METEOROLOGY. 143 



miles an hour, he feels a current of air equal in velocity to his 

 own ; the wind appears to blow at that rate. The direction of 

 winds may be modified by various causes: when two or more 

 currents meet from different directions, the general direction 

 will be a resultant one, the consequence of the several forces, 

 as in the case of trade winds. 



Winds have received various distinctive appellations accord- 

 ing to the phenomena which they present : thus we have the 

 trade winds, the land and sea breezes* the harmattan, the 

 monsoon, the simoon, the sirocco, whirlwind, hurricane and 

 tornado. A brief description only of each of these varieties 

 can here be given. 



Land and sea breezes. These winds prevail mostly among 

 the islands of the torrid zone ; but more or less in all maritime 

 countries. They are mild, balmy breezes, which blow towards 

 the shores during the day, and from off the land towards the 

 sea during the night time. Their phenomena is explained as 

 follows : during the day the land becomes heated by the rays 

 of the sun, the heat of the ground rarifies the air, which 

 consequently rises to the higher regions, while the cold air 

 from off the ocean rushes in to supply its place ; thus producing 

 a breeze inland as long as the sun continues to warm the earth. 

 This is called the sea breeze. 



During the absence of the sun, the earth, which radiates its 

 accumulated heat faster than the sea, becomes cooler, and the 

 direction of the breeze is changed : the air from off the ocean 

 rises, while the colder air from the land rushes in to supply its 

 place, just as in the case of the sea breeze. This night wind 

 which blows off the land is called the land breeze. As the 

 central part of an island becomes warmer than its shores, the 

 breeze will be the strongest in the midland : " its current will 

 also be performed in a constant gyration; so that the air which 

 flows in upon the land by day, rises, flows out above, and 

 returns again in the same current : and the process is similar 



