Page:Popular Science Monthly Volume 88.djvu/272

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What Is Hoarfrost?

IN every-day English the word "rime" is synonymous with "hoarfrost" and is apphed to the fine white deposit which replaces dew in cold weather. Hoarfrost is sometimes defined as "frozen dew," but it is more often a direct deposit of small ice crystals from the atmosphere, the invisible water vapor turning to ice without passing through the liquid form. In recent technical literature the term

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���Hoarfrost is a powerful but mischievous magician. Above, a beautiful effect created on a tree; on the right, a wire rope

"rime" has a different meaning. It is limited in its application to those striking deposits of rough ice or of feathery crystals which sometimes form on exposed objects surrounded by fog, when the temperature is below freezing. This formation is, in its turn, distinguished from the smooth coating of ice which results from rain in cold weather, and to which the name "glazed frost" is now applied. Heavy deposits of glazed frost often load branches, wires, etc., to the breaking point, and give us the familiar phenomenon of an "ice storm."

���Of all these various frost deposits, true rime perhaps presents the most curi- ous forms, and these reach their fullest development on mountain summits and in the polar regions. Beautiful tufts and fringes of ice form on objects of small diameter, such as twigs and wires, and along the angles of square posts and the like, but not on broad sur:^ces. The deposit is almost or quite confined to the windward side, and grows against the wind.

At the former meteorological observa- tory on Ben Nevis these ice feathers were sometimes seen to grow at the rate of two inches an hour. In the winter of 1884-5, according to Mr. R. T. Omond, "during a long continuance of strong southwesterly winds and cold weather a post four inches square grew into a slab of snow some five feet broad and one foot thick in less than a week ; the crystalline mass then fell off by its own weight and a new set began to form."

The anemometers and other out-of-door instruments at the observatory were generally so coated with rime in winter as to be useless.

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��A Curious Tobacco Pipe-Borer

RAVELERS among the Sioux Indians are very much impressed with the per- fect smoothness of the bore in their pipe-stems. Without the use of a tool of any kind, they make a perfect bore in the twigs of ash trees, which they use for musical instruments and for pipes. To accomplish this end, they employ the larva of a but- terfly which inhabits the ash The Indians remove the pith for about three inches from the stick they wish bored. Into this cavity, they place one of the larvse of a brown butterfly, which gradually eats its way down through the pith until the bore is com- pleted. A little heat applied to the wood expedites the work of the larvse. The Indians consider both the tube made in this way and the larva as sacred as their idols.

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