writer.," Both algebra, in the true sense of the term, and the term itself (al-jabr) we owe to him. Apart from mathematics, Khawarazmi also did pioneer work in the fields of astronomy, geography and the theory of music.

It was due to another exponent of Arab civilization, Omar Khayyam (1040-1123), that algebra made an enormous leap forward, two centuries after Khawarazmi. Known in the West as the author of Rubayat, a poem made famous by Edward Fitzgerald's translation, he was admired in the East mainly as a mathematician. In his use of analytical geometry, he anticipated the geometry of Descartes. Commissioned by the Seijuk Sultan Halikshah to reform the Persian calendar, he prepared a calendar said to be more accurate than the Gregorian one in use to the present day. For, whereas the latter leads to an error of one day in 3,300 years, in Omar Khayyam's calendar that error is one day in 5,000 years.
Because of their Islamic faith, it was essential for the Arabs to obtain a more precise knowledge of astronomy and geography than was already avail-

  able: a Muslim is obliged to perform a number of religious observances with distinctly astronomicgeographical implications. When he prays, he must face Mecca; if he wishes to perform the pilgrimage to Mecca, he must first know in what direction and what distance he will have to travel. Yet a thousand years ago such ajourney might take months or even years, for the would-be pilgrim might have been living in Spain, Sicily or Asia Minor-all of these forming parts of the medieval Arab Empire. During Ramadan, the month of fast, when between sunrise and sunset he has to abstain from food and drink, he must know in advance the precise moment at which the moon rises and sets. All these functions required a detailed knowledge of astronomy and geography.

It was, thus, under the great Caliph Ma'mun (813-833) that the Arabs set out upon their astronomical investigations. Ma'mun-a son of Harun al-Rashid of Arabian Nights fame-built a special observatory in Palmyra, Syria, and gradually, his scientists determined the length of a degree, thus establishing longitude and latitude.


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