COSMIC PHILOSOPHY 



accounted for, after calculating the combined 

 effects of all the interior planets in producing 

 such irregularities, it occurred to him that the 

 unexplained irregularities could only be due 

 to the gravitative force of some undiscovered 

 planet outside of Uranus ; and the discovery of 

 Neptune was the result of this most brilliant 

 hypothesis. Now, the mental act involved in 

 this deduction was essentially a classification of 

 cases. The case of the unexplained perturba- 

 tions was mentally ranked along with the sev- 

 eral cases of explained perturbations presented 

 by the solar system, as being similarly due to 

 gravitative force ; and to the number of known 

 cases in which planets deflect each other from 

 the regular paths in which they would other- 

 wise move, a new hypothetical case was added. 

 Comparing, now, this mental operation with 

 that of the naturalist who, by virtue of certain 

 observed likenesses of structure and function, 

 ranks together lions and elephants and seals 

 in the class of mammals, we may conclude 

 roughly that the one process consists in the for- 

 mation of a group o^ like cases, while the other 

 consists in the formation of a group of like 

 things. And since by the expression " like 

 cases " we mean merely " like sets of relations 

 among two or moxe given groups of things," it 

 follows that we may characterize Reasoning as 

 the classification of relations, while Classification, 



