When Ptolemy's work, and through it the geography of the Greeks, became known in Western Europe at the beginning of the fifteenth century, it created a greater stir in the learned world than even the discovery of America did later; the circle of geographical ideas was greatly changed, and the world was regarded with new eyes as a sphere. The doctrine of the possibility of circumnavigating the earth was especially framed and scientifically established by the celebrated astronomer Toscanelli of Florence. But this was not a new doctrine; for the Greeks, Eratosthenes and Posidonius, for example (cf. vol. i. pp. 77, 79), had already announced it clearly enough, and even in the Middle Ages it was not forgotten. We saw that Mandeville, the writer of fabulous narratives, fully understood the possibility of sailing round the globe, and related ancient tales about such a voyage (cf. p. 271). But at the close of the fifteenth century the idea was seriously taken up by two men of action, both Genoese. One of them was Columbus, the other Cabot. Whether the latter had already conceived the idea before the first voyage of Columbus we do not know for certain, but it is not improbable; the thought was latent in the age, and many must have come near it. Another force impelling men to the western voyage, and perhaps as powerful a one as these scientific speculations, was the belief in the mythical world of enticing islands that lay out in the ocean to the west of Europe and Africa; the Isles of the Blest of the Greeks and the Atlantis of Plato, conceptions, originally derived from the East, which were still alive, though in other forms. There lay Antillia, the Isle of the Seven Cities, mythical islands of the Arabs, and the Irish legendary world, Brandan's isles and many others; some of them had had a part in creating the Norse idea of Wineland and the White Men's Land; now they were given a fresh lease of life, and power over the imagination of Western Europe. Possibly in connection with echoes of tales of the Norsemen's discoveries--coming from Iceland to Bristol, and thence to the continent--these mythical islands helped to form a widespread belief in countries in the far west across the ocean. The fact that the Portuguese, as has been said, really found islands, the Azores, out in the Atlantic in 1427, also contributed to establish this belief. From these islands many expeditions set out in the course of the fifteenth century to search for new lands farther west.[278]