I.] Darwinism Verified. 9 



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 move- 

 ments were just such as must occur 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 attractions 

 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 was simple, and 

 admitted of precise mathematical treatment ; and 

 it is owing to this that the law of gravitation has 

 become the most illustrious example which the 

 history of science can furnish of a completely verified 

 hypothesis. 



To look for similar conciseness of verification in 

 the case of the Dai^winian theory would be to 



