ATMOSPHEROLOGY,. — HOAR-FROST. 439 



tion of molecules to one another, when in a state of 

 invisible solution. In the crystallization of water, 

 and of many salts, an accurately formed needle or 

 other regular figure, is consolidated by an instan- 

 taneous shoot or rapid progression through the sub- 

 stance of the crystallizing liquor ; but the fonnation 

 of hoar-frost crystals is accomplished by a slow and 

 gradual deposition of particles, brought into contact 

 with the crystallizing surface by the motion of the 

 air. And it is a fact worthy of notice, that a con- 

 tinued accession of new particles, adds nothing to 

 the thickness of the crystal that first appears, but 

 merely extends its principal surface, and as it ex- 

 tends, completes the several arrangements of the 

 particles corresponding with the shaft, vane, and 

 rachis of a feather. This principle in crystallogra- 

 phy, which tends to produce a perfect figure, and 

 operates so beautifully in the formation of snow 

 flakes, as to complete each of the six-sides or radii 

 of the crystal, after the same plan and dimensions, 

 suggested to me not only an argument for giving to 

 the molecules of crystals a certain polarity, or attrac- 

 tion for inducing them to unite together by one side 

 rather than another, but also induced an opinion, that 

 complete figures are formed in consequence of the mu- 

 tual attractions of the crystallizing integrant particles, 

 requiring an equilibrium of weight or of attractions 

 round the nucleus or central particle of the crystal. 

 Thus, ill the formation of snow-crystals, it appears. 



