Q. Why does a farrier put the horse-shoe on hot?
A. That it may stick the closer, when it has contracted by cold.
Q. Why does a stove make a cracking noise, when a fire is very hot?
A. The iron stove expands by heat, and (as it swells) the parts rub both against each other, and against the bricks around, driving them further off; and this produces a cracking noise.
Q. Why does a stove make a similar cracking noise, when a large fire is taken down?
Q. Why does the plaster round a stove crack and fall away?
A. When the fire is lighted, the iron-work (which expands more than the brick-work and plaster) pushes away the bricks and plaster: but when the fire is put out, the metal shrinks again, and leaves the “setting” behind.
Q. Why does the plaster fall away?
A. As a chink is left (between the “setting” and the stove), the plaster will frequently fall away from its own weight.
Q. What other cause contributes to bring the plaster down?
A. As the heat of the fire varies, the size of the iron stove varies also; and this swelling and perpetually contracting, keeps up such a constant disturbance about the plaster, that it cracks and falls off, leaving the fire-place very unsightly.
A. Heat expands the metal; and as the metal is increased in bulk, it occupies a larger space, (or, in other words, rises higher in the tube.)
Q. Why is a glass broken, when hot water is poured into it?
A. Because the inside of the glass is expanded by the hot water, and not the outside; so the glass snaps for want of flexibility.
Q. Why is not the outside of the glass expanded by the hot water, as well as the inside?
A. Glass is a non-conductor of heat; and, therefore, breaks before the heat of the inner surface is conducted to the outside.
Q. Why does a glass snap, because the inner surface is hotter than the outer?
A. Glass is expanded by heat; and as the inner surface expands, it stretches the outer surface till it snaps.
Q. Why is a china cup broken, if hot water be poured over it, or into it?
Q. Why does the bottom come off, if a glass beaker be set on a warm hob?
A. Glass is a non-conductor; and, as the bottom of the glass (from the warmth of the hot stove) expands, before the sides are heated, the two parts separate the one from the other.
Q. What is meant by liquefaction?
A. The state of being melted; as ice is melted by the heat of the sun.
Q. Why is ice melted by the heat of the sun?
A. The heat of the sun (entering the solid ice) forces its particles asunder, till their attraction of cohesion is sufficiently overcome, to convert the solid ice into liquid. (See p. 112.)
Q. Why are metals melted by the heat of fire?
A. The heat of the fire (entering the solid metal) forces its particles asunder, till their attraction of cohesion is sufficiently overcome, to convert the solid metal to a liquid.
Q. Why is water converted to steam by the heat of fire?
A. The heat of the fire (entering the water) divides its globules into very minute bubbles, which (being made lighter than air) fly off from the surface in the form of steam.
Q. Why does not wood melt, like metal?
A. Because the heat of the fire decomposes the wood into gas, smoke, and ashes; and the different parts separate from each other.
Q. What is meant by vaporization?
A. The conversion of liquid into vapour; as water is converted into vapour by the heat of the sun.
Q. What are clouds?
Q. What is the difference between a fog and a cloud?
A. Clouds and fogs differ only in one respect. Clouds are elevated above our heads: but fogs come in contact with the surface of the earth.
Q. If clouds are water, why do they float on the air?
A. 1st—The vapour of clouds is composed of very minute bubbles (called ves’cicles), which float like soap bubbles: and
2ndly—Warm air (between the bubbles) keeps them apart, and makes the mass lighter; and the currents of air (which constantly ascend from the warm earth) buoy them up.
Q. Why does vapour sometimes form into clouds, and sometimes rest upon the earth as mist or fog?
Q. Are all clouds alike?
A. No. They vary greatly in density, height, and colour.
Q. What is the chief cause of fog and clouds?
A. The changes of the wind.
Q. How can the changes of the wind affect the clouds?
A. If a cold current of wind blows suddenly over any region, it condenses the invisible vapour of the air into cloud or rain: but if a warm current of wind, blows over any region, it disperses the clouds, by absorbing their vapour.
Q. What countries are the most cloudy?
A. Those where the winds are most variable, as Britain.
Q. What countries are the least cloudy?
A. Those where the winds are not variable, as Egypt.
Q. What distance are the clouds from the earth?
Q. What clouds are the lowest?
A. Those that are most highly electrified: lightning clouds are rarely more than about 700 yards above the ground; and very often actually touch the earth with one of their edges.
Q. What is the thickness of the clouds?
A. Some clouds are 20 square miles in surface, and above a mile in thickness; while others are only a few yards or inches.
Q. How can persons ascertain the thickness of a cloud?
A. As the tops of high mountains are generally above the clouds; therefore, travellers (who climb the mountains) may pass quite through the clouds, into a clear blue firmament, when they may see the clouds beneath their feet.
Q. Why are the clouds so variable in shape?
Q. How can electricity affect the shape of clouds?
A. If one cloud be full of electricity, and another not, they will be attracted to each other, and either coalesce,—diminish in size,—or vanish altogether.
Q. Which clouds assume the most fantastic shapes?
A. Those that are the most highly electrified.
Q. What effect have winds on the shape of clouds?
A. They sometimes absorb them entirely: sometimes increase their volume and density; and sometimes change the position of their parts.
Q. How can winds absorb clouds altogether?
A. A warm dry wind will convert the substance of the clouds into invisible vapour, and carry it in its own current.
Q. How can winds increase the bulk and density of clouds?
Q. How can winds change the shape of clouds by altering the position of their parts?
A. Because clouds are so voluble and light, that every breath of wind changes the position of those ves’cicles or bubbles.
Q. What are the general colours of the clouds?
A. White and grey, when the sun is above the horizon: but red, orange, and yellow, at sun-rise and sun-set.
The blue sky cannot be considered as clouds at all.
Q. Why are the last clouds of evening generally of a red tinge?
A. Because red rays are the least refrangible of all; and, therefore, are the last to disappear.
Q. What is meant by being “less refrangible”?
A. Being less able to be bent. Blue and green rays being very easily bent (by the resistance of the air) are thrown off from the horizon; but red rays not being bent back in the same way, give a tinge to the evening clouds.
A. Because red rays are the least refrangible of all, and not being bent back by the air (like blue and green), strike upon the horizon, and give a tinge to the morning clouds.
Q. Why is not the reflection of clouds always alike?
A. Because their size, density, and situation in regard to the sun, vary perpetually; so that sometimes one colour is reflected, and sometimes another.
Q. What regulates the motion of the clouds?
A. The motion of the clouds is generally directed by the winds; but sometimes electricity will influence their motion also.
Q. How do you know that clouds move by other influences besides wind?
A. Because we often see in calm weather small clouds meeting each other from opposite directions.
Q. How do you know that electricity affects the motion of the clouds?
Q. Into how many classes are the different sorts of clouds generally divided?
A. Into three classes:—viz. Simple, Intermediate, and Compound.
Q. How are simple clouds sub-divided?
A. 1.—Cirrus. 2.—Cum’ulus; and 3.—Stra’tus.
Q. What are cirrus clouds?
A. Clouds like fibres, loose hair, or thin streaks, are called cirrus clouds.
Q. Why are these clouds called cirrus?
A. From the Latin word, cirrus (“a lock of hair, or curl”): they are the most elevated of all clouds.
Q. What do cirrus clouds portend?
A. When the streamers point upwards, the clouds are falling, and rain is at hand: but when the streamers point downwards, expect easterly wind or drought.
Q. What are cum’ulus clouds?
Q. Why are these monster masses called cum’ulus clouds?
A. From the Latin word, cum’ulus (a mass or pile).
Q. What do cum’ulus clouds foreshow?
A. When these piles of cloud are fleecy, and sail against the wind, they indicate rain; but when their outline is very hard, and they come up with the wind, they foretell fine weather.
Cumulus clouds should be smaller towards evening than they are at noon. If they increase in size at sun-set, a thunder-storm may be expected in the night.
Q. What are stra’tus clouds?
A. Creeping mists, especially prevalent in a summer’s evening: these clouds rise at sun-set in low damp places, and are always nearer the earth, than any other sort of cloud.
Q. Why are these mists called stra’tus clouds?
A. From the Latin word, stra’tus (“laid low,” or “that which lies low”).
Q. How are the intermediate clouds sub-divided?
Q. What are cirro-cum’ulus clouds?
A. When cirrus clouds spring from a massy centre; or when heavy masses of cloud terminate at their edges in long streaks, or what are called “mares’ tails.”
A system of small round clouds may be called cirro-cum’ulus.
Q. What do cirro-cum’ulus clouds generally forebode?
A. Continued drought, or hot dry weather.
Q. What are cirro-stra’tus clouds?
A. They compose what is generally called a “mackarel sky.” This class of clouds always indicate rain and wind; hence the proverb—
Q. How are compound clouds sub-divided?
A. Compound clouds are also sub-divided into two sorts. 1.—The Cum’ulo-stra’tus; and 2.—The Nimbus.
Q. What is meant by cum’ulo-stra’tus clouds?
Q. What do the cumulo-stratus clouds foretell?
A. A change of weather; either from fine to rain, or from rain to fine weather.
Q. What are nimbus clouds?
A. Nimbus is the Latin word for “clouds which bring a storm;” and all clouds from which rain falls are so named.
Q. What appearance takes place in the clouds at the approach of rain?
A. The cum’ulus cloud becomes stationary, and cirrus streaks settle upon it, forming cumulo-stratus clouds; which are black at first, but afterwards of a grey colour.
Q. Why do clouds gather round mountain-tops?
A. Because (as they float along) they dash against the mountains; and (being arrested in their motion) collect round the top.
A. 1st—They act as screens to arrest the radiation of heat from the earth:
2ndly—They temper the heat of the sun’s rays: and
3rdly—They are the great store-houses of rain.
Q. Why is wind said to blow up the clouds?
A. When a dry wind travels over sea, and accumulates more vapour than the air can sustain, it relinquishes a part (as it flies along) in the form of clouds.
Q. Why does wind sometimes drive away the clouds?
A. When wind travels over dry climes or thirsty deserts, it becomes so dry itself, that it absorbs vapour from the clouds, and disperses them.
Q. What is the cause of a red sun-set?
Q. Why is a red sun-set an indication of a fine day to-morrow?
A. Because (notwithstanding the cold of sun-set) the vapours of the earth are not condensed into clouds. Our Lord referred to this prognostic in the following words: “When it is evening ye say, it will be fair weather, for the sky is red.” (Matt. xvi. 2.)
Q. What is the cause of a coppery yellow sun-set?
A. Because the vapour of the air is actually condensed into clouds; in which case it “refracts” (or bends) the yellow rays of the sun towards the horizon, where they are reflected at sun-set.
Q. Why is a yellow sunset an indication of wet?
A. Because the vapours of the air are already condensed into clouds; rain, therefore, may be shortly expected.
Q. What is the cause of a red sun-rise?
A. Vapour in the upper region of the air just on the point of being condensed.
A. Because the higher regions of the air are laden with vapour, on the very point of condensation, which the rising sun cannot disperse. Hence our Lord’s observation, “In the morning (ye say) it will be foul weather to-day, for the sky is red and lowering.” (Matt. xvi. 3.)
Q. Why is a grey morning an indication of a fine day?
A. Because that air alone contiguous to the earth is damp and full of vapour. There are no vapours in the higher regions of the air to reflect red rays; and hence the morning-light looks grey.
Q. What difference (in the state of the air) is required, to make a grey and red sunrise?
A. In a grey sunrise, only that portion of air contiguous to the earth is filled with vapour; all the rest is clear and dry. But in a red sunrise the air in the upper regions is so full of vapour that the rising sun cannot disperse it.
Q. Why is a grey sunset an indication of wet?
Q. The proverb says, “A rainbow in the morning is the shepherd’s warning:” why is it so?
A. A rainbow can only be formed when the clouds (containing or dropping rain) are opposite the sun: a morning rainbow, therefore, is always in the west, and indicates that bad weather is on the road to us.
Q. Why does a rainbow in the west indicate that bad weather is on the road to us?
A. Because our heavy rains are usually brought by west or south-west winds; and, therefore, clouds which reflect the colour of the rainbow in the west, are coming up with the wind, bringing rain with them.
Q. The proverb says, “A rainbow at night, is the shepherd’s delight;” why is it so?
Q. Why does a rainbow in the east indicate that bad weather is leaving us?
A. As west and south-west winds bring rain, if the clouds have been driven from the west to the east, they have passed over us, and are going away from us.
Q. What is meant by an aurora borea’lis, or northern light?
A. A luminous white cloud in the north of the sky at night-time. Sometimes streaks of blue, purple, and red,—and sometimes flashes of light, are seen also.
In our island this phenomenon generally rises from a dark cloud (running from the north to the east and west) elevated about 10 or 20 degrees above the horizon: above this dark bed of clouds the luminous white light appears.
Q. What is the cause of the aurora borealis, or northern light?
A. Electricity in the clouds.
Q. Why is the aurora borealis generally a white light?
Q. Why are there sometimes different colours in the aurora borealis, such as yellow, red, and purple?
A. Because the electric fluid passes through air of different densities. The most rarefied air produces a white light; the most dry air, red; and the most damp produces yellow streaks.
Q. Does the aurora borealis forbode fine weather or wet?
A. When its corruscations are very bright, it is generally followed by stormy moist unsettled weather.
Q. Why does a haze round the sun indicate rain?
A. Because the haze is caused by very fine rain falling in the upper regions of the air; when this is the case, a rain of 5 or 6 hours continuance, may be expected.
A. Because the halo is caused by fine rain falling in the upper regions of the air. The larger the halo the nearer the rain-clouds, and the sooner may rain be expected.
Q. Why does a black mist bring wet weather?
A. The mist is black, because it is overshadowed by dense clouds or masses of vapour; and, therefore, it forebodes wet.
Q. Why does a white mist indicate fine weather?
A. The mist is white, because no clouds blacken it with their shadow; and (as the sky is cloudless) fine weather may be expected.
Q. Why do we feel almost suffocated in a hot cloudy night?
A. Because the heat of the earth (being unable to escape into the upper region of the air, in consequence of the clouds) floats, like a sea of heat, on the surface of the earth.
A. Because the heat of the earth can readily escape into the upper regions of the air, and is not confined and pent-in by thick clouds.
Q. Why do we feel depressed in spirits on a wet murky day?
A. 1st—Because when the air is laden with vapour, it has less oxygen.
2ndly—The air being lighter than usual, does not balance the air in our body: and
3rdly—Moist air has a tendency to relax the nervous system.
Q. What is meant by the “air balancing the air” in our body?
A. The human body is filled with air of the same density as that around: if, therefore, we ascend into purer air, or descend into denser air, the balance is destroyed, and we feel oppressed and suffocated.
Q. Why do we feel oppressed and suffocated if the air around is not of the same density as that in our body?
Q. Why do persons who ascend in balloons feel pain in their eyes, ears and chest?
A. Because the air in the upper regions is more rare than the air in their bodies; and (till the equilibrium is restored) great pain is felt in all the more sensitive parts of the body.
Q. Why do persons who descend in diving-bells feel pain in their eyes, ears and chest?
A. Because the air in the sea is more dense than the air in their bodies; and (till the equilibrium is restored) great pain is felt in all the more sensitive parts of the body.
Q. Why does the sea heave and sigh just previous to a storm?
A. The density of the air (just previous to a storm) is very suddenly diminished, but the air in the sea is not so quickly affected; therefore the sea heaves and sighs in its effort to restore an equilibrium.
A. Because the air is suddenly and very greatly rarefied; and (as the density of the air is diminished) its power to transmit sound is diminished also.
Q. How do you know that rarefied air cannot transmit sound so well as dense air?
A. Because the sound of a bell (in the receiver of an air-pump) cannot be heard at all, after the air has been partially exhausted; and a pistol fired on a high mountain would not sound louder than a common cracker.
Q. Why do we feel braced and light-hearted on a fine spring or frosty morning?
A. 1st—Because there is more oxygen in the air on a fine frosty morning, than there is on a wet day: and
2ndly—A brisk and frosty air has a tendency to brace the nervous system.
Q. Why do dogs and cats (confined to a room) feel lazy and drowsy at the approach of rain?
Q. Why do horses neigh, cattle low, sheep bleat, and asses bray, at the approach of rain?
A. 1st—As the air does not contain its full proportion of oxygen, they feel a difficulty in breathing: and
2ndly—As damp relaxes their nerves, they feel languid and uneasy.
Q. Why do candles and fires burn with a bluer flame in wet weather?
A. As the air contains less oxygen in wet weather, the heat of fire is less intense: and the flame is blue, because the fuel is not thoroughly consumed.
Q. Why do hills, &c. appear larger in wet weather?
A. Because (when the air is laden with vapour) the rays of light are more dispersed, and produce a larger reflection; objects, therefore, seen at a distance, appear larger.
Q. Why do trees, &c. in wet weather appear further off than they really are?
Q. Why does the sun seem larger when he sets and rises, than he does at noon?
A. Because the rays pass through more of the vapoury atmosphere which surrounds the earth; and this vapoury atmosphere acts like a magnifying glass.
It is very manifest that the lines D C are shorter than the lines E C: if, therefore, A be the earth, and D G E the boundary of the atmosphere round the earth, then the rays M E C (at the horizon) will pass through more of the atmosphere, than the rays S D C, which are more elevated.