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SYDNEY CHAPMAN, ESQ., M.A., D.SC, ON 



In earlier times the North Star was usually regarded as the point 

 to which the compass was directed. 



When Gilbert's treatise was written, it was well known that 

 the compass does not usually point true north, as, on his hypo- 

 thesis of the earth as a spherical magnet with its poles on the 

 axis of rotation, it should do. The error or declination of the 

 compass first claimed serious attention among Western navigators 

 at the time of Columbus' first voyage to the New World in 1492. 

 At that time the error of the compass in Europe was not great, 

 and if noticed was probably thought to be due to an imperfec- 

 tion of the instrument. A few days' voyage out from the Canary 

 Islands, however, the ship's pilot discovered that the needle 

 varied to the west of north by a whole point of the compass 

 (11J°). The seamen were thrown into terror and dismay, 

 probably feeling that if the compass no longer remained faithful 

 to the Northern Star, " all their foundations were out of joint." 

 Columbus, who was troubled by no such fears, on learning the 

 cause of their disquiet successfully allayed the distress by telling 

 them that the needle truly pointed north, but that the Pole 

 Star had a motion of its own. His great authority in astro- 

 nomical learning caused this fictitious explanation to be accepted, 

 but he seems also to have secretly altered the compass card so 

 that the needle appeared to have become tiue once more. 

 Columbus himself recognized the incident as the discovery of a 

 new fact of nature, viz., that the compass diverges from true 

 north by an amount which varies from place to place. In crossing 

 from Europe to America he had gone from places of slight easterly 

 declination to regions where the compass pointed west of north. 



This fact took some time to become generally known, after 

 which it was apparent that, if the compass was to retain its 

 full value in na\dgation, the error in its direction at different 

 places must be ascertained and allowed for. Voyagers began 

 to make observations of the compass declination at various 

 points on their course, when the sun and stais made it possible 

 to determine astronomically the direction of true north. Chait- 

 makers also began to enter these observations at the corre- 

 sponding points on their maps, for the benefit of later navigators 

 in those regions, who might be compelled, by cloudy weather 

 to rely solely on their compass for direction. A better way of 

 indicating the declination on maps was afterwards introduced, 

 the first person to apply the method being Halley, the second 

 Astronomer Royal (1720-1742). 



