Page:Popular Science Monthly Volume 78.djvu/441

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any change in their appearances necessarily means changes in the atmosphere itself—changes that usually precede one or another type of weather,

A familiar proverb of this class runs as follows:

A red sun has water in his eye.

Now the condition that most favors a red sun is a great quantity of dust—smoke particles are particularly good—in a damp atmosphere. Smoke alone, in sufficient quantity, will produce this effect, but it is intensified by the presence of moisture. The blue and other short wavelength colors, as we call them, of sun light are both scattered and absorbed to a greater extent by a given amount of dust or other substances, such as water vapor, than is the red; and this effect, since it is proportional to the stjuare of the volume, becomes more pronounced as the particles coalesce. Hence when the atmosphere is heavily charged with dust particles that have become moisture laden, as they will in a humid atmosphere, and therefore relatively bulky, we see the sun as a fiery red ball. We know, too, that this dust has much to do with rainfall for, as was first proved many years ago by the physicist Aitken, cloud particles, and, therefore, rain, will not, under ordinary conditions, form in a perfectly dust-free atmosphere, but will readily form about dust motes of any kind in an atmosphere that is sufficiently damp.

A red sun, therefore, commonly indicates the presence of both of the essential rain elements, that is, dust and moisture: and while the above is not the whole story, either of the meteorological effects due to dust in the air, or of the formation of rain, it is sufficient to show how well founded the proverb under consideration really is. And also this other one that says:

"If red the sun begin his race,
Be sure the rain will fall apace."

Sky Colors

"Men judge by the complexion of the sky
The state and inclination of the day."

There are many proverbs, ranging from the good and useful to the misleading and absurd, concerning the color of the sky at sunrise and sunset.

From Shakespeare we have the well-known lines:

"A red mom that ever yet betokened
Wreck to the seaman, tempest to the field,
Sorrow to the shepherds, woe unto the birds,
Gusts and foul flaws to herdsmen and to herds."

Besides these stately verses there are many proverb jingles that express substantially the same idea. One of them puts it thus:

"Sky red in the morning
Is a sailor's sure warning;