THE JACKSTAFF.
The removal of the Line of Demarcation from the supposed meridian of non-variation of the needle did not prevent the phenomena of terrestrial magnetism becoming of vast importance in the dispute between the Crowns of Spain and Portugal. It characterizes the difference between the imaginative and somewhat fantastic quality of Columbus’ mind and the cooler, more practical, and better administrative apprehension of Sebastian Cabot, that while each observed the phenomenon of the variation of the needle, and each imagined it a clew to some system of determining longitude, to Columbus it was associated with wild notions of a too-ample revolution of the North Star about the true pole.[386] It was not disconnected in his mind from a fancy which gave the earth the shape of a pear; so that when he perceived on his voyage a clearing of the atmosphere, he imagined he was ascending the stem-end of the pear; where he would find the terrestrial paradise.[387] To Cabot the phenomenon had only its practical significance; and he seems to have pondered on a solution of the problem during the rest of his life, if, as Humboldt supposes, the intimations of his death-bed in respect to some as yet unregistered way of discovering longitude refer to his observations on the magnetic declination.[388]
The idea of a constantly increasing declination east and west from a point of non-variation, which both Columbus and Cabot had discovered, and which increase could be reduced to a formula, was indeed partly true; except, as is now well known, the line of non-variation, instead of being a meridian, and fixed, is a curve of constantly changing proportions.[389]
THE BACKSTAFF.
The earliest variation-chart was made in 1530 by Alonzo de Santa Cruz;[390] and schemes of ascertaining longitude were at once based on the observations of these curves, as they had before been made dependent upon the supposed gradation of the change from meridian to meridian, irrespective of latitude.[391] Fifty years later (1585), Juan Jayme made a voyage with Gali from the Philippine Islands to Acapulco to test a “declinatorum” of his own invention.[392] But this was a hundred years (1698-1702) before Halley’s Expedition was sent,—the first which any government fitted out to observe the forces of terrestrial magnetism;[393] and though there had been suspicions of it much earlier, it was not till 1722 that Graham got unmistakable data to prove the hourly variation of the needle.[394]
The earliest map which is distinctively associated with the views which were developing in Columbus’ mind was the one which Toscanelli sent to him in 1474. It is said to have been preserved in Madrid in 1527;[395] and fifty-three years after Columbus’ death, when Las Casas was writing his history, it was in his possession.[396] We know that this Italian geographer had reduced the circumference of the globe to nearly three quarters of its actual size, having placed China about six thousand five hundred miles west of Lisbon, and eleven thousand five hundred miles east. Japan, lying off the China coast, was put somewhere from one hundred degrees to one hundred and ten degrees west of Lisbon; and we have record that Martin Pinzon some years later (1491) saw a map in Rome which put Cipango (Japan) even nearer the European side.[397]
