THE FOUR EXPERIMENTAL METHODS. 427 



elude, therefore, that the solidification of a substance from a 

 liquid state is an invariable antecedent of its crystallization. 



ID this example we may go farther, and say, it is not only 

 the invariable antecedent but the cause ; or at least the proxi 

 mate event which completes the cause. For in this case we 

 are able, after detecting the antecedent A, to produce it arti 

 ficially, and by finding that &amp;lt;i follows it, verify the result of 

 our induction. The importance of thus reversing the proof 

 was strikingly manifested when by keeping a phial of water 

 charged with siliceous particles undisturbed for years, a 

 chemist (I believe Dr. Wollaston) succeeded in obtaining 

 crystals of quartz ; and in the equally interesting experiment 

 in which Sir James Hall produced artificial marble, by the 

 cooling of its materials from fusion under immense pressure : 

 two admirable examples of the light which may be thrown 

 upon the most secret processes of nature by well-contrived 

 interrogation of her. 



But if we cannot artificially produce the phenomenon A, 

 the conclusion that it is the cause of a remains subject to 

 very considerable doubt. Though an invariable, it may not 

 be the unconditional antecedent of a, but may precede it as 

 day precedes night or night day. This uncertainty arises 

 from the impossibility of assuring ourselves that A is the only 

 immediate antecedent common to both the instances. If we 

 could be certain of having ascertained all the invariable ante 

 cedents, we might be sure that the unconditional invariable 

 antecedent, or cause, must be found somewhere among them. 

 Unfortunately it is hardly ever possible to ascertain all the 

 antecedents, unless the phenomenon is one which we can 

 produce artificially. Even then, the diificulty is merely 

 lightened, not removed : men knew how to raise water in 

 pumps long before they adverted to what was really the 

 operating circumstance in the means they employed, namely, 

 the pressure of the atmosphere on the open surface of the 

 water. It is, however, much easier to analyse completely 

 a set of arrangements made by ourselves, than the whole 

 complex mass of the agencies which nature happens to be 

 exerting at the moment of the production of a given phe- 



