MATTER AND FORCE. 59 



His conclusion was, that the attraction of the masses 

 was simply the sum of the attractions of their con- 

 stituent particles. 



This result seems so obvious that you will perhaps 

 wonder at my dwelling upon it; but it really marks a 

 turning point in our notions of force. You have 

 probably heard of certain philosophers of the ancient 

 world named Democritus, Epicurus, and Lucretius. 

 These men adopted, developed, and diffused the doc- 

 trine of atoms and molecules, which found its consum- 

 mation at the hands of the illustrious John Dalton. 

 But the Greek and Roman philosophers I have named, 

 and their followers, up to the time of Newton, pictured 

 their atoms as falling and flying through space, hitting 

 each other, and clinging together by imaginary hooks 

 and claws. They missed the central idea that atoms 

 and molecules could come together, not by being for- 

 tuitously knocked against each other, but by their own 

 mutual attractions. This is one of the great steps 

 taken by Newton. He familiarised the world with the 

 conception of molecular force. 



Newton, you know, was preceded by a grand fellow 

 named John Kepler a true working man who, by 

 analysing the astronomical observations of his master, 

 Tycho Brahe, had actually found that the planets 

 moved as they are now known to move. Kepler knew 

 as much about the motion of the planets as Newton 

 did; in fact, Kepler taught Newton and the world 

 generally the facts of planetary motion. But this was 

 not enough. The question arose Why should the 

 facts be so? This was the great question for Newton, 

 and it was the solution of it which renders his name 

 and fame immortal. Starting from the principle that 

 every particle of matter in the solar system attracts 

 every other particle by a force which varies as the in- 

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