A. A weather-glass, or instrument to show the changes of the weather, by marking the variations in the weight of air.

A. An instrument to show how hot or cold anything is.

A. In a thermometer the mercury is sealed up from the air:

In a barometer the mercury is left exposed (or open) to the air.

A. The heat of the air passing through the glass tube into the mercury, causes it to expand more or less, and rise in the tube accordingly.

A. That the air may press upon it freely; and as this pressure is more or less, the mercury rises or falls in the tube.

A. When air is warm or moist, it is lighter than usual:

When it is cold or dry, it is heavier: and as a barometer marks whether the air be light or heavy, it indicates these changes.

A. Because the mercury in the tube rises and falls, as the air becomes lighter or heavier: and we can generally tell by the weight of the air, what kind of weather to expect.

A. Yes; the atmosphere in England varies as much as one-tenth part more or less.

A. To warn sailors how to regulate their ships, before squalls come on.

A. As the barometer will tell when wind, rain, or storm is at hand, the sailor can make his ship trim before it overtakes him.

A. Yes; there are ten special rules to direct us how to know the changes of weather, by marking the mercury of a barometer.

A. The barometer is highest of all during a long frost; and it generally rises with a north-east wind.

A. Because long frost condenses the air very greatly; and the more air is condensed, the greater is its pressure on the mercury of the barometer.

A. Because north-east winds make the air both cold and dry: the air, therefore, is both condensed, and without vapour.

A. The barometer is lowest of all during a thaw which follows a long frost: it generally falls with south and western winds.

A. 1st—Because the air (which had been much dried by the frost) absorbs the moisture of the fresh warm current of wind from the south or south-west: and

2ndly—The air (which had been much condensed by the frost) is suddenly expanded by the warm wind which is introduced.

A. Because south and west winds come heavily laden with vapour; and vaporized air is lighter than dry air.

A. All winds make the barometer drop, except eastern winds: those winds which blow from the south, and south-west make it drop the lowest.

A. Wind is caused by a partial vacuum in some parts of the globe; and as the air rushes in to supply this deficiency, its general pressure is lessened, and the barometer falls.

A. While the barometer stands above 30°, the air must be very dry or very cold, or perhaps both, and no rain may be expected.

A. If the air be very dry it will absorb moisture, and not part with what it has in rain.

A. If the air be very cold it is so much condensed, that it has already parted with as much moisture as it can spare.

A. When the barometer stands very low indeed, there is never much rain, although a fine day will seldom occur at such times.

A. There will be short heavy showers, with sudden squalls of wind from the west.

A. Because the air must be very warm, or very moist, or perhaps both.

A. If the air be very warm it will have a tendency to imbibe more moisture, and not to part with what it has.

A. If the air be ever so moist, rain will never fall till cold air has been introduced to condense the vapour; and the moment that the cold air is introduced, the barometer will rise.

A. In summer-time (after a long continuance of fair weather) the barometer will fall gradually for 2 or 3 days before rain comes; but if the fall of the mercury be very sudden, a thunder-storm is at hand.

A. When the sky is cloudless, and seems to promise fair weather, if the barometer be low, the face of the sky will soon be suddenly overcast.

A. Dark dense clouds will pass over without rain, when the barometer is high; but if the barometer be low, it will often rain without any gathering of clouds.

A. The higher the barometer, the greater is the probability of fair weather.

A. Because the air contains but very little vapour. The drier the air, the higher does the mercury of the barometer rise.

A. When the mercury is in a rising state, fine weather is at hand; but when the mercury is in a sinking state, foul weather is near.

A. Because the air is becoming more dry, and therefore its pressure is greater.

A. Because the air is laden with vapour, or disturbed by wind.

A. Because vaporized air is lighter than dry air, and therefore its pressure is less on the mercury of the barometer.

A. If (in frosty weather) it begins to snow, the barometer generally rises to 32°, where it remains as long as the snow continues to fall; if, after this, the weather clear up, you may expect very severe cold.

A. If it be convex (i. e. higher in the middle than at the sides;) it is in a rising state.

A. If it be concave (i. e. hollow in the middle) it is in a falling state.

A. The sides of the mercury rub against the glass tube, and are delayed by it, so that the middle part rises faster than the sides.

A. The sides of the mercury rub against the glass tube, and are delayed by it, so that the middle part sinks faster than the sides.

A. Thunder is generally preceded by hot weather, and followed by cold and showery weather.

A. A great and sudden change (either from hot to cold, or from cold to hot) is generally followed by rain within 24 hours.

A. The cold condenses the air and its vapour; which, being condensed and squeezed out, falls in rain.

A. Because the air is quickly saturated with moisture; and as soon as night comes on, the temperature is lowered again, and some of the abundant moisture falls in rain.

A. Because the evaporation (which was checked by the cold) is carried on very rapidly, in consequence of the diminished pressure of the air.

(N. B. The less the pressure of the air, the more rapidly it evaporates moisture.)

A. In winter time.

A. Because the difference of temperature between the torrid and temperate zones is so great, that the state of the air is perpetually disturbed by their mixing together.

A. In summer time.

A. Because the temperature of our island is so nearly equal to that of the torrid zone, that its state is not much disturbed by interchange of currents.

A. North and east winds make the mercury rise; all other winds make it sink; but south and west winds make it sink lower than any other winds.

A. No, not of themselves; but because cold weather is generally either dry, or rough with north-east winds, therefore the mercury rises in cold weather; and because warm weather is often moist or fanned by south-west winds, therefore, the mercury sinks.

A. Because the warm air of the torrid zone contains much more vapour than the condensed air of the frigid zone; and the moister the air, the less is its pressure.

A. In May and August; next to these, in June, March, September, and April.

A. In November and February; then in October, July, December, and January.

A. March and June; then May and August; then April and November.

A. October and February; then July and September; then January and December.

A. Because the heat is constantly increasing; and the capacity of the air to absorb and retain moisture increases likewise.

A. Because the heat is constantly decreasing, and the capacity of the air to retain moisture decreases also; so that (although it often rains) yet the air is always on the point of saturation.

A. Because frost condenses the air; and condensed air is heavier than rarefied air.

A. Because the air is both warmer (or more rarefied), and also filled with vapour.

A. If the rise be sudden, fine weather will not continue long:

If the fall be sudden, foul weather will not continue long.

A. If the mercury fluctuates much, the weather will be very changeable and unsettled.

The fall of the barometer.

In very hot weather, the fall of the mercury denotes thunder.

Except in very hot weather, the sudden falling of the barometer denotes high wind.

In frosty weather, the fall of the barometer denotes thaw.

If wet weather happens soon after the fall of the barometer, expect but little of it.

In wet weather if the barometer falls, expect much wet.

In fair weather, if the barometer falls much and remains low, expect much wet in a few days, and probably wind.

N. B. The barometer sinks lowest of all for wind and rain together, next to that for wind (except it be an east or north-east wind).

The rise of the barometer.

In winter the rise of the barometer presages frost.

In frosty weather, the rise of the barometer presages snow.

If fair weather happens soon after the rise of the barometer, expect but little of it.

In wet weather, if the mercury rises high and remains so, expect continued fine weather in a day or two.

In wet weather, if the mercury rises suddenly very high, fine weather will not last long.

N. B. The barometer rises highest of all for north and east winds; for all other winds it sinks.

If the barometer be unsettled.

If the motion of the mercury be unsettled, expect unsettled weather.

If it stand at “much rain” and rise to “changeable,” expects fair weather of short continuance.

If it stand at “fair” and fall to “changeable,” expect foul weather.

N. B. Its motion upwards indicates the approach of fine weather: its motion downwards indicates the approach of foul weather.