TERRESTRIAL MAGNETISM, ETC. 271 



other times of the history of terrestrial magnetism 

 more than two magnetic poles. Indeed, Halley 

 had seemingly strong reason for inferring two 

 north poles from observations of early navigators, 

 showing large westerly variation of the compass in 

 Hudson's Bay, and in Smith's Sound (longitude 80 

 W., latitude 78 N.), and at sea in the north-west 

 Atlantic ; at different times, from 1616 to 1682, 

 when the compass in England was pointing due 

 north (in the earlier part of the period a few 

 degrees to the east of north, in the latter a few 

 degrees to the west). It may be that the present 

 tendency to converge to a point in the unexplored 

 Siberian Arctic sea may be a relic of a north 

 magnetic pole which existed in Halley's time and 

 has since ceased to exist ; but the amount of trust- 

 worthy information available scarcely suffices to 

 justify such a conclusion. One thing is certain, the 

 distribution of terrestrial magnetism has been 

 changing ever since accurate observations were 

 made upon it, and it is now enormously different 

 from what it was in the year 1600. 



Observations of Gilbert's contemporaries served 



