, a native of Biroun, in the province of Khovarezme, who flourished about the beginning of the eleventh century, attained the title of Ai-Mohakapad, or the subtle philosopher, on account of his knowledge of the sciences, and particularly his skill in astrology. He was contemporary and rival to Avicenna, a more celebrated Arabian writer. Abou-rihan wrote some treatises oa Geography, the fixed stars, and the sphere.3