404 CLIMATE 



to ocean (page 35), so breezes may at one time blow from 

 mountain to valley, at another time from valley to mountain. 



Since winds are caused by a variation in the density of air, 

 the greater the difference in temperature between two places, 

 the more rapid is the inrush and outrush of air and the stronger 

 and fiercer and more rapid is the wind. The velocity of wind, 

 or the speed at which it travels, varies from a few miles an hour 

 to 100 or more miles an hour. A light breeze, just sufficient 

 to rustle the leaves of trees, moves from i to 5 miles an hour ; a 

 breeze strong enough to make whitecaps on the ocean and to 

 sway branches moves from 15 to 20 miles an hour; a gale fierce 

 enough to break branches and blow down fences, or to tear sails 

 from boats, moves 35 to 75 miles an hour; and a hurricane 

 which uproots trees, carries away roofs, and destroys houses 

 moves 100 miles or more an hour. 



In many places it is easy to foretell what the weather will 

 be from the direction of the wind. On the Atlantic coast and 

 in most of the eastern part of the United States east winds and 

 southeast winds bring rain; west winds bring clear weather. 

 On the Pacific coast and in the western parts of this country 

 west winds and southwest winds bring rain, and east winds 

 bring clear weather. 



