178 THE GREEK ASTRONOMY. 



bles. In the 13th century, Nasir Eddin published Tables of the Stars, 

 dedicated to Ilchan, a Tartar prince, and hence termed the Ilchanic 

 Tables. Two centuries later, Ulugh Beigh, the grandson of Tamerlane, 

 and prince of the countries beyond the Oxus, was a zealous practical 

 astronomer ; and his Tables, which were published in Europe by Hyde 

 in 1665, are referred to as important authority by modern astronomers. 

 The series of Astronomical Tables which we have thus noticed, in 

 which, however, many are omitted, leads us to the Alphonsine Tables, 

 which were put forth in 1488, and in succeeding years, under the aus- 

 pices of Alphonso, king of Castile ; and thus brings us to the verge 

 of modern astronomy. 



For all these Tables, the Ptolemaic hypotheses were employed ; and, 

 for the most part, without alteration. The Arabs sometimes felt the 

 extreme complexity and difficulty of the doctrine which they studied ; 

 but their minds did not possess that kind of invention and energy by 

 which the philosophers of Europe, at a later period, won their way 

 into a simpler and better system. 



Thus Alpetragius states, in the outset of his "Planetarum Theorica," 

 that he was at first astonished and stupefied with this complexity, but 

 that afterwards " God was pleased to open to him the occult secret in 

 the theory of his orbs, and to make known to him the truth of their es- 

 sence, and the rectitude of the quality of their motion." His system 

 consists, according to Delambre, 43 in attributing to the planets a spiral 

 motion from east to west, an idea already refuted by Ptolemy. Geber 

 of Seville criticises Ptolemy very severely, 44 but without introducing 

 any essential alteration into his system. The Arabian observations 

 are in many cases valuable ; both because they were made with more 

 skill and with better instruments than those of the Greeks ; and also 

 because they illustrate the permanence or variability of important ele- 

 ments, such as the obliquity of the ecliptic and the inclination of the 

 moon's orbit. 



We must, however, notice one or two peculiar Arabian doctrines. 

 The most important of these is the discovery of the Motion of the 

 Sun's Apogee by Albategnius. He found the Apogee to be in longi- 

 tude 82 degrees ; Ptolemy had placed it in longitude 65 degrees. The 

 difference of IV degrees was beyond all limit of probable error of cal- 

 culation, though the process is not capable of great precision ; and the 

 inference of the Motion of the Apogee was so obvious, that we cannot 



Delambre, M. A. p. 7. " J/. A. p. ISO, &c. 



