MATTER AND FORCE. 385 



the savage, and his sensations of muscular force, we pass 

 on to the observation of force exerted between a magnet 

 and rubbed amber and the bodies which they attract, 

 rising, by an unbroken growth of ideas, to a conception of 

 the force by which sun and planets are held together. 



This idea of attraction between sun and planets had 

 become familiar in the time of Newton. He set himself 

 to examine the attraction: and here, as elsewhere, we find 

 the speculative mind falling back for its materials upon 

 experience. It had been observed, in the case of magnetic 

 and electric bodies, that the nearer they were brought to- 

 gether the stronger was the force exerted between them; 

 while, by increasing the distance, the force diminished 

 until it became insensible. Hence the inference that the 

 assumed pull between the earth and the sun would be 

 influenced by their distance asunder. Guesses had been 

 made as to the exact manner in which the force varied with 

 the distance; but Newton supplemented the guess by the 

 severe test of experiment and calculation. Comparing the 

 pull of the earth upon a body close to its surface, with its 

 pull upon the moon, 240,000 miles away, Newton rigidly 

 established the law of variation with the distance. But on 

 his way to this result Newton found room for other con- 

 ceptions, some of which indeed, constituted the necessary 

 stepping-stones to his result. The one which here con- 

 cerns 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 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 Democ- 

 ritus, Epicurus, and Lucretius. These men adopted, 

 developed, and diffused the doctrine of atoms and mole- 

 cules, which found its consummation at the hands of the 

 illustrious John Dalton. But the Greek and Roman phi- 

 losophers 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 centra 1 



