These snow rollers grow in size both in diameter and in length, as they roll along, and attain various sizes from a few inches in diameter up to two feet in diameter. Some of the rolls are overturned by the boisterous winds in such a manner as to form a hollow snow arch, and hence some of the rolls are hollow even when matured. Hundreds of these rather mysterious snow formations occur to the acre of land, and they form both on a dead level and upon inclines.
That snow crystal study is extremely fascinating is well shown, for Mr. Bentley declares that although he works out of doors for hours at a time, when often his hands are well-nigh frost-bitten by the intense cold, in below zero weather, yet he is himself almost unconscious of discomfort or real suffering from the cold, so keenly interested and intent is he at the time, in securing some new and wonderful type of crystal to add to his already large collection of snow jewels.
87. Unusually symmetrical and clearly defined
88. Singular detail; dotted centre design
89. Trigonal crystal, very cold storm type
To make a collection of the snow crystals it is necessary, first of all, to make a receiving board. This is just a flat board covered with black velvet or wool material. The operator then places the board in a favourable position for catching the flakes as they descend, and then closely watches the receiving board as flake after flake alights upon the black surface. His eye will become sufficiently trained by experience at last to detect a fairly perfect specimen. If such a crystal alights—and sometimes it is weary waiting, for in a storm lasting an entire day, frequently but two or three perfect crystals deign to alight upon the receiving board—but when the perfect crystal arrives, then with infinite skill, and just the right touch, which must be acquired by practice, the little crystal is gently lifted upon a tiny, sharp-pointed stick, transferred to the slide and photographed as quickly as possible, before it has had an opportunity to dissolve, and become again a mere drop of uninteresting moisture. The camera used is photo-micrographic, or a camera with a microscopic attachment.
Regarding the formation of the snow into crystalline forms, we are told that the molecules and atoms of all substances when allowed freedom of movement, form themselves into many definite shapes and designs called crystals. Minerals, gold, silver, iron, sulphur, when melted and permitted to cool, gradually show this crystallising power. And by dissolving saltpetre in water and allowing the solution to slowly evaporate, large crystals will form, more or less symmetrical, as the salt is converted into vapour. Alum readily crystallises in the same way. The diamond is crystallised carbon, and all precious stones are examples of mineral crystals. It would be quite an interesting and novel experiment to photograph some of these crystals formed of minerals such as saltpetre, alum and others, and to compare them with the structural formation of snow crystals.