Page:Popular Science Monthly Volume 78.djvu/451

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"Every wind has its weather."

There are numerous proverbs based on the directions and changes of the wind, but their value, in the main, is only local, except when taken in connection with the height and rate of change of the barometer. However, in middle latitudes the direction of ordinary undisturbed winds is from west to east. Therefore, a radically different direction commonly indicates an approaching, or, at any rate, not very distant, storm. There is, then, some justification for such proverbs as the following:

"When the smoke goes west,
Gude weather is past;
When the smoke goes east,
Gude weather comes neist."

"When the wind's in the south.
The rain's in its mouth."

"The wind in the west
Suits every one best."


"And now the mists from earth are clouds in heaven."

The height, extent and shapes of clouds depend upon the humidity and upon the temperature and motion of the atmosphere, and consequently they often furnish reliable warnings of the coming weather.

One proverb correctly says:

"The higher the clouds, the finer the weather."

As already explained, the formation of clouds is caused mainly by cooling due to convection; the rising mass of air expanding and losing heat because of the work it does in lifting the weight that presses upon it. Now the greater the height reached the colder, correspondingly, is the air, and hence we correctly infer that high clouds are formed only at the expense of much cooling and, therefore, that the amount of moisture they contain can not be great enough to produce falling or bad weather.

This proverb must be restricted to stratus and other of the more common clouds. It does not apply to those thin wispy or cirrus clouds, the highest of all, that float from five to eight miles above sea-level, for, as every one knows:

"Mackerel scales and mares' tails
Make lofty ships carry low sails."

Part of the air that forms the strong upward currents near the