CHARACTER OF THE EXPERIMENTALIST. 583 



atmosphere of gas, a consequence being drawn from each 

 case, and that one hypothesis ultimately selected which 

 yields results agreeing with experiments upon the pressure 

 and density of the terrestrial atmosphere. 



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

 reality, the greater part of the Principia is purely hy- 

 pothetical, endless varieties of causes and laws being 

 imagined 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 un- 

 questionable deductive reasoning; and the value of each 

 hypothesis was entirely decided by the comparison of its 

 consequences 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 advocate throughout this book. 

 Francis Bacon held that science should be founded on 

 experience, but he mistook the true mode of using experi- 

 ence, and, in attempting to apply his method, ludicrously 

 failed. Newton did not less found his method on experi- 

 ence, but he seized the true method of treating it, and 

 applied it with a power and success never since equalled. 

 It is a great mistake to say that modern science is the 

 result of the Baconian philosophy ; it is the Newtonian 

 philosophy and the Newtonian method which have led to 

 all the great triumphs of physical science, and I repeat 

 that the Principia forms the true " Novum Organum." 



In bringing his theories to a decisive experimental verifi- 

 cation, Newton showed, as a general rule, exquisite skill 

 and ingenuity. In his hands a few simple pieces of appa- 

 ratus were made to give results involving an unsuspected 

 depth of meaning. His most beautiful experimental in- 

 quiry was that by which he proved the differing refrangibi- 

 lity of rays of light. To suppose that he originally dis- 

 covered the power of a prism to break up a beam of white 

 light would be a mistake, for he speaks of procuring a 

 glass prism to try the " celebrated phenomena of colours." 

 But we certainly owe to him the theory that white light is 

 a mixture of rays differing in refrangibility, and that lights 

 which differ in colour, differ also in refraugibility. Other 



