Aristotle held a position of preëminent authority among the Moslems in all matters scientific. Arabic scholars had received his writings both through Syriac translations and direct from Greek texts. Vast commentaries on his works were made by Avicenna (Ibn Sīnā, 980–1037 A. D.) in the Eastern Caliphate and by Averroës (Ibn Rushd, 1126–1198 A. D.) in Spain. Aristotelian astronomy, as distinguished from Ptolemaic, was reproduced with modifications in the work _On the Sphere_ of Al-Biṭrūjī of Cordova, known to the Christians as Alpetragius.[323] By the end of the twelfth century, owing to the rising interest in Aristotelianism in Europe (the “flood of Aristotelianism,” as Duhem calls it), translations had been done from the Arabic into Latin of a large number of Aristotelian works on astronomy, physics, meteorology, and many other subjects.[324] It was in these works that most of Aristotle’s thought and observation in geography had found expression. Aristotelian physical geography, transmitted through these channels, was destined to dominate the geographical speculations of many Christian writers of the thirteenth century. INFLUENCE OF PTOLEMY’S “ALMAGEST” The Moslems of the Eastern Caliphate also had become familiar with Ptolemy’s _Almagest_ and _Geography_ through Syriac translations and through versions of the original Greek text.[325] A manuscript of the _Kitāb al-Majisṭī_, or _Almagest_, was translated into Arabic in the days of Hārūn ar-Rashīd by that caliph’s vizier, Yaḥyā, and other translations appeared during the middle part of the ninth century. Study of the _Almagest_ stimulated Arabic scholars and incited them to write such original treatises of their own as Al-Farghānī’s (Alfraganus’) On the _Elements of Astronomy_, Al-Battānī’s _On the Movements of the Stars_, or _Astronomy_,[326] and Ibn Yūnūs’ _Ḥakīmī Tables_. INFLUENCE OF PTOLEMY’S “GEOGRAPHY” Furthermore, Ptolemy’s _Geography_ was certainly known to the Moslems in Syriac translations and probably also in copies of the original Greek text.[327] With the _Geography_ as a model a number of Arabic treatises, usually entitled _Kitāb ṣūrat al-arḍ_, or _Book of the Description of the Earth_, were composed at an early period of Islam and served as bases on which later geographical writers built more complex systems. One of the most significant was the _Kitāb ṣūrat al-arḍ_ of Al-Khwārizmī, composed about the time of Al-Maʾmūn (813–833 A. D.), the full text of which was discovered forty-four years ago by Spitta.[328] From another book of the same sort and title Al-Battānī derived the geographical details included in his _Astronomy_.[329] The latter was translated into Latin during the twelfth century; and Al-Khwārizmī’s work was known in Europe at second hand.[330] AZ-ZARQALĪ AND THE “TOLEDO TABLES”