14 GREAT MEN OF SCIENCE 



manner; they were merely assumed to be likewise moving in 

 certain paths around the sun, but of different diameters. 

 The fixed stars were assumed to be the background upon 

 which the motions were observed, and to be very much 

 farther away from us than the sun and all the planets. The 

 only body that still remained as revolving around the earth 

 was the moon, but this, as Hipparchus had already found, 

 is much nearer to us than all other heavenly bodies. This 

 view of the planetary system as a stationary sun and moving 

 earth, was already that of the school of Pythagoras; which is 

 a proof of the lofty flights of which those minds were capable, 

 although in their case it was not the result of firmly founded 

 investigation. Copernicus was able to make it so, since he 

 had Hipparchus' thorough observations at his service, and 

 was not satisfied until completely certain that other possibili- 

 ties, suggested before his time or occurring to himself, did 

 not agree in the same simple manner with observed reality, 

 as did this assumption of the moving earth. But this assump- 

 tion then became for him a reality recognised as such; he 

 shows himself as a true investigator of nature when he states 

 that he has found that, and how the earth moves: 'AH this, 

 however difficult and almost incomprehensible it may seem 

 to many, and however much it may be opposed to the ideas 

 of the great majority, all this we shall, with God's help, make 

 clearer than the sun in the course of this work, at least for 

 all those who are not completely devoid of all mathematical 

 knowledge.' 



He also expressly draws a very remarkable conclusion from 

 his discovery. If the earth describes yearly a path of great 

 diameter around the sun, the fixed stars cannot by any means 

 be so near to us as was thought at that time. For there are 

 no visible signs of a semi-annual change in distance, as for 

 example, a variation in magnitude or brightness. The not 

 very large sphere, to which all fixed stars were imagined 

 as fastened, and which enclosed the Universe, could not 



