From the fancies of Astrology, in which the early Arabs largely indulged, and which, though discountenanced by Mahomet himself, have never been wholly abandoned by their descendants, a not unnatural transition, led to the study of Astronomy. Under the patronage of the Abbaside Caliph Al-Mamun (813-833 A. D.) this science made rapid progress. Astronomy was zealously studied in the famous schools of Bagdad and Cordova. The _Almagest_, or System of Astronomy, by Ptolemy, was translated into Arabic by Alhazi and Sergius as early as 812. In the Tenth Century, Albaten observed the advance of the line of the apsides in the earth’s orbit; Mohammed-ben-Jeber-al-Batani, the obliquity of the ecliptic; Alpetragius wrote a theory of the planets; and Abul-Hassan-Ali, on astronomical instruments. The obliquity of the ecliptic, the diameter of the earth, and even the precession of the equinoxes, were then calculated with commendable accuracy; and shortly after, Abul-Mezar’s _Introduction to Astronomy_ and his _Treatise on the Conjunction of the Planets_, with the _Elements_ of Al-Furjanee (though this last author was largely indebted to the Egyptian labors of Ptolemy), proved that the caliph’s liberality had been well bestowed. But Al-Batinee, a native of Syria (879-920 A. D.), surpassed all his predecessors in the nicety alike of his observations and computations. Geber, at Seville, constructed (1196 A. D.) the first astronomical observatory on record; and Ebn-Korrah in Egypt proved by his example that the Arabs could be even better astronomers than the Greeks. Ulug Bekh, grandson of the great Tamerlane, was a diligent observer. He established an academy of astronomers at Samarcand, the capital of his dominions, and constructed magnificent instruments. Ulug Bekh, too, made a catalogue of the fixed stars—the only one that had been compiled since that of Hipparchus, sixteen centuries previously.