g the earlier part of
serene and settled weather, the mercury commonly stands high, and is
stationary.[17]

Instances of fine weather, with a low glass, occur exceptionally, but
they are always preludes to a duration of wind or rain, _if not both_.

After very warm and calm weather, rain or a storm is likely to occur;
or at any time when the atmosphere has been _heated_ much above the
usual temperature of the season.

Allowance should invariably be made for the previous state of the
instrument during some days as well as hours, because its indications
may be affected by remote causes, or by changes close at hand. Some of
these changes may occur at a greater or less distance, influencing
neighbouring regions, but not visible to each observer whose barometer,
nevertheless, feels their effect.

There may be heavy rains or violent winds beyond the horizon, out of
view of an observer, by which his instruments may be affected
considerably, though no particular change of weather occurs in his
immediate locality.

It may be repeated, that the longer a change of wind or weather is
foretold by the barometer before it takes place, the longer the presaged
weather will last; and, conversely, the shorter the warning, the less
time whatever causes the warning; whether wind or a fall of rain, hail,
or snow, will continue.

Sometimes severe weather from an equatorial[18] direction, not lasting
long, may cause no great fall of the barometer, because followed by a
_duration_ of wind from polar regions:--and at times it may fall
considerably with polar winds and fine weather, apparently against these
rules, because a _continuance_ of equatorial wind is about to follow. By
such changes as these one may be misled, and calamity may be the
consequence if not thus forewarned.

The veering of the winds is a direct consequence of the earth's
rotation, while currents of air from the polar regions are alternating
or contending with others from the equator.

The polar currents are cold, dry, and heavy. Those from the equatorial
parts of the world are warm, moist, and comparatively light. Their
alternate or combined action, with the agencies of solar heat and
electricity, cause the varieties of weather that we experience.

It is not intended to discourage attention to what is usually called
"weather wisdom." On the contrary, every prudent person will combine
observation of the elements with such indications as he may obtain from
instrumen