A Guide to the Scientific Knowledge of Things Familiar
CHAPTER XI.
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.