580 COSMOS. 



netic ani a Li'onomical methods were anxiously sougtit, in ordei 

 to determine, on land and at sea, those points which are inter- 

 sected by the ideal line of demarkation. The imperfect con- 

 dition of science, and of all the instruments used at sea in 1493 

 to measure space and time, were unequal to afibrd a practical 

 solution to so difficult a problem. Under these circumstances, 

 Pope Alexander VI. actually rendered, without knowing it, 

 an essential service to nautical astronomy and the physical 

 science of terrestrial magnetism by his presumption in dividing 

 half the globe between two powerful states. From that time 

 forth the maritime powers were continually beset by a host 

 of impracticable proposals. Sebastian Cabot, as we learn from 

 his friend, Richard Eden, boasted on his death-bed of having 

 had a " divine revelation made to him of an infallible meth- 

 od of finding geographical longitude." This revelation con- 

 sisted in a firm conviction that magnetic declination changed 

 regularly and rapidly with the meridian. The cosmographer 

 Alonso de Santa Cruz, one of the instructors of Charles V., un- 

 dertook, although certainly from very imperfect observations, 

 to draw up the first general variation chart* in the year 1530 

 and, therefore, one hundred and fifty years before Halley. 



The advance or movemejit of the magnetic lines, the knowl- 

 edge of which has generally been ascribed to Gassendi, was 

 not even conjectured by William Gilbert, although Acosta, 

 "from the instruction of Portuguese navigators," had at a 

 much earlier period assumed that there were four lines with- 

 out declination over the earth's surface.! No sooner was the 



* In corroboration of this statement regarding Sebastian Cabot on hia 

 death-bed, see the well-written and critically-historical work by Biddle, 

 entitled A Memoir of Sebastian Cabo (p. 222). " We do not know 

 with certainty," says Biddle, " either the year of the death or the 

 ijurying-place of the great navigator who gave to Great Britain almost 

 an entire continent, and without whom (as without Sir Walter Raleigh) 

 tlie English language would perhaps not have been spoken by many 

 millions who now inhabit America." On the materials according to 

 which the variation chart of Alonso de Santa Cruz was compiled, as 

 well as on the variation compass, whose construction allowed altitudes 

 of the sun to be taken at the same time, see Navarrete, Noticia biogra- 

 fica del cosmografo Alonso de Saiita Cruz, p. 3-8. The first variation 

 compass was constructed before 1525, by an ingenious apothecary of 

 Seville, Felipe Guillen. The endeavors to learn more exactly the di- 

 rection of the curves of magnetic declination were so earnest, that in 

 1585 Juan Jayme sailed with Francisco Gali from Manilla to Acapulco 

 merely for the purpose of trying in the Pacific a declination instrument 

 which he had inventei. See my Essai Politique sur la Nouvelle Ea 

 pagne, t. iv., p. 110. 



* Acosta. Hist. Natural de las Liiias, lib. i.. cap. )7 These foui 



