TERRESTRIAL MAGNETISM, ETC. 273 



turned, and began to come back from west towards 

 the north, very slowly at first, and with gaining 

 speed ever since, till now (1879) it has become 

 reduced to 18 40', and is diminishing at the rate 

 of nearly a fifth of a degree annually. 1 



From 1605 to 1609, at the Cape of Good Hope, 

 the variation altered from half a degree east to 

 one-fifth of a degree west, and from that time it has 

 been becoming more and more westerly. The 

 needle seems now, at the Cape of Good Hope, to 

 be returning, or about to return, towards the north, 

 and may probably enough again point due north 

 there a few hundred years hence. 



Corresponding observations as to the magnetic 

 dip have been made at different places. After the 

 discovery of the dip by Robert Norman in 1576, 

 when he found its amount in London to be 71 50', 

 it increased gradually till about 1723, when it was 

 74 42', and since that time it has been decreasing 

 till it is now 67 36' ; and it is now decreasing 

 about 2' annually. At the Cape of Good Hope 



1 [N T ote added August, 1890.] Since 1881 the rate of diminution 

 of the westerly variation in London has become less than half what 

 it was from 1879 to 1880. The variation in 1890 is 17 26' west. 



VOL. III. T 



