228 THE PRINCIPLES OF SCIENCE. 



strikes the reader of the work as the exhaustiveness of his 

 treatment, and the almost infinite power of his insight. 

 If he treats of central forces, it is not any one law of force 

 which he discusses, but many, or almost all imaginable 

 cases, the laws and results of each of which he sketches 

 out in a few pregnant words. If his subject is a resisting 

 medium, it is not air or water alone, nor any one resisting 

 medium, but resisting media in general. We have a 

 good example of his method in the Scholium to the twenty- 

 second proposition of the second book, in which he runs 

 rapidly over many possible suppositions as to the laws of 

 the compressing forces which might conceivably act in an 

 atmosphere of gas, a consequence being drawn from each 

 case, and that one hypothesis ultimately selected whic 

 yields results agreeing with experiments upon the pressu 

 and density of the terrestrial atmosphere. 



Newton said that he did not frame hypotheses, but, i 

 reality, the greater part of the ' Principia ' is purely hyp 

 thetical, endless varieties of causes and laws being ima- 

 gined which have no counterpart in nature. The most 

 grotesque hypotheses of Kepler or Descartes were not 

 more imaginary. But Newton's comprehension of logical 

 method was perfect ; no hypothesis was entertained unless 

 it was definite in conditions, and admitted of unquestion- 

 able deductive reasoning ; and the value of each hypo- 

 thesis was entirely decided by the comparison of its conse- 

 quences with facts. I do not entertain a doubt that the 

 general course of his procedure is identical with that view 

 of the nature of induction, as the inverse application of 

 deduction, which I have advocated throughout these 

 volumes. Francis Bacon held that science should be 

 founded on experience, but he wholly mistook the true 

 mode of using experience, and in attempting to apply his 

 method he ludicrously failed. Newton did not less found 

 his method on experience, but he seized the true method 



