A STUDY OF SNOW CRYSTALS. 81 



that the depth and solidity seen in some crystals when the photo- 

 graphs are mounted as stereoscopic views can not be in some ade- 

 quate manner reproduced in engravings, for this adds not a little to 

 an understanding of the manner in which the crystal has been 

 formed. Yet something of this can be seen in the figures as here 

 given. A careful study of this internal structure not only reveals 

 new and far greater elegance of form than the simple outlines ex- 

 liibit, but by means of these wonderfully delicate and exquisite 

 figures much may be learned of the history of each crystal, and the 

 changes through which it has passed in its journey through cloud- 

 land. Was ever life history written in more dainty hieroglyphics! 

 It is well known that crystals which form in a low temperature are 

 smaller and more compact than those formed in a warmer atmos- 

 phere. As the higher cloud strata are colder than those nearer the 

 earth, the snow crystals which originate there are smaller and less 

 branched than those from lower clouds. Such are shown in Figs. 2, 

 20, and 22, while crystals from the warmer clouds are more often 

 like Figs. 24 and 25. The small, compact crystals of the upper clouds 

 do not always remain of their original form or size, for, as they fall 

 through layer after layer of clouds, each layer subjecting them to its 

 own special conditions, they may be greatly modified, and by the 

 time they reach the earth they may closely resemble the crystals 

 from lower clouds, though they can usually be distinguished from 

 them by an examination of the internal structure, as well as by, in 

 some cases, their general form. All crystals falling from high cloud 

 strata, the cirrus or cirro-stratus, are not changed; especially is this 

 true in a great storm, or when the temperature of the lower clouds 

 is low, and in any case some are much more completely transformed 

 than others. One crystal may pass through cloud layers not very 

 unlike that from which it came, and of course will not be greatly 

 changed. Another may encounter here a quiet cloud layer and 

 there a tumultuous layer, here a lower, there a higher temperature, 

 here a dense and there a thin cloud mass, and by all of these condi- 

 tions may be affected. 



Examples of crystals which have been little changed are shown in 

 Figs. 3, 7, and 8, while Figs. 12, 13, 14, and 16 show more 

 completely modified crystals. Total transformation, such as the 

 change of one type into another, does not often occur. The 

 nucleus retains its original form, to which various additions are made 

 during the downward passage. Composite crystals may, however, 

 be formed during the passage through diverse cloud layers, though 

 they are not common, as shown in Figs. 11 and 19. Usually, how- 

 ever, the tabular, compact, small crystals of the high clouds continue 

 their development at lower levels upon the original plan, though be* 



VOL. LIII. — 8 



