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A History of Sea Power by Stevens and Westcott

Showing the voyages of columbus

straw so that it shall float

upon the water, the needle will instantly turn toward the pole-star; though the night be never so dark, yet shall the mariner be able by the help of this needle to steer his course aright. But no master-mariner," he adds, "dares to use it lest he should fall under the imputation of being a magician."[1] By the end of the 13th century the compass was coming into general use; and when Columbus sailed he had an instrument divided as in later times into 360 degrees and 32 points, as well as a quadrant, sea-astrolabe, and other nautical devices. The astrolabe, an instrument for determining latitude by measuring the altitude of the sun or other heavenly body, was suspended from the finger by a ring and held upright at noon till the shadow of the sun passed the sights. The cross-staff, more frequently used for the same purpose by sailors of the time, was a simpler affair less affected by the ship's roll; it was held with the lower end of the cross-piece level with the horizon and the upper adjusted to a point on a line between the eye of the observer and the sun at the zenith. By these various means the sailor could steer a fixed course and determine latitude. He had, however, as yet no trustworthy means of reckoning longitude and no accurate gauge of distance traveled. The log-line was not invented until the 17th century, and accurate chronometers for determining longitude did not come into use until still later. A common practice of navigators, adopted by Columbus, was to steer first
north or south along the coast and then due west on the parallel thought to lead to the destination sought.

[Footnote 1: Dante's tutor Brunetto Latini, quoted in THE DISCOVERY OF AMERICA, Fiske, Vol. I, p. 314.]


With the revival of classical learning in the Renaissance, geographical theories also became less wildly imaginative than in the medieval period, the charts of which, though beautifully colored and highly decorated with fauna and flora, show no such accurate knowledge even of the old world as do those of the great geographer Ptolemy, who lived a thousand years before. Ptolemy (200 A.D.), in company with the majority of learned men since Aristotle, had declared the earth to be round and had even estimated its circumference with substantial accuracy, though he had misled later students by picturing the Indian Ocean as completely surrounded by Africa, which he conceived to extend indefinitely southward and join Asia on the southeast, leaving no sea-route open from the Atlantic. There was another body of opinion of long standing, however, which outlined Africa much as it actually is. Friar Roger Bacon, whose interest in the compass has already been mentioned, collected statements of classical authorities and other evidence to show that Asia could be reached by sailing directly westward, and that the distance was not great; and this material was published in Paris in a popular _Imago Mundi_ of 1410. In general, the best geographical knowledge of the period, though it underestimated the distance from Europe westward to Asia and was completely ignorant of the vast continents lying between, gave support to the theories which the voyages of Diaz, Vasco da Gama, and Columbus magnificently proved true.

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