well; neither the one nor the other was possessed of a daily weather map. The wind was a fair barometer; the blinking of the stars was an excellent hygrometer. The discovery of the underlying principles of barometric pressure was the beginning of modern meteorology. The use of the barometer quickly appealed to sailors, and practically every deep-water vessel in the world is equipped with one. Transportation companies, lighting companies, farmers and manufacturers find it a necessity. The invention of the aneroid barometer has popularized its use tremendously.
In the hands of one without experience, or without training in the use of it, the barometer is usually a disappointment. To the trained observer, or to the observer who has gained wisdom by experience, it is an instrument of the highest value. To be serviceable in forecasting weather conditions it must be watched—not casually but systematically. The experience that comes from intelligent study of pressure changes will enable an observer to command most gratifying results.
General Pressure Indications.—As a rule, pressure changes should not be considered by themselves; they should be studied in conjunction with changes in temperature, humidity and wind direction. There are, however, certain general weather conditions indicated by changes in barometric pressure which hold good:
A gradual rise of the barometer indicates settled fair weather.
A rise from a very low pressure indicates wind and clearing weather—the more rapid the rise, the stronger the wind. Rapid changes in pressure indicate early and marked changes in the weather.
A sudden rise in pressure indicates as great a change as a sudden fall.
The wind is apt to blow hardest when, after having been very low, the barometer begins to rise.
Should the pressure continue to remain low after the sky has cleared, expect more rain within twenty-four hours.—Prince.
If the pressure falls two or three tenths of an inch in four hours or less, expect gale winds.—Prince.
In summer a sudden fall in pressure indicates a thunder-storm; if it does not rise when the storm ceases, unsettled weather may be expected.
A fall in pressure not accompanied by stormy conditions indicates a severe storm at a distance.
A steady but very slow fall in pressure indicates that the low and its storm conditions is moving slowly. “Long falling, long last; short notice, soon past.”—Fitzroy.
