122 



The Realm of Nature 



CHAP. 



lower atmosphere. They also produce air currents 

 toward the poles in the opposite direction as south- 

 west and north-west winds, which gradually die away 

 about the polar circles, where the equator-seeking winds 

 meet, check, and rise above them. Hence in the tem- 

 perate zones the surface winds should be parallel to the 



FIG. 22. Theoretical Circulation of the Atmosphere, after Fen-el. The arrows 

 show the directions of the winds over the surface and of the vertical move- 

 ments of air. 



pole-seeking upper winds, while between the two are the 

 equator-seeking middle winds. In the tropics and the polar 

 circles there are only the lower equator-seeking winds and 

 the upper polar-seeking winds, as shown in the diagram. 



178. Zones of Winds and Calms. This theoretical 

 circulation divides the Earth's surface into zones, which 

 roughly correspond to those of solar climate ( 125). In 

 the tropical belts of high pressure, from which surface winds 



