22 CLASSICS OF MODERN SCIENCE 

 nothing else than the fact that the mathematicians do not agree with 

 one another in their investigations. In the first place, they are so 

 uncertain about the motions of the sun and moon that they cannot 

 find out the length of a full year. In the second place, they apply 

 neither the same laws of cause and effect, in determining the motions 

 of the sun and moon and of the five planets, nor the same proofs. 

 Some employ only concentric circles, others use eccentric and epicy- 

 clic ones, with which, however, they do not fully attain the desired 

 end. They could not even discover nor compute the main thing — 

 namely, the form of the universe and the symmetry of its parts. It 

 was with them as if some should, from different places, take hands, 

 feet, head, and other parts of the body, which, although very beau- 

 tiful, were not drawn in their proper relations, and, without making 

 them in any way correspond, should construct a monster instead 

 of a human being. 



Accordingly, when I had long reflected, on this uncertainty of 

 mathematical tradition, I took the trouble to read again the books 

 of all the philosophers I could get hold of, to see if some one of them 

 had not once believed that there were other motions of the heavenly 

 bodies. First I found in Cicero that Niceties had believed in the 

 motion of the earth. Afterwards I found in Plutarch, likewise, that 

 some others had held the same opinion. This induced me also to 

 begin to consider the movability of the earth, and, although the theory 

 appeared contrary to reason, I did so because I knew that others 

 before me had been allowed to assume rotary movements at will, in 

 order to explain the phenomena of these celestial bodies. I was of 

 the opinion that I, too, might be permitted to see whether, by pre- 

 supposing motion in the earth, more reliable conclusions than hitherto 

 reached could not be discovered for the rotary motions of the spheres. 

 And thus, acting on the hypothesis of the motion which, in the follow- 

 ing book, I ascribe to the earth, and by long and continued observa- 

 tions, I have finally discovered that if the motion of the other planets 

 be carried over to the relation of the earth and this is made the basis 

 for the rotation of every star, not only will the phenomena of the 

 planets be explained thereby, but also the laws and the size of the stars ; 

 all their spheres and the heavens themselves will appear so harmoni- 

 ously connected that nothing could be changed in any part of them 

 without confusion in the remaining parts and in the whole universe. 



