94 OBSERVATIONS OF SCORESBY. 



the regular hexagon, which becomes thin, and 

 diminishes in size as the cold increases ; aggre- 

 gations of hexagons, which occur chiefly at low 

 temperatures ; and lastly, combinations of hexa- 

 gons with spines or radii. (Arctic Regions, vol. i. 

 p. 432.) It is therefore clear, that the form of 

 crystals depends on the arrangement of their 

 particles, and not on their essential nature. But 

 if it be a fact that caloric is the agent which regu- 

 lates the distance of atoms or particles from one 

 another, and causes all their movements, whether of 

 union or separation, it must obviously determine the 

 various modes of their arrangement, whether in the 

 solid, liquid, or gaseous states. And as the atomic 

 composition of water in every state is the same, 

 it is impossible to comprehend why it should 

 assume various crystalline forms, as observed by 

 Kepler, Cassini, and Scoresby, without admitting 

 that its particles are surrounded with different 

 quantities of caloric, on assuming these different 

 forms.* 



* The various crystalline forms are now generally arranged in 

 six divisions or systems, as in the following classification by 

 Gustav Rose : 1. The cubic or tessular. 2. The square prismatic, 

 (in which the lateral edges, like the terminal planes, are parallel.) 

 3. The rhombohedric. 4. The right prismatic. 5. The oblique 

 prismatic. 6. The doubly oblique prismatic. 



In all crystalline bodies the form is angular, and the arrange- 

 ment of their particles rectilinear. In those of which all the sides 

 and angles are alike, the expansion by caloric is equal in all direc- 

 tions, as in the cube, the regular octohedron, and the rhomboidal 

 dodecahedron ; and the refraction of light is single, when they are 

 of uniform temperature and density, as it in the transparent gases, 



