INDUCTION OF COPERNICUS. 38& 



absurd opinion, yet since I knew that, in previous 

 times, others had been allowed the privilege of 

 feigning what circles they chose, in order to explain 

 the phenomena, I conceived that I also might take 

 the liberty of trying whether, on the supposition of 

 the earth's motion, it was possible to find better 

 explanations than the ancient ones, of the revolu- 

 tions of the celestial orbs. 



"Having then assumed the motions of the 

 earth, which are hereafter explained, by laborious 

 and long observation I at length found, that if the 

 motions of the other planets be compared with the 

 revolution of the earth, not only their phenomena 

 follow from the suppositions, but also that the 

 several orbs, and the whole system, are so con- 

 nected in order and magnitude, that no one part 

 can be transposed without disturbing the rest, and 

 introducing confusion into the whole universe." 



Thus the satisfactory explanation of the ap- 

 parent motions of the planets, and the simplicity 

 and symmetry of the system, were the grounds on 

 which Copernicus adopted his theory ; as the crav- 

 ing for these qualities was the feeling which led 

 him to seek for a new theory. It is manifest that 

 in this, as in other cases of discovery, a clear and 

 steady possession of abstract Ideas, and an aptitude 

 in comprehending real Facts under these general 

 conceptions, must have been leading characters in 

 the discoverer's mind. He must have had a good 

 geometrical head, and great astronomical know- 



