280 EPOCHS IN THE HISTORY OF THE CONTEMPLATION OP 



endeavoured to cause " a physical Hue of demarcation to be 

 converted into a political one." 



The influence which the discovery of America, and the 

 great nautical enterprizes connected with it exercised so 

 rapidly on all physical and astronomical knowledge, is most 

 strikingly felt when we recal the first impressions of those 

 who lived at the period, and the wide range of scientific 

 endeavours of which the most important part belongs to the 

 first half of the sixteenth century. Columbus has not only 

 the incontestable merit of having first discovered a " line 

 without magnetic variation," but also of having, by his 

 considerations on the progressive increase of westerly declina- 

 tion in receding from that line, given the first impulse to 

 the study of terrestrial magnetism in Europe. The circum- 

 stance, that almost every where the ends of a freely suspended 

 magnet do not point exactly to the north and south geo- 

 graphical poles, might easily have been recognised, even with 

 very imperfect instruments, in the Mediterranean, and in other 

 places where the declination amounted in the twelfth century 

 to more than eight or ten degrees. But it is not improbable 

 that the Arabs, or the Crusaders who were in contact with 

 Eastern nations from 1096 to 1270, in spreading the use of 

 Chinese or Indian compasses, may also have called attention, 

 even at that early period, to the circumstance of magnetic 

 needles pointing in different parts of the world to the north- 

 east or to the north-west, as to a long-known phenomenon. 

 "We know positively from the Chinese Penthsaoyan, which 

 was written under the dynasty of the Song ( 432 ) between 

 1111 and 1117, that the manner of measuring the amount 

 of westerly declination had been then long understood. 



