Recent writers, and among them the great philosopher Humboldt, have shown that in all probability the declination or variation of the magnet was known as early as the twelfth century; but this important discovery has been generally ascribed to Columbus. His son Ferdinand states that on the 14th September 1492, his father, when about 200 leagues from the island of Ferro, noticed for the first time the variation of the needle. “A phenomenon,” says Washington Irving, “that had never before been remarked.” “He perceived,” adds this author, “about nightfall that the needle, instead of pointing to the north star, varied half a point, or between five and six degrees, to the northwest, and still more on the following morning. Struck with this circumstance, he observed it attentively for three days, and found that the variation increased as he advanced. He at first made no mention of this phenomenon, knowing how ready his people were to take alarm; but it soon attracted the attention of the pilots, and filled them with consternation. It seemed as if the laws of nature were changing as they advanced, and that they were entering another world, subject to unknown influences. They apprehended that the compass was about to lose its mysterious virtues; and without this guide, what was to become of them in a vast and trackless ocean? Columbus tasked his science and ingenuity for reasons with which to allay their terrors. He told them that the direction of the needle was not the polar star, but to some fixed and invisible point: the variation was not caused by any failing in the compass, but because this point, like the heavenly bodies, had its changes and revolutions, and every day described a circle round the pole. The high opinion that the pilots entertained of Columbus as a profound astronomer gave weight to his theory, and their alarm subsided.” Thus, although it is possible that the variation of the needle had been noticed before the time of Columbus, it is evident that he had discovered the amount of the variation, and that it varied in different latitudes. The great philosopher Humboldt observes on this point, that “Columbus has not only the incontestible merit of having first discovered a line without magnetic variation, but also of having, by his considerations on the progressive increase of westerly declination in receding from that line, given the first impulse to the study of terrestrial magnetism in Europe.”