NATURAL HISTORY. 6t 



the action of the wind, and by the reaction of the di- 

 rect wind, which reigns solely as soon as the obstacle 

 is removed. 



The winds are more violent in mountainous places 

 than in plains ; and the higher we ascend, the more 

 the power of the wind increases, until we reach the 

 common height of the clouds, which is about one quar- 

 ter or one third of a league perpendicular height. 

 Beyond that height, the sky is generally serene, espe- 

 cially in summer, and the wind is said to be even im- 

 perceptible on the tops of the highest mountains. 



A current of air increases in velocity, like a current 

 of water, where the space of its passage is contracted 

 The wind which is but slightly felt in a wide and o- 

 pen plain, becomes violent in passing through a nar- 

 row passage between two mountains, or between two 

 lofty buildings ; and the point of the most violent ac- 

 tion of the wind is above the structures or mountain 

 straits. For the air being compressed by the resistance 

 of these obstacles, has a greater mass, density and the 

 same velocity subsisting : the effort or gust of wind, 

 the momentum becomes much stronger ; this is the 

 cause that near a church, or a castle, the winds seem 

 to be much stronger than they are at a certain distance 

 from these edifices. I have often remarked, that the 

 wind reflected from a building that stands by itself, 

 is stronger than the direct wind that produced it. 

 And since I have endeavoured to discover the reason 

 of this, I have been able to find no other than the a- 

 bove. The impelled air compresses against the build- 

 ing, and is reflected, not only with its former velocity, 

 but also with a greater body, wliich, in fact, render*, 

 its action much more violent. 



