Aleteor*. 121 



of the year. These winds are called 

 monsoons, and owe their origin to causes 

 similar to what has been pointed out. 



When the gusts of wind come from 

 different quarters at the same time, and 

 meet in a certain place, there the air ac- 

 quires a circular, or rotatory, or screw- 

 like motion, either ascending or descend- 

 ing, as it were, round an axis, and this 

 axis sometimes is stationary, and at other 

 times moves on, in a particular direction. 

 This phenomenon, which is called a 

 whirlwind, gives a whirling motion to 

 dust, sand, water, part of a cloud, and 

 sometimes even to bodies of great weight 

 and bulk ; carrying them either upwards 

 or downwards, and lastly scatters them 

 about in different directions. 



The water-spout has been attributed 

 principally, if not entirely, to the meeting 

 of different winds. In that case the air 

 in its rotation acquires a centrifugal mo- 

 tion ; whence it endeavours to recede 

 from the axis of the whirl, in conse- 

 quence of which a vacuum, or, at least a 

 considerable rarefaction of air, takes place 

 about the axis, and, when the whirl takes 

 place at sea, or upon water, the water ri- 



