[Sidenote: Columbus observes eclipse of the moon.]
It was while in this suspense that Columbus took advantage of an eclipse of the moon, to ascertain his longitude. His calculations made him five hours and a half west of Seville,--an hour and a quarter too much, making an error of eighteen degrees. This mistake was quite as likely owing to the rudeness of his method as to the pardonable errors of the lunar tables of Regiomontanus (Venice, 1492), then in use. These tables followed methods which had more or less controlled calculations from the time of Hipparchus.
The error of Columbus is not surprising. Even a century later, when Robert Hues published his treatise on the Molineaux globe (1592), the difficulties were in large part uncontrollable. "The most certain of all for this purpose," says this mathematician, "is confessed by all writers to be by eclipses of the moon. But now these eclipses happen but seldom, but are more seldom seen, yet most seldom and in very few places observed by the skillful artists in this science. So that there are but few longitudes of places designed out by this means. But this is an uncertain and ticklish way, and subject to many difficulties. Others have gone other ways to work, as, namely, by observing the space of the equinoctial hours betwixt the meridians of two places, which they conceive may be taken by the help of sundials, or clocks, or hourglasses, either with water or sand or the like. But all these conceits, long since devised, having been more strictly and accurately examined, have been disallowed and rejected by all learned men--at least those of riper judgments--as being altogether unable to perform that which is required of them. I shall not stand here to discover the errors and uncertainties of these instruments. Away with all such trifling, cheating rascals!"
The weather moderating, Columbus stood out of the channel of Saona on September 24, and meeting the other caravels, which had weathered the storm, he still steered to the east. They reached the farthest end of Española opposite Porto Rico, and ran out to the island of Mona, in the channel between the two larger islands. Shortly after leaving Mona, Columbus, worn with the anxieties of a five months' voyage, in which his nervous excitement and high hopes had sustained him wonderfully, began to feel the reaction. His near approach to Isabella accelerated this recoil, till his whole system suddenly succumbed. He lay in a stupor, knowing little, remembering nothing, his eyes dim and vitality oozing. Under other command, the little fleet sorrowfully, but gladly, entered the harbor of Isabella.