Geology 



from the tropic towards the Arctic Circle constant south 



winds, gradually dying away towards a polar calm with 



descending air currents. 



In the Southern Hemisphere these winds would be 



reversed ; between tropic and equator, south winds 



would prevail, 

 and north 

 winds from the 

 tropic towards 

 the Antarctic 

 Circle. 



The effect of 

 the seasons on 

 this ideal ar- 

 rangement 

 would be to 

 shift the zones 

 northward in 

 the northern 

 summer, so 

 that the Dol- 

 drums would 



FIG. i. Theoretical Circulation of the Atmosphere. OCCUpy 



region of the 



calms of Cancer, and southward in the southern 

 summer. 



An examination of a map of the world will show 

 that there is far more land in the Northern than in the 

 Southern Hemisphere, a circumstance which destroys 

 the balance, and has the effect of shifting the various 

 belts towards the north, as owing to the irregular 

 distribution of land and water the heat-equator, or line 



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