It should not, however, be forgotten that while views concerning the sphericity of the earth were gradually making their impression, geographical knowledge was extending itself through the efforts of explorers. The boldest adventurers were gradually pressing their way into the far north. The inhabitants of Iceland--perhaps from their geographical isolation--were especially adventurous. Within the present century the evidence has been made complete that America was visited and explored in the eleventh century, and that accounts of these explorations in detail became a part of the national literature. But Iceland was so isolated from the rest of Europe that these explorations seem to have made no impression, even if they were at all known. The first allusion to the discovery of America by the Scandinavians ever printed was that of Adam von Bremen, in his work issued from the press at Copenhagen in 1579. Although the work had been in manuscript for centuries, there is no evidence that these explorations made any impression upon the literature or knowledge of the time. If Columbus visited Iceland, it is probable that he became acquainted with the traditions of these western voyages. It is of course possible that he obtained positive information from the stories that may have been current among the seafaring men of Iceland in the fifteenth century. But the matter is left in doubt by the fact that no such knowledge was ever revealed by Columbus after his return; and it hardly seems probable that he would have kept such an item of information locked up in his own brain at a time when he was trying to bring every argument to bear upon the Portuguese and Spanish courts. While these numerous intellectual purveyors were bringing to the mind of Columbus their varied stores of information, an event occurred which must have had a powerful influence in shaping and intensifying his purpose. In the year 1474 there was living at Florence the venerable astronomer and geographer Toscanelli. This eminent savant, now seventy-eight years of age, after having enjoyed the honours of connection with nearly all the learned societies of that day, had been greatly interested in the recently published book of Marco Polo. From the account given by this Venetian traveller, Toscanelli had arrived at certain interesting views in regard to the size of the earth. He had satisfied himself that the open water between western Europe and eastern Asia could be crossed in a voyage of not more than three thousand miles. The letters of Toscanelli have been preserved, and they form a most interesting part of the history of this period. We cannot quote from them at any length, but the importance of the correspondence is sufficient to justify a concise statement of the particular significance of the letters.