96 A Short History of Astronomy [CH. iv. 



it is probable that a very large part of his time during the 

 last 30 years of his life was devoted to astronomy. 



73. We are so accustomed to associate the revival of 

 astronomy, as of other branches of natural science, with 

 increased care in the collection of observed facts, and to 

 think of Coppernicus as the chief agent in the revival, that 

 it is worth while here to emphasise the fact that he was in 

 no sense a great observer. His instruments, which were 

 mostly of his own construction, were far inferior to those 

 of Nassir Eddin and of Ulugh Begh (chapter in., 62, 63), 

 and not even as good as those which he could have pro- 

 cured if he had wished from the workshops of Niirnberg ; 

 his observations were not at all numerous (only 27, which 

 occur in his book, and a dozen or two besides being known), 

 and he appears to have made no serious attempt to secure 

 great accuracy. His determination of the position of one 

 star, which was extensively used by him as a standard of 

 reference and was therefore of special importance, was in 

 error to the extent of nearly 40' (more than the apparent 

 breadth of the sun or moon), an error which Hipparchus 

 would have considered very serious. His pupil Rheticus 

 ( 74) reports an interesting discussion between his master 

 and himself, in which the pupil urged the importance of 

 making observations with all imaginable accuracy; Copper- 

 nicus answered that minute accuracy was not to be looked 

 for at that time, and that a rough agreement between theory 

 and observation was all that he could hope to attain. 

 Coppernicus moreover points out in more than one place 

 that the high latitude of Frauenburg and the thickness of 

 the air were so detrimental to good observation that, for 

 example, though he had occasionally been able to see the 

 planet Mercury, he had never been able to observe it 

 properly. 



Although he published nothing of importance till towards 

 the end of his life, his reputation as an astronomer and 

 mathematician appears to have been established among 

 experts from the date of his leaving Italy, and to have 

 steadily increased as time went on. 



In 1515 he was consulted by a committee appointed by 

 the Lateran Council to consider the reform of the calendar, 

 which had now fallen into some confusion (chapter n.. 



