LAWS OF MAGNETIC PHENOMENA. 51 



in Europe anterior to 1200. It was afterwards 

 found 3 that the needle does not point exactly 

 towards the north. Gilbert was aware of this 

 deviation, which he calls the variation, and also, 

 that it is different in different places 4 . He main- 

 tained on theoretical principles also 5 , that at the 

 same place the variation is constant; probably in 

 his time there were not any recorded observations 

 by which the truth of this assertion could be tested ; 

 it was afterwards found to be false. The alteration 

 of the variation in proceeding from one place to 

 another was, it will be recollected, one of the cir- 

 cumstances which most alarmed the companions of 

 Columbus in 1492. Gilbert says 6 , "Other learned 

 men have, in long navigations, observed the dif- 

 ferences of magnetic variation, as Thomas Hariot, 

 Robert Hues, Edward Wright, Abraham Kendall, all 

 Englishmen : others have invented magnetic instru- 

 ments and convenient modes of observation, such as 

 are requisite for those who take long voyages, as 

 William Borough in his book concerning the varia- 

 tion of the compass, William Barlo in his supple- 

 ment, William Norman in his New Attractive. This 

 is that Robert Norman (a good seaman and an 

 ingenious artificer,) who first discovered the dip 

 of magnetic iron." This important discovery was 

 made 7 in 1576. From the time when the difference 

 of the variation of the compass in different places 



8 Before 1269. Enc. Met. p. 737. 4 De Magnete, lib. iv. c. 1. 

 8 c. 3. 6 Lib. i. c. 1. I Enc. Met. p. 738. 



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