Part 4

Hence, supposing the three causes to act together--in extreme cases--the mercury might range from about 31 (30.9) inches to near 27 inches, which has happened occasionally.

Generally, however, as the three act much less strongly, and are less in accord--ordinary varieties of weather (the wind varying as usual--with more or less cloudiness, or rain) occur much more frequently than extreme changes.

Another general rule requires attention; which is, that the wind usually veers, shifts, or goes round, with the sun, (right-handed in northern places, left-handed in the southern parts of the world,) and that, when it does not do so, or backs, more wind or bad weather may be expected instead of improvement.

In a barometer the mercury begins to rise occasionally before the conclusion of gale, sometimes even at its commencement, as the equilibrium of the atmosphere begins to be restored. Although the mercury falls lowest before high winds, it frequently sinks considerably before heavy rain only. The barometer falls, but not always, on the approach of thunder and lightning, or when the atmosphere is highly charged with electricity. Before and during the earlier part of serene and settled weather, the mercury commonly stands high, and is stationary.

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 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 instruments.

The more carefully and accurately these two sources of foreknowledge are compared and combined, the more satisfactory will the results prove.

A few of the more marked signs of weather--useful alike to seaman, farmer, and gardener, are the following:

Whether clear or cloudy, a rosy sky at sunset presages fine weather; a red sky in the morning, bad weather, or much wind (if not rain):--a grey sky in the morning fine weather; a high dawn, wind; a low dawn; fair weather.

Soft-looking or delicate clouds foretell fine weather, with moderate or light breezes;--hard edged oily-looking clouds, wind. A dark, gloomy, blue sky is windy;--but a light, bright blue sky indicates fine weather. Generally, the softer clouds look, the less wind (but perhaps more rain) may be expected;--and the harder, more "greasy," rolled, tufted, or ragged, the stronger the coming wind will prove. Also, a bright yellow sky at sunset presages wind; a pale yellow, wet:--and thus by the prevalence of red, yellow, or grey tints, the coming weather may be foretold very nearly: indeed, if aided by instruments, almost exactly.

Small inky-looking clouds foretell rain; a light scud, driving across heavy clouds, wind and rain; but if alone, wind only.

High upper clouds crossing the sun, moon, or stars, in a direction different from that of the lower clouds, or wind then blowing, foretell a change of wind (beyond tropical latitudes).

After fine clear weather the first signs (in the sky) of change are usually small, curled, streaked, or spotty clouds, followed by an overcasting of vapour, that grows into cloudiness. This murky appearance, more or less oily or watery, as wind or rain will prevail, is a sure sign. The higher and more distant the clouds seem to be, the more gradual, but extensive, the coming change of weather will prove.

Generally speaking, natural, quiet, delicate tints or colours, with soft undefined forms of clouds, foretell fine weather: but gaudy or unusual hues, with hard, definite outlines, presage rain and wind.

Misty clouds forming, or hanging on heights, show wind and rain coming--if they remain, or descend. If they rise, or disperse, the weather will improve, or become fine.

When sea birds fly out early, and far to seaward, moderate wind and fair weather may be expected. When they hang about the land, or over it, sometimes flying inland, expect a strong wind, with stormy weather. As many creatures, besides birds, are affected by the approach of rain or wind, such indications should not be slighted by the observer of weather.

There are other signs of a coming change in the weather known less generally than may be desirable; and, therefore worth notice here.

When birds of long flight, such as swallows and others, hang about home and fly low--rain or wind may be expected. Also when animals seek sheltered places, instead of spreading over their usual range: when pigs carry straw to their sties; and when smoke from chimneys does not ascend readily, (straight upwards during a calm,) an unfavourable change may be looked for.

Dew is an indication of fine weather. So is fog. Neither of these two formations occurs under an overcast sky, or when there is much wind. One sees the fog occasionally rolled away, as it were, by wind--but not formed while it is blowing.

Remarkable clearness of atmosphere, near the horizon; distant objects, such as hills, unusually visible; or raised (by refraction); and what is called "a good hearing day" may be mentioned among signs of wet, if not wind, to be expected.

More than usual twinkling of the stars; indistinctness or apparent multiplication of the moon's horns; haloes; "wind-dogs;" and the rainbow; are more or less significant of increasing wind, if not approaching rain.