6S A VOYAGE TO Book VII, 



to check their course, there is not time sufficient for 

 the mists to collect themselves, and, hy an increase 

 of gravity, to descend in the manner of rain. Others 

 have attributed it to the natural cold brought by 

 the south wind, which continue the atmosphere in a 

 certain degree of heat during the whole year, and thus 

 increase the magnitude of the particles of the air, 

 Avhich with the nitrous effluvia acquired in its pas- 

 sage over the surface of the sea, together with 

 those of the several minerals with which this coun- 

 try abounds, lessen its velocity, and consequently its 

 power of uniting the vapours so as to form drops 

 wliose gravity is greater than that of the air. To 

 this we may add, that the rays of the sun not exert- 

 ing a force suflicient for uniting and putting them 

 in motion, the heat being greatly lessened by the 

 coldness of the wind, the fog cannot be converted 

 into drops of rain. For while the weight of the 

 cloud does not exceed that of the air, by which it is 

 supporied, it cannot precipitate. 



I SHALL not censure this, or any other hypothesis, 

 formed for explaining the above pha^nomenon, not 

 being certain that I have myself discovered the true 

 cause; I shall however give the reader my thoughts, 

 and leave them to the discussion of philosophers. In 

 order to this I shall lay down some preliminary prin- 

 ciples, w hich m;iy serve as a foundation to those who 

 shall apply themselves to discover the true cause of 

 this pliaMiomenon, with some instructions for judg- 

 ing of the several hypotheses that have been formed 

 on tliis extraordinary subject. 



1. ÍT is to be supposed, that throughout the whole 

 country of Valles, no other winds are known du- 

 ring the w hole year, than the southerly, that is, be- 

 tween the S. and S. E. and this not only on the land, 

 but also to V. certain distance at sea; it evidently ap^ 

 pearing that the winds are limited between the S. 

 dna b. E. It u therefore very strange that some 



>vriters 



