A large part of Greek science which has come down to us owes its preservation to a very singular incident in the history of learning. In the ninth century, after the Arabs had been converted to Mohammedanism, and on the basis of that faith had swiftly organized a great and cultivated empire, the scholars of that folk became deeply interested in the remnants of Greek learning which had survived in the monastic and other libraries about the eastern Mediterranean. So greatly did they prize these records, which were contemned by the Christians, that it was their frequent custom to weigh the old manuscripts in payment against the coin of their realm. In astronomy, mathematics, chemistry, and geology the Arabian students, building on the ancient foundations, made notable and for a time most important advances. In the tenth century of our era they seemed fairly in the way to do for science what western Europe began five centuries later to accomplish. In the fourteenth century the centre of Mohammedan strength was transferred from the Arabians to the Turks, from a people naturally given to learning to a folk of another race, who despised all such culture. Thenceforth in place of the men who had treasured and deciphered with infinite pains all the records of earlier learning, the followers of Mohammed zealously destroyed all the records of the olden days. Some of these records, however, survived among the Arabs of Spain, and others were preserved by the Christian scholars who dwelt in Byzantium, or Constantinople, and were brought into western Europe when that city was captured by the Turks in the fifteenth century. Already the advance of the fine arts in Italy and the general tendency toward the study of Nature, such as painting and sculpture indicate, had made a beginning, or rather a proper field for a beginning, of scientific inquiry. The result was a new interest in Greek learning in all its branches, and a very rapid awakening of the scientific spirit. At first the Roman Church made no opposition to this new interest which developed among its followers, but in the course of a few years, animated with the fear that science would lead men to doubt many of the dogmas of the Church, it undertook sternly to repress the work of all inquirers.