112 LIGHT SCIENCE FOR LEISURE HOURS. 



which lie to the west of Greenland. The third is that 

 pursued by Russian explorers who have attempted to 

 cross the frozen seas which surround the northern 

 shores of Siberia. 



In considering the limits of the unknown north- 

 polar regions, we shall also have to take into account 

 the voyages which have been made around the northern 

 shores of the American Continent in the search for a 

 " northwestern passage." The explorers who set out 

 upon this search found themselves gradually forced to 

 seek higher and higher latitudes if they would find a 

 w r ay round the complicated barriers presented by the 

 ice-bound straits and islands which lie to the north of 

 the American Continent. And it may be noticed in 

 passing, as a remarkable and unforeseen circumstance, 

 that the farther north the voyagers went the less severe 

 was the cold they had to encounter. "We shall see that 

 this circumstance has an important bearing on the con- 

 siderations we shall presently have to deal with. 



One other circumstance respecting the search for 

 the northwest passage, though not connected very 

 closely with our subject, is so singular and so little 

 known that we feel tempted to make mention of it at 

 this point. The notion with which the seekers after a 

 northwest passage set out was simply this, that the 

 easiest way of reaching China and the East Indies was 

 to pursue a course resembling as nearly as possible that 

 on which Columbus had set out if only it should 



