A single observation reading of the barometer is of no significance.
Readings must be taken at different intervals or the results will be
misleading. The important thing about the barometer is to watch the rise
and fall, particularly, whether it is gradual or rapid. From no single
reading can you make an observation or a forecast. A rapid rise
indicates that a strong wind is apt to blow. A rapid fall indicates that
the weather will be unsettled, and that strong winds are apt to blow.
Both indicate a change in the weather, depending upon many things,
particularly, however, the direction from which the wind blows. If an
observer stands with the wind blowing on his back, the area of low
barometric pressure will be at his left, and that of high barometric
pressure at his right. With low pressure in the west and high pressure
in the east, the wind will be from the south; but with low pressure in
the east and high pressure in the west, the wind will be from the north.
The barometer rises for northerly winds, from northwest by the north to
eastward, for dry, or less wet weather, for less wind, or for more than
one of these changes—except on a few occasions, when rain, hail, or snow
comes from the northward with strong wind. The barometer falls for
southerly wind, from southeast, by the south, to the westward, for wet
weather, for stronger wind, or for more than one of these changes,
except on a few occasions, when moderate wind with rain or snow comes
from the northward.