- Historic Sites
Christopher Columbus, Mariner
December 1955 | Volume 7, Issue 1
Everyone, we repeat, admitted that the Earth was a i sphere, and the convention of dividing a circle or sphere into 360 degrees had been arrived at by the Greeks. But how long was a degree? On your answer to that depended your estimate of the size of the Earth. Ptolemy of Alexandria, whose book was the geographical Bible of Columbus’s day, said that it was 50 nautical miles ∗ long—the correct measure is 60. Alfragan, a Moslem geographer of the ninth century, said the degree measured 66 nautical miles, but Columbus misread him and decided that Alfragan’s degree was 45 miles long and that Alfragan, not Ptolemy, was right. In other words, he underestimated the size of the world by 25 per cent.
∗ I use in this book the standard nautical mile of 2000 yards, which is equivalent to one minute of latitude or to one minute of longitude on the equator. The old authorities I quote used different units, but I have reduced them all to nautical miles.
Besides this mistake on the size of the globe, Columbus made another colossal error in reckoning how far eastward Asia stretched. The actual combined length of Europe and Asia is roughly 130 degrees from Cape St. Vincent to Peiping, or 150 degrees to Tokyo. Ptolemy guessed that it was 180 degrees, which was half the circumference of the globe. Marinus of Tyre, an earlier authority whom Columbus naturally preferred, stretched out this land mass to 225 degrees. Marco Polo, who took two or three years to cross Asia by land, made some rough calculations and tacked on 28 degrees more for China and 30 degrees additional for Japan; this, added to Marinus’s 225 degrees, would place Tokyo on the meridian that runs through Western Cuba, Chattanooga, Grand Rapids and Western Ontario! Moreover, as Columbus proposed to jump off from the western Canary Islands, which lie on a parallel 9 degrees west of Cape St. Vincent, he figured he would have only 68 degrees of westing to make before hitting the coast of Japan. Combining that gross miscalculation with his underestimate of the length of a degree, he figured that the length of the ocean voyage from the Canaries to Japan would be 2400 nautical miles. The actual air-line distance is 10,600 miles!
Columbus did not, however, come to this conclusion all by himself. He had the support of a learned physician of Florence, Paolo Toscanelli, who dabbled in astronomy and mathematics. Toscanelli, believing Marco Polo’s estimate of the length of Asia to be correct, had written to a Portuguese friend in 1474, urging him to persuade the King to organize a voyage west to Japan, “most fertile in gold,” and to the Chinese province of Mangi. He envisioned a voyage of 3000 miles from Lisbon to Cipangu (Japan) and 5000 miles from Lisbon to Quinsay (Hangchow), and sent a chart to demonstrate his theory. Columbus, tremendously excited when he heard about this, wrote to the Florentine sage asking for more details, and received an encouraging letter and another chart, which he carried with him on his great voyage of discovery. This correspondence took place shortly after Columbus’s return from the Gold Coast, in 1481 or early 1482. The Toscanelli letter and chart were always his Exhibits “A” and “B.”
Of course he had other exhibits as well: some literary, others practical. There were plenty of Biblical texts besides Psalm 19—“The isles that are in the sea shall be troubled at thy departure” (Ezekiel xxvi 18), “And His dominion shall be from sea even to sea, and from the river even to the ends of the earth” (Zechariah ix 10; repeated in Psalm 72, verse 8), “The isles saw it, and feared; the ends of the earth were afraid, drew near, and came” (Isaiah xli 5). Aristotle was said to have written that one could cross the Ocean from Spain to the Indies in a few days. Strabo, the Greek geographer who lived at the time of Christ, wrote that it had actually been attempted by mariners of his day, who returned “through want of resolution and the scarcity of provisions.” Pierre d’Ailly’s Imago Mundi , Columbus’s bedside book for years-his copy, still preserved at Seville, is covered by hundreds of manuscript notes—insisted that the Ocean was “of no great width” between Morocco and the eastern coast of Asia, that it could be navigated in a few days with a fair wind.
Thus, very early in the game, Columbus, absolutely convinced of the truth of his theory, brushed aside all doubts and difficulties and began collecting every possible text or quotation that could be used to support it. For instance, the statement in the apocryphal Second Book of Esdras (vi 42), “Six parts hast thou dried up,” was frequently used by Columbus to prove that six sevenths of the globe is land; ergo , the Ocean covers only one seventh of the globe and cannot be very broad.