THE EARTH A MAGNET. 27 



But we have considered only a single region of the 

 earth's surface. Arago's opinion will seem still more 

 just when we examine the change which has taken 

 place in what we may term the ' magnetic aspect ' of 

 the whole globe. The line which separates the region 

 of westerly magnets from the region of easterly 

 magnets now runs, as we have said, across Canada and 

 eastern Brazil in one hemisphere, and across Russia, 

 Asiatic Turkey, the Indian Ocean, and West Australia 

 in the other ; besides having an outlying oval to the 

 east of the Asiatic continent. Now these lines have 

 swept round a part of the globe's circuit in a most 

 singular manner since 1600. They have varied alike 

 in direction and complexity. The Siberian oval, now 

 distinct, was in 1787 merely a loop of the eastern line 

 of no declination. The oval appears now to be continu- 

 ally diminishing, and will one day probably disappear. 



We find here presented to us a phenomenon as 

 mysterious, as astonishing, and as worthy of careful 

 study as any embraced in the wide domains of science. 

 But other peculiarities await our notice. 



If a magnetic needle of suitable length be carefully 

 poised on a fine point, or, better, be suspended from a 

 silk thread without torsion, it will be found to exhibit 

 each day two small but clearly perceptible oscillations. 

 M. Arago, from a careful series of observations, deduced 

 the following results : 



At about eleven at night, the north end of the needle 

 begins to move from west to east, and having reached 

 its greatest easterly excursion at about a quarter-past 



