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 is no evidence that any intercourse existed between Arabic and Indian astronomers either before or after this time, excepting the travels of Albiruni. But we should be very slow to deny the probability that more extended communications actually did take place.

Better informed are we regarding the way in which Greek science, in successive waves, dashed upon and penetrated Arabic soil. In Syria the sciences, especially philosophy and medicine, were cultivated by Greek Christians. Celebrated were the schools at Antioch and Emesa, and, first of all, the flourishing Nestorian school at Edessa. From Syria, Greek physicians and scholars were called to BagdadBaghdad [sic]. Translations of works from the Greek began to be made. A large number of Greek manuscripts were secured by Caliph Al Mamun (813–833) from the emperor in Constantinople and were turned over to Syria. The successors of Al Mamun continued the work so auspiciously begun, until, at the beginning of the tenth century, the more important philosophic, medical, mathematical, and astronomical works of the Greeks could all be read in the Arabic tongue. The translations of mathematical works must have been very deficient at first, as it was evidently difficult to secure translators who were masters of both the Greek and Arabic and at the same time proficient in mathematics. The translations had to be revised again and again before they were satisfactory. The first Greek authors made to speak in Arabic were Euclid and Ptolemæus. This was accomplished during the reign of the famous Haroun-al-Raschid. A revised translation of Euclid's Elements was ordered by Al Mamun. As this revision still contained numerous errors, a new translation was made, either by the learned Honein ben Ishak, or by his son, Ishak ben Honein. To the thirteen books of the Elements were added the fourteenth, written by Hypsicles, and the fifteenth by Damascius. But it remained for