56 TERRESTRIAL MAGNETISM. 



conversion of a physical line into a political line of demar- 

 cation. The "raya," on which the "agujas de marear" 

 point direct to the pole-star, became the boundary line 

 between the crowns of Castile and Portugal by virtue of a 

 Papal decree, whose arrogance proved of great and lasting, 

 though undesigned and unforeseen, benefit to the enlarge- 

 ment of nautical astronomy and the improvement of mag- 

 netic instruments, in consequence of the importance which 

 naturally attached to determining, with astronomical accuracy, 

 the geographical longitude of such a boundary on both sides 

 of the equator. (Humboldt, Examen critique de la Geogr. 

 , T. iii. p. 54.) Felipe Guillen, of Seville (1525), and, at a 

 still earlier period, probably the cosmographer Alonso de 

 Santa Cruz, teacher of mathematics to the young Emperor 

 Charles V., constructed new " variation compasses/' with 

 which solar altitudes could be taken. In 1530 a century 

 and a half, therefore, before Halley the same Alonso 

 de Santa Cruz drew the first general "variation map/' 

 founded, it must be admitted, on very imperfect materials. 

 The voyage of Juan Jayme, who sailed from the Philippines 

 to Acapulco with Francisco Gali in 1585, solely for the 

 purpose of trying, during the long passage across the Pacific, 

 a new declination instrument which he had invented, shows 

 how animated an impulse had been given in the 16th 

 century, and after the death of Columbus, to the study of 

 terrestrial magnetism, by the controversy respecting the 

 Papal " line of demarcation." 



This disposition to pursue observation could not but be 

 accompanied by its unfailing attendant, if not, as is still 

 oftener the case, its precursor, a fondness for theoretical 

 speculations. Many of the old sea-stories of the Indians, 



