CLIMATE 311 



According to this classification, the tropical zones are the zones (1 ) 

 where the sun is vertical at some time during the year, (2) where 

 variations in the length of day and night are least, (3) where the 

 annual insolation is greatest, (4) where the range of annual insola- 

 tion is least, and consequently (5) where the annual range of tem- 

 perature is least. 



The intermediate (temperate) zones are the zones (1) where the 

 sun's rays are never vertical, (2) where the days and nights are 

 very unequal, but where the sun 

 is never above or below the hori- 

 zon for 24 hours together, (3) 

 where the amount of insolation is 

 less than below the tropics, and 

 (4) its annual range greater. 



The polar zones are the zones 

 (1) where the days and nights are 

 sometimes more than 24 hours 

 long. They are the zones (2) of 

 least annual insolation, and (3) 



of greatest range of insolation in 



,, ,. ., Fig. 259. Diagram showing the 



the course of the year. % ones> as defi * ed by latitu | e . 



According to this definition 



of the zones, each of the tropical zones is about 23J^ wide, each 

 of the intermediate zones about 43, and each of the polar zones 

 about 23^. 



This classification is simple, but the limits of the zones do not 

 always separate one sort of climate from another. Thus the climate 

 of the belts where the trade-winds blow is much the same every- 

 where; but the trades extend beyond the tropics. 



Zones defined by winds. 1 If climatic zones be defined by the 

 direction of prevailing winds, the tropical (or trade-wind) zones 

 are the zones where the trade-winds blow. They extend somewhat 

 beyond the tropics, even to latitudes of 30 or 35 on the eastern 

 sides of the oceans. The intermediate zones lie poleward from the 

 trade-wind zones, and are characterized by prevailing westerly 

 winds and variable climate, but they have no definite poleward 

 1 Davis, Elementary Meteorology. 



