ALEXANDRIAN OR HELLENISTIC PERIOD 



world was flat, the Pythagoreans out in Italy taught 

 that the world is a sphere and that the apparent mo- 

 tions of the heavenly bodies are really due to the actual 

 motion of the earth itself. They did not, however, 

 vault to the conclusion that this true motion of the 

 earth takes place in the form of a circuit about the 

 sun. Instead of that, they conceived the central body 

 of the universe to be a great fire, invisible from the 

 earth, because the inhabited side of the terrestrial 

 ball was turned away from it. The sun, it was held, 

 is but a great mirror, which reflects the light from the 

 central fire. Sun and earth alike revolve about this 

 great fire, each in its own orbit. Between the earth 

 and the central fire there was, curiously enough, sup- 

 posed to be an invisible earthlike body which was given 

 the name of Anticthon, or counter-earth. This body, 

 itself revolving about the central fire, was supposed to 

 shut off the central light now and again from the sun 

 or from the moon, and thus to account for certain 

 eclipses for which the shadow of the earth did not 

 seem responsible. It was, perhaps, largely to account 

 for such eclipses that the counter-earth was invented. 

 But it is supposed that there was another reason. The 

 Pythagoreans held that there is a peculiar sacredness 

 in the number ten. Just as the Babylonians of 

 the early day and the Hegelian philosophers of a 

 more recent epoch saw a sacred connection between 

 the number seven and the number of planetary 

 bodies, so the Pythagoreans thought that the uni- 

 verse must be arranged in accordance with the num- 

 ber ten. Their count of the heavenly bodies, includ- 

 ing the sphere of the fixed stars, seemed to show 



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