THE ASTRONOMICAL WRITINGS OF SCOT 103 



The sun, for example, at noonday of the summer 

 solstice stood, they saw, at his highest point in the 

 heavens, while he sank to his lowest on the shortest 

 day of winter. Between these extremes he held 

 gradually every intermediate position, and as he was 

 meanwhile supposed to be moving in a circular path 

 round the earth, his course came to be conceived of 

 as a spiral alternately rising and declining. How 

 was this spiral motion to be explained ? 



Each sphere, said Alpetrongi, has its own 

 poles, which differ from those of the pinmiim mobile, 

 and thus each, while following the motion of the 

 ninth sphere, accomplishes at the same time 

 another revolution about its own proper poles. 

 From the combination of these two movements 

 arises one of the nature of a spiral which fully 

 accounts for the seeming deviations of the heavenly 

 bodies to north or south. 1 



Such were the contributions of this philosopher 

 to the astronomy of his time. They were the fruit, 

 he assures us, of patient study of the ancients, and 

 specially of Aristotle and his commentators. He 

 offered them to his age as a distinct improvement 

 on the cumbrous theories of Ptolemy, and as an 

 advance even upon that of Azarchel, whom, in 

 the main, he acknowledges as his master in science. 

 Antiquated and childish as his explanations may 

 seem to us, we cannot help feeling that he had at 

 least grasped firmly some of the chief problems of 

 the sky. He stood in the line of that inquiry 

 and patient progress which have issued in the mar- 

 vellous discoveries of later times. 



Scot's version of the Sphere of Alpetrongi has 



1 See the excellent account in Munk. 



