The other great work of Eratosthenes was his “Geographies,” including all previous knowledge on the subject, just as the “Elements” of Euclid had included all previous mathematical knowledge. The “Geographies” were in three books, and to them was attached a map of the known world. (See p. 37). It is, of course, full of inaccuracies—_e g._ Great Britain is too large, India fails to be a peninsula and the Caspian Sea connects with the Arctic Ocean. But it is conceived in the scientific spirit. It represents the world as Eratosthenes thought it was, not as he thought it ought to be. When he knows nothing, he inserts nothing; he is not ashamed to leave blank spaces. He bases it on such facts as he knew, and had he known more facts he would have altered it. The other great geographer, Claudius Ptolemy, belongs to a later period (A.D. 100) but it is convenient to notice him here. Possibly he was a connection of the late royal family, but nothing is known of his life. His fame has outshone Eratosthenes’, and no doubt he was more learned, for more facts were at his disposal. Yet we can trace in him the decline of the scientific spirit. Observe his Map of the World (p. 39). At first sight it is superior to the Eratosthenes Map. The Caspian Sea is corrected, new countries—_e.g._ China—are inserted, and there are (in the original) many more names. But there is one significant mistake. He has prolonged Africa into an imaginary continent and joined it up to China. It was a mere flight of his fancy: he even scattered this continent with towns and rivers. No one corrected the mistake and for hundreds of years it was believed that the Indian Ocean was land bound. The age of enquiry was over, and the age of authority had begun, and it is worth noting that the decline of science at Alexandria exactly coincides with the rise of Christianity. (iii). ASTRONOMY AND THE CALENDAR. Astronomy develops on the same lines as Geography. There is an early period of scientific research under Eratosthenes, and there is a later period in which Claudius Ptolemy codifies the results and dictates his opinions to posterity. He announced, for example, that the Universe revolves round the Earth, and this “Ptolemaic” Theory was adopted by all subsequent astronomers until Galileo, and supported by all the thunders of the Church. Yet another view had been put forward, though Ptolemy ignores it. Aristarchus of Samos, working at Alexandria with Eratosthenes, had suggested that the earth might revolve round the sun, and it is only a chance that this view was not stamped as official and imposed as orthodox all through the Middle Ages. We do not know what Aristarchus’ arguments were, for his writings have perished, but we may be sure that, working in the 3rd century B.C., he had arguments and did not take refuge in authority. Astronomy under the Ptolemies was a serious affair—lightened only by the episode of Berenice’s Hair.