Samuel Eliot Morison, writing of Columbus, points out that every sailor knew that the world was round from seeing ships hull-down on the horizon. Aristotle--who

Samuel Eliot Morison, writing of Columbus, points out that every sailor knew that the world was round from seeing ships hull-down on the horizon. Aristotle--who counted for an awful lot in the Middle Ages--inferred the roundness from the earth's shadow on the moon, as I recall.