ASTRONOMY 167 



ment of the heaven and the heavenly bodies, which 

 movement they considered as being apparent, they 

 endowed the earth with a movement of rotation on 

 itself. Their doctrine, preserved by Cicero amongst 

 others, certainly guided Copernicus in his investiga- 

 tions, for he twice quotes the passage from Cicero 

 (Qua esti ones Academicae priores, II, 39), in which 

 Hicetas is erroneously called Nicetas. This passage 

 is as follows : 



" According to Theophrastus, Nicetas of Syracuse 

 professed the opinion that the sun, moon and all the 

 celestial bodies remained motionless, and that nothing 

 moves in the world, except the earth, which, turning 

 round its axis at a great speed, produces the same 

 appearances as those observed when it was supposed 

 that the earth was fixed and the heaven in motion. 

 Some think that Plato, in the Timaeus, said the same 

 thing in a somewhat more obscure manner." * 



As M. Duhem remarks, 2 the little that we know of 

 the systems elaborated by the Pythagoreans to explain 

 the celestial movements is enough to awaken our 

 astonishment and admiration. The fecundity and the 

 ingenuity of the Hellenic mind are surprising : scarcely 

 had it found itself at grips with the astronomical 

 problem when it multiplied its attempts at solution, 

 and attacked it in most diverse ways. The conceptions 

 of the Pythagorean school had in fact an incalculable 

 influence on astronomy, for they distinguished for the 

 first time between movements which are real and move- 

 ments which are only apparent ; they bring into 

 relief the fact that outside the data immediately 

 furnished by the senses there must be sought a har- 

 monious reason to explain them. 



Plato incorporates in his teaching the principal 

 elements of the Pythagorean astronomy. He retains 



1 Quoted after 13 Duhem, Systems I, p. 22. 



2 Ibid., p. 27. 



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