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ON THE RELATION BETWEEN THE POLYHEDRAL AND 

 SPHEROIDAL THEORIES OF CRYSTALLIZATION; AND 

 THE CONNEXION OF THE LATTER WITH THE EXPE- 

 RIMENTS OF PROFESSOR MITSCHERLICH. 



By J. F. DANIELL, F.R.S., 



Professor of Chemistry in King's College, London. 



E Molecular Philosophy, which is the subject of the 

 following paper, is situated on the very confines of human 

 knowledge on that ill-defined and misty line where the most 

 exalted intellect must be conscious that its powers begin to 

 fail. Towards this debateable region it is, in general, sound 

 discretion in the practical philosopher not to advance too far. 

 Within its confines an ignis fatuus has too often been mis- 

 taken for the light of truth, and high energies have been 

 wasted which might have brought forth substantial fruit on 

 firmer ground. 



It is for this reason that the professors of the Royal Insti- 

 tution have ever acted most wisely in excluding from their 

 lessons of chemistry the Atomic Doctrine, and have confined 

 themselves to the exposition of the theory of Definite Propor- 

 tions. Had they followed certain illustrious examples, which 

 have not been wanting, of dogmatizing upon the number and 

 weight of ultimate atoms, instead of developing the beautiful 

 relations of chemical equivalents, chemistry, in the place of 

 that captivating simplicity which its aspect now presents in 

 our systems, would have exhibited that kind of pseudo-mathe- 

 matical confusion, which, from this and other analogous 

 causes, too often obscures the doctrines of other justly cele- 

 brated schools. 



But although this recondite and mental philosophy should 

 not be mingled up with practical science, there is no reason 

 why it may not be studied apart: on the contrary; a more 

 noble exercise for the faculties cannot be conceived than the 

 speculations to which it leads, when bounded by a proper dis- 

 cretion. As science slowly advances we gradually raise our 

 point of sight, and we may reasonably expect that our horizon 

 will consequently extend; and objects, which before were but 

 dimly discerned, will become more distinct, and our judgments 



