256 THE HISTORY OF SCIENCE 



means of breaking down English credit. He did try 

 to prevent the English from exchanging exports for 

 European gold, while permitting imports in the hope 

 of depleting England of gold. But in pursuing this 

 policy he thought he was proceeding on the ground 

 of immemorial practice, while he was merely pitting 

 the seventeenth-century doctrine of Locke against 

 the doctrine of Adam Smith which had superseded it. 



According to one scientific hypothesis, "Species 

 originated by means of natural selection, or, through 

 the preservation of favored races in the struggle for 

 life." This assumption was rightly subjected to close 

 scrutiny in 1859 and the years following. The ephem- 

 eral nature of the vast majority of hypotheses and 

 the danger to progress of accepting an unverified 

 assumption justify the demand for demonstrative 

 evidence. The testimony having been examined, it 

 is our privilege to state and to support the opposing 

 hypothesis. It was thus that the hypothesis that the 

 planets move in circular orbits, recommended by its 

 simplicity and aesthetic quality, was forced to give 

 way to the hypothesis of elliptical orbits. Newton's 

 hypothesis that light is due to particles emitted by 

 all luminous bodies yielded, at least for the time, to 

 the theory of light vibrations in an ether pervading 

 all space. The path of scientific progress is strewn 

 with the ruins of overthrown hypotheses. Many of 

 the defeated assumptions have been merely implicit 

 errors of the mail in the street, and they are over- 

 thrown not by facts alone, but by new hypotheses 

 verified by facts and leading to fresh discoveries. 



According to John Stuart Mill, " It appears . . . 

 to be a condition of a genuinely scientific hypothesis, 



