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 on the other hand, are apt to have a high value. Weather science now has treatises of inestimable value, but no book from which weather knowledge may be obtained surpasses wind and sky.

Indications of Heavenly Bodies.—It is hardly necessary to note that such indications are due to the effects of the varying moisture content of the air, together with slight refractions and diffractions caused by the moisture of the air.

The halo around the sun or the moon is neither more nor less than a very faint rainbow caused by the refraction of light rays as they pass through mist or very thin cloud matter. It is therefore a phenomenon of humidity.

Before the rising of a wind the fainter stars are not visible, even on a clear night.—.

Mixed air currents cause so much refraction of light that feeble points of light are not perceived. With clear, still air the stars are very bright. In astronomical observatories, observations made on windy nights have but little value, so great is the blurring from refraction. The higher, the power of the telescope, the greater the impairment of visibility.