164 Parallel of Rome, de V Isle's and 



nomenclature of the crystals also allude to some remarkable 

 circumstance of the crystalline form. 



I shall now proceed to philosophical crystallography, 

 which might be called the philosophy of mineralogy, ft 

 does not consist in searching for the primary causes of phe- 

 nomena ; nothing can be less philosophical than such a re- 

 search ; primary causes will ever be beyond the reach of the 

 human mind. The immortal Newton was the first to point 

 out to us, by the method followed in his admirable book of 

 the Principia, that the only true philosophical way of treat-' 

 ing a physical science, or of explaining a natural fact, was 

 to demonstrate that it was the mathematical consequence of 

 a general law, grounded on an aggregate of facts already ob- 

 served and capable of correct calculation. If any one of 

 these conditions be wanting, we immediately launch out 

 into hypothesis; explanations become vague; and, however 

 much we may be persuaded of the truth of our assertions, 

 \ve can acquire no certainty. 



Let us apply these principles to our two writers. De ITsle, 

 in declaring that the various forms observed in crystals of 

 .ne substance are only modifications of one constant 

 primitive form, certainly announced a most important truth. 

 It was a flash of genius ; but in a philosophical inquiry, to 

 prove it, and not simply to say it, was the necessary step. 

 On the first inspection of his crystallographical tables, a 

 student is tempted to think that important truth demon- 

 strated ; bjt, on a closer examination, the impression is 

 C ->ne away. The same order pervades every table. By slight 

 passages the student is led from the simpler to the more 1 

 compound forms, and after every passage is tempted to say, 

 This can only be amodiiicationof the primitive. Then when- 

 the real crystals and the figures of the tables are compared 1 

 together, and all those of the same species (with a very few 

 exceptions) are found in the same table, how easy it is to 

 persuade ourselves that nature must operate by similar pas- 

 sages when producing the various forms of crystals ! and 

 the primitive of the table before us must be the primitive 

 of the crystal under examination. In a word, it is the 

 most simple form; and first impressions greatly strengthen 

 the illusion. If persuasion was the sole object of philo- 

 sophy, De ITsle would have been a powerful philosopher j 

 but philosophy must convince, demonstrate, and wrest con- 

 sent, however violently opposed. An enemy must not> 

 therefore, be able to make use of the same arms, or adduce 

 the same proofs, to establish a contrary opinion. Neverthe- 

 less, such would be the case with Mr. de P Isle's tables,, and 



the 



