508 THE PRINCIPLES OF SCIENCE. [CHAP. 



filled with the scientific spirit, telling us how he tried 

 theory after theory in order to discover one which was in 

 accordance with the motions of Mars. 1 Huyghens, who 

 possessed one of the most perfect philosophical intellects, 

 followed the deductive process combined with continual 

 appeal to experiment, with a skill closely analogous to 

 that of Newton. As to Descartes and Leibnitz, they fell 

 into excess in the use of hypothesis, since they sometimes 

 adopted hypothetical reasoning to the exclusion of ex- 

 perimental verification. Throughout the eighteenth cen- 

 tury science was supposed to be advancing by the pur- 

 suance of the Baconian method, but in reality hypothetical 

 investigation was the main instrument of progress. It is 

 only in the present century that physicists began to recog- 

 nise this truth. So much opprobrium had been attached 

 by Bacon to the use of hypotheses, that we find Young 

 speaking of them in an apologetic tone. " The practice of 

 advancing general principles and applying them to par- 

 ticular instances is so far from being fatal to truth in all 

 sciences, that when those principles are advanced on suf- 

 ficient grounds, it constitutes the essence of true phi- 

 losophy;" 2 and he quotes cases in which Davy trusted 

 to his theories rather than his experiments. 



Herschel, who was both a practical physicist and an 

 abstract logician, entertained the deepest respect for 

 Bacon, and made the " Novum Organum " as far as 

 possible the basis of his own admirable Discourse on 

 the Study of Natural Philosophy. Yet we find him in 

 Chapter VII. recognising the part which the formation 

 and verification of theories takes in the higher and more 

 general investigations of physical science. J. S. Mill 

 carried on the reaction by describing the Deductive 

 Method in which ratiocination, that is deductive rea- 

 soning, is employed for the discovery of new oppor- 

 tunities of testing and verifying an hypothesis. Never- 

 theless throughout the other parts of his system he 

 inveighed against the value of the deductive process, 

 and even asserted that empirical inference from par- 

 ticulars to particulars is the true type of reasoning. 



1 Horrocks, Opera Posthuma (1673), P- 2 7^- 

 * Young's Works, vol. i. p. 593. 



