50 CRYSTALLISATION AND COHESION. 



CHAPTER V. 



CRYSTALLOGENIC FORCES. 



Crystallisation and Molecular Force distinguished Experimental 

 Proof Polarity of Particles forming a Crystal Difference 

 between Organic and Inorganic Forms Decomposition of 

 Crystals in Nature Substitution of Particles in Crystals 

 Pseudomorphism Crystalline Form not dependent on Che 

 n deal Nature Isomorphism Dimorphi sin Theories of 

 Crystal logenic Attraction Influence of Electricity and Mag- 

 netismPhenomena during Crystallisation Can a change of 

 Form take place in Primitive Atoms? Illustrative Example 

 of Crystallisation. 



tc CRYSTALLISATION is a peculiar and most admirable 

 work of nature's geometry,, worthy of being studied 

 by all the power of genius,, and the whole energy of the 

 mind, not on account of the delight which always 

 attends the knowledge of wonders, but because of its 

 vast importance in revealing to us the secrets of nature ; 

 for here she does, as it were, betray herself, and, laying- 

 aside all disguise, permits us to behold, not merely the 

 results of her operations, but the very processes them 

 selvss." Such is the language of an Italian philosopher, 

 Gulielmini ; and it is the striking peculiarity of behold- 

 ing the process of the formation of the regular geometric 

 figures of crystals, the gradual accretion of particle to 

 particle, which induces us to separate crystallization from 

 mere molecular aggregation. Without doubt the forma- 

 tion of a crystal and the production of an amorphous 

 block are due to powers which bear a close resemblance 

 in many points ; but they present remarkable differences 

 *n others. 



