Hundreds of drawings of this variety of snow crystal have been made by various ob servers, among them Dr. Scoresby and James Glaisher of England, Prof. S. Squinalial of Italy, and Mrs. F. E. Chickering of Port land, Maine. Many of these have been pub lished in textbooks and other publications. More recently the aid of photography has been invoked in securing and perpetuating the like nesses of these beautiful but fleeting forms. During the winter of 1902-03 Dr. Neuhauss of Berlin secured microphotographs of them, and about the same time Herr Sigson of Russia and Dr. Nordenskifild of Stockholm also secured microphotographs. Many of these were pub fished in the Meteorologische Zeitschrift for 1894, in a paper issued by the Geological Soci ety of Stockholm, and also in a book by Dr. G. Hellman, entitled (Schneekrystalle.' The pio neer in this work, however, seems to have been W. A. Bentley of Jericho, Vt., who began the photographing of them during the winter of 1885. By the spring of 1904 the microphoto graphs secured by him numbered over 1,100, no two alike. Many of these were published in a publication issued by the United States Weather Bureau, entitled (Studies Among the Snow Crystals, Winter of 1902.' These photo graphic studies, in connection with the meteor ological ones made simultaneously, have greatly increased our knowledge of these most interest ing crystal forms.
The manner in which the snow crystals form is this: They crystallize in a liquid (the air) of small density, which is often in a agitation where the crystals are forming, and whose degree of density, humidity, is ever changing; and usually among a multitude of uncongealed or uncrystallized particles of vapor, called cloud. The commonly accepted theory is that these visible cloud-particles unite to form the true snow-crystals. This is doubt less true, in so far as the granular varieties are concerned, but the true crystalline varieties probably form direct from the invisible water molecules floating in the air, before these unite to form the vastly larger cloud-particles. It is possible that the cloud-particles are essentially the dross, residue, or excess of moisture left over during the process of crystal-building. A portion, at least, of this residue or excess of moisture ascends, and is congealed in the upper air, into the semblance of minute snow-crystals; appearing in the form of the cirrus cloud above, and often around all storms of great duration or magnitude. Many occurrences are on rec ord of snowfalls occurring from skies clear or nearly free from visible clouds, and this lends additional weight to this theory. So very light are many of the snow-crystals, especially while they are in a, nuclear or uncompleted state, and so strong are the expanding, uprushing air-cur rents within many portions of great storms, that it must be assumed that many crystals are wafted upward, perhaps repeatedly, and ac quire growths at greater altitudes than that wherein the nuclei originated, before they at tain sufficient weight to fall to earth. Doubt
less the multitudinous changes of form and structure that many of the crystals undergo within} the clouds during growth are due to these many vertical and horizontal flights within the clouds and to the great and ever changing variety of meteorological and other conditions prevailing therein, each of which im presses its especial condition upon them.
The production and deposition of the snow, occurring, as it does, over so large a portion of the earth's surface, are phenomena of great magnitude and importance. Snow not only changes the whole aspect of nature but it also serves many useful purposes. It conserves the heat of the earth and protects vegetation from the intense cold of winter and even in northern regions, where deep snows occur, it is not considered a serious impediment to travel or commerce. A track once made, the compacted snow affords an excellent roadbed, over which heavy loads of merchandize can be easily and quickly transported on sleighs. But while in the abstract its manifestations are beneficent, in the concrete, some of them are otherwise. Much damage often results from the great inundations caused by the sudden melting of deep snow over large areas, and its sudden ac cumulation to great depths often causes a tem porary blockade of railroad service and travel in general. A large fall of damp snow or sleet sometimes accumulates so heavily upon tele graph and telephone poles and wires and upon the limbs and smaller trees of the forests, that they break under the great weight. Snow-slides from the steep sides of mountains sometimes occur and bury and destroy whole villages. Al together the snow fills a most important place in nature's plan. Not only is it beautiful in itself, composed of the most graceful crystal forms that occur in nature, but it plays an im portant part in beautifying earth and sky, for est and mountain.
The measurement of snowfall is often a matter of considerable difficulty, on account of the drifting caused by the winds. Various types of gauges are used to collect the snow fall over a given area and measure the amount of water formed by its melting. Hollow tubes are used to gather and weigh fallen snow so that the total amount of snow over a given area may be estimated. Stakes planted in the ground are also employed for this purpose.