CHAPTER XI.. 2.--Liquefaction.

2.--LIQUEFACTION.

3.--VAPORIZATION.

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?

A. Moisture evaporated from the earth, and collected in the upper regions of the air.

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?

A. When the surface of the earth is warmer than the air, the vapour of the earth (being condensed by the chill air) becomes mist or fog. But when the air is warmer than the earth, the vapour rises through the air, and becomes cloud.

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?

A. Some thin light clouds are elevated above the highest mountain-top; some heavy ones touch the steeples, trees, and even the earth: but the average height is between one and two miles.

(Streaky curling clouds, like hair, are often five or six miles high.)

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?

A. The shape of clouds depends upon two things:--Their state of electricity, and the wind.

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?

A. A cold current of wind will condense the invisible vapour of the air, and add it to the clouds as it passes by.

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.

Q. Why are MORNING CLOUDS generally of a RED tinge?

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?

A. Because clouds often meet from opposite directions; and (after they have discharged their opposite electricities into each other) vanish altogether.

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?

A. Cum'ulus clouds are lumps like great sugar-loaves,--volumes of smoke,--or mountain towering over mountain.

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?

A. Into two sorts. 1.--The Cirro-Cum'ulus; and 2.--The Cirro-Stra'tus.

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--

"Mackarels' scales and mares' tails Make lofty ships to carry low sails."

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?

A. Those clouds which assume all sorts of gigantic fancy forms; such as vast towers and rocks,--huge whales and dragons,--scenes of battle,--and cloudy giants. This class of clouds is the most romantic and strange of all.

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.

Q. What is the USE of CLOUDS?

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?

A. Because the vapour of the air is not actually condensed into clouds, but only on the point of being condensed; in which state it bends the red rays of the sun towards the horizon, where they are reflected at 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.

Q. Why is a RED and LOWERING sky at SUNRISE an indication of a WET DAY?

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?

A. If the air on the surface of the earth be very damp at sunset, it is a proof that the air is saturated with vapour, and wet may be expected: hence the proverb--

"Evening red and morning grey Will set the traveller on his way; But evening grey and morning red Will bring down rain upon his head."

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?

A. As a rainbow is always opposite to the sun, therefore a rainbow at night is in the east, and indicates that bad weather is leaving us.

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?

A. Because the electric fluid passes through air extremely rarefied: and whenever electric fluid passes through air much rarefied, it always produces 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.

Q. Why is a HALO round the MOON a sure indication of RAIN?

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.

Q. Why do we feel more SPRIGHTLY in a clear bright night?

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?

A. If the air around be more dense, it will squeeze our body in by its weight: if it be less dense, the air in our body will blow us out.

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.

Q. Why is the AIR so universally STILL just PREVIOUS to a TEMPEST?

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?

A. 1st--Because the air does not contain its full proportion of oxygen: and

2ndly--Because the damp relaxes their nervous system, and makes them drowsy.

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?

A. Because the fog or mist diminishes the light reflected from the object; and as the object becomes more dim, it seems to be further off.

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.

Q. Why does the MOON appear LARGER at her RISING and SETTING, than when above our heads?

A. Because the rays pass through more of the vapoury atmosphere which surrounds the earth; and this vapoury atmosphere magnifies the moon, just like a magnifying glass.

Q. Why do CATS RUB their EARS when it is likely to rain?

A. Either because the air is full of vapour, and its humidity (piercing between the hair of the cat) produces an itching sensation; or more probably, because the air is overcharged with electricity.

Q. How can the ELECTRICITY of air produce a sensation of ITCHING?

A. If the air is overcharged with electricity, the hair of the cat is overcharged also; and this makes her feel as if she were covered with cobwebs.

Q. Why does the CAT keep RUBBING herself?

A. Her hair will not lie smooth, but has a perpetual tendency to become turgid and ruffled; so the cat keeps rubbing her coat and ears, to smooth the hair down, and brush away the feeling of cobwebs.

Q. Why do our HEADS and SKIN itch before rain?

A. Probably because the air is overcharged with electricity; and, therefore, a sensation (like that of cobwebs) irritates the skin, and produces an itching.

Q. Why do we HEAR distant CLOCKS more distinctly when rain is near at hand?

A. Because the air is filled with vapour, and water is a better conductor of sound than dry air.

Q. Why do we hear CHURCH-BELLS further, just previous to rain?

A. Because the air is filled with vapour, and vapour is a better conductor of sound than dry air.

Q. Why do DOORS SWELL, when RAIN is at hand?

A. Because the air is filled with vapour, which (penetrating into the pores of the wood) forces the parts further apart, and swells the door.

Q. Why do DOORS SHRINK in DRY weather?

A. Because the moisture is absorbed from the wood; and, as the particles are brought closer together, the size of the door is lessened, (or in other words, the wood shrinks).

Q. Why is the AIR filled with offensive SMELLS previous to a coming RAIN?

A. Because the volatile parts, (which rise from dunghills, sewers, &c.), being laden with vapour, are unable to rise so readily, as when they are rarefied by a bright sun.

Q. Why do FLOWERS smell SWEETER and STRONGER just previous to RAIN?

A. Because the volatile parts (which constitute the perfume of flowers) are laden with vapour; and (being unable to rise) are confined to the lower regions of the air.

Q. Why do HORSES and other animals stretch out their necks, and SNUFF up the AIR, just previous to a fall of RAIN?

A. Because they smell the odour of plants and hay, and delight to snuff in their fragrance.

Q. Why does SMOKE FALL when RAIN is at hand?

A. The air being less dense in wet weather, cannot buoy up smoke so readily, as when more dry and heavy.

Q. Why do SWALLOWS FLY LOW when RAIN is at hand?

A. Because the insects (of which they are in pursuit) have fled from the cold upper regions of the air, to the warm air near the earth: and as their food is low, the swallows fly low.

Q. Why do these INSECTS seek the lower regions of the air in WET weather, more than in FINE weather?

A. Because they are forced downward, by some current of cold air which drives them down.

Q. Why does a DOWNWARD current of COLD AIR bring RAIN?

A. Because it condenses the warm vapour; which then descends in rain.

Q. The proverb says, "A SINGLE MAGPIE in spring, FOUL WEATHER will bring:" why is this the case?

A. In cold stormy weather, one magpie alone will leave its warm snug nest in search of food, while the other stays with the eggs or young ones; but in fine mild weather (when their brood will not be injured by cold) both the magpies will fly out together.

Q. Why is it UNLUCKY for ANGLERS to see a SINGLE MAGPIE in spring?

A. Because when magpies fly abroad singly, the weather is cold and stormy; but when both birds fly out together, the weather is warm and mild, which is favourable for fishing.

Q. Why do SEA GULLS fly about the SEA in FINE weather?

A. Because they live upon fish, which are found near the surface of the sea in fine weather.

Q. Why may we expect STORMY RAINS, when SEA GULLS assemble on the land?

A. Because the fish (on which they live) leave the surface of the sea in stormy weather, and go down too deep for the gulls to get at them; they are obliged, therefore, to feed on the worms and larvæ which are driven out of the ground at such times.

Q. Why does the PETREL always fly to the SEA during a storm?

A. Because the petrel lives upon sea insects, which are always to be found in abundance about the spray of swelling waves.

(The Petrel is a bird of the duck-kind, which lives in the open sea. They run on the top of the sea, and are called Petrels, or rather Peter-els, from "St. Peter," in allusion to his walking on the sea, to go to Jesus.)

Q. Why do CANDLES and LAMPS SPIRT when RAIN is at hand?

A. Because the air is filled with vapour, and the humidity penetrates the wick; where (being formed into steam) it expands suddenly, and produces a little explosion.

Q. Why does a DROP of WATER sometimes ROLL along a piece of hot iron without leaving the least trace?

A. If the iron be very hot indeed, the bottom of the drop is turned into vapour, before the drop can evaporate; and the vapour thus formed buoys the drop up, without allowing it to touch the iron at all.

Q. Why does it ROLL?

A. The current of air (which is always passing over the heated surface) drives it along.

Q. Why does a LAUNDRESS put a little SALIVA on an IRONING-BOX to know if it be hot enough?

A. If the saliva sticks to the box and is evaporated, the box is not hot enough; but if the saliva runs along the box, it is.

Q. Why is the BOX HOTTER if the saliva RUNS ALONG THE BOX, than if it adheres to it till it is evaporated?

A. If the saliva runs along the box, the iron is hot enough to convert the bottom of the drop of spittle into vapour; but if the saliva will not roll, the box is not hot enough to convert the bottom of the drop of spittle into vapour.