32 LIGHT SCIENCE FOR LEISURE HOURS. 



and the eastern parts of China. It is very noteworthy 

 also, that in the westerly region the declination is much 

 greater than in the easterly. Over the whole of Asia, 

 for instance, the needle points almost due north. On 

 the contrary, in the north of Greenland and of Baffin's 

 Bay, the magnetic needle points due west ; while still 

 farther to the north (a little westerly), we find the 

 needle pointing with its north end directly toward the 

 south. 



In the presence of these peculiarities, it would be 

 pleasant to speculate. We might imagine the existence 

 of powerfully magnetic veins in the earth's solid mass, 

 coercing the magnetic needle from a full obedience to 

 the true polar summons. Or the comparative effects 

 of oceans and of continents might be called into play. 

 But, unfortunately for all this, we have to reconcile 

 views founded on fixed relations presented by the earth 

 with the process of change indicated above. Let us 

 consider the declination in England alone. 



In the fifteenth century there was an easterly dec- 

 lination. This gradually diminished, so that in about 

 the year 1657 the needle pointed due north. After 

 this the needle pointed toward the west, and contin- 

 ually more and more, so that scientific men, having 

 had experience only of a continual shifting of the 

 needle in one direction, began to form the opinion that 

 this change would continue, so that the needle would 

 pass, through northwest and west, to the south. In 



