A. Wind is air in motion.

A. The principal causes are the variations of heat and cold, produced by the succession of day and night, and the four seasons.

A. Heat rarefies the air, and causes it to expand.

A. If a bladder half full of air (tied tight round the neck), were laid before a fire, the heat of the fire would expand the air so much, that the bladder would soon be entirely inflated; (in this case, the air in the bladder is expanded to twice its original bulk, by the heat of the fire).

A. It causes the air to ascend through colder strata, as a cork (put at the bottom of a basin of water) would ascend through the water.

A. When a boy sets fire to the cotton of his balloon, the flame heats the air inside the balloon; and the air becomes so light, that it ascends, and carries the balloon with it.

A. Air is condensed by cold, or squeezed into a smaller compass; in consequence of which, it becomes heavier, and descends towards the ground.

A. After the bladder is fully inflated, (by lying before the fire), if it be taken away from the fire, the bladder will collapse, and show that it is not half full.

A. The skin will become wrinkled, shrivelled, and flabby, because there is not sufficient air inside to fill it out.

A. As soon as the cotton of the balloon is burnt out, the air inside becomes cold again, and the balloon falls to the earth.

A. No; the air is not heated by the rays of the sun, because air (like water) is a very bad conductor.

A. By convection, thus:—The sun heats the earth, and the earth heats the air resting upon it; the air thus heated rises, and is succeeded by other air, which is heated in a similar way, till all is warmed by “convective currents.”

A. Streams of air heated by the earth, which rise upwards and carry heat with them, are called “convective currents” of hot air.

A. Yes; there are always two currents of air in the room we occupy, one of hot air flowing out of the room, and another of colder air flowing into the room.

A. If I hold a lighted candle near the crevice at the top of the door, the flame will be blown outward (towards the hall); but if I hold the candle at the bottom of the door, the flame will be blown inwards (into the room).

A. Because as the air of the room is warmed by the fire, &c., it ascends; and (floating about the upper part of the room) some of it escapes through the crevice at the top of the door, and thus produces a current of air outwards (into the hall).

A. Because after the warm air of the room has ascended to the ceiling, or made its escape into the hall, &c., a partial vacuum is made at the bottom of the room; and cold air (from the hall) rushes under the door to supply the void.

A. A vacuum means a place from which the air has been taken: and a “partial vacuum” means, a place from which a part of its air has been taken away. Thus when the air on the floor ascends to the ceiling, a partial vacuum is made on the floor.

A. It is filled up by colder air, which rushes (under the door, and through the window crevices) into the room.

A. If I dip a pail into a pond and fill it with water, a hole (or vacuum) is made in the pond as big as the pail; but the moment I draw the pail out, the hole is filled up by the water around.

A. The heated air which ascends from the bottom of a room, is as much taken away, as the water in the pail; and (as the void was instantly supplied by other water in the pond) so the void of air is supplied by a current from without.

A. The sun heats the earth, and the earth heats the air resting upon it; as the warm air ascends, the void is filled up by a rush of cold air to the place, and this rush of air we call wind.

A. Yes; there is always some motion in the air; but the violence of the motion is perpetually varying.

A. As the earth is always turning round, the vertical rays of the sun are always varying.

A. The rays made at noon-day: when the sun is in a direct line above any place, his rays are said to be “vertical” to that place.

A. Suppose the brass meridian of a globe to represent the vertical rays of the sun; as you turn the globe round, different parts of it will pass under the brass rim, in constant succession.

A. Yes; as each place passes under the brass meridian, it is noon-day to one half, and mid-night to the other.

A. If we suppose the brass meridian to be the vertical sun, the whole column of air beneath will be heated by the noon-day rays; that part which the sun has left, will become gradually colder and colder; and that part to which the sun is approaching, will grow constantly warmer and warmer.

A. Yes; the air over the place which has passed the meridian is cooling: the air under the vertical sun is the hottest; and the air which is over the place about to pass under the meridian, is increasing in heat.

A. The air always seeks to preserve an equilibrium; so the cold air rushes to the void, made by the upward current of the warmer air.

A. Because the direction of the wind is subject to perpetual interruptions from hills and valleys, deserts and seas.

A. Suppose a wind, blowing from the north, comes to a mountain, as it cannot pass through it, it must either rush back again, or fly off at one side (as a marble when it strikes against a wall).

A. Yes; many mountains are capped with snow, and the warm air is condensed as it comes in contact with them; but as soon as the temperature of the wind is changed, its direction may be changed also.

Suppose A B C to be three columns of air. A, the column of air which is cooling down; B, the column to which the sun is vertical; and C, the column which is to be heated next. In this case the cold air of A will rush towards B C, because the air of B and C is hotter than A. But suppose now C to be a snow-capped mountain. As the hot air of B reaches C, it is chilled; and (being now colder than the air behind) it rushes back again towards A, instead of following the sun.

A. When the ocean rolls beneath the vertical sun, the water is not made so hot as the land; and (as another change of temperature is produced) another obstacle is offered to the uniform direction of the wind.

A. 1st—Because the evaporation of the sea is greater than that of the land:

2ndly—The waters are never still: and

3rdly—The rays of the sun strike into the water, and are not reflected from its surface, as they are by land.

A. As water absorbs heat by being converted into vapour; the surface of the sea is continually losing heat by evaporation.

A. As one portion is heated it rolls away, and is succeeded by another; and this constant motion prevents one part of the sea from being heated more than another.

A. When air from the hot earth reaches the sea, it is often condensed, and either rushes back again, or else its violence is very greatly abated.

A. Yes. As passing clouds screen the direct heat of the sun from the earth, they diminish the rarefication of the air also: and this is another cause why neither the strength nor direction of the wind is uniform.

A. Without doubt they would. If the whole earth were covered with water, the winds would always follow the sun, and blow from east to west. Their irregularity is owing to the interspersion of sea and land, and the irregularities of the earth’s surface.

A. Yes; in those parts of the world, where these obstructions do not exist; as on the Atlantic and Pacific Ocean, the winds are pretty uniform.

A. They are called “Trade Winds.”

A. Because (as they blow uniformly in one direction) they are very convenient to those who carry on trade by means of these oceans.

A. That in the northern hemisphere blows from the north-east: that in the southern hemisphere from the south-east.

A. Because the polar current, combining with the equatorial current, give the wind a new direction.

A. The rotation of the earth upon its axis.

A. As the heat in the torrid zone is always greatest, and at the poles the least, therefore a constant current of air rushes from the poles towards the equator.

A. When these currents of air meet at the equator, they clash together, and fly off in a new direction.

A. Yes, in the open sea; that is, in the Atlantic and Pacific Oceans for about 30 deg^s. each side of the equator.

A. No; nor yet in those parts of the Atlantic and Pacific which verge on the land.

A. Because when Arabia, Persia, India, and China, are exposed to the enormous heat of their summer sun, the air is so rarefied, that the colder air from the south pole rushes towards these nations, and not to the equator; in consequence of which, a south-west wind is produced for six months of the year.

A. When the sun has left the northern side of the equator for the southern, then the southern part of the torrid zone is most heated; and the cold air from the north (rushing towards the southern tropic) is diverted to the north-east, where it continues for the other six months of the year.

A. They are called monsoons; and blow from the north-east from September to April, and from the south-west for the other six months of the year.

A. No; our island (having a continent on one side, and a sea on the other) has a most variable climate.

A. We generally find that easterly winds prevail during the spring of the year, and westerly winds are most common in the summer and autumn.

S-West winds are most frequent in July and August. N-East winds in January, March, April, May, June; and most seldom in July, September, and December.

A. The winds in December and January are generally the highest. Those in February and November the next; and those in August and September the least boisterous.

A. Because the sun is furthest south in those months; and (as the heat in these northern regions rapidly decreases) the contrast between our temperature and that of the torrid zone is greater in December and January, than in any other two months throughout the year.

A. As the air always seeks to preserve an equilibrium, therefore the greater the contrast, the more violent will be the rush of air to equalize the two volumes.

A. August and September are our warmest months, when we approach nearer to the heat of the torrid zone than in any other two months; therefore, the air (to and from the equator) moves with less velocity in our northern hemisphere.

A. If the cool air of the polar regions did not rush into the torrid zone, it would become so hot, that no human being could endure it. If (on the other hand) the hot air from the torrid zone did not modify the polar regions, they would soon become insufferably cold.

A. Because, as they come over the vast continents of Asia and Europe, they absorb very little water.

A. Being thirsty when they reach our island, they readily imbibe moisture from the air and clouds; and, therefore, bring dry weather.

A. The north wind comes from the polar regions, over mountains of snow, and seas of ice; in consequence of which, it is very cold.

A. As they come from regions colder than our own, they are warmed by the heat of our island; and (as their temperature is raised) they absorb moisture from every thing they touch; in consequence of which, they are both dry and parching.

A. The south wind comes over the hot sandy deserts of Africa, and is heated by the land it traverses.

A. The south wind (being much heated by the hot sands of Africa) imbibes water very plentifully, as it passes over the Mediterranean Sea and British Channel.

A. As soon as it reaches our cold climate, it is condensed, and its vapour is squeezed out (as water from a wet sponge).

A. The west winds come over the Atlantic Ocean, and are laden with vapour: if, therefore, they meet with the least chill, some of the vapour is squeezed out.

A. Because some sudden change of temperature has condensed the vapour of the air into clouds.

A. Because some dry wind (blowing over the clouds) has imbibed their moisture, and carried it off in invisible vapour.

A. As it comes from the torrid zone, and crosses the ocean, the hot wind is laden with vapour; and as some of the heat escapes (as soon as it reaches our northern island) the vapour is condensed, and precipitated as rain.

A. As it comes from a climate colder than our own, its capacity for imbibing vapour is increased when it reaches our island; in consequence of which, it dries the air, dispels the clouds, and promotes evaporation.

A. If the wind be colder than the clouds, it will condense their vapour into rain: if the wind be warmer than the clouds, it will dissolve them, and cause them to disappear.

A. Because they generally blow from the east or north-east; and, therefore, sweep over the continent of Europe.

A. They dry the soil (which is saturated with the floods of February), break up the heavy clods, and fit the land for the seeds which are committed to it.

A. Because it comes in with blustering east winds, which are essential to dry the soil, which would otherwise rot the seed committed to it.

A. Because the water (evaporated by the high winds) falls again in showers to fertilize the earth, and breaks the violence of the winds.

A. Because it indicates that there has been a continuance of dry weather; and unless March be dry, the seed will rot in the wet soil.

A. Because the dry cold winds of March prepare the soil for seeds, which germinate, and produce fruit in the autumn.

A. Because, if March be wet, so much of the seed rots in the ground, that the autumn crops are spoiled.

A. Because, if the spring be very mild, vegetation gets too forward, and is pinched by the nightly frosts, so as to produce neither fruits nor flowers.

A. Because if the vegetation of spring be backward, the frosty nights will do no harm; for the fruits and flowers will not put forth their tender shoots, till the nights become too warm to injure them.

A. Before seeds can germinate, three things are essential:—Darkness, Heat, and Moisture. April showers supply the principal nourishment on which seeds depend for existence.