A STUDY OF S.\WW CRYSTALS. 



79 



plete crystals, and there ma}' not be half so many. The greater 

 number of perfect crystals is found in widespread storms, or blizzards, 

 while the local storms produce most often granular or imperfect 

 forms. So marked is this distinction that very often the character 

 and extent of a storm may be in general determined by an examina- 

 tion of the crystalline forms obtained. Extensive storms produce 

 smaller crystals, more uniform in size, less clustered in flakes, and 

 in greater variety than local storms. Figs. 1 to 20, inclusive, are 

 crystals from general storms, while Figs. 23 and 24 are those of local 

 storms. When the temperature is very low while a local storm is 

 raging, its crystals resemble those of the blizzard more closely. 



Some forms are common to both classes of storms. Probably be- 

 cause identical conditions do not occur frequently, the crystalline 

 forms of each storm during a winter may differ from each other, one 

 type appearing abundantly in one storm, a different type in the next, 

 and so on. Conversely, the types most common in a given storm may 

 reappear after an interval of months or years — as, for example, those 

 obtained during the great blizzard of March, 1888, were repeated in 

 the storms of February 16, 1892, and March 3, 1896, and most of 

 these were of forms such as Figsi 13, 14, and 15, while unusual 

 types, such as Figs. 7, 9, and 17, occurred in the storms of February 

 24, 1893, and February 13, 1894. 



Not only do different storms afford different types of crystals, 

 but different parts of the same storm, if it be general, give different 

 forms. In this region, the northern and western portions of the 

 storm area produce more perfect crystals than the southern and 

 eastern, and from this we infer a difference in the atmospheric con- 

 ditions in these portions, the former being more quiet and otherwise 

 favorable to crystallization. 



What has been called granular snow is shown in Figs. 4, 6, and 

 23. In this very common form we find only loose, irregular, sub- 

 crystalline forms, which are larger and heavier than others. This is 

 formed in the middle or lower cloud layers, and when these are dis- 

 turbed by wind, or otherwise rendered unsuitable for crystallization. 

 Sometimes, perhaps always, these granular masses have nuclei of true 

 crystals. Granular snow may explain the origin of the great rain- 

 drops which often fall during a thundershower. It is probable that 

 such drops have a snow origin. Most, if not all, hailstones also origi- 

 nate in granular snow, as their thin, opaque centers and concentric 

 rings of opaque, snowlike ice show. 



The superiority of photography over drawing in securing details 

 of structure may be readily seen if one compares any of the accom- 

 panying figures with the ordinary drawings of snowflakes, or even 

 with the finest illustrations hitherto published. It is unfortunate 



