CHAPTER X 

 WIND AND WEATHER 



Wind is a vital part of the weather that influences our 

 daily lives so greatly. It brings to inland areas the mois- 

 ture that the sun has vaporized from large bodies of wa- 

 ter and which here falls as rain to refill streams and to 

 satisfy the thirst of crops and forests and other living 

 things. It refreshes us on hot days. It helps dry the fam- 

 ily washing, and pumps the water on many a farm. It 

 drives a host of sailing vessels across ocean and lake. 

 Although we stand in awe of its tremendous force when 

 it whirls in mighty hurricanes that lay waste the land and 

 raise the sea to fury, or, as a tornado, twists along its 

 narrow path of destruction, yet, as a whole, wind is much 

 more man's friend than his enemy. 



The pressure of wind on our faces tells us that it is simply 

 air in motion. Motion is a form of energy, so we naturally 

 expect to find the sun, the original source of all energy, respon- 

 sible for wind. Winds are horizontal movements of the air caused 

 by differences in temperature. The air in great sections of the 

 atmosphere, heated by sun-warmed areas of the earth beneath, 

 becomes lighter and rises, leaving areas of low air pressure. 

 Colder, heavier air from other sections, with higher air pressure, 

 rushes in to replace it. There is a continual tendency of the air 

 to pass from an area of high pressure to an area of low pres- 

 sure. In this way, winds are caused, their velocity and force 

 depending upon the differences in air pressure of the two areas. 

 As a result we have great movements in the currents of air, gov- 

 erned by laws so well established that weather men can predict 

 with increasing certainty the path and intensity of storms. 



This relation of heat to air currents may be illustrated by 

 holding a piece of smoking wood near the draft entrance of a 

 stove. The direction the smoke takes shows that the unwarmed 

 air of the room is passing into the draft entrance to take the 

 place of the air that has become heated and is rising. 



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