By this time all men of science had ceased to believe that the world was flat; they thought of it as a perfect round, but fixed at the centre in space. Many had guessed at the size of the earth. Some said it was forty thousand miles round, but Eratosthenes was not content with guessing. He studied the length of the shadow thrown by the sun at Alexandria and compared it with that thrown by the sun at Syene, near the first cataract of the Nile, some five hundred miles distant, and, as he thought, in the same longitude. The differences in the length of these two shadows he calculated would represent one-fiftieth of the circumference of the earth which would accordingly be twenty-five thousand miles. There was no one to tell him whether he had calculated right or wrong, but we know to-day that he was wonderfully right. But he must know more. He must find out how much of this earth was habitable. To the north and south of the known countries men declared it was too hot or too cold to live. So he decided that from north to south, that is, from the land of Thule to the land of Punt (Somaliland), the habitable earth stretched for some three thousand eight hundred miles, while from east to west--that is, from the Pillars of Hercules (Straits of Gibraltar) to India--would be some eight thousand miles. All the rest was ocean. Ignoring the division of the world into three continents, he divided it into two, north and south, divided by the Mediterranean and by a long range of mountains intersecting the whole of Asia. Then the famous librarian drew a map of the world for his library at Alexandria, but it has perished with all the rest of the valuable treasure collected in this once celebrated city. We know that he must have made a great many mistakes in drawing a map of his little island world which measured eight thousand miles by three thousand eight hundred miles. It must have been quaintly arranged. The Caspian Sea was connected with a Northern Ocean, the Danube sent a tributary to the Adriatic, there was no Bay of Biscay, the British Isles lay in the wrong direction, Africa was not half its right size, the Ganges flowed into the Eastern Ocean, Ceylon was a huge island stretching east and west, while across the whole of Asia a mountain chain stretched in one long unbroken line. And yet, with all his errors, he was nearer the truth than men three centuries later. CHAPTER VI PYTHEAS FINDS THE BRITISH ISLES For some centuries past men had been pushing eastward, and to west, vast lands lay unexplored, undreamt of, amongst them a little far-off island "set in a silver sea." Pytheas was the first explorer to bring the world news of the British Isles.