THE WEATHEJB 



32. Winds about a "low" cyclones. Since a low area is 

 usually more or less nearly circular in form and surrounded 

 by higher pressures, it follows that the air will tend to move 

 into the low area from all sides. If there were nothing to 

 direct the course of the wind except its tendency to blow 

 toward the lowest pressure, the wind would blow from all 

 directions straight across 

 the isobars toward the 

 center of low pressure. It 

 takes only a very slight ex- 

 amination of the weather 

 maps, in which the wind 

 direction is indicated by 

 arrows, to show that, while 

 the wind does blow into the 

 low areas, it does not blow 

 straight toward the center 

 of the " low." Instead of 

 moving as we should ex- 

 pect, the air turns a little 

 to its right. That is, at a, 

 point north of the " low " 

 the air is moving not south 

 but southwesterly ; at a 

 point east of the " low " it 

 may be moving northwest 

 instead of west; and so 

 likewise for other places in 

 the vicinity of the " low." 



The reason for this deviation of the wind from the expected 

 direction lies in the rotation of the earth on its axis. The ro- 

 tation does not cause the wind to blow, but it does affect the 

 direction of the wind. The effect of rotation upon moving 

 bodies may be illustrated by pouring water upon a rotating 

 globe. If the globe (which should be a smooth one) is placed 



FIG. 23. Deflection-on a rotating globe 



Water was poured upon the top of the globe 



while it was rotating from left to right. The 



direction of water is reversed after crossing 



the equator 



