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THE NATIONAL GEOGRAPHIC MAGAZINE 



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Photograph by Oscar Halldin 

 SEA-GULLS, GREEN BAY, SPITZB-ERGEN 

 The birds took flight when the photographer sneezed. 



We have all of us learned in school 

 that, per square mile per hour, there is 

 more heat received from the sun at the 

 earth's Equator than anywhere else ; but 

 in the minds of most of us this truth is 

 only a half-truth, and therefore the most 

 dangerous sort of error, for we have com- 

 monly failed to grasp its interpretative 

 corollary, that while each hour of sunlight 

 brings most heat to the Equator, the hours 

 of sunlight per day in summer increase 

 in number as we go north. 



WHEN THE ARCTIC GETS MORE HEAT 

 THAN THE EQUATOR 



This would give a perfect balance if the 

 sunlight lengthened proportionally as the 

 heat per hour lessened. That is not the 

 case. As you go north, the length of day 

 in midsummer increases more rapidly 

 than the amount of heat per hour de- 

 creases; so that, although the heat per 

 hour received at Winnipeg is less than it 

 is in New Orleans, the amount of heat 

 received per day is greater. That is one 

 reason why Winnipeg is frequently hotter 

 than New Orleans in July. 



For something like five weeks every 



summer more heat per day is received 

 from the sun on a square mile in the 

 Arctic than at the Equator. If the North 

 Pole were located on an extensive low 

 land, remote from high mountains or any 

 large bodies of water, it would be about 

 as hot as the Equator on the Fourth of 

 July. There is, however, at the Pole and 

 in many places in the remote north a local 

 refrigeration that tempers what otherwise 

 would be unbearable heat. The winters 

 are long, and under certain conditions a 

 great deal of "cold'' may be stored up. 



In the polar basin we have an ocean 

 thousands of miles across and thousands 

 of feet deep, and all this water during the 

 long winter is chilled to the vicinity of 

 30 ° Fahrenheit above zero. 



There is also a certain amount of ice 

 floating around on the surface. We have, 

 therefore, a vast store of "cold" to neu- 

 tralize the terrific downpour of the sum- 

 mer sun's heat, and it is probable that the 

 air ten feet above the middle of the polar 

 ocean is seldom warmer, even in July, 

 than 50 or 55 ° Fahrenheit above zero. 

 Higher up it would be somewhat warmer. 



This means that conditions of flying, so 



