REPORT ON THE MAGNETISM OF THE EARTH. 107 



and as it is probable that for some time subsequent to the dis- 

 covery of the directive property of the needle the deviation in 

 Europe was not of sufficient magnitude to have been easily de- 

 tected by means of the rude instruments then in use, it may 

 very likely be owing to this circumstance that we have not 

 earlier records of the variation*. That Columbus, the most 

 scientific navigator of his age, when he commenced his career 

 of discovery, and undertook to show the western route to India, 

 was not aware of it, is clear, since the discovery during his first 

 voyage has been attributed to him. However, although Co- 

 lumbus may have noticed that the needle did not in every situa- 

 tion point due north, and Adsiger, long before him, may even 

 have rudely obtained the amount of its deviation, the first ob- 

 servations of the variation on which any reliance can be placed 

 appear to have been made about the middle of the sixteenth 

 century, and shortly afterwards it was well known that the va- 

 riation is not the same in all places f . 



2. Change in the Direction of the Needle. — When it was 

 first determined by observation, about 1541, that the needle 

 did not point to the pole of the earth, it was found that this vari- 

 ation from the meridian, at Paris, was about 7° or 8° towards 

 the east. In 1550 it was observed 8° or 9° east; and in 

 1580, 11 1° east. Norman appears to have been the first who 

 observed the variation with any degree of accuracy in Lon- 

 don. He states that he observed it to be 11° 15' east J, but he 

 was not aware that it does not remain constant in the same 

 place §. In 1580, Burough found the variation at Limehouse 

 to be 11^° or 11^° east||, and his observations appear to be 



• Another reason why the variation was not earlier observed may be that the 

 natural magnet was first used for the purposes of navigation, and its directive 

 line was that which pointed to the pole star. As it was therefore considered 

 that the natural magnet indicated the direction of the meridian, and it was 

 found that a needle touched by it had the directive power, when the needle was 

 introduced it was assumed that this also pointed in the meridian. 



t The Netv Attractive, by Robert Norman, chap. ix. London 1596. 



X Ibid. No date is given for this observation ; but from the circumstance of 

 Burough referring to Norman's book in the preface to his Discourse of the Va- 

 riation of the Compasse, dated 1581, (the copy of this to which I have access 

 was printed in 1596, but the Bodleian Library contains one printed in 1581,) 

 it would appear that there must have been an earlier edition of Norman's book 

 than that of 1596, and that his observations must have been made before 1581. 

 Bond, Philosophical Transactions, vol. viii. p. 6066, gives 1576 as the date of 

 Norman's observations. 



§ " And although this variation of the needle be found in travaile to be divers 

 and changeable, yet at anie land or fixed place assigned, it remaineth alwaies 

 one, still permanent and abiding." New Attractive, chap. ix. 



II The mean of his observations, which do not differ 20', is 11° 19' east. 



