THE CONQUEST OF TIME AND SPACE 



later by Gillebrand, Professor of Geometry at Graham 

 College. Dr. Halley, the celebrated astronomer — 

 whose achievements have been recalled to succeeding 

 generations by the periodical return of the comet 

 that bears his name — ^gave the matter attention, 

 and in a paper before the Royal Society in 1692 he 

 pointed out that the direction of the needle at London 

 had changed in a little over a century (between 1580 

 and 1692) from 11 degrees 15 minutes East to 6 degrees 

 West, or more than 17 degrees. 



Halley conclusively showed that similar variations 

 occurred at all other places where records had been 

 kept. He had already demonstrated, a few years 

 earlier, that the deviations of the compass noted at sea 

 are not due to the varying attractions of neighbor- 

 ing bodies of land, but to some influence having to do 

 with the problem of terrestrial magnetism in its larger 

 aspects. Halley advocated the doctrine, which had 

 first been put forward by William Gilbert, that the 

 earth itself is a gigantic magnet, and that the action 

 of the compass is dependent upon this terrestrial source 

 and not, as many navigators believed, on the influence 

 of a magnetic star, or on localized deposits of lode- 

 stone somewhere in the unknown regions of the North. 



Further observations of the records presently made 

 it clear that there are also annual and even daily varia- 

 tions of the compass of slight degree. The fact of 

 diurnal variations was first discovered by Mr. Graham 

 about the year 17 19. More than half a century later 

 it was observed by an astronomer named Wales, who 

 was accompanying Captain Cook on his famous voyage 



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