CRYSTALLOGRAPHY. 5 



in long feathered lines over the glass — Jack Frost's work being 

 the making of crystals. Water cannot solidify without crystal- 

 lizing, and neither can iron nor lead, nor any mineral material, 

 with perhaps half a dozen exceptions. Crystallization produces 

 masses made of crystalline grains when it cannot make distinct 

 crystals. Granite mountains are mountains of crystals, each 

 particle being crystalline in nature and structure. The lava 

 current, as it cools, becomes a mass of crystalline grains. In 

 fact the earth may be said to have crystal foundations ; and if 

 there is not the beauty of external form, there is everywhere 

 the interior, profounder beauty of universal law — the same law 

 of symmetry which, when external circumstances permit, leads 

 to the perfect crystal with regular facets and angles. 



Crystals are alone in making known the fact that this law 

 of symmetry is one of the laws of cohesive attraction, and that 

 under it this attraction not only brings the particles of matter 

 into forms of mathematical symmetry, but often develops scores 

 of brilliant facets over their surface with mathematical exact- 

 ness of angle , and the simplest of numerical relations in their 

 positions. Crystals teach also the more wonderful fact that 

 the same species of matter may receive, under the action of this 

 attraction, through some yet incomprehensible changes in its 

 condition, a great diversity of forms — from the solid of half a 

 dozen planes to one of scores. The following figures represent a 

 few of the forms in a common species, pyrite, a compound of 

 iron and sulphur. 



~F* 



r 



-■3=F~\ 



II 



ii 



V-U7 



