20 LIGHT SCIENCE FOR LEISURE HOURS. 



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 Kussia, Asiatic 

 Turkey, the Indian Ocean, and West Australia in the 

 other, besides having an outlying oval to the east 

 of the Asiatic continent. These lines have swept 

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

 manner since 1600. They have varied alike in direc- 

 tion 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 continually 

 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 

 eight in the morning, returns towards the west to attain 

 its greatest westerly excursion at a quarter-past one. 

 It then moves again to the east, and having reached its 



