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Page:Popular Science Monthly Volume 90.djvu/42

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26

��Popular Science Monthly

���Yr^AtZ IrK "^^"'^^l^i^E;, These beautiful deposits assume two principal forms, the feathery

Sd iesi.n ?hf "'• ^^" ^""TV ^^' ™°^^ ^°"^"^°" ^"d the more striking in appearance ana design. The same pane of glass will exhibit entirely different designs on different nights

��exists at all times in the air, and not from raindrops; though, on the other hand, rain IS often the final product of snow that melts before it reaches the ground.

The true structure of a mass of ice may, however, be made evident by an experiment that Tyndall was fond of performing in his public lectures. Through a slab of clear ice, revealing no trace of structure, he passed the beam of an electric lamp, the light falling upon a screen. The image of the slab was magnified by a lens. While the

��light of the lamp was transmitted freely, its heat was partly absorbed by the ice, and produced an interesting transforma- tion. _ Numerous six-rayed stars and com- binations of such stars appeared here and there on the screen. These "ice-flowers," as they are called, resulted from the melt- ing of crystals locked up in the block of ice; they were, in fact, hollow spaces, retaining the form of the original crystals but filled with water.

The invisible moisture of the air produces

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