72 AVOYAGETO Book VII. 



its too great a6tivity hinders them from uniting. 

 Hence in fiimmer the atmofphere is clear, or free 

 from vapours. 



In winter the rays of the fun being lefs perpendi- 

 cular to the furface of the earth, the atmofphere be- 

 comes confiderably more condenfed, but the winds 

 from the fouth much more fo, as being loaded with 

 the frigorific particles from the frozen zone, which 

 particles it communicates to the vapoujs as they 

 ifllie from the earth ; and confequently renders them 

 much more condenfed than in lum.mer : hence they 

 are hindered from rifing v/ith the famiC celerity as 

 before. 



To thefe muft be added tv/o other reafons, one, 

 that the rays of the fun for want of fufficient adlivity 

 dilTipates the vapours lefs, fo that they rife much 

 flower. The other, that the region where the wind 

 has its greateft velocity being, in this feafon, near 

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

 and thus they continue contiguous to its furface, 

 where they ftill follow the fame diredion, and form 

 the moid fog then felt and having lefs fpace to di- 

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

 fequently, fooner come into contadl, and when fuf- 

 Jficiently condenfed, defcend in a Garua. 



In the middle of the day the garua ceafes, being 

 then difperfed, which proceeds from the fun's rari- 

 fying the atmofphere, whence the vapours afcend and 

 remain fufpended at a greater height, and thus they 

 are rendered more tenuious, and being raifed to a 

 region where they have more room to dilate, they are . 

 fo far difperfed as to become imperceptible. 



AftePv all, it muft be owned that both in fum- 

 mer and winter, fome vapours mull furmount the 

 diiiiculty of the wind in that region where its velo- 

 city is greateil, and getting above it afcend to a 

 greater height ^ though not indeed in the very part 

 Vv^here they firft reached this current of wind, but 



