Bcimce progress. 



No. 26. April, 1896. Vol. V. 



THE GENERAL BEARINGS OF MAGNETIC 



OBSERVATIONS. 



IF necessity be the surest prompter of invention, it is not 

 too much to say that the necessity of the navigator 

 has been a most potent factor in producing the observer of 

 the elements of Terrestrial Magnetism. The traveller on 

 land might rest during darkness until daylight enabled him 

 to resume his journey ; but the seaman on the trackless 

 ocean was dependent upon the indications of his compass 

 by day and night ; and after the discovery of Columbus 

 that the magnetic Declination or Variation of the needle 

 from the direction of the geographical North varied in 

 amount with the Latitude and Longitude, a new impetus 

 was given to observation. 



The publication of Gilbert's grand discovery that the 

 earth is a magnet and the director of the freely suspended 

 needle, followed by the discovery of the secular change in 

 the value of the Declination, naturally added to the desire 

 of both landsmen and seamen to know as much as possible 

 concerning that great magnet, both from purely scientific 

 reasons and to meet the practical ends of the navigator. 

 Thus the seventeenth and eighteenth centuries were re- 

 markable for the number of observers both of the magnetic 

 Dip and Declination. 



So important had a correct knowledge of the Declination 



become to the requirements of navigation, as early as the 



close of the seventeenth century, that Halley, under the 



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