follow the same direction, and form 

 the moist fog^hcn felt : and having less space to di- 

 late themselves than at a greater height, they, con- 

 sequently, sooner come into contact, and wlieu suf- 

 ficiently condensed, descend in a guara. 



In the middle of the day the garua ceases, being 

 then dispersed, which proceeds from sun's rare- 

 fying the atmosphere, whence the vapours ascend and 

 remain suspended at a greater height, and thus they 

 are rendered more tenuious ; and being raised to a 

 region where they have more room to dilate, they are 

 so far dispersed as to become imperceptible. 



Aftfíí all, it must be owned that both in sum- 

 mer and winter, some vapours must surmount the 

 diííiculty of the wind in that region where its velo- 

 city is greatest, and getting above it ascend to a 

 greater height; though not indeed in the very part 

 where they iirst reached this current of wind^, but 



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