June ii, 1903 j 



NATURE 



131 



" to occur, especially as regards the branching forms, and 

 whenever, as must often happen, subsequent growth takes 

 place around and upon such broken crystals, irregular, un- 

 symmetrical forms result. Doubtless, we may attribute the 

 ori^^in of some of the odd oblong crystals to the fact that 

 crystallisation sometimes takes place around and upon a 

 long broken branch, or other long portion detached by frac- 

 ture from some preexisting crystal. Other odd forms seem 

 to owe their abnormal character to design rather than 

 accident. Columnar forms and, in a less degree, small 

 solid tabular forms, being relatively so much heavier and 

 more compact than stellar and similar branching forms, 

 are much less likely than these to be wafted about and to 

 receive modification's due to wind action. 



Among the other causes of modification of forms, we 

 must mention the close proximity of two or more crystals 

 during one or more stages of their growth. This close 

 proximity while developing would probably cause a greater 

 growth of those portions of each contiguous crystal that lie 

 farthest away from the crystal closely adjoining, and thus 

 perfect symmetry would be' impaired. 



Considerable modifications of form are frequently due to 

 the aggregation upon the crystals of amorphous or granular 

 material, contributed by relatively coarse cloud spherules, 

 particles of mist, or minute rain drops. Frail light, branch- 

 ing stellar and other forms are often rendered coarse and 



Fig. 3. — Nos. 742-750. 



heavy by such additions taking place around and upon every 

 angle of the crystals, so that they fall quickly to the earth.' 

 Perfect crystals are frequently covered over and lines of 

 beauty obliterated by such granular coatings. Granulation 

 often proceeds to such a degree, and the true crystals are so 

 deeply coated over and imbedded within it, that the character 

 of the nucleus does not reveal itself, except under the closest 

 examination. Such heavy granular covered crystals possess 

 great interest for many reasons ; they show when the 

 character of the snow is due to the aggregation of relatively 

 coarse cloud particles, or minute rain drops, and not to the 

 aggregation of the much smaller molecules of water, pre- 

 sumably floating freely about between them. They also 

 offer a complete explanation of the formation and growth 

 of the very large rain drops that often fall from thunder- 

 clouds and other rainstorms, if we accept the conclusion 

 that such large drops result from the melting, or merging 

 together, of one or more of the large granular crystals. 

 For many reasons (among which we mention the almost 

 invariable presence of low cloud strata when granulation 

 occurs, and the aggregation occurring on perfect crystals, 

 while these are presumably within the low clouds, rather 

 than the occurrence of such aggregations as a distinct 

 identity by itself) we are led to infer that, as a rule, the 

 heavy granular covered crystals are peculiarly a product 

 of the lower or intermediate cloud strata. 



Chronological List of Snowstorms and Photomicrographs. 

 — We now pass to the analysis of the photomicrographs of 

 individual snow crystals secured during the remarkably 



NO. 1754, VOL. 68] 



Fig. 4.— Nos. 783-7Q1. 



favourable winter of 1901-2. The, number of individual 

 crystals is very considerable, and the beautiful or odd and 

 interesting ones form a large percentage of the whole 

 number ; many of them deserve special mention and pro- 

 longed close study. Considering them in chronological 

 order, the snow forms of the blizzards of November, 1901, 

 first demand our attention. 



1901, November 26. — Eighteen different forms were photo- 

 graphed on this date, and among them two, Nos. 716 and 

 718 (Fig. i), are very choice and beautiful. These exhibit 

 a rather unusual and notable peculiarity, viz. a plain or 

 delicately lined nucleus contrasted with a brecciated, boldly 

 designed external portion ; the latter approaching granu- 

 lation, as though the nuclear portion was formed in clouds 

 that were less dense and humid than those in which the 

 outline portions were added. No. 712 is a fine example of 

 the star-shaped form of crystal, exhibiting an extreme and 

 slender development of the six primary rays without any 

 corresponding development of the secondary rays. Many of 

 the branching forms of this date were observed to be broken, 

 as though by the action of violent winds. 



#l« 



816-824. 



Xovctiihrr 2-. -Continuation of the same storm. Crystal 

 types small, granular, and irregular, succeeded later by 

 medium-sized, rather compact crystalline tabular forms and 



