106 LITERATURE OF THE ARABS. 



dallah ibn Sahal, and Yahia ibn Mansor, were emi- 

 nent writers on this science, and their Astronomical 

 Tables were admired for their exactness. Albathani 

 (or Albategni), one of the most learned men that 

 adorned the court of Moktader, was justly renown- 

 ed as the author of the Sabian Tables, drawn up from 

 the astronomical observations which he made in the 

 course of forty years (A. D. 879 921), at Racca, on 

 the Euphrates. His laborious researches were of 

 the highest importance to the science. He gave a 

 new and improved theory of the sun, from which 

 some valuable results were derived; and supplied the 

 defects of the Ptolomaean Tables by his more accurate 

 observations. His work on " The Science of the 

 Stars/' which is still extant, long held a very high 

 place in the estimation of philosophers. We owe to 

 him a more correct calculation of the obliquity of 

 the ecliptic than had hitherto been made j he also 

 determined the annual movement of the equinoxes, 

 and found the duration of the tropical year to be 

 365 days and a decimal fraction. 



His contemporary, Ibn Korrah, likewise observed 

 the declination of the ecliptic ; distinguished the mo- 

 tion of the apogee of the sun and planets from that of 

 the stars in longitude ; and, what is most important 

 of all, ascertained that the solar revolution was com- 

 pleted in 365 days, 6 hours, 9 minutes, and 12 se- 

 conds ; a calculation not very different from that now 

 in use. Arzakel, the reputed author of the Toledan 

 Tables, who flourished towards the end of the ele- 

 venth century, was famous for his hypothesis to 

 account for the diminution of the sun's eccentricity, 

 which he conceived to have taken place since the 

 time of Ptolemy, and the motion of the sun's apogee. 



