Note 184 — Chapter V · 1493-1506.

Columbus writing from Española in October, 1498, says: “Each time that I sail from Spain to India, as soon as I have proceeded about a hundred nautical miles to the west of the Azores, I perceive an extraordinary alteration in the movement of the heavenly bodies, in the temperature of the air, and in the character of the sea. I have observed these alterations with especial care, and I notice that the mariner’s compass, whose declination had hitherto been northeast, was now changed to northwest; and when I had crossed this line, as if in passing the brow of a hill, I found the ocean covered with such a mass of sea-weed, similar to small branches of pine covered with pistachio nuts, that we were apprehensive that for want of a sufficiency of water our ships would run upon a shoal. Before we reached the line of which I speak, there was no trace of any such sea-weed. On the boundary line, one hundred miles west of the Azores, the ocean is found still and calm, being scarcely ever moved by a breeze. On my passage from the Canary Islands to the parallel of Sierra Leone, we had to endure a frightful degree of heat, but as soon as we had crossed the above-mentioned line, the climate changed, the air became temperate, and the freshness increased the farther we proceeded.”

“It is evident that the extract from the third voyage is but an amplification of his first account, and expresses his conviction that west of the Azores, where the declination was a little easterly, it changed to the westward, being nearly zero at Corvo, and gradually increasing to one point or 11° W., at a distance of 300 nautical miles W. of the longitude of Corvo. The position of Rosario on the S.E. part of the island of Corvo is, according to the Carta Esferica de las Islas Azores, Madrid, 1855, in latitude 39° 41´ and longitude 24° 53´ west of San Fernando, or in 31° 07´ west of Greenwich (according to the Conn. des Temps), 100 leagues or 300 nautical miles west of this longitude would correspond (in latitude 28°) to 5° 40´, and would bring the Columbus line in longitude 36° 47´ W.”—An inquiry into the variation of the compass off the Bahama Islands at the land fall of Columbus in 1492. By Charles A. Schott. p. 51.