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THE POPULAR SCIENCE MONTHLY 



Ptolemy. 



the spheres. He conceived each planet as held in place by being fixed 

 in a celestial crystalline sphere which, in its rotation about the sun 

 as center, carried the planet with it. Having observed that the planets 

 move at different rates, it followed that the various spheres had dif- 

 ferent rates of rotation, and Pythagoras believed that some law con- 

 trolled their motions. This he expressed by supposing that each 

 sphere emitted sounds or notes like the strings of a harp, and the har- 

 mony was expressed by the belief that the several notes united in a 

 beautiful celestial harmony of most exquisite music. More fantastic 

 than suggestive, yet here in the far-away dawn of scientific history is 

 the foreshadowing of the great thought which two millenniums later 

 was given in Newton's universal law of gravitation. 



The fate of Anaxagoras warned Pythagoras against being too overt 



