Snow Beauties
by Wilson A. Bentley

What magic is there in the rule of six that compels the snowflake to conform so rigidly to its laws? Here is a gem bestrewn realm of nature possessing the charm of mystery, of the unknown, sure richly to reward the investigator. For something over a quarter of a century I have been studying it and the work has proved to be wonderfully fascinating, for each favorable snowfall, during all these years has brought things that were new and beautiful to my hand. I have never yet found a time when I could entertain an idea of relinquishing it. During the time that I have carried on the work, I have secured sixteen hundred photo-micrographs of snow crystals alone, and no two are alike. Is there room for enthusiasm here? Doubtless these pictures serve to represent with some fairness almost every type and variety of snow that occurs in nature, but they show scarcely an infinitesimal fraction of the individual variation of form and interior design among the countless myriads of crystals comprising each type.

The clouds, and the tiny liquid particles - water dust- of which they consist, play no part in true snow crystal formation. They coalesce only to form the amorphous - granular - varieties of the snow, or to coat true, mature crystals with granular material. The true crystals, forming the bulk of the snowfall, are formed directly from the almost infinitely small and invisible molecules of Water in solution within the air, and floating between the vastly larger cloud particles.

Most of the crystals are, of course, imperfect, made so especially during thick and heavy snowfalls, largely as a result of crowding and bunching during development, or to fracturing due to violent winds. In general, the western quadrants of wide spread storms furnish the majority of the more perfect tabular shapes. As a rule low clouds, if relatively warm, tend to produce the more rapidly growing open branching forms, and the inter mediate and upper clouds, if relatively much colder, the more solid, close columnar and tabular forms. Sometimes, however, crystals differing but slightly or not at all from those falling from storm clouds, drop out of apparently cloud-free skies.

Much wonder has been excited, because the snow crystals exhibit such a bewildering diversity and beauty. They form with in a very thin gaseous solvent, the air, and this allows the molecules of water an unexampled freedom of motion and adjustment while arranging themselves in crystal form. The fact doubtless largely explains why the crystals of snow far exceed other crystals in complexity and symmetry. Snow crystals, like all crystals of water, develop under the hexagonal system and invariably divide into six. Nothing absolutely certain is known as to why they grow thus, except as it is assumed that the number and arrangement of the attractive and repellent poles possessed by the molecules of water, impose this habit of growth upon them. This dividing into six is necessarily discussed and best explained in somewhat technical sounding terms. We may assume each water particle or molecule possesses two opposite primary poles, positive and negative, corresponding in direction with the main tabular axis of the crystals, and in addition three of six equidistant secondary poles arranged around what may be called the equatorial diameter of the molecules. Water, being a dia magnetic substance, and susceptible to polar repulsion, presumably has a tendency to arrange itself thus, in a position between and at right angles to the primary electro-magnetic poles. This alignment of the lines of growth, opposite to the lines of greater magnetic force, would compel the crystals of snow to grow mainly outward in the directions of their equatorial diameters and secondary poles. This theory would perhaps best explain why the crystals grow upon thin tabular or in the hollow columnar form, and increase so little in the direction of their main axes, that is, in the direction in which, it is assumed their main positive and negative poles lie.

Each of the six parts or segments of the crystals, while in process of growth, increases simultaneously outward, yet each one usually grows independently and by itself. So each of the six parts may, for all practical purposes, be considered as being a separate crystal by itself, and the whole as being an aggregate of growing crystals. And the law under which they form not only gives them a general hexagonal plan of growth, but in addition gives them two specific secondary habits of growth under the same plan.
We may best distinguish these as the outward or ray habit, and the concentric or layer habits of growth respectively. The ray habit causes growth to occur always outward and away from the nucleus. This tends to produce open branching forms. Crystals that grow rapidly, or within relatively warm low clouds, usually build upon this plan. In the case of the concentric or layer habit, growth tends to arrange itself in massive form, around the nucleus. This tends to produce the close, solid flakes. Slowly growing crystals, as the columnar, form solid tabular hexagons, and all such as crystallize in a very cold atmosphere, or at great altitudes, usually grow according to this latter habit. Snow producing clouds, if single, are perhaps as a rule of some depth, or if double, or multiple, vary one with another in temperature. The growth, habits and conditions under which the crystals form therefore are commonly unstable, with a multiplicity of diverse conditions, tending to hasten or to retard their rates of development, and momentarily, at least, to change or modify their forms. This state of things may cause them to grow after solid plans at one moment and altitude, after branching plans at another, after composite plans at yet others, and tends to cause them to become increasingly complex in outline and structure as growth progresses.
In those especial cases where the crystals form and grow wholly within a single relatively thin and uniform cloud, as within low detached clouds, for instance, they are likely to follow from start to finish after one single, uniform plan, and all be very much like each other. The frail branching snow crystals, falling during snow flurries, are oftentimes of this character. In some cases, the crystals will form composite fashion, after but two specific plans. A solid, mosaic centerpiece portion will form within a cold upper air stratum and, falling earthward, acquire branching additions at some lower, warmer level. Composite crystals of this character perhaps exceed all others in beauty of design, combining into one, as they do, the two most beautiful types of snow.

It is all most marvelous and mysterious, these changing habits of growth, and this momentary shifting about of the points of maximum development. Growth ofttimes occurs in alternate order, first at the corners of the hexagon, and then at the sides. In some cases, this pendulum-like swing of outgrowth may continue from beginning to end.

But perhaps the most wonderful fact of all is the marvelously symmetrical way in which all this is accomplished. If a set of spangles or branches, or tiny hexagons or other adornments, form and grow at certain points upon any one of the six, or alternate, rays, or segments, similar or identical ones are almost sure to form at the same places and moments on all of the others, so that the balance of form is always kept unimpaired.

It appears as if the magic that does this might be, in part at least, of an electric nature, and due to the presence of tiny electric charges around their peripheries. Would not the presence at certain points, and the absence at others, of tiny electric charges, shifting momentarily about, as fresh charges collected, and causing momentary realignments in the locations of the several charges, stimulate growth at certain points and retard it at others? It seems worth while tentatively to advance this theory, as a possible explanation of these perplexing mysteries. But it is a fascinating mystery this, that the crystals assume such a marvelous diversity of form, though forced by the crystallographic law under which they come into being to assume always the hexagonal form. Six rays or parts, there always are, yet what an amazing variety these parts exhibit among themselves. Individual crystals of the open, branching variety, differ one from another, in the shape, size or thickness of their primary rays and these rays in turn, in the number, size or shape, of the secondary branches that they possess. Those of solid tabular form differ as to their layers, or segments, and in the number and arrangement of the air tubes and shadings within them. Similarly those of a quasi-open formation vary in individual cases. In their spangles, the tiny hexagons composing them, as well as in the way in which these are combined with each other, or with rays, and arranged around the central nucleus. Yet in innumerable cases the crystals assume, at some one or more stages of growth, identical forms and outlines. It often happens that their nuclei, or ultimate outlines are alike, yet it seems to be rarely the case that any two pass through a long series of such changes of form. Hence the astonishing variety.

Snow crystals are noted among crystals, because they bridge over and include within themselves so much of the solvent, air, wherein they form. This remarkable habit, in connection with the multitudinous changes of form, gives great richness and complexity to their interior designs, and lends endless interest to their study. The air tubes and shadings have a biographical value, for they outline more or less perfectly, transitionary forms. The air tubes are largely formed while the crystals or parts of such, are in process of solidification, as at the moment when branch unites to branch, layer to layer, or segment to segment, and so growth may be traced through its successive stages.

The snow crystals being, in the truest sense, exquisite works of art in themselves, charmingly adapt themselves to a great variety of uses in the industrial arts, and in various other ways. These uses are steadily broadening, though they and their artistic possibilities have been as yet hardly discovered or realized by artisans in general. Metal workers and wall paper manufacturers are, however, beginning to realize their value, and there should be a great field of usefulness for them in these lines. They also seem well adapted for use in designing patterns for porcelain, china, glassware and many other things. Silk manufacturers are beginning to see their adaptability as patterns. Their value as models in the realm of pure art is also being demonstrated. Their uses as models in schools of art, and craft shops are steadily increasing. Only recently Dr. Denman W. Ross, lecturer at Harvard on the theory of pure design, has adopted a large number for classroom use. Prof. James Ward Stimsom used them to illustrate the ‘beauty of nature's art,' in his book, ‘The Gate Beautiful.'

Perhaps their greatest field of usefulness, however, is along other lines as objects for nature study, and for illustrating the forms of water. They should be invaluable to the crystallographer, for they show the forms and habits of growth of crystals in a most charming way.
Certain it is that normal and high schools, universities and museums both here and abroad, are finding them most useful in an educational way. One university alone - Wisconsin - has over one thousand lantern slides of snowflakes.
Indeed it seems likely that these wonderful bits of pure beauty from the skies will soon come into their own, and receive the full appreciation and study to which their exquisite loveliness and great scientific interest entitle them.