CHAPTER IV.
THE USE OF ANEROID BAROMETERS.
The Aneroid, like the Mercurial barometer may be used either as a weather indicator or in the measurement of altitudes. When used in the former capacity, the Aneroid, especially at sea, possesses some obvious advantages. Aside from its superior compactness of form and its portability, it responds more readily to the changes in atmospheric pressure than the Mercury column, and thereby serves more efficiently to warn the mariner of sudden tempests.
The words Rain—Change—Fair seen stamped or engraved on the dial of many barometers have, of course, no special significance, and are now rarely seen on first-class instruments of either kind. The probable changes of weather indicated by changes of the barometer are briefly set forth in the following:
RULES FOR FORETELLING THE WEATHER.
A Rising Barometer.
A “rapid” rise indicates unsettled weather.
A “gradual” rise indicates settled weather.
A “rise” with dry air, and cold increasing in summer, indicates wind from Northward; and if rain has fallen better weather is to be expected.
A “rise” with moist air, and a low temperature, indicates wind and rain from Northward.
A “rise” with southerly wind indicates fine weather.