80 A Short History of Astronomy [Cn. ill . 



(939 or 940-998), the author of a voluminous treatise on 

 astronomy also known as the Almagest, which contained 

 some new ideas and was written on a different plan from 

 Ptolemy's book, of which it has sometimes been supposed 

 to be a translation. In discussing the theory of the moon 

 Abul Wafa found that, after allowing for the equation of 

 the centre and for the evection, there remained a further 

 irregularity in the moon's motion which was imperceptible 

 at conjunction, opposition, and quadrature, but appreciable 

 at the intermediate points. It is possible that Abul Waia 

 here detected an inequality rediscovered by Tycho Brahe 

 (chapter v., in) and known as the variation, but it 

 is equally likely that he was merely restating Ptolemy's 

 prosneusis (chapter n., 48).* In either case Abul Wafa's 

 discovery appears to have been entirely ignored by his 

 successors and to have borne no fruit. He also carried 

 further some of the mathematical improvements of his 

 predecessors. 



Another nearly contemporary astronomer, commonly 

 known as Ibn Yunos (?-ioo8), worked at Cairo under 

 the patronage of the Mahometan rulers of Egypt. He 

 published a set of astronomical and mathematical tables, 

 the Hakemite Tables, which remained the standard ones for 

 about two centuries, and he embodied in the same book 

 a number of his own observations as well as an extensive 

 series by earlier Arabian astronomers. 



61. About this time astronomy, in common with other 

 branches of knowledge, had made some progress in the 

 Mahometan dominions in Spain and the opposite coast 

 of Africa. A great library and an academy were founded 

 at Cordova about 970, and centres of education and learning 

 were established in rapid succession at Cordova, Toledo, 

 Seville, and Morocco. 



The most important work produced by the astronomers 

 of these places was the volume of astronomical tables 

 published under the direction of Arzachel in 1080, and 

 known as the Toletan Tables, because calculated for an 

 observer at Toledo, where Arzachel probably lived. To 



* A prolonged but indecisive controversy has been carried on, 

 chiefly by French scholars, with regard to the relations of Ptolemy, 

 Abul Wafa, and Tycho in this matter. 



