“I have navigated the sea during twenty-three years, without noteworthy interruption; I have seen all the Levant and the Ponent; what is called the Northern Way,--that is England; and I have sailed to Guinea.” As there is no other evidence that he went to England, it is probable that the allusion here is to that northern voyage, which, as we have already seen, had had the seas about Iceland as its destination. Though it is not easy to conjecture how the phrase, “twenty-three years without noteworthy interruption,” is to be reconciled with what we elsewhere learn of the years just before 1492, yet it is not difficult to understand how all the voyages referred to may have been made during that period. Before the discovery of the Cape of Good Hope by Bartholomew Diaz in December of 1487, the remotest navigable sea was not far away. To visit the North, the West, or the South was not an enterprise of long duration; and the mariner who had explored the Black Sea, the Mediterranean, the Atlantic from the equator to Iceland and the Baltic, might well claim to be familiar with all the seas that were navigable to a European. Such were the most important of the experiences, which, so far as we can now know, gave form and fibre to the character of Columbus. If the years were full of turbulent experiences, it is evident that they were also years full of absorbing thought. Soon after Columbus reached Lisbon, even if not before, he became possessed with the great idea that important discoveries could be made by sailing due west. Was the idea original with him? Was such a notion entertained by others? These questions, on which so much of the credit of Columbus depends, can only be answered after we take at least a brief survey of the geographical knowledge of the time. It will perhaps never be known who first propounded the theory of the sphericity of the earth; but we are certain that it was systematically taught by the Pythagoreans of southern Italy in the sixth century before Christ. With the writings of Pythagoras, Plato was familiar, and perhaps it was from this bold western speculator that the great Athenian philosopher received the impression that finally ripened into an unquestioning belief. Pythagoras believed the earth to be a sphere, and his views and theories are set forth in two of Plato’s works. But it was the great successor of Plato who was to have the credit of giving these views systematic form. In a treatise “On the Heavens” Aristotle gave a formal summary of the grounds leading to a belief in the earth’s sphericity. Greece bequeathed this doctrine to Rome, where it was specifically taught by Pliny and Hyginus, and was referred to with seeming approval by Cicero and Ovid. From the literature of Rome it passed into many of the school-books of the Middle Ages.