Page:Popular Science Monthly Volume 45.djvu/44

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32
THE POPULAR SCIENCE MONTHLY.

of particles have the same general configuration as the finished ornaments hundreds of times as large — six to eight inches wide at the base and projecting twelve to sixteen inches. A slight variation in the direction or velocity of the wind makes them more complex and adds greatly to their beauty; but a change of as much as sixty degrees in the direction wrenches them from their supports. They come away entire, and lie in heaps under the trees like autumn leaves, and may be collected and preserved in a cold, sheltered place until they gradually evaporate.

The process of formation is an interesting study. It is impossible to follow the course of the fine particles of snow dust which make up the most beautiful forms; but at a temperature of twenty-five to thirty degrees above zero the frozen moisture

PSM V45 D044 Frost aggregation in a windy place.jpg

Fig. 4.

comes in minute pellets of ice which may be watched with a good microscope as they strike a chosen spot. The development of the ice-forms is much more rapid than that of the snow-forms; otherwise the processes seem to be identical.

On the edges of fiat surfaces, and along the diameters of round bodies, lines of particles are deposited as the wind rushes past the obstruction. Then begins a twofold growth, caused by the direct