Darwinism Verified. 9 



served phenomena of nature. But in the direct- 

 ness with which this question can be answered 

 there is great difference between the two theories. 

 The Newtonian hypothesis asserted the existence 

 of a general physical property of matter, and could 

 therefore be tested by a single crucial instance, 

 such as was afforded by the simple case of the 

 planetary motions. Kepler's three laws comprised 

 in succinct form a very complete description of the 

 movements of the planets ; and when it was shown 

 that these movements were just such as must oc- 

 cur according to the theory of gravitation, the 

 theory was rightly regarded as verified. Further 

 confirmatory instances could but repeat the same 

 lesson, as when the irregularities of movement, 

 due to the attractions exercised by the various 

 planets upon each other, were likewise seen to 

 conform strictly to the hypothesis. Nor was any 

 alteration or enlargement of the original theory 

 required in order to obtain the supreme triumph 

 of verified prediction, as when Clairaut foretold 

 the precise amount of delay in the reappearance 

 of Halley's comet, caused by the interfering attrac- 

 tions of Jupiter and Saturn, or as when Leverrier 

 and Adams discovered the existence of Neptune 

 through its effects upon the motions of Uranus. 

 In all these cases the physical principle involved 



