VARIATION-CHAETS. 55 



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 raya, on which the agujas de marear point directly 

 to the polar star, became the line of demarcation between the 

 kingdoms of Portugal and Castille ; and from the importance 

 of determining with astronomical exactness the geographical 

 length of such a boundary in both hemispheres, and over 

 every part of the earth's surface, an arrogant Papal decree, 

 although it failed in effecting this aim, nevertheless exerted a 

 beneficial effect on the extension of astroiiomico-nautical 

 science and on the improvement of magnetic instruments. 

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

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

 cosmographer Alonso de Santa Cvuz, teacher of mathematics 

 to the young Emperor Charles V., constructed new variation 

 compasses by which solar altitudes could be taken. The latter 

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

 up the first general variation chart, although it was certainly 

 based upon very imperfect materials. We may form some 

 idea of the interest that had been excited in reference to ter- 

 restrial magnetism in the 1 6th century, after the death of 

 Columbus, and during the contest regarding the line of 

 demarcation, when we find that Juan Jay me made a voyage 

 in 1585, with Francisco Gali, from the Philippines 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 observation, 

 we trace the same tendency to theoretical speculations which 

 always accompanies or even more frequently precedes the 

 former. Many old traditions current amongst 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 immoveably fixing the entire 

 vessel. The effect of such delusions as these was to give rise 

 to a conception of the concurrence, at the poles, o lines 01 

 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 the Geography of Ptolemy, we 



