As he still moved westerly the magnetic line was found to move farther and farther away from the pole as it had before the 13th approached it. To an observer of Columbus's quick perceptions, there was a ready guess to possess his mind. This inference was that this line of no variation was a meridian line, and that divergences from it east and west might have a regularity which would be found to furnish a method of ascertaining longitude far easier and surer than tables or water clocks. We know that four years later he tried to sail his ship on observations of this kind. The same idea seems to have occurred to Sebastian Cabot, when a little afterwards he approached and passed in a higher latitude, what he supposed to be the meridian of no variation. Humboldt is inclined to believe that the possibility of such a method of ascertaining longitude was that uncommunicable secret, which Sebastian Cabot many years later hinted at on his death-bed.
The claim was made near a century later by Livio Sanuto in his Geographia, published at Venice, in 1588, that Sebastian Cabot had been the first to observe this variation, and had explained it to Edward VI., and that he had on a chart placed the line of no variation at a point one hundred and ten miles west of the island of Flores in the Azores.
Various views.
These observations of Columbus and Cabot were not wholly accepted during the sixteenth century. Robert Hues, in 1592, a hundred years later, tells us that Medina, the Spanish grand pilot, was not disinclined to believe that mariners saw more in it than really existed and that they found it a convenient way to excuse their own blunders. Nonius was credited with saying that it simply meant that worn-out magnets were used, which had lost their power to point correctly to the pole. Others had contended that it was through insufficient application of the loadstone to the iron that it was so devious in its work.
PART OF MERCATOR'S POLAR REGIONS, 1569.
[From R. Mercator's Atlas of 1595.]
Better understood.
What was thought possible by the early navigators possessed the minds of all seamen in varying experiments for two centuries and a half. Though not reaching such satisfactory results as were hoped for, the expectation did not prove so chimerical as was sometimes imagined when it was discovered that the lines of variation were neither parallel, nor straight, nor constant. The line of no variation which Columbus found near the Azores has moved westward with erratic inclinations, until to-day it is not far from a straight line from Carolina to Guiana. Science, beginning with its crude efforts at the hands of Alonzo de Santa Cruz, in 1530, has so mapped the surface of the globe with observations of its multifarious freaks of variation, and the changes are so slow, that a magnetic chart is not a bad guide to-day for ascertaining the longitude in any latitude for a few years neighboring to the date of its records. So science has come round in some measure to the dreams of Columbus and Cabot.