86 A Short Historv of Astronomy [Cn. HI. 



of learning. He inveighs warmly against excessive adher- 

 e*nce to authority, especially to that of Aristotle, whose 

 books he wishes burnt, and speaks strongly of the import- 

 ance of experiment and of mathematical reasoning in 

 scientific inquiries. He evidently had a good knowledge 

 of optics and has been supposed to have been acquainted 

 with the telescope, a supposition which we can hardly 

 regard as confirmed by his story that the invention was 

 known to Caesar, who when about to invade Britain sur- 

 veyed the new country from the opposite shores of Gaul 

 with a telescope ! 



Another famous book of this period was written by the 

 Yorkshireman John Halifax or Holywood, better known 

 by his Latinised name Sacrobosco, who was for some time 

 a well-known teacher of mathematics at Paris, where he 

 died about 1256. His Sphaera Mundiv^ an elementary 

 treatise on the easier parts of current astronomy, dealing 

 in fact with little but the more obvious results of the 

 daily motion of the celestial sphere. It enjoyed immense 

 popularity for three or four centuries, and was frequently 

 re-edited, translated, and commented on : it was one of 

 the very first astronomical books ever printed ; 25 editions 

 appeared between 1472 and the end of the century, and 

 40 more by the middle of the iyth century. 



68. The European writers of the Middle Ages whom we 

 have hitherto mentioned, with the exception of Alfonso and 

 his assistants, had contented themselves with collecting and 

 rearranging such portions of the astronomical knowledge 

 of the Greeks and Arabs as they could master ; there were 

 no serious attempts at making progress, and no observations 

 of importance were made. A new school, however, grew 

 up in Germany during the i5th century which succeeded 

 in making some additions to knowledge, not in themselves 

 of first-rate importance, but significant of the greater inde- 

 pendence that was beginning to inspire scientific work. 

 | George Purbach, born in 1423, became in 1450 professor 

 of astronomy and mathematics at the University of Vienna, 

 which had soon after its foundation (1365) become a 

 centre for these subjects. He there began an Epitome 

 of Astronomy based on the Almagest, and also a Latin 

 version of Ptolemy's planetary theory, intended partly 



