40 LIGHT SCIENCE FOR LEISURE HOURS. 



we find a more considerable divergence, so that instead 

 of there being a northern pole of greatest intensity 

 nearly coincident with the northern magnetic pole, 

 which we have seen lies to the north of the American 

 Continent, there are two northern poles, one in Siberia 

 nearly at the point where the river Lena crosses the 

 Arctic circle, the other not so far to the north only a 

 few degrees north, in fact, of Lake Superior. In the 

 south, in like manner, there are also two poles, one on 

 the Antarctic circle, abotit 130 E. long., in Adelie 

 Island, the other not yet precisely determined, but 

 supposed to lie on about the 240th degree of longitude, 

 and south of the Antarctic circle. Singularly enough, 

 there is a line of lower intensity running right round 

 the earth along the valleys of the two great oceans, 

 " passing through Behring's Straits and bisecting the 

 Pacific, on one side of the globe, and passing out of 

 the Arctic Sea by Spitzbergen and down the Atlantic, 

 on the other." 



General Sabine discovered that the intensity of the 

 magnetic action varies during the course of the year. 

 It is greatest in December and January in 1>oth hemi- 

 spheres. If the intensity had been greatest in winter, 

 one would have been disposed to have assigned sea- 

 sonal variation of temperature as the cause of the 

 change. But as the epoch is the same for both hemi- 

 spheres, we must seek another cause. Is there any 

 astronomical element which seems to correspond with 



