/. D. Dana on Cohesive Attraction. 365 



crystallized material ; and any one familiar with granite can pic] 

 out its mineral grains and exhibit their crystalline character ; and 

 if granite is crystallized in its intimate texture, so are all aggre- 

 gate rocks made up of granite material. Indeed a general survey 

 of the inorganic world develops the truth that here the power of 

 crystallization rules, like vitality in the organic kingdoms. A 

 crystalline texture may not always be apparent. This is the case 

 internally with ice, or a fragment of quartz crystal, although there 

 is no doubt that in each of these instances, the forces of crystal- 

 lization were the cause of solidification. This is also true of the 

 finest grained steel, as just observed, and some basaltic rocks. 

 Hut we find, from the transitions in structure, that the apparent 



absence is owing to the extreme minuteness of the grains and the 





compactness of texture. 



If then, crystallization and solidification are properly one and 

 the same process, the laws that govern in crystallization are the 

 laws of cohesive attraction. The science of crystals instead of 

 treating only of certain singular polyhedral forms assumed by 

 Minerals, is the study of the fundamental agency by which inor- 

 ganic matter is governed in its aggregations: and in place of 

 occupying a short chapter in our text-books on physics, and there, 

 as would often seem, in the way or out of place, it should be 

 Made to stand prominently forth as embodying and exemplifyin 

 some of the widest elemental truths of nature. 



J^et us then look at the facts, in order to arrive at these laws. 

 ome °f the deductions are by no means new. We commence 

 ^lth the simplest principles, in order to present a genera! view of 

 tne subject ; and a few familiar facts in crystallography are illus- 

 trated with figures, as the subject may interest some who are not 

 acquainted with them. 



1- It is, in the first place, an established fact that the different 

 kinds of inorganic matter have each a distinct mode of crystal- 

 lization. Every species has certain fixed, determinate, angles, 

 *hich characterize the structure, both of the crystal and the 

 crystalline grains in a compact mass. Galena crystallizes with a 

 cubical structure ; and even in a granular mass, this structure 

 ma y with care be detected by the rectangular cleavages. So in 

 granular limestone, or common white marble, the oblique angles 

 of the grains are precisely those of the perfect crystals of calc spar. 

 As this is a general truth, these fixed angles, for each species of 

 Matter, in some way characterize molecular or cohesive attraction. 



Again : crystals have plane surfaces, and are prisms or allied 

 forms. Now if the attraction acted alike in every direction it 

 w ould make only spheres ; to produce polygonal forms there 

 m u s t, therefore, be specific directions in which the attraction acts 

 jttore strongly than in others. For a cube or prism, there must 

 ^ at least three such directions, corresponding with axes in the 



