CAUSE OF COLD IN ARCTIC REGIONS. 171 



period, torn from its cliffs by some mighty glacier 

 and slowly rolled and rounded, for hundreds of years 

 perhaps, down the scarred slopes of its native valley. 



THE GREAT EGG-SHAPED ROOK. 



The primary cause of the intense and prolonged 

 cold of the arctic regions is the shortness of the 

 time during which they are under the influence of 

 the sun's rays. For a few months in summer the 

 sun shines brightly, but, owing to the position of 

 the globe, obliquely on the poles. During part of 

 that period it shines at mid-night as well as at 

 mid-day. But during the greater part of the year 

 its beams throw but a feeble light there, and for 

 several months in winter there is absolutely no day 

 at all nothing but one long dismal night of dark- 

 ness, that seems as if the bright orb of day had 

 vanished from the heavens for ever. 



The length of this prolonged day in summer, and 

 this dreary night in winter, depends, of course, upon 

 latitude. The length of both increases as we ap- 

 proach the poles. The long daylight in summer is 

 exceedingly delightful. We once saw the sun de- 



