126 LIGHT SCIENCE FOR LEISURE HOURS. 



Greenland. It follows that, densely as the ice may 

 be packed at times in the seas by which Hudson, 

 Scoresby, and other captains, have attempted to reach 

 the North Pole, the frozen masses must in reality be 

 floating freely, and there must therefore exist channels 

 through which an adventurous seaman might manage 

 to penetrate the dangerous barriers surrounding the 

 polar ocean. 



In such an expedition, chance unfortunately plays 

 a large part. Whalers tell us that there is great un- 

 certainty as to the winds which may blow during an 

 arctic summer. The icebergs may be crowded by 

 easterly winds upon the shores of Greenland, or by 

 westerly winds upon the shores of Spitzbergen, or, 

 lastly, the central passage may be the most encum- 

 bered, through the effects of winds blowing now from 

 the east and now from the west. Thus the arctic 

 voyager has not merely to take his chance as to the 

 route along which he shall adventure northward, but 

 often, after forcing his way successfully for a consider- 

 able distance, he finds the ice-fields suddenly closing 

 in upon him on every side, and threatening to crush 

 his ship into fragments. The irresistible power with 

 which, under such circumstances, the masses of ice 

 bear down upon the stoutest ship has been evidenced 

 again and again ; though, fortunately, it not unfre- 

 quently happens that some irregularity along one side 

 or the other of the closing channel serves as a sort of 



