150 THE PRINCIPLES OF SCIENCE. 



becoming gaseous absorb heat ; that all metals are 

 elements ; that they are all good conductors of heat and 

 electricity ; that all the alkaline metals are monad 

 elements ; that all foraminifera are marine organisms ; 

 that all parasitic animals are non- mammalian ; that 

 lightning never issues from stratous clouds a ; that pumice 

 never occurs where only Labrador felspar is present b : 

 and scientific importance may attach even to such ap 

 parently trifling observations as that white cats having 

 blue eyes are deaf c . 



The process of inference by which all such truths are 

 obtained may readily be exhibited in a precise symbolic 

 form. We must have one premise specifying in a dis 

 junctive form all the possible individuals which belong 

 to a class ; we resolve the class, in short, into its con 

 stituents. We then need a number of propositions each 

 of which affirms that one of the individuals possesses a 

 certain property. Thus the premises must be of the 

 form 



A = B! 01 D|. .:...! PI Q 



B- BX 



C = CX 



Q = QX. 



Now if we substitute for each alternative of the first 

 premise its description as found among the succeeding 

 premises we obtain 



A = BXI CXI ......... IPXIQX 



or 



A = (B!C| 



a Arago s Meteorological Essays, p. 10. 



b Lyell s Elements of Geology, Fourth ed. p. 373. 



c Darwin s Variation of Animals, &c. 



