64 FRAGMENTS OF SCIENCE 



of variation with the distance. But on his way to this 

 result Newton found room for other conceptions, some 

 of which, indeed, constituted the necessary stepping- 

 stones to his result. The one which here concerns us 

 is, that not only does the sun attract the earth, and the 

 earth attract the sun, as wholes, but every particle of 

 the sun attracts every particle of the earth, and the re- 

 verse. His conclusion was that the attraction of the 

 masses was simply the sum of the attractions of their 

 constituent 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 prob- 

 ably heard of certain philosophers of the ancient world 

 named Democritus, Epicurus, and Lucretius. These men 

 adopted, developed, and diffused the doctrine of atoms 

 and molecules, which found its consummation at the 

 hands of the illustrious John Dalton. But the Greek 

 and Eoman philosophers I have named, and their fol- 

 lowers, 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 fortuitously knocked 

 against each other, but by their own mutual attractions. 

 This is one of the great steps taken by Newton. He 

 familiarized 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 ana- 

 lyzing the astronomical observations of his master, Tycho 

 Brahe, had actually found that the planets moved as they 



