Little Masterpieces of Science: Explorers

by Unknown

On Thursday, the 13th of September, he notes that the ships were encountering adverse currents. He was now three degrees west of Flores, and the needle of the compass pointed as it had never been observed before, directly to the true north. His observation of this fact marks a significant point in the history of navigation. The polarity of the magnet, an ancient possession of the Chinese, had been known perhaps for three hundred years, when this new spirit of discovery awoke in the fifteenth century. The Indian Ocean and its traditions were to impart, perhaps through the Arabs, perhaps through the returning Crusaders, a knowledge of the magnet to the dwellers on the shores of the Mediterranean, and to the hardier mariners who had pushed beyond the pillars of Hercules, so that the new route to that same Indian Ocean was made possible in the fifteenth century. The way was prepared for it gradually. The Catalans from the port of Barcelona pushed out into the great Sea of Darkness under the direction of their needles, as early at least as the twelfth century. The pilots of Genoa and Venice, the hardy Majorcans and the adventurous Moors, were followers of almost equal temerity.

A knowledge of the variation of the needle came more slowly to be known to the mariners of the Mediterranean. It had been observed by Peregrini as early as 1269, but that knowledge of it which rendered it greatly serviceable in voyages does not seem to be plainly indicated in any of the charts of these transition centuries, till we find it laid down on the maps of Andrea Bianco in 1436.

It was no new thing then when Columbus, as he sailed westward, marked the variation, proceeding from the northeast more and more westerly; but it was a revelation when he came to a position where the magnetic north and the north star stood in conjunction, as they did on this 13th of September, 1492. 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 divergence 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.

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.

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 had moved westward with erratic inclinations, until to-day it is not far from a straight line from Carolina to Guinea. 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 neighbouring to the date of its records. So science has come around in some measure to the dreams of Columbus and Cabot.

But this was not the only development which came from this ominous day in the mid-Atlantic in that September of 1492. The fancy of Columbus was easily excited, and notions of a change of climate, and even aberration of the stars were easily imagined by him amid the strange phenomena of that untracked waste.

While Columbus was suspecting that the north star was somewhat wilfully shifting from the magnetic pole, now to a distance of 5° and then of 10°, the calculations of modern astronomers have gauged the polar distance existing in 1492 at 3° 28´, as against the 1° 20´ of to-day. The confusion of Columbus was very like his confounding an old world with a new, inasmuch as he supposed it was the pole star and not the needle which was shifting.

He argued from what he saw, or what he thought he saw, that the line of no variation marked the beginning of a protuberance of the earth, up which he ascended as he sailed westerly, and that this was the reason of the cooler weather which he experienced. He never got over some notions of this kind, and he believed he found confirmation of them in his later voyages.

Even as early as the reign of Edward III. of England, Nicholas of Lynn, a voyager to the northern seas, is thought to have definitely fixed the magnetic pole in the Arctic regions, transmitting his views to Cnoyen, the master of the later Mercator, in respect to the four circumpolar islands, which in the sixteenth century made so constant a surrounding of the north pole.