WINDS. 285 



occurs between the permanent and tempornrv currents, giving rise to con- 

 stant fluctuations in the strength and direction of the winds. 



629. The driest winds of the United States are west and 

 character of north- west winds, since ther blow over great tracts of land, 

 the winds of and have httle opportunity of absorbing moistura 

 States ? The south winds are generally warm and productive of 



rain, since coming from tropical countries, they are highly 

 heated, and readUy absorb moisture as they pass over the ocean. As soon, 

 however, as they reach a cold cUnaate they are condensed, and can no longer 

 hold all their vapor in suspension; in consequence of which some of it is de- 

 posited as rain. 



630. Otlier disturbances of the air occasion a variety of phenomena known 

 as "Simoons," "Hurricanes," "Tornadoes," ""Water-Spouts," etc. 



What Is a Si- ^31. The Siiiioon is an intensely hot wind 

 """""^ that prevails upon the vast deserts of Africa 

 and the arid plains of Asia, causing great suffering, and 

 often destruction of whole caravans of men and animals 

 when encountered. Its origin is to be sought in the pecu- 

 liarities of the soil and the geographical position of the 

 countries where it occurs. 



" The surface of the deserts of Africa and Asia is composed of dry sand, 

 which the vertical rays of the sun render burning to the touch. The heat of 

 these regions is insupportable, and their atmosphere like the breath of a fur- 

 nace. "When, under such circumstances, the wind rises and sweeps over 

 these plains, it is intensely hot and destitute of moisture, and at the same time 

 bears aloft with it great clouds of fine sand and dust — a dreadful visitant to 

 the traveler of the desert." 



whatisaHor- ^hc Hurricanc is a remarkable storm wind, 

 ricane? peculiar to certain portions of the world. It 

 rarely takes its rise beyond the tropics, and it is the only 

 storm to dread within the region of the trade-winds. 



Hurricanes are especially distinguished from all other kinds of tempests by 

 their extent, irresistible power, and the sudden changes that occur in tho 

 direction of the wind. 



In the northern hemisphere, the hurricane 



At what times ^ , . , . r- , i 



and locations most irequcntly occurs m the regions oi tu9 

 most frequent- Wcst Indics ; in the southern hemisphere, it 

 '^*^*" occurs in the neighborhood of the Island of 



Mauritius, in the Indian Ocean. They also seem to be 

 confined to particular seasons ; thus the West Indian 

 occur from August to October ; the Mauiitian from Feb- 

 ruary to April. 



