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!C!D|..:...!P!Q 

 B = BX 

 C = CX 



Now if we substitute for each alternative of the first 

 premise its description as found among the succeeding 

 premises we obtain 



A = BXI CXI I PXI QX 



or 



A = (BIG -I- |-Q)X. 



a Arago's Meteorological Essays, p. 10. 



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



Darwin's Variation of Animals, &c. 



