ATMOSPHEROLOGY. — SNOW. 429 



are produced probably by the correct application of 

 two similar crystals upon one another. 



2. A lamellar or spherical nucleus^ with spinous 

 ramifications in different planes. — This genus not 

 being easily represented, is not illustrated by any 

 figure. It consists of two or three species. 



a. The fundamental figure, consisting of a lamel- 

 lar crystal of any of the species above described, from 

 the lateral and terminal planes of which arise small 

 spines, similar to the collateral ramifications of Fig. 1 . 

 Plate VIII. These spines arise either from one or 

 both of the lateral planes or principal surfaces, or 

 from both lateral and terminal planes ; and always 

 maintain the usual angle of 60° with the plane from 

 which they take their rise. The diameter of this 

 figure sometimes exceeds the fourth of an inch. 

 This species falls most frequently at a temperature 

 of 20° or 25°. 



h. Having a spherular nucleus, giving rise to ra- 

 dii in all directions. In the former species, the cen- 

 tral figure is a transparent crystal ; in this it consists 

 of a small rough white concretion. The spines or 

 radii are similar in both figures. The diameter of 

 this seldom reaches a quarter of an inch. The form 

 is echinose. This species falls when the degree of 

 cold is near the freezing, and sometimes in rather 

 low temperatures. 



3. Fine spiculce or six-sided prisms. — These 

 are sometimes very delicate and crystalline ; at 

 others white and rough. The finest specimens, 



