Columbus did not, as many imagine, make the first observations of the existence of magnetic variation, for this is set down upon the charts of Andrea Bianco, but he was the first who remarked, on the 13th of September, 1492, that “2½ degrees east of the island of Corvo, in the Azores, the magnetic variation changed and passed from N.E. to N.W.” Washington Irving thus describes the discovery (“History ... Ch. Columbus,” Paris, 1829, Vol. I. p. 198): “On the 13th of September, in the evening, being about two hundred leagues from the island of Ferro (the smallest of the Canaries), Columbus, for the first time, noticed the variation of the needle, a phenomenon which had never before been remarked. He perceived, about nightfall, that the needle, instead of pointing to the North Star, varied about half a point, or between five and six degrees to the north-west, 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 into another world, subject to unknown influences (Las Casas, ‘Hist. Ind.,’ l. i. c. 6). They apprehended that the compass was about to lose its mysterious virtues; and, without that 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 to the polar star but to some fixed and invisible point. The variation, therefore, was not caused by any fallacy in the compass, but by the movement of the North Star itself, which, like the other heavenly bodies, had its changes and revolutions, and every day described a circle around the pole. The high opinion that the pilots entertained of Columbus as a profound astronomer gave weight to his theory, and their alarm subsided.” Humboldt says: “We can, with much certainty, fix upon three places in the _Atlantic line of no declination_ for the 13th of September, 1492, the 21st of May, 1496 and the 16th of August, 1498.”