THE FINITE UNIVERSE 



same means that Adams and Leverrier were able 

 to predict the discovery of a new planet and to fix 

 at a given moment its exact place in the heavens. 

 Thither the telescopes were turned, and there 

 Neptune was found. That was, no doubt, the 

 highest triumph the Newtonian theory had yet re- 

 ceived. The prediction that Sirius was a double- 

 star, and the finding of its dark companion, was 

 hardly less striking. It now seems doubtful if any 

 change will ever have to be made in Newton's law. * 

 It will stand. 



We may add, then, a third constant to our con- 

 ception, and say that all matter whatsoever has 

 the same attractive force. It would puzzle an en- 

 lightened savage if he were told that a given mass 

 of impalpable air exerts the same power of attrac- 

 tion as a like mass of iron or lead. There are plenty 

 of folk who are not savage to whom this fact and 

 all its implications have never been clear. I have 

 known many who never had heard of Galileo's 

 famous experiment of dropping a one and a ten 

 pound weight from the Leaning Tower of Pisa, and 

 proving that they reach the earth in the same time. 

 Generally they do not believe it is true. No argu- 

 ment in the world could convince them that in a 

 vacuum a feather falls at the same rate as a can- 

 non-ball. 



Moreover, nothing at first sight seems more con- 

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