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is likely to follow, and if the mercury falls as quickly as it rose, the equatorial current has obtained the mastery and the storm is near at hand. In such a case the old barometer phrase "very dry" is wholly delusive.
The barometer is affected by the operation of at least three causes, thus enunciated by Fitzroy:—
1st. The direction of the wind—the N.E. wind tending to raise it most, the S.W. to lower it most, and wind from points of the compass between them, proportionally as they are nearer one or the other extreme point.
N.E. and S.W. may therefore be called the wind's poles.
The range, or difference of height shown, due to change of direction only, from one of these bearings to the other (supposing strength or force and moisture to remain the same) amounts in these latitudes to about half an inch (as read off).
2nd. The amount, taken by itself, of vapour, moisture, wet, rain, or snow, in the wind, or current of air (direction and strength remaining the same) seems to cause a change amounting, in an extreme case, to about half an inch.
3rd. The strength or force alone of wind, from any quarter (moisture and direction being unchanged) is preceded, and foretold, or accompanied by a fall or rise, according as the strength will be greater or less, ranging, in an extreme case, to more than 2 inches.
Hence, supposing the three causes to act together, in extreme cases, the height would vary from near thirty-one inches (30.90) to
