452 INDUCTION. 



that A is the antecedent connected with the conse- 

 quent a by a law of causation. B and C, we may say, 

 cannot be causes of a, since on its second occurrence 

 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 antece- 

 dents 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 ante- 

 cedent of its crystallization. 



In this example we may go farther, and say, it is 

 not only the invariable antecedent but the cause. 

 For in this case we are able, after detecting the ante- 

 cedent 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 never 

 more strikingly manifested than when, by keeping a 

 phial of water charged with siliceous particles undis- 

 turbed 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-con- 

 trived interrogation of her. 



But if we cannot artificially produce the phenome- 

 non A, the conclusion that it is the cause of a remains 



