Columbus writes out reasons for his belief.
We learn from the Historie that its writer had found among the papers of Columbus the evidence of the grounds of his belief in the western passage, as under varying impressions it had been formulated in his mind. These reasons divide easily into three groups: First, those based on deductions drawn from scientific research, and as expressed in the beliefs of Ptolemy, Marinus, Strabo, and Pliny; second, views which the authority of eminent writers had rendered weightier, quoting as such the works of Aristotle, Seneca, Strabo, Pliny, Solinus, Marco Polo, Mandeville, Pierre d'Ailly, and Toscanelli; and third, the stories of sailors as to lands and indications of lands westerly.
From these views, instigated or confirmed by such opinions, Columbus gradually arranged his opinions, in not one of which did he prove to be right, except as regards the sphericity of the earth; and the last was a belief which had been the common property of learned men, and at intervals occupying even the popular mind, from a very early date.
Sphericity of the earth.
Transmission of the belief in it.
The conception among the Greeks of a plane earth, which was taught in the Homeric and Hesiodic poems, began to give place to a crude notion of a spherical form at a period that no one can definitely determine, though we find it taught by the Pythagoreans in Italy in the sixth century before Christ. The spherical view and its demonstration passed down through long generations of Greeks, under the sanction of Plato and their other highest thinkers. In the fourth century before Christ, Aristotle and others, by watching the moon's shadow in an eclipse, and by observing the rising and setting of the heavenly bodies in different latitudes, had proved the roundness of the earth to their satisfaction; Eratosthenes first measured a degree of latitude in the third century; Hipparchus, in the second century, was the earliest to establish geographical positions; and in the second century of the Christian era Ptolemy had formulated for succeeding times the general scope of the transmitted belief. During all these centuries it was perhaps rather a possession of the learned. We infer from Aristotle that the view was a novelty in his time; but in the third century before Christ it began to engage popular attention in the poem of Aratus, and at about 200 B. C. Crates is said to have given palpable manifestation of the theory in a globe, ten feet in diameter, which he constructed.
The belief passed to Italy and the Latins, and was sung by Hyginus and Manilius in the time of Augustus. We find it also in the minds of Pliny, Cicero, Virgil, and Ovid. So the belief became the heirloom of the learned throughout the classic times, and it was directly coupled in the minds of Aristotle, Eratosthenes, Strabo, Seneca, and others with a conviction, more or less pronounced, of an easy western voyage from Spain to India.
Seneca's Medea.
Cosmas.