Movements <>f the Atmosphere. 



563 



;ily descending and flowing outward below, maintain- 

 ing an anti-cyclonic system of winds like that of the upper 

 part of Fig. 261. Between the high area at the poles and 

 the tropical high pressure belts, where the two systems of 



- 



FIG. 262. Diagram of tlie World system of winds. (Adapted from 



Ferrel.) 



surface winds meet, there is, in the judgment of Eerrel, a 

 tendency to develop a third or polar calm belt, over which 

 the air rises to return as an upper current to the tropical 

 calm belts, or else back again to the poles. 



716. Wind Zones. There is thus a tendency for the sur- 

 face winds of the globe to divide into six zones, separated 

 by five calm belts, two tropical or trade wind zones, two 

 temperate or anti-trade wind zones and two polar zones, as 



