Page:Popular Science Monthly Volume 45.djvu/50

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38
THE POPULAR SCIENCE MONTHLY.

were sometimes as large as the apples, and always had from twelve to twenty perfectly shaped petals, from one inch to two inches and three quarters long.

It often happens that the clouds clear away and the temperature rises a few degrees while the direction of the wind is still unchanged. Then the outer surfaces of the frost-forms become glazed and the softer filling is blown out. They may be taken off entire, and need no greater care in handling than fine china. They are thin as eggshells and translucent, and under the microscope show long rows of minute cells, separated by delicate filiform partitions. A contrary wind unclasps their hold and the ground is strewn with the curious wreckage. They may be kept for many days in a cold place.

In sheltered places, a little way down on the leeward side of the mountain, the deposits of frozen vapor are similar to the hoarfrost seen in the lowlands, but greatly exaggerated in size and profusion, and are usually in the form of small rosettes, set as thickly as possible upon all surfaces of trees, rocks, or buildings. The frost on the windows of all unoccupied rooms varies in shape and amount according as the temperature is higher or lower.

At fifteen degrees above zero, small fern-shaped figures are made, about a quarter or a half an inch long. At lower temperatures they decrease in size and increase in numbers, until.

PSM V45 D050 Freezing effects of wind on various objects.jpg
Fig. 11. Fig. 12.

at thirty degrees below zero, the panes are quite covered with tiny frost ferns, twenty-five of which have been counted in a space an inch square, every one perfect in outline. Above fifteen degrees above zero the shape changes to something like the Hypnum moss.

Fig. 13 represents part of a pane. The temperature fell below fifteen degrees for a short time, allowing the accumulation of a few of the fern-forms, and then rose rapidly to twenty-five degrees, with the result here shown. The moisture condenses upon the windows of inhabited rooms just about as it does everywhere else.