32 LIGHT SCIENCE FOR LEISURE HOURS. 



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, about 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.' 



Colonel Sabine discovered that the intensity of the 

 magnetic action varies during the course of the year. 

 It is greatest in December and January in both 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 as- 

 tronomical element which seems to correspond with the 

 law discovered by Sabine ? There is one very impor- 

 tant element. The position of the perihelion of the 

 earth's orbit is such that the earth is nearest to the sun 

 on about the 31st of December or the 1st of January. 

 There seems nothing rashly speculative, then, in con- 

 cluding that the sun exercises a magnetic influence on 



