44 INDUCTION. 



common cause, and therefore independent of collocations. The 

 uniformities, on the other hand, in the order of superposition 

 of strata on the earth, are empirical laws of a much weaker 

 kind, since they not only are not laws of causation, but there 

 is no reason to believe that they depend on any common 

 cause : all appearances are in favour of their depending on the 

 particular collocation of natural agents which at some time or 

 other existed on our globe, and from which no inference can 

 be drawn as to the collocation which exists or has existed in 

 any other portion of the universe. 



6. Our definition of an empirical law including not 

 only those uniformities which are not known to be laws of 

 causation, but also those which are, provided there be reason 

 to presume that they are not ultimate laws ; this is the proper 

 place to consider by what signs we may judge that even if an 

 observed uniformity be a law of causation, it is not an ultimate 

 but a derivative law. 



The first sign is, if between the antecedent a and the con 

 sequent b there be evidence of some intermediate link ; some 

 phenomenon of which we can surmise the existence, though 

 from the imperfection of our senses or of our instruments we 

 are unable to ascertain its precise nature and laws. If there 

 be such a phenomenon (which may be denoted by the letter 

 x), it follows that even if a be the cause of b, it is but the 

 remote cause, and that the law, a causes b, is resolvable into 

 at least two laws, a causes x, and x causes b. This is a very 

 frequent case, since the operations of nature mostly take place 

 on so minute a scale, that many of the successive steps are 

 either imperceptible, or very indistinctly perceived. 



Take, for example, the laws of the chemical composition 

 of substances ; as that hydrogen and oxygen being combined, 

 water is produced. All we see of the process is, that the 

 two gases being mixed in certain proportions, and heat or 

 electricity being applied, an explosion takes place, the gases 

 disappear, and water remains. There is no doubt about the 

 law, or about its being a law of causation. But between the 

 antecedent (the gases in a state of mechanical mixture, 



