Among the scientific men of this period we find Ptolemy, whose name for more than a thousand years was coextensive with the sciences of astronomy and geography. He was a native of Alexandria, and flourished about the latter part of the second century. The best known of his works is his "Great Construction of Astronomy." He was the first to indicate the true shape of Spain, Gaul, and Ireland; as a writer, he deserves to be held in high estimation. Galen (fl. 130 A.D.) was a writer on philosophy and medicine, with whom few could vie in productiveness. It was his object to combine philosophy with medical science, and his works for fifteen centuries were received as oracular authorities throughout the civilized world. 7. CONTINUED DECLINE OF GREEK LITERATURE.--The adoption of the Christian religion by Constantine, and his establishment of the seat of government in his new city of Constantinople, concurred in causing the rapid decline of Greek literature in the fourth and following centuries. Christianity, no longer the object of persecution, became the dominant religion of the state, and the profession of its tenets was the shortest road to influence and honor. The old literature, with its mythological allusions, became less and less fashionable, and the Greek poets, philosophers, and orators of the better periods gradually lost their attractions. Greek, the official language of Constantinople, was spoken there, with different degrees of corruption, by Syrians, Bulgarians, and Goths; and thus, as Christianity undermined the old classical literature, the political condition of the capital deteriorated the language itself. Other causes accelerated the decadence of Greek learning: the great library at Alexandria, and the school which had been established in connection with it, were destroyed at the end of the fourth century by the edict of Theodosius, and the conquest of Egypt by the Saracens in the seventh century only completed the work of destruction. Justinian closed the schools of Athens, and prohibited the teaching of philosophy; the Arabs overthrew those established elsewhere, and there remained only the institutions of Constantinople. But long before the establishment of the Turks on the ruins of the Byzantine empire, Greek literature had ceased to claim any original or independent existence. The opposition between the literary spirit of heathen Greece and the Christian scholarship of the time of Constantine and his immediate successors, which grew up very gradually, was the result of the Oriental superstitions which distorted Christianity and disturbed the old philosophy. The abortive attempt of the Emperor Julian to create a reaction in favor of heathenism was the cause of the open antagonism between the classical and Christian forms of literature. The church, however, was soon enabled not only to dictate its own rules of literary criticism, but to destroy the writings of its most formidable antagonists.