56 COSMOS. 



The idea of a curve of no declination in the Atlantic was 

 associated in the easily excited fancy of Columbus with oth- 

 er somewhat vague views of alterations of climate, of an 

 anomalous configuration of the earth, and of extraordinary 

 motions of the heavenly bodies, in which he found a motive 

 for converting a physical into a political boundary line. Thus 

 the ra2/a, on which the agujas de marear point directly to the 

 polar star, became the line of demarkation between the king- 

 doms of Portugal and Castillo ; and from the importance of 

 determining with astronomical exactness the geographical 

 length of such a boundary in both hemispheres, and over ev- 

 ery part of the earth's surface, an arrogant Papal decree, al- 

 though it failed in effecting this aim, nevertheless exerted a 

 beneficial effect on the extension of astronomico-nautical 

 science and on the improvement of magnetic instruments. 

 (Humboldt, Examen Crit. de la Geog., t. iii., p. 54.) Felipe 

 Guillen, of Seville, in 1525, and probably still earlier the 

 cosmographer Alonso de Santa Cruz, teacher of mathematics 

 to the young Emperor Charles V., constructed new variation 

 compasses by which solar altitudes could be taken. The lat- 

 ter in 1530, and therefore fully 150 years before Halley, drew 

 up the first general variation chart; nlthough it was certain- 

 ly based upon very imperfect materials. We may form 

 some idea of the interest that had been excited in reference 

 to terrestrial magnetism in the IGth century, after the death 

 of Columbus, and during the contest regarding the line of 

 demarkation, when we find that Juan Jayme made a voyage 

 in 1585, with Francisco Gali, from the Philipines to Aca- 

 pulco, for the sole purpose of testing by a long trial in the 

 South Sea a Declinatorium of his own invention. 



Amid this generally diffused taste for practical observa- 

 tion we trace the same tendency to theoretical speculations 

 which always accompanies or even more frequently precedes 

 the former. Many old traditions current among Indian and 

 Arabian sailors speak of rocky islands which bring death and 

 destruction to the hapless mariner, by attracting, through 

 their magnetic force, all the iron which connects together 

 the planks of the ship, or even by immovably fixing the en- 

 tire vessel. The effect of such delusions as these was to 

 give rise to a conception of the concurrence, at the poles, of 

 lines of magnetic variation, represented materially under the 

 image of a high magnetic rock lying near one of the poles. 

 On the remarkable chart of the New Continent, which was 

 added to the Latin edition of 1508 of tlie Geography of 



