Further, though there were astronomers, yet they were incompetent and of little value from a practical point of view. Lastly, the ancients had yet to learn the essential value of the loadstone. Hence their mariners were not fitted for such long voyages as were to be made later on by the Portuguese. The early Mediterranean mariners were efficient so long as they kept within the confines of their own enormous lake, for their voyaging was practically coastal. Even when they had to sail North and South they had such places as Rhodes to enable them to break their journey and make a good departure from. They could never lose themselves for long, for they knew the aspect of the various promontories and bays. They could “smell” their way through most channels even when the light failed them. And remember, too, that theirs were not big ships if compared with the caravels which were to come later. There were plenty of oarsmen in the warships if it became necessary to claw off a lee shore, and these shallow-draught vessels could float in the most shallow channels. But if they had been called upon to cross the Atlantic or, rounding the South of Africa, traverse the Indian Ocean, they would have soon lost themselves when out of sight of land for many days; so they kept to their own sea and left the discovering of the world to others who should come centuries later. Hipparchus had been the first to make a catalogue of the stars about the year 150 B.C. Pass over a somewhat barren interval till you come to the year A.D. 150 and you find Ptolemy correcting the tables of Hipparchus. In Ptolemy we have the summit of classical knowledge as reached during the times of the ancients. His account of the universe and the movements of the heavenly bodies had a great influence on the seafarers in the Middle Ages, and so on the world’s discoveries. Now Ptolemy’s geography was based for the most part on “itineraries.” These, in modern parlance, were simply guide-books for travellers: that is to say, they consisted of tables and routes showing the stopping-places. Such data as these afforded had been obtained for the most part from military campaigns--especially Roman--and from the voyages made by sailors, but also from merchants. Ptolemy made a wonderful improvement in cartographical representation by introducing correction with converging meridians, this method having been commenced by Hipparchus. But Ptolemy was singularly fortunate to have been living at the time when the Roman Empire was at its height, and so enabled to obtain a mass of geographical details through the extensive administration of this far-reaching dominion.