THE FOUR EXPERIMENTAL METHODS. 279 



tion by producing it : if we succeeded in such a random trial it could only 

 be by accident. But if we can observe a in two different combinations, 

 abc and ade ; and if we know, or can discover, that the antecedent cir- 

 cumstances in these cases respectively were ABC and A D E, we may 

 conclude by a reasoning similar to that in the preceding example, that A is 

 the antecedent connected with the consequent a by a law of causation. 

 B and C, we may say, can not be causes of a, since on its second occur- 

 rence they were not present ; nor are D and E, for they were not present on 

 its first occurrence. A, alone of the five circumstances, was found among 

 the antecedents of a in both instances. 



For example, let the effect a be crystallization. We compare instances 

 in which bodies are known to assume crystalline structure, but which have 

 no other point of agreement ; and we find them to have one, and as far as 

 we can observe, only one, antecedent in common : the deposition of a solid 

 matter from a liquid state, either a state of fusion or of solution. We 

 conclude, therefore, that the solidification of a substance from a liquid state 

 is an invariable antecedent of its crystallization. 



In this examplp we may go further, and say, it is not only the invariable 

 antecedent but the cause ; or at least the proximate event which completes 

 the cause. For in this case we are able, after detecting the antecedent A, 

 to produce it artificially, and by finding that a follows it, verify the result 

 of our induction. The importance of thus reversing the proof was strik- 

 ingly manifested when, by keeping a phial of water charged with siliceous 

 particles undisturbed for years, a chemist (I believe Dr. Wollaston) suc- 

 ceeded in obtaining crystals of quartz; and in the equally interesting ex- 

 periment in which Sir James Hall produced artificial marble by the cool- 

 ing 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 can not 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 onhj immediate 

 antecedent common to both the instances. If we could be certain of hav- 

 ing ascertained all the invariable antecedents, wo might be sure that the 

 imconditional 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 artificial- 

 ly. Even then, the difficulty 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 press- 

 ure of the atmosphere on the open surface of the water. It is, however, 

 much easier to analyze completely a set of arrangements made by our- 

 selves, than the whole complex mass of the agencies which nature happens 

 to be exerting at the moment of the production of a given phenomenon. 

 We may overlook some of the material circumstances in an experiment 

 with an electrical machine; but we shall, at the worst, be better acquainted 

 with them than with those of a thunder-storm. 



The mode of discovering and proving laws of nature, which we have 

 now examined, proceeds on the following axiom : Whatever circumstances 

 can be excluded, without prejudice to the phenomenon, or can be absent 

 notwithstanding its presence, is not connected with it in the way of causa- 



