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VII. — On the Molecular Formation of Crystals. By Robert T. Forstee, A.M. 



Read May 14, 1855. 



All the theories which have been advanced to account for the phenomena of 

 crystallization have been, with one exception, but short-lived ; and indeed it 

 may safely be doubted if any occupy such a position as to entitle them to much 

 credit. 



The subject is one of much interest ; and although the consideration that 

 so many able minds have failed in the attempt to investigate it may naturally 

 deter an inquirer, still, the prize is sufficient to persuade him to hazard the 

 attempt. 



I shall first take a short review of the many theories which have been ad- 

 vanced in explanation of the phenomena, and I trust I shall be able to show 

 that some were unquestionably faulty, and all undoubtedly and confessedly 

 deficient. 



Passing by the many absurd theories advanced on the subject in ancient 

 times, the first whom we find deserving of notice is Christian Huygens. In 

 his celebrated work on Double Refraction he considered the crystals of Iceland 

 spar to be built up of spheroids, which, by their unequal density, separated the 

 incident light into two rays. He did not, however, show why the spheroids 

 are so aggregated. 



Such was the germ of a theory which, in the hands of Wollaston, Brewster, 

 and Dana, has obtained some status. None of these writers, however, have 

 taken the smallest account of cleavage, a phenomenon which is certainly the 

 most remarkable in the whole of crystallography, and which was the origin 



