218 HISTORY OF MAGNETISM. 



appear easy to trace with certainty the period of this discovery 

 Passing over certain legends of the Chinese, as at any rate not bearing 

 upon the progress of European science, 3 the earliest notice of this pro- 

 perty appears to be contained in the Poem of Guyot de Provence, 

 who describes the needle as being magnetized, and then placed in or 

 on a straw, (floating on water, as I presume :) 



Puis sc torne la pointe tonte 

 Centre 1'estoile sans doute ; 



that is, it turns towards the pole-star. This account would make the 

 knowledge of this property 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 varia- 

 tion, and also, that it is different in different places. 4 He maintained 

 on theoretical principles also, 5 that at the same place the variation is 

 constant ; probably in his time there were not any recorded observa- 

 tions by which the truth of this assertion could be tested ; it was 

 afterwards found to be false. The alteration of the variation in pro- 

 ceeding from one place to another was, it will be recollected, one of 

 the circumstances which most alarmed the companions of Columbus 

 in 1492. Gilbert says, 6 " Other learned men have, in long navigations, 

 observed the differences of magnetic variations, as Thomas Hariot, 

 Robert Hues, Edward Wright, Abraham Kendall, all Englishmen : 

 others have invented magnetic instruments and convenient modes of 

 observation, such as are requisite for those who take long voyages, as 

 "William Borough in his Book concerning the variation of the compass, 

 William Barlo in his supplement, William Norman in his New 

 Attractive. This is that Robert Norman (a good seaman and an in- 

 genious 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 

 became known, it was important to mariners to register the variation 

 in all parts of the world. Halley was appointed to the command of a 

 ship in the Pioyal Navy by the Government of William and Mary, 

 with orders " to seek by observation the discovery of the rule for tho 

 variation of the compass." He published Magnetic Charts, which 



2 Enc. Met. art. Magnetism, p. 73fi. 3 Before 1269. Enc. Met. p. 737. 

 * De Magnete, lib. iv. c. 1. 6 c. 3. c Lib. i. c. 1. * Enc Mat. p. 738. 



