II.
We have thus far endeavoured to show the true bases of construction, and how that crystallization proceeds onwards from the simple forms to the more complex, and have selected from numerous varieties a few of the best types illustrative of this progress. Our limits will scarcely permit us further to individualise these beautiful creations; yet, not to mislead, it is necessary to refer to an intermediate order, in which the hexagon star is laden with divergent spiculæ between groups of prisms. [Fig. 36], selected from this very numerous class of figures, was one of several observed during the cold weather, following upon the general thaw, which terminated the long-continued and severe frost of 1855. The spiculæ were icicle-like, of the utmost delicacy, opaque, and well defined; the prisms, on the contrary, were watery, almost rounded, and, as it seemed, on the verge of dissolution. The entire figure had the appearance of two distinct orders of formation—the prisms which belong to a very low temperature, and the spiculæ which are commonly formed at and about the freezing-point. [Fig. 37] is another of the same class, and in a very intermediate state; the additions to the main radii are neither prisms nor spiculæ, yet partaking of the character of both: its peculiarity consists in the tertiary incrustations being placed downwards towards the centre. This form has been observed only during very severe cold.
[Fig. 38] is somewhat analogous to the crystals of water; its centre is hexagonal, but the prisms are irregular crystalline incrustations of the utmost delicacy and transparency; it was of large size, fully half an inch in diameter, and glistening like a fragment of talc among the snow-flakes, was discernible at a considerable distance.
Fig. 35.
[Fig. 39] ([page 156]) is a specimen of a double crystal; that is, two similar crystals united by an axis at right angles to the plane of each. It is highly complex, and the effect of each is more than doubled by the arrangement. Crystals so united are not unfrequent in severe weather.
During one winter our observations numbered nearly two hundred varieties.
Fig. 36.
The series of small drawings given on pages 137, 138, and 139, were made with a lens of moderate power, but they are not equal in value or structural detail to those drawn beneath the microscope. They are among the most elementary figures observed; and, as illustrative of the first principles of formation, are chiefly worthy of consideration. Of more elaborate figures drawn beneath the microscope, besides those more immediately referred to in the text, examples are given in [Fig. 40], [41], and [42].
The idea of observing snow crystals is by no means original. We know for certain that Aristotle observed them; also Descartes, Greu, Kepler, and Drs. Nettes and Scoresby of modern times. Sir Edward Belcher also devoted a considerable degree of attention to the study of the crystals of snow in the Arctic regions. There the radial arms were seldom less than an inch in length, and might be seen, according to Sir Edward Belcher, drifted in heaps into the crannies and recesses of the ice. They were seldom to be obtained in a perfect condition, generally separating, by reason of their weight and size, on descending to the ground.
Fig. 37.