METEOROLOGY. 145 



Monsoons are a modification of the trade winds, which occur 

 mostly in the Indian ocean, and north of 10 south latitude. 

 The south-east winds blow from April to October, and are 

 frequently attended by rain : from October to April they blow 

 from the north-east, and are dry. The change from one 

 monsoon to another is usually attended by violent storms. 



The simoon is a hot, pestilential wind, which, during certain 

 seasons of the year, blows northward from the deserts of Africa 

 and Arabia. This wind, after being modified by passing over 

 the Mediterranean sea, is called in the south of Italy, the 

 sirocco; its poisonous effects are supposed to depend on its 

 dry ness. 



Whirlwinds are such as have a rapid gyratory, as well as 

 progressive motion. Hurricanes are generally whirlwinds con- 

 fined to a narrow path, with a forward motion, sometimes not 

 exceeding 15 miles an hour. 



A wind which moves at the rate of 4 or 5 miles an hour is 

 called a gentle breeze; when its velocity is 15 or 20 miles an 

 hour, it is a gale; when 30 to 40 miles an hour, a high wind; 

 and when 100 miles an hour, a hurricane or tornado, Hurri- 

 canes are more frequent on the shores of China and the Indies 

 than in any other part of the world. 



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