ioo A Short History of Astronomy [CH. IV. 



paid little attention, presented the opinions quoted as 

 more than vague speculations ; none of them gave any 

 substantial reasons for, much less a proof of, their views ; 

 and Coppernicus, though he. may have been glad, after the 

 fashion of the age, to have the support of recognised 

 authorities, had practically to make a fresh start and 

 elaborate his own evidence for his opinions. 



It has sometimes been said that Coppernicus proved 

 what earlier writers had guessed at or suggested ; it would 

 perhaps be truer to say that he took up certain floating ideas, 

 which were extremely vague and had never been worked 

 out scientifically, based on them certain definite funda- 

 mental principles, and from these principles developed 

 mathematically an astronomical system which he shewed to 

 be at least as capable of explaining the observed celestial 

 motions as any existing variety of the traditional Ptolemaic 

 system. The Coppernican system, as it left the hands of 

 the author, was in fact decidedly superior to its rivals as 

 an explanation of ordinary observations, an advantage which 

 it owed quite as much to the mathematical skill with which 

 it was developed as to its first principles ; it was in many 

 respects very much simpler ; and it avoided certain 

 fundamental difficulties of the older system. It was how- 

 ever liable to certain serious objections, which were only 

 overcome by fresh evidence which was subsequently 

 brought to light. For the predecessors of Coppernicus 

 there was, apart from variations of minor importance, but 

 one scientific system which made any serious attempt to 

 account for known facts ; for his immediate successors there 

 were two, the newer of which would to an impartial mind 

 appear on the whole the more satisfactory, and the further 

 study of the two systems, with a view to the discovery of 

 fresh arguments or fresh observations tending to support 

 the one or the other, was immediately suggested as an 

 inquiry of first-rate importance. 



76. The plan of the De Revolutionibus bears a general 

 resemblance to that of the Almagest. In form at least 

 the book is not primarily an argument in favour of the 

 motion of the earth, and it is possible to read much of 

 it without ever noticing the presence of this doctrine. 



Coppernicus, like Ptolemy, begins with certain first prin- 



