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 for it became even more favourable. The Emir Adud-ed-daula (978-983) gloried in having studied astronomy himself. His son Saraf-ed-daula erected an observatory in the garden of his palace, and called thither a whole group of scholars.[7] Among them were Abul Wefa, Al Kuhi, Al Sagani.

Abul Wefa (940-998) was born at Buzshan in Chorassan, a region among the Persian mountains, which has brought forth many Arabic astronomers. He forms an important exception to the unprogressive spirit of Arabian scientists by his brilliant discovery of the variation of the moon, an inequality usually supposed to have been first discovered by Tycho Brahe.[11] Abul Wefa translated Diophantus. He is one of the last Arabic translators and commentators of Greek authors. The fact that he esteemed the algebra of Mohammed ben Musa Hovarezmi worthy of his commentary indicates that thus far algebra had made little or no progress on Arabic soil. Abul Wefa invented a method for computing tables of sines which gives the sine of half a degree correct to nine decimal places. He did himself credit by introducing the tangent into trigonometry and by calculating a table of tangents. The first step toward this had been taken by Al Battani. Unfortunately, this innovation and the discovery of the moon's variation excited apparently no notice among his contemporaries and followers. "We can hardly help looking upon this circumstance as an evidence of a servility of intellect belonging to the Arabian period." A treatise by Abul Wefa on "geometric constructions" indicates that efforts were being made at that time to improve draughting. It contains a neat construction of the corners of the regular polyedrons on the circumscribed sphere. Here, for the first time, appears the condition which afterwards became very famous in the Occident, that the construction be effected with a single opening of the compass.