Yet another name must be mentioned, viz., the Spanish-Arab astronomer Ibn Abd-ar-Rahman Es-Zerkel, Europeanized as Arzachal. He first resided at Toledo, at the court of its sovereign, Mamun, for whom he made an astrolabe, which he called in his honour the Mamunian. He then went to Seville, where he wrote for Motamid bin Abbad (A.D. 1069-1091) a treatise on the use of certain instruments. During his residence at Toledo he constructed two clepsydras, the waters of which decreased and increased according to the waning and growing of the moon, and these two basins were destroyed only in A.D. 1133 by Alphonse VI., when he took Toledo. Arzachal left a work on eclipses, and on the revolution of years, as well as the tables of the sky, to which the name of Toledan tables have been given. His writings, but especially the last, which must have been consulted by the editors of the Alphonsine tables, were never translated, and exist only in manuscript in libraries where but few scholars can consult them. Arzachal made many observations in connection with the sun, and was also the inventor of the astronomical instrument called after his name, Zerkalla. He died A.D. 1080. Before leaving this subject it may be mentioned that Makkari, in his great encyclopaedia of Spain, enumerates fifteen astronomers of Andalusia, all more or less known in their time. Also that Bedei-ul-Astrolabi and Ibn Abdul-Rayman distinguished themselves as makers of astronomical instruments, and inventors of new ones. While Arzachal was the greatest representative of Arab astronomy in the West, Umar Khayam, the astronomer, mathematician, freethinker, and poet, was its greatest representative in the East, in Persia, where he died A.D. 1123. A great deal in Arabic literature has been written about grammar, and, until its principles were finally laid down and established, it was always a source of continual controversy between different professors and different schools. Abul Aswad ad-Duwali has been called the father of Arabic grammar. It is said that the Khalif Ali laid down for him this principle: the parts of speech are three, the noun, the verb, and the particle, and told him to form a complete treatise upon it. This was accordingly done; and other works on the subject were also produced, but none of them are apparently now extant. Muhammad bin Ishak has stated that he saw one of them, entitled 'Discourse on the Governing and the Governed Parts of Speech;' and the author of the 'Fihrist' also alludes to this work. Abul-Aswad died at Busra in A.D. 688, aged eighty-five, but some years later his two successors in this branch of literature (viz., Al-Khalil and Sibawaih) far surpassed him in every way.