fogs are made up of frost flakes or spicules. Another visibility 

 problem is that of mirage. Due to the differential density of air, 

 light cannot pass through the boundary between the layer of cold 

 air along the surface and the warmer air above. The surface of 

 the ground is obscured and images are inverted. 



Glare is a common problem during the period when the sun is 

 above the horizon and the sky is overcast. On sea-ice or on snow- 

 covered land everything looks equally white. Eye strain and snow 

 blindness come from an attempt to distinguish features in this gen- 

 eral whiteness. (Rest the eyes by viewing regularly any marked 

 contrasts that may exist — particularly areas of open water.) 



In the absence of fog, the degree of visibility is very great. 

 Normal horizontal visibility in the Arctic is 50 miles, and under 

 special conditions visibility for 150 miles is possible. This poses 

 a military problem of concealment. 



Sound travels with great clarity in the dry, cold air. Sharp 

 sounds can be distinctly heard at distances of 10 miles or over. 



The areas having these general characteristics of the Arctic 

 and Subarctic include northern Alaska, the northern two-thirds 

 of Canada and Labrador, Greenland, Iceland, the northern por- 

 tions of Scandinavia in the Lapp country, the northern sections 

 of the Soviet Union, including the lower basins of the famous 

 north-flowing rivers (Ob, Yenisei, Lena), and all of the islands 

 and seas north of these mainlands. 



PREDOMINANCE OF THE ARCTIC SEA 



Looking at the top of the world, the Arctic Sea (also referred 

 to as Arctic Ocean) is seen to be an arm or gulf of the Atlantic 

 Ocean, joined to it by the wide strait of the Norwegian and Green- 

 land Seas. Unlike the impression gained from a world map on 

 the Mercator projection, the Arctic Sea is comparatively small 

 in area. The two great land masses of the Eastern and Western 

 Hemispheres are separated by relatively short distances across this 

 mediterranean. Great circle flight routes between major power 

 centers lie over the Arctic. In economic terms, however, the uses 

 of these routes have been shortcuts to nowhere up to the present 

 time. 



In ge leral, the peoples of the two hemispheres consider the value 

 and use of the arctic basin on quite dissimilar bases. The Soviet 

 Union, needing an outlet for the interior of the continent, is look- 

 ing north and is using the seas bordering the central basin as a 

 seasonal supply route. Russian interest in her northern sections 



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