EMPIRICAL LAWS. 309 



observe in the production and subsequent life of an animal or a vop^e- 

 table, resting upon the Method of Agreement only, are mere empirical 

 laws ; but though the antecedents in those sequences may not be the 

 causes of the consequents, both the one and the other are probably, in 

 the main, successive stages of a progressive effect originating iu a 

 common cause, and therefore independent of collocations. The unifor- 

 mities, on the otlier hand, in the order of superposition of strata on the 

 earth, are empirical laws of a much weaker kind, since they are not 

 only not laws of causation, but there is no reason to believe that they 

 depend upon any common cause : all appearances are in favor of 

 their depending upon the particular collocation of natural agents which 

 primitively existed on our globe, and from which no inference can be 

 dra\vn as to the collocation which exists or has existed iu 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 causa- 

 tion, it is not an ultimate but a derivative law. 



The first sign is, if between the antecedent a and the consequent b 

 there be evidence of some intermediate link ; some phenomenon of 

 which we can collect the existence, although 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 h, 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 substan- 

 ces ; 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, heated or elec- 

 trified), and the consequent (the production of water), there must be 

 an inteiTnediate process which we do not see. For if we take any 

 portion whatever of the water, and subject it to analysis, we find that 

 it always contains some hydrogen and some oxygen : nay, the very 

 same proportions of them, namely, two-thirds, in volume, of hydrogen, 

 and one-third oxygen. This is true of a single drop ; it is true of the 

 minutest portion which our instruments are capable of appreciating. 

 Since, then, the smallest perceptible portion of the water contains both 

 those substances, portions of hydrogen and oxygen smaller than the 

 smallest perceptible must have come together in every such minute 

 portion of space ; must have come closer together than when the gases 

 were in a state of mechanical mixture, since (to mention no other 

 reasons) the water occupies far less space than the gases. Now as we 

 cannot see this contact or close approach of the minute particles, we 



