Snow Crystals 



33 



Those formed in moderate weather and 

 light winds or in low clouds are apt to 

 have frail branches and to be of a feath- 

 ery type, No. 920 ; mixed forms, Nos. 

 821 and 831, grew partly in low and 

 partly in high clouds. High winds 

 give broken and irregular forms, and 

 much moisture the very granular crys- 

 tals, No. S07. 



These heavy granular-covered crystals 

 are peculiarly a product of the lower or 

 intermediate cloud strata, and especially 

 of moist snow storms. In intense cold 

 they are rare, while the columnar and 

 solid tabular then become common. 



About four-fifths of the perfect forms 

 occur within the west and north quad- 

 rants of great storms. 



The most common forms outlined 

 within the nuclear or central portions 

 of the crystals are a simple star of six 

 rays, a solid hexagon, and a circle. 

 The subsequent additions assume a be- 

 wildering variety of shapes, each of 

 which usually differs widely from the 

 one that preceded it and from the prim- 

 itive nuclear form at its center. 



By bearing in mind the fact that 

 crystals evolved within the upper clouds 

 tend toward solidity, and the crystals 

 formed in lower clouds tend toward 

 open branches and feathery forms, it is 

 possible to trace the history and travels 

 of a great man}- of the crystals. No. 

 821 was probably star-shaped at birth 

 and was formed in low clouds. As- 

 cending air currents carried it upward 

 until it reached a considerable height, 

 where it assumed the solid hexagonal 

 form which we see outlined around the 

 Star-shaped nucleus. Its greater weight 

 now caused it to descend to lower levels, 

 where it acquired still further growth. 

 No. 83] originated at a high altitude, 

 then descended, and completed its 

 gjrowth entirely at low levels. No. 850 

 originated in and was also completed in 

 the upper clouds. No. 920 was born and 

 matured entirely in lower clouds. No. 

 565 was probably formed on a long 

 broken branch 



Columnar forms like 857 or solid tab- 

 ular, 746, are naturally heavier than the 

 open forms ; they are not therefore 

 likely to be wafted about in so many 

 directions and hence to be modified and 

 become so intricate as the light, feathery 

 crystals. 



No. 702 is one of the oddest and most 

 remarkable crystals ever photographed. 

 By some extraordinary combination of 

 circumstances, during the latter stages 

 of its growth the aqueous material of 

 which it was built was apparently 

 brought to it from one direction only. 



The perfect symmetry of Nos. 785 

 and 792 greatly resembles, in ideal per- 

 fection, the beautiful drawings of the 

 English observers Scoresby and Glai- 

 sher, and leads us to think that, con- 

 trary to the conclusions reached by some 

 recent observers, such drawings may be 

 quite true to nature and more reliable 

 than we have been led to suppose. 



No. 785 is considered by the author 

 the peer of any in his whole collection ; 

 No. 735, a beautiful starfish design, is 

 a somewhat rare form. Prof. S. Squin- 

 abol, of the University of Padua, made 

 drawings of a snow T crystal found in 

 Genoa in 1S87 that closely resembles 

 this form. Mr Bentley does not at- 

 tempt to explain the delicate, beautiful , 

 and unique central details of No. 779. 



