286 OPERATIONS SUBSIDIARY TO INDUCTION. 



merits, a separation of circumstances usually conjoined. The 

 principle of the method is, that facts which increase or dimi- 

 nish together, and disappear together, are either cause and 

 effect, or effects of a common cause. When it has been ascer- 

 tained that this relation really subsists between the variations, 

 a connexion between the facts themselves may be confidently 

 laid down, either as a law of nature or only as an empirical 

 law, according to circumstances. 



That the application of this Method must be preceded by 

 the formation of such a series as we have described, is too 

 obvious to need being pointed out ; and the mere arrangement 

 of a set of objects in a series, according to the degrees in 

 which they exhibit some fact of which we are seeking the law, 

 is too naturally suggested by the necessities of our inductive 

 operations, to require any lengthened illustration here. But 

 there are cases in which the arrangement required for the 

 special purpose, becomes the determining principle of the* 

 classification of the same objects for general purposes. This 

 will naturally and properly happen, when those laws of the 

 objects which are sought in the special inquiry enact so prin- 

 cipal a part in the general character and history of those 

 objects exercise so much influence in determining all the 

 phenomena of which they are either the agents or the theatre 

 that all other differences existing among the objects are 

 fittingly regarded as mere modifications of the one pheno- 

 menon sought ; effects determined by the co-operation of some 

 incidental circumstance with the laws of that phenomenon. 

 Thus in the case of animated beings, the differences between 

 one class of animals and another may reasonably be considered 

 as mere modifications of the general phenomenon, animal life ; 

 modifications arising either from the different degrees in 

 which that phenomenon is manifested in different animals, or 

 from the intermixture of the effects of incidental causes 

 peculiar to the nature of each, with the effects produced by 

 the general laws of life ; those laws still exercising a predomi- 

 nant influence over the result. Such being the case, no other 

 inductive inquiry respecting animals can be successfully carried 

 on, except in subordination to the great inquiry into the uni- 



