level of the sea) with a continuance of it, is indicative of fine weather and moderate winds.

The barometer is said to be falling when the mercury in the tube is sinking, at which time its upper surface is sometimes concave or hollow. The barometer is rising when the mercurial column is lengthening; its upper surface being then, as in general, convex or rounded.[14]

A rapid rise of the barometer indicates unsettled weather. A slow rise, or steadiness, with dryness, shows fair weather.

A considerable and rapid fall is a sign of stormy weather and rain. Alternate rising and sinking show very unsettled weather.

The greatest depressions of the barometer are with gales from the S.E., Southward, or S.W.; the greatest elevations, with winds from the N.W., Northward, or N.E., or when calm.

Although the barometer generally falls with a Southerly, and rises with a Northerly wind, the contrary sometimes occurs; in which cases the Southerly wind is dry and the weather fine; or the Northerly wind is wet and violent.[15]

When the barometer sinks considerably, high wind, rain, or snow will follow: the wind will be from the Northward if the thermometer is low (for the season)—from the Southward if the thermometer is high.

Sudden falls of the barometer, with a Westerly wind, are sometimes followed by violent storms from N.W. or North.

If a gale sets in from the Eastward or S.E., and the wind veers by the South, the barometer will continue falling until the wind becomes S.W., when a comparative lull may occur; after which the gale will be renewed; and the shifting of the wind towards the N.W. will be indicated by a fall of the thermometer as well as a rise of the barometer.

Three things appear to affect the mercury in a barometer:—

1. The direction of the wind—the North-east wind tending to raise it most—the South-west to lower it the 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 extreme bearings (rather than poles?)

The range, or difference of height, of the mercury, 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 (shown by the barometer as read off).

2. The amount, taken by itself, of vapour, moisture, wet, rain, hail, 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.

3. The strength or force alone of wind from any quarter (moisture and direction being unchanged) is preceded, or foretold, by a fall or rise, according as the strength will be greater or less, ranging, in an extreme case, to more than two inches.

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.[16] Before and during 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 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