2G2 HISTORY OF FORMAL ASTRONOMY. 



CHAPTER II. 



..NDUCTIOX OF COPERNICUS. THE HELIOCENTRIC THEORY ASSERTED 



OX FORMAL GROUNDS. 



IT will be recollected that the formal are opposed to the 

 grounds of a theory ; the former term indicating that it gives a 

 satisfactory account of the relations of the phenomena in Space and 

 Time, that is, of the Motions themselves ; while the latter expression 

 implies further that we include in our explanation the Causes of the 

 motions, the laws of Force and Matter. The strongest of the consider- 

 ations by which Copernicus was led to invent and adopt his system of 

 the universe were of the former kind. He was dissatisfied, he says, in 

 his Preface addressed to the Pope, with the want of symmetry in the 

 Eccentric Theory, as it prevailed in his days ; and weary of the uncer- 

 tainty of the mathematical traditions. He then sought through all 

 the works of philosophers, whether any had held opinions concerning 

 the motions of the world, different from those received in the estab- 

 lished mathematical schools. He found, in ancient authors, accounts 

 of Philolaus and others, who had asserted the motion of the earth. 

 " Then," he adds, " I, too, began to meditate concerning the motion of 

 the earth ; and though it appeared an absurd opinion, yet since I knew 

 that, in previous times, others had been allowed the privilege of feign- 

 ing 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 expla- 

 nations than the ancient ones, of the revolutions of the celestial orbs. 



" Having then assumed the motions of the earth, which are here- 

 after explained, by laborious and long observation I at length found, 

 that if the motions of the other planets be compared with the revolu- 

 tion of the earth, not only their phenomena follow from the suppo- 

 sitions, but also that the several orbs, and the whole system, are so 

 connected 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 apparent motions of the 

 planets, and the simplicity and symmetry of the system, were the 



