By far the most important, varied and beautiful snow crys tals are those that comprise the tabular class. Crystals of this class assume delicate, starry, branching forms, solid plate forms and those exhibiting all gradations between the solid and wholly open forms. Rarely is it that any two of them are just alike. The beauty of outline and richness of interior of such crystals are so great as to have attracted the attention and admira tion of all students of the snow from the earliest times to the present. They far transcend in beauty, diversity and perfect symmetry the crystals of any mineral species.
The conditions under which the snow crystals form is unique. They crystallize while floating about unsupported in a fluid, the air, of small and varying density. This permits the atoms and molecules of which snow, like all other crystals, is built a much greater freedom of movement while arranging themselves in crystal form than is possible when most crystals are formed. Often the air and clouds wherein they form are in a state of agitation, and vary within their different parts in density, tern perature and water content. Sometimes snow crystallizes among a multitude of uncon gealed fluid droplets, called cloud. Contrary to popular belief, how ever, the true crystals are not made of such, though they may collect and freeze upon them in a white opaque manner, or upon themselves to make granular snow, the "graupeln" of the Ger mans. True snow crystals are formed directly from the invisi ble and vastly smaller atoms and molecules of water floating be tween the cloud droplets. Among the many proofs of this, aside from general considerations, is the fact that scanty snowfalls frequently occur from clear skies.
As a result of various unfavourable conditions in cloudland, such as winds, overcrowding, the presence of fluid cloud droplets, etc., the majority of tabular snow crystals fail to attain their natural beauty and symmetry. The most wonderful forms seem to occur within the anterior quadrants of widespread general storms, or during snowfalls that occur between two closely lying storms. The formation of crys tals may be determined by some law. It is likely that almost every cyclonic storm produces per fect forms somewhere within its anterior quadrants. There is doubtless a somewhat invariable rule of distribution of the vari ous types of snow within cyclonic storms, columns, or columns and solid plates to one quadrant, granular forms to another, branching crystals to others, etc.
The feature of chief beauty and interest about the tabular snow crystals, in addition to beauty of outline, is the richness of their interior designs. This richness of interior is due to the presence of minute air tubes and shadings therein, which appear dark when viewed under certain conditions. These interior air tubes and shadings frequently ap pear in the semblance of tiny rods, dots, lines, etc., often ar ranged in a marvellously sym metrical manner and outlining geometrical forms. They are caused as a result of the bridging over and inclusion of air as the branches, segments and various adornments grow and unite one to another. Because of this they
outline more or less perfectly the various stages of growth and the transitional forms that the crystals assumed in cloudland. Their arrangement doubtless depends largely upon habits of growth. In case of branchy growth they are arranged for the most part at angles of 6o° alongside the main and secondary rays. In cases of more solid growth they are often arranged with their greater dimensions in hexagonal order around the nucleus.
The rare beauty of the more perfect specimens of snow crystals has attracted the attention and excited the admiration of natural ists from quite early times. We find in the Bible, in the Book of Job, the query, "bast thou entered into the treasures of the snow?" Many naturalists through the years have made attempts to draw them. During later times many observers, among them Dr. Scoresby and Dr. Glaisher of England, Prof. Squinabol of Italy, Mrs. Chickering of the United States and Dr. Dobrowolski of Poland, made excellent drawings of them. More recently the aid of photography has been employed to portray these evanescent forms. W. A. Bentley of Jericho, Vt., seems to have been the pioneer photomicrographer of snow crystals. Securing the first photomicrographs in 1885, he has continued the work up to the present, making 4,800 photomi crographs, no two alike. In 1903 and soon afterwards Dr. Neu hauss of Berlin, Dr. Nordens kiold of Sweden and Herr Sigson of Russia also made photomicro graphs of crystals.
The formation and deposition of the snow, occurring over so large a portion of the earth's sur face and in such enormous quan tities as almost to defy computation, constitute a phenomenon of great magnitude and import. The snow forms one of the links in a natural system of continental irrigation, to make possible veg etal and animal life thereon. In winter it conserves the heat of the earth and protects vegetation. It has also served a useful purpose as an aid in transportation, as its icy mantle forms an excellent roadbed over which produce, etc., can be easily drawn in sleds. Snow when compacted and pressed into glacial ice or when melted and converted into streams, rivers, etc., also plays an important part in inland erosion, in the tearing down of mountains and the conversion of rocks into soil.
Yet, like the beneficent, life giving rain, the snow sometimes becomes a destructive agent. The melting of the snows of winter sometimes produces disastrous floods which do great damage. A heavy fall of snow, if accompa nied with severe winds, piles the snow into deep drifts along high ways and railroads, thus traffic. Not the least of the de structive effects of the snow is the breaking of trees, telephone poles, etc., by the weight of a damp, heavy fall of snow upon them. In mountain regions the snow sometimes accumulates so deeply upon the sides of moun tains that great masses break off and descend as destructive avalanches into the valleys, doing great damage and sometimes burying and destroying whole villages. (W. A. BEN.)