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Title: A Guide to the Scientific Knowledge of Things Familiar
Author: Brewer, Ebenezer Cobham, 1810-1897
Language: English
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A GUIDE TO THE SCIENTIFIC KNOWLEDGE OF THINGS FAMILIAR;
BY
THE REV. DR. BREWER,
TRINITY HALL, CAMBRIDGE,
HEAD MASTER OF KING'S COLLEGE SCHOOL,
NORWICH,
IN UNION WITH KING'S COLLEGE, LONDON.
LONDON:
JARROLD AND SONS, 47, ST. PAUL'S CHURCHYARD,
ALSO HAMILTON AND CO., SIMPKIN AND CO.,
AND WHITTAKER AND CO.
PREFACE.
Of all science, none is more generally interesting than that which
explains the common phenomena of life. We see that salt and snow are
both white, a rose red, leaves green, and the violet a deep purple; but
how few persons ever ask the reason why! We know that a flute produces a
musical sound, and a cracked bell a discordant one--that fire is hot,
ice cold, and a candle luminous--that water boils when subjected to
heat, and freezes from cold; but when a child looks up into our face and
asks us "why,"--how many times is it silenced with a frown, or called
"very foolish for asking such silly questions!" The object of the
present book is to explain about 2000 of these "silly questions" (which
are often more easily asked than answered) in language so simple that a
child may understand it, yet not so childish as to offend the
scientific; and in order that the answers may be strictly correct, not
only the most approved modern authors have been consulted, but the
manuscript has been submitted sheet by sheet to the revision of two
gentlemen of acknowledged reputation for scientific attainments. To the
REV. A. BATH POWER, M. A. especially, great obligation is due, for a
careful revision of the whole manuscript, for many excellent hints, and
useful additions. In conclusion, so much diligence has been bestowed
upon this little work for nearly ten years, so much useful information
has been supplied by scientific friends, and so minute a revision has
been made of every answer, that it is no presumption to express a hope
that this "Guide to the Scientific Knowledge of Things Familiar" will
become generally useful and acceptable, not only to the young, but to
those advanced to maturer life.
In this work some questions occur more than once, because they serve to
illustrate different principles; and whenever cognate questions occur,
the answers have been rendered as similar as possible, in order to
assist the memory of the learner.
SUBJECTS OF THE CHAPTERS.
PART I.--HEAT.
I.--The SUN a source of heat
II.--ELECTRICITY a source of heat
Thunder and lightning
III.--CHEMICAL ACTION a source of heat
III.--Combustion
IV.--Smoke and smoky chimneys
V.--Lamps and candles
VI.--Animal heat
VII.--MECHANICAL ACTION a source of heat
VII.--Percussion
VIII.--Friction
VIII.--Compression
IX.--EFFECTS OF HEAT
X.--Expansion
XI.--Liquefaction
XI.--Vaporization (clouds)
XII.--Evaporation
XIII.--COMMUNICATION OF HEAT
XIII.--Conduction
XIV.--Absorption
XV.--Reflection
XVI.--Radiation (dew)
XVII.--Convection (boiling)
PART II.--AIR.
XVIII.--AIR
Rust
Tarnish
XIX.--CARBONIC ACID GAS
Froth
Effervescence
Fermentation, &c.
XX.--CARBURETTED HYDROGEN GAS
Fire damp
Safety lamp
XXI.--PHOSPHURETTED HYDROGEN GAS
Ignis fatuus
Ghosts
XXII.--WIND
XXIII.--BAROMETER
Ten special Rules
XXIV.--SNOW. HAIL. RAIN
XXV.--WATER
XXVI.--ICE
Frost
Freezing mixtures
XXVII.--LIGHT
Reflection
Telescopes
Refraction
Spectacles
Rainbows
Colour
XXVIII.--SOUND
Ear trumpets
Echoes
XXIX.--MISCELLANEOUS
Attraction
Anti-putrescents
Sleep
Dreams
Glossary
Index
PART I.
HEAT.
INTRODUCTION.
Q. _What is heat?_
A. The sensation of warmth.
Q. _How is this sensation produced?_
A. When we touch a substance of higher temperature than ourselves, the
warmer substance keeps parting with its heat, till both are of equal
temperature.
Q. _What is that "stream of heat" called, which flows thus, from one
body, to another?_
A. CALO'RIC. _Caloric_, therefore, is the _matter of heat_, which passes
from body to body; but HEAT is the _sensation, of warmth_, produced by
the influx of Calo'ric.
Q. _What are the four principal_ SOURCES _of heat_?
A. 1.--The Sun. 2.--Electricity. 3.--Chemical Action: and 4.--Mechanical
Action.
Q. _What are the principal_ EFFECTS _of heat_?
A. Expansion, Liquefaction, Vaporization, and Ignition.
CHAPTER I.
Q. _What is the_ PRINCIPAL _source of Heat_?
A. The SUN.
Q. _Why do_ BURNING GLASSES _set fire to substances submitted to their
power_?
A. The rays of the sun, collected by the Burning Glass, are all _bent to
one point_, called the "focus;" thus the heat and light, (which should
be diffused over the _whole_ glass,) being gathered together into one
point, are very greatly increased.
Q. _Why is there a_ DARK RIM _round this focus_?
A. Because the rays of light, which should have fallen there, are _bent
into the focus_, and the space around, (being deprived of these rays) is
accordingly darkened.
Q. _Are_ ALL _the rays bent into one point_?
A. No, not quite all: and, therefore, the rim round the focus is only
_slightly_ shadowed.
CHAPTER II.
Q. _What is the second chief source of heat?_
A. ELECTRICITY.
Q. _What is_ LIGHTNING?
A. Lightning is only an _Electric Spark, taken from the clouds_.
Q. _What causes the discharge of an electric cloud?_
A. When a cloud, _overcharged_ with electric fluid, approaches another
which is _under-charged_, the fluid rushes from the former into the
latter, till both have the same quantity.
Q. _Is there any OTHER cause of lightning, besides the one just
mentioned?_
A. Yes; sometimes mountains, trees, and steeples, will discharge a
lightning cloud floating near; and sometimes electric fluid rushes out
of the _earth_, into the clouds.
Q. _What produces ELECTRICITY in the CLOUDS?_
A. 1st--The evaporation from the earth's surface.
2ndly--The chemical changes perpetually going on: and
3rdly--Currents of air of unequal temperature, excite electricity by
_friction_, as they pass by each other.
Q. _How HIGH are the LIGHTNING-CLOUDS from the earth?_
A. Electrical clouds are the _lowest of all clouds_; they are rarely
more than 700 yards above the ground; and sometimes, they actually
_touch the earth_ with one of their edges.
Q. _How high are the clouds generally?_
A. In a _fine_ day, the clouds are often 4 or 5 miles above our head;
but the average height of the clouds is from 1-1/2 to 2 miles.
Q. _Why is lightning sometimes_ FORKED?
A. When the lightning-cloud is a long way off, the _resistance of the
air_ is so great, that the electrical current is diverted into a zig-zag
course.
Q. _Why does the resistance of the air make the lightning zig-zag?_
A. As the lightning _condenses_ the air, in the immediate advance of its
path; it keeps flying from side to side, in order to pass where there is
the _least resistance_.
Q. _How does lightning_ CONDENSE _the air in the immediate advance of
its path_?
A. The air is condensed by the _rapidity_ of the lightning-flash.
Q. _Why is_ FORKED LIGHTNING _more_ DANGEROUS _than a straight flash_?
A. Whatever _resists_ the flash, _diverts its course_; and when
_terrestrial_ objects offer resistance to the current, they are in great
danger of being destroyed.
Q. _Why are there sometimes_ TWO _flashes of forked lightning at the
same moment_?
A. Sometimes (in very severe storms) a flash of lightning will divide
_into two or more parts_; and then each branch assumes the zig-zag
form.
Q. _Why is the FLASH sometimes quite STRAIGHT?_
A. When the lightning-cloud hovers _near the earth_, as the flash meets
with very little resistance, it is _not diverted_; or (in other words)
the flash is straight.
Q. _What is the cause of_ SHEET LIGHTNING?
A. It is only the _reflection of distant flashes_, not distinctly
visible: and sometimes several flashes (from different clouds)
intermingle, and form one vast blaze or sheet of lightning.
Q. _Which_ FORM _of lightning is the most_ DANGEROUS?
A. The _ball_ of fire is by far the most dangerous; and the _zig-zag_
lightning is next in danger. _Sheet_ lightning is not often attended
with danger.
Q. _Why are_ BALLS OF FIRE _so very dangerous?_
A. Because (whenever they fall) much mischief is occasioned by their
_bursting_, which they always do, with an explosion like that of a
cannon.
Q. _Do these_ BALLS OF LIGHTNING _ever run along the ground?_
A. Yes; they often run a considerable way along the ground, then _stop_
for a little time, and _burst in numberless pieces_: sometimes _each of
these pieces_ will explode; and at other times, the _whole ball_ will
burst at once, producing most mischievous consequences.
Q. _What mischief will these balls of fire produce?_
A. They will set houses and barns on fire; and kill all cattle and human
beings, which happen to be in their course.
Q. _Why does LIGHTNING sometimes KILL men and beasts?_
A. When the electric current passes through a man or beast, it produces
so _violent an action upon the nerves_, that it destroys life.
Q. _When is a person struck dead by lightning?_
A. Only when his body forms a part of the lightning's path: i. e. when
the electric fluid (in its way to the earth) actually passes _through
his body_.
Q. _Why are MEN sometimes MAIMED by lightning?_
A. Because lightning strikes with amazing force, whatever opposes it:
and if a man stand in the way, it strikes him such a blow, as to maim
him.
Q. _What is THUNDER?_
A. Lightning _parts the air_ through which it passes; and when the
parted air _closes_ again, the noise made by the concussion, is called
Thunder.
Q. _Why does lightning PART the air through which it passes? It does not
part a rod of iron._
A. Iron is a _conductor_, and therefore allows the fluid to go freely
through it: but air being a _non-conductor_, _resists_ the lightning;
which, therefore, rips it open, in order to pass through it.
Q. _Why is THUNDER sometimes ONE VAST CRASH?_
A. When the lightning-cloud is near the earth, as the flash is
_straight_,--the whole volume of air (through which it passes)
_collapses at once_; and produces one unbroken sudden _crash_.
Q. _What is meant by the air collapsing?_
A. When the rent air _closes again_, it is said to collapse.
Q. _Why is the PEAL sometimes an IRREGULAR mangling broken ROAR?_
A. When the lightning-cloud is a long way off, as the flash is zigzag,
the air does not collapse _all at once_; and as we hear the concussion
of one part after another, the peal is broken, protracted, and
irregular.
Q. _Which part of the collapsing air do we hear first?_
A. That part _nearest_ the _earth_; then the strata above; and last of
all, _that_ in the immediate vicinity of the cloud.
Q. _What is meant by_ "STRATA _of air?_"
A. If a board were laid upon the earth, and several other boards were
piled upon it, this pile would represent strata of wood.
Q. _How does this illustration apply to the air?_
A. A layer of air covers the earth; another layer rests upon _it_; and
thus layer is piled upon layer, for 50 miles in height. Each layer is a
"stratum" of air; and the _plural_ of stratum is strata.
Q. _Why do we hear the collapsing of the air NEAREST the earth FIRST?_
A. Because sound takes a whole _second of time_ to travel 380 yards; but
the air is ripped from top to bottom instantaneously: if, therefore, the
cloud were 1000 yards off, we should hear the collapsing of the lowest
strata nearly _three seconds_, before we heard that in the immediate
vicinity of the cloud.
Q. _Why is the THUNDER sometimes like a deep GROWL?_
A. When the storm is _far distant_, the thunder sounds like a deep
growl.
Q. _Does not SCENERY affect the sound of thunder?_
A. Yes; the _flatter_ the country, the more unbroken the peal:
_Mountain_ scenery _breaks_ the peal, and makes it harsh and irregular.
Q. _What is the cause of ROLLING THUNDER?_
A. The rolling is produced by the _reverberation_ of the thunder along
the massive clouds.
Q. _What is meant by the reverberation?_
A. The echo.
Q. _Why is a flash of lightning generally followed by a POURING RAIN?_
A. The cloud _collapses_, as soon as the electric fluid has left it; and
the water it contained is squeezed out.
Q. _Why is a flash of lightning generally followed by a GUST of WIND?_
A. The flash _rent the air asunder_ through which it darted; and when
the two parts collapse, a rapid motion is produced, which we call
_wind_: the _vibration_ of the thunder contributes also to agitate the
air.
Q. _What is meant by the_ "VIBRATION _of the thunder_?"
A. The quivering motion it gives to the air, by its loud sound.
Q. _Why is there NO THUNDER to what is called SUMMER LIGHTNING?_
A. Because the lightning-clouds are _so far off_, that the sound of the
thunder is _lost_, before it reaches the earth.
Q. _Do_ THUNDER-BOLTS _ever drop from the clouds?_
A. No; the notion of _thunder-bolts_ falling from the clouds, arises
from the _globular_ form, that is sometimes assumed by a flash of
lightning.
Q. _Why is the_ THUNDER _often several moments_ AFTER _the FLASH?_[1]
A. The flash travels nearly _a million_ times faster than the thunder;
if, therefore, the thunder has _far to come_, it will not reach the
earth till a considerable time _after the flash_.
[1] The speed of lightning is so great, that it would go 480 times round
the earth in one minute: whereas, thunder would go scarcely 13 miles in
the same space of time.
Q. _Can we not tell the DISTANCE of a thunder-cloud, by observing the
interval which elapses between the flash and the peal?_
A. Yes; the flash is _instantaneous_, but the thunder will take a whole
_second of time_ to travel 380 yards: hence, if the flash is 5 seconds
before the thunder, the cloud is 1900 yards off.
(i. e. 380 × 5 = 1900 yards.)
Q. _What PLACES are most DANGEROUS to be in, during a STORM?_
A. It is very dangerous to be near a tree, or lofty building; it is
dangerous also, to be near a river, or any running water.
Q. _Why is it DANGEROUS to be NEAR a TREE, or lofty building, during a
thunder-storm?_
A. Because a tall pointed object, (like a tree or spire,) will
frequently _discharge_ a lightning-cloud; and then the electric fluid
_will pass down it_, in its way to the earth.
Q. _How can a TREE or SPIRE DISCHARGE a lightning-cloud?_
A. A lightning-cloud (floating over a _plain_) may be _too far off_ to
be discharged by it; but as a tree, or spire, would _shorten_ the
distance between the cloud and its conductor, it might no longer be too
far off a conductor to be discharged.
Q. _Is not air a CONDUCTOR of lightning?_
A. No; dry air is _not_ a conductor of lightning; and therefore, the
flash _rends it in twain_, to get to some conductor.
Q. _Why would it be dangerous to stand near a tree or spire, while
lightning is passing down it?_
A. Because the electric fluid (called lightning) always rushes down the
_outside_ of the tree or spire; and if any one were standing near, might
pass through _him_, and kill or maim him.
Q. _Does lightning go through the inside or outside of a tree?_
A. It rolls down the _outside_ of a _tree_; but passes through the
_inside_ of a _man_.
Q. _Why does lightning pass down the OUTSIDE of a tree?_
A. Lightning always makes choice of the best conductors; and the
_outside_ of a tree is a better conductor than the inside.
Q. _Why does lightning pass through the INSIDE of a man?_
A. As the _fluids_ of the human body make a better conductor than the
_skin_, therefore lightning passes _through_ a man, and not down the
skin.
Q. _Why is it DANGEROUS to be near a deep RIVER, or any other running
water, during a thunder-storm?_
A. Because running water is a good conductor; and lightning always takes
in its course the _best conductors_.
Q. _Why is it dangerous for a man to be near water, in a thunder-storm?_
A. Because the _height of a man_ may be sufficient to discharge a cloud:
and (if there were no _taller_ object nigh) the lightning might make the
_man_ its conductor to the water.
Q. _Why is it DANGEROUS to RING CHURCH-BELLS during a thunder-storm?_
A. For two reasons: 1st--Because the steeple may _discharge_ the
lightning-cloud, in consequence of its mere _height_.
2ndly--The swinging of the bells causes _a current of air_, which
collects electric fluid.
Q. _Why is it unsafe to RUN or DRIVE FAST during a thunder-storm?_
A. The rapid motion of running causes a _current of air_, which collects
electric fluid, and is often fatal.
Q. _What PARTS of a DWELLING are most DANGEROUS during a thunder-storm?_
A. The fire-place, (especially if the fire be _lighted_); the attics and
cellar. It is also dangerous to sit close by the walls; to ring the
bell; or to bar the shutters, during a thunder-storm.
Q. _Why is it DANGEROUS to sit BEFORE a FIRE, during a thunder-storm?_
A. Because the heated air and soot are conductors of lightning;
especially when connected with such excellent conductors as the stove,
fender, and fire-irons.
Q. _Why are the ATTICS and CELLAR DANGEROUS, during a thunder-storm?_
A. Lightning sometimes passes _from the clouds_ to the earth, and
sometimes _from the earth_ to the clouds; and therefore, the _middle
story_ of a house is always the safest to be in, during a thunder-storm.
Q. _When does lightning pass FROM THE EARTH to the CLOUDS?_
A. When the clouds are in a "negative" state of electricity.
Q. _When does lightning pass FROM THE CLOUDS to the EARTH?_
A. When the clouds are in a "positive" state of electricity.
Q. _What is meant by the clouds being in a "positive state of
electricity?"_
A. When the clouds contain _more_ electric fluid than they _generally_
do, they are said to be in a _positive_ state of electricity.
Q. _What is meant by the clouds being in a "negative state of
electricity?"_
A. When the clouds contain _less_ electric fluid than they _ought_ to
do, they are said to be in a _negative_ state of electricity.
Q. _Does the flash proceed from a negative or positive body?_
A. Always from a _positive_ body, or one over-burdened with electric
fluid.
Q. _When lightning flashes from the earth to the clouds, what is the
flash called?_
A. It is called the "returning stroke;" because the earth (being
over-burdened with electric fluid) _returns_ the surplus quantity to the
clouds.
Q. _Why is it DANGEROUS to lean BACK AGAINST A WALL during a
thunder-storm?_
A. Because the electric fluid sometimes runs down the _wall_ of a house
or room; and (as a man is a better conductor than a brick wall), would
make _him_ its path, and injure him.
Q. _Why is it dangerous to RING a BELL during a thunder-storm?_
A. Bell-wire is an _excellent conductor_; and (if a person were to touch
the bell-handle), the electric fluid, passing down the wire, might run
through his hand and injure it.
Q. _Why would the lightning run through a man touching a bell-handle?_
A. Because the human body is a better conductor than the _wall_ (between
the bell-handle and the floor); and as lightning always chooses the
_best_ conductors for its path, it would (in this case) pass through the
_man_, and injure him.
Q. _Why is it DANGEROUS to BAR a SHUTTER during a thunder-storm?_
A. The iron shutter-bar is an _excellent conductor_; and (if a person
were touching the bar), the electric fluid passing down it, might run
from the bar _through the person touching it_, and injure him.
Q. _Why is it dangerous to be in a CROWD during a thunder-storm?_
A. For two reasons. 1st--Because a _mass_ of people form a _better
conductor_ than an individual: and
2ndly--The _vapour_ from a crowd _increases the danger_ of such a place.
Q. _Why is a MASS of bodies a better conductor than a single body?_
A. _Each_ living body is a _conductor of electricity_; and a connected
_mass_ of such conductors is more likely to be struck, than a _single
individual_.
Q. _Why is the danger increased by the_ VAPOUR _which rises from a
crowd?_
A. _Vapour_ is a conductor, and therefore, may determine the shock;
especially when connected with so many living bodies.
Q. _Why is a THEATRE dangerous, during a thunder-storm?_
A. Because the _crowd assembled_ there, and the _great vapour_ arising
from so many living bodies, render a theatre an _excellent conductor of
lightning_.
Q. _Why is a_ FLOCK _of sheep in greater danger than a smaller number?_
A. Because _each_ sheep is a _conductor_ of lightning, and the _greater
the number_, the _better its conducting power_; besides, the _vapour_
arising from a flock of sheep _increases its conducting power_, and its
danger.
Q. _Why is a HERD of cattle in danger during a storm?_
A. 1st--The _number_ of living bodies increases the conducting power of
the _animal fluids_: and
2ndly--The _vapour_ arising from a herd is also a good conductor.
Q. _If a person be ABROAD in a thunder-storm, what place is the SAFEST?_
A. Any spot about 20 or 30 feet from some tall tree or building; unless
that spot be near to running water.
Q. _Why would it be safe to stand 20 or 30 feet from some tall tree, in
a thunder-storm?_
A. Because the lightning would always choose the _tall tree_ as a
conductor, rather than the _shorter man_; and he would not be
sufficiently near the tree, to be injured by the electric current
passing down it.
Q. _If a person be in A CARRIAGE in a thunder-storm, in what way can he
travel most SAFELY?_
A. He should not lean _against_ the carriage; but sit upright, without
touching any of the four sides.
Q. _Why should not a person lean AGAINST the carriage in a storm?_
A. Because the electric fluid might run down the sides of the carriage;
and (if a person were leaning against the sides), would make choice of
_him_ for a conductor, and perhaps destroy life.
Q. _If a person be in A HOUSE during a thunder storm, what place is
SAFEST?_
A. Any room in the _middle story_. The _middle_ of the room is best;
especially if you place yourself on a mattrass, bed, or hearth-rug.
Q. _Why is the MIDDLE STORY of a house SAFEST in a thunder-storm?_
A. Because (even if the fluid _struck_ the house), its strength would be
exhausted before it reached the middle story.
Q. _Why is the MIDDLE of the ROOM more SAFE, than any other part of it,
in a thunder-storm?_
A. Because, if the lightning came into the room at all, it would come
down the _chimney_ or _walls_ of the room; and therefore, the further
distant from these, the better.
Q. _Why is a MATTRASS BED, or HEARTH-RUG a good security against injury
from lightning?_
A. Because they are all _non-conductors_; and, as lightning always takes
in its course the _best_ conductors, it would not select such things as
these.
Q. _Is it better to be WET or dry during a storm?_
A. To be _wet_: if a person be in the open field, the best thing he can
do, is to stand about 20 feet from some tree, and get _completely
drenched to the skin_.
Q. _Why is it better to be WET than dry?_
A. Because the _wet clothes_ would form a far _better conductor_ than
the _fluids of our body_; and, lightning would roll down the wet
clothes, _without touching our body at all_.
Q. _What is the SAFEST thing a person can do to avoid injury from
lightning?_
A. He should draw his bedstead into the middle of his room, commit
himself to the care of God, and go to bed; remembering that our Lord has
said, "The very hairs of your head are all numbered."
Q. _What is a LIGHTNING-CONDUCTOR?_
A. A metal rod fixed in the earth, running up the whole height of a
building, and rising in a point above it.
Q. _What metal is the best for this purpose?_
A. Stout copper wire.
Q. _Why is COPPER wire better than iron?_
A. 1st--Because copper is a better conductor than iron:
2ndly--It is not so easily fused or melted: and
3rdly--It is not so much injured by weather.
Q. _What is the GOOD of a lightning-conductor?_
A. Metal wire is a most excellent conductor; and as the lightning makes
choice of the _best conductors_, it would run down the _metal wire_,
rather than the _bricks_ of the building.
Q. _How far will the beneficial influence of a lightning-conductor
extend?_
A. It will protect a circumference all round, the diameter of which is
(at least) 4 times as long as that part of the rod, which _rises above
the building_.
Q. _Give me an example._
A. If the rod rise 2 feet above the house, it will protect the building
for (at least) 8 feet all round.
Q. _Why are not lightning-conductors more generally used?_
A. Because they are often productive of more harm than good.
Q. _How can lightning-conductors be productive of HARM?_
A. If the rod be _broken_ by weather or accident, the electric fluid
(being obstructed in its path) will rend the building into fragments.
Q. _Is there any OTHER evil to be apprehended from a lightning rod?_
A. Yes; if the rod be not big enough to conduct the _whole_ current to
the earth, the lightning will _fuse_ the metal, and greatly injure the
building.
Q. _How stout is it needful for the copper wire to be, that it may
conduct the fluid safely to the earth?_
A. It should be (at least) _one inch_ in diameter.
Q. _Why does LIGHTNING sometimes KNOCK DOWN HOUSES and churches?_
A. The steeple, or chimney is first struck; the lightning then darts to
the iron bars and cramps employed in the building; and (as it darts from
bar to bar) shatters to atoms the bricks and stones, which oppose its
progress.
Q. _Can you tell me how St. Bride's Church (London) was nearly destroyed
by lightning, about 100 years ago?_
A. The lightning first struck the metal vane, and ran down the rod; it
then darted to the iron cramps, employed to support the building; and
(as it flew from bar to bar) smashed the stones of the church, which lay
between.
Q. _Why did the lightning fly about from place to place, and not pass
down in a straight course?_
A. Because it always takes in its course the _best conductors_; and will
fly both right and left, in order to reach them.
Q. _Why does LIGHTNING turn MILK SOUR?_
A. Lightning causes the gases of the air (through which it passes) to
_combine_, and thus produces a poison, called _nitric acid_; some small
portion of which, mixing with the milk, turns it sour.[2]
(N. B. Sometimes, the mere _heat_ of the air, during the storm, turns
milk sour.)
[2] The air is composed of two gases, called oxygen and hydrogen,
_mixed_ together, but _not combined_. If oxygen is _combined_ with
nitrogen, it produces five deadly poisons, viz.--nitrous oxide, nitric
oxide, hyponitrous acid, nitrous acid, and nitric acid, according to the
proportion of each gas in the combination.
Q. _What is the difference between COMBINING and MIXING?_
A. When different ingredients mingle _without undergoing any chemical
change_, they are said to be _mixed_; but when the natural properties of
each are _altered by the union_, then those ingredients are said to be
_combined_.
Q. _Give me an example._
A. If different coloured sands be shaken together in a bottle, the
various grains will _mix_ together, but not combine: but if water be
poured on quick lime, the water will _combine_ with the lime, and not
mix with it.
Q. _Why are the different grains of sand said to be MIXED, when they are
shaken together?_
A. Because they are mingled together, but the property of each grain
remains the _same as it was before_.
Q. _Why is water poured on lime, said to COMBINE with it?_
A. Because the properties, both of the water and the lime, are _altered_
by the mixture: the lime alters the character of the water, and the
water alters the character of the lime.
Q. _Do oxygen and nitrogen COMBINE, or only MIX together, in common
atmospheric air?_
A. They only _mix_ together, as grains of sand would do, when shaken in
a bottle. When oxygen and nitrogen _combine_, they do not constitute
_air_, but acid _poisons_.
Q. _Why does LIGHTNING turn BEER SOUR, although contained in a close
cask?_
A. If the beer be _new_, and the process of fermentation not complete,
lightning will so _accelerate_ the process, as to turn the liquor sour.
Q. _Why is NOT old beer and strong PORTER made SOUR by lightning?_
A. Because the _fermentation is complete_ already; and, therefore, is
not affected by electrical influence.
Q. _Why is METAL sometimes FUSED by lightning?_
A. Because the dimension of the metal is _too small_, to afford a path
for the electric current.
Q. _Why does LIGHTNING PURIFY the AIR?_
A. For two reasons: 1st--Because the oxygen and nitrogen of the air
_combine_,[3] and produce "nitric acid:"
2ndly--Because the agitation of the storm _stirs up the air_.
[3] The oxygen and hydrogen are not _combined_, but simply _mixed_ in
the ordinary air; but the lightning causes the mixed elements to
_combine_.
Q. _How does the production of nitric acid purify the air?_
A. Nitric acid acts very powerfully in _destroying exhalations_, arising
from putrid vegetable and animal matters.
Q. _Why is LIGHTNING more common in SUMMER and AUTUMN, than in spring
and winter?_
A. The heat of summer and autumn produces _great evaporation_; and the
conversion of _water to vapour_, always develops _electricity_.
Q. _Why does a THUNDER-STORM generally follow very DRY weather, and
rarely succeeds continued WET?_
A. The clouds are _always_ charged with electricity; but _dry air_
(being a non-conductor), will not conduct the surplus fluid from the
clouds to the earth: so it violently _rends the dry air_ with a flash,
in order to relieve the cloud, and reach the earth.
Q. _What is the general DIRECTION of a THUNDER-STORM?_
A. Either from east to west; or else from north to south.
Q. _Why is ELECTRICITY excited by FRICTION?_
A. Electricity, like heat, exists in _all_ matter; but is often in a
_latent state_: friction _disturbs_ it, and brings it into active
operation. (see p. 31.)
Q. _Why is a TREE sometimes SCORCHED by lightning, as if it had been set
on fire?_
A. Lightning scorches it by its own _positive heat_, just the same as
fire would.
Q. _Why is the BARK of a TREE often ripped quite off by a flash of
lightning?_
A. As the lightning runs down the tree, it develops the latent heat so
_rapidly_, that it carries the bark of the tree along with it, while it
seeks to escape.
Q. _Why are BOUGHS of TREES broken off by lightning?_
A. The _mechanical force_ of lightning is very great; and when the flash
strikes a tree, it will often break off the boughs by the _force_ with
which it strikes against it.
Q. _Why is an electric shock felt MOST at the ELBOW JOINT?_
A. Because the path of the fluid is _obstructed by the joint_: and the
shock felt at the elbow is caused by the fluid _leaping from one bone to
another_.
CHAPTER III.
Q. _What is the third chief source of heat?_
A. CHEMICAL ACTION.
Q. _What is meant by chemical action being the source of heat?_
A. Many things, when their chemical constitution is changed, (either by
the abstraction of some of their gases, or by the combination of others
not before united,) evolve _heat_, while the change is going on.
Q. _Explain by illustration what you mean._
A. Water is cold, and sulphuric acid is cold; but if these two _cold_
liquids be mixed together, they will produce _boiling heat_.
Q. _Why will COLD WATER, mixed with SULPHURIC ACID, produce heat?_
A. Because water (being _lighter_ than sulphuric acid), is _condensed_
by the heavier liquid; and its heat is _squeezed out_, as water from a
sponge.
Q. _Why does COLD WATER, poured on LIME, make it intensely HOT?_
A. The heat is evolved by the chemical action, produced by the cold
water combining with the lime.
Q. _Where does the heat come from?_
A. It was in the water and lime before; but was in a _latent state_.
Q. _Was there heat in the cold water and lime, before they were mixed
together?_
A. Yes. _All_ bodies contain heat; the coldest ice, as well as the
hottest fire.
Q. _Is there HEAT even in ICE?_
A. Yes. But it is _latent_, (i. e. not perceptible to our senses).[4]
[4] Latent, from the Latin word, Lateo, (to lie hid.)
Q. _How do you know there is heat, if you cannot perceive it?_
A. Thus:--Ice is 32° by the thermometer; but if ice be _melted_ over a
fire, (though 140° of heat are thus absorbed,) it will feel no _hotter_
than it was before. (_i. e. it will be only 32°, and not 172°_)[5].
[5] 32°, i. e. 32 degrees; 140°, i. e. 140 degrees, &c.
Q. _What becomes of the 140°, which went into the ice to melt it?_
A. It is hidden in the water; or (to speak more scientifically) it is
stored up in a _latent state_.
Q. _How much heat may be thus secreted or made latent?_
A. _All_ things contain a vast quantity of latent heat; but, as much as
1140° of heat may remain latent in _water_.
Q. _How can 1140° of heat be added to water, without being perceptible
to our feelings?_
A. 1st--140° of heat are hidden in the water, when ice is melted by the
sun or fire.
2ndly--1000° more of heat are secreted, when water is converted into
steam. Thus, before ice is converted into steam, 1140° of heat become
_latent_.[6]
[6] Thus, one pint of boiling water, (212° according to the
thermometer,) will make 1800 pints of steam; but the steam is no hotter
to the touch than boiling water, both are 212°: therefore, when water is
converted into steam, 1000° of heat become latent. Hence, before ice is
converted to steam, it must contain 1140° of latent heat.
Q. _Can we be made to FEEL the heat of ICE or snow?_
A. Yes. Into a pint of snow put half as much salt; then plunge your hand
into the liquid; and it will feel so intensely cold, that the snow
itself will seem quite _warm_ in comparison to it.
Q. _Is SALT and SNOW really COLDER than snow?_
A. Yes, many degrees; and by dipping your hand into the mixture
_first_, and into snow _afterwards_, the mere snow will seem to be
comparatively warm.
Q. _What is FIRE?_
A. Combustion is another instance of heat, arising from chemical action.
Q. _What two things are essential to produce combustion?_
A. Fuel and air.
Q. _What are the elements of fuel?_
A. As bread is a compound of flour, yeast, and salt; so fuel is a
compound of hydrogen and carbon.
Q. _What are the ELEMENTS of atmospheric AIR?_
A. The air is a compound of oxygen and nitrogen _mixed_ together; in the
proportion of five gallons of nitrogen, to one of oxygen.
Q. _What is CARBON?_
A. The solid part of fuel. It abounds also in all animal bodies, earths,
and minerals.
Q. _Mention some different SPECIES of CARBON._
A. Common charcoal, lamp-black, coke, black lead, and the diamond, are
all varieties of carbon.
Q. _What is HYDROGEN?_
A. An inflammable gas. The gas used in our streets, is only the hydrogen
gas _driven out of coals by heat_.
Q. _What are the peculiar characteristics of hydrogen gas?_
A. Though this gas _itself_ will _burn_, yet a candle will _not_ burn
when immersed in it; nor can an animal live in it. Hydrogen gas is the
lightest of all known substances.[7]
[7] Hydrogen gas may be made thus:--Put some pieces of zinc or iron
filings into a glass: pour over them a little sulphuric acid (vitriol),
diluted with twice the quantity of water; then cover the glass over for
a few minutes, and hydrogen gas will be given off.
EXP. If a flame be put into the glass, an EXPLOSION will be made.
If the experiment be tried in a phial, which has a piece of tobacco-pipe
run through the cork; and a light held a few moments to the top of the
pipe, a FLAME will be made.
If a balloon be held over the phial, (so that the gas can inflate it,)
the balloon will ascend in a very few minutes.
Q. _What is OXYGEN?_
A. A gas, much heavier than hydrogen; which gives brilliancy to flame,
and is essential to animal life.[8]
[8] Oxygen gas is much more troublesome to make than hydrogen. The
_cheapest_ plan is to put a few ounces of manganese (called the black
oxide of manganese) into an iron bottle, furnished with a bent tube;
set the bottle on a fire till it becomes red hot, and put the end of the
tube into a pan of water. In a few minutes, bubbles will rise through
the water; these bubbles are oxygen gas.
These bubbles may be collected thus:--Fill a common bottle with water;
hold it topsy-turvy over the bubbles which rise through the pan, but be
sure the mouth of the bottle be held _in the water_. As the bubbles rise
into the bottle, the water will run out; and when all the water has run
out, the bottle is full of gas. Cork the bottle while the _mouth remains
under water_; set the bottle on its base; cover the cork with lard or
wax, and the gas will keep till it be wanted.
N. B. The _quickest_ way of making oxygen gas, is to rub together in a
mortar half an ounce of oxide of copper, and half an ounce of chlorate
of potassa. Put the mixture into a common oil flask, furnished with a
cork which has a bent tube thrust through it. Heat the bottom of the
flask over a candle or lamp; and when the mixture is red hot, oxygen gas
will be given off. Note--the tube must be immersed in a pan of water,
and the gas collected as before.
(Chlorate of potassa may be bought at any chemist's; and oxide of copper
may be procured by heating a sheet of copper red hot, and when cool,
striking it with a hammer: the scales that peel off, are oxide of
copper.)
EXP. Put a piece of red hot charcoal, (fixed to a bit of wire,) into
your bottle of oxygen gas; and it will throw out most dazzling sparks of
light.
Blow a candle out; and while the wick is still red, hold the candle (by
a piece of wire,) in the bottle of oxygen gas; the wick will instantly
ignite, and burn brilliantly.
(Burning sulphur emits a _blue_ flame, when immersed in oxygen gas.)
Q. _What is NITROGEN?_
A. Nitrogen is another invisible gas. It _will not_ burn, like hydrogen;
and an animal cannot live in it: it abounds in animal and vegetable
substances, and is the chief ingredient of the common air.[9]
[9] Nitrogen gas may easily be obtained thus:--Put a piece of burning
phosphorus on a little stand, in a plate of water; and cover a bell
glass over. (Be sure the edge of the glass stands _in the water_.) In a
few minutes the air will be decomposed, and nitrogen alone remain in the
bell glass.
(N.B. The white fume which will arise and be absorbed by the water in
this experiment, is phosphoric acid; i. e. phosphorus combined with
oxygen of the air.)
Q. _Why is there so much nitrogen in the air?_
A. In order to _dilute_ the oxygen. If the oxygen were not thus diluted,
fires would burn out, and life would be exhausted too quickly.
Q. _What three elements are necessary to produce COMBUSTION?_
A. Hydrogen gas, carbon, and oxygen gas; the two former in the _fuel_,
and the last in the _air_ which surrounds the fuel.
Q. _What causes the combustion of the fuel?_
A. The hydrogen gas of the fuel being set free, and excited by a piece
of lighted paper, instantly _unites_ with the _oxygen of the air_, and
makes a yellow flame: this flame heats the _carbon of the fuel_,
which also unites with the oxygen of the air, and produces _carbonic
acid gas_.
Q. _What is carbonic acid gas?_
A. Only carbon (or charcoal) combined with oxygen gas.
Q. _Why does FIRE produce HEAT?_
A. 1st--By liberating _latent heat_ from the air and fuel: and
2ndly--By throwing into _rapid motion_ the _atoms of matter_.
Q. _How is latent HEAT liberated by COMBUSTION?_
A. When the _oxygen_ of the air combines with the _hydrogen_ of the
fuel, the two gases _condense into water_; and latent heat is _squeezed
out_, as water from a sponge.
Q. _How are the ATOMS OF MATTER DISTURBED by COMBUSTION?_
A. 1st--When _hydrogen_ of fuel and _oxygen_ of air _condense into
water_, a _vacuum_ is made; and the air is disturbed, as a _pond_ would
be, if a pail of water were taken out of it: and
2ndly--When the _carbon_ of fuel and _oxygen_ of air _expand into
carbonic acid gas_, the air is _again_ disturbed, as it would be by
the explosion of _gunpowder_.
Q. _How does fire condense HYDROGEN and OXYGEN into WATER?_
A. The _hydrogen of fuel_ and _oxygen of air_ (liberated by combustion)
combining together, _condense into water_.
Q. _How does fire expand CARBON into CARBONIC ACID GAS?_
A. The _carbon of fuel_ and _oxygen of air_ (combining together in
combustion) expand into a gas, called _carbonic acid_.
Q. _Why is a FIRE (after it has been long burning) RED HOT?_
A. When coals are heated _throughout_, the carbon is so completely mixed
with the oxygen of the air, that the _whole surface is in a state of
combustion_, and therefore _red hot_.
Q. _In a BLAZING fire, why is the UPPER surface of the COALS BLACK, and
the LOWER surface RED?_
A. Carbon (being very solid) requires a great degree of heat to make it
unite with the oxygen of the air. When fresh coals are put on, their
_under_ surface is heated before the upper surface; and one is _red_ (or
in a state of combustion), while the other is _black_.
Q. _Which burns the quicker, a BLAZING fire, or a RED HOT one?_
A. A _blazing_ fire burns out the fuel quickest.
Q. _Why do BLAZING COALS BURN QUICKER than red hot ones?_
A. In red hot coals, only the _mere surface_ is in a state of
combustion, because the carbon is _solid_; but in a _blazing_ fire,
(where the gases are escaping), the _whole volume of the coal
throughout_ is in a state of decomposition.
Q. _What is SMOKE?_
A. _Unconsumed_ parts of fuel (principally carbon), separated from the
solid mass, and carried up the chimney by the current of hot air.
Q. _Why is there MORE SMOKE when COALS are FRESH added, than when they
are red hot?_
A. Carbon (being solid), requires a great degree of heat to make it
unite with oxygen, (or, in other words, to bring it into a state of
perfect combustion): when coals are fresh laid on, _more carbon is
separated_ than can be _reduced to combustion_; and so it flies off in
smoke.
Q. _Why is there so LITTLE SMOKE with a RED HOT FIRE?_
A. When a fire is red hot, the _entire surface_ of the coals is in a
_state of combustion_; so a very little flies off unconsumed, as smoke.
Q. _Why are there DARK and BRIGHT SPOTS in a CLEAR cinder FIRE?_
A. Because the _intensity_ of the combustion is _greater in some parts_
of the fire, than it is in _others_.
Q. _Why is the intensity of the combustion so unequal?_
A. Because the air flies to the fire in various and unequal currents.
Q. _Why do we see all sorts of GROTESQUE FIGURES in hot COALS?_
A. Because the _intensity_ of combustion is so _unequal_, (owing to the
gusty manner in which the air flies to the fuel; and the various shades
of red, yellow, and white heat mingling with the black of the unburnt
coal), produce strange and fanciful resemblances.
Q. _Why does PAPER BURN more readily than wood?_
A. Merely because it is of a _more fragile texture_; and, therefore, its
component parts are more easily heated.
Q. _Why does WOOD BURN more readily than coal?_
A. Because it is not so _solid_; and, therefore, its elemental parts are
more easily separated, and made hot.
Q. _When a FIRE is LIGHTED, why is PAPER laid at the BOTTOM, against the
grate?_
A. Because paper (in consequence of its fragile texture), so very
readily catches fire.
Q. _Why is WOOD laid on the top of the paper?_
A. Because wood, (being more _substantial_), _burns longer_ than
paper; and, therefore, affords a _longer contact of flame_ to heat the
coals.
Q. _Why would not paper do without wood?_
A. Because paper burns out so _rapidly_, that it would not afford
sufficient _contact of flame_ to heat the coals to combustion.
Q. _Why would not WOOD do WITHOUT shavings, straw, or paper?_
A. Because wood is too _substantial_ to be heated into combustion, by
the flame issuing from a mere _match_.
Q. _Why would not the paper do as well, if placed on the TOP of the
coals?_
A. As every blaze _tends upwards_, if the paper were placed on the _top_
of the fire, its blaze would afford _no contact of flame_ to fuel lying
_below_.
Q. _Why should COAL be placed ABOVE the wood?_
A. As every flame tends _upwards_, if the wood were _above the coal_,
the _flame_ would not rise _through the coal_ to heat it.
Q. _Why is a FIRE KINDLED at the LOWEST BAR of a grate?_
A. As every flame tends _upwards_; when a flame is made at the _bottom_
of a fire, it _ascends through the fuel_ and heats it: whereas, if the
fire were lighted from the _top_, the flame would _not come into
contact_ with the fuel piled below.
Q. _Why does COAL make such EXCELLENT FUEL?_
A. Because it is so very _hard_ and _compact_, that it burns away very
slowly.
Q. _Why will CINDERS become RED HOT, quicker than COALS?_
A. Because they are _more porous_ and _less solid_; and are, therefore,
sooner reduced to a state of combustion.
Q. _Why will not IRON CINDERS burn?_
A. Iron cinders are _cinders saturated with oxygen_; they are unfit for
fuel, because they can imbibe _no more oxygen_, being saturated already.
Q. _Why are CINDERS lighter than COALS?_
A. Because their vapour, gases, and volatile parts, have been driven off
by _previous combustion_.
Q. _Why will not STONES do for fuel, as well as COALS?_
A. Because they contain no _hydrogen_ (or inflammable gas) like coals.
Q. _Why will not WET KINDLING light a fire?_
A. 1st--Because the moisture of the wet kindling prevents the _oxygen of
the air from getting to the fuel_ to form it into carbonic acid gas:
and
2ndly--The heat of the fire is perpetually _drawn off_, by the
conversion of _water_ into _steam_.
Q. _Why does DRY wood burn BETTER than GREEN?_
A. 1st--Because no heat is _carried away_, by the conversion of _water
into steam_: and
2ndly--The pores of dry wood _are filled with air_, which supply the
fire with oxygen.
Q. _Why do TWO pieces of WOOD burn BETTER than ONE?_
A. 1st--Because they help to entangle the _heat of the passing smoke_,
and _throw it on the fuel_: and
2ndly--They help to _entangle the air_ that passes over the fire, and
create a kind of _eddy_ or draught.
Q. _Why does SALT CRACKLE when thrown into a FIRE?_
A. Salt contains _water_; and the _cracking_ of the salt is owing to the
sudden _conversion of the water into steam_.
Q. _Why will not wood or paper burn, if they are steeped in a solution
of POTASH, phosphate of LIME, or AMMONIA (hartshorn)?_
A. Because any "al'kali" (such as potash) will _arrest the hydrogen_ (as
it escapes from the fuel), and prevent its _combination_ with the
_oxygen of air_.
Q. _What is an al'kali?_
A. The con'verse of an _acid_; as _bitter_ is the con'verse of _sweet_,
or _insipid_ the con'verse of _pungent_.
Q. _Why does a JET of FLAME sometimes burst into the room THROUGH THE
BARS OF A STOVE?_
A. The iron bars conduct heat to the _interior of some lump of coal:_
and its volatile gas (bursting through the weakest part) is kindled by
the glowing coals over which it passes.
Q. _Why is this JET sometimes of a GREENISH YELLOW colour?_
A. When a lump of coals lies _over the hot bars_, or the coals below it
are not _red hot_, the gas which bursts from the lump _escapes unburnt_,
and is of a greenish colour.
Q. _Why does the gas escape UNBURNT?_
A. Because neither the _bars_ nor _coals_ (over which it passes) are
_red-hot_.
Q. _Why does a BLUISH FLAME sometimes flicker on the surface of hot
cinders?_
A. Gas from the hot coals _at the bottom of the grate_ mixing with the
_carbon of the coals above_, produces an inflammable gas (called
carbonic oxide), which burns with a blue flame.
Q. _Why is the FLAME of a good fire YELLOW?_
A. Because both the hydrogen and carbon of the fuel are in a state of
_perfect combustion_. It is the _white heat of the carbon_, which gives
the pale yellow tinge to the flaming hydrogen.
Q. _What is LIGHT?_
A. Rapid _undulations_ of a fluid called _ether_, striking on the eye.
Q. _How does COMBUSTION make these undulations of LIGHT?_
A. The atoms of matter (set in motion by heat) _striking against_ this
ether, produce _undulations_ in it; as a _stone_ thrown into a stream,
would produce undulations in the _water_.
Q. _How can UNDULATIONS of ether produce LIGHT?_
A. As _sound_ is produced by _undulations of air_ striking on the
_ear_; so _light_ is produced by undulations of _ether_ striking on the
_eye_.
Q. _What is ETHER?_
A. A very subtile fluid, which pervades and surrounds _every thing we
see_.
Q. _Mention a simple experiment to prove that LIGHT is produced by rapid
MOTION._
A. When a fiddle-string is _jerked_ suddenly, its rapid vibration
produces a grey _light_; and when a carriage wheel revolves very
quickly, it sends forth a similar light.
Q. _Does HEAT ALWAYS produce LIGHT?_
A. No: the heat of a stack of hay, or reeking dunghill, though very
_great_, is not sufficient to produce _light_.
Q. _Why is a YELLOW FLAME brighter than a RED HOT COAL?_
A. Because _yellow rays_ always produce the greatest amount of _light_;
though _red rays_ produce the greatest amount of _heat_.
Q. _Why is the LIGHT of a fire MORE INTENSE sometimes than at others?_
A. The _intensity_ of fire-light depends upon the _whiteness_ to which
the carbon is reduced, by combustion. If the carbon be _white hot_, its
_combustion is perfect_, and the light intense; if not, the light is
obscured by _smoke_.
Q. _Why will not CINDERS BLAZE, as well as FRESH coals?_
A. The _flame_ of coals is made chiefly by _hydrogen gas_. As soon as
this gas is consumed, the hot cinders produce only an _invisible_ gas,
called carbonic acid.
Q. _Where does the hydrogen gas of a fire come from?_
A. The _fuel is decomposed_ (by combustion) into its simple elements,
carbon and hydrogen gas. (see p. 33)
Q. _Why does not a FIRE BLAZE on a FROSTY NIGHT, so long as it does upon
another night?_
A. The air (being very cold) _rushes to the fire so rapidly_, that the
coals burn out _faster_, and the inflammable gas _is sooner consumed_.
Q. _Why does a FIRE burn CLEAREST on a FROSTY night?_
A. Because the volatile gases are quickly consumed; and the solid
carbon _plentifully supplied with air_, to make it burn bright and
intensely.
Q. _Why does a FIRE burn more intensely in WINTER than in SUMMER time?_
A. Because the air is _colder_ in winter, than in summer-time.
Q. _How does the COLDNESS of the air increase the HEAT of a fire?_
A. For two reasons: 1st--Because cold air being more _condensed_ than
hot air, contains a greater _body_: and
2ndly--Cold air _rushes more quickly to the fire_, and supplies more
_oxygen_.
Q. _Why does the SUN, shining on a FIRE, make it DULL, and often put it
out?_
A. 1st--When the sun shines, the air is rarefied; and, therefore, _flows
more slowly to the fire_.
2ndly--As the air is _rarefied_, even that which _reaches_ the fire,
_affords less nourishment_.
Q. _Why does the air flow to the fire more TARDILY for being RAREFIED?_
A. The greater the _contrast_ (between the _external air_, and that
_which has been heated by the fire_) the more _rapid_ will be the
current of air towards that fire.
Q. _Why does rarefied air afford LESS NOURISHMENT to fire, than cold
air?_
A. Because it is _spread out_, (like a piece of gold _beaten into
leaf_); and as a square inch of gold _leaf_ will not contain so much
gold as a square inch of _bullion_--so, a square inch of _rarefied_ air
has less _body_, than a square inch of _cold air_.
Q. _Why does a FIRE burn more fiercely in the OPEN AIR?_
A. 1st--Because the _air out-of-doors_ is more _dense_, than the air
in-doors: and
2ndly--Because air is _more freely supplied_ to a fire out-of-doors.
Q. _Why is the air out-of-doors more DENSE than that in-doors?_
A. Because the circulation is more free; and as soon as any portion has
been _rarefied_, it instantly escapes, and is supplied by _colder
currents_.
Q. _Why does not a FIRE burn so freely in a THAW, as in a FROST?_
A. During a thaw, the air is filled with _vapour_; and, both _moves too
slowly_, and is _too much diluted_ to nourish the fire.
Q. _Why does a FIRE burn so fiercely in WINDY weather?_
A. In windy weather the _air is rapidly changed_, and affords plentiful
nourishment to the fire.
Q. _Why do a pair of BELLOWS get a fire up?_
A. A pair of bellows, (like the wind), _drives the air more rapidly to
the fire_; and the plentiful supply of oxygen soon makes the fire burn
intensely.
Q. _Why is a CANDLE BLOWN OUT by the breath, and not made more intense,
like a fire?_
A. As the flame of a candle is confined to a _very small wick_, it is
_severed_ from it by the breath; and (being unsupported) _must go out_.
Q. _Why is a SMOULDERING WICK sometimes REKINDLED by blowing it?_
A. The breath carries the air to it with _great rapidity_; and the
oxygen of the air kindles the _red hot wick_, as it kindles charred
wood.
Q. _Why is not the red hot wick kindled by the air AROUND it, without
BLOWING it?_
A. Because oxygen is not supplied with sufficient freedom, unless it be
_blown_ to the wick.
Q. _When is this experiment most likely to succeed?_
A. In _frosty_ weather; because the air contains more oxygen then,
_being condensed by the cold_.
Q. _Why does a POKER, LAID ACROSS a dull FIRE, revive it?_
A. For two reasons. 1st--Because the poker _concentrates the heat_, and
therefore increases it: and
2ndly--Because the poker _arrests the air_ which passes over the fire,
and _produces a draught_.
Q. _Why do SEVERAL PIECES of WOOD or coal burn BETTER than ONE?_
A. When there are two or three pieces of wood on a fire, the air
_(circulating round them) produces an eddy_ or draught, which draws up
the fire.
Q. _Why are STOVES fixed on the FLOOR of a room?_
A. In order that the air, _on the lower part of the room_, may be heated
by the fire.
Q. _Would not the air of the lower part of a room be heated equally
well, if the stoves were fixed higher up?_
A. No; the heat of a fire has a very little effect upon the air _below
the level of the grate_; and, therefore, every grate should be as _near
to the floor_ as possible.
Q. _Why are our FEET so COLD when we sit close by a good fire?_
A. As the fire consumes the air which passes over it, _cold air_ rushes
through the crevices of the doors and windows _along the bottom of the
room_ to supply the deficiency; and these currents of cold air, _rushing
constantly over our feet_, deprive them of their warmth.
Q. _If a piece of PAPER be laid FLAT on a clear fire, it will NOT BLAZE,
but CHAR. Why so?_
A. The carbon of a clear fire, being sufficiently hot to unite with the
oxygen of the air, _produces carbonic acid gas_, which soon envelops
the paper laid flat upon the cinders: but carbonic acid gas will not
_blaze_.
Q. _If you BLOW the paper, it will BLAZE immediately. Why so?_
A. By blowing, or opening the door suddenly, _the carbonic acid is
dissipated_, and the paper is instantly fanned into flame.
Q. _Why does WATER EXTINGUISH a FIRE?_
1st--Because the water _forms a coating_ over the fuel, and keeps it
from the air:
2ndly--The conversion of _water into steam_, draws off the _heat_ of the
burning fuel.
Q. _Why does a LITTLE WATER make a fire FIERCER, while a LARGER quantity
of water puts it OUT?_
A. Water is composed of _oxygen and hydrogen_; when, therefore, the fire
can decompose the water into its simple elements, it serves for _fuel_
to the flame.
Q. _How can WATER serve for FUEL to fire?_
A. The _hydrogen_ of the water will burn with a _flame_; and the
_oxygen_ of the water will increase the _intensity_ of that flame.
Q. _If a house be on fire, is too LITTLE water worse than NO water at
all?_
A. Certainly. Unless the water be supplied so plentifully as _to quench
the fire_, it will increase the _intensity_, like fuel.
Q. _When will water EXTINGUISH FIRE?_
A. When the supply is so rapid and abundant, that the fire cannot
_convert it into steam_.
Q. _Does not a very LITTLE water SLACKEN the heat of fire?_
A. Yes, _till it is converted into steam_; but then it increases the
_intensity_ of fire, and acts like fuel.
Q. _Why does the WICK of a candle (when the flame has been blown out)
CATCH FIRE so readily?_
A. As the wick is already _very hot_, a little _extra_ heat will throw
it into flame.
Q. _Why does the EXTRA heat revive the flame?_
A. Because it again liberates the _hydrogen_ of the tallow, and ignites
it.
Q. _Cannot WOOD be made to BLAZE without actual contact with fire?_
A. Yes; if a piece of wood be held _near_ the fire for a little time it
will blaze, even though it does not _touch_ the fire.
Q. _Why will WOOD BLAZE, even if it does not touch the fire?_
A. The heat of the fire _drives out the hydrogen gas_ of the wood; which
is inflamed by contact with the red-hot coals.
Q. _Why will a NEIGHBOUR'S HOUSE sometimes CATCH FIRE, though no flame
of the burning house ever touches it?_
A. The heat of the burning house sets at liberty _the hydrogen gas_ of
the neighbouring wood-work, which is ignited by the flames or red-hot
bricks of the house on fire.
Q. _What is COKE?_
A. Coal freed from its volatile gases, by the action of artificial heat.
Q. _Why do ARNOTT'S STOVES sometimes SMELL so strong of SULPHUR?_
A. The fire is made of coke, which contains sulphur; and, whenever the
draught is not rapid enough _to drive the sulphur up the flue_, it is
emitted into the room.
Q. _What is meant by SPONTANEOUS COMBUSTION?_
A. Ignition produced by the action of _one uninflamed_ body on another.
Q. _Give an example of spontaneous combustion._
A. Goods packed in a warehouse will often catch fire of _themselves_;
especially such goods as cotton, flax, hemp, rags, &c.
Q. _Why do such GOODS sometimes CATCH FIRE of themselves?_
A. Because they are piled together in very _great masses_ in a _damp_
state or place.
Q. _Why does this produce spontaneous combustion?_
A. The damp produces _decay_ or the decomposition of the goods, and the
great heat of the piled-up mass makes the decaying goods _ferment_.
Q. _How does this FERMENTATION produce COMBUSTION?_
A. During fermentation, _carbonic acid gas_ is given off by the
goods,--a slow combustion ensues,--till at length the _whole pile_
bursts into _flame_.
Q. _Why is the HEAT of a LARGE MASS of goods GREATER than that of a
smaller quantity?_
A. Because compression _squeezes out_ heat, as water is squeezed from a
sponge; and as the goods of a large pile are greatly _compressed_, much
of their latent heat is _squeezed out_.
Q. _Why do HAY-STACKS sometimes CATCH FIRE of themselves?_
A. Either because the hay was got up _damp_, or because rain has
penetrated the stack.
Q. _Why will a HAY-STACK CATCH FIRE if the hay be damp?_
A. Damp hay soon _decays_, and undergoes a _state of fermentation_;
during which, _carbonic acid gas_ is given off, and the stack catches
_fire_.
Q. _Why does roasted COFFEE sometimes CATCH FIRE spontaneously?_
A. The _heat_ of coffee is greatly increased by being _roasted_; and the
_carbon of the coffee_ uniting with the _oxygen of the air_, produces
_carbonic acid gas_, and bursts into _flame_.
Q. _Why do old RAGS, used for CLEANING LAMPS and CANDLES, sometimes set
a HOUSE on FIRE?_
A. Because they very readily _ferment_, and (during fermentation) throw
off exceedingly inflammable gases.
(N.B. Lamp-black mixed with linseed oil is more liable to spontaneous
combustion, than anything that servants handle.)
CHAPTER IV.
SMOKE.
Q. _Why does SMOKE ASCEND the chimney?_
A. As the air of the room passes over the fire, it becomes _heated_; and
(being thus made _lighter_,) ascends the chimney, carrying the smoke
with it.
Q. _What is SMOKE?_
A. Small particles of carbon, separated by combustion from the fuel, but
not _consumed_.
Q. _Why do SMOKE and steam CURL, as they ascend?_
A. Because they are moved in a _right line_, and then _pushed on all
sides_; and this forces them into a _circular_ motion.
Q. _What are BLACKS?_
A. When the hot air of the chimney has been cooled by the _external_
air, it can no longer _buoy up_ the solid smoke; so it falls to the
earth in condensed flakes, called "blacks."
Q. _Why are there NO BLACKS in the smoke of a RAILWAY engine?_
A. The smoke of a railway engine consists chiefly of _watery vapour_,
which dissolves in air, as sugar does in water; but the smoke of a
common chimney consists of small fragments of _unburnt fuel_.
Q. _Why does a "COPPER HOLE" DRAW up more fiercely than an OPEN stove?_
A. As the air, which supplies the copper hole, must pass _through the
furnace_, it becomes exceedingly _heated_, and rushes up the chimney
with great violence.
Q. _What produces the ROARING noise made by a COPPER-HOLE fire?_
A. Air rushing rapidly through the crevices of the _iron door_, and up
the _chimney flue_.
Q. _Why is the ROAR LESS, if the copper-hole DOOR be thrown OPEN?_
A. Because _fresh_ air gets access to the fire _more easily_; and as the
air is not so intensely heated, its motion is not so _violent_.
Q. _Why do some CHIMNEYS SMOKE?_
A. If fresh air is not admitted into a room, _as fast as it is consumed
by the fire_, a current of air _will rush down the chimney_ to _supply
the deficiency_, and bring the smoke along with it.
Q. _What prevents air being supplied, as fast as it is consumed by the
fire?_
A. Leather and curtains round the doors; sand-bags at the threshhold and
on the window-frames; and other contrivances to keep out the draught.
Q. _Why is it needful for cold fresh air to be so constantly supplied?_
A. If water be taken with a pail out of a river, _other_ water will rush
towards the hole, as soon as the pail is lifted out; and if air be taken
from a room, (as it is, when some of it goes up the chimney) _other air_
will rush towards the void to fill it up.
Q. _Why will it come down the chimney?_
A. Because if doors and windows are all made _air-tight_, it can get to
the room in no _other_ way.
Q. _What is the best REMEDY in such a case?_
A. The _speediest_ remedy is to open the door or window: but by far the
_best_ remedy is to carry a small tube from the hearth into the external
air.
Q. _Why is that the BEST remedy?_
A. Because the fire will be plentifully supplied with air by the tube;
the doors and windows may all remain air-tight; and we may enjoy a warm
fireside, without the inconvenience of draughts and cold feet.
Q. _Why is a CHIMNEY raised so high above the ROOF?_
A. If it were not so, it would smoke; as all funnels do which are too
short.
Q. _What is meant by the funnel, or flue of a chimney?_
A. That part of a chimney through which _the smoke passes_, is called
the funnel, or flue.
Q. _Why does a CHIMNEY SMOKE, if the funnel be very short?_
A. Because the _draught_ of a short flue _is too slack_ to carry the
smoke up the chimney.
Q. _Why is the DRAUGHT of a SHORT FLUE more SLACK that that of a long
one?_
A. For many reasons. 1st--_The fire is always dull and sluggish_ if the
chimney be too short.
2ndly--The smoke rolls _out_ of the chimney, before it has acquired its
_full velocity_.
3rdly--The wind, rain, and air, have more influence over a _short_
funnel, than over a _long_ one.
Q. _Why is the FIRE always DULL and sluggish if the CHIMNEY-FLUE be very
SHORT?_
A. Because the draught is so bad: and as the rarefied air _passes up the
chimney very tardily_, _fresh air_ flows as tardily _towards the fire_,
to supply it with _oxygen_.
Q. _On what does the INTENSITY of fire depend?_
A. The _intensity_ of fire is always in proportion to the _quantity of
oxygen_ with which it is supplied.
Q. _Why does not SMOKE acquire its full VELOCITY in a SHORT funnel?_
A. Because the _higher_ smoke ascends in a flue, (provided it be clear
and hot) the _faster_ it goes; (as a stone falls faster and faster the
lower it descends): if, therefore, a _funnel be very short_, the smoke
never acquires its full velocity.
Q. _Does the DRAUGHT of a chimney depend on the SPEED of the SMOKE
through the flue?_
A. Yes. The more quickly _hot_ air flies _up the chimney_, the more
quickly _cold_ air will rush _towards the fire_ to supply the place;
and, therefore, the _longer the flue_, the _greater the draught_.
Q. _Why is the DRAUGHT of a LONG FLUE greater than that of a short one?_
A. Because the _higher_ smoke ascends, the _faster_ it goes; (as a stone
falls faster and faster, the nearer it approaches to the earth): if,
therefore, a funnel be _long_, the smoke acquires great _velocity_, and
the _draught_ is great.
Q. _If a CHIMNEY be TOO SHORT, and cannot be lengthened, what is the
best REMEDY to prevent smoking?_
A. To _contract the opening of the chimney_ contiguous to the stove.
Q. _Why will a_ SMALLER OPENING _against the stove_ PREVENT _the_
SMOKING?
A. As all the air (which enters the chimney) _must pass near the fire_,
it will become _greatly heated_, and _rise rapidly_ through the funnel;
and this _increase of heat_ will compensate for the _shortness of the
flue_.
Q. _Why will a_ ROOM SMOKE, _if there be_ TWO FIRES _in it?_
A. Because the _fiercer_ fire will exhaust the most air; and draw from
the _smaller_ one, to supply its demand.
Q. _Why will a chimney_ SMOKE _if there be a_ FIRE _in_ TWO ROOMS
_communicating with each other?_
A. Whenever the _door_ between the two rooms _is opened_, air will rush
from the chimney of the _inferior_ fire, to supply the _other_; and
_both_ rooms will be filled with smoke.
Q. _What is the_ REMEDY _in this case?_
A. Let a tube be carried from the hearth of each stove, into the
external air; and then _each_ fire will be so _well_ supplied, that
neither will need to borrow from the other.
Q. _Why do VESTRY CHIMNEYS so often SMOKE?_
A. Because the wind (striking against the steeple) _is reflected back_;
and tumbles down the vestry chimney, forcing the smoke _into the room_.
Q. _WHAT WINDS make vestry chimneys smoke?_
A. Those from the north-east or south-east; according to the position of
the vestry.
Q. _Why will the EASTERN winds make VESTRIES SMOKE, more than those from
the west?_
A. Because they _strike against the steeple_, and _bound back_ to the
vestry chimney: but _western_ winds cannot rebound over the roof of a
church.
(N. B. The _steeple_ of a church is always due _west_, and the _other_
end of the church due _east_; if, therefore, a _western_ wind rebound,
it would rebound to the _west_, or _away from the church_, and not
towards it.)
Q. _Why does a HOUSE in a VALLEY very often SMOKE?_
A. Because the wind (striking against the surrounding hills) _rebounds
back again upon the chimney_, and destroys its draught.
Q. _What is the common REMEDY in both these cases?_
A. To fix a _cowl_ on the chimney top, to turn like a weather-cock, and
present its back to the wind.
Q. _Why will not a COWL always PREVENT a chimney SMOKING?_
A. If the wind be _strong_, it will keep the _opening_ of the cowl
_towards the steeple or hill_; and then the reflected wind will _blow
into the cowl_, and _down the chimney_.
Q. _As a cowl is such a poor remedy, can any OTHER be devised?_
A. If the chimney flue can be carried _higher_ than the steeple or
hills, no wind can enter the flue.
Q. _Why cannot the wind enter a chimney flue, if it be carried up HIGHER
than the steeple or hills?_
A. Because the reflected wind would strike against the _sides_ of the
chimney-flue, and not pass over the _opening_ at all.
Q. _In what OTHER cases will a CHIMNEY SMOKE?_
A. If both door and chimney be placed on _the same side of a room_, the
chimney will often smoke.
Q. _Why will a CHIMNEY SMOKE, if the DOOR and STOVE are both on the SAME
SIDE?_
A. Because when the door is opened, a current of air will _blow into the
chimney-place_, and drive the smoke into the room.
Q. _What REMEDY can be applied to this evil?_
A. The door must be set _opposite_ to the chimney, or nearly so; and
then the draught from the door _will blow the smoke up the chimney_, and
not into the room.
Q. _Why will a CHIMNEY SMOKE if it NEEDS SWEEPING?_
A. Because the obstruction in the chimney (presented by the loose soot,
to the free passage of the smoke) _delays its current_, and prevents the
draught.
Q. _Why will a CHIMNEY SMOKE, if OUT OF REPAIR?_
A. 1st--Because the _loose mortar and bricks_ obstruct the smoke: and
2ndly--The _cold air_ (oozing through the chinks) _chills the air in the
chimney_, and prevents its ascent.
Q. _Why will an ARNOTT'S STOVE SMOKE, if the joints of the flue do not
fit air-tight?_
A. Because the _cold air_ (which gets through the joints) _chills the
air in the flue_, and prevents its ascent.
Q. _Why does an old fashioned FARM CHIMNEY-PLACE so often smoke?_
A. Because the opening is so _very large_, that much of the air which
goes up the chimney, _has never passed near the fire_; and this cold air
mixing with the other, so _reduces its temperature_, that it ascends
very slowly, and the draught is destroyed.
Q. _Why does a chimney smoke, if the DRAUGHT be SLACK?_
A. Because, unless the current of air up the chimney be very powerful,
it cannot _buoy the smoke up_ through the flue.
Q. _If the opening of a chimney be TOO LARGE, what REMEDY can be
applied?_
A. The chimney-place must be contracted.
Q. _Why will CONTRACTING the chimney-place PREVENT its SMOKING?_
A. As the air will then pass _nearer the fire_, it will be _more
heated_, and fly up the chimney _much faster_.
Q. _Why do almost all CHIMNEYS SMOKE in GUSTY weather?_
A. The gust (blowing the air _away_ from the top of the chimney)
_removes_ (for a time) _all resistance to the smoke_: but when the wind
_lulls_ again, the _resistance of the air suddenly returns_--the
_draught_ is _checked_--and a puff of smoke rushes into the room.
Q. _What is the use of a CHIMNEY-POT?_
A. When the opening of a chimney is _large_, the top must be contracted
by a chimney-pot, in order to increase the draught.
Q. _How does a CHIMNEY-POT INCREASE the DRAUGHT of a chimney?_
A. As the _same quantity_ of hot air has to escape _through a much
smaller opening_, it must pass through more quickly.
Q. _Why do tin BLOWERS help to get a fire up?_
A. Because they compel the air to go _through_ the fire, and not _over_
it; therefore the fire is well supplied with oxygen, and the draught
greatly increased.
Q. _Why does a tin BLOWER INCREASE the DRAUGHT?_
A. As all the air which enters the chimney has to pass _through_ the
fire, it is much hotter, and ascends the chimney very fast; and the
faster the air _flies up the chimney_, the faster it rushes _towards the
fire_ also.
Q. _Why does a parlour often SMELL disagreeably of SOOT in SUMMER-TIME?_
A. The air in the _chimney_ (being _colder_ than the air in the
_parlour_) _descends into the room_, and leaves a disagreeable smell of
soot behind.
Q. _Why are the CEILINGS of PUBLIC OFFICES so BLACK and filthy?_
A. The heated air ascending, carries the dust and fine soot to the
ceiling; where the hot _air_ escapes through the plaster, and _leaves
the soot and dust_ behind.
Q. _Why are SOME parts of the ceiling BLACKER and more filthy than
others?_
A. As the air cannot penetrate the thick _joists_ of the ceiling, _it
passes by those parts_, and deposits its soot and dust on those which
are more penetrable.
Q. _What is CHARCOAL?_
A. Wood which has been exposed to a red heat, till it has been deprived
of all its gases and volatile parts.
Q. _Why is a CHARCOAL FIRE hotter than a wood fire?_
A. Because so large a quantity of _water_ has been abstracted from the
fuel, by the red heat to which it has been already exposed.
Q. _Why does charcoal REMOVE the TAINT of meat?_
A. Because it absorbs all odoriferous effluvia, whether they arise from
putrefying animal or vegetable matter.
Q. _Why is WATER PURIFIED by being filtered through charcoal?_
A. Charcoal absorbs the _impurities_ of the water, and removes all
disagreeable tastes and smells, whether they arise from animal or
vegetable matter.
Q. _Why are water and wine CASKS CHARRED inside?_
A. _Charring_ the inside of the cask reduces it to a _kind of charcoal_;
and charcoal (by absorbing animal and vegetable impurities) keeps the
liquor sweet and good.
Q. _Why does a piece of BURNT BREAD, steeped in impure WATER, make it
fit to drink?_
A. The surface of the bread is reduced to _charcoal_ by being burnt; and
the charcoal surface of the bread _abstracts all the impurities of the
water_, and makes it palatable.
Q. _Why should the TOAST and WATER, placed by the side of the sick, be
made of BURNT BREAD?_
A. The surface of the bread being _reduced to charcoal_ by being burnt,
prevents the water from being affected by the impurities of the sick
room.
Q. _Why are TIMBERS, which are to be exposed to damp, CHARRED?_
A. _Charcoal undergoes no change_ by exposure to air and water;
therefore timber will resist weather _much longer_, after it has been
charred.
CHAPTER V.
LAMPS AND CANDLES.
Q. _Of what are OIL, TALLOW, and WAX composed?_
A. Principally of carbon and hydrogen gas. The _solid_ part is carbon,
the _volatile_ part is gas.
Q. _What is CARBON?_
A. A solid substance, generally of a black colour; well known under the
forms of charcoal, lamp-black, coke, black-lead, &c.
Q. _What is HYDROGEN GAS?_
A. The principal ingredient of water. It is well known in the form of
common _coal gas_: it burns so readily that it used to be called
"inflammable air."[10]
[10] To make hydrogen gas, see p. 34.
Q. _Why does a CANDLE BURN when lighted?_
A. The heat of the lighted wick _decomposes the tallow_ into its
elementary parts of carbon and hydrogen; and the _hydrogen of the
tallow_, combining with the _oxygen of the air_, produces _flame_.
Q. _Why is the FLAME of a candle HOT?_
A. 1st--Because the flame liberates _latent heat_ from the air and
tallow: and
2ndly--It throws into _rapid motion_ the _atoms of matter_.
Q. _How is LATENT HEAT liberated by the flame of a CANDLE?_
A. When the _hydrogen_ of the tallow and _oxygen_ of the air _combine_,
they _condense into water_; and much of their latent heat is _squeezed
out_.
Q. _How are the ATOMS of MATTER disturbed by the flame of a candle?_
A. 1st--When the _hydrogen_ of the tallow and _oxygen_ of the air
_condense into water_, a _vacuum_ is made; and the air is disturbed, as
a _pond_ would be, if a pail of _water_ were taken out.
2ndly--When the _carbon_ of tallow and _oxygen_ of the air expand into
_carbonic acid gas_, the air is _again_ disturbed; in a similar way as
by the explosion of _gunpowder_.
Q. _Why does the flame of a CANDLE produce LIGHT?_
A. The chemical changes made by combustion, excite _undulations of
ether_, which (striking the eye) produce light. (see p. 46.)
Q. _Why is the FLAME of a CANDLE YELLOW?_
A. Only the _outer_ coat of the flame is yellow; the _lower_ part of the
flame is _violet_; and the _inside_ of the flame is _hollow_.
Q. _Why is the outside of the flame YELLOW?_
A. Because the _carbon of the tallow_ (being in a state of _perfect
combustion_) is made white-hot.
Q. _Why is the BOTTOM part PURPLE of the flame of a candle?_
A. The _bottom part_ of the flame is _overladen with hydrogen_, raised
from the tallow by the burning wick; and this _half-burnt gas_ gives a
_purple_ tinge to the flame.
Q. _Why is the INSIDE of the flame of a candle HOLLOW?_
A. Because it is _filled with vapour_, raised from the candle by the
_heat of the wick_.
Q. _Describe the different parts of the FLAME of a common CANDLE._
A. The flame consists of _three cones_. The innermost cone is hollow;
the intermediate cone of a dingy purple hue; and the outside cone is
yellow.
Q. _Why is the intermediate cone of a flame PURPLE, as well as the
BOTTOM of the flame._
A. Because the gases are not in a state of _perfect combustion_; but
contain an _excess of hydrogen_, which gives this cone a purple tinge.
Q. _Why is not the MIDDLE cone in a state of perfect combustion, as well
as the OUTER cone?_
A. Because the outer cone _prevents the oxygen of the air_ from getting
freely to the _middle of the cone_; and without the free access of
oxygen gas, there is no such thing as complete combustion.
Q. _Why does the FLAME of a candle point UPWARDS?_
A. The flame _heats the surrounding air_, which (being hot) _rapidly
ascends_, and drives the flame upwards at the same time.
Q. _Why is the FLAME of a candle POINTED at the top, like a cone?_
A. The _upper_ part of a flame is more _volatile_ than the lower parts;
and as it affords _less resistance to the air_, is reduced to a mere
point.
Q. _Why is the UPPER part of a flame more VOLATILE than the lower
parts?_
A. The _lower_ parts of the flame are laden with unconsumed gas and
watery vapour; which present considerable resistance to the air.
Q. _Why is the FLAME of a candle BLOWN OUT by a puff of breath?_
A. As the flame of a candle is attached to a _very small wick_, a puff
of breath _severs the flame from the wick_; and it goes out for want of
support.
Q. _Why does the FLAME of a candle make a GLASS DAMP, which is held over
it?_
A. The _hydrogen of the tallow_ combining with the _oxygen of the air_,
produce a "watery vapour," which is condensed by the _cold glass_ held
above the flame.
Q. _Why does our hand, held ABOVE a candle, suffer from the heat of the
flame so much more, than when it is placed BELOW the flame, or on ONE
SIDE of it?_
A. Because the hot gases and air (in their ascent) _come in contact_
with the hand placed _above_ the flame: but when the hand is placed
_below_ the flame, or on _one side_, it only feels heat from
_radiation_.
Q. _Why is a RUSH LIGHT extinguished so much more quickly than a
cotton-wicked candle?_
A. As the _rush_ wick is _smooth_ and _hard_, the _mere motion of the
air_ (produced by carrying the candle from one place to another,) is
sufficient to sever the flame from the rush.
Q. _Why is it more difficult to blow out a COTTON wick?_
A. The _cotton_ wick is _quite full of small threads_ or filaments,
which help to _hold the flame on the wick_, like the roots of a tree.
Q. _Why does an EXTINGUISHER put a candle out?_
A. Because the air in the extinguisher _is soon exhausted of its oxygen_
by the flame: and when there is no _oxygen to support it_, the flame
goes out.
Q. _Why does not a candle set fire to a PIECE OF PAPER twisted into an
extinguisher, and used as such?_
A. 1st--Because the flame very soon _exhausts the little oxygen_
contained in the paper extinguisher: and
2ndly--The flame invests the _inside of the paper extinguisher_ with
_carbonic acid gas_, which prevents it from blazing.
Q. _Why is a LONG WICK never upright?_
A. Because it is bent by its own weight.
Q. _Why is a LONG WICK covered with an EFFLORESCENCE at the top?_
A. The knotty or flowery appearance of the top of a wick arises _from an
accumulation of particles partly separated_, but still loosely hanging
to the wick.
Q. _Why is not the END of a long wick BURNT OFF, as it hangs over the
flames?_
A. Because the length of the wick so diminishes _the heat of the flame_,
that it is not _hot_ enough to burn it off.
Q. _Why do PALMER'S METALLIC WICKS never need SNUFFING?_
A. The wick is divided into two parts, each of which _bends outward_ to
the outside of the flame; where the _end is intensely heated_, and
_separated_ from the wick by the current of air up the candle.
Q. _Why do common CANDLES require to be SNUFFED?_
A. Because the heat of the flame is _not sufficient to consume the
wick_; and the _longer_ the wick grows, the _less heat_ the flame
produces.
Q. _Why do WAX CANDLES NEVER need SNUFFING?_
A. The wick of _wax_ candles is made _of very fine thread_, which the
heat of the flame is sufficient to consume: but the wick of _tallow_
candles is made _of coarse cotton_, which is too substantial to be
consumed by the heat of the flame, and must be cut off by _snuffers_.
Q. _Why does a PIN, stuck in a RUSH-LIGHT, EXTINGUISH it?_
A. Because a _pin_ (being a good conductor), _carries away the heat of
the flame from the wick_, and prevents the combustion of the tallow.
Q. _What is the SMOKE of a CANDLE?_
A. Solid particles of carbon separated from the wick and tallow, but not
consumed.
Q. _Why are SOME particles consumed and not OTHERS?_
A. The _combustion of the carbon_ depends upon its _combining with the
oxygen of the air_: but as the outer surface of the flame _prevents the
access of air to the interior parts_, therefore much of the carbon of
those parts passes off in smoke.
Q. _Why do LAMPS SMOKE?_
A. Either because the _wick is cut unevenly_, or else because _it is
turned up too high_.
Q. _Why does a LAMP SMOKE when the WICK is cut UNEVENLY?_
A. 1st--Because the _points of the jagged edge_ (being very easily
separated from the wick,) _load the flame with more carbon than it can
consume_: and
2ndly--As the heat of the flame is _greatly diminished by these bits of
wick_, it is unable to consume _even the usual quantity of smoke_.
Q. _Why does a LAMP SMOKE when the WICK is turned up too HIGH?_
A. Because more carbon is separated from the wick _than can be consumed
by the flame_.
Q. _Why do not "Argand burners" smoke?_
A. Because a current of air passes through the _middle of the flame_;
and therefore the carbon of the _interior_ is consumed, as well as that
_in the outer coating of the flame_.
Q. _Why does a LAMP-GLASS DIMINISH the SMOKE of a lamp?_
A. Because it both _concentrates and reflects the heat of the flame_; in
consequence of which, the heat is so greatly increased, _that very
little carbon escapes unconsumed_.
CHAPTER VI.
ANIMAL HEAT.
Q. _What is the cause of ANIMAL HEAT?_
A. Animal heat is produced _by the combustion of hydrogen and carbon_ in
the capillary veins.
Q. _What are CAPILLARY VEINS?_
A. Veins _as small as hairs_ running _all over the body_; so called from
the Latin word "capilla'ris" (_like a hair_).
Q. _Do these CAPILLARY VEINS run all over the human body?_
A. Yes. Whenever blood _flows from a wound_, some _vein_ must be
divided; and as you cannot insert a needle into _any part of the body
without bringing blood_, therefore these little veins must run _through
every part_ of the human frame.
Q. _How do HYDROGEN gas and CARBON get into these very little veins?_
A. The food we eat is _converted into blood_, and blood contains both
_hydrogen_ and _carbon_.
Q. _How does COMBUSTION take place in the veins?_
A. The _carbon of the blood_ combines with the _oxygen of the air we
breathe_, and forms into _carbonic acid gas_.
Q. _What BECOMES of this CARBONIC ACID GAS formed in the human blood?_
A. Some of it is _thrown off by the breath_; and the rest of it is
_absorbed by the blood_, to keep up the animal heat.
Q. _What is the cause of the COMBUSTION of FIRE?_
A. The _carbon of fuel_ unites with the _oxygen of the air_, and forms
_carbonic acid gas_.
Q. _What is the cause of the COMBUSTION of a CANDLE or LAMP?_
A. The _carbon of the oil or tallow_ unites with the _oxygen of the
air_, and forms _carbonic acid gas_.
Q. _What is the cause of SPONTANEOUS COMBUSTION?_
A. The piled-up goods _ferment from heat and damp_; and (during
fermentation) _carbonic acid gas is formed_, as in the two former cases.
Q. _Does the HEAT of the HUMAN BODY arise from the SAME CAUSE as the
heat of FIRE?_
A. Yes, precisely. The _carbon of the blood_, combining with the _oxygen
of air inhaled_, produces _carbonic acid gas_, which is attended with
combustion.
Q. _If animal heat is produced by COMBUSTION, why does not the human
body BURN UP like a coal or candle?_
A. It actually does so. Every muscle, nerve, and organ of the body,
actually _wastes away like a burning candle_; and (being reduced to air
and ashes) is rejected from the system as useless.
Q. _If every bone, muscle, nerve, and organ, is thus consumed by
combustion, why is not the BODY entirely CONSUMED?_
A. It would be so, unless the parts destroyed _were perpetually
renewed_: but as a lamp will not go out, _so long as it is supplied with
fresh oil_; neither will the _body_ be consumed, _so long as it is
supplied with sufficient food_.
Q. _When a man is STARVED, what parts of the body go first?_
A. First the _fat_, because it is the most combustible; then the
_muscles_; last of all the _brain_; and then the man dies, like a
_candle which is burnt out_.
Q. _Why does WANT of sufficient NOURISHMENT often produce MADNESS?_
A. After the _fat and muscles_ of the body have been consumed by animal
combustion, the _brain_ is next attacked; and (unless the patient dies)
_madness must ensue from starvation_.
Q. _Why does a man SHRINK when STARVED?_
A. A starved man shrinks _just as a fire does_, unless it be supplied
with sufficient fuel.
Q. _What is the FUEL of the BODY?_
A. _Food is the fuel of the body_; and the _carbon of the food_ mixing
with the _oxygen of the air_, evolves heat in the same way that a fire
or candle does.
Q. _Why is EVERY part of the BODY WARM?_
A. As the capillary veins run through every part of the human body, and
the combustion of blood _takes place in the capillary veins_, therefore
_every part of the body is warm_.
Q. _Why does RUNNING make us WARM?_
A. When we run, _we inhale air more rapidly_; and the rapidity with
which we inhale air _fans the combustion of our body_, as a pair of
_bellows_ quickens the flame of a common fire.
Q. _How does INHALING AIR RAPIDLY make the body feel WARM?_
A. As the combustion of the blood is _more rapid_, (in consequence of
the introduction _of more oxygen from the air_), therefore _the blood is
more heated_, and every part of the body is warmer also.
Q. _Why does HARD WORK produce HUNGER?_
A. Because it produces _quicker respiration_; by which means a _larger
amount of oxygen is introduced into the lungs_, and the _capillary
combustion increased_. Hunger _is the notice_ (given by our body) to
remind us, _that our food-fuel must be replenished_.
Q. _Why does SINGING make us HUNGRY?_
A. Singing _increases respiration_; and as _more oxygen_ is introduced
into the lungs, _our food-fuel is more rapidly consumed_.
Q. _Why does READING ALOUD make us feel HUNGRY?_
A. Reading aloud _increases respiration_; and as _more oxygen_ is
introduced into the lungs, _our food-fuel is more rapidly consumed_.
Q. _Why do we feel MORE HUNGRY in the DAY-TIME than in the NIGHT-TIME?_
A. As we _breathe more slowly during sleep_, therefore, less _oxygen_ is
introduced into the lungs _to consume our food-fuel_.
Q. _Why do we need WARMER CLOTHING by NIGHT than by DAY?_
A. 1st--Because the _night is generally colder_ than the day.
2ndly--As our _respiration is slower_, our _animal combustion is slower
also_; in consequence of which, _our bodies are more cold_.
Q. _Why do we PERSPIRE when very HOT?_
A. The pores of the body are _like the safety valves of a steam-engine_;
when the heat of the body is too great, the combustible gas and grease
_flow out in perspiration_, instead of _burning in the blood_.
Q. _Why do persons feel LAZY and averse to exercise, when they are
HALF-STARVED or ILL-FED?_
A. _Animal food_ contains great nourishment, and produces a desire for
_active occupations_; but when the body is not supplied with strong
food, this desire for muscular action _ceases_, and the person grows
slothful.
Q. _Why have persons, who follow HARD OUT-OF-DOORS OCCUPATIONS, more
APPETITE than those who are engaged in SEDENTARY pursuits?_
A. Hard bodily labour in the open air _causes much oxygen to be conveyed
into the lungs by inspiration_; the combustion of the food is carried on
quickly; _animal heat increased_; and need for nutritious food more
quickly indicated _by craving hunger_.
Q. _Why have persons who follow SEDENTARY PURSUITS less APPETITE than
ploughmen and masons?_
A. 1st--The air they inhale _is not so pure_, because its oxygen is
partly exhausted: and
2ndly--Their respiration is neither _so quick nor strong_, and therefore
the combustion of their food is carried on more slowly.
Q. _Why do we like strong MEAT and GREASY food when the WEATHER is very
COLD?_
A. Strong meat and grease contain large portions of _hydrogen_, which
(when burned in the blood) produce a larger amount of heat than any
other kind of food.
Q. _Why do persons EAT MORE food in COLD weather, than in hot?_
A. In _cold_ weather the body requires more fuel _to keep up the same
amount of animal heat_; and as we _put more coals on a fire on a cold
day_ to keep our _room warm_, so we _eat more food on a cold day_ to
keep our _body warm_.
Q. _Why does COLD produce HUNGER?_
A. 1st--The air contains more _oxygen_ in cold weather; and as _fires
burn fiercer_, so _animal combustion is more rapid_: and
2ndly--We are more _active_ in cold weather; and increased respiration
acts _like a pair of bellows_ on the capillary combustion.
Q. _Why does rapid DIGESTION produce a craving APPETITE?_
A. This is a wise providence to _keep our bodies in health_; in order
that the _body itself_ may not be consumed, it gives notice (by hunger)
that the _capillary fires need replenishing_.
Q. _Why do we feel a desire for ACTIVITY in cold weather?_
A. 1st--Because activity increases the warmth of the body, _by fanning
the combustion of the blood_: and
2ndly--The _strong food_ we eat creates a desire for muscular exertion.
Q. _Why are the Esquimeaux so passionately fond of TRAIN OIL and WHALE
BLUBBER?_
A. Oil and blubber contain a very _large amount of hydrogen_, which is
exceedingly combustible; and as these people live in climates of intense
cold, the heat of their bodies is increased by the _greasy nature of
their food_.
Q. _Why do we feel a dislike to strong meat and greasy foods in very hot
weather?_
A. Strong meat and grease contain so much _hydrogen_, that they would
make us _intensely hot_; and therefore we refuse them in hot weather.
Q. _Why do we like fruits and vegetables so very much in hot weather?_
A. Fruits and vegetables contain _less carbon_ than meat, and therefore
produce _less blood_: instead of blood, _they combine into water_ as
they are digested, and keep the body cool.
Q. _Why do people say that FRUITS and VEGETABLES COOL the BLOOD?_
A. 1st--Because they _deprive the blood of carbon_, which is the chief
cause of animal heat: and
2ndly--These gases coalesce into _water_, which greatly tempers the
animal heat.
Q. _Why do we feel LAZY and averse to activity in very HOT WEATHER?_
A. 1st--Because muscular activity would increase the heat of the body,
by _quickening the respiration_: and
2ndly--The food we eat in hot weather, _not being greasy_, naturally
abates our desire for bodily activity.
Q. _Why do the inhabitants of tropical countries live chiefly upon rice
and fruit?_
A. Rice and fruit by digestion _are mainly converted into water_, and
(by cooling the blood) prevent the tropical heat from feeling so
oppressive.
Q. _Why are POOR PEOPLE generally AVERSE to CLEANLINESS?_
A. 1st--_Cleanliness increases hunger_; and as poor people are generally
_ill-fed_, they are averse to cleanliness.
2ndly--_Dirt is warm_, (thus pigs who love _warmth_, are fond of
_dirt_); and as poor people are generally _ill-clad_, they like the
_warmth of dirt_.
Q. _Why are POOR PEOPLE generally AVERSE to VENTILATION?_
A. 1st--Because ventilation _increases the oxygen of the air_,--the
_combustion of food_,--and the _cravings of appetite_: and
2ndly--Ventilation _cools the air of our rooms_: poor people, therefore,
(who are generally ill-clad) love the _warmth_ of an ill-ventilated
apartment.
Q. _Why does FLANNEL, &c. make us WARM?_
A. Flannel and warm clothing do not _make_ us warm, but merely _prevent
the body from becoming cold_.
Q. _How does flannel, &c. prevent the body from becoming cold?_
A. Flannel (being a bad conductor) will _neither carry off the heat of
the body into the cold air_, nor suffer the cold of the air _to come
into contact with our warm bodies_; and thus it is that flannel clothing
keeps us warm.
Q. _Why are FROGS and FISHES COLD-BLOODED animals?_
A. Because they consume _so little air_; and without a plentiful supply
of air, combustion is so slow, that very little animal heat is evolved.
Q. _Why is a DEAD BODY COLD?_
A. Air is no longer conveyed to the lungs after respiration has ceased;
and, therefore, animal heat _is no longer evolved by combustion_.
CHAPTER VII.
MECHANICAL ACTION.
1.--PERCUSSION.
Q. _How is heat produced by MECHANICAL ACTION?_
A. 1.--By Percussion. 2.--By Friction. 3.--By Condensation.
Q. _What is meant by PERCUSSION?_
A. _The act of striking_; as when a blacksmith strikes a piece of iron
on his anvil with his hammer.
Q. _Why does BEATING IRON make it RED-HOT?_
A. _Beating_ the iron _condenses the particles_ of the metal; and
squeezes out its latent heat, as water from a sponge.
Q. _Does COLD iron contain HEAT?_
A. Yes; _every thing_ contains heat; but when a thing _feels cold_, its
heat is LATENT.
Q. _What is meant by LATENT HEAT?_
A. Heat _not perceptible to our feeling_. When anything contains _heat_
without _feeling_ the hotter for it, that heat is called "_latent_."
(See p. 31.)
Q. _Does COLD iron contain latent HEAT?_
A. Yes; and when a blacksmith _compresses the particles_ of the iron by
his hammer, he _squeezes out_ this latent heat, and makes the iron
red-hot.
Q. _How did blacksmiths use to LIGHT THEIR MATCHES before the general
use of lucifers?_
A. They used to place a soft iron nail upon their anvil; strike it two
or three times with a hammer; and the point became _sufficiently hot to
light a brimstone match_.
Q. _How can a NAIL (beaten by a hammer) IGNITE a brimstone MATCH?_
A. As the particles of the nail are _compressed by the hammer_, it
cannot contain _so much heat as it did before_; so some of it _flies
out_ (as water flows from a sponge when it is squeezed).
Q. _Why does STRIKING a FLINT against a piece of STEEL produce a SPARK?_
A. The blow _condenses_ those parts of the flint and steel which strike
_together_, and squeezes out their latent heat.
Q. _How does this development of HEAT produce a SPARK?_
A. A very small fragment (either of the steel or flint) _is knocked off
red-hot_, and sets fire to the tinder on which it falls.
Q. _Why is it needful to keep BLOWING the TINDER with the breath?_
A. Because _blowing_ the tinder, drives the _oxygen of the air_ towards
it.
Q. _Where does the OXYGEN of the air COME FROM, which is blown to the
lighted tinder?_
A. The air itself is composed of two gases (_nitrogen and oxygen_) mixed
together.
(Every 5 lbs. of common air contain 4 lbs. of nitrogen, and 1 lb. of
oxygen.)
Q. _What is the good of BLOWING OXYGEN GAS to lighted tinder?_
A. Oxygen gas _supports combustion_; and lighted tinder is _quickened by
the breath_, in the same way as a dull fire is revived by a _pair of
bellows_.
Q. _Why do HORSES sometimes STRIKE FIRE with their FEET?_
A. When iron horse-shoes strike against the flint-stones of the road,
_very small fragments_ (either of the shoe or stones) are _knocked off
red-hot_, and look like sparks.
Q. _What makes these fragments RED-HOT?_
A. The percussion _condenses_ the part struck, _and squeezes out its
latent heat_.
CHAPTER VIII.
2.--FRICTION.
3.--CONDENSATION.
Q. _What is meant by FRICTION?_
A. The act of _rubbing two things together_; as the Indians rub two
pieces of _wood_ together to produce fire.
Q. _How do the Indians produce FIRE, by merely RUBBING TWO PIECES of dry
WOOD TOGETHER?_
A. They take a piece of dry wood (sharpened to a point), which they rub
quickly up and down a _flat piece_, till a _groove_ is made; and the
_saw-dust_ (collected in this groove) soon _catches fire_.
Q. _Why does the saw-dust of the WOOD CATCH FIRE by RUBBING?_
A. The _latent heat_ of the wood is _developed by friction_; because the
particles of the wood are _squeezed closer together_, and the heat pours
out, as water from a sponge.
(The best woods for this purpose are _box-wood_ against _mulberry_, or
_laurel_ against _poplar_ or _ivy_.)
Q. _Do not CARRIAGE WHEELS sometimes CATCH FIRE?_
A. Yes; if the wheels be _dry_,--or _fit too tightly_,--or _revolve very
rapidly_,--they often catch fire.
Q. _Why do wheels catch fire in such cases?_
A. The _friction_ of the wheels against _the axle-tree_ is so great,
that their _latent heat is disturbed_, and produces ignition.
Q. _What is the use of GREASING CART WHEELS?_
A. The grease _lessens the friction_; and (by diminishing the
_friction_) the latent heat is less disturbed.
Q. _Why is the TOP of a MOUNTAIN COLDER than the VALLEY beneath,
although it be two or three miles nearer to the sun?_
A. 1st--Because the air on a mountain is _less compressed_, than the air
in a valley.
2ndly--It is _more rarefied_: and
3rdly--It is _less heated by reflection_.
Q. _Why is air COLDER on a mountain "because it is LESS COMPRESSED?"_
A. As the air in a _valley_ is more compressed (by the mass of air
above) than that on the top of a _mountain_, therefore _more heat runs
out_; just as more water runs from a sponge, the closer it is _squeezed
together_.
Q. _Why is a mountain-top COLDER than a valley, "because the AIR there
is MORE RAREFIED?"_
A. As the air is _more rarefied_, its heat is _diffused over a larger
space_ and is _less_ intense; just as a candle would _show less light_
in a _large_ room, than in a _small_ one.
Q. _Why is a mountain-top COLDER than a valley, "because the AIR there
is LESS HEATED by REFLECTION?"_
A. Air is _not_ heated by the _sun_, but by _reflection from the surface
of the earth_; and as there is _no earth_ round a _mountain-top_ to
reflect heat, therefore the air there is intensely cold.
Q. _Why does RUBBING our HANDS and FACES make them feel WARM?_
A. Chiefly because the friction _excites the latent heat_ of our hands
and faces, and makes it sensible to our feeling.
Q. _When a man has been almost DROWNED, why is suspended animation
RESTORED by RUBBING?_
A. The vital heat of the body (which had become _latent_ by the action
of the water) is _again developed by friction_: and, as soon as this
animal heat can be excited, the vital powers of the body are restored.
Q. _Why do two pieces of ICE (rubbed together) MELT?_
A. Ice contains 140 _degrees of latent heat_, and (when two pieces are
_rubbed together)_ their _particles are compressed_, and this _latent
heat_ rolls out and _melts the ice_.
Q. _Are not FORESTS sometimes SET on FIRE by friction?_
A. Yes; when two branches or trunks of trees (blown about by the wind)
_rub violently against each other_, their _latent heat is developed_,
and sets fire to the forest.
Q. _What is meant by COMPRESSION?_
A. The act of _bringing parts nearer together_; as a sponge is
_compressed_ by being _squeezed in the hand_.
Q. _Cannot HEAT be evolved from common air merely by COMPRESSION?_
A. Yes; if a piece of _German tinder_ be placed at the _bottom of a
glass tube_, and the air in the tube _compressed by a piston_,[11] the
tinder will catch fire.
[11] In a common syringe or squirt, the _handle_ part which _contains
the sucker_ (and is forced up and down), is called "The Piston."
Q. _Why will the tinder catch fire?_
A. Because the _air is compressed_; and its _latent heat being squeezed
out_, sets fire to the tinder at the bottom of the tube.
CHAPTER IX.
EFFECTS OF HEAT.
1.--EXPANSION.
Q. _What are the principal EFFECTS of HEAT?_
A. 1.--Expansion. 2.--Liquefaction. 3.--Vaporization. 4.--Evaporation;
and 5.--Ignition.
Q. _Does HEAT EXPAND the AIR?_
A. Yes; if a bladder (partially filled with air) be tied up at the neck,
and _laid before the fire_, the air will _swell_ till the bladder
_bursts_.
Q. _Why will the AIR SWELL, if the bladder be laid before the fire?_
A. Because the heat of the fire _gets between the particles of air_, and
drives them _further apart from each other_; which causes the bladder to
expand.
Q. _Why do unslit CHESTNUTS CRACK with a loud noise, when ROASTED?_
A. Chestnuts contain a great deal of air, which is expanded by the heat
of the fire; and, as the thick rind prevents the air from escaping, it
violently _bursts through, slitting the rind_, and making a great noise.
Q. _What occasions the loud CRACK or report which we hear?_
A. 1st--The _sudden bursting of the rind_ makes a report, in the same
way as a piece of _wood_ or _glass_ would do, if _snapped in two_: and
2ndly--The _escape of hot air_ from the chestnut makes a report also, in
the same way as _gunpowder_, when it escapes from a _gun_.
Q. _Why does the sudden BURSTING of the rind, or SNAPPING of a piece of
wood, make a REPORT?_
A. As the attraction of the parts is suddenly overcome, _a violent jerk_
is given to the air; this jerk produces _rapid undulations_ in the air,
which (striking upon the ear) give the brain the sensation of _sound_.
Q. _Why does the ESCAPE OF AIR from the chestnut, or the EXPLOSION of
GUNPOWDER, produce a REPORT?_
A. Because a quantity of air (suddenly let loose) _pushes against the
air around_, in order to make _room for itself_; and as the _air of the
chestnut_ slaps against the _air of the room_, a _report_ is made, (as
when I _slap_ a book or table).
Q. _If a CHESTNUT be SLIT, it will NOT CRACK; why is this?_
A. Because the _heated air_ of the chestnut can _freely escape_ through
the _slit in the rind_.
Q. _Why does an APPLE spit and SPURT about, when roasted?_
A. An apple contains a vast quantity of _air_, which (being expanded by
the heat of the fire) _bursts through the peel_, carrying the juice of
the apple along with it.
Q. _Does an APPLE contain MORE AIR, in proportion, than a CHESTNUT?_
A. Yes, much more. There is as much condensed air in a common apple, as
would fill a space 48 _times as big as the apple itself_.
Q. _Where is all this quantity of AIR stowed in the APPLE?_
A. The _inside_ of an apple is _made up of little cells_ (like a
_honey-comb_), each of which contains a portion of the air.
Q. _When an APPLE is ROASTED, why is one part made SOFT, while all the
rest remains hard?_
A. When an apple is roasted, the air in the _cells next to the fire_ is
expanded and flies out; the _cells are broken_, and their juices _mixed
together_; so the apple _collapses_ (from loss of air and juice), and
feels _soft_ in those parts.
Q. _What is meant by the "apple COLLAPSING?"_
A. The _plumpness_ gives way, and the apple becomes _flabby_ and
_shrivelled_.
Q. _Why do SPARKS of fire start (with a crackling noise) from pieces of
WOOD laid upon a FIRE?_
A. The _air_ in the wood (expanded by the heat), _forces its way through
the pores of the log_; and carries along with it the _covering of the
pore_, which resisted its passage.
Q. _What is meant by the "PORES of the WOOD?"_
A. Very small _holes in the wood_, through which the _sap_ circulates.
Q. _What are the SPARKS OF FIRE, which burst from the WOOD?_
A. Very small pieces of wood _red hot_, separated from the log by the
_force of the air_, as it bursts from its confinement.
Q. _Why does DEAL make more snapping than any OTHER WOOD?_
A. The pores of deal are _very large_, and contain much _more air_ than
wood of a _closer grain_.
Q. _Why does DRY WOOD make more SNAPPING than GREEN WOOD?_
A. In _green wood_ the pores are filled with _sap_, and therefore
contain _very little air_; but in _dry_ wood the sap is _dried up_, and
the pores are filled with _air_ instead.
Q. _Why does DRY wood BURN more easily than GREEN or wet wood?_
A. Because the pores of dry wood are _filled with air_, which supports
combustion; but the pores of green or wet wood are filled with _vapour_,
which extinguishes flame.
Q. _Why does VAPOUR EXTINGUISH FLAME?_
1st--Because the coat of water (which wraps the fuel round) prevents
the _oxygen_ of the air from getting to the _fuel_, to form into
_carbonic acid gas_: and
2ndly--Heat is perpetually carried off, by the formation of the sap or
water _into steam_.
(Carbonic acid gas is a compound of carbon and oxygen. The solid part of
the fuel is _carbon_, and one of the gases of the air is oxygen.)
Q. _What has CARBONIC ACID GAS to do with COMBUSTION?_
A. Combustion is produced by the _chemical action_ which takes place,
while the _carbon_ of fuel unites with the _oxygen_ of air, and forms
"_carbonic acid gas_." (See p. 36.)
Q. _Why do STONES SNAP and fly about, when heated in the FIRE?_
A. The air in the stones (expanded by the heat of the fire), _meets with
great resistance_ from the close texture of the stone; and, therefore,
_bursts forth with great violence_, tearing the stone to atoms, and
forcing the fragments into the room.
Q. _Must not AIR be very STRONG, to shatter into atoms a hard stone?_
A. Yes. All the dreadful effects of _gunpowder_ are merely the results
of the _sudden expansion of air_.
Q. _When bottled ALE and PORTER is set before a FIRE, why is the CORK
FORCED OUT sometimes?_
A. If the bottle be _not quite full_, there will be _air_ between the
liquor and the cork; this _air_ (expanded by the heat of the fire)
_forces out the cork_.
Q. _Why does ALE or PORTER FROTH more, after it has been set before the
fire?_
A. The _froth_ of ale or porter _depends upon the pressure_ to which it
is subjected; and as the air (between the liquor and the cork) is
_expanded_ by the heat, _it presses against the liquor_, and increases
the quantity of froth.
Q. _Why is the FROTH of ale and porter INCREASED by PRESSURE?_
A. Because the liquor absorbs _carbonic acid_ so long as it is under
_pressure_; and the moment that the pressure is _removed_, the carbonic
acid _escapes_ in foam or froth.
Q. _When a boy makes a BALLOON, and sets fire to the cotton or sponge
(which has been steeped in spirits of wine), why is the balloon
INFLATED, or blown out?_
A. The _air_ inside the balloon is _expanded by the flame_, till the
whole balloon is _blown out_ without a crumple.
Q. _Why does the BALLOON RISE, after it has been inflated by the
expanded air?_
A. The same quantity of air is expanded _to three or four times its
original volume_; and is made so much _lighter than common air_, that
even when all the paper, wire, and cotton are added, it is still lighter
bulk for bulk.
Q. _What is meant by being lighter "bulk for bulk?"_
A. If the balloon be 3 square feet in size, it is _lighter_ (when
inflated) than 3 square feet of _common air_, and therefore _floats
through it_; as a cork (at the bottom of a tub of water) would rise to
the surface.
Q. _Why does SMOKE RUSH UP a CHIMNEY?_
A. The heat of the fire _expands the air in the chimney_; and (being
thus made _lighter_ than the air around), it _rises up the chimney_, and
carries the smoke in its current.
Q. _Why has a LONG CHIMNEY a greater DRAUGHT than a short one?_
A. Because air rises faster and faster the _higher it ascends_ in a
chimney flue; the same as a stone falls faster and faster the _nearer
it approaches to the ground_.
Q. _Why will a LONG chimney SMOKE, unless the FIRE be pretty FIERCE?_
A. If the fire be not pretty fierce, its heat will not be sufficient to
_rarefy all the air in the chimney_; and then the chimney will _smoke_.
Q. _Why will the chimney smoke, if the fire be not BIG enough to heat
ALL the air in the CHIMNEY FLUE?_
A. Because the _cold air_ (condensed in the upper part of the flue),
_will sink from its own weight_, and sweep the ascending smoke _back
with it_ into the room.
Q. _What is the use of a COWL upon a chimney-pot?_
A. The cowl acts as a _screen against the wind_, to prevent it from
blowing into the chimney.
Q. _What HARM would the WIND do, if it were to BLOW into a CHIMNEY?_
A. 1st--It would prevent the smoke from getting out: and
2ndly--The _cold air_ (introduced into the chimney by the wind) _would
fall down the flue_, and drive the smoke with it _back into the room_.
Q. _Why does a SMOKE-JACK turn round in a chimney?_
A. The current of hot air up the chimney, striking against the _oblique
vanes of the smoke-jack_, drives them round and round; in the same way
as the sails of a _wind-mill_ are driven round by the _wind_.
Q. _Why are some things SOLID, others LIQUID, and others GASEOUS?_
A. As _heat_ enters any substance, _it drives its particles further
asunder_; and a _solid_ (like _ice_) becomes a _liquid_; and a _liquid_
(like _water_) becomes a _gas_.
Q. _Why does WATER SIMMER before it boils?_
A. The particles of water _near the bottom of the kettle_ (being formed
into _steam_ sooner than the rest) _shoot upwards_; but are _condensed_
again (as they rise) _by the colder water_, and produce what is called
"simmering."
Q. _What is meant by SIMMERING?_
A. A gentle tremor or _undulation_ on the surface of the water. When
water _simmers_, the bubbles _collapse beneath the surface_, and the
steam is condensed to _water again_: but when water _boils_, the bubbles
_rise to the surface_, and _steam is thrown off_.
Q. _Why does a KETTLE SING when the water simmers?_
A. Because the _air_ (entangled in the water) escapes by _fits and
starts_ through the _spout of the kettle_; which makes a noise like a
wind instrument, when it is blown into.
Q. _Why does NOT a kettle SING, when the water BOILS?_
A. As _all_ the water is _boiling hot_, the steam meets with no
_impediment_, but freely escapes in a continuous stream.
Q. _When does a kettle sing most?_
A. When it is set on a _hob_ to boil.
Q. _Why does a kettle SING MORE when it is set on the SIDE of a fire,
than when it is set in the MIDST of the fire?_
A. When the kettle is set on the _hob_ to boil, the heat is applied very
_partially: one side is hotter than the other_, and therefore the steam
is more _entangled_.
Q. _Why does a KETTLE sing, when the boiling water begins to COOL
again?_
A. Because the _upper_ surface cools _first_; and the steam (still
rising from the lower parts of the kettle) is _again entangled_, and
escapes fitfully.
Q. _Why does BOILING WATER SWELL?_
A. Water (like air) _expands by heat_. The heat of the fire drives the
particles of water _further apart from each other_; and (as they are not
_packed so closely together_) they take up _more room_; or (in other
words) the water _swells_.
Q. _What is meant when it is said, "that HEAT drives the PARTICLES of
water further APART from each other."_
A. Water is composed of little globules, like very small grains of sand;
the heat _drives_ these particles _away from each other_; and (as they
then require more _room_) the water _swells_.
Q. _Why does BOILING WATER BUBBLE?_
A. Water contains _air_; and (as the water is heated) _the air is driven
out_, and raises a _bubble_ in that part of the water which resists its
escape.
Q. _Why does a KETTLE sometimes BOIL OVER?_
A. Liquids _expand very much by heat_; if, therefore, a kettle be
_filled with cold water_, some of it must _run over_ as soon as it is
_expanded by heat_.
Q. _But I have seen a KETTLE BOIL OVER, although it has not been filled
FULL of WATER; how do you account for THAT?_
A. If a fire be _very fierce_, the air is expelled so _rapidly_, that
the _bubbles are very numerous_; and (towering one above the other)
_reach the top of the kettle, and fall over_.
Q. _Why is a pot, which is full to OVERFLOWING (while the water is
boiling HOT), NOTHING LIKE FULL, when it has been taken off the fire for
a short time?_
A. When the water was _swelled by boiling heat_, it filled the pot even
to overflowing; but as soon as the water is _condensed by cold_, it
_contracts_ again, and occupies a much less space.
Q. _Why does the water of a KETTLE run out of the SPOUT when it BOILS?_
A. Because the steam cannot escape _so fast as it is formed_, and (being
_confined in the kettle_) _presses on the water with great power_, and
forces it out of the spout.
Q. _How can the PRESSURE of STEAM on the SURFACE of the water, FORCE the
water through the KETTLE-SPOUT?_
A. In the same manner as _the pressure of air_ on the _mercury of a
barometer_, forces the _quicksilver up the glass tube_.
Q. _What causes the RATTLING NOISE so often made by the LID of a
saucepan or boiler?_
A. The steam (seeking to escape) _forces up the lid_ of the boiler, and
the _weight_ of the lid causes it to _fall back again_: this being done
_frequently_, produces a rattling noise.
Q. _If the steam COULD NOT LIFT UP THE LID of the boiler, how would it
escape?_
A. If the lid fitted so tightly, that the steam could not raise it up,
the boiler would _burst into fragments_, and the consequences might be
fatal.
Q. _When steam pours out from the spout of a kettle, the STREAM begins
apparently HALF AN INCH off the SPOUT; why does it not begin CLOSE to
the spout?_
A. Steam is really _invisible_; and the half-inch (between the spout and
the "_stream of mist_") is the _real steam_, before it has been
condensed by air.
Q. _Why is not ALL the stream INVISIBLE, as well as that half-inch?_
A. As the steam _comes in contact with the colder air_, the invisible
particles (being _condensed_), roll one into another, and look like a
thick mist.
Q. _What BECOMES OF the STEAM? for it soon vanishes._
A. After it is condensed into mist, it is _dissolved by the air_, and
dispersed abroad as _invisible vapour_.
Q. _And what BECOMES of the INVISIBLE VAPOUR?_
A. Being _lighter than air_, it _ascends_ to the upper regions, where
(being again _condensed_) it contributes to form _clouds_.
Q. _Why does a METAL SPOON, left in a saucepan, RETARD the process of
BOILING?_
A. The metal spoon (being an excellent _conductor_) _carries off the
heat from the water_; and (as heat is carried off by the spoon) the
water takes a longer time to boil.
Q. _Why will a POT (filled with water) NEVER BOIL, when immersed in
ANOTHER vessel full of water also?_
A. Because water can _never be heated above the boiling point_: all the
heat absorbed by the water after it _boils_, is employed in _converting
the water into steam_.
Q. _How does the conversion of water into steam prevent the INNER POT
from BOILING?_
A. The moment the water in the larger pot is _boiling hot_ (or 212°),
_steam is formed_, and _carries off some of its heat_; therefore, 212
_degs._ of heat can never _pass through it_, to raise the _inner_
vessel to the _same heat_.
Q. _Why do SUGAR, SALT, &c. RETARD the process of BOILING?_
A. Because they have a tendency to _fix_ water by chemical attraction;
and therefore retard its _conversion into steam_.
Q. _If you want water to boil, without COMING IN CONTACT with the
SAUCEPAN, what plan must you adopt?_
A. _Immerse the pot_ (containing the water you want to boil) in a
saucepan containing _strong brine_, or sugar.
Q. _Why would the INNER vessel boil, if the OUTER vessel contained
strong BRINE?_
A. Though _water_ boils at 212 _degs._ of heat, yet _brine_ will not
boil till raised to 218 or 220 _degs._ Therefore, 212 _degs._ of
heat may easily pass through brine _to raise the vessel immersed in it
to boiling heat_, before any of it is _carried off by steam_.
Q. _Why will brine impart to another vessel MORE than 212°, and water
NOT SO MUCH?_
A. Because both liquids will _impart heat_ till they _boil_, and then
_they can impart heat no longer_.
Q. _Why can they impart no extra heat after they boil?_
A. Because all _extra_ heat is spent _in making steam_. Hence water will
_not_ boil a vessel of water immersed in it, because it cannot impart to
it 212 _degs._ of heat: but _brine_ will, because it can impart _more
than_ 212 _degs. of heat_, without being converted itself into steam.
Ether boils at 104 _degs._
Alcohol - - 173-1/2 "
Water - - 212 "
Water with one-fifth salt 219 "
Syrup boils at 221 "
Oil of turpentine, 304 "
Sulphuric acid 472 "
Linseed oil - 640 "
&c. &c.
Any liquid which boils at a _lower_ degree can be made to boil if
immersed in a liquid which boils at a higher degree. Thus a _cup of
ether_ can be made to boil in a saucepan of _water_. A _cup of water_ in
a saucepan of _brine or syrup_. But a _cup of water_ will _not_ boil if
immersed in _ether_; nor a _cup of syrup_ in _water_.
Q. _Why are CLOUDS HIGHER on a FINE DAY?_
A. 1st--Because the _air_ (expanded by heat) _drives them higher up_:
and
2ndly--The _clouds themselves are lighter_, and therefore _more
buoyant_.
Q. _Why are the CLOUDS LIGHTER on a FINE DAY?_
A. Because their mists are either _absorbed by the dry air_, or
_vapourized_ by the hot sun.
Q. _Why is a CUP PUT topsy-turvy into a FRUIT-PIE?_
A. Its principal use is to _hold the crust up_, and _prevent it from
sinking_, when the cooked fruit gives away under it.
Q. _Does not the cup PREVENT the FRUIT of the pie from BOILING OVER?_
A. No, by no means; it would rather tend to _make it boil over_, than
otherwise.
Q. _Why would the cup tend rather to MAKE the FRUIT BOIL OVER?_
A. As soon as the pie is put into the oven, the _air_ in the cup will
_begin to expand_, and drive every particle of juice from under it; the
pie dish, therefore, will have a cup-full _less room_ to hold its fruit,
than if the cup were _taken out_.
Q. _If the juice is driven OUT of the cup, why is the CUP always FULL of
JUICE, when the pie is cut up?_
A. Immediately the pie is drawn, the _air_ in the cup begins to
_condense again_, and _occupy a smaller space_; in consequence of which,
there is no longer _enough air to fill the cup_, and so _juice_ rushes
in _to fill up the deficiency_.
Q. _Why does JUICE rush into the cup, because the cup is NOT FULL of
AIR?_
A. As the external air _presses upon the surface of the juice_, it
rushes into the cup _unobstructed_; as mercury rises through the tube of
a barometer through similar pressure.
CHAPTER X.
EXPANSION FROM HEAT.
_(Continued.)_
Q. _Does heat expand every thing ELSE BESIDES air and water?_
A. Yes; _every_ thing (that man is acquainted with) is expanded by heat.
Q. _Why does a COOPER make his HOOPS RED-HOT, when he puts them on a
tub?_
A. 1st--As _iron expands by heat_, the hoops will be _larger_ when they
are red-hot; and will, therefore, _fit more easily on the tub_: and
2ndly--As _iron contracts by cold_, the hoops will _shrink_ as they cool
down, and _girt the tub with a tighter grasp_.
Q. _Why does a WHEELWRIGHT make his hoops RED-HOT, which he fixes on the
NAVE of a WHEEL?_
A. 1st--That they may _fit on more easily_: and
2ndly--That they may _girt the nave more tightly_.
Q. _Why will the wheelwright's HOOP FIT the nave MORE EASILY, because
they are made RED-HOT?_
A. As _iron expands by heat_, the hoops will be _larger_ when they are
hot; and (being larger) will go on the nave more _easily_.
Q. _Why will the HOOPS, which have been PUT ON HOT, girt the nave more
FIRMLY?_
A. As _iron contracts by cold_, the hoops will _shrink as they cool
down_; and, therefore, _girt the nave with a tighter grasp_.
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?_
A. The iron stove _contracts again_, as soon as the fire is removed;
and (as it shrinks into a smaller space) the parts _rub against each
other again_, and the _bricks are again disturbed_; and this produces a
cracking noise.
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.
Q. _Why does the MERCURY of a THERMOMETER RISE in hot weather?_
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?_
A. China is a _non-conductor_; and, as the _inner surface expands by the
heat_, before the _outer one_, _it forms an arch_, and pulls the parts
of the cup asunder.
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.
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_.
[Illustration: 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.]
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.
CHAPTER XII.
4.--EVAPORATION.
Q. _What is meant by EVAPORATION?_
A. The dissipation of liquid by its being _converted into vapour_.
Q. _What EFFECTS are produced by evaporation?_
A. The _liquid vaporized absorbs heat_ from the body whence it issues;
and the _body deprived of the liquid_ by evaporation, _loses heat_
thereby.
Q. _If you WET your FINGER in your mouth, and hold it up in the air, why
does it FEEL COLD?_
A. The saliva quickly _evaporates_; and (as it evaporates) _absorbs heat
from the finger_, which makes it feel cold.
Q. _If you BATHE your TEMPLES with ether, why does it allay INFLAMMATION
and feverish heat?_
A. Ether very rapidly _evaporates_; and (as it evaporates) _absorbs heat
from the burning head_, producing a sensation of cold.
Q. _Why is ETHER better for this purpose than WATER?_
A. Because it requires _less heat to convert it into vapour_; and
therefore it evaporates much more _quickly_.
(Ether is converted into steam with 104 _degs._ of heat, but water
requires 212 _degs._ of heat to convert it into steam.)
Q. _Why does ETHER very greatly RELIEVE a SCALD or BURN?_
A. Because it _evaporates very rapidly_; and (while it is converted into
vapour) _carries off the heat of the burn_.
Q. _Why do we FEEL so COLD when we have WET FEET or CLOTHES?_
A. As the wet of our shoes or clothes _evaporates_, it _keeps absorbing
heat from the body_, which makes it feel cold.
Q. _Why do WET FEET or CLOTHES give us "COLD?"_
A. Because the evaporation _absorbs heat from the body so abundantly_,
that it is _lowered below its natural standard_; and therefore health is
injured.
Q. _Why is it DANGEROUS to SLEEP in a DAMP BED?_
A. Because the _heat of the body_ is continually absorbed _in converting
the damp of the sheets into vapour_; and as heat is abstracted from the
body, its temperature is reduced _below the healthy standard_.
Q. _Why do we not feel the same sensation of cold, if we throw a
MACINTOSH over our WET CLOTHES?_
A. The macintosh _prevents evaporation_, because the steam cannot escape
through the air-tight fabric; and (as the _wet cannot evaporate_ from
the clothes) no heat is absorbed from our bodies.
Q. _Why do NOT SAILORS get COLD, who are so often wet all day with
SEA-WATER?_
A. The _salt_ of the sea _retards evaporation_; and (as the heat of the
body is drawn off _very gradually_) the sensation of cold is prevented.
Q. _Why does SPRINKLING a HOT ROOM with water COOL IT?_
A. The heat of the room causes a _rapid evaporation of the sprinkled
water_; and as the water evaporates, _it absorbs heat from the room_,
and cools it.
Q. _Why does WATERING the STREETS and roads COOL THEM?_
A. The hot streets and roads part with their heat _to promote the
evaporation of the water sprinkled on them_.
Q. _Why does a SHOWER of RAIN seem to COOL the AIR in summer-time?_
A. The earth (being wet with the rain) _parts with its heat to promote
evaporation_; and as the _earth_ is cooled, it _cools the air_ also.
Q. _Why is LINEN DRIED by being exposed to the WIND?_
A. The air (blowing over the linen) _promotes evaporation_, by removing
the vapour from the _surface of the wet linen_, as soon as it is
formed.
Q. _Why is LINEN DRIED sooner in the open AIR, than in a confined room?_
A. Because the particles of vapour are more rapidly removed from the
surface of the linen by evaporation.
Q. _Why are WET SUMMERS generally SUCCEEDED by COLD WINTERS?_
A. Because the great evaporation (carried on through the wet summer)
_reduces the temperature of the earth lower than usual_, and produces
cold.
Q. _Why is ENGLAND WARMER than it used to be, when AGUES were so
common?_
A. Because it is _better drained_ and _better cultivated_.
Q. _Why does DRAINING land promote WARMTH?_
A. Because it _diminishes evaporation_; in consequence of which _less
heat_ is abstracted from the earth.
Q. _Why does CULTIVATION increase the WARMTH of a country?_
A. 1st--Because _hedges and belts of trees_ are multiplied;
2ndly--Because the land is _better drained_;
3rdly--Because the land is _dug and ploughed;_ and
4thly--Because the vast _forests are cut down_.
Q. _Why do HEDGES and BELTS of TREES promote WARMTH?_
A. Because they _retard evaporation_, by keeping off the _wind_.
Q. _If belts of trees promote WARMTH, why do FORESTS produce COLD?_
A. 1st--Because they _detain and condense the passing clouds_:
2ndly--They prevent the access of both _wind and sun_:
3rdly--The soil of forests is always _covered with long damp grass,
rotting leaves, and thick brushwood_: and
4thly--There are always many hollows in every forest _full of stagnant
water_.
Q. _Why do LONG GRASS and ROTTING LEAVES promote COLD?_
A. Because _they are always damp_; and the evaporation which they
promote, _is constantly absorbing heat_ from the earth beneath.
Q. _Why do DIGGING and PLOUGHING help to make a country WARM?_
A. Digging and ploughing help _to pulverize the soil_, by admitting
_air into it_, and this increases its mean temperature.
Q. _Why are FRANCE and GERMANY WARMER now, than when the vine would not
ripen there?_
A. Chiefly because _their vast forests have been cut down_; and the soil
is better _drained and cultivated_.
Q. _What becomes of the WATER of PONDS and TUBS in summer-time?_
A. Ponds and tubs in summer-time are often left dry, because their water
is _evaporated by the air_.
Q. _How is this EVAPORATION PRODUCED and carried on?_
A. The air contains heat, and changes the _surface of the water into
vapour_; this vapour (blending with the air) _is soon wafted away_;
while _fresh_ portions of air _blow over the water_, and produce a
_similar evaporation_; till the pond or tub is left quite dry.
Q. _Why are the WHEELS of some machines kept CONSTANTLY WET with WATER_?
A. _To carry off the heat_ (arising from _the rapid motion_ of the
wheels) _by evaporation_, as soon as it is developed.
Q. _Why is MOULD HARDENED by the SUN?_
A. Because (when the moisture of the mould has been _evaporated by the
sun_) the earthy particles _come into closer contact_, and the mass
becomes more solid.
Q. _Show the WISDOM of GOD in this arrangement._
A. If the soil did not become _crusty and hard in dry weather_, the
_heat and drought would penetrate the soil_, and kill both seeds and
roots.
Q. _Why is TEA cooled FASTER in a SAUCER than in a cup?_
A. Because _evaporation is increased_ by _increasing the surface_; and
as tea in a saucer _presents a much larger surface to the air_, its heat
is more rapidly carried off by evaporation.
(The subject of "convection" will be treated of in a future chapter, and
would scarcely be understood in this place.)
Q. _Why is not the VAPOUR of the SEA SALT?_
A. Because the _salt_ is always _left behind_, by the process of
evaporation.
Q. _Why does a WHITE CRUST appear (in hot weather) upon CLOTHES wetted
by sea water?_
A. The white crust is the _salt of the water_ left on the clothes by
evaporation.
Q. _Why does this WHITE CRUST always DISAPPEAR in WET weather?_
A. In _wet_ weather the _moisture of the air dissolves the salt_; and,
therefore, it no longer remains visible.
Q. _Why should NOT persons, who take violent exercise, WEAR very THICK
CLOTHING?_
A. When the heat of the body is increased by exercise, _perspiration
reduces the heat_ (by evaporation) _to a healthy standard_: as thick
clothing _prevents this evaporation_, and confines the heat and
perspiration _to the body_, it is injurious to health.
CHAPTER XIII.
COMMUNICATION OF HEAT.
1.--CONDUCTION.
Q. _How is HEAT COMMUNICATED from one body to another?_
A. 1. By Conduction. 2. By Absorption. 3. By Reflection. 4. By
Radiation: and 5. By Convection.
Q. _What is meant by CONDUCTION of heat?_
A. Heat communicated from one body to another, _by actual contact_.
Q. _Why does a PIECE of WOOD (blazing at ONE end) NOT FEEL HOT at the
OTHER end?_
A. _Wood is a bad conductor of heat_; and, therefore, heat does not
traverse freely through it: hence, though one end of a stick be
blazing-hot, the other end may be quite cold.
Q. _Why do SOME THINGS feel so much COLDER than others?_
A. Principally because _they are better conductors_; and, therefore,
draw off the heat from our body (which touches them) so much faster.
Q. _What are the BEST CONDUCTORS of HEAT?_
A. _Dense solid bodies_, such as metal and stone.
Q. _Which METALS are the most RAPID CONDUCTORS of HEAT?_
A. _Silver_ is the best conductor, then _copper_, then _gold_ or _tin_,
then _iron_, then _zinc_, and then _lead_.
Q. _What are the WORST CONDUCTORS of HEAT?_
A. All _light and porous bodies_, such as hair, fur, wool, charcoal, and
so on.
Q. _Why are COOKING VESSELS so often furnished with WOODEN HANDLES?_
A. Wood is _not a good conductor, like metal_; and, therefore, many
vessels (which are exposed to the heat of the fire) _have wooden
handles, lest they should burn our hands_ when we take hold of them.
Q. _Why is the HANDLE OF A METAL TEA-POT made of WOOD?_
A. As _wood is a bad conductor_, the heat of the boiling water is _not
so quickly conveyed to the wooden handle_, nor so quickly _poured into
the hand_ by it, as when the handle is made of metal.
Q. _Why would a METAL HANDLE BURN the HAND of the tea-maker?_
A. As metal is an _excellent conductor_, the heat of the boiling water
_rushes quickly into the metal handle_, and _into the hand that touches
it_.
Q. _How do you know that a METAL HANDLE would be HOTTER than a WOODEN
one?_
A. By _touching the metal collar_ into which the wooden handle is fixed:
though the _wooden handle is quite cold_, this _metal collar is
intensely hot_.
Q. _Why do persons use paper or WOOLLEN KETTLE-HOLDERS to take hold of a
kettle with?_
A. Paper and woollen are both very _bad conductors of heat_; and,
therefore, the heat of the kettle does _not readily pass through them to
the hand_.
Q. _Does the heat of the boiling kettle NEVER get through the woollen or
paper kettle-holder?_
A. Yes; but though the kettle-holder became as hot as the kettle itself,
it would never _feel_ so hot.
Q. _Why would not the kettle-holder FEEL so hot as the kettle, when it
really is of the same temperature?_
A. Because (being a very _bad_ conductor) _it disposes of its heat so
slowly_, that it is _scarcely perceptible_; but metal (being an
_excellent_ conductor) disposes of its heat so _quickly_, that the
sudden influx is painful.
Q. _Why then does HOT METAL feel so much MORE intensely WARM than HOT
WOOL?_
A. Because it gives out a much _greater quantity of heat in the same
space of time_; and the _influx_ of heat is, therefore, _more
perceptible_.
Q. _Why does MONEY in our pocket feel so HOT, when we stand BEFORE a
FIRE?_
A. Metal is an _excellent conductor_; and, therefore, becomes rapidly
heated. For the same reason it becomes _rapidly cold_, when it comes in
contact with a body _colder than itself_.
Q. _Why does a PUMP-HANDLE feel intensely COLD in WINTER?_
A. As metal is an _excellent conductor_, when the hot hand touches the
cold pump-handle, the heat passes rapidly _from the hand into the iron_;
and this rapid loss of heat produces a sensation of intense coldness.
Q. _Is the iron HANDLE of the pump really COLDER than the wooden PUMP
itself?_
A. No; every inanimate substance (exposed to the same temperature)
possesses the _same degree of heat_.
Q. _Why then does the IRON HANDLE seem so MUCH COLDER than the WOODEN
PUMP?_
A. Merely because the _iron is a better conductor_; and, therefore,
_draws off the heat from our hand_ much more rapidly than wood does.
Q. _Why does a STONE or marble HEARTH feel to the feet so much COLDER
than a CARPET or hearth-rug?_
A. Because _stone and marble are good conductors_, but _woollen carpets
and hearth-rugs_ are very _bad conductors_.
Q. _Why does the STONE HEARTH make our FEET COLD?_
A. As soon as the hearth-stone has absorbed a portion of heat from our
foot, it instantly disposes of it, and _calls for a fresh supply_; till
the hearth-stone has become of the _same temperature as the foot placed
upon it_.
Q. _Do not the woollen CARPET and HEARTH-RUG, also, conduct heat from
the human body?_
A. Yes; (but being very _bad conductors_) they convey _the heat away so
slowly_, that it is scarcely perceptible.
Q. _Is the COLD HEARTH-STONE and WARM CARPET then of the SAME
TEMPERATURE?_
A. Yes; everything in the room is _really of the same temperature_; but
some feel colder than others _because they are better conductors_.
Q. _How LONG will the hearth-stone feel cold to the feet resting on it?_
A. Till the _feet and the hearth-stone are both of the same
temperature_; and then the sensation of cold in the hearth-stone will go
off.
Q. _Why would not the HEARTH-STONE feel COLD, when it is of the SAME
temperature as our FEET?_
A. Because the heat would no longer _rush out of our feet into the
hearth-stone_, in order to produce an equilibrium.
Q. _Why does the HEARTH-STONE (when the fire is lighted) feel so much
HOTTER than the HEARTH-RUG?_
A. The hearth-stone is an _excellent conductor_; and, therefore, _parts
with its heat more readily_ than the woollen hearth-rug; which (being a
very _bad conductor_) parts with its heat reluctantly.
Q. _Why does PARTING with HEAT RAPIDLY make the HEARTH-STONE feel WARM?_
A. As the heat of the stone rushes _quickly into our foot_, it raises
its temperature _so suddenly_, that we cannot _help perceiving the
increase of heat_.
Q. _Why does the non-conducting power of the HEARTH-RUG prevent its
feeling so HOT as it really is?_
A. Because it parts with its heat _so slowly and gradually_, that we
scarcely _perceive its transmission_ into our feet.
Q. _When we plunge our HANDS into a basin of WATER, why does it produce
a sensation of COLD?_
A. Though the water (in which we wash) _is really warmer_ than the air
of our bed-room; yet because it is a _better conductor_, it _feels
colder_.
Q. _Why does the CONDUCTING power of water make it feel COLDER than the
air, though in reality it is WARMER?_
A. Because _it abstracts heat from our hands so rapidly_, that we feel
its loss; but the air abstracts heat _so very slowly_, that its _gradual
loss is hardly perceptible_.
Q. _Is water a GOOD CONDUCTOR of heat?_
A. No; _no liquid is a good conductor_ of heat; but yet water is a _much
better conductor than air_.
Q. _Why is WATER a BETTER CONDUCTOR of heat than AIR?_
A. Because _it is less subtile_; and the conducting power of any
substance depends upon _its solidity_, or the _closeness of its
particles_.
Q. _How do you know that WATER is NOT a GOOD CONDUCTOR of heat?_
A. Because water may be made to _boil at its surface_, without imparting
sufficient heat to _melt ice a quarter of an inch below the boiling
surface_.
Q. _Why are NOT LIQUIDS GOOD CONDUCTORS of heat?_
A. Because the heat (which should be transmitted) _produces
evaporation_, and _flies off in the vapour_.
Q. _Why does a POKER (resting on the fender) feel so much COLDER than
the HEARTH-RUG, which is further off the fire?_
A. The poker (being an excellent conductor) _draws heat from the hand
much more quickly than the rug_, which is a bad conductor: and,
therefore, (though both are _equally warm_) the poker seems to be much
colder.
Q. _Why are HOT BRICKS (wrapped in cloth) employed in cold weather to
KEEP the FEET WARM?_
A. Bricks are _bad conductors_ of heat, and cloth or flannel _still
worse_: therefore a hot brick (wrapped in flannel) will _retain its heat
a very long time_.
Q. _Why is a TIN PAN (filled with HOT WATER) employed as a FOOT WARMER?_
A. Because _polished tin_ (being a bad radiator of heat) _keeps hot a
very long time_; and warms the feet resting upon it.
Q. _What is meant by being a "bad RADIATOR of heat?"_
A. To radiate heat is to _throw off heat by rays_, as the sun; a
polished tin pan does _not throw off the heat of boiling water_ from its
surface, but _keeps it in_.
Q. _Why is the TIN FOOT-WARMER covered with FLANNEL?_
A. 1st--To prevent the perspiration of the foot from taking off the
_polish_ of the tin:
2ndly--Flannel is a _very bad conductor_; and, therefore, helps to keep
the tin hot _longer_: and
3rdly--If the feet were _not protected_, the conducting surface of the
tin _would feel painfully hot_.
Q. _What harm would it be if the POLISH of the tin were injured by the
perspiration of our feet?_
A. _Polished_ tin throws off its heat _very slowly_; but dull,
scratched, painted, or dirty tin, _throws off its heat very quickly_:
if, therefore, the tin foot-warmer were to _lose its polish_, it would
_get cold in a much shorter time_.
Q. _Why are FURNACES and stoves (where much HEAT is required) built of
porous BRICK?_
A. As bricks are bad conductors, they _prevent the escape of heat_: and
are, therefore, employed where great heat is required.
Q. _Why are FURNACE DOORS, &c. frequently COVERED with a paste of CLAY
and SAND?_
A. Because this paste is a _very bad conductor of heat_; and, therefore,
prevents the _escape of heat from the furnace_.
Q. _If a stove be placed in the MIDDLE of a room, should it be made of
bricks or IRON?_
A. A stove in the _middle of a room_ should be made of _iron_; because
iron is an _excellent conductor_, and rapidly communicates its heat to
the air around.
Q. _Why does the Bible say, that God "giveth SNOW like WOOL?"_
A. As _snow is a very bad conductor of heat_, it protects vegetables and
seeds from the frost and cold.
Q. _How does the non-conducting power of SNOW PROTECT VEGETABLES from
the FROST and cold?_
A. As snow is a bad conductor, it prevents the _heat_ of the earth _from
being drawn off_ by the cold air which rests upon it.
Q. _Why are WOOLLENS and FURS used in COLD weather for CLOTHING?_
A. Because they are _very bad conductors_ of heat; and, therefore,
_prevent the warmth of the body from being drawn off_ by the cold air.
Q. _Do not woollens and furs actually IMPART heat to the body?_
A. No; they merely _prevent the heat of the body from escaping_.
Q. _Where would the heat ESCAPE to, if the body were NOT wrapped in wool
or fur?_
A. The heat of the body would _fly off into the air_; for the cold air
(coming into contact with our body) _would gradually draw away its
heat_, till it was as cold as the air itself.
Q. _What then is the PRINCIPAL USE of CLOTHING in winter-time?_
A. _To keep the body air-tight_; and prevent the _external air_ (or
wind) from _coming into contact with it_, to absorb its heat.
Q. _Why are BEASTS COVERED with FUR, HAIR, or WOOL?_
A. Because fur, hair, and wool are very _slow conductors of heat_; and
(as dumb animals cannot be clad like human beings) God has given them a
_robe of hair_ or wool, to _keep them warm_.
Q. _Why are BIRDS covered with DOWN or FEATHERS?_
A. Because down and feathers are _very bad conductors of heat_; and (as
birds cannot be clad like human beings) God has given them a _robe of
feathers to keep them warm_.
Q. _Why are WOOL, FUR, HAIR, or FEATHERS such SLOW CONDUCTORS of heat?_
A. Because a _great quantity of air_ lurks entangled between their
fibres; and _air is a very bad conductor of heat_.
Q. _If AIR be a BAD CONDUCTOR of heat, why should we not feel as warm
WITHOUT clothing, as when we are wrapped in wool and fur?_
A. Because the air (which is cooler than our body) _is never at rest_;
and, therefore, fresh particles (perpetually passing over our body)
_keep drawing off the heat little by little_.
Q. _Why does the ceaseless CHANGE of air tend to DECREASE the WARMTH of
a naked body?_
A. Thus:--the air which cases the body _absorbs as much heat from it as
it can, while it remains in contact_; it is then blown away, and makes
room for a _fresh coat of air_, which does the _same_.
Q. _Does the AIR (which encases a naked body) become by contact as WARM
as the BODY itself?_
A. It would do so, if it remained _motionless_; but as it remains only
_a very short time_, it absorbs as much heat as it _can in the time_,
and passes on.
Q. _Why do we feel COLDER in WINDY WEATHER, than in a CALM day?_
A. Because (in windy weather) the particles of air _pass over us more
rapidly_; and every _fresh_ particle takes from us _some_ portion of
heat.
Q. _Show the wisdom of God in making the AIR a BAD CONDUCTOR._
A. If air were a _good conductor_ (like iron and stone) the heat would
be drawn _so rapidly from our body_, that we must be _chilled to death_.
Similar evils would be felt also by all the animal and vegetable world.
Q. _Does not the bad conducting power of air enable persons to judge
whether an EGG be NEW or STALE?_
A. Yes; touch your tongue against the shell at the larger end; if it
_feels warm_ to the tongue, the _egg is stale_; if _not_, it is
new-laid.
Q. _Why will the SHELL of a STALE EGG feel WARM to the tongue?_
A. Between the shell and the "white of the egg" _there is a small
quantity of air_, which _expands in a stale egg_, from the _shrinking of
the white_.
Q. _Why does the expansion of air (at the end of an egg) make it feel
WARM to the tongue?_
A. As air is a very bad conductor, the _more air an egg contains_, the
_less heat will be drawn from the tongue_ when it touches the shell.
Q. _Why do ladies FAN themselves in summer, to make their FACES COOL?_
A. The fan _puts the air in motion_, and makes it pass more _rapidly
over their face_; and (as the temperature of the _air is always lower_
than that of the human _face_) each puff of air _carries off some
portion of heat_ from the face.
Q. _Does FANNING the air make the AIR itself COOLER?_
A. No; fanning makes the _air hotter and hotter_.
Q. _Why does FANNING the air increase its HEAT?_
A. By causing the air continually to _absorb heat from the human body_
which it passes over.
Q. _If fanning makes the AIR HOTTER, how can it make a PERSON feel
COOLER?_
A. Fanning makes the _air hotter_, but the _face cooler_; because it
keeps _taking the heat out of the face_, and _giving it to the air_.
Q. _Why is BROTH COOLED by BLOWING it?_
A. The breath causes a rapid _change of air_ to pass over the broth; and
(as the air is not so hot as the broth) _it keeps absorbing heat_, and
thus makes the broth cooler and cooler.
Q. _Would not the air absorb heat from the broth just as well WITHOUT
BLOWING?_
A. No; _air is a very bad conductor_; unless, therefore, _the change be
rapid_, the air nearest the surface of the broth _would soon become as
hot as the broth itself_.
Q. _But would not the hot air PART with its heat instantly to the
CIRCUMJACENT air?_
A. No; not instantly. Air is so bad a conductor, _that it parts with its
heat very slowly_: unless, therefore, the air be kept in _continual
motion_, it would _cool the broth very slowly indeed_.
Q. _Why does WIND generally feel COOL?_
A. Wind is only air in motion; and the more quickly the _air passes over
our body_, the more rapidly it _absorbs the heat_ therefrom.
Q. _Why does AIR ABSORB heat more QUICKLY by being set in MOTION?_
A. Because every fresh gust of air _absorbs a fresh portion of heat_;
and the more rapid the _succession of gusts_, the greater will be the
quantity of air absorbed.
Q. _If the AIR were HOTTER than our body, would the WIND feel COOL?_
A. No; if the air were _hotter than our body_, it would feel
_insufferably hot_.
Q. _Why would the AIR feel INTENSELY HOT, if it were WARMER than our
BLOOD?_
A. Because then the wind would _add to the heat of_ our body, instead of
_diminishing it_.
Q. _Is the AIR EVER as HOT as the human BODY?_
A. Not in _this_ country: in the hottest summer's day, the air is always
10 or 12 _degrees cooler than the human body_.
Q. _Is the EARTH a GOOD CONDUCTOR of heat?_
A. No; the power of _conducting_ heat depends upon the _continuity of
matter_; if the particles of which a thing is composed are not
_continuous_, they have very little power to _conduct heat_.
Q. _Why is the earth (BELOW the SURFACE) WARMER in WINTER than the
surface itself?_
A. Because the earth is a _bad conductor of heat_; and, therefore
(although the ground be frozen) the frost never penetrates _above an
inch or two below the surface_.
Q. _Why is the earth (BELOW the SURFACE) COOLER in SUMMER than the
surface itself?_
A. Because the earth is a _bad conductor of heat_; and, therefore,
(although the surface be scorched with the burning sun) the intense heat
cannot penetrate to _the roots_ of the plants and trees.
Q. _Shew the WISDOM of GOD in making the EARTH a BAD CONDUCTOR._
A. If the _heat and cold could penetrate the earth_ (as freely as the
heat of a fire penetrates iron), the springs would be dried up in summer
and frozen in winter, and all vegetation would perish.
Q. _Why is WATER from a SPRING so COOL in SUMMER?_
A. As the earth is a _bad conductor_, the burning rays of the sun can
penetrate only a few inches below the surface; in consequence of which,
the _springs of water are not affected_.
Q. _Why is it COOL under a SHADY tree in a hot summer's day?_
A. 1st--Because the overhanging foliage _screens off the rays of the
sun_:
2ndly--As the rays of the sun are warded off, _the air_ (beneath the
tree) _is not heated by the reflection of the earth_: and
3rdly--The leaves of trees, being _non-conductors_, allow no heat to
penetrate through them.
Q. _Why do the LAPLANDERS wear SKINS, with the FUR INWARDS?_
A. The _dry skin_ prevents the _wind from penetrating to their body_;
and as the _fur_ contains a _quantity of air_ between its hairs (which
soon _becomes heated by the body_) the Laplander is clad in _a case of
hot air, impervious to the cold and wind_.
Q. _Why does a LINEN SHIRT feel COLDER than a COTTON ONE?_
A. _Linen is a much better conductor_ than cotton; and, therefore, (as
soon as it touches the body) _it more rapidly draws away the heat_, and
produces a sensation of cold.
Q. _Why is the FACE COOLED by wiping the temples with a fine CAMBRIC
HANDKERCHIEF?_
A. The fine fibres of the cambric have a _strong capillary attraction
for moisture_; and are _excellent conductors of heat_: thus the moisture
and heat are _both abstracted from the face_, and a sensation of
coolness is produced.
"Capillary attraction," i. e. _the attraction of a thread or hair_. The
wick of a candle is wet with grease, because the melted tallow runs up
the cotton from capillary attraction.
Q. _Why would not a COTTON handkerchief do as well?_
A. The coarse fibres of cotton have much less capillary attraction, and
are _nothing like such good conductors_ as linen: and, therefore, wiping
the face with a _cotton handkerchief_, increases the sensation of
warmth.
CHAPTER XIV.
2.--ABSORPTION OF HEAT.
Q. _What is the difference between CONDUCTING heat, and ABSORBING heat?_
A. To _conduct_ heat, is to _transmit it from one body to another_
through a conducting medium: to _absorb_ heat, is to _suck it up_, as a
sponge sucks up water.
Q. _Give me an example._
A. _Black cloth absorbs_, but does not _conduct heat_: thus, if black
cloth be laid in the sun, _it will absorb the rays_ very rapidly; but if
_one end of the black cloth_ be made hot, it would not _conduct the
heat_ to the _other_ end.
Q. _Are good CONDUCTORS of heat, good ABSORBERS also?_
A. No; every _good conductor of heat_ is a _bad absorber of it_; and _no
good absorber of heat_ can be a _good conductor_ also.
Q. _Is IRON a good ABSORBER of heat?_
A. No; _iron is a good conductor_, but a very _bad absorber_ of heat.
Q. _Why do the FENDER and FIRE-IRONS (which lie upon it) remain COLD,
although they are before a good fire?_
A. Because the metal fender and fire-irons have very _little capacity
for absorbing heat_; although they are soon made hot (by conduction),
when placed in _contact_ with the hot fire or stove.
Q. _Why does a KETTLE boil faster, when the bottom and back are COVERED
with SOOT?_
A. The _black soot absorbs heat_ very quickly from the fire, and the
metal _conducts it to the water_.
Q. _Why will not a NEW KETTLE boil so fast as an OLD one?_
A. Because the _bottom and sides_ of a new kettle are _clean and
bright_; but in an _old_ kettle _are covered with soot_.
Q. _Why would the KETTLE be SLOWER BOILING, if the BOTTOM and BACK were
CLEAN and bright?_
A. _Bright_ metal does _not absorb heat_, but _reflect it_ (i. e. throw
the heat _back_ again); and as the heat is _thrown off from the surface
of bright metal_, therefore, a new kettle is longer boiling.
Q. _Why do we wear WHITE LINEN and a BLACK outer DRESS, if we want to be
warm?_
A. The _black outer dress_ quickly _absorbs heat from the sun_, and
conveys it to the body; and the _white linen_ (being a _bad_ absorbent)
abstracts no heat from the warm body.
Q. _Why do persons WEAR WHITE dresses in SUMMER time?_
A. White _throws off the heat of the sun by reflection_, and is,
therefore, a very bad absorbent of heat; in consequence of which, it
never becomes _so hot from the scorching sun_ as dark colours do.
Q. _Why do NOT persons WEAR WHITE dresses in WINTER time?_
A. _White will not absorb heat_, like black and other dark colours; and,
therefore, _white_ dresses are _not so warm as dark ones_.
Q. _What COLOURS are WARMEST for dresses?_
A. For _outside_ garments _black is the warmest_, and then such colours
as _approach nearest to black_ (as dark blue and green). _White is the
coldest colour_ for external clothing.
Q. _Why are DARK COLOURS (for external wear) so much WARMER than LIGHT
ONES?_
A. Because _dark colours absorb heat from the sun_ more abundantly than
_light_ ones.
Q. _How can you prove that DARK colours are WARMER than LIGHT ones?_
A. If a piece of _black_ cloth and a piece of _white_ were laid upon
snow, in a few hours the _black cloth will have melted the snow
beneath_; whereas the _white_ cloth will have produced little or _no
effect upon it at all_.
N. B. The darker any colour is, the warmer it is, because it is a better
absorbent of heat. The order may be thus arranged:--1. Black (warmest of
all).--2. Violet.--3. Indigo.--4. Blue.--5. Green.--6. Red.--8. Yellow:
and 9. White (coldest of all).
Q. _Why are BLACK KID GLOVES so HOT in summer time?_
A. 1st--Because the _black absorbs the solar heat_: and
2ndly--The _kid_ will not allow the heat of the hand _to escape through
the glove_.
Q. _Why are LISLE THREAD GLOVES so COOL in summer time?_
A. 1st--Because thread _absorbs the perspiration of the hands_: and
2ndly--It _conducts away the heat_ of our hot hands.
Q. _Are Lisle thread gloves ABSORBENTS of heat?_
A. As Lisle thread gloves are generally of a _grey or lilac colour_,
they do _not absorb solar heat_.
Q. _Why is a PLATE-WARMER made of UN-PAINTED BRIGHT TIN?_
A. Bright tin reflects (or _throws back_) _the heat_, which issues from
the fire in rays; and (by reflecting the heat upon the meat) assists
greatly in roasting it.
Q. _Why would not the tin REFLECTOR do as well if it were PAINTED?_
A. If the tin reflector were _painted_, it would be utterly spoiled,
because it would then _absorb_ heat, and _not reflect it at all_. A
plate-warmer should be kept _very clean, bright, and free from all
scratches_.
Q. _Why should a REFLECTOR be kept so very CLEAN and free from
SCRATCHES?_
A. If a reflector be _spotted, dull, or scratched_, it will _absorb_
heat, instead of _reflecting_ it; and, therefore, would be of no use
whatsoever as a _reflector_.
Q. _Why does HOAR-FROST remain on TOMBSTONES, long after it has melted
from the GRASS and GRAVEL-WALKS of a church-yard?_
A. Tomb-stones being _white_, will _not absorb heat_, like the darker
grass and gravel; and, therefore, _the white tombstones_ (being so much
colder) _retain the hoar-frost_ after it has melted from other things.
Q. _If black absorbs heat, why have those who live in HOT climates BLACK
SKINS, and not WHITE skins (which would not absorb heat at all)?_
A. Though the black skin of the negro _absorbs heat_ more plentifully
than the _white skin of a European_, yet the _blackness_ prevents the
sun from _blistering_ or _scorching it_.
Q. _How is it known that the BLACK colour prevents the sun from either
BLISTERING or SCORCHING the skin?_
A. If you put a _white glove_ on _one hand_, and a _black glove_ on _the
other_ (when the sun is burning hot), the hand with the _white_ glove
will be _scorched_, but _not the other_.
Q. _Which hand will FEEL the HOTTER?_
A. The hand with the _black glove_ will _feel_ the _hotter_, but it will
not be _scorched_ by the sun; whereas the hand with the _white glove_
(though much _cooler_) will be _severely scorched_.
Q. _Why does the BLACK skin of a NEGRO NEVER SCORCH or BLISTER with the
hot sun?_
A. Because the _black colour absorbs_ the heat,--conveys it _below the
surface_ of the skin, and converts it to _sensible heat_ and
_perspiration._
Q. _Why does the WHITE EUROPEAN SKIN BLISTER and SCORCH when exposed to
the hot sun?_
A. Because the _white will not absorb_ the heat; and, therefore, the hot
sun _rests on the surface of the skin_, and scorches it.
Q. _Why has a NEGRO BLACK EYES?_
A. The black colour of a negro's eyes defends them from the strong light
of the tropical sun. If a negro's eyes were not _black_, the sun would
_scorch them_, and every negro would be blind.
Q. _Why is WATER KEPT COOLER (in summer time) in a BRIGHT TIN POT, than
in an EARTHEN one?_
A. Because bright metal will _not absorb_ the heat of the summer sun,
like an _earthen_ vessel.
Q. _Why is BOILING water KEPT HOT in a BRIGHT TIN VESSEL longer, than in
an earthen one?_
A. Because bright tin will not suffer the heat of the boiling water _to
escape in rays_, as an earthen vessel does.
CHAPTER XV.
3.--REFLECTION OF HEAT.
Q. _What is meant by REFLECTING HEAT?_
A. To reflect heat, is _to throw it back in rays_ from the surface of
the reflecting body, towards the place from whence it came.
Q. _What are the BEST REFLECTORS of heat?_
A. All _bright_ surfaces, and _light colours_.
Q. _Are GOOD ABSORBERS of heat GOOD REFLECTORS also?_
A. No; those things _which absorb heat best, reflect_ heat _worst_; and
those _which reflect heat worst, absorb_ it _best_.
Q. _Why are those things which ABSORB HEAT unable to REFLECT it?_
A. Because if any thing _sucks in heat_ like a sponge, it cannot _throw
it off_ from its surface; and if any thing _throws off heat_ from its
surface, it cannot _drink it in_.
Q. _Why are REFLECTORS always made of LIGHT-COLOURED and highly POLISHED
METAL?_
A. Because _light_ coloured and _highly polished metal_ makes the best
of all reflectors.
Q. _Why do not PLATE-WARMERS BLISTER and scorch the WOOD behind?_
A. Because the bright tin front _throws the heat of the fire back
again_, and will not allow it to penetrate to the wood behind.
Q. _If metal be such an excellent CONDUCTOR of heat, how can it REFLECT
heat, or throw it off?_
A. Polished metal is a _conductor of heat_, only when _that heat is
communicated by actual contact_; but whenever heat _falls upon bright
metal in rays_, it is _reflected back again_, and the metal remains
_quite cool_.
Q. _What is meant by "heat falling upon metal IN RAYS," and not "by
contact"?_
A. If a piece of tin were thrust _into_ a fire, it would be _in actual
contact with the fire_; but if it be _held before a fire_, the heat of
the fire _falls upon it in rays_.
Q. _What is the use of the TIN SCREEN or REFLECTOR used in ROASTING?_
A. The tin reflector _throws the heat of the fire back upon the meat_;
and, therefore, assists the _process of roasting_ and helps _to keep the
kitchen cool_.
Q. _How does a tin REFLECTOR tend to keep the KITCHEN COOL?_
A. Because it _confines the heat to the hearth_, and prevents it from
being dispersed throughout the kitchen.
Q. _Why does a LAMP GLASS DIMINISH the SMOKE of a LAMP?_
A. As _glass is a reflector_, it reflects the heat of the lamp _back
upon the flame_; in consequence of which, _less carbon escapes
unconsumed_ (as smoke).
Q. _Why are SHOES HOTTER for being DUSTY?_
A. 1st--Because dust absorbs heat: and
2ndly--As it destroys the _blackness of our shoes_, it prevents them
from _throwing off the heat of our feet in rays_.
Q. _Why can we not SEE into the ROAD or STREET, when a CANDLE is lighted
in a room?_
A. _Glass is a reflector_; and, therefore, throws the rays of the candle
_back into the room_, and thus prevents our seeing into the road or
street.
Q. _Why can persons in the DARK STREET see into a ROOM (lighted by a
candle or lamp)?_
A. The pupil of the eye _expands greatly_, when persons are in the dark;
and, therefore, when any one in the dark street looks into a light room,
_his dilated pupil_ sees every thing distinctly.
Q. _Why does it always FREEZE on the TOP of a MOUNTAIN?_
A. Air is heated _by the reflection of the earth_, and not by the rays
of the sun; and, as there is no earth round a mountain-top _to reflect
heat_, therefore, it remains intensely cold.
CHAPTER XVI.
4.--RADIATION.
Q. _What is meant by RADIATION?_
A. Radiation means _the emission of rays_: thus the sun radiates both
light and heat; that is, it emits _rays of light and heat_ in all
directions.
Q. _When is heat RADIATED from one body to another?_
A. When the two bodies are _separated by a non-conducting medium_: thus
the sun _radiates_ heat towards the earth, because the _air comes
between_ (which is a very bad conductor).
Q. _On WHAT does RADIATION DEPEND?_
A. On the _roughness_ of the radiating surface: thus if metal be
_scratched_, its radiating power is increased, because the _heat has
more points to escape from_.
Q. _Does a FIRE RADIATE heat?_
A. Yes; and because _burning fuel emits rays of heat_, therefore we
_feel warm_ when we stand before a fire.
Q. _Why does our FACE FEEL uncomfortably HOT, when we approach a FIRE?_
A. Because the fire radiates heat upon the face; which (not being
_covered_) feels the effect immediately.
Q. _Why does the fire catch the FACE more than the REST of the body?_
A. The _rest_ of the body is _covered with clothing_, which (being a
_bad conductor_ of heat) prevents the same sudden and rapid
transmission of heat to the skin.
Q. _Do those substances which RADIATE heat, ABSORB heat also?_
A. Yes. Those substances which _radiate most_, also _absorb most heat_:
and those which _radiate least_, also _absorb the least_ heat.
Q. _Does any thing ELSE radiate heat, BESIDES the SUN and FIRE?_
A. Yes; _all_ things radiate heat in _some_ measure, but _not equally
well_.
Q. _What things RADIATE heat the NEXT BEST to the sun and fire?_
A. All _dull_ and _dark substances_ are _good radiators_ of heat; but
all _light_ and _polished substances_ are _bad radiators_ of heat.
Q. _Why does a POLISHED METAL TEA-POT make BETTER TEA than a black
earthen one?_
A. As polished metal is a very _bad radiator_ of heat, it _keeps the
water hot much longer_; and the hotter the water is, the better it
"draws" the tea.
Q. _Why will not a DULL BLACK TEA-POT make good tea?_
A. Because the heat of the water _flies off so quickly_ through the dull
black surface of the tea-pot, that the _water is rapidly cooled_, and
will not "draw" the tea.
Q. _Do not pensioners, and most aged cottagers, prefer the little BLACK
EARTHEN TEA-POT to the bright METAL one?_
A. Yes; because they _set it on the hob "to draw;"_ in which case, the
little _black tea-pot_ will make the _best tea_.
Q. _Why will a BLACK TEA-POT make better tea than a bright metal one, if
it be set upon the HOB to DRAW?_
A. Because the black tea-pot will _absorb heat plentifully_ from the
fire, and keep the water _boiling hot_: whereas, a bright _metal_
tea-pot (set upon the hob) would _throw off_ the heat by _reflection_.
Q. _Then sometimes a BLACK EARTHEN tea-pot is the best, and sometimes a
bright METAL one?_
A. Yes; when the tea-pot is _set on the hob "to draw,"_ the black
_earth_ is the _best_, because it _absorbs heat_: but when the tea-pot
is _not_ set on the hob, the bright _metal_ is the _best_, because it
_radiates heat very slowly_, and therefore _keeps the water hot_.
Q. _Why does a SAUCEPAN which has been USED, boil QUICKER than a NEW
ONE?_
A. Because the bottom and back are _covered with soot_; and the _black
soot_ rapidly _absorbs the heat_ of the glowing coals.
Q. _Why should the FRONT and LID of a SAUCEPAN be clean and BRIGHT?_
A. As they do not come in contact with the fire, they cannot _absorb
heat_; and (being bright) they will not suffer _the heat to escape_ by
radiation.
Q. _In what state should a SAUCEPAN be, in order that it may BOIL
QUICKLY?_
A. All those parts which _come in contact with the fire_ should be
covered with _soot_, to absorb heat; but all the _rest_ of the saucepan
should be as _bright as possible_, to prevent the _escape of heat_ by
radiation.
Q. _Why is it said that "SATURDAY'S KETTLE BOILS the FASTEST?"_
A. Because on Saturday the _front_ and _top_ of the kettle are generally
_cleaned_ and _polished;_ but the _bottom_ and _back_ of the kettle are
_never_ cleaned.
Q. _Why should NOT the BOTTOM and BACK of a kettle be CLEANED and
polished?_
A. Because they _come in contact with the fire_, and (while they are
covered with black soot) _absorb heat freely_ from the burning coals.
Q. _Why should the FRONT and TOP of a kettle be CLEAN and well
polished?_
A. Because polished metal _will not radiate heat_; and, therefore,
(while the front and top of the kettle are well polished) _the heat is
kept in_, and not suffered to escape by radiation.
Q. _Why is the INSIDE of a KETTLE and SAUCEPAN WHITE?_
A. _White will not radiate heat_: if, therefore, the inside of a boiler
be _white_, the liquor in it is _kept hot much longer_.
Q. _Why is the BOTTOM of a KETTLE nearly COLD, when the WATER is BOILING
HOT?_
A. Black soot is a very _bad conductor of heat_; and, therefore, the
heat of the boiling water is some considerable time, before it gets
_through the soot_ which adheres to the bottom of the kettle.
Q. _Why is the LID of a KETTLE so intensely HOT, when the water boils?_
A. The bright metal lid of the kettle _is an admirable conductor_ of
heat; and, therefore, _the heat from the boiling water pours into our
hand_ the moment we touch it.
Q. _Show the benefit of SMOKE in COOKING._
A. The carbon of the fuel (which flies off in smoke) naturally
_blackens_ all culinary vessels set upon the fire to boil, and thus
renders them fit for use.
("Culinary vessels" are vessels used in kitchens for cooking, as
saucepans, boilers, kettles, &c.)
Q. _How does SMOKE make culinary vessels FIT for USE?_
A. If it were not for the _smoke_, (which gathers round a kettle or
saucepan) _heat would not be absorbed_, and the process of boiling would
be greatly retarded.
Q. _Why is boiling water KEPT HOT best in a BRIGHT METAL pot?_
A. Because bright metal being a _bad radiator_ will not _throw off the
heat_ of the boiling water _from its surface_.
Q. _Why is WATER KEPT COLD in summer-time in a BRIGHT METAL pot, better
than in an EARTHEN vessel?_
A. Because bright metal _will not absorb heat_ from the hot air, like an
_earthen vessel_; in consequence of which, the water is kept cooler.
Q. _Why are DINNER-COVERS made of BRIGHT TIN or SILVER?_
A. Light-coloured and highly-polished metal _is a very bad radiator of
heat_; and, therefore, bright tin or silver will not allow the heat of
the cooked food _to escape through the cover by radiation_.
Q. _Why should a MEAT-COVER be very brightly POLISHED?_
A. If the cover be _dull or scratched_ it will _absorb heat from the hot
food beneath it_; and (instead of _keeping it hot_) will _make it cold_.
Q. _Why should a SILVER MEAT-COVER be PLAIN, and not CHASED?_
A. If the cover be _chased_, it will _absorb the heat of the food_
covered by it; and instead of _keeping it hot_, will _make it cold by
absorption_.
Q. _What is DEW?_
A. Dew is the _vapour of the air condensed_, by coming in contact with
bodies _colder than itself_.
Q. _Why is the GROUND sometimes COVERED with DEW?_
A. The _earth is more heated_ by solar rays _than the air_, during the
_day_; but at _night_, the earth _parts with more heat_ than the _air_,
and becomes (in consequence) 5 or 10 degrees _colder_.
Q. _How does the EARTH being COLDER than the AIR account for the
deposition of DEW?_
A. As soon as the air _touches the cold earth_, its warm vapour is
_chilled_, and _condensed into dew_.
Q. _Why is the surface of the GROUND COLDER in a FINE clear NIGHT, than
in a CLOUDY one?_
A. On a fine clear star-light night, _heat radiates from the earth
freely_, and is lost in open space: but on a _cloudy_ night, the clouds
_arrest the process of radiation_.
Q. _Why is DEW deposited only on a FINE clear NIGHT?_
A. Because, when the night is _clear_ and _fine_, the _surface of the
ground radiates heat most freely_; and (being cooled down by this loss
of heat) _chills the vapour of the air into dew_.
Q. _Why is there NO DEW on a dull CLOUDY NIGHT?_
A. The clouds _arrest the radiation of heat from the earth_; and (as the
heat cannot freely escape) the surface is not sufficiently cooled down
_to chill the vapour of the air into dew_.
Q. _Why is a CLOUDY NIGHT WARMER than a FINE one?_
A. Because the clouds _prevent the radiation of heat from the earth_;
and, therefore, the surface of the earth remains _warmer_ on a dull
cloudy night.
Q. _Why is DEW most ABUNDANT in situations most EXPOSED?_
A. Because the radiation of heat _is not arrested_ by houses, trees,
hedges, or any other thing.
Q. _Why is there scarcely any DEW under a shady TREE?_
A. The shady head of the tree both _arrests the radiation of heat from
the earth_, and also radiates some of its own heat _towards the earth_;
and, therefore, the ground (underneath a tree) _is not sufficiently
cooled_ down to chill the vapour of the air into dew.
Q. _Why is there never much DEW at the foot of WALLS and HEDGES?_
A. 1st--Because the wall or hedge acts as a screen, _to arrest the
radiation of heat from the earth_: and
2ndly--The wall or hedge also _radiates some portion of heat_ towards
the earth.
Q. _How do these things prevent the deposition of dew?_
A. As the ground (beneath a wall, tree, or hedge) is _not cooled by the
radiation of heat_, it remains of the _same temperature as the air_
above it; in consequence of which, the vapours of the air are _not
chilled by it into dew_.
Q. _Why is there little or NO DEW beneath a FLOWER-AWNING, although that
awning be open on all four sides?_
A. 1st--Because the awning _arrests the radiation of heat from the
ground beneath_: and
2ndly--It _radiates some of its own heat downwards_; in consequence of
which, the ground beneath an awning is _not sufficiently cooled down_ to
chill the vapour of air into dew.
Q. _How can a thin covering of BASS or even MUSLIN protect trees from
FROST?_
A. Because _any covering_ prevents the _radiation of heat from the
tree_; and if the tree be _not cooled down by radiation_, the vapour of
the air will _not be frozen_ as it comes in contact with it.
Q. _Why is the BASS or CANVASS itself (which covers the tree) always
DRENCHED with DEW?_
A. The bass or canvass covering _radiates heat_ both _upwards and
downwards_; and is, therefore, _so cooled down_, that it readily _chills
all the vapour of the air_ (which passes over it) _into dew_.
Q. _Why does SNOW at the foot of a HEDGE or WALL melt sooner, than in an
open field?_
A. Because the hedge or wall _radiates heat into the snow beneath_,
which melts it.
Q. _Why is there NO DEW after a WINDY NIGHT?_
A. 1st--Because the wind _evaporates the moisture_, as fast as it is
deposited; and
2ndly--It _disturbs the radiation of heat_, and diminishes the
deposition of dew thereby.
Q. _Why are VALLEYS & HOLLOWS often thickly covered with DEW, although
they are sheltered?_
A. The surrounding hills prevent the _repose of air_ (in the valleys)
_from being disturbed_; but do not _overhang_ and _screen_ them, so as
to _arrest their radiation_.
Q. _Why does DEW FALL more ABUNDANTLY on SOME THINGS than upon OTHERS?_
A. Because some things _radiate heat more freely_ than others, and
therefore become _much cooler_ in the night.
Q. _Why are things which RADIATE HEAT MOST FREELY, always the most
THICKLY COVERED with DEW?_
A. Because the vapour of the air is _chilled into dew_, the moment it
comes in contact with them.
Q. _What kind of things RADIATE HEAT most FREELY?_
A. Grass, wood, and the leaves of plants, radiate heat _very freely_:
but polished metal, smooth stones, and woollen cloth, part with their
heat _very tardily_.
Q. _Do the leaves of ALL plants radiate heat EQUALLY WELL?_
A. No. Rough _woolly leaves_ (like those of a holly-hock) radiate heat
much _more freely_, than the _hard smooth polished leaves_ of a common
laurel.
Q. _Shew the WISDOM of GOD in making grass, the leaves of trees, and ALL
VEGETABLES, EXCELLENT RADIATORS of heat._
A. As vegetables _require much moisture_, and would often perish without
a plentiful deposit of dew, God wisely made them to _radiate heat
freely_, so as to _chill the vapour_ (which touches them) _into dew_.
Q. _Will polished METAL, smooth STONES, and woollen CLOTH, readily
collect DEW?_
A. No. While grass and the leaves of plants _are completely drenched
with dew_, a piece of _polished metal_, or of _woollen cloth_ (lying on
the same spot) will be _almost dry_.
Q. _Why would POLISHED METAL and WOOLLEN CLOTH be DRY, while grass and
leaves are drenched with DEW?_
A. Because the polished metal and woollen cloth _part with their heat so
slowly_, that the vapour of the air is _not chilled into dew_ as it
passes over them.
Q. _Why is a GRAVEL WALK almost DRY, when a grass plat is covered thick
with DEW?_
A. _Grass_, (_being a good radiator_) throws off its heat very _freely_;
but _gravel (being a very bad radiator)_ parts with its heat very
_reluctantly_.
Q. _Is that the reason why GRASS is SATURATED with DEW, and the GRAVEL
is NOT?_
A. Yes. When the vapour of warm air comes in contact with the _cold
grass_, it is instantly chilled into dew; but (as the gravel is _not so
cold as the grass_) the vapour of air is _not so freely condensed_ as it
passes over the gravel.
Q. _Why does DEW rarely fall upon hard ROCKS and BARREN lands?_
A. Rocks and barren lands are so _compact_ and _hard_, that they can
neither _absorb nor radiate much heat_; and (as their _temperature
varies but very little_) very little _dew_ distils upon them.
Q. _Why does DEW fall more abundantly on CULTIVATED soils, than on
BARREN lands?_
A. Because cultivated soils (being _loose and porous_) _absorb_ heat
freely during the day, and _radiate it_ by night; and (being _much
cooled by the rapid radiation of heat_) as the vapour of the air passes
over them, it is plentifully _condensed into dew_.
Q. _Shew the WISDOM of GOD in this arrangement._
A. Every plant and inch of land which _needs the moisture of dew_, is
adapted to _collect it_; but _not a single drop even of dew is wasted_,
where its refreshing moisture is _not required_.
Q. _Shew the WISDOM of GOD in making polished METAL and woollen CLOTH
BAD RADIATORS of heat._
A. If polished metal collected dew as easily as grass, it could _never
be kept dry_, and _free from rust_. Again, if woollen garments
collected dew as readily as the leaves of trees, we should be _often
soaking wet_, and subject to _constant colds_.
Q. _Shew how this affords a beautiful illustration of GIDEON'S MIRACLE,
recorded in the book of Judges, VI. 37, 38._
A. The _fleece of wool_ (which is a _very bad radiator_ of heat) was
_soaking wet_ with dew: when the _grass_ (which is a most _excellent
radiator_) was _quite dry_.
Q. _Was not this CONTRARY to the laws of NATURE?_
A. Yes; and was, therefore, a plain _demonstration of the power of God_,
who could change the very _nature of things_ at his will.
Q. _Why do our CLOTHES FEEL DAMP, after walking in a fine evening in
SPRING or AUTUMN?_
A. Because the vapour (_condensed by the cold earth_) lights upon them,
like dew.
Q. _Why are WINDOWS often covered with thick MIST, and the frames wet
with standing WATER?_
A. The temperature of the _external air_ always _falls at sun-set_, and
_chills the window-glass_, with which it comes in contact.
Q. _How does this account for the MIST and WATER on a WINDOW?_
A. As the warm vapour of the room _touches the cold glass_, it is
_chilled_ and _condensed into mist_; and the mist (collecting into
drops) _rolls down the window-frame_ in little streams of water.
Q. _Does the GLASS of a window COOL down more RAPIDLY than the AIR of
the room itself?_
A. Yes; because the air is _kept warm by fires_, and the _animal heat_
of the people in the room; in consequence of which, the _air of a room
suffers very little diminution of heat_ from the setting of the sun.
Q. _Whence arises the VAPOUR of a ROOM?_
A. 1st--The very _air_ of the room _contains vapour_:
2ndly--The _breath_ and _insensible perspiration_ of the inmates
_increase_ this vapour: and
3rdly--_Hot dinners_, the _steam of tea_, &c. contribute to _increase it
still more_.
Q. _What is meant by "the INSENSIBLE PERSPIRATION?"_
A. From every part of the human body an _insensible and invisible
perspiration issues_ all night and day; not only in the hot weather of
_summer_, but also in the coldest day of _winter_.
Q. _If the perspiration be both INSENSIBLE and INVISIBLE, how is it
KNOWN that there IS any such perspiration?_
A. If you put your naked arm _into a clean dry glass cylinder_, the
_perspiration_ of your arm will soon _condense_ on the glass, like mist.
Q. _Why are CARRIAGE WINDOWS very SOON covered with thick MIST?_
A. The warm vapour of the carriage _is condensed the moment it touches
the cold glass_, and covers it over with a thick mist.
Q. _Why is the glass window COLD enough to condense the vapour of the
carriage?_
A. Because the _inside_ of the carriage is much _warmer_ than the
_outside_, and the glass window is made cold by contact with the
_external air_.
Q. _Where does the WARM vapour of the carriage come from?_
A. The warm _breath_ and _insensible perspiration_ of the persons riding
in the carriage, load the air of it with warm vapour.
Q. _What is the cause of the pretty FROST-WORK seen on bed-room WINDOWS
in winter-time?_
A. The _breath_ and _insensible perspiration_ of the sleeper (coming in
contact with the ice-cold window) is _frozen_ by the cold glass, and
forms those beautiful appearances seen in our bed-rooms in a winter
morning.
Q. _Why is the GLASS of a window colder than the WALLS of a room?_
A. Glass is a very _excellent radiator_; and, therefore, most _rapidly
parts with its heat_.
Q. _Why is a TUMBLER of cold WATER made quite DULL with mist, when
brought into a room FULL of PEOPLE?_
A. Because the _hot vapour of the room_ (coming in contact with the cold
tumbler) _is condensed upon it_; and changes its invisible and gaseous
form for that of a _thick mist_.
Q. _Why is a GLASS made quite DULL, by laying a HOT HAND upon it?_
A. The _insensible perspiration_ of the hot hand is _condensed_ upon the
cold glass, and thus made perceptible.
Q. _Why are WINE-GLASSES made quite DULL when they are brought into a
room FULL of COMPANY?_
A. The _hot vapour of the room_ (coming in contact with the cold
wine-glasses) _is condensed_ upon them, and covers them with vapour like
dew.
Q. _Why does this misty appearance GO OFF after a little time?_
A. Because the glass becomes of the _same temperature_ as the _air of
the room_, and will no longer _chill the vapour_ which touches it, and
_condense it into mist_.
Q. _Why is a WINE-GLASS (brought out of a CELLAR into the AIR) covered
with a thick MIST in summer-time?_
A. The vapour of the hot air is _condensed_ by the cold glass, and
covers it as a thick mist.
Q. _Why does BREATHING on a GLASS make it quite DULL?_
A. Because the hot breath is _condensed_ by the cold glass; and,
therefore, covers it with a thick mist.
Q. _Why do WALLS stand thick with WET in a sudden THAW?_
A. The walls (being thick) cannot _change their temperature so fast_ as
the thin air can; and, therefore, they _retain their cold_ after the
thaw has set in.
Q. _How does RETAINING their COLD account for their being so WET?_
A. As the vapour of the warm air _touches the cold wall_, it is
_chilled_ and _condensed into water_, which _sticks to the wall_, and
sometimes trickles down in little streams.
Q. _Why does a thick WELL-BUILT HOUSE contract more DAMP of this kind,
than an ORDINARY one?_
A. Because the walls are much _thicker_; and (if the frost has
penetrated _far into the bricks_) it takes a long time to reduce them to
the _same temperature as the air_.
Q. _Why are BANISTERS, &c. DAMP after a THAW?_
A. The wooden banister (being made of some very close-grained, varnished
wood) cannot _change its temperature so fast_ as the air; and,
therefore, _remains cold_ some time after the thaw has set in.
Q. _How does THIS account for the BANISTERS being DAMP?_
A. The vapour of the warm air (_coming in contact with the cold
banister_) is _chilled_, and condensed into _water upon it_.
Q. _Why is our BREATH VISIBLE in WINTER and NOT in SUMMER?_
A. In _winter_ the coldness of the air condenses our breath into
_visible vapour_; but in _summer_ the air is _not cold enough_ to
condense it into visible vapour.
Q. _Why are our HAIR and the BRIM of our HAT often covered with little
drops of pearly DEW in winter-time?_
A. The breath (issuing from our mouth and nose) _is condensed into
drops_, as it comes in contact with our cold hair or hat; and (being
condensed) hangs there in little dew-drops.
Q. _Why does the STEAM of a RAILWAY BOILER often pour down, like fine
rain, when the steam is "let off?"_
A. The steam from the steam-pipe (when the air is cold) _is condensed by
contact with the chill air_, and falls like fine rain.
Q. _Why is there LESS DEW when the WIND is EASTERLY, than when the wind
is WESTERLY?_
A. _Easterly_ winds cross the _continent of Europe_, and, (as they pass
over _land_) are _dry_ and _arid_; but _westerly_ winds cross the
_Atlantic Ocean_; and (as they pass over _water_) are _moist_ and _full
of vapour_.
Q. _How does the DRYNESS of an eastern wind PREVENT DEW-FALLS?_
A. As the easterly winds are _dry_, they _imbibe_ the moisture of the
air; and, therefore, there _is very little_ left to be condensed into
_dew_.
Q. _How does the MOISTNESS of a western wind PROMOTE dew-falls?_
A. As the westerly winds are _saturated with vapour_, they require a
_very little reduction of heat_ to cause a _copious deposition of dew_.
Q. _When is DEW most COPIOUSLY distilled?_
A. After a hot day in summer or autumn, with the _wind in the west_.
Q. _Why is DEW distilled most COPIOUSLY after a HOT day?_
A. Because the surface of the earth _radiates_ heat very freely at
sunset; and (becoming thus _much colder than the air_) _chills its
vapour_, and condenses it into dew.
Q. _Does not AIR radiate heat, as well as the EARTH and its various
plants?_
A. No. The air _never radiates heat_, nor is the air itself _made hot_
by the _rays of the sun_.
Q. _How is the AIR made HOT or COLD?_
A. By _convection of hot or cold currents_.
Q. _What is meant by "CONVECTION of hot and cold currents?"_
A. The air (which is heated by the surface of the earth) _ascends,
warming the air_ through which it passes. _Other_ air (being warmed in a
similar way) _also ascends, carrying heat_; till _all the air_ is made
hot.
Q. _Is the AIR made COLD in a similar way?_
A. Yes. The air resting on the earth is _made cold by contact_: this
cold air makes the _air above it cold_; and cold currents or winds
_shake the whole together_, till all becomes of one temperature.
Q. _Why is MEAT very subject to TAINT on a MOON-LIGHT night?_
A. In a bright moon-light night, _meat radiates heat very freely_; and
is, therefore, soon _covered with dew_, which produces _rapid
decomposition_.
Q. _Why do PLANTS GROW RAPIDLY in MOON-LIGHT nights?_
A. In bright moon-light nights _rapid radiation is carried on_, and _dew
is plentifully deposited_ on young plants, which conduces much to their
growth and vigour.
Q. _Why is evening DEW INJURIOUS to HEALTH?_
A. Because the condensed vapours are always laden with _noxious
exhalations from the earth_: this is especially the case in _marshy_
countries.
Q. _Is HONEY-DEW a similar thing to DEW?_
A. No. Honey-dew is a sweet liquid _shed by a very small insect_ (called
the aphis), and deposited in autumn _on the under surface_ of favourite
leaves.
Q. _Does HONEY-DEW INJURE leaves, or do them good?_
A. It injures them very much, because it _fills the pores_ of the leaf
with a _thick clammy liquid_; and, therefore, prevents the leaf from
_transpiring and absorbing_.
Q. _What EFFECT has honey-dew upon the APPEARANCE of a leaf?_
A. After a little time, the leaf (being _smothered_ and _starved_)
begins to turn a _dingy yellow_.
Q. _Are not ANTS very FOND of HONEY-DEW?_
A. Yes; and they crawl up the loftiest trees, in order to obtain it.
Q. _What is the cause of MIST (or earth-fog)?_
A. If the _night has been very calm_, a _rapid_ radiation of heat has
taken place in the earth; in consequence of which, the _air_ (resting on
the earth) _is made so cold_, that its vapour is _chilled_, and
condensed into a thick mist.
Q. _Why does not the MIST become DEW?_
A. Because the chill of the air _is so rapid_, that vapour is condensed
_faster than it can be deposited_; and (covering the earth in a mist)
_prevents any further radiation of heat_ from the earth.
Q. _When the earth can no longer RADIATE heat upwards, does it continue
to CONDENSE the vapour of the air?_
A. No; the air (in contact with the earth) becomes about _equal in
temperature_ with the surface of the earth itself; for which reason, the
mist is _not condensed into dew_, but remains _floating above the earth_
as a thick cloud.
Q. _Why does this MIST seem to RISE HIGHER and HIGHER, and yet remain
quite as dense below as before?_
A. The air _resting on the earth_ is first chilled, and _chills the air_
resting on _it_; the air which touches _this new layer of mist_ being
also _condensed_, layer is added to layer; and the mist seems to be
_rising_, when (in fact) it is only _deepening_.
Q. _Why does MIST and DEW VANISH as the SUN rises?_
A. Because the condensed vapour is _again rarefied by the heat of the
sun_, and separated into invisible particles.
Q. _Why is a DEW-DROP ROUND?_
A. Because every part of the drop _is equally balanced_; and, therefore,
there is no cause why _one part_ of the drop _should be further from the
centre_ than _another_.
Q. _Why is the DEW-DROP on a broad leaf sometimes FLATTENED?_
A. Whenever two or more drops of dew _roll together_, they make one
large _spheroid_ (or flattened drop).
Q. _Why will DEW-DROPS ROLL ABOUT CABBAGE-PLANTS, POPPIES, &c. without
wetting the surface?_
A. The leaves of cabbages and poppies are _covered with a very fine
powder_; and the dew-drop rolls over this fine powder, as a drop of rain
_over dust_, without wetting the surface.
Q. _Why does not the drop of RAIN WET the DUST over which it rolls?_
A. Because it is driven from grain to grain by _capillary repulsion_.
Q. _Why does not the DEW-DROP WET the POWDER of the CABBAGE-plant?_
A. Because it is driven from grain to grain by _capillary repulsion_.
Q. _Why will DEW-DROPS ROLL over ROSES, &c. without wetting their
petals?_
A. The leaves of a rose _contain an essential oil_, which prevents them
from absorbing the dew immediately.
Q. _Why can a SWAN or DUCK dive under water WITHOUT being WETTED?_
A. Because their feathers are covered _with an oily secretion_, which
repels the water.
Q. _What is the cause of MIST?_
A. When currents of air _from land_ mix with currents of air _from
water_, the currents _from the water are condensed into mist_ by the
colder currents _blowing from the land_.
Q. _Why are the currents of air from the LAND COLDER than those blowing
over WATER?_
A. Because the earth _radiates heat very freely_, and (being greatly
cooled down) _cools the air also_ which comes in contact with it.
Q. _Why is not the AIR, which passes over WATER, so COOL as that which
passes over LAND?_
A. Because _water does not cool down at sun-set_, so fast as the _land_
does; and, therefore, the air in contact with it is _warmer_.
Q. _Why does not WATER cool down so fast as LAND?_
A. 1st--Because the _surface_ of water is _perpetually changing_, and as
fast as _one_ surface is made cold, _another_ is presented: and
2ndly--The moment water is made cold _it sinks_, and _warmer portions of
water rise to occupy its place_: therefore, before the _surface of water
is cooled_, the _whole volume_ must be made cold; which is not the case
with land.
Q. _What is the cause of a "pea-soup" LONDON FOG?_
A. These fogs (which occur generally in the winter time) are occasioned
thus:--Some current of air (being suddenly _cooled_) _descends into the
warm streets_, preventing the rise of the smoke, and _forcing it back in
a mass_ towards the earth.
Q. _Why are there not ALWAYS FOGS every night?_
A. Because the air will always hold in solution a certain quantity of
vapour, (which varies according to its temperature): and when the air is
_not saturated with vapour_, it may be condensed without parting with
it.
Q. _Why are there EVER FOGS at night?_
A. If the air be _pretty well saturated with vapour_ during the day, as
soon as its capacity for holding vapour _is lessened by the cold night_,
it deposits some of the superabundant vapour in the form of dew or fog.
Q. _Why is there very OFTEN a fog over MARSHES and RIVERS at
night-time?_
A. The air of marshes is almost _always near saturation_; and,
therefore, the _least depression of temperature_, will compel it to
relinquish some part of its moisture in dew or fog.
Q. _What is the DIFFERENCE between DEW and RAIN?_
A. In _dew_, the condensation is made _near the earth's surface_:
In _rain_, the drops fall _from a considerable height_; but the cause of
both is the same, viz.--COLD _condensing the vapour of the air_, when
it is near the point of _saturation_.
Q. _Why does MIST and FOG VANISH at sunrise?_
A. Because the condensed particles are again _changed into invisible
vapour_, by the heat of the sun.
Q. _What is the difference between a MIST and FOG?_
A. MIST is generally applied to _vapours condensed on marshes, rivers_,
and _lakes_.
FOG is generally applied to _vapours condensed on land_, especially if
those vapours are _laden with smoke_.
Q. _What is the reason why condensed vapour sometimes forms into CLOUDS,
and sometimes into FOG?_
A. If the surface of the EARTH be _hotter than the air_, then the vapour
of the earth (_being chilled by the cold air_) becomes FOG: but if the
AIR be _hotter than the earth_, the vapour _rises through the air_, and
becomes CLOUD.
Q. _If cold air produces FOG, why is it not foggy on a FROSTY MORNING?_
A. 1st--Because _less vapour is formed on a frosty day_; and
2ndly--The vapour _is frozen upon the ground_ before it can rise from
the earth, and becomes HOAR-FROST.
Q. _Why are FOGS more general in AUTUMN than in spring?_
A. In spring _the earth is not so hot_ as it is in autumn. In AUTUMN the
_earth_ is generally _warmer than the air_; and, therefore, the vapour
(issuing from the earth) _is condensed into fog_ by the chill air.
Q. _Why are FOGS more common in VALLEYS than on HILLS?_
A. 1st--Because valleys _contain more moisture than hills_: and
2ndly--They are _not exposed to so much wind_, (which dissipates the
vapour).
Q. _How does WIND dissipate FOGS?_
A. Either by _blowing them away_; or else by _dissolving them into
vapour again_.
Q. _What is HOAR-FROST?_
A. There are two sorts of hoar-frost: 1.--FROZEN DEW: and 2.--FROZEN
FOG.
Q. _What is the cause of the GROUND hoar-FROST, or frozen DEW?_
A. Very _rapid radiation of heat from the earth_; in consequence of
which, the _surface is so cooled down_, that it _freezes the dew_
condensed upon it.
Q. _Why is HOAR-FROST seen only after a very CLEAR NIGHT?_
A. Unless the night has been very clear indeed, the earth will not have
thrown off heat enough by radiation, to _freeze_ the vapour condensed
upon its surface.
Q. _Why does HOAR-FROST very often COVER the GROUND and TREES, when the
water of rivers is not frozen?_
A. Hoar-frost is not the effect of cold in the _air_, but the cold of
the _earth_ (produced by excessive radiation); in consequence of which,
_the dew_ (condensed upon it) _is frozen_.
Q. _Why is the HOAR-FROST upon GRASS and VEGETABLES much thicker than
that upon lofty TREES?_
A. Because the air (resting on the _surface of the ground_) is much
colder after sun-set, than the _air higher up_; in consequence of
which, more vapour is condensed and frozen there.
Q. _Why is the AIR (resting on the surface of the EARTH) colder than
that in the HIGHER regions?_
A. Because the _earth radiates more heat_ than the _leaves of lofty
trees_; and, therefore, _condenses and freezes_ the vapour of the air
_more rapidly_.
Q. _Why are EVERGREENS often FROST-BITTEN, when lofty trees are NOT?_
A. Evergreens do not _rise far above the surface of the earth_; and (as
the air _contiguous to the earth_ is much _colder than that in the
higher regions_) therefore, the _low evergreen is often frost-bitten_,
when the lofty tree is uninjured.
Q. _Why are TOMB-STONES covered with HOAR-FROST, long after it has
melted from every object around?_
A. _White is a very bad absorbent of solar heat_; and, therefore, the
_white tomb-stone_ remains _too cold_ to thaw the frost congealed upon
its surface.
Q. _Why is there little or NO HOAR-FROST under SHRUBS and shadowy
TREES?_
A. 1st--Because the leafy shrubs and trees _arrest the process of
radiation_ from the earth: and
2ndly--Shrubs and trees _radiate a little heat_ towards the earth; and,
therefore, the _ground beneath_ is never _cold enough to congeal the
little dew_ which rests upon it.
Q. _What is the cause of that HOAR-FROST which arises from FROZEN FOG?_
A. The thick fog (which invested the earth during the night) is
condensed _by the cold frost_ of early morning, and _congealed upon
every object_ with which it comes in contact.
CHAPTER XVII.
5.--CONVECTION.
Q. _What is meant by the CONVECTION of HEAT?_
A. Heat communicated _by being carried_ to another thing or place; as
the hot water resting on the _bottom_ of a kettle, carries heat to the
water _through which it passes_. (_see p._ 246).
Q. _Are LIQUIDS good CONDUCTORS of heat?_
A. No; liquids are _bad conductors_; and are, therefore, made hot by
_convection_.
Q. _Why are LIQUIDS BAD CONDUCTORS of heat?_
A. Because heat _converts a liquid into steam_, and flies off with the
vapour, instead of being _conducted through the liquid_.
Q. _Explain how WATER is made HOT?_
A. The water _nearest the fire is first heated_, and (being heated)
_rises to the top;_ other cold water succeeds, is _also_ heated, and
rises in turn; and this interchange keeps going on, _till all the water
boils_.
Q. _Why is WATER in such continual FERMENT, when it is BOILING?_
A. This commotion is mainly produced by the _ascending and descending
currents_ of hot and cold water.
The escape of _air_ from the water contributes also to increase this
agitation.
Q. _How do these two currents PASS each other?_
A. The _hot ascending current_ passes close by the _metal sides_ of the
kettle; while the _cold descending current_ passes _down the centre_.
Q. _Why does BOILING WATER BUBBLE?_
A. The bubbles are _portions of steam_ (formed at the bottom of the
vessel) which _rise to the surface_, and escape into the air.
Q. _Why does a KETTLE RUN OVER, when the water BOILS?_
A. As the heat insinuates itself between the particles of water, _it
drives them asunder_; and (as the particles of water are _driven apart
from each other_) the _same_ vessel will no longer hold the expanded
water, and some runs over.
Q. _Why does a KETTLE SING, when it is ABOUT to BOIL?_
A. Water contains _a great deal of air_, which (being expanded by the
heat of the fire) escapes by fits _through the spout of the kettle_;
which sings in the same way as a trumpet does, when a person blows in
it.
Q. _Why does WATER BOIL?_
A. Boiling is the effect of a _more violent escape of air_ from the
heated water; when, therefore, the air is _not permitted to escape_,
water will _never boil_.
Q. _Why is HEAT applied to the BOTTOM, and not to the top of a KETTLE?_
A. Because the heated water _always ascends to the surface_, heating the
water through which it passes: if, therefore, heat were applied to the
_top of a vessel_, the water _below the surface_ would _never be
heated_.
Q. _As the lower part of a GRATE is made RED-HOT by the fire ABOVE, why
would not the WATER boil, if fire were applied to the TOP?_
A. The _iron_ of a grate is an _excellent conductor_; and, therefore, if
_one_ part be heated, the heat is conducted to _every other part_: but
_water_ is a _very bad conductor_, and will not diffuse heat in a
similar way.
Q. _How do you know that WATER is a BAD CONDUCTOR of heat?_
A. When a blacksmith immerses his red-hot iron in a tank of water, the
water which _surrounds_ the red-hot iron is made _boiling hot_, but the
water _below_ the surface remains quite cold.
Q. _If you wish to COOL LIQUIDS, where should the cold be applied?_
A. To the _top of the liquid_; because the _cold_ portion will always
_descend_, and allow the warmer parts to come in contact with the
cooling substance.
Q. _Does BOILING water get hotter by being KEPT on the FIRE?_
A. No; not if the steam be suffered to escape.
Q. _Why does not boiling water get HOTTER, if the steam be suffered to
ESCAPE?_
A. Because _as fast as the water boils_, it is converted into _steam_;
and the steam _carries away_ the additional heat, as fast as it is
communicated.
Q. _Is STEAM visible or INVISIBLE?_
A. Steam is _invisible_; but when it comes in contact with the air
(being _condensed into small drops_) it instantly becomes visible.
Q. _How do you know that STEAM is INVISIBLE?_
A. If you look at the spout of a boiling kettle, you will find that the
steam (which issues from the spout) is always invisible _for about half
an inch_; after which, _it becomes visible_.
Q. _Why is the steam INVISIBLE for only HALF AN INCH, and not either all
INVISIBLE or all VISIBLE?_
A. The air is not able to condense the steam as it first issues from the
spout, but when it _spreads_ and comes in contact with a larger volume
of air, the _invisible steam_ is readily condensed into _visible drops_.
Q. _Why is our BREATH VISIBLE in winter-time?_
A. Because _it is condensed by the cold air_ into small drops, which are
visible to the eye.
Q. _Why do STEAM-ENGINES sometimes BURST?_
A. Steam is very _elastic_; and this elasticity increases in a greater
proportion than the heat which produces it; unless, therefore, some
_vent_ be freely allowed, the steam heaves and swells, till it bursts
the vessel which confined it.
Q. _What BECOMES of the steam, after it has been condensed?_
A. It is _dissolved by the air_, and forms a part of its invisible
vapour.
Q. _Is AIR a good CONDUCTOR?_
A. No; _air is a very bad conductor_, and is heated (like water) _by
convection_.
Q. _How is a ROOM WARMED by a STOVE?_
A. The air _nearest the fire_ is made hot _first_; _the cold air
descends_, is heated also, and rises in turn; and this goes on, _till
all the air of the room is warmed_.
Q. _Why are FIRES placed on the FLOOR of a room, and not towards the
CEILING?_
A. As heated air always _ascends_, if the fire were not _near the
floor_, the lower part of the air (which we want to be the warmest)
would never be benefited by the fire at all.
Q. _If you take a POKER out of the fire, and hold the HOT END DOWNWARDS,
why is the HANDLE so intensely HOT?_
A. Because the hot end of the poker _heats the air around it_, and this
hot air (in its ascent) _scorches the poker_, and the _hand which holds
it_.
Q. _How should a RED-HOT POKER be carried so as not to BURN our
fingers?_
A. With the hot end _upwards_; because then the air (heated by the
poker) _would not pass over our hand_ to scorch it.
Q. _Why is a POKER (resting on the FENDER) COLD; but if it leans against
the STOVE, intensely warm?_
A. The poker is an _excellent conductor_; while, therefore, it rests
against the hot stove, the heat of the stove is _conducted into the
poker_; but when it _rests on the fender_, it does not come in _contact
with the hot stove_.
Q. _Why does it feel so COLD, when it rests on the FENDER?_
A. Not being so warm as our hand, it _imbibes the heat from it_ with
such _rapidity_, that our loss of heat is _palpable_, and produces the
sensation of coldness.
Q. _Why are FLUES (which are carried through a church or room) always
BLACKENED with BLACK LEAD?_
A. In order that the heat of the flue _may be more readily diffused_
throughout the room. Black lead radiates heat more freely than any other
known substance.
Q. _Why do country people touch the thick end of an EGG with their
TONGUE, to know if it be STALE or not?_
A. The thick end of an egg always contains _a little air_ (between the
shell and the white); but, when the egg is stale, _the white shrinks_,
and the air expands.
Q. _How can the TONGUE tell from this, whether the egg be STALE or FRESH
laid?_
A. As air is a _very bad conductor_, if the egg be _stale_, it will feel
much _warmer to the tongue_, than if it be new-laid.
Q. _Why will the big end of an egg feel WARMER to the tongue, because it
contains more AIR?_
A. As air is a _bad conductor_, it will draw off the heat of the tongue
_very slowly_, and, therefore, _appear warm_; but when there is only a
_very little air in the egg_ (as the _white_ is a pretty good
conductor), the heat of the tongue will be _more rapidly_ drawn off, and
the egg _appear colder_.
Q. _Why is the large END of an EGG CRACKED, when put into a saucepan to
boil?_
A. _To let the air out_; if the large end were _not cracked_, the air
(expanded by the heat) _would enter the white of the egg_, and give it
an _offensive taste_.
PART II.
AIR.
CHAPTER XVIII.
Q. _Of what is atmospheric AIR composed?_
A. Principally of two gases, _oxygen_ and _nitrogen_; mixed together in
the following proportion: viz. 1 part of oxygen, to 4 parts of nitrogen.
Q. _What are the uses of the OXYGEN of the air?_
A. It is the _oxygen_ of the air which _supports combustion_, and
_sustains life_.
Q. _What is meant when it is said, that the OXYGEN of the air "SUPPORTS
COMBUSTION?"_
A. It means this; that it is the _oxygen of the air_ which makes _fuel
burn_.
Q. _How does the OXYGEN of the air make FUEL BURN?_
A. The fuel being decomposed (by heat) into _hydrogen_ and _carbon_; the
_carbon combines with the oxygen of the air_, and produces _combustion_.
Q. _What does the combination of carbon and oxygen produce?_
A. The _carbon of the fuel_ combining with the _oxygen of the air_ makes
CARBONIC ACID GAS. (_see pp. 36, 37_).
Q. _What becomes of the HYDROGEN of the FUEL?_
A. Hydrogen (being very inflammable) _burns with a blaze_, and is the
cause of the _flame_ which is produced by combustion. (_see p. 34_).
Q. _What becomes of the NITROGEN of the air, amidst all these changes
and combinations?_
A. The _nitrogen of the air escapes_, and is _absorbed by the leaves_ of
grass, trees, and various other vegetables.
Q. _What is meant when it is said, that OXYGEN "SUSTAINS LIFE?"_
A. It means this: if a person _could not inhale oxygen_, he would _die_.
Q. _What GOOD does this inspiration of OXYGEN do?_
A. 1st--It gives _vitality to the blood_: and
2ndly--It is the _cause of animal heat_.
Q. _How is FOOD converted into BLOOD?_
A. After it is swallowed, it is dissolved in the stomach into a _grey
pulp_; it then passes into the intestines, and is converted by the
"bile" _into a milky substance_ (called _chyle_).
Q. _What BECOMES of the milky substance, called CHYLE?_
A. It is absorbed by the vessels called "_lacteals_," and poured into
the veins _on the left side of the neck_.
Q. _What becomes of the chyle AFTER it is POURED into the VEINS?_
A. It then _mingles with the blood_, and is itself _converted into
blood_.
Q. _How does the OXYGEN we inhale MINGLE with the BLOOD?_
A. The oxygen of the air mingles with the blood _in the lungs_, and
converts it into a _bright red colour_.
Q. _What colour is the blood BEFORE it is oxydized in the lungs?_
A. _A dark purple._ The oxygen turns it to _a bright red_.
Q. _Why are PERSONS so PALE who live in CLOSE ROOMS and CITIES?_
A. The blood derives its redness from the _oxygen_ of the air inhaled;
but, as the air in close rooms and cities _is not fresh_, it is
_deficient in oxygen_, and cannot turn the blood to a beautiful bright
red.
Q. _Why are PERSONS who live in the OPEN AIR and in the country, of a
RUDDY complexion?_
A. As the blood derives its bright red colour from the _oxygen_ of the
air inhaled, therefore, country-people (who inhale _fresh air_) are more
ruddy than citizens.
Q. _Why is not the air in CITIES so FRESH as that in the COUNTRY?_
A. Because it is impregnated with the _breath of its numerous
inhabitants_, the _odour of its sewers_, the _smoke of its fires_, and
many other impurities.
Q. _How does the COMBINATION of OXYGEN with the BLOOD produce animal
HEAT?_
A. The principal element of the blood is _carbon_, which (combining with
the oxygen of the air inhaled) produces _carbonic acid gas_, (in the
same way as burning fuel.) (_see pp._ 33, 36).
Q. _What becomes of the NITROGEN of the air, after the oxygen enters the
blood?_
A. The nitrogen is _exhaled_, and taken up by the leaves of trees and
other vegetables. (_see p._ 35).
Q. _Why does the vitiated air (after the oxygen has been absorbed) COME
OUT of the MOUTH, and not sink into the stomach?_
A. The vitiated air (being _heated by the heat of the body_) _ascends
naturally_, and passes by the _heavier fresh air_ (which we inhale)
without obstruction or injury.
Q. _If (both in combustion and in respiration) the OXYGEN of the air is
CONSUMED, and the NITROGEN REJECTED--Why are not the PROPORTIONS of the
AIR DESTROYED?_
A. Because the _upper surface of vegetable leaves_ (during the day)
_gives out oxygen_ and _absorbs nitrogen_, and thus the proper balance
is perpetually restored.
Q. _Show how God has made ANIMAL and VEGETABLE life DEPENDENT on each
other?_
A. _Animals_ require _oxygen_ to keep them alive, and _draw it from the
air_ by inspiration; the upper surface of _leaves_ (all day long) _gives
out oxygen_, and thus supplies the air with the _very gas_ required by
man and other animals.
Q. _Do not animals EXHALE the VERY GAS needed by VEGETABLES?_
A. Yes; animals reject the _nitrogen of the air_ (as not suited to the
use of animal life), but _vegetables absorb it_, as it is the food they
live on; and thus the vegetable world restores the equilibrium of the
air, disturbed by man and other animals.
Q. _Is AIR a good CONDUCTOR?_
A. No; air is a very _bad conductor_.
Q. _How is AIR HEATED?_
A. By "convective currents."
Q. _What are meant by "CONVECTIVE CURRENTS?"_
A. When a portion of air is heated, _it rises upward in a current_,
carrying the heat with it: other _colder air succeeds_, and (being
_heated_ in a similar way) _ascends also_; and these are called
convective currents.
("Convective currents;" so called from the Latin words, cum-vectus
(_carried with_) because the _heat_ is "carried with" the current.)
Q. _Is AIR HEATED by the RAYS of the SUN?_
A. No; air is _not heated_ (in any sensible degree) _by the action of
the sun's rays_ passing through it.
Q. _Why then is the AIR HOTTER on a SUNNY DAY, than on a CLOUDY one?_
A. On a fine day, the sun _heats the surface of the earth_, and the air
(resting on the earth) _is heated by contact_; as soon as it is heated
_it ascends_, and _other_ air succeeding is _heated in a similar way_,
till all is heated by convection.
Q. _If AIR be a BAD CONDUCTOR, why does hot IRON get COLD, by being
EXPOSED to the AIR?_
A. A piece of hot iron exposed to the air, is made cold--1st--By
"convection;" and
2ndly--By "radiation."
Q. _How is hot iron (exposed to the air) made cold by CONVECTION?_
A. The air around the iron (being intensely heated by contact) rapidly
ascends, _carrying some of its heat with it_: other air succeeds,
_absorbs more heat_, ascends, and gives place to that which is _colder_;
till the hot iron _is cooled completely down_.
Q. _How is hot iron cooled by RADIATION?_
A. While the heat of the iron is being carried off by "convection," it
is _throwing off heat_ (on all sides) _by radiation_.
Q. _What is meant by RADIATION?_
A. Heat emitted (in all directions) from any surface, by _innumerable
rays_.
Q. _Why is BROTH COOLED by being left exposed to the AIR?_
A. Hot broth throws off _some_ heat by _radiation_; but it is _mainly_
cooled down _by convection_.
Q. _How is hot BROTH cooled down by CONVECTION?_
A. The air _resting on the hot broth_ (being heated) _ascends_; _colder_
air succeeding _absorbs more heat_, and _ascends also_; and this process
is repeated, till the broth is _made cool_.
Q. _Why is hot TEA and BROTH COOLED faster, for being STIRRED about?_
A. 1st--The agitation assists the liquor in _bringing its hottest
particles to the surface_:
2ndly--The action of stirring _agitates the air_, and brings it
_quicker_ to the broth or tea: and
3rdly--As the hottest particles are more rapidly brought into contact
with the air, therefore _convection is more rapid_.
Q. _Why is HOT TEA, &c. cooled more rapidly by BLOWING it?_
A. Because the heated air is _blown more rapidly away_; in consequence
of which, _cold air more rapidly succeeds_ to _absorb heat_ from the
surface of the tea or broth.
Q. _If a shutter be closed in the day-time, the stream of light
(piercing through the crevice) seems in CONSTANT AGITATION. WHY is
this?_
A. The air (in the sun-beam piercing through the shutter-crevice) is
_more heated_, than _that in its neighbourhood_; the convective current,
therefore, is _distinctly seen_, where little motes and particles of
dust are _thrown into agitation_ by the _violence_ of the current.
Q. _Why is the GALLERY of a CHURCH or theatre HOTTER than the AISLE or
pit?_
A. The hot air ascends from the _bottom_ to the _top of the room_, and
cold air (from the doors and windows) flies to the _bottom_ to supply
its place.
Q. _Why does a CROWDED ROOM produce HEAD-ACHE?_
A. Because we breathe air _vitiated by the crowd_.
Q. _How does a CROWD VITIATE the AIR of a ROOM?_
A. Whenever we breathe, the elements of the air are _separated_ in the
lungs, _some of the oxygen is absorbed by the blood_, and some of it is
converted into _carbonic acid gas_, and exhaled with the nitrogen.
Q. _Is ALL the NITROGEN REJECTED by the lungs?_
A. Yes; all the nitrogen of the air is always exhaled.
Q. _What is CARBONIC ACID GAS?_
A. As carbon has a very great affinity for oxygen, therefore, whenever
they are exposed to heat, they _combine_, and form carbonic acid gas
(or what is vulgarly called fixed air).
Q. _Is CARBONIC ACID GAS wholesome?_
A. No; it is quite _fatal to animal life_; and whenever it is inhaled,
it acts like a narcotic poison, (producing drowsiness which ends in
death).
Q. _Why is a CROWDED ROOM UNWHOLESOME?_
A. Because the oxygen of the air is either _absorbed by the lungs_, or
substituted for _carbonic acid gas_, which is a noxious poison.
Q. _Mention the historical circumstances, so well known in connection
with the "BLACK HOLE of CALCUTTA."_
A. In the reign of George II, the Raja (or Prince) of Bengal[12] marched
suddenly to Calcutta to drive the English from the country; as the
attack was unexpected, the English were obliged to submit, and 146
persons were taken prisoners.
[12] The Sur Raja, at Dowlat; a young man of violent passions, who had
but just succeeded to the throne. A. D. 1756.
Q. _What became of these prisoners?_
A. They were driven into a place about 18 feet square, and 15 or 16 feet
in height, with only two small grated windows. 123 of the prisoners died
in one night; and (of the 23 who survived) the larger portion died of
putrid fevers, after they were liberated in the morning.
Q. _Why were 123 persons SUFFOCATED in a few hours, from confinement in
this close hot PRISON-hole?_
A. Because the _oxygen of the air_ was soon consumed by so many lungs,
and its place supplied by _carbonic acid_ exhaled by the hot breath.
Q. _Why do persons in a crowded CHURCH feel DROWSY?_
A. 1st--Because the crowded congregation _inhale a large portion of the
oxygen of the air_, which alone can sustain vitality and healthy action:
and
2ndly--The air of the church is impregnated with carbonic acid gas,
which (being a strong narcotic) produces drowsiness in those who inhale
it.
Q. _Why did the captives in the BLACK HOLE die SLEEPING?_
A. 1st--Because the _absence of oxygen_ quickly affects the vital
functions, depresses the nervous energies, and produces a lassitude
which ends in death: and
2ndly--The _carbonic acid gas_ inhaled by the captives (being a narcotic
poison) would also produce _drowsiness and death_.
Q. _Why do PERSONS, who are so much in the OPEN AIR, enjoy the best
HEALTH?_
A. Because the air they inhale is _much more pure_.
Q. _Why is COUNTRY AIR more PURE than the air in CITIES?_
A. 1st--Because there are fewer inhabitants to vitiate the air:
2ndly--There are more trees to restore the equilibrium of the vitiated
air: and
3rdly--The free circulation of air keeps it pure and wholesome (in the
same way as running streams are pure and wholesome, while stagnant
waters are the contrary).
Q. _Why does the SCANTINESS of a country POPULATION render the COUNTRY
AIR more PURE?_
A. Because the fewer the inhabitants, _the less carbonic acid will be
exhaled_; and thus country people will inhale _pure oxygen_, instead of
air _impregnated with the narcotic poison_, called carbonic acid gas.
Q. _Why do TREES and FLOWERS help to make country AIR WHOLESOME?_
A. Because trees and flowers _absorb the carbonic acid_ generated by the
lungs of animals, putrid substances, and other noxious exhalations.
Q. _Why is the AIR of CITIES LESS wholesome than COUNTRY air?_
A. 1st--Because there are _more inhabitants_ to vitiate the air:
2ndly--The _sewers_, _drains_, _bins_, and _filth of a city_, very
greatly vitiate the air:
3rdly--The streets and alleys prevent a free circulation: and
4thly--Besides all this, there are fewer trees to absorb the excess of
carbonic acid gas, and _restore the equilibrium_.
Q. _Why are PERSONS who live in CLOSE ROOMS and crowded CITIES,
generally SICKLY?_
A. Because the air they breathe is not pure, but is both _defective in
oxygen_, and impregnated with _carbonic acid gas_.
Q. _Where does the CARBONIC ACID of close ROOMS and CITIES COME from?_
A. From the lungs of the inhabitants, the sewers, drains, and so on:
besides, trees and gardens are not numerous enough _to absorb the
noxious gas_ as fast as it is generated.
Q. _What BECOMES of the CARBONIC ACID of crowded cities?_
A. Some of it is _absorbed by vegetables_, and the rest is _blown away
by the wind_, and diffused through the whole volume of the air.
Q. _Does not this constant diffusion of carbonic acid affect the PURITY
of the WHOLE AIR?_
A. No; because after it is thus diffused, _it is carried to various
lands_, and _absorbed_ in its passage by the _vegetable world_.
Q. _Why do persons who ascend in balloons feel intense pain in their
eyes and ears?_
A. Because the air of the upper regions is _more rarefied than the air
on the earth_; and the air inside their bodies (seeking to become of the
same rarity) _bursts through their eyes and ears_, producing an intense
pain.
Q. _Why is it often PAINFUL, and difficult to BREATHE, on a MOUNTAIN
top?_
A. Because the pressure of air on the mountain top is _not so great as
on the plain_; and the air inside our bodies (seeking to become of the
same rarity) _bursts through the pores of the body_, and produces great
pain.
Q. _Why do we feel OPPRESSED just PREVIOUS to a STORM?_
A. Because the air is _greatly rarefied by heat and vapour_; and the air
inside us (seeking to become of the same rarity) produces an oppressive
and suffocating feeling.
Q. _Why do DIVERS suffer great pain in their eyes and ears under water?_
A. Because the air at the bottom of the sea _is more dense_ than the air
_on the surface_; and while the air inside the diver's body is settling
into the same density, he feels oppressed with pain, especially in the
ears.
Q. _Why is this PAIN felt especially about the EARS of a DIVER?_
A. The ear is fitted with a small membrane called _the drum_ (or
tympanum), through which the dense air bursts, and the rupture very
often _produces incurable deafness_.
Q. _Why do our CORNS ache just previous to RAIN?_
A. Previous to rain, the density of air is greatly lowered (as every one
knows from the fall of the barometer); in consequence of an unequal
pressure, _our feet swell_; but the hard corn, _not being elastic_, is
painfully stretched and pressed.
(Some of this pain is due to electricity.)
Q. _Why do CELLARS feel WARM in WINTER?_
A. As the external air has not free access into cellars, they remain at
a _pretty even temperature_, which (in winter time) is about 10 degrees
_warmer_ than the external air.
Q. _Why do CELLARS feel COLD in SUMMER time?_
A. As the external air has not free access into cellars, they remain at
a _pretty even temperature_, which (in summer time) is about 10 degrees
_colder_ than the external air.
Q. _Why does lightning strike the OAK-tree more frequently than any
OTHER tree?_
A. 1st--Because the _grain of the oak, being closer_ than that of any
other tree, renders it a better conductor: and
2ndly--The _sap_ of the oak contains a _large quantity of iron_ in
solution, which is a most admirable conductor of lightning.
Q. _Why does AIR rust IRON?_
A. The _oxygen of the air_ combines with the _surface of the iron_, and
produces _oxide of iron_, which is generally called rust.
This rust is a species of combustion.
Q. _Why does hot iron SCALE and PEEL off, when struck with a HAMMER?_
A. The _oxygen of the air_ very readily unites with _the surface of the
hot iron_, and forms a metallic oxide (or rust) which scales off when
struck with a hammer.
Q. _Does iron RUST in DRY air?_
A. No; iron undergoes no change in dry air.
Q. _Why do STOVES and FIRE-IRONS become RUSTY, in rooms which are not
OCCUPIED?_
A. Because the air is damp; and moist air _oxidizes_ (or rusts) iron and
steel.
Q. _In what part of the year is it most difficult to keep STOVES and
FIRE-IRONS BRIGHT?_
A. In _autumn and winter_; because the capacity of the air for holding
water _being on the decrease_, its vapour is deposited on every-thing
with which it comes in contact.
Q. _Why does GREASING iron prevent its becoming RUSTY?_
A. Because _grease_ prevents the humidity of air from coming in contact
with the _surface of the iron_.
Q. _Why do not STOVES rust so frequently as POKERS and TONGS?_
A. Because stoves are generally _covered with plumbago_, or black lead.
Q. _What is plumbago, or black lead?_
A. A mixture of charcoal and iron filings.
A most excellent varnish to prevent rust is made of 1 pint of fat oil
varnish, mixed with 5 pints of highly rectified spirits of turpentine,
rubbed on the iron or steel with a piece of sponge. This varnish may be
applied to bright stoves and even mathematical instruments, without
injuring their delicate polish.
Q. _Why does ornamental STEEL (of a purple or LILAC colour) rust more
readily than polished WHITE steel?_
A. Because the lilac tinge is produced by _partial oxidation_; and the
process which forms rust has, therefore, _already_ commenced.
Q. _How can lilac STEEL be kept FREE from RUST?_
A. By keeping it in a very _dry place_; for then no additional oxygen
will come in contact with it, to increase its amount of rust.
Q. _Do any OTHER metals (besides iron) combine rapidly with oxygen?_
A. Yes; copper, lead, mercury, and even silver to some extent.
Q. _Why does COPPER TARNISH?_
A. The tarnish of copper is caused by its _oxidation_; that is, the
oxygen of the air combines with the surface of the copper, and instead
of _rusting it_, covers it with a _dark tarnish_.
Q. _Why does LEAD lose its BRIGHTNESS, and become DULL and of a DARKER
hue, by being exposed to the air?_
A. The vapour of the air combines with the lead, and _oxidizes its
surface_; but instead of becoming _rusty_, the surface becomes _dull_,
and of a _darker colour_.
Q. _Why is it difficult to keep SILVER BRIGHT?_
A. Because the vapour of the air oxidizes its surface, and _tarnishes_
it.
Q. _Why do silver TEA-POTS and SPOONS tarnish more quickly than silver
ore or bullion?_
A. Because alloy (of some _baser_ metal) is used to make it more _hard
and lasting_; and this _alloy_ oxidizes more quickly than silver itself.
Q. _Why does GERMAN silver turn a dingy yellow in a few hours?_
A. German silver has a great affinity for oxygen, and shows its
oxidation by a _sickly yellow tarnish_, instead of rust.
Q. _If quicksilver (or mercury) is tarnished like copper and lead,--Why
does it preserve its BRILLIANCY in BAROMETERS and THERMOMETERS?_
A. Because _air_ is excluded from it, and no moisture comes in contact
with it to _oxidize_ (or _tarnish_ it).
Q. _Is GOLD affected by the atmosphere?_
A. Not readily: gold will never combine with oxygen of itself, (or
without aid).
Q. _Which of the METALS is capable of resisting oxidation altogether?_
A. Plat'inum; in consequence of which, the graduated arcs of delicate
instruments for observation are made of plat'inum instead of any _other_
metal.
Q. _Why is PLAT'INUM used for the graduated arcs of delicate
mathematical instruments, instead of any other metal?_
A. Because it will never oxidize; but retain its _bright surface_ in all
weathers free from both _rust and tarnish_.
Q. _Before plat'inum was discovered, which of the metals was employed
for the same purpose?_
A. Gold.
Platinum, (a white metal), so called from "plata," the Spanish word for
_silver_. It was first introduced into England by Mr. Wood, (A. D. 1749)
from South America.
Q. _For what other SCIENTIFIC purposes is PLAT'INUM now used?_
A. For crucibles in which _acids_ are employed, and for galvanic
batteries.
Q. _Why are CRUCIBLES (in which acids are employed) made of PLAT'INUM?_
A. Because the acid would act upon _other metals_, or upon _glass_, and
prevent the experimenter's success.
Q. _Which of the METALS have the GREATEST affinity to OXYGEN?_
A. Those called _potassium_ and _sodium_.
Potassium and sodium derive their names from potash and soda. Potassa is
the oxide of potassium; and soda is the oxide of sodium.
Q. _How is the affinity of potassium and sodium for oxygen shewn?_
A. They _decompose water_ the moment they are brought into contact with
it.
Q. _What effect has POTASSIUM on WATER?_
A. It _catches fire_ the moment it is thrown into water, and burns with
a vivid flame, which is still further increased by the combustion of
_hydrogen_ separated from the water.
(N.B. Water is composed of oxygen and hydrogen; and potassium separates
the two gases.)
Q. _What effect has SODIUM on WATER?_
A. It does _not take fire_ as potassium does, but undergoes very rapid
_oxidation_.
Q. _Is the FURR of KETTLES an oxide?_
A. No; the furr (or deposit of boiling water) is a precipitate of
_lime and mineral salt_, separated from the water by the process of
boiling.
Q. _Is not this FURR of boiling water often DANGEROUS?_
A. Yes; especially in _tubular boilers_, such as those employed in
railways.
Q. _Why is this FURR especially TROUBLESOME in RAILWAY engines?_
A. Because it is a _bad conductor of heat_; in consequence of which, it
hinders the evaporating effect of the fire, and prevents the economy of
fuel.
Q. _Why is this FURR especially DANGEROUS in RAILWAY engines?_
A. Because when it is deposited in the boilers, they are likely to
become _over-heated_; and then _explosion_ will take place from the
sudden generation of highly elastic steam.
Q. _Why cannot RAILWAY engines be fed with BRACKISH WATER?_
A. Because brackish water contains _mineral salt_, which makes a much
larger deposit of furr, than that which contains _only vegetable
matter_.
CHAPTER XIX.
CARBONIC ACID GAS.
Q. _What is CHOKE DAMP?_
A. _Carbonic acid gas_ accumulated at the bottom of wells and pits,
which renders them noxious, and often fatal.
Q. _Why is not this carbonic acid TAKEN UP by the AIR, and DIFFUSED, as
it is in cities?_
A. Because (being _heavier than common air_) it cannot _rise from the
well or pit_; and no wind can get to it to blow it away.
Q. _Is CARBONIC ACID WHOLESOME?_
A. No; it is _fatal to animal life_, when inhaled through the mouth;
acting on the stomach, _as a narcotic poison_ (i. e. a poison which
produces death from drowsiness).
Q. _How can any one KNOW, if a place be infested with CARBONIC ACID
GAS?_
A. If a pit or well contain carbonic acid, _a candle_ (let down into it)
_will be instantly extinguished_. The rule, therefore, is this--Where a
_candle will burn, a man can live_; but _what will extinguish a candle_,
will _also destroy life_.
Q. _Why does a MINER lower a CANDLE into a mine, before he descends?_
A. Because the _candle will be extinguished_, if the mine contains
carbonic acid gas: but if the candle is _not extinguished_, the mine is
_safe_, and the man may fearlessly descend.
Q. _Why are PERSONS sometimes KILLED, by leaning over BEER VATS?_
A. Vats (where beer has been made) contain a _large quantity of carbonic
acid gas_, produced by the "vinous fermentation" of the beer; and when a
man incautiously _leans over a beer vat_, and inhales the carbonic acid,
he is immediately _killed_ thereby.
Q. _Why are PERSONS often KILLED, who enter BEER VATS to clean them?_
A. Carbonic acid (being _heavier than atmospheric air_) often rests upon
the _bottom of a vat_: when, therefore, a person enters the vat, and
_stoops to clean the bottom_, he inhales the pernicious gas, which
_kills_ him.
Q. _Why are the JUNGLES of Jarva and Hindostan so FATAL to life?_
A. Because vast quantities of _carbonic acid_ are thrown off by decaying
_vegetables_; and (as the wind cannot penetrate the thick brushwood to
blow it away) _it settles there_, and destroys animal life.
Q. _Why are PERSONS sometimes KILLED by having a CHARCOAL FIRE in their
bed-rooms?_
A. When charcoal is burned, the _carbon of the charcoal_ unites with the
_oxygen of the air_, and forms _carbonic acid gas_, which is a narcotic
poison.
Q. _Why does the carbonic acid gas of a CHARCOAL FIRE RISE and DISPERSE
itself about the room; whereas the carbonic acid gas of a BEER VAT
SETTLES near the FLOOR?_
A. The carbonic acid gas of a charcoal fire _is heated_ by the
_combustion of the fuel_, and rises; but the carbonic acid gas of a beer
vat is _not_ heated, and, therefore, rests on the _bottom of the vat_.
Q. _Why do persons throw LIME into BINS to PREVENT their offensive
SMELL, in summer time?_
A. Bins contain large quantities of _carbonic acid gas_, which readily
_combines with lime_, and produces "_carbonate of lime_," which is
entirely free from all offensive odour.
Q. _Why do persons throw LIME into SEWERS in summer time?_
A. Sewers (like bins) contain large quantities of _carbonic acid_, which
readily _combines with lime_, and produces _carbonate of lime_; and thus
the offensive gas of the sewer is neutralized.
Q. _Can carbonic acid be removed in any way BESIDES by LIME?_
A. Yes; _water_ thrown into a pit will disperse the carbonic acid.
Q. _What effect has WATER on CARBONIC ACID GAS?_
A. Water (under _pressure_) _absorbs_ carbonic acid gas; and _parts_
with it (when the _pressure is removed_) in the form of EFFERVESCENCE.
Q. _Why does AERATED WATER effervesce, when the CORK is removed?_
A. While the _cork was fastened down_, the water _absorbed_ the carbonic
acid; but the moment _the pressure is removed_ (by taking out the cork)
the gas is given out with _effervescence_.
Q. _Why does SODA WATER effervesce?_
A. Soda water contains 8 times its own bulk of carbonic acid gas, which
makes its escape in _effervescence_, the moment that the _cork is
removed_.
Q. _Why does GINGER POP fly about in froth, when the string of the cork
is cut?_
A. All vinous fermentation produces carbonic acid gas. While the _cork
is fast_, the water of the liquor _absorbs_ the carbonic acid; but the
moment that the _pressure is removed_, the gas is given off in
_effervescence_.
Q. _Why does BOTTLED ALE froth, more than DRAUGHT ale?_
A. Because the _pressure_ is greater in a _bottle_ than in a tub which
is perpetually tapped: and effervescence is always produced _in
proportion to the pressure_.
Q. _Why does bottled ALE and PORTER become "LIVELY" and FROTHY by being
SET before the FIRE?_
A. The heat of the fire _expands the air_ (between the liquid and the
cork), and as this air expands, _it presses the liquid down_, which
causes effervescence.
Q. _What produces the FROTH of BOTTLED PORTER?_
A. The _carbonic acid gas_, produced by its _vinous fermentation_; which
is _absorbed by the liquor_ so long as the bottle is _well corked_, but
is _given off in froth_ as soon as the pressure of the cork is
_removed_.
Q. _What gives the pleasant ACID taste to soda water, ginger beer,
champagne, and cider?_
A. The presence of _carbonic acid_, generated by fermentation, and
liberated by effervescence when the pressure of the cork is removed.
Q. _Why does fresh SPRING WATER SPARKLE, when poured from one vessel to
another?_
A. Because fresh spring and pump water contain _carbonic acid_; and it
is the presence of this gas _which makes the water sparkle_.
Q. _What is the FERMENTATION of BEER and WINE?_
A. The production of carbonic acid gas and al'cohol.
Q. _How is CARBONIC ACID GAS produced by FERMENTATION?_
A. Malt and fruit _both contain sugar_; and sugar consists of carbon,
oxygen, and hydrogen. In fermentation, a part of the _carbon and oxygen_
of the sugar escape, _in the form of carbonic acid gas_.
Carbonic acid gas is a compound of carbon and oxygen, in the following
proportions:--3 lbs. of carbon and 8 lbs. of oxygen will form 11 lbs. of
carbonic acid gas. Now, 100 lbs. of white sugar contains 43 lbs. of
carbon; 50 lbs. of oxygen; and 7 lbs. of hydrogen.
Q. _How is AL'COHOL produced by FERMENTATION?_
A. The _hydrogen of the sugar_ combines with the _residue of the oxygen
and carbon_ to form "AL'COHOL."
Q. _What is AL'COHOL?_
A. Al'cohol is the _spirit_ of wine or beer, obtained by _fermentation_.
(100 gallons of alcohol consist of 38 gallons of oxygen; 43-1/2 of
carbon; 15 of hydrogen; and 3-1/2 of nitrogen.)
Q. _Why is BARLEY MALTED?_
A. Because _germination_ is produced by the artificial heat; and in
germination the _starch of the grain_ is converted into _sugar_.
Q. _How is barley malted?_
A. The barley is _moistened with water_, and _heaped up_; by which
means, great _heat_ is produced, which makes the _barley sprout_.
Q. _Why is not the BARLEY suffered to GROW, as well as SPROUT?_
A. Plants in the _germ_ contain _more sugar_ than in any _other state_;
as soon as the germ _puts forth shoots_, the _sugar_ of the plant is
_consumed_, to _support the shoot_.
Q. _How is BARLEY PREVENTED from SHOOTING, in the process of MALTING?_
A. The barley is _put into a kiln_ as soon as it sprouts; and the _heat_
of the kiln checks or _destroys the young shoot_.
Q. _Why is YEAST put into BEER to make it WORK?_
A. Yeast supplies the beer with _nitrogen_, which is one of the
ingredients of alcohol.
Alcohol consists of _oxygen_, _carbon_, and _hydrogen_, (obtained from
the sugar of malt), and _nitrogen_, (obtained from yeast).
Q. _Why is it NOT needful to put YEAST into WINE?_
A. Because fruit contains _carbon_, _hydrogen_, _oxygen_, and
_nitrogen_, in the form of "gluten;" and, therefore, ferments
_spontaneously_.
(Gluten is explained fully in the Appendix.--Turn to the word in the
Index.)
Q. _Does not MALT contain carbon, hydrogen, oxygen, and nitrogen, as
well as FRUIT?_
A. No; the sugar of malt contains _carbon_, _hydrogen_, and _oxygen_,
but _no nitrogen_; in consequence of which, _yeast_ (which contains
_nitrogen_) is _added to the wort_.
Q. _Why do NOT GRAPES ferment while they hang on the VINE?_
A. 1st--Because the skin lets out the _water of the pulp_, which causes
the grapes to shrivel and dry up: and
2ndly--The skin _prevents_ the admission of _oxygen into the pulp_, from
the air without.
Q. _What is the FROTH or SCUM of fermented LIQUORS?_
A. _Carbonic acid gas_, which (being heavier than common air) _settles
on the top of the liquor_, in the form of scum.
Q. _Why does a small piece of raw MEAT, or a few RAISINS improve FLAT
BEER?_
A. 1st--Because they supply it with _nitrogen_ to form it into al'cohol.
2ndly--As the raw meat, &c. _putrifies_, it gives off _carbonic acid
gas_ into the beer, which gives it "life."
Q. _Why is BEER FLAT, if the cask be open too long?_
A. Because _too much of the carbonic acid gas_ (produced by
fermentation) is suffered to _escape_.
Q. _How is the CARBONIC ACID GAS of BEER generated?_
A. The saccharine (or sugar) of the malt is converted by _fermentation_
into carbonic acid gas and alcohol.
Q. _Why does BEER turn FLAT, if the VENT PEG be left OUT of the tub?_
A. Because the _carbonic acid gas escapes_ through the vent hole.
Q. _Why will NOT beer RUN OUT of the tub, till the VENT PEG is taken
out?_
A. When the tap is turned, _air rushes through the tap_ into the bottom
of the tub, and _holds the liquor in_.
The _upward_ pressure of air is illustrated by the
following simple experiment:--Fill a wine-glass with water; cover the
top of the glass with a piece of writing paper; turn the glass topsy
turvy, and the water will not run out. The paper is used merely to give
the air a medium sufficiently dense to act against.
Q. _Why does the BEER RUN FREELY, immediately the VENT PEG is taken
out?_
A. As soon as the vent peg is taken out, air rushes _through the vent
hole_ at the _top of the tub_,--presses the liquor _down_, and _forces
it through the tap_.
Q. _Why does liquor flow reluctantly out of a BOTTLE held upside down?_
A. Because the _upward pressure of the air_ prevents the liquor from
flowing out.
Q. _Why should a bottle be held OBLIQUELY, in order to be emptied of its
liquor?_
A. Because _air_ will then _flow into the bottle_, and help the liquor
out by _balancing the upward pressure_.
Q. _Why does wine (poured from a bottle QUICKLY) SPIRT about without
going into the decanter?_
A. The liquor fills the _top of the decanter_ (like a _cork_), and
leaves _no room_ for the air inside _to escape_; therefore, the decanter
(being _full of air_) refuses to admit the _wine_.
Q. _Why is BEER made STALE, by being exposed to the AIR?_
A. Because air _absorbs its carbonic acid_, which gave it "life."
Q. _Why is PORTER made STALE, by being exposed to the AIR?_
A. Because air _absorbs its carbonic acid_, which gave it "life."
Q. _Why does the EFFERVESCENCE of soda water and ginger beer so soon go
off?_
A. Because air _absorbs the carbonic acid_, which produced the
effervescence.
Q. _Why is BOILED WATER FLAT and insipid?_
A. Because the whole of the _carbonic acid is expelled_ by boiling, and
_absorbed by the air_.
Q. _Why does WATER become FLAT and insipid, after it has been DRAWN some
time?_
A. Because air _absorbs its carbonic acid_; and when its carbonic acid
is absorbed, the water is flat and insipid.
Q. _Why should spring WATER (used for WASHING) be exposed to the AIR?_
A. Spring water _contains carbonic acid_; but (by being exposed to the
_air_) this carbonic acid is _absorbed_, and the water becomes _more
soft_.
Q. _Why does YEAST make BREAD LIGHT?_
A. Flour contains a small portion of _saccharine matter_ (or sugar); and
the yeast (mixing with this) produces _fermentation_, as it does in
brewing.
Q. _How does FERMENTATION make the DOUGH RISE?_
A. During fermentation, _carbonic acid gas is evolved_; but the sticky
texture of the dough will not allow it to _escape_, so it _forces up
little bladders_ all over the dough.
Q. _Why is DOUGH placed BEFORE the FIRE?_
A. 1st--Because the heat of the fire _increases the fermentation_: and
2ndly--It _expands the gas_ which is confined in the little bladders; in
consequence of which, the bladders are _blown up larger_, and the dough
becomes lighter and more porous.
Q. _Why is BREAD HEAVY, if the dough be removed from the fire?_
A. Because the dough _gets cold_, and then the air in the bladders
_condenses_,--the paste falls,--and the bread is close and heavy.
Q. _Whence does the HEAT of FIRE arise?_
A. The _carbon of fuel_ (when heated) _combines with the oxygen of the
air_, and produces _carbonic acid gas_: again, the _hydrogen of the
fuel_ combining with _other portions of oxygen_, condenses into _water_;
by which chemical actions _heat is evolved_.
Q. _Whence does the HEAT of our own BODY arise?_
A. The _carbon of the blood_ combines with the _oxygen of the air
inhaled_, and produces _carbonic acid gas_; which produces heat in a way
similar to burning fuel.
Q. _Whence does the HEAT of a DUNGHILL arise?_
A. The _straw, &c. of the dunghill_ undergoes _fermentation_ as it
decays: the fermentation produces _carbonic acid gas_, and heat is
evolved by a species of combustion (as in the two former cases).
Q. _What changes do VEGETABLES undergo from PUTREFACTION?_
A. The _hydrogen of the vegetables_ combines with the _oxygen of the
air_, and forms _water_: again, the _carbon of the vegetables_ combines
with _oxygen of the air_, and forms _carbonic acid gas_. Putrefaction,
therefore, is only another species of combustion.
Q. _What changes do ANIMAL bodies undergo from PUTREFACTION?_
A. The same as vegetables, with this addition--they give out _ammonia_,
_sulphur_, and _phosphorus_ also; which causes the _offensive smell_ of
putrefying animal bodies.
Q. _Why is LIME heated by a KILN?_
A. All marl and chalk abound _in carbonic acid_; and (when heated by a
fire) the carbonic acid _flies off in gas_, producing great heat.
Q. _What is MORTAR?_
A. Lime mixed with sand and water.
Q. _What is LIME?_
A. _Lime-stone burnt_ produces lime.
Q. _Why is the lime-stone BURNT, in order to make it into LIME?_
A. The fire _expels the carbonic acid_, and converts the hard lime-stone
into a _loose powder_.
Q. _Why does MORTAR become HARD, after a few days?_
A. Because the lime _re-imbibes_ the carbonic acid of the air, which was
_expelled by fire_; and the loose _powder_ again becomes as hard as the
original _lime-stone_.
Q. _Why is MORTAR adhesive?_
A. When the carbonic acid is expelled, the hard lime-stone is _converted
into a loose powder_, which (being mixed with sand and water) becomes a
_soft and sticky plaster_; but, as soon as it is placed between bricks,
it _imbibes carbonic acid again_, and hardens into _lime-stone_.
CHAPTER XX.
CARBURETTED HYDROGEN GAS.
Q. _What is CHOKE-DAMP?_
A. _Carbonic acid gas_ accumulated at the bottom of wells and pits. It
is called CHOKE damp, because it _chokes_ (or suffocates) _every animal
that inhales it_. (_see p._ 264).
Q. _What is marsh-gas or FIRE-DAMP?_
A. _Carburetted hydrogen gas_ accumulated on marshes, in stagnant
waters, and coal pits; it is frequently called "inflammable air."
Q. _What is CARBURETTED HYDROGEN GAS?_
A. _Carbon_ combined with _hydrogen_.
Q. _How may CARBURETTED HYDROGEN GAS be PROCURED on marshes?_
A. By _stirring the mud_ at the bottom of any stagnant pool, and
collecting the gas (as it escapes upwards) in an inverted glass vessel.
Q. _What is COAL GAS?_
A. _Carburetted hydrogen_ extracted from coals, by the heat of _fire_.
Q. _Why is carburetted hydrogen gas called FIRE-DAMP, or inflammable
air?_
A. Because it very readily _catches fire and explodes_, when a light is
introduced to it.
Q. _Why is carburetted hydrogen gas frequently called MARSH GAS?_
A. Because it is generated in _meadows and marshes_ from putrefying
vegetable substances. (_See ignis fatuus_, _p._ 285).
Q. _What gas is evolved by the WICK of a burning CANDLE?_
A. _Carburetted hydrogen gas_: that is, the _carbon and hydrogen_ of the
tallow _combine into a gas_ from the heat of the flame; and this gas is
_carburetted hydrogen_, or inflammable air.
Q. _Why do COAL-MINES so frequently EXPLODE?_
A. Because the _carburetted hydrogen gas_ (which is generated in these
mines by the coals) explodes, when a light is incautiously introduced.
Q. _How can miners SEE in the coal-pits, if they may NEVER introduce a
LIGHT?_
A. Sir Humphrey Davy invented a lantern for the use of miners, called
"the Safety Lamp," which may be used without danger.
Q. _Who was SIR HUMPHREY DAVY?_
A. A very clever chemist, born in Cornwall. (1778--1829).
Q. _What kind of thing is the SAFETY LAMP?_
A. It is a kind of lantern _covered with a fine gauze wire_, instead of
glass or horn.
Q. _How does this fine GAUZE WIRE prevent an EXPLOSION in the coal
mine?_
A. 1st--Because flame will _never pass through fine gauze wire_: and
2ndly--Though the wire get _red-hot_, it will not ignite the gas; for
carburetted hydrogen gas can be ignited only by _flame_.
(N. B. The interstices of the gauze wire must not exceed the 7th of an
inch in diameter.)
Q. _Why will not FLAME PASS THROUGH very fine wire-GAUZE?_
A. Because the metal wire is a very _rapid conductor of heat_; and when
the flame of burning gas in the lamp reaches the wire gauze, the heat
(which is needful to produce flame) is _conducted away by the wire_, and
the flame is _extinguished_.
Q. _Does the gas of the COAL-PIT get THROUGH the wire gauze INTO the
LANTERN?_
A. Yes; but the inflammable gas ignites and burns _inside the lamp_: as
soon, however, as this is the case, _the miner is in danger_, and should
withdraw.
Q. _Why is the miner in DANGER, if the gas ignites and burns in the
INSIDE of the safety-lamp?_
A. Because the heat of the burning gas will soon _destroy the wire
gauze_, and then the flame (being free) will set fire to the mine.
CHAPTER XXI.
PHOSPHURETTED HYDROGEN GAS.
Q. _From what does the very OFFENSIVE EFFLUVIA of CHURCH-YARDS arise?_
A. From a gas called PHOSPHURETTED HYDROGEN; which is _phosphorus_
combined with _hydrogen gas_.
Q. _What is PHOSPHORUS?_
A. A pale amber-coloured substance, resembling wax in appearance. The
word is derived from two Greek words, which mean "_to produce or carry
light_." ([Greek: phôs-pherein]).
Q. _How is PHOSPHORUS OBTAINED?_
A. By heating bones to a white heat; by which means the animal matter
and charcoal are _consumed_, and what is left is called "_phosphate of
lime_."
Q. _How is PHOSPHATE OF LIME converted into PHOSPHORUS?_
A. It is reduced to _powder_, and mixed with _sulphuric acid_; which
(being heated and filtered) is converted into _phosphorus_.
Q. _Of what are LUCIFER MATCHES made?_
A. Of phosphorus; and above 250 thousand lbs. of phosphorus are used
every year in London alone, merely for the manufacture of lucifer
matches.
Q. _Why does a PUTREFYING dead BODY SMELL so offensively?_
A. From the _phosphuretted hydrogen gas_, which always arises from
putrefying animal substances.
The escape of _ammonia_ and _sulphur_ contributes also to this offensive
effluvia.
Q. _What is the cause of the IGNIS FATUUS, Jack o'Lantern, or Will o'the
Wisp?_
A. This luminous appearance (which haunts meadows, bogs, and marshes)
arises from the _gas of putrefying animal and vegetable substances_;
especially decaying fish.
Q. _What gases arise from these PUTREFYING substances?_
A. _Phosphuretted hydrogen gas_ from putrefying _animal_ substances: and
_Carburetted hydrogen_, (or inflammable gas) from fermenting _vegetable_
matters.
Some persons erroneously think that the AURORA BOREALIS, or Northern
Lights, may be attributed to the same gases, burning in the upper
regions of the air.
Q. _How are these gases IGNITED on bogs and meadows?_
A. By the electricity of the air, the rays of the sun, some accidental
spark, the lamp of some traveller, or in some similar way.
And sometimes from the spontaneous combustion of some dung-heaps, &c. in
the locality.
Q. _Why does an ignis fatuus or Will o'the Wisp FLY from us when we RUN
to MEET it?_
A. When we run _towards_ an ignis fatuus, we produce a current of air,
which drives the light gas _forwards_.
Q. _Why does an ignis fatuus run AFTER us, when we FLEE from it in
fright?_
A. When we run _away_ from the ignis fatuus, we produce a current in the
way we run, which _attracts_ the light inflammable gas in the _same
course_.
Q. _Is not a kind of Jack o'Lantern sometimes produced by an INSECT?_
A. Yes; a swarm of luminous insects sometimes passes over a meadow, and
produces an appearance exactly like that of the ignis fatuus.
Q. _May this meteoric appearance be attributed to any OTHER cause,
besides those mentioned?_
A. Yes; if many horses, sheep, pigs, or oxen, are pastured on a meadow,
the _animal vapour_ arising from them (strongly electrified by the air)
_will ignite_, and produce a luminous appearance.
Q. _May not many GHOST stories have risen from some ignis fatuus lurking
about church-yards?_
A. Perhaps _all_ the ghost stories (which deserve any credit at all)
have arisen from the ignited gas of church-yards lurking about the
tombs, to which _fear_ has added its own creations.
CHAPTER XXII.
WIND.
Q. _What is WIND?_
A. Wind is _air in motion_.
Q. _What PUTS the air in motion, so as to produce WIND?_
A. The principal causes are the _variations of heat and cold_, produced
by the succession of _day and night_, and the _four seasons_.
Q. _What effect has HEAT upon the air?_
A. Heat _rarefies_ the air, and causes it to _expand_.
Q. _How do you KNOW that heat causes the air 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).
Q. _What EFFECT is produced upon air by RAREFACTION?_
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.
Q. _How do you KNOW that rarefied air ASCENDS?_
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_.
Q. _What effect is produced upon AIR by COLD?_
A. Air is _condensed by cold_, or squeezed into a smaller compass; in
consequence of which, _it becomes heavier_, and descends towards the
ground.
Q. _How do you KNOW that air is CONDENSED by COLD?_
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.
Q. _What is meant by the bladder "COLLAPSING?"_
A. The skin will become _wrinkled, shrivelled, and flabby_, because
there is not sufficient air inside to _fill it out_.
Q. _How do you KNOW that CONDENSED air will DESCEND?_
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_.
Q. _Does the SUN HEAT the AIR as it does the EARTH?_
A. No; the air is _not heated by the rays of the sun_, because air (like
water) is a very _bad conductor_.
Q. _How is the AIR HEATED?_
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."
Q. _What is meant by "CONVECTIVE CURRENTS of air?"_
A. Streams of air heated by the earth, which _rise upwards_ and _carry
heat with them_, are called "convective currents" of hot air.
Q. _Is the air in a ROOM in perpetual motion, as the air ABROAD is?_
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.
Q. _How do you KNOW, that there are these TWO currents of air in every
occupied 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_).
Q. _Why would the flame be blown OUTWARDS (towards the HALL), if the
candle were held at the TOP of the door?_
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_).
Q. _Why would the flame be blown INWARDS (into the ROOM), if the candle
were held at the BOTTOM of the door?_
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.
Q. _What is meant by a "partial VACUUM being made, at the BOTTOM of the
ROOM?"_
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_.
Q. _And how is the VACUUM filled UP again?_
A. It is filled up by _colder air_, which rushes (under the _door_, and
through the _window_ crevices) into the room.
Q. _Give me an ILLUSTRATION._
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.
Q. _Show how this illustration APPLIES._
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_.
Q. _What is the CAUSE of WIND?_
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.
Q. _Does the WIND ALWAYS blow?_
A. Yes; there is always _some_ motion in the air; but the _violence_ of
the motion is perpetually varying.
Q. _Why is there always SOME motion in the air?_
A. As the earth is _always turning round_, the vertical rays of the sun
are always _varying_.
Q. _What do you mean by "the VERTICAL RAYS of the SUN?"_
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.
Q. _How are the VERTICAL rays of the sun always VARYING?_
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_.
Q. _And is it NOON-DAY to the place over which the SUN is VERTICAL?_
A. Yes; as each place passes _under the brass meridian_, it is
_noon-day_ to _one_ half, and _mid-night_ to the _other_.
Q. _Show how this ROTATION of the earth affects the AIR._
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_.
Q. _Then there are THREE qualities of air about this spot?_
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_.
Q. _How does this VARIETY in the HEAT of AIR produce WIND?_
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_.
Q. _Why does not the wind ALWAYS BLOW ONE way, following the direction
of the SUN?_
A. Because the direction of the wind is subject to perpetual
interruptions from _hills and valleys_, _deserts and seas_.
Q. _How can HILLS and MOUNTAINS ALTER the course of the WIND?_
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_).
Q. _Do MOUNTAINS affect the wind in any OTHER way?_
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.
Q. _How can the OCEAN affect the direction of the WIND?_
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_.
Q. _Why is not the WATER of the sea made so HOT by the vertical sun, as
the surface of the LAND?_
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_.
Q. _Why does the EVAPORATION of the sea prevent its surface from being
HEATED by the vertical sun?_
A. As water _absorbs_ heat by being _converted into vapour_; the surface
of the sea is continually _losing heat by evaporation_.
Q. _How does the MOTION of the sea prevent its surface from being HEATED
by the vertical sun?_
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_.
Q. _How is the WIND affected by the SEA?_
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_.
Q. _Do CLOUDS affect the WIND?_
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_.
Q. _Would the winds blow regularly from east to west, if these
OBSTRUCTIONS were REMOVED?_
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.
Q. _Do winds NEVER blow REGULARLY?_
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.
Q. _What are the winds, which blow over the ATLANTIC and PACIFIC Ocean,
called?_
A. They are called "Trade Winds."
Q. _Why are they 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.
Q. _In what DIRECTION do the TRADE WINDS blow?_
A. That in the _northern_ hemisphere blows from the _north-east_: that
in the _southern_ hemisphere from the _south-east_.
Q. _Why do they not blow from the FULL NORTH and SOUTH?_
A. Because the _polar current_, combining with the _equatorial current_,
give the wind a _new direction_.
Q. _What is the CAUSE of the EQUATORIAL current?_
A. The rotation of the earth upon its axis.
Q. _What is the cause of the POLAR CURRENT?_
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_.
Q. _How does the COMBINATION of these two currents give a new direction
to them both?_
A. When these currents of air meet at the equator, they _clash
together_, and fly off in a new direction.
Q. _Do trade winds blow from the north-east and south-east ALL the YEAR
ROUND?_
A. Yes, _in the open sea_; that is, in the Atlantic and Pacific Oceans
for about 30 degs. each side of the equator.
Q. _Do the TRADE WINDS blow uniformly from north-east and south-east in
the INDIAN OCEAN?_
A. No; nor yet in those parts of the _Atlantic_ and _Pacific_ which
_verge on the land_.
Q. _Why do not the trade winds blow uniformly from north-east and
south-east in the INDIAN OCEAN?_
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_.
Q. _How does it blow for the OTHER 6 months?_
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.
Q. _What are the six-month trade winds called?_
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.
Q. _Have WE any regular winds in ENGLAND?_
A. No; our island (having a _continent on one side_, and a _sea on the
other_) has a most _variable_ climate.
Q. _Have the winds in England NO general direction throughout the year?_
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.
Q. _When are the WINDS in ENGLAND generally the HIGHEST?_
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.
Q. _Why are the winds of Europe generally HIGHEST in DECEMBER and
JANUARY?_
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.
Q. _Why does this CONTRAST of heat increase the VIOLENCE of the WINDS?_
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.
Q. _Why are the winds in Europe generally the most PLACID during the
months of SEPTEMBER and AUGUST?_
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.
Q. _Show the GOODNESS and WISDOM of GOD in the constant tendency of air
to equilibrium._
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_.
Q. _Why are EAST WINDS in England generally DRY?_
A. Because, as they come over the _vast continents_ of Asia and Europe,
they absorb _very little water_.
Q. _Why does their imbibing so little water make them DRY winds?_
A. Being thirsty when they reach our island, they readily imbibe
moisture from the air and clouds; and, therefore, _bring dry weather_.
Q. _Why is the NORTH WIND in England generally COLD?_
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_.
Q. _Why are NORTH WINDS in England generally DRY and biting?_
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_.
Q. _Why is the SOUTH WIND generally WARM in England?_
A. The south wind comes over the hot sandy deserts of Africa, and is
heated by the land it traverses.
Q. _Why does the SOUTH WIND often bring us RAIN?_
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.
Q. _Why does the SATURATION of the south wind cause RAIN?_
A. As soon as it reaches our cold climate, _it is condensed_, and its
vapour is squeezed out (as water from a wet sponge).
Q. _Why are WEST WINDS in England generally RAINY?_
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.
Q. _Why is a fine CLEAR DAY sometimes OVERCAST in a few minutes?_
A. Because some _sudden change of temperature_ has condensed the vapour
of the air _into clouds_.
Q. _Why are CLOUDS sometimes DISSIPATED quite as suddenly?_
A. Because some _dry wind_ (blowing over the clouds) has _imbibed their
moisture_, and carried it off in invisible vapour.
Q. _Why does a SOUTH-WEST wind bring us RAIN?_
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.
Q. _Why does a NORTH-EAST wind RARELY bring 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.
Q. _Why does WIND sometimes bring RAIN, and sometimes FINE weather?_
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.
Q. _Why are MARCH winds DRY?_
A. Because they generally blow from the east or north-east; and,
therefore, _sweep over the continent of Europe_.
Q. _What is the USE of MARCH winds?_
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.
Q. _Why does "MARCH COME IN like a LION?"_
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.
Q. _Why does "MARCH GO OUT like a LAMB?"_
A. Because the water (evaporated by the high winds) falls again in
_showers_ to fertilize the earth, and _breaks the violence of the
winds_.
Q. _Why is it said that "A bushel of MARCH DUST is worth the king's
ransom?"_
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.
Q. _Why is it said "A DRY cold MARCH never BEGS BREAD?"_
A. Because the _dry cold winds_ of March prepare the soil for _seeds_,
which germinate, and produce fruit in the autumn.
Q. _Why is it said that "A WET MARCH makes a SAD autumn?"_
A. Because, if _March be wet_, so much of the seed _rots in the ground_,
that the autumn crops are spoiled.
Q. _Why is it said that "MARCH FLOWERS make NO summer BOWERS?"_
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.
Q. _Why is it said "A LATE SPRING makes a FRUITFUL YEAR?"_
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_.
Q. _Why is it said that "APRIL SHOWERS bring MAY FLOWERS?"_
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.
Q. _Does RAIN-water possess any fertilizing properties BESIDES that of
mere MOISTURE?_
A. Yes; rain-water contains "AMMONIA," to which much of its fertilizing
power may be attributed.
(Ammonia is a compound of nitrogen and hydrogen. Common hartshorn is
only ammonia and water.)
Q. _Why has God made NOVEMBER a very RAINY month?_
A. Because the rain hastens the _putrefaction of the fallen leaves_, and
this makes the earth fertile.
Q. _Why is there MORE rain FROM SEPTEMBER to MARCH than from March to
September?_
A. From September to March, the temperature of the air is _constantly
decreasing_; on which account, its _capacity for holding vapour_ is on
the _decrease_, and the vapour is precipitated as rain.
Q. _Why is there LESS rain FROM MARCH to SEPTEMBER, than from September
to March?_
A. From March to September, the temperature of the air is _constantly
increasing_; on which account, _its capacity for holding vapour_ is on
the _increase_, and very little is precipitated as rain.
Q. _Why is the RISING SUN in summer accompanied with a BREEZE?_
A. Because the heat of the rising sun _stops the radiation of heat_
from the earth, and _warms its surface_.
Q. _How does this WARMTH produce a BREEZE?_
A. The air (resting on the earth's surface) is _warmed by contact_,
ascends upwards, and _colder air rushes in_ to fill up the void, which
is the cause of the _morning_ breeze.
Q. _Why is there often an EVENING BREEZE during the summer months?_
A. The earth _radiates heat at sun-set_, and the air is cooled down
quickly by contact: this condensation causes a _motion in the air_,
which is the evening breeze.
Q. _Why are TROPICAL ISLANDS always subject to a SEA-breeze every
MORNING (i. e. a breeze blowing from the sea to the land)?_
A. The solar rays are unable to heat the surface of the _sea_ as they do
the _earth_; therefore, the _air resting on the earth_ is more _heated_
than the _air resting on the sea_; and the colder sea air blows _inland_
to restore the equilibrium.
Q. _Why is the LAND BREEZE UNHEALTHY?_
A. Because it is frequently loaded with exhalations from _putrefying
animal_ and _vegetable_ substances.
Q. _Why is the SEA BREEZE fresh and HEALTHY?_
A. Because it passes over the fresh sea, and is _not_ laden with noxious
exhalations.
It is _healthy_, therefore, to walk on the sea-beach before ten o'clock
in the morning; but _unhealthy_ after sun-set.
Q. _Why is there generally a fresh breeze from the SEA (in English
watering places) during the summer and autumn MORNINGS?_
A. As the _land_ is _more heated by the sun_ than the _sea_; therefore,
air resting on the _land_ is hotter than air resting on the _sea_; in
consequence of which, cooler sea air glides _inland_, to restore the
equilibrium.
Q. _Why does the SEA BREEZE feel COOL?_
A. As the sun cannot make the surface of the _sea_ so hot as the surface
of the _land_; therefore, the air which blows from the sea, feels
_cooler than the air of the land_.
Q. _Why are TROPICAL ISLANDS subject to a LAND BREEZE every EVENING
(i. e. a breeze blowing from the land towards the sea)?_
A. The _surface of land_ cools down _faster_ (after sun-set) than the
surface of the _sea_: in consequence of which, the air of the cold land
_is condensed, sinks down_, and spreads itself into the warmer _sea
air_, causing the LAND BREEZE.
Q. _Why is the LAND BREEZE COOL?_
A. As the surface of the land is cooled at sun-set _quicker than the
surface of the sea_; therefore, the seaman feels the air from the land
to be chill.
Q. _Why is the TEMPERATURE of ISLANDS more EQUABLE than that of
CONTINENTS?_
A. Because the _water_ around the island _absorbs_ the extreme heat of
summer, and _gives out_ heat to mitigate the extreme cold of winter.
Q. _Why does the sea round an island GIVE OUT heat in winter?_
A. Unless the _sea be frozen_ (which is rarely the case), it is _warmer_
than the frozen land; and, therefore, the warmth of the sea air (mixing
with the cold land air) helps to mitigate the intense cold.
Q. _Why are there WAVES in the sea?_
A. The wind (acting on the surface of the sea) _piles up ridges of
water_, which leave behind an _indentation_: as the water on all sides
rushes to _fill up this indentation_, the disturbance spreads on all
sides, and billow rolls after billow.
Q. _Why does WIND in England generally feel COLD?_
A. Because a _constantly changing surface_ comes in contact with our
body, to draw off its heat.
Q. _Why is a ROOM (even without a fire) generally WARMER than the OPEN
AIR?_
A. As the air in a room is _not subject to much change_, it soon becomes
of the same temperature as our skin, and no longer feels cold.
Q. _Why do we generally feel COLDER out-of-doors?_
A. Because the air (which surrounds us) _is always changing_; and as
fast as _one_ portion of air has become warmer by contact with our body,
_another colder portion_ surrounds us to absorb more heat.
Q. _Why are HOT FOODS made COOL by BLOWING them?_
A. Blowing causes the air (which covers the hot food) _to change more
rapidly_; in consequence of which, the hot air is _quickly blown away_,
and gives place to fresh _cold air_.
Q. _Why do ladies FAN THEMSELVES in hot weather?_
A. By the action of the fan, _fresh particles of air_ are perpetually
brought in contact with the face, and every fresh particle of air
_absorbs some heat_ from the skin.
Q. _Does the fan COOL the AIR?_
A. No; it makes the _air hotter_, by imparting to it the heat _out of
our face_: but it cools the _face_ blown upon, by transferring its heat
to the _air_.
Q. _Is the AIR in SUMMER time ever so hot as our bodies?_
A. No, not in England. In the hottest day in summer, the air of England
is 15 or 20 degrees cooler than the human body.
Q. _How fast does wind travel?_
A. A gentle breeze goes at about the rate of 5 miles an hour. A high
wind from 20 to 60. A hurricane from 80 to 100 miles an hour.
Q. _How is the VELOCITY of WINDS ascertained?_
A. By observing the velocity of the clouds, and by an instrument for the
purpose.
This instrument is called an ANEMOMETER.
Q. _How is the VELOCITY of the CLOUDS ascertained?_
A. By observing the speed of their shadow along the ground; which is
found in a high wind to vary from 20 to 60 miles an hour.
Q. _Why is there always a strong DRAUGHT through the KEYHOLE of a door?_
A. As the air of the room we occupy is _warmer than the air in the
hall_, therefore the cold hall air _rushes through the keyhole_ into the
room, and causes a draught.
Q. _Why is there always a strong DRAUGHT UNDER the DOOR, and through the
crevice on each side?_
A. The cold air _rushes from the hall_ under the door, &c. into the
room, to supply the _void_ caused in the room (by the escape of warm
air up the chimney, &c.)
Q. _Why is there always a DRAUGHT through the WINDOW crevices?_
A. The external air (being colder than the air of the room we occupy)
rushes through the window crevices _to supply the deficiency_, caused by
the escape of air up the chimney, &c.
Q. _Why is there more DRAUGHT if you open the LOWER SASH of a window,
than if you open the UPPER sash?_
A. If the _lower_ sash be open, the _cold external air_ will rush more
freely _into the room_; but if the _upper_ sash be open the _heated air
of the room_ will _rush out_; and (of course) there will be less
draught.
Q. _By which means is the ROOM better VENTILATED, by opening the lower
or the upper sash?_
A. A room is better _ventilated_ by opening the _upper sash_; because
the hot vitiated air (which always ascends towards the ceiling) _can
better escape_.
Q. _By which means is a HOT ROOM more quickly COOLED--By opening the
upper or the lower sash?_
A. A hot room is _cooled more quickly_ by opening the _lower sash_;
because the cold air can enter more freely by an _under_ current, than
by one _higher up_.
Q. _Why does WIND DRY damp LINEN?_
A. Because dry wind (like a dry sponge) imbibes the particles of vapour
from the surface of the linen, as fast as they are formed.
Q. _Which is the HOTTEST PLACE in a church, chapel, or theatre?_
A. The gallery.
Q. _Why is the GALLERY of all public places HOTTER than the lower parts
of the building?_
A. Because the heated air of the room _ascends_, and all the _cold air_
(which can enter through the doors and windows) _keeps to the floor_,
till it has become heated.
Q. _Why do PLANTS often grow out of WALLS and TOWERS?_
A. Because sometimes the _wind_ blows the seed there with the dust; and
sometimes _birds_ (flying over) drop the seed which they had formerly
eaten.
CHAPTER XXIII.
BAROMETER.
Q. _What is a BAROMETER?_
A. A weather-glass, or instrument to show the changes of the weather, by
marking the _variations in the weight of air_.
Q. _What is a THERMOMETER?_
A. An instrument to show how _hot or cold_ anything is.
Q. _What is the DIFFERENCE between a THERMOMETER and a BAROMETER?_
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.
Q. _If the mercury of the thermometer be SEALED UP from the air, how can
the air AFFECT it?_
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.
Q. _Why is the TUBE of a BAROMETER left OPEN?_
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.
Q. _How can weather be affected by the WEIGHT of the air?_
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_.
Q. _How can you tell (by looking at a BAROMETER) what KIND of WEATHER it
will be?_
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.
Q. _Does the WEIGHT of the air VARY MUCH?_
A. Yes; the atmosphere in England varies as much as _one-tenth part_
more or less.
Q. _What is the chief USE of a BAROMETER?_
A. To warn _sailors_ how to _regulate their ships_, before squalls come
on.
Q. _How can a BAROMETER warn SAILORS to regulate their SHIPS?_
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.
Q. _Are there any RULES which can be depended on?_
A. Yes; there are _ten special rules_ to direct us how to know the
changes of weather, by marking the mercury of a barometer.
Q. _What is the 1ST SPECIAL RULE in regard to the barometer?_
A. The barometer is _highest of all_ during a _long frost_; and it
generally rises with a _north-east wind_.
Q. _Why is the barometer HIGHEST of all during a long FROST?_
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.
Q. _Why does the barometer generally RISE with a NORTH-EAST wind?_
A. Because NORTH-EAST winds make the air both _cold and dry_: the air,
therefore, is both _condensed_, and _without vapour_.
Q. _What is the 2ND SPECIAL RULE in regard to the barometer?_
A. The barometer is _lowest of all_ during a _thaw which follows a long
frost_: it generally falls with SOUTH and WESTERN winds.
Q. _Why does the barometer fall LOWEST of all at the BREAKING UP of a
long FROST?_
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.
Q. _Why does the barometer fall very low with SOUTH and WEST winds?_
A. Because SOUTH and WEST winds come heavily _laden with vapour_; and
_vaporized_ air is lighter than _dry air_.
Q. _What effect has WIND on the mercury?_
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_.
Q. _Why do WINDS generally make the mercury of a barometer DROP?_
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.
Q. _What is the 3RD SPECIAL RULE in regard to the barometer?_
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.
Q. _Why will there be NO RAIN if the AIR be very DRY?_
A. If the air be very _dry_ it will _absorb moisture_, and not part with
what it has _in rain_.
Q. _Why will there be NO RAIN if the AIR be very COLD?_
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.
Q. _What is the 4TH SPECIAL RULE in regard to the barometer?_
A. When the barometer stands _very low_ indeed, there is never _much_
rain, although a _fine day_ will seldom occur at such times.
Q. _What kind of WEATHER will it be when the barometer is UNUSUALLY
LOW?_
A. There will be _short heavy showers_, with sudden _squalls of wind_
from the _west_.
Q. _Why will there be VERY LITTLE RAIN if the barometer be UNUSUALLY
LOW?_
A. Because the air must be very _warm_, or very _moist_, or perhaps
_both_.
Q. _Why will there be little or no rain, if the_ AIR _be very_ WARM?
A. If the air be very warm it will have a tendency to _imbibe more
moisture_, and not to part with what it has.
Q. _Why will there be little or no rain if the air be MOIST, and the
barometer remains very LOW?_
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_.
Q. _What is the 5TH SPECIAL RULE in regard to the barometer?_
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.
Q. _What is the 6TH SPECIAL RULE in regard to the barometer?_
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_.
Q. _What is the 7TH SPECIAL RULE in regard to the barometer?_
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_.
Q. _What is the 8TH SPECIAL RULE in regard to the barometer?_
A. The _higher_ the barometer, the greater is the probability of _fair
weather_.
Q. _Why is the barometer HIGH in FINE weather?_
A. Because the air contains but _very little vapour_. The _drier_ the
air, the _higher_ does the mercury of the barometer rise.
Q. _What is the 9TH SPECIAL RULE in regard to the barometer?_
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.
Q. _Why does the mercury RISE at the approach of FINE weather?_
A. Because the air is becoming more _dry_, and therefore its _pressure_
is greater.
Q. _Why does the mercury SINK at the approach of FOUL weather?_
A. Because the air is _laden with vapour_, or _disturbed by wind_.
Q. _Why does VAPOUR in the air make the mercury SINK?_
A. Because vaporized air is _lighter than dry air_, and therefore its
_pressure is less_ on the mercury of the barometer.
Q. _What is the 10TH SPECIAL RULE in regard to 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_.
Q. _How can you know if the MERCURY of the barometer be RISING?_
A. If it be _convex_ (i. e. higher in the _middle_ than at the _sides_;)
it is in a _rising state_.
Q. _How can you tell if the MERCURY of the barometer be about to FALL?_
A. If it be _concave_ (i. e. _hollow_ in the _middle_) it is in a
_falling state_.
Q. _Why is the mercury CONVEX when it is RISING?_
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_.
Q. _Why is the mercury CONCAVE when it is FALLING?_
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_.
Q. _What effect does a THUNDER-STORM produce on the weather?_
A. Thunder is generally _preceded by hot_ weather, and _followed by
cold_ and showery weather.
Q. _What effect does a SUDDEN CHANGE produce on the 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_.
Q. _Why is a sudden CHANGE from HOT to COLD followed by RAIN?_
A. The cold _condenses the air_ and its vapour; which, being condensed
and squeezed out, _falls in rain_.
Q. _Why is a sudden CHANGE from COLD to HOT followed by 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.
Q. _Why is the air quickly SATURATED with MOISTURE, when HEAT succeeds
rapidly from COLD?_
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.)
Q. _When does the barometer VARY MOST?_
A. In winter time.
Q. _Why does the barometer vary MORE in WINTER than in SUMMER 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.
Q. _When does the barometer VARY LEAST?_
A. In summer time.
Q. _Why does the barometer vary LESS in SUMMER than in WINTER 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.
Q. _What effect has WIND on the barometer?_
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.
Q. _Have HEAT and COLD any effect on the barometer?_
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.
Q. _Why is the mercury of a barometer LOWER in the TORRID than in the
FRIGID zones?_
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_.
Q. _In what MONTHS is the barometer HIGHEST?_
A. In May and August; next to these, in June, March, September, and
April.
Q. _In what MONTHS is the barometer LOWEST?_
A. In November and February; then in October, July, December, and
January.
Q. _What are the DRIEST months?_
A. March and June; then May and August; then April and November.
Q. _What are the WETTEST months?_
A. October and February; then July and September; then January and
December.
Q. _Why is there LESS wet from MARCH to AUGUST, than there is from
August to March?_
A. Because the _heat is constantly increasing_; and the capacity of the
air to absorb and retain moisture increases likewise.
Q. _Why is there MORE wet from AUGUST to MARCH, than there is from March
to August?_
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.
Q. _Why does the mercury of a barometer RISE in a FROST?_
A. Because frost _condenses the air_; and condensed air is heavier than
_rarefied_ air.
Q. _Why does the mercury of a barometer FALL in a THAW?_
A. Because the air is both _warmer_ (or more rarefied), and also filled
with _vapour_.
Q. _What does a SUDDEN rise or fall of the barometer indicate?_
A. If the _rise_ be sudden, fine weather will not continue long:
If the _fall_ be sudden, foul weather will not continue long.
Q. _What sort of weather may we expect if the barometer be very
FLUCTUATING?_
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.
CHAPTER XXIV.
SNOW. HAIL. RAIN.
Q. _What is SNOW?_
A. The condensed vapour of the air _frozen_, and precipitated to the
earth.
Q. _What is the CAUSE of SNOW?_
A. When the air is nearly saturated with vapour, and condensed by a
current of air _below freezing point_, some of the vapour is squeezed
out, and frozen into snow.
A few years ago, some fishermen (who wintered at Nova-Zembla), after
they had been shut up in a hut for several days, _opened the window_,
and the cold external air rushing in, instantly condensed the air of the
hut, and the vapour (which was squeezed out) fell on the floor _in a
shower of snow_.
Q. _Why does SNOW fall in WINTER time?_
A. Because the sun's rays are too _oblique_ to heat the surface of the
earth; and (as the _earth has no heat_ to radiate into the air) the air
is very cold.
Q. _What is SLEET?_
A. When flakes of snow (in their descent) pass through a bed of air
_above freezing point_, they melt; and fall to the earth as half-melted
snow or sleet.
Q. _What is the USE of SNOW?_
A. To keep the _earth warm_, and to _nourish_ it.
Q. _How can snow keep the EARTH WARM?_
A. Because it is a very _bad conductor_; in consequence of which, the
earth which is covered with snow, very rarely descends _below freezing
point_, even when the air is 15 or 20 degrees colder.
Q. _Why is SNOW a BAD CONDUCTOR of heat and cold?_
A. Because _air_ is confined and entangled between the crystals, and
_air_ is a very _bad conductor_; when, therefore, the earth is covered
with snow, it cannot throw off its heat by radiation.
Q. _Tell me the words of the PSALMIST_ (cxlvii. 16.) _respecting snow,
and explain what he means._
A. The Psalmist says--"The Lord giveth snow like wool:" and he means not
only that snow is as _white as wool_, but that it is also as _warm as
wool_.
Q. _Why is WOOL WARM?_
A. Because _air_ is entangled between the fibres of the wool, and air is
a _bad conductor_.
Q. _Why is SNOW WARM?_
A. Because _air_ is entangled between the crystals of the snow, and air
is a _bad conductor_.
Q. _Why does SNOW NOURISH the earth?_
A. Because it supplies it with _moisture_ for a considerable time; which
penetrates slowly into the soil, and insinuates itself through every
clod, ridge, and furrow.
Q. _Why is there NO SNOW in SUMMER time?_
A. No snow reaches the general surface of the earth in summer time,
because the _heat of the earth_ melts it in its descent.
Q. _Why are some MOUNTAINS ALWAYS COVERED with SNOW?_
A. 1st--Because the _air is more rarefied_; and rarefied air _abstracts
heat_ which it holds in a _latent state_:
2ndly--As the mountain top is _not surrounded by earth_ to radiate heat
into the air; therefore, the snow is _not melted_ in its descent, but
falls on the mountain, and lies there.
Q. _Why is SNOW WHITE?_
A. Snow is formed of an infinite number of very minute crystals and
prisms, which reflect all the colours of the rays of light; and these
colours _uniting_ before they meet the eye, cause snow to appear white.
Q. _What is HAIL?_
A. Rain, which has passed in its descent _through some cold bed of air_,
and has been frozen into drops of ice.
Q. _Why is ONE bed of air COLDER than another?_
A. This is frequently caused by _electricity_ in the air, _unequally
distributed_.
Q. _Why is HAIL frequently accompanied with THUNDER and LIGHTNING?_
A. 1st--Because the _congelation of water into hail_ disturbs the
electricity of the air: and
2ndly--The _friction_ (produced by the fall of hail) excites it still
more.
Q. _Why does HAIL fall generally in SUMMER and AUTUMN?_
A. 1st--Because the _air is more highly electrified_ in summer and
autumn: and
2ndly--The vapours (being rarefied) ascend to the more elevated regions,
where the _cold is greater_ than it is nearer the earth.
Q. _What TWO things are essential to cause HAIL?_
A. Two _strata of clouds_ having _opposite electricities_, and _two
currents of wind_. The _lower cloud_ (being negative) is the one
_precipitated_.
Q. _What is RAIN?_
A. The vapour of the clouds or air _condensed_, and precipitated to the
earth.
Q. _Why is the vapour of the air or clouds PRECIPITATED?_
A. When the air is _saturated with vapour_, if a cold current
_condenses_ it, it is no longer _able to hold all its vapour_ in
solution, and some of it is squeezed out, and falls as rain.
Q. _Why does RAIN fall in DROPS?_
A. The vapoury particles in their descent _attract each other_; and
those which are sufficiently near, _unite_ and form into a drop.
Q. _Why does not the COLD of NIGHT ALWAYS cause rain?_
A. When the air is not _near saturation_ (although condensed by the
chill of evening), it will still be able to hold its vapour in solution.
Q. _Why does a PASSING CLOUD often drop RAIN?_
A. Because the cloud (travelling about on the wind) comes into contact
with _something that chills it_; and its vapour being squeezed out,
_falls to the earth as rain_.
Q. _Why are RAIN-DROPS sometimes much LARGER than at OTHER times?_
A. When the rain-cloud is floating _near the earth_, the drops are
large, because such a cloud is _much more dense_ than one which is more
elevated.
The size of the rain-drop is increased according to the _rapidity_ with
which the vapours are condensed.
Q. _Does not WIND sometimes INCREASE the SIZE of rain-drops?_
A. Yes; by blowing two or more drops into one.
Q. _Why do CLOUDS FALL in RAINY weather?_
A. 1st--Because the _clouds are heavy_ with abundant vapour: and
2ndly--As the density of the air is _diminished_, it is less able to
buoy the clouds up.
Q. _How do you KNOW that the DENSITY of the air is DIMINISHED in RAINY
weather?_
A. Because the _mercury of a barometer falls_.
Q. _Why is RAIN-water more FERTILIZING than PUMP-water?_
A. Because it contains a compound of hydrogen and nitrogen (called
_ammonia_), which is a very excellent food for young plants.
Q. _Why is NOVEMBER made by God to be a RAINY MONTH?_
A. Because rain _hastens the putrefaction of the fallen leaves_ by
causing fermentation.
Q. _Why does RAIN PURIFY the AIR?_
A. 1st--Because it _beats down the noxious exhalations_ collected in the
air, and _dissolves_ them:
2ndly--It mixes the air of the _upper_ regions with that of the _lower
regions_: and
3rdly--It _washes the earth_, and sets in motion the stagnant _sewers
and ditches_.
Q. _Why are MOUNTAINOUS countries more RAINY than flat ones?_
A. The air (striking against the side of the mountains) is _carried up
the inclined plane_, and brought in contact with the _cold air of the
higher regions_, by which it is _condensed_, and its _vapour squeezed
out_.
Q. _Why does a SPONGE SWELL when it is WETTED?_
A. Because the water _penetrates the pores_ of the sponge, and drives
the particles of the sponge _further from each other_; in consequence of
which, the _bulk_ of the sponge is greatly _increased_.
Q. _Why do FIDDLE-strings SNAP in WET weather?_
A. Because the moisture of the air (penetrating the string) _causes it
to swell_; and (as the cord _thickens_) its _tension is increased_, and
the string snaps.
Q. _Why does PAPER PUCKER when it is WETTED?_
A. Because the moisture (penetrating the paper) _drives its particles
further apart_; and (as the moisture is absorbed _unequally_ by the
paper) some parts are more enlarged than others; in consequence of
which, the paper _blisters_ or _puckers_.
Q. _Why do the weather toys called CAPU'CHINS lift the cowl over the
figures in wet weather, and remove it in dry?_
A. The cowl of the capu'chin is _fastened to a piece of cat-gut_. When
the weather is _wet_, the moisture _swells the cat-gut_ and it is
_shortened_, by which means the _cowl is pulled up_; but in _dry_
weather, the _string is loosened_, and the cowl falls down.
Q. _In another weather toy, the MAN comes out in WET weather, and the
LADY in FINE:--Why is this?_
A. The two figures are attached to a piece of _cat-gut_ in such a
manner, that when the _cat-gut is shortened by moisture_, it pulls the
_man out_; but when it is _loose_, the woman _falls out by her own
weight_.
Q. _Why are WET STOCKINGS DIFFICULT to PULL ON?_
A. The moisture (by penetrating the threads of the stockings) causes
them to _shrink in size_.
Q. _What is the MOST RAINY spot in ENGLAND?_
A. Keswick (in Cumberland); and then Kendal (a market town in
Westmoreland).
(In Keswick, about 63 inches of rain fall in a year. In Kendal, 58;
Manchester, 38; Liverpool, 34; Dublin and Cambridge, 25; Lincoln, 24;
London, 21; and in Paris, only 18.)
Q. _In which PART of the DAY does the MOST RAIN fall?_
A. More rain falls by _night_ than by day; because the cold night
_condenses the air_, and diminishes its capacity for holding vapour in
solution.
Q. _Does more rain fall in SUMMER or in WINTER time?_
A. There are _more rainy days_ from September to March; but _heavier_
rains between March and September.
Q. _Why are there MORE RAINY DAYS from September to March, than from
March to September?_
A. Because the temperature of the air is _constantly decreasing_, and
its capacity for vapour decreases also; in consequence of which, it is
perpetually obliged to _part with some of its vapour_ in rain.
Q. _In what PART of the WORLD does RAIN fall MOST ABUNDANTLY?_
A. Near the _equator_; and the quantity of rain _decreases_ as we
approach the _poles_.
Q. _Why does MORE RAIN fall at the EQUATOR than at the POLES?_
A. Because the _contrast_ between the _night and day_ is very great. The
hot air _absorbs moisture very abundantly_ during the day; and when the
cold night _condenses_ the air, it is unable to _retain the moisture
imbibed_, and some of it falls in rain.
CHAPTER XXV.
WATER.
Q. _What is WATER?_
A. Water is composed of _two gases_, oxygen and hydrogen.
(In 9 lbs. of water, 8 are oxygen, and 1 is hydrogen.)
Q. _Why is WATER FLUID?_
A. Because its particles are kept separate by _latent heat_; but when a
certain quantity of this latent heat is driven out, _water becomes
solid_, and is called ice.
Q. _How can WATER be converted into a GAS?_
A. By increasing its _latent heat_, the particles, of water are again
_subdivided into invisible steam_.
Q. _Why is PUMP water called HARD water?_
A. Because it is laden with foreign matters, and will not readily
_dissolve substances_ immersed in it.
Q. _What makes PUMP-water HARD?_
A. Because when it filters through the earth, it becomes impregnated
with _sulphate of lime_, and many other impurities from the _earths and
minerals_ with which it comes in contact.
Q. _Why is it difficult to WASH our HANDS clean with HARD water?_
A. Because the _soda of the soap_ combines with the _sulphuric acid_ of
the hard water, and the _oil of the soap_ with the _lime_, and float in
flakes on the top of the water.
N.B. Sulphate of lime consists of sulphuric acid and lime.
Q. _Why is it difficult to wash in SALT WATER?_
A. Because salt water contains _muriatic acid_; and the _soda of soap_
combines with the _muriatic acid of the salt water_, and produces a
cloudiness.
Q. _Why does a BLACK HAT turn RED at the SEA SIDE?_
A. The _muriatic acid of the sea-water_ disturbs the _gallic acid of the
black dye_, and turns it _red_.
Q. _Of what is SOAP made?_
A. Of kelp (or the ashes of sea-weed dried and burnt in a pit) mixed
with oil or fat.
YELLOW SOAP is made of whale-oil, soda, and resin. SOFT SOAP is made of
oil and potash. HARD SOAP of oil and soda.
Q. _Why does WATER CLEAN dirty LINEN?_
A. Because the _oxygen_ of the water attaches itself to the _stains of
the linen_, and _dissolves_ them; as oxalic acid dissolves ink spots.
Q. _Why does SOAP greatly INCREASE the cleansing power of water?_
A. 1st--Because soap _increases the oxygen_ of the water: and
2ndly--It _neutralizes the grease_ of the things washed.
Q. _Why is RAIN WATER SOFT?_
A. Because it has _not come in contact with earths and minerals_.
Q. _Why is it MORE EASY to WASH with SOFT water than with HARD?_
A. Because it unites freely with the soap, _dissolving_ it instead of
_decomposing it_, as hard water does.
Q. _Why do WOOD ASHES make HARD water SOFT?_
A. 1st--Because the _carbonic acid of the wood ashes_ combines with the
_sulphate of lime in the hard water_, and converts it into _chalk_: and
2ndly--The _sulphuric acid of the water_ combines with the _potash of
the wood ashes_, and prevents it from neutralizing the oily matter of
the soap.
Q. _Why has RAIN water such an UNPLEASANT SMELL, when it is collected in
a rain water tub or tank?_
A. Because it is impregnated with _decomposed organic matter_, washed
from roofs, trees, or the casks in which it is collected.
Q. _Why does WATER MELT SUGAR?_
A. Because very minute particles of water _insinuate themselves into
the pores_ of the sugar, and force the crystals _apart from each other_.
Q. _Why does WATER MELT SALT?_
A. Because very minute particles of water insinuate themselves into the
_pores of the salt_, and force the crystals _apart from each other_.
Q. _Why does melted SUGAR or SALT give a FLAVOUR to the WATER?_
A. Because the sugar or salt (being disunited into very minute pieces)
_floats about the water_, and mixes with _every part_.
Q. _Why does HOT water melt sugar and salt QUICKER than COLD water?_
A. 1st--Because the _heat_ of the water entering the pores of the sugar
or salt, _opens a passage for the water_: and
2ndly--The _particles of hot water_ being _smaller_ than those of cold,
can _more readily penetrate_ the pores of salt or sugar.
Q. _Why is SEA-water SALT?_
A. 1st--Because it contains _mines of salt_ at the bottom of its bed:
2ndly--It is impregnated with _bituminous matter_, which is brackish:
and
3rdly--It contains many _putrid substances_, which increase its
brackishness.
Q. _Why is NOT RAIN-water SALT, although most of it is evaporated from
the SEA?_
A. Because _salt will not evaporate_; and, therefore, when sea-water is
turned to vapour, its _salt is left behind_.
Q. _Why does STAGNANT water PUTREFY?_
A. Because leaves, plants, insects, &c. are decomposed in it.
Q. _Why is STAGNANT water full of WORMS, EELS, &c.?_
A. Because numberless insects _lay their eggs_ in the leaves and plants
which float on the surface; these eggs are soon hatched, and produce
swarms of worms, eels, and insects.
Q. _Why are FLOWING waters FREE from these IMPURITIES?_
A. 1st--Because the motion of running water _prevents its fermentation:_
2ndly--It _dissolves the putrid substances_ which happen to fall into
it: and
3rdly--It casts _on the bank_ (by its current) such substances as it
cannot _dissolve_.
Q. _Why does RUNNING water OSCILLATE and WHIRL in its current?_
A. 1st--Because it _impinges against its banks_, and is perpetually
diverted from its forward motion: and
2ndly--Because the _centre_ of a river _flows faster_ than its _sides_.
Q. _Why do the SIDES of a river flow more TARDILY than its CENTRE?_
A. Because they _rub against the banks_, and are delayed in their
current thereby.
Q. _Why does SOAPY water BUBBLE?_
A. Because the soap _makes the water tenacious_, and prevents the
bubbles from _bursting_ as soon as they are formed.
Q. _Why will not water bubble WITHOUT SOAP?_
A. Because it is not tenacious enough _to hold together the bubbles_
that are formed.
Q. _When SOAP BUBBLES are blown from a pipe, why do they ASCEND?_
A. Because they are _filled with warm breath_, which is lighter than
air.
CHAPTER XXVI.
ICE.
Q. _What is ICE?_
A. FROZEN WATER. When the air is reduced to 32 degrees of heat, water
will no longer remain in a _fluid state_.
Q. _Why is SOLID ICE LIGHTER than WATER?_
A. Because water _expands by freezing_; and as the _bulk is increased_,
the _gravity_ must be _less_.
Nine cubic inches of water become ten when frozen.
Q. _Why do EWERS BREAK in a FROSTY NIGHT?_
A. Because the water in them _freezes_; and as the _water is expanded by
frost_, it bursts the ewers to make room for its increased volume.
Q. _Why does it not expand UPWARDS (like boiling water), and RUN OVER?_
A. Because the _surface_ is first frozen, and the frozen surface acts as
a _plug_, which is more difficult to burst than the earthen ewer
itself.
Q. _Why do TILES, STONES, and ROCKS often SPLIT in winter?_
A. Because the moisture (which they imbibed) _freezes_, and by its
expansion _splits the solid mass_.
Q. _In winter time, FOOT-MARKS and WHEEL-RUTS are often covered with an
icy NET-WORK, through the interstices of which the soil is clearly
seen,--WHY does the water freeze in NET-WORK?_
A. The water in these hollows froze first at the _sides_ of the
foot-prints: other crystals gradually shot across the water, and would
have _covered the whole surface_, had not the earth _absorbed_ the water
before it had time to freeze.
Q. _In winter time these FOOT-MARKS and WHEEL-RUTS are sometimes covered
with a perfect SHEET of ice, and not an icy net-work,--Why is THIS?_
A. The _air being colder_ and the _earth harder_ (than in the former
case), the _entire surface_ of the foot-print is frozen over, before the
earth can _draw the water in_.
Q. _Why is not the ice SOLID in these ruts?--WHY is there only a very
thin FILM or NET-WORK of ice?_
A. Because the earth _absorbs the water_, and leaves the icy _film
behind_.
Q. _Does not water expand by HEAT as well as COLD?_
A. Yes; it expands as soon as it is more than 42 degrees _till it
boils_, and then it flies off in steam.
[Illustration: Here A B measures the bulk of a portion of water at 42
degrees.
It goes on increasing in bulk to C D, when it boils. It also goes on
increasing in bulk to E F, when it freezes.]
Q. _Why do WATER-PIPES frequently BURST in FROSTY weather?_
A. Because the water in them _freezes_; and as the water _expands by
frost_, it bursts the pipes to make room for its increased volume.
Q. _When does WATER begin to EXPAND from cold?_
A. Water (which is wisely ordained by God to be an _exception_ to a
very general rule) _contracts_ till it is reduced to 42 degrees, and
then it _expands till it freezes_.
(Water freezes at 32°.)
Q. _Why does water expand when it freezes?_
A. Because it is converted into _solid crystals_, which _do not fit
close_, like the particles of water.
Q. _Why is the water at the BOTTOM of a river NEVER FROZEN?_
A. Because when water is colder than 42 degrees, it instantly _ascends
to the surface_; and (if it freezes) _floats there_ till it is melted.
(When a river is frozen, the water below the surface is never less than
42°.)
Q. _Show the WISDOM of GOD in this wonderful exception to a general
law._
A. If ice were _heavier than water_, it would _sink_; and a river would
soon become a solid _block of ice_, which could never be dissolved.
Q. _Why does not the cold ICE on the SURFACE of a river CHILL the water
BENEATH, and make it freeze?_
A. 1st--Water is a _very bad conductor_, and is heated or chilled by
CONVECTION only:
2ndly--If the ice on the surface were to communicate its _coldness_ to
the water beneath, the _water beneath_ must communicate its _heat to the
ice_, and the ice would instantly _melt_: and
3rdly--The ice on the surface acts as a _shield_ to _prevent the cold
air from penetrating the river_ to freeze it below the mere crust.
Q. _Why does WATER FREEZE at the SURFACE first?_
A. Because the surface is in _contact with the air_, and the air
_carries away its heat_.
Q. _Why does the coat of ice grow THICKER and THICKER, if the frost
CONTINUES?_
A. Because the _heat of the water_ (immediately below the frozen
surface) _passes through the pores of the ice_ into the _cold air_.
Q. _Why then are not WHOLE RIVERS FROZEN (layer by layer) till they
become solid ice?_
A. Because water is _so slow a conductor_, that our frosts never
continue _long enough_ to convert a whole river into a solid mass of
ice.
Q. _Why does not RUNNING water freeze so fast as STILL water?_
A. 1st--Because the motion of the current _dissolves the crystals_ as
fast as they are formed; and
2ndly--The heat of the _under_ surface is more freely distributed to the
_upper_ surface by the _rolling water_.
Q. _When RUNNING water is FROZEN, why is the ICE generally very ROUGH?_
A. Because little flakes of ice are first formed and _carried down the
stream_, till they meet some _obstacle_ to _stop_ them; _other_ flakes
of ice (_impinging against them_) are arrested in like manner; and the
_edges_ of the different flakes _overlapping_ each other, _make the
surface rough_.
Q. _Why do SOME parts of a RIVER FREEZE LESS than OTHERS?_
A. Because _springs_ issue from the bottom, and (as they bubble upwards)
_thaw the ice_, or make it thin.
Q. _When persons FALL into a RIVER in winter time, why does the WATER
feel remarkably WARM?_
A. Because the _frosty air_ is at least 10 or 12 degrees _colder_ than
the water.
(The water below the surface is at least 42°; but the air 32°, or even
less.)
Q. _Why is SHALLOW water FROZEN QUICKER than DEEP water?_
A. Because (as the _whole volume_ of water must be cooled to 42 degrees
before the _surface can be frozen_) it will take a longer time to cool
down a _deep_ bed of water than a _shallow_ one.
Q. _Why is SEA-WATER RARELY FROZEN?_
A. 1st--Because the _mass of water is so great_ that it requires a very
long time to cool the whole volume down to 42 degrees:
2ndly--The _ebb and flow_ of the sea interfere with the cooling
influence of the air: and
3rdly--_Salt_ never freezes till the surface is cooled down at least 25
degrees _below the freezing point_.
Q. _Why do some LAKES RARELY if ever FREEZE?_
A. 1st--Because they are _very deep_:
2ndly--Because their water is supplied by _springs_, which bubble from
the bottom.
Q. _Why does the DEPTH of the water RETARD its FREEZING?_
A. As the _whole volume of water_ must be reduced to 42 degrees before
the _surface will freeze_, the _deeper_ the water, the _longer_ it will
be before the whole volume is thus reduced.
Q. _Why do SPRINGS at the bottom of a lake PREVENT its FREEZING?_
A. Because they keep continually sending forth _fresh water_, which
prevents the lake from being reduced to the necessary degree of
coldness.
Q. _Why is it COLDER in a THAW than in a FROST?_
A. When frozen water is _thawed_, it absorbs _heat from the air and
objects around_ to melt its ice, in consequence of which the cold is
greatly increased.
Q. _Why is it WARMER in a FROST than in a THAW?_
A. When water freezes it _gives out its latent heat_, in order that it
may be converted into _solid ice_; and as much _heat is liberated_ from
the water into the air, we feel warmer.
Q. _Why does SALT DISSOLVE ICE?_
A. Water freezes at 32°, but salt and water will not freeze _till the
air is 25° colder_: if, therefore, salt be added to frozen water it
becomes _liquid_, unless the thermometer stands below 7°, (which it
never does in our island).
Q. _Will any thing do INSTEAD of SALT?_
A. Yes; any _acid_, such as sulphuric, nitric, &c.
Q. _Why are SALT and SNOW mixed together, colder than SNOW?_
A. When _salt_ is mixed with snow, it _dissolves the crystals_ into a
fluid; and whenever a solid is converted to a liquid, _heat is
absorbed_, and the cold made more intense.
Q. _Why does FROST make the EARTH CRACK?_
A. During the warm weather the earth _absorbed abundance of moisture_,
which the winter _freezes_: and (as water _expands_ by frost) the
expanding water _thrusts the particles of earth apart from each other_,
and leaves a chink or crack behind.
Q. _Show the WISDOM of GOD in this arrangement._
A. These _cracks_ in the earth let in the air, the dew and rain, and
many gases favourable to vegetation.
Q. _Why does the EARTH CRUMBLE in SPRING?_
A. In spring the _ice_ of the clods _dissolves_, and the particles of
earth (which had been held apart by the expanded ice) are left
_unsupported_, and tumble into minute parts (because their _cement is
dissolved_).
Q. _Why does MORTAR CRUMBLE away in FROST?_
A. If the mortar was not _dried in the warm weather_, its moisture
_freezes_, _expands_, and thrusts the particles of the mortar away from
each other; but (as soon as the frost goes) the _water condenses_ and
leaves the mortar full of cracks and chinks.
Q. _Why does STUCCO PEEL from a WALL in FROSTY weather?_
A. If the stucco was not _dried in the warm weather_, its moisture
_freezes_, _expands_, and thrusts its particles away from the wall; but
as soon as the water condenses again by the thaw, the stucco (being
unsupported) _falls by its own weight_.
Q. _Why cannot BRICKLAYERS and PLASTERERS work in FROSTY weather?_
A. Because the bricks and plaster would _start from their position_ as
soon as the _frost_ came and expanded the mortar.
Q. _Why do BRICKLAYERS COVER their work with STRAW in spring and
autumn?_
A. Because straw is a non-conductor, and prevents the mortar of their
new work from _freezing_ during the cold nights of spring and autumn.
Q. _Why are WATER-PIPES often covered with STALL-LITTER in winter time?_
A. Because straw (being a non-conductor) prevents the _water of the
pipes from freezing_, and the _pipes from bursting_.
Q. _Why are delicate TREES covered with STRAW in WINTER?_
A. Because straw (being a non-conductor) prevents the _sap of the tree_
from being frozen.
Q. _Can WATER be FROZEN in any way BESIDES by frosty weather?_
A. Yes; in very many ways. For example--a bottle of water wrapped in
_cotton_, and frequently _wetted with ether_, will soon freeze.
Q. _Why would WATER FREEZE if the bottle were kept constantly wetted
with ETHER?_
A. Because _evaporation_ would carry off the heat of the water, and
reduce it to _freezing point_.
Q. _Why does ETHER freeze under the RECEIVER of an AIR-pump, when the
air is exhausted?_
A. Because _evaporation_ is very greatly increased by the _diminution of
atmospheric pressure_; and the ether freezes by evaporation.
FREEZING MIXTURES.
1. If nitre be dissolved in water, the heat of the liquid will be
reduced 16 degrees.
2. If 5 oz. of nitre, and 5 of sal-ammoniac (both finely powdered) be
dissolved in 19 oz. of water, the heat of the liquid will be reduced 40
degrees.
3. If 3 lbs. of snow be added to 1 lb. of salt, the mixture will fall to
0° (or 32 degrees below freezing point).
The two following are the coldest mixtures yet known:--
1. Mix 3 lbs. of muriate of lime with 1 lb. of snow.
2. Mix 5 lbs. of diluted sulphuric acid with 4 lbs. of snow.
Q. _Why is it more easy to SWIM in the SEA than in a RIVER?_
A. Because the _specific gravity_ of salt water is _greater than that of
fresh_, and therefore it _buoys_ up the swimmer better.
Q. _How do cooks ascertain if their BRINE be SALT ENOUGH for pickling?_
A. They put an _egg into their brine_. If the egg _sinks_ the brine is
_not strong enough_, if the egg _floats_ it _is_.
Q. _Why will the EGG SINK if the brine be NOT STRONG enough for
pickling?_
A. As an egg is _heavier than water_, it will _sink_ if immersed
therein; but if as much _salt_ be added as the water can dissolve, the
egg will _float_.
Q. _Why will the EGG FLOAT in strong BRINE?_
A. Because the specific gravity of _salt and water_ is greater than that
of water _only_.
Q. _Why do persons SINK in water when they are UNSKILFUL SWIMMERS?_
A. 1st--Because (in their floundering about) they _take in water_ at
their nose and mouth, which makes them _heavier_:
2ndly--FEAR _contracts the body_; and as the body is compressed by fear
into a smaller compass, it becomes _heavier_: and
3rdly--The water and fear _take away the breath_; and when the breath is
taken from the body, its _bulk is reduced_, and it becomes _heavier_.
Q. _Why can QUADRUPEDS swim MORE EASILY than MAN?_
A. 1st--Because the _trunk_ of a quadruped is _lighter than water_, and
this is the greatest part of them:
2ndly--The _position_ of a beast in water is a _natural_ one.
Q. _Why is it MORE DIFFICULT for a MAN to swim than for a BEAST?_
A. Because the _head and limbs_ of a man (like those of a beast) are
_heavier_ than water, and these compose more than _half his body_:
2ndly--The _position_ of a man in water is _unnatural_ to him.
Q. _Why can FAT men SWIM more EASILY than SPARE men?_
A. _Fat is lighter than water_; and the _fatter_ a man is, the more
_buoyant_ will he be.
Q. _How are FISHES able to ASCEND to the SURFACE of water?_
A. Fishes have an _air-bladder_ near their abdomen: when this bladder is
_filled with air_, the fish increases in size; and (being lighter)
ascends through the water to its surface.
Q. _How are fishes able to DIVE in a minute to the BOTTOM of a stream?_
A. They _expel the air_ from their air-bladder; in consequence of which,
their _size is diminished_, and they sink instantly.
CHAPTER XXVII.
LIGHT.
Q. _What is LIGHT?_
A. Rapid undulations of a fluid called ether, striking on the optic
nerve of the eye. (_See p. 46._)
The _heat_ of fire or of the sun sets the atoms of _matter_ in motion;
and these atoms, striking against the fluid _ether_, cause it to
undulate.
Q. _How FAST does LIGHT TRAVEL?_
A. Light travels so fast, that it would go eight times round the earth,
while a person counts "ONE."
Q. _Does ALL light travel equally fast?_
A. Yes; the light of the sun, or the light of a candle, or the light
from houses, trees, and fields.
Q. _Where does the LIGHT of HOUSES, TREES, and FIELDS come from?_
A. The light of the _sun_ (or of some lamp or candle) is _reflected from
their surfaces_.
Q. _Why are SOME surfaces BRILLIANT like glass and steel, and OTHERS
DULL like lead?_
A. Those surfaces which _reflect the most light_, are the most
_brilliant_; and those which _absorb_ light are _dull_.
Q. _What is meant by REFLECTING LIGHT?_
A. Throwing the rays of light _back again_, from the surface on which
they light.
Q. _What is meant by ABSORBING LIGHT?_
A. Letting the rays of light _sink below the surface_ which they touch,
so as not to be seen.
Q. _Why can a THOUSAND persons SEE the SAME OBJECT at the same time?_
A. Because it throws off from its surface _an infinite number of rays in
all directions_; and one person sees _one_ portion of these rays, and
another person _another_.
Q. _Why is the EYE PAINED by a SUDDEN light?_
A. Because the pupil of the eye is _burdened with rays_, before it has
had time to contract.
Q. _Why does it give us PAIN, if a CANDLE be brought suddenly towards
our BED at night time?_
A. In the dark _the pupils of the eyes dilate_ very much, in order to
_admit more rays_. When a candle is brought before them, the enlarged
pupil is _overladen with rays_, and feels pained.
Q. _Why CAN we BEAR the candle-light after a few moments?_
A, Because the pupil _contracts again_ almost instantly, and adjusts
itself to the quantity of light which falls upon it.
Q. _Why can we SEE NOTHING, when we leave a WELL-LIGHTED room, and go
into the DARK ROAD or street?_
A. Because the pupil (which _contracted_ in the bright room) does not
_dilate instantaneously_; and the contracted pupil is not able to
_collect rays enough_ (from the dark road or street) to enable us to see
before us.
Q. _Why do we SEE BETTER, when we get USED to the dark?_
A. Because the pupil _dilates_ again, and is able to gather together
more rays; in consequence of which, we see more distinctly.
Q. _If we look at the SUN for a few moments, why do all OTHER things
appear DARK?_
A. Because the pupil of the eye (which was _very much contracted_ by
looking at the sun) is _too small_ to collect sufficient rays from
_other objects_, to enable us to distinguish their colours. (_See_
"accidental colours.")
Q. _If we watch a bright FIRE for a few moments, why does the ROOM seem
DARK?_
A. Because the pupil of the eye (which was very much _contracted_ by
looking at the fire) is _too small_ to collect sufficient rays from the
objects around, to enable us to distinguish their colours.
Q. _Why can we see the PROPER COLOUR of every object again, after a few
minutes?_
A. Because the pupil _dilates_ again, and accommodates itself to the
light around.
Q. _Why can TIGERS, CATS, and OWLS see in the DARK?_
A. Because they have the power of _enlarging the pupil of their eyes_,
so as to collect several scattered rays of light; in consequence of
which, they can _see distinctly_ when it is not light enough for us to
see _any thing at all_.
Q. _Why do CATS and OWLS SLEEP almost all DAY?_
A. As the pupil of their eyes is _very broad_, daylight _fatigues_ them;
so they close their eyes for relief.
Q. _Why do CATS keep WINKING, when they sit before a FIRE?_
A. As the pupil of their eyes is _very broad_, the light of the fire
_pains_ them; and they keep shutting their eyes to relieve the sensation
of too much light.
Q. _Why do TIGERS, CATS, OWLS, &c. PROWL by NIGHT for prey?_
A. As these animals cannot see distinctly in _strong daylight_, they
_sleep_ during the _day_: and as they can see clearly in the _dark_,
they prowl then for prey.
Q. _Why do GLOW-WORMS glisten by NIGHT only?_
A. Because the light of day is _so much stronger_, that it _eclipses_
the feeble light of a glow-worm; in consequence of which, glow-worms are
_invisible by day_.
Q. _Why can we not see the STARS in the DAY-TIME?_
A. Because the light of day is so powerful, that it _eclipses the feeble
light of the stars_: in consequence of which, they are invisible by day.
Q. _Why can we see the STARS even at MID-DAY, from the bottom of a deep
WELL?_
A. As the rays of the sun never come _directly over a well_, but the
rays of the _stars_ do; therefore the light from those stars (in such a
situation) is more clear than the light of the _sun_.
Q. _What is the USE of TWO EYES, since they present only one image of
any object?_
A. The use of two eyes is to _increase the light_, or take in _more rays
of light_ from the object looked at, in order that it may appear _more
distinct_.
Q. _Why do we NOT see things DOUBLE, with TWO EYES?_
A. 1st--Because the _axis of both eyes is turned to one object_; and,
therefore, the _same impression_ is made on the ret´ina of _each eye_.
2ndly--The nerves (which receive the impression) have _one point of
union_, before they reach the brain.
Q. _Why do we SEE OURSELVES in a GLASS?_
A. The rays of light from our face _strike against the surface of the
glass_, and (instead of being absorbed) _are reflected_, or sent back
again to our eye.
Q. _Why are the rays of light REFLECTED by a MIRROR?_
A. Because they cannot _pass through the impenetrable metal_ with which
the back of the glass is covered; so they _rebound back_, just as a
_marble_ would do if it struck against a wall.
Q. _When a marble is rolled towards a wall, what is that path THROUGH
WHICH IT RUNS called?_
A. The line of the _angle of incidence_.
Q. _When a marble REBOUNDS back again, what is the path it THEN
describes called?_
A. The line of the _angle of reflection_.
Q. _When the light of our face goes TO the GLASS, what is the path
through which it goes CALLED?_
A. The line of the _angle of incidence_.
Q. _When the light of our face is reflected BACK again from the mirror,
what is this RETURNING path called?_
A. The line of the _angle of reflection_.
Q. _Why does our reflection in a mirror seem to APPROACH us as we walk
TOWARDS it, and to RETIRE FROM us as WE retire?_
A. Because the line _of the angle of incidence_ is always _equal_ to the
_line and angle of reflection_.
[Illustration: Here CA, EA and DB, FB are the lines of the angle of
incidence; and GA, KA and HB, LB are the lines of the angle of
reflection. When the arrow is at CD, its shadow will appear at GH,
because the line CA=GA and the angle CAB=angle GAB, &c.; and the same
may be said about the point D.]
Q. _Why can a man see his WHOLE PERSON reflected in a LITTLE MIRROR not
6 inches in length?_
A. Because the _line of the angle of incidence_ is always equal to the
_line and angle of reflection_.
Take the last figure--CD is much larger than the mirror AB; but the head
of the arrow C is reflected obliquely behind the mirror to G; and the
barb D appears at H.--Why? Because the line CA=AG and the angle
CAB=angle GAB, &c. The same may be said of the point D.
Q. _Why does a SHADOW in WATER always appear TOPSY-TURVY?_
A. Because the _line of the angle of incidence_ is always equal to the
_line and angle of reflection_.
[Illustration: Here the arrow-head A strikes the water at F, and is
reflected to D; and the barb B strikes the water at E, and is reflected
to C.
If a spectator stands at G, he will see the reflected lines CE and DF,
produced as far as G.
It is very plain that the more elevated object A will strike the water,
and be projected from it more perpendicularly than the point B, and
therefore the shadow will seem inverted.]
Q. _When we see our SHADOW in WATER, why do we seem to STAND on our
HEAD?_
A. Because the _line of the angle of incidence_ is always equal to the
_line and angle of reflection_.
Suppose our head to be at A, and our feet at B; then the shadow of our
head will be seen at D, and the shadow of our feet at C. (_See last
figure._)
Q. _Why do WINDOWS seem to BLAZE at SUN-RISE and SUN-SET?_
A. Because glass is a good _reflector of light_; and the rays of the sun
(striking against the window glass) _are reflected_, or thrown back.
Q. _Why do NOT windows reflect the NOON-DAY rays also?_
A. They do, but the _reflection is not seen_.
Q. _Why is the reflection of the RISING and SETTING sun seen in the
window, and NOT that of the NOON-DAY sun?_
A. As the angle of _incidence_ always equals the _angle of reflection_,
therefore the rays of the noon-day sun enter the glass _too
perpendicularly_ for their reflection to be seen.
[Illustration: Here AB represents a ray of the noon-day sun striking the
window at B; its reflection will be at C:
But DB (a ray of the rising or setting sun) will be reflected to E (the
eye of the spectator).]
Q. _Why can we not see the REFLECTION of the SUN in a WELL, during the
day-time?_
A. Because the rays of the SUN _fall so obliquely_, that they _never
reach the surface of the water_ at all, but strike against the brick
sides.
[Illustration: Let BDEC be the well, and DE the water.
The ray AB strikes against the brick-work _inside_ the well; and
The ray AC strikes against the brick-work _outside_ the well.
None will ever touch the water DE.]
Q. _Why do we see the MOON reflected in a WELL very OFTEN?_
A. As the rays of the MOON are not so _oblique_ as those of the sun,
they will often reach the water. _(See next figure.)_
Q. _Why are the STARS REFLECTED in a WELL, although the SUN is NOT?_
A. As the rays of the STARS are not so _oblique_ as those of the sun,
they will often reach the water.
[Illustration: Here the moon's rays AB, AC, both strike the water DE,
and are reflected by it.]
Q. _In a sheet of water at noon, the sun appears to shine upon only ONE
spot, and all the REST of the water seems DARK,--WHY is this?_
A. Because the rays (which fall at various degrees of obliquity on the
water) are _reflected at similar angles_; but as only those which _meet
the eye of the spectator_ are visible, all the sea will appear dark but
_that one spot_.
[Illustration: Here of the rays SA, SB, and SC, only the ray SC meets
the eye of the spectator D.
The spot C, therefore, will appear luminous to the spectator D, but no
other spot of the water ABC.]
Q. _At night the MOON seems to be reflected from only ONE SPOT of a lake
of water, while all the REST seems DARK,--WHY is this?_
A. Because the rays (which fall at various degrees of obliquity on the
lake) _are reflected at similar angles_; but as only those which _enter
the eye of the spectator_ will be visible, all the water will appear
dark _but that one spot. (See last figure.)_
Q. _Why are MORE STARS visible from a MOUNTAIN, than from a PLAIN?_
A. As the air _absorbs and diminishes light_, the _higher we ascend_,
the _less light will be absorbed_.
Q. _Why does the SUN seem LARGER at his RISE and SET, than it does at
NOON?_
A. Because the earth is surrounded by air, which acts like a _magnifying
glass_; and when the sun is near the horizon (as its rays _pass through
more of this air_), it is more magnified.
[Illustration: Here SC represents a ray of the sun at noon, and MC a ray
of the sun near the horizon. DEG represents the air or atmosphere around
the earth.
Because EC is longer than DC, therefore the rays of the sun at M pass
through _more air_ than the rays of the sun at S, and the sun is more
magnified.]
Q. _Why does the RISING and SETTING MOON appear so much LARGER, than
after it is risen higher above our heads?_
A. Because the earth is surrounded by air, which acts _like a magnifying
glass_; and when the moon is near the horizon (as its rays pass through
more of this air) it is more magnified. _(See last figure.)_
Q. _When CANDLES are LIGHTED, we CANNOT SEE into the STREET or
road,--WHY is this?_
A. 1st--Because glass is a _reflector_, and throws the candle-light
_back into the room again_; and
2ndly--The pupil of the eye (which has become _contracted_ by the light
of the room) is _too small_ to collect rays enough from the dark street,
to enable us to _see into it_.
Q. _Why can't persons in the street SEE into a WELL-LIGHTED ROOM?_
A. Because the pupil of their eyes is _much dilated by the dark_, and
cannot collect from the window sufficient rays to enable them to _see
into the room_.
Q. _Why do we often see the FIRE REFLECTED in our parlour WINDOW in
winter time?_
A. Because glass is a _good reflector_; and the rays of the fire
(striking against the window-glass) _are reflected back into the room
again_.
Q. _Why do we often see the shadow of our CANDLES in the window, while
we are sitting in our parlour?_
A. Because the rays of the candle (striking against the glass) are
_reflected back into the room_: and the _darker_ the night, the
_clearer_ the reflection.
Q. _Why is this reflection more clear, if the external AIR be DARK?_
A. Because the reflection is not then _eclipsed_ by the brighter rays of
the sun _striking on the other side of the window_.
Q. _Why is the SHADOW of an object (thrown on the wall) LARGER and
larger, the CLOSER any object be held to the CANDLE?_
A. Because the rays of light _diverge_ (from the flame of a candle) _in
straight lines_, like lines drawn from the centre of a circle.
[Illustration: Here the arrow A held close to the candle, will cast the
shadow BF on the wall: while the same arrow held at C, would cast only
the little shadow D E.]
Q. _When we enter a long AVENUE of TREES, WHY does the avenue seem to
get NARROWER and narrower till it appears to MEET?_
A. Because the _further the trees are off_, the more _acute will be the
angle_ that any two will make with our eye.
[Illustration: Here the width between the trees A and B will seem to be
as great as the line AB: But the width between the trees C and D will
seem to be no more than EF.]
Q. _In a long straight STREET, WHY do the houses seem to APPROACH NEARER
and nearer as they are more DISTANT?_
A. Because the more _distant the houses_ are, the more _acute will be
the angle_ which any two make with our eye.
Thus in the last figure--
If A and B were two houses at the top of the street, the street would
seem to be as wide as the line A B:
And if C and D were two houses at the bottom of the street, the street
at the bottom would seem to be no wider than E F.
Q. _In an AVENUE of TREES, WHY do they seem to be SMALLER as their
distance increases?_
A. Because the _further the trees are off_, the more _acute will be the
angle_ made by their perpendicular height with our eye.
[Illustration: Here the first tree A B will appear the height of the
line A B; but the last tree C D will appear only as high as the line E
F.]
Q. _In a long straight STREET, WHY do the houses seem to be SMALLER and
smaller the FURTHER they are OFF?_
A. Because the _further any house is off_, the more _acute will be the
angle_ made by its perpendicular height with our eye.
Thus in the last figure--
If A B be a house at the top of the street, its perpendicular height
will be that of the line A B.
If C D be a house at the bottom of the street, its perpendicular height
will appear to be that of E F.
Q. _Why does a man on the TOP of a MOUNTAIN or church spire seem to be
no BIGGER than a CROW?_
A. Because the angle made by the _perpendicular height of the man_ (at
that distance) _with our eye_, is no bigger than the perpendicular
height of a _crow close by_.
[Illustration: Let AB be a man on a distant mountain or spire, and CD a
crow close by:
The man will appear only as high as the line CD, which is the height of
the crow.]
Q. _Why does the MOON appear to us so much BIGGER than the STARS, though
in fact it is a great deal SMALLER?_
A. Because the moon is _very much nearer to us_ than any of the stars.
[Illustration: Let AB represent a fixed star, and CD the moon.
AB, though much the larger body, will appear no bigger than EF; whereas
the moon (CD) will appear as big as the line CD to the spectator G.
The moon is 240,000 miles from the earth, not quite a quarter of a
_million_ of miles. The nearest fixed stars are 20,000,000,000,000.
(i. e. 20 billions.)
If a ball went 500 miles an hour, it would reach the moon in twenty
days: but it would not reach the nearest fixed star in 4,500,000 years.
Had it begun, therefore, when Adam was created, it would be no further
on its journey than a coach (which has to go from the bottom of Cornwall
to the top of Scotland) after it has past about three-quarters of a
mile.]
Q. _Why does the MOON (which is a sphere) APPEAR to be a FLAT surface?_
A. It is _so far off_, that we cannot distinguish any difference between
the _length of the rays_ which issue from the _edge_, and those which
issue from the _centre_.
[Illustration: The rays AD and CD appear to be no longer than the ray
BD; but if all the rays seem of the same length, the part B will not
seem to be nearer to us than A and C, and therefore ABC will look like a
flat or straight line.
The rays AD and CD are 240,000 miles long.
The ray BD is 238,910 miles long.]
Q. _Why do the SUN and STARS (which are spheres) appear to be FLAT
surfaces?_
A. Because they are such an _immense way off_, that we can discern _no
difference of length_ between the rays which issue from the _edge_, and
those which issue from the _centre_ of these bodies.
The rays AD and CD appear no longer than BD; and as B appears to be no
nearer than A or C, therefore ABC must all seem equally distant; and ABC
will seem a flat or straight line. (See last figure.)
Q. _Why does DISTANCE make an object INVISIBLE?_
A. Because the angle (made by the _perpendicular height_ of the distant
object _with our eye_) is so very _acute_, that _one_ line of the angle
_merges in the other_.
[Illustration: Here the tree AD would not be visible to the spectator C,
even if he were to approach as far as B; because no visible
perpendicular can be inserted between the two lines AC, DC, till after
the point B is past; when the tree will appear like a very little
speck.]
Q. _Why do TELESCOPES enable us to SEE objects INVISIBLE to the naked
eye?_
A. Because they _concentrate several rays_ within the tube of the
telescope, and _bend them upon the mirror or lens_, which acts as a
_magnifying glass_.
Q. _When a SHIP (out at sea) is approaching the shore, why do we SEE the
small MASTS before we see the bulky HULL?_
A. Because the _earth is round_, and the _curve_ of the sea _hides the
hull_ from our eyes, after the tall _masts_ have become visible.
[Illustration: Here only that part of the ship above the line AC can be
seen by the spectator A; the rest of the ship is hidden by the swell of
the curve DE.]
Q. _What is meant by REFRACTION?_
A. The _bending of a ray of light_, as it passes from one medium to
another.
Q. _How is a ray of light BENT, as it passes from one medium to
another?_
A. When a ray of light passes into a _denser_ medium, it is bent
_towards the perpendicular_. When it passes into a _rarer_ medium, it is
bent _from_ the perpendicular.
[Illustration: Suppose DE to be a perpendicular line.
If AB (a ray of light,) enters the water, it will be bent _towards_ the
perpendicular to C.
If (on the other hand) CB (a ray of light) emerges _from_ the water, it
would be bent _away from_ the perpendicular towards A.]
Q. _Why does a SPOON (in a glass of water) always appear BENT?_
A. Because as the light of the spoon _emerges from the water_, it is
_refracted_.
And the spoon looks like ABC. (See the last figure.)
Q. _Why does a river always appear more shallow than it really is?_
A. Because the light of the bottom of the river is REFRACTED as it
emerges out of the water: and (as a stick is not so long when it is
_bent_, as it is when it is _straight_) so the river seems less deep
than it really is.
Q. _How much deeper is a river than it seems to be?_
A. One-third. If, therefore, a river seems only 4 feet deep, it is
really 6 feet deep.
N. B. Many boys get out of their depth in bathing, in consequence of
this deception. Remember, a river is always one-third deeper than it
appears to be:--thus, if a river seems to be 4 feet deep, it is in
reality 6 feet deep, and so on.
Q. _Why do fishes always seem to be nearer the surface of a river than
they really are?_
A. Because the rays of light from the fish are _refracted_ as they
emerge from the eye: and (as a bent stick is not so far from end to end
as a straight one) so the fishes appear nearer our eye than they really
are.
Q. _Why are some persons NEAR-SIGHTED?_
A. Because the COR´NEA of their eye is so _prominent_, that the image of
distant objects is reflected _before it reaches the_ RET'INA; and,
therefore, is not distinctly seen.
N.B. The cor´nea shields the CRYSTALLINE LENS, and is more or less
convex according to the lens which it covers.
Q. _What is meant by the "COR'NEA of the EYE?"_
A. All the _outside_ of the visible part of the _eye-ball_.
[Illustration: The curve A B C is called the COR'NEA.
If this curve be too prominent (or convex), the eye is near-sighted.
If too flat (or concave), the eye is far-sighted.]
Q. _What is meant by the "RET'INA of the EYE?"_
A. The net-work which lines the _back of the eye_, is so called.
[Illustration: The net-work ABC is called the ret'ina, and the
projecting part DEF is called the cor'nea.]
Q. _What sort of GLASSES do NEAR-SIGHTED persons wear?_
A. If the cor'nea be _too convex_ (or projecting), the person must wear
double _concave glasses_, to counteract it.
Q. _What is meant by "DOUBLE CONCAVE GLASSES?"_
A. Glasses hollowed in _on both sides_.
[Illustration: The figure A is double concave, or concave on both
sides.]
Q. _What is meant by the "IMAGE of objects being reflected BEFORE it
reaches the RET'INA?"_
A. If the cor'nea be _too convex_, the image of a distant object is
reflected (on the vitreous humours of the eye) _before it reaches the
ret'ina_.
[Illustration: Thus the image is reflected at DE, instead of on ABC (the
ret'ina).]
Q. _What is the use of DOUBLE CONCAVE SPECTACLE glasses?_
A. Near-sighted spectacles _cast the reflection further back;_ and the
image (being _thrown upon the ret'ina_) becomes visible.
Q. _Why are OLD people FAR-SIGHTED?_
A. Because the humours of their eyes _are dried up by age_, and the
COR'NEA _sinks in_, or becomes flattened.
Q. _Why does the FLATTENING of the COR'NEA prevent persons seeing
objects which are NEAR?_
A. As the cor'nea _is too flat_, the image of any near object is formed
_behind the RET'INA of the eye_, and is not seen at all.
[Illustration: The reflection is made at DE, instead of at ABC (the
retina).]
Q. _What sort of GLASSES do OLD people WEAR?_
A. As their cor'nea is _not sufficiently convex_, they must use _double
convex glasses_, to enable them to see objects near at hand.
Q. _What sort of glasses are DOUBLE CONVEX SPECTACLE-GLASSES?_
A. Glasses which _curve outwards_ on both sides.
[Illustration: The figure A is double convex, or convex on both sides.]
Q. _What is the USE of DOUBLE CONVEX spectacle-glasses?_
A. As the image of near objects is reflected _behind the RET'INA_, these
double convex glasses _shorten the focus of the eye_, and bring the
image _into the eye_ (upon the ret'ina).
Q. _Why do NEAR-SIGHTED persons bring objects CLOSE to the eye, in order
to SEE THEM?_
A. As the distance between the _front and back of their eye is too
great_, distant objects are reflected _before they reach the ret'ina_;
therefore, near-sighted persons bring the objects _closer_, in order
that the reflection _may be cast further back_, (to reach the ret'ina).
Q. _Why do OLD people HOLD objects FURTHER OFF, in order to see them
better?_
A. As the distance between the _front and back of their eye is not great
enough_, the reflection of near objects is thrown _beyond the ret'ina_;
therefore, they hold objects _a long way off_, in order to bring their
images _forward_ (so as to cast it on the ret'ina).
Q. _Why are HAWKS able to see such an IMMENSE way off?_
A. Because they have a muscle in the eye which enables them to _flatten
their cor'nea_, by drawing back the crystalline lens.
This muscle is called the "marsupium."
Q. _Why can HAWKS not only see such a long way off, but also objects
within half-an-inch of their eye?_
A. Because their eyes are furnished with a broad circular rim which
_confines the action of this muscle_, and throws the _cor'nea forward_.
Q. _Into how many PARTS may a RAY of LIGHT be DIVIDED?_
A. Into three parts: BLUE, YELLOW, and RED.
N.B. These 3 colours, by combination, make seven. 1.--RED. 2.--Red and
yellow form ORANGE. 3.--YELLOW. 4.--Yellow and blue make GREEN.
5.--BLUE. 6 and 7.--Shades of blue called INDIGO and VIOLET.
Q. _How is it KNOWN, that a ray of light consists of several different
colours?_
A. Because, if a ray of light be cast upon a triangular piece of glass
(called a prism), it will be distinctly divided into seven colours:
1.--Red; 2.--Orange; 3.--Yellow; 4.--Green; 5.--Blue; 6.--Indigo; and
7.--Violet.
Q. _Why does a PRISM DIVIDE a ray of light into VARIOUS COLOURS?_
A. Because all these colours have _different refractive powers_. Red is
refracted _least_, and blue the _most_; therefore, the _blue_ colour of
the ray will be bent to the _top_ of the prism, and the _red_ will
remain at the _bottom_.
[Illustration: Here the ray AB received on a prism, would have the blue
part bent up to C; the yellow part to D; and the red part no further
than E.]
Q. _What is meant by the REFRACTION of a ray?_
A. _Bending it_ from its straight line.
Thus the ray AB of the last figure is refracted at B into three courses,
C, D, and E.
Q. _What is the cause of a RAINBOW?_
A. When the clouds opposite the sun _are very dark_, and rain is _still
falling_ from them, the rays of the bright sun _are divided by the
rain-drops_, as they would be by a prism.
[Illustration: Let A, B, and C be three drops of rain; SA, SB, and SC
three rays of the sun. SA is divided into the 3 colours; the blue and
yellow are bent _above_ the eye D, and the _red_ enters it.
The ray SB is divided into the three colours; the blue is bent _above_
the eye, and the red falls _below_ the eye D; but the _yellow_ enters
it.
The ray SC is also divided into the three colours. The blue (which is
bent most) enters the eye; and the other two fall below it. Thus the eye
sees the blue of C, and all drops in the position of C; the yellow of B,
and of all drops in the position of B; and the red of A, &c.; and thus
it sees a rainbow.]
Q. _Does EVERY person see the SAME colours from the SAME DROPS?_
A. No; _no two persons_ see the _same rainbow_.
To another spectator the rays from SB might be _red_ instead of yellow;
the ray from SC, yellow; and the blue might be reflected from some drop
below C. To a _third_ person the red may issue from a drop above A, and
then A would reflect the yellow, and B the blue, and so on.
Q. _Why are there often TWO RAINBOWS at one and the same time?_
A. In _one_ rainbow we see the rays of the sun _entering the rain-drops
at the top_, and reflected to the eye _from the bottom_.
In the _other_ rainbow, we see the rays of the sun _entering the
rain-drops at the bottom_, and reflected to the top, whence they reach
the eye.
[Illustration: Here the ray SA strikes the drop at A,--is refracted or
bent to B,--is then reflected to C, where it is refracted again, and
reaches the eye of the spectator.]
[Illustration: Here the ray SB strikes the drop at B,--is refracted to
A,--is then reflected to C,--is again reflected to D, when it is again
refracted or bent till it reaches the eye of the spectator.]
Q. _Why are the COLOURS of the SECOND bow all REVERSED?_
A. Because in _one_ bow we see the rays which enter at the _top_ of the
raindrops, _refracted from the bottom_:
But in the _other_ bow we see the rays which enter at the _bottom_ of
the raindrops (after two reflections), _refracted from the top_.
[Illustration: Here A, B, C, represent three drops of rain in the
PRIMARY (or inner) RAINBOW.
The _least_ refracted line is RED, and BLUE the _most_.
So the RED (or _least_ refracted rays) of all the drops in the position
of A,--the YELLOW of those in the position of B,--and the BLUE (or the
_most_ refracted rays) of the lowest drops, all meet the eye D, and form
a rainbow to the spectator.
The reason why the primary bow exhibits the stronger colours is
this--because the colours are seen after _one_ reflection and _two_
refractions; but the colours of the secondary (or upper) rainbow undergo
_two_ reflections and _three_ refractions.]
[Illustration: Here also the _least_ refracted ray is RED, and the
_most_ refracted BLUE (as in the former case); but the position of each
is reversed.]
Q. _Why does a SOAP BUBBLE exhibit such VARIETY of COLOURS?_
A. The changing colour of the bubble depends upon the changing
_thickness of the film_ through which the ray passes.
Q. _How does the THICKNESS of the FILM affect the COLOUR of the soap
bubble?_
A. Because different _degrees of thickness_ produce different _angles of
refraction_, and, therefore, different colours reach the eye.
Q. _Why is the SOAP BUBBLE so constantly CHANGING its THICKNESS?_
A. As the bubble is _suspended_, the water keeps _running down from the
top_ to the bottom of the bubble, till the crown becomes so _thin_ as to
burst.
Q. _Why are the late EVENING CLOUDS RED?_
A. Because RED rays (being the _least refrangible_) are the _last to
disappear_.
[Illustration: Here it will be seen that the red ray PA, being reflected
on the horizon at A, will be visible to us; but the YELLOW and BLUE rays
will be hidden by the curve of the earth.]
Q. _Why are the early MORNING clouds RED?_
A. Because RED rays (being the _least refrangible_) are the _first to
appear_.
_See last figure._--It is evident that PA (the red rays) will be
reflected on the horizon before either the yellow or blue ones.
Q. _What becomes of the BLUE and YELLOW rays?_
A. They are refracted _below the horizon_, and are soon made invisible
by the _curve of the earth_. (_See last figure._)
Q. _Why are the EDGES of CLOUDS more LUMINOUS than their CENTRES?_
A. Because the _body of vapour is thinnest_ at the edges of the clouds.
Q. _What is the cause of morning and evening TWILIGHT?_
A. When the sun is below the horizon, the rays (which strike upon the
atmosphere or clouds) _are bent down towards the earth_, and produce a
little light called twilight.
_See figure on p. 399._--Here the rays of PA will give _some_ light.
Q. _Why is a ray of LIGHT composed of VARIOUS COLOURS?_
A. If solar light were of _one colour only_, all objects would appear of
_that one colour_ (or else black.)
Q. _Why are some things of ONE COLOUR, and some of ANOTHER?_
A. As every ray of light is composed of all the colours of the rainbow,
_some_ things reflect _one of these colours_, and some _another_.
Q. _Why do some things reflect ONE COLOUR, and some ANOTHER?_
A. Because the _surface_ of things is so _differently constructed_, both
physically and chemically; and, therefore, _some_ things reflect _one_
ray; some _two rays_; some _all_ the rays; and some _none_.
Q. _What mainly determines the COLOUR of any object?_
A. The fluid or gas either _in_ the body, or on its _surface_.
N. B. Nitrogen gives green,--Oxygen gives red,--Hydrogen gives blue
colours.
Q. _Why does DYING a silk, &c. CHANGE its COLOUR?_
A. Because the materials used in dyeing _alter the chemical
construction_ of the substance dyed.
Q. _Why is a ROSE RED?_
A. Because the surface of a rose _absorbs the blue and yellow_ rays of
light, and _reflects_ only the _red_ ones.
Q. _Why does a rose absorb the yellow and blue rays, and reflect the
RED?_
A. Because the action of the sun's rays on the oxygen (accumulated in
the petals) produces an _acid_ which turns them _red_.
The leaves which compose a flower, are called PETALS.
Q. _Why is a VIOLET BLUE?_
A. Because the surface of the violet _absorbs the red and yellow_ rays
of the sun, and _reflects_ the _blue_ only.
Q. _Why do violets absorb the red and yellow rays, and reflect the
BLUE?_
A. Because the petals of the violet contain an _alkali_, which gives
them a _purple tinge_.
Q. _Why is a PRIMROSE YELLOW?_
A. Because the surface of the primrose _absorbs the blue and red_ rays
of solar light, and _reflects_ the _yellow_ ones.
All plants which have much alkali in their ash, have blue or yellow
flowers.
Those which have acid in their ash, have orange, pink, or red flowers.
N. B. Anti-acids (like soda) are called ALKALIS.
Q. _Why are some things BLACK?_
A. Because they _absorb all the rays of light_, and reflect _none_.
Q. _Why are some things WHITE?_
A. Because they _absorb none of the rays of light_, but reflect them
_all_.
Q. _Why are COALS BLACK?_
A. Because they _absorb all the rays of the sun_ which impinge upon
them, and stifle their reflection.
Q. _Why is SNOW WHITE?_
A. Snow consists of a vast number of crystals (or small prisms), which
separate the rays into their elemental colours; but as these crystals
are very numerous, the colours _unite again_ before they meet the eye,
and _appear white_.
N. B. The combination of _all_ colours makes WHITE.
Q. _Why is SUGAR WHITE?_
A. Sugar consists of a vast number of small crystals, which separate the
rays into their elemental colours; but as these crystals are very
numerous, the colours _unite again_ before they meet the eye, and appear
_white_.
Q. _Why is SALT WHITE?_
A. Salt consists of a vast number of small crystals, which reflect the
various rays of light from different points of the salt; and as these
colours _unite_ before they meet the eye, the salt appears to be
_white_.
N. B. The combination of _all_ colours makes WHITE.
Q. _Why are the LEAVES of plants GREEN?_
A. Because the _carbon_ of the leaves is a _bluish olive_, and the _sap_
and _tissue of the cells_, YELLOW; when, therefore, the _yellow sap_
flows into the _blue carbon_, it produces a _green leaf_.
Q. _Why are leaves a LIGHT green in SPRING?_
A. Because the young leaves of spring have _more sap_ than _carbon_;
and, therefore, the _yellow_ of the green prevails.
Q. _Why are leaves a YELLOWISH BROWN in AUTUMN?_
A. Because the _carbon_ of the leaves is _dying away_, and the yellow
tinge of the _tissue_ and _falling sap_ prevails over the blue.
Q. _Why are plants a PALE YELLOW when kept in the DARK?_
A. Solar light is essential for the production of _carbon_; and as
plants kept in the dark _lose their carbon_, they lose the _blue colour_
which should convert their yellow sap to _green_.
Q. _Why are POTATOES YELLOW?_
A. Potatoes are grown _underground_, and, therefore, contain very little
_carbon_ (or blue colour); hence the _yellow sap_ of the potato is not
converted to green by carbon.
Q. _Why are potatoes (which grow EXPOSED to the air and light) GREEN?_
A. Because the sun-light _increases their carbon_; which (mingling with
the yellow sap) turns the potato _green_.
Q. _Why is it DANGEROUS to SLEEP in a room which contains LIVING
PLANTS?_
A. Because they _exhale carbon in the dark_ in the form of CARBONIC ACID
GAS, which is destructive to animal life.
Q. _Why are SOME things (like glass) TRANSPARENT?_
A. In transparent bodies (like glass) all the rays of light _emerge on
the opposite side_.
Q. _Why are SOME things SHINING and splendid?_
A. Those objects which _reflect the most rays_ are the most _splendid_;
and those which _absorb_ them most, are _dull_.
Q. _Why are DESERTS so DAZZLING in summer time?_
A. Because each separate grain of sand _reflects the rays of the sun_
like a mirror.
Q. _If you move a stick (burnt at one end) ROUND pretty briskly, it
seems to make a CIRCLE OF FIRE,--WHY is this?_
A. Because the eye _retains the image_ of any bright object, _after the
object itself is withdrawn_; and as the spark of the stick returns
_before the image has faded_ from the eye, therefore, it seems to form a
_complete circle_.
Q. _If separate figures (as a man and a horse) be drawn on separate
sides of a card, and the card TWISTED quickly, the man seems to be
seated on the horse,--WHY is this?_
A. Because the image of the horse _remains upon the eye_ till the _man_
appears.
The Thaumatrope is constructed on this principle.
Q. _Why do the STARS TWINKLE?_
A. Fixed stars are _so far off_, that their rays of light do not strike
upon the eye _in a continuous flow_, but at _intervals_: when their rays
_reach the eye_, the star becomes _visible_, and then is obscured _till
the next batch of rays arrive_; and this _perpetually_ occurring, makes
a kind of _twinkling_.
Q. _If we look at a RED-hot FIRE for a few minutes, WHY does every thing
seem TINGED with a BLUISH GREEN colour?_
A. Because bluish green is the "ACCIDENTAL COLOUR" of red: and if we fix
our eye upon _any colour whatsoever_, when we turn aside, we see every
object tinged with _its accidental colour_.
Q. _If we wear BLUE GLASSES, (when we take them off,) every thing
appears tinged with ORANGE,--WHY is this?_
A. Because _orange_ is the "_accidental colour_" of blue: and if we look
through _blue glasses_, we shall see its "_accidental colour_," when we
lay our glasses aside.
Q. _If we look at the SUN for a few moments, every thing seems tinged
with a VIOLET colour,--WHY is this?_
A. Because _violet_ is the "accidental colour" of _yellow_ light; and as
the sun is _yellow_, we shall see its "accidental colour" _blue_, when
we turn from gazing at it.
Q. _Does not the DARK SHADOW (which seems to hang over every thing after
we turn from looking at the sun) arise from our eyes being DAZZLED?_
A. Partly so: the pupil of the eye is _very much contracted_ by the
brilliant light of the sun, and does not adjust itself immediately to
the feebler light of terrestrial objects; but, independent of this, the
"ACCIDENTAL COLOUR" of the sun being _dark violet_, would tend to throw
a shadow upon all things. (_See p. 366._)
Q. _Why is BLACK glass for spectacles the BEST for wear?_
A. Because _white_ is the accidental colour of _black_; and if we wear
_black glasses_, every thing will appear _in white light_, when we take
them off.
Q. _Why does every thing seem shadowed with a BLACK MIST, when we take
off our common SPECTACLES?_
A. Because the glasses are _white_, and black being its "accidental
colour," every thing appears in a _black shade_, when we lay our glasses
down.
The accidental colour of red is bluish green.
" " " of orange " blue.
" " " of violet " yellow.
" " " of black " white.
And the converse of this is true:--
The accidental colour of bluish green is red.
" " " of blue " orange.
" " " of yellow " violet.
" " " of white " black.
(The law of an accidental colour is this--The accidental colour is
always half the spectrum. Thus, if we take half the length of the
spectrum by a pair of compasses, and fix one leg in any colour, the
other leg will hit upon its accidental colour.)
N. B. The spectrum means the seven colours--Red, orange, yellow, green,
blue, indigo, and violet, divided into seven equal bands, and placed
side by side in the order just mentioned.
CHAPTER XXVIII.
SOUND.
Q. _What is SOUND?_
A. The vibration of some sonorous substance produces motion in the air
called SOUND WAVES, which strike upon the _drum of the ear_, and give
the sensation of sound.
Q. _What are MUSICAL SOUNDS?_
A. Regular and uniform successions of vibrations, which are always
pleasing to the ear.
Q. _How FAST does SOUND TRAVEL?_
A. About 13 miles in a minute, or 1142 feet in a second of time.
Q. _How fast does LIGHT TRAVEL?_
A. Light would go 8 times round the whole earth, while sound is going
its 13 miles.
Q. _Why are SOME things SONOROUS, and others NOT?_
A. The sonorous quality of any substance depends upon its _hardness and
elasticity_.
Q. _Why are COPPER and IRON SONOROUS, and not LEAD?_
A. Copper and iron are _hard and elastic_; but as lead is neither hard
nor yet elastic, it is _not sonorous_.
Q. _Of what is BELL-METAL made?_
A. Of _copper and tin_ in the following proportions:--In every 5 pounds
of bell-metal, there should be 1 lb. of tin, and 4 lbs. of copper.
Q. _Why is this mixture of tin and copper used for BELL-METAL?_
A. Because it is much _harder_ and more _elastic_ than either of the
pure metals.
Q. _Why is the SOUND of a bell STOPPED by TOUCHING the bell with our
finger?_
A. The weight of the finger _stops the vibrations_ of the bell; and as
soon as the bell _ceases to vibrate_, it ceases to make sound-waves in
the air.
Q. _Why does a SPLIT BELL make a HOARSE disagreeable sound?_
A. The _split_ of the bell causes a _double vibration_; and as the
sound-waves _clash and jar_, they impede each other's motion, and
produce discordant sounds.
Q. _Why does a FIDDLE-STRING give a musical sound?_
A. The bow drawn across the string _causes it to vibrate_, and this
vibration of the string _sets in motion the sound-waves of the air_, and
produces musical notes.
Q. _Why does a DRUM sound?_
A. The parchment head of the drum _vibrates_ from the blow of the
drum-stick, and sets in motion the sound-waves of the air.
Q. _Why do MUSICAL GLASSES give sounds?_
A. Because the glasses _vibrate_ as soon as they are struck, and set in
motion the sound-waves of the air.
Q. _Why do FLUTES, &c. produce musical sounds?_
A. The breath of the performer causes the _air in the flute to vibrate_,
and sets in motion the sound-waves of the air.
Q. _Why do PIANO-FORTES produce musical sounds?_
A. The _keys of the piano_ (being struck with the finger) lift up a
little hammer which _knocks against a string_; and the vibration thus
produced, sets in motion the sound-waves of the air.
Q. _Why are SOME notes BASS and some TREBLE?_
A. _Slow_ vibrations produce _bass or deep sounds_; whereas, _quick_
vibrations produce _shrill or treble sounds_.
Q. _Why is an instrument FLAT when the STRINGS are UNSTRUNG?_
A. Because the vibrations are _too slow_; in consequence of which, the
sounds produced are not _shrill_ or _sharp_ enough.
Q. _Why can persons living a mile or two from_
_a town HEAR the BELLS of the town-church SOME TIMES, and not at
OTHERS?_
A. Fogs, rain, and snow, obstruct the passage of sound; but when the air
is _cold and clear_, sound is propagated more easily.
Q. _Why can we NOT hear sounds (as distant church bells) in RAINY
weather, so well as in FINE weather?_
A. Because the falling rain _interferes with the undulations of the
sound-waves_, and breaks them up.
Q. _Why can we not hear sounds (as distant church bells) in SNOWY
weather, so well as in FINE weather?_
A. Because the falling snow _interferes with the undulations of the
sound-waves_, and stops their progress.
Q. _Why can we HEAR distant clocks MOST distinctly in CLEAR COLD
weather?_
A. Because the air is most _uniform_ then: there are not _two currents
of air_ (one up and one down) to interrupt the sound-waves.
Q. _Why can persons hear the VOICES of men in conversation for a MILE
distant, near the POLES, in winter time?_
A. Because the air is very _cold and very clear_; in consequence of
which, there are not _two currents of air_ (one up and one down) to
interrupt the sound-waves.
Captain Ross heard the voices of his men in conversation, a mile and a
half from the spot where they stood.
Q. _Why are not SOUNDS (such as distant church bells) heard so
distinctly on a HOT DAY as in FROSTY weather?_
A. Because there are _two currents of air_; the current of _hot_ air
_ascending from the earth_, and the current of _colder_ air _falling
towards_ the earth; and these two currents _break up the sound-waves_.
Q. _Why can we not hear SOUNDS (such as distant clocks) so distinctly in
a thick MIST or HAZE, as in a CLEAR night?_
A. Because the mist _diminishes the velocity_ of the sound-waves, and
(by overburdening them with vapour) _limits their length_.
Q. _Why do we hear SOUNDS better by NIGHT than by DAY?_
A. 1st--Night air is _more uniform_, because the ascending currents of
air (raised by the action of the sun's rays) _cease_ as the evening
advances; and
2ndly--Night is more _still_ from the suspension of business, and the
cessation of the hum of men.
Q. _How should PARTITION WALLS be made to PREVENT the voices in
adjoining rooms from being HEARD?_
A. The space between the laths (or canvass) should be filled with
_shavings or saw-dust_; and then no sound would ever pass from one room
to another.
Q. _Why would SHAVINGS or saw-dust PREVENT the transmission of sound
from room to room?_
A. Because there would be _several different media_ for the sound to
pass through: 1st--the air;
2ndly--the laths and paper;
3rdly--the saw-dust or shavings;
4thly--the air again: and every _variety_ diminishes the _strength of
the sound-waves_.
Q. _Why can DEAF people hear through an EAR TRUMPET?_
A. The ear trumpet restrains _the spread of the voice_, and limits the
_diameter of the sound-waves_; in consequence of which, their
_strength_ is increased.
Q. _Why are MOUNTAINS so NOISELESS and quiet?_
A. Because the air of mountains is _very rarefied_; and as the air
becomes _rarefied_, sound becomes less _intense_.
Q. _How do you know that the RARETY of air DIMINISHES the intensity of
SOUND?_
A. If a bell be rung in the receiver of an air-pump, the sound becomes
_fainter and fainter_ as the air is exhausted, till at last it is quite
_inaudible_.
Q. _What is the cause of ECHO?_
A. Whenever a sound-wave strikes against any _obstacle_ (such as a wall
or hill), _it is reflected_ (or thrown back); and this _reflected sound_
is called an ECHO.
The same laws govern echo as light. (_See p. 370._)
Q. _What places are most FAMOUS for ECHOES?_
A. Caverns, grottoes, and ruined abbeys; the areas of antique halls; the
windings of long passages; the aisles of cathedral churches; mountains,
and ice-bergs.
Q. _Why are caverns, grottoes, and ruined abbeys FAMOUS for ECHOES?_
A. 1st--Because the sound-waves cannot pass _beyond_ the cavern or
grotto, and _must flow back_:
2ndly--The _return waves_ (being entangled by the cavern) are _detained_
for a short time, and come _deliberately_ to the ear.
Q. _Why are antique halls, winding passages, and cathedral aisles FAMOUS
for ECHOES?_
A. Because the sound-waves _cannot flow freely forward_, but strike
against the winding walls perpetually, and are beaten _back_.
Q. _Why are MOUNTAINS and ice-bergs FAMOUS for ECHOES?_
A. Because they present a _barrier_ to the sound-waves _which they
cannot pass_; and are sufficiently elastic to _throw them back_.
Q. _Why do not the walls of a ROOM or church produce ECHO?_
A. Because sound travels with such _velocity_, that the echo is _blended
with the original sound_, and produce but _one impression_ on the ear.
Sound travels 13 miles in a minute.
Q. _Why do very LARGE buildings (as cathedrals), often REVERBERATE the
voice of the speaker?_
A. Because the walls are _so far off from the speaker_, that the echo
does not _get back in time_ to blend with the original sound; and,
therefore, _each_ is heard separately.
Q. _Why do SOME echoes repeat only ONE syllable?_
A. The _further_ the echoing body is _distant_, the _more sound_ it will
_reflect_. If, therefore, the echoing body be _near_, it will repeat but
one syllable.
Q. _Why does an ECHO sometimes repeat TWO or more syllables?_
A. Because the echoing body is _far off_; and, therefore, there is time
for one reflection _to pass away_ before _another_ reaches the ear.
Q. _Why do WINDOWS RATTLE when CARTS pass by a house?_
A. 1st--Glass is _sonorous_; and the air communicates its vibrations to
the glass, which echoes the same sound: and
2ndly--The _window-frame is shaken_ by the sound-waves _impinging
against the window_, and contributes to the noise.
CHAPTER XXIX.
MISCELLANEOUS.
Q. _Why do the BUBBLES in a CUP OF TEA range round the SIDES of the
CUP?_
A. Because the cup _attracts them_.
Q. _Why do all the LITTLE BUBBLES tend towards the LARGE ones?_
A. Because the large bubbles (being the superior masses) _attract them_.
Q. _Why do the BUBBLES of a CUP OF TEA FOLLOW a TEA-SPOON?_
A. Because the tea-spoon _attracts them_.
Q. _Why are the SIDES of a pond covered with LEAVES, while the MIDDLE of
the pond is quite CLEAR?_
A. Because the shore _attracts_ the leaves to itself.
Q. _Why do all fruits, &c. (when severed from the tree) FALL to the
EARTH?_
A. Because the earth _attracts them_.
Q. _Why do persons (who water PLANTS) very_
_often pour the water into the SAUCER, and not OVER the PLANTS?_
A. Because the water in the saucer is _supped up_ by the mould (through
the hole at the bottom of the flower-pot), and is transferred to the
stem and leaves of the plant by CAPILLARY ATTRACTION, (_See p. 84_).
Q. _Why is vegetation on the MARGIN of a RIVER more LUXURIANT than in an
open FIELD?_
A. Because the porous earth on the bank _sups up water_ to the roots of
the plants by CAPILLARY ATTRACTION.
Q. _Why is a LUMP of SUGAR (left at the bottom of a cup) so LONG in
MELTING?_
A. Because _as it melts_, it makes the tea above it _heavier_; and (so
long as it remains at the bottom) is surrounded by tea fully _saturated_
with sugar; in consequence of which, the _same_ portions of liquid will
hold _no more sugar in solution_.
Q. _Why does the LUMP of SUGAR MELT more QUICKLY when STIRRED ABOUT?_
A. Because _fresh portions of unsaturated tea_ keep coming in contact
with the lump, and soon dissolve it.
Q. _Why does a PIECE OF SUGAR (held in a spoon at the TOP of our tea)
melt very RAPIDLY?_
A. Because as the tea becomes _sweetened_, it _descends to the bottom of
the cup_ by its own gravity; and _fresh_ portions of unsweetened tea are
brought constantly into contact with the sugar, till the lump is
entirely dissolved.
Q. _How can a SICK ROOM be kept FREE from unhealthy EFFLUVIA?_
A. Vinegar boiled with myrrh, or camphor, sprinkled in a sick room, will
_entirely correct putridity_.
Q. _Why does LIME destroy the offensive smells of BINS, SEWERS, &c.?_
A. Because it combines with the _carbonic acid_ of these places, and
converts it into CARBONATE OF LIME, which is entirely _free from smell_.
Q. _Why does CHLORIDE of LIME fumigate a sick room?_
A. Because the chlorine absorbs the _hydrogen of the stale air_; and by
this means removes both the _offensive smell_ and the _infection_ of a
sick room.
Q. _How can the TAINT of MEAT be removed?_
A. Either by washing with PYROLIGNEOUS ACID,--covering it for a few
hours with common CHARCOAL,--or by putting a _few lumps of charcoal_
into the _water in which it is boiled_.
Q. _Why do these things DESTROY the TAINT of meat?_
A. Because they _combine_ with the _putrescent particles_, and
neutralize their offensive taste and smell.
Q. _Why should BED-ROOMS, COTTAGES, HOSPITALS, and STABLES, be washed
occasionally with LIME-WHITE?_
A. Because the lime _is very caustic_, and removes all organic matters
adhering to the walls.
Q. _How can MOULDINESS be prevented?_
A. The perfume of _any essential oil_ will prevent mouldiness from ink,
paste, preserves, &c.
Alum, salt of amber, borax, nitre, salt, camphor, charcoal, and
pyroligneous acid, are all excellent antiseptics.
Salt, corrosive sublimates, copperas, and alum, all arrest the decay of
timber. (_See p. 426._)
Q. _Why will strong SOUCHONG TEA POISON FLIES?_
A. Because it produces _prussic acid_, which destroys their _nervous
system_.
Q. _Why is strong GREEN TEA UNWHOLESOME?_
A. Because it contains _prussic acid_, which destroys the _nervous
system_.
Q. _Why is a DEAD man TALLER than a living man?_
A. Because at death the CARTILAGES are _relaxed_. So, also, after a
night's rest, a man is _taller_ than when he went to bed.
Q. _What is SLEEP?_
A. Sleep is the _rest of the brain_ and _nervous system_.
Q. _Why can we not SEE, when we are asleep with our EYES OPEN?_
A. Because the "RET´INA of the eye" is _inactive_ and at rest.
Q. _Why can we not HEAR in sleep?_
A. Because the drum or "TYMPANUM of the ear" is placid and at rest.
Q. _Why can we not TASTE when we are asleep?_
A. Because the nerves _at the end of the tongue_ (called papillæ) are
inactive and at rest.
Q. _Why can we not FEEL when we are asleep?_
A. Because the _ends of the nerves_ (called papillæ), situated in the
skin, are inactive and at rest.
Q. _Why have persons in sleep no WILL of their own, but may be moved at
the will of ANY one?_
A. Because the "CEREBELLUM" (or _posterior_ part of the brain) is
inactive and at rest.
Q. _Why have DREAMERS no power of JUDGMENT or REASON?_
A. Because the "CEREBRUM" (or _front_ of the brain) is inactive and at
rest.
Q. _Why are DREAMS such FOOLISH and INCONSISTENT things?_
A. Because the "PINEAL GLAND" is acting _without the brain_; and the
_faculty of thinking_ exists in the "PINEAL GLAND," but the _faculty of
judgment_ in the "CEREBRUM of the brain."
The cerebrum of the brain occupies the top and front of the skull. The
PINEAL GLAND is a small conical gland (about the size of a pea) _in the
brain_.
Q. _Why do some persons LOSE all POWER of SENSATION?_
A. Because the "CEREBRUM" (or _front_ of their brain) _has been
injured_.
Q. _Why are many persons IDIOTS?_
A. Because the "CEREBELLUM of the brain" _has been removed_ by some
accident, or _injured by some disease_.
The cerebellum is all the posterior part of the brain.
Q. _Why does a person FEEL when he is TOUCHED?_
A. The ends of certain nerves (called PAPILLÆ) situated in the skin
_erect themselves_ when touched, and produce a nervous sensation called
FEELING.
Q. _Why are persons able to TASTE DIFFERENT FLAVOURS?_
A. Because the "PAPILLÆ" of the tongue and palate _erect themselves_
when food touches them, and produce a nervous sensation called TASTE.
Q. _Why do very OLD people LOSE the power of VOLITION, SENSATION, and
THOUGHT?_
A. Because their _brain ossifies_; and as the "_cerebrum_" (or _front_
of the brain) goes, they lose the power of _sensation and reason_; and
as the "_cerebellum_" (or _posterior_ part of the brain) goes, they lose
the power of _volition_.
Q. _Why are OLD people UNABLE to WALK?_
A. Because their _muscles become rigid_.
GLOSSARY.
ACETIC ACID, commonly called Distilled Vinegar.
CITRIC " " Juice of Lemons.
NITRIC " " Aqua Fortis.
OXALIC " " Salt of Lemons.
SULPHURIC " " Oil of Vitriol.
SULPHATE OF LIME " Plaster of Paris.
" MAGNESIA " Epsom Salts.
" SODA " Glauber Salts.
" ZINC " White Vitriol.
NITRATE OF SILVER " Lunar Caustic.
ACETATE OF COPPER " Verdigris.
MURIATE OF SODA " Table Salt.
TARTRATE OF POTASH " Tartar Emetic.
CARBONATE OF AMMONIA " Smelling Salts.
" LIME " Chalk, Marble, &c.
SUPER-ACETATE OF LEAD " Sugar of Lead.
OXIDE OF LEAD " Goulard.
SUBLIMATES are chemical preparations, the basis of
which is quicksilver. In CORROSIVE SUBLIMATES, the
quicksilver is _extinguished_, either by vitriol, potter's clay, or
some other ingredient.
SUBLIMATION is a similar process to distillation; only
_solids_(such as metals) are employed, instead of _liquids_.
Thus the fine _blue_ used by painters is a sublimate, and
made thus:--Take 2 parts of quicksilver, 3 flower of
brimstone, 8 sal ammoniac; and (having ground them)
put them with the quicksilver into a glass retort, luted at
the bottom; place the retort in a sand-heat; and (when the
moisture is given off) you will have a splendid blue
sublimate for painting.
INDEX.
ABSORBERS, best, 192
not conductors, 185
not reflectors, 192
radiators, 197
ABSORPTION of HEAT, 184
not conduction, 184
of light, 364
ACCIDENTAL COLORS, 407, 408
Acetate of lead, 426
Acetic acid, 426
Acid of drinks, 269
of fermentation, 269
Activity affected by cold, 91
" by heat, 93
Aerated water, 267
Aeronauts feel pain, 254
Age affects the sensation, thought, judgment, 425
power of walking, 425
AIR, 240
always in motion, 293
bad conductor, 13, 177, 178
bad radiator, 219, 237
cold, 177
colder than blood, 181
composed of two gases, 27, 240
cooled by convection, 220
" by rain, 159
cools hot iron, 246
density diminished by rain, 337
descends when cold, 289
double current in a room, 290
dries linen, 160
elements of, 33
expanded by heat, 103
full of smells, 152
gets fire up, 50
healthful, 252
heated, 219, 245, 246, 289
" not by sun, 290
in a room, 252
inflammable, _see hydrogen_
in summer, 313
of cities unhealthy, 243, 253
of the country healthy, 243, 252
on land colder than on water, 224
on land cold at night, 230
preserved normal, 244
purified by lightning, 27
rusts iron, 257
still before a tempest, 146
strong, 108
varies in temperature, 335
Aisles famous for echoes, 417
Alcohol, 109, 270, 271
ALE, 109
bottled, 268
froth of, 109
froth increased by heat, 268
Alkali, 45
Anenometer, 314
Anglers hate a magpie, 153
Angle of incidence, 370
of reflection, 370
Animal heat, 83, 85, 243, 277
Animals and vegetables co-dependent, 244
Ants love honey-dew, 221
Appetite, 89, 90, 91
(_See hunger._)
Apples full of air, 105
roasted, 105
soft, 106
April showers, 307
Aqua fortis, 426
Argand lamps, 83
Arnott's stoves smell of sulphur, 56
smoke, 69
Ascent in balloons painful, 145
Ashes soften water, 345
Asses bray in wet weather, 148
Aurora borealis, 142, 285
coloured, 143
white, 142
a prognostic, 143
Avenues, 380
Azote, _see nitrogen_
Bales catch fire spontaneously, 57
Balloons, 146
inflated, 109
rise, 110
Balls of fire, 6
Banisters wet, 216
Barley malted, 270
BAROMETER, 317
affected by cold, 328
" frost, 329
" heat, 328
" thaw, 329
" wind, 327
rules for its rise and fall, 330
sudden change in, 330
use of, 319
varies most in winter, 327
" least in summer, 327
when highest, 328
" lowest, 328
Barren land collects no dew, 209
Bass notes in music, 412
Bass preserves flowers from frost, 206
Bathing, danger of, 387
with ether for inflammation, 157
Beakers broken by hot water, 126
Beasts covered with hair, 176
Beds damp, 157
BEER, fermentation of, 269
flat, 273
froth increased by bottling, 268
froth increased by heat, 268
raisins and raw meat improve it, 273
stale, 275
soured by lightning, 27
not _old_ beer, 27
spoiled, if the vent-peg be left out, 273
yeast added to make it work, 271
Beer-vats dangerous, 265
Bells heard at a distance, 412
cracked, sound harsh, 411
silenced by a touch, 411
Bell-metal, 410
Bellows, 51
Bins purified, 266
Birds covered with feathers, 176
BLACK, 402
cloth warm, 186
eyes, 191
glass for spectacles, 408
hat turns red at the sea-side, 344
Hole of Calcutta, 250
kid gloves, 188
lead, 258
" prevents rust, 258
mist, 144
skin, 190
tea-pot, 197
" used by cotters, 198
" set on a hob to draw, 198
will never blister, 190
Blacks, 60
none to railway engines, 60
Blacksmiths strike fire by nails, 96
Bladders inflated by heat, 103
BLAZE, blue, 46
green, 45
yellow, 46
between the bars of a grate, 45
Blazing coals burn quickly, 39
Blood red, 242
purple, 242
Blowers, 70
Blowing cools broth, 180, 247, 312
tea, 248
Blue, 401
glasses, 407
sky, 132
sublimate, 426
Body warm, 87
BOILING, 234
WATER bubbles, 114, 283
makes it flat, 275
is in a ferment, 232
rattles, 116
runs over, 115, 233
swells, 114
one pot will not boil in another, 118
retarded by a spoon, 117
" by salt, sugar, 118
Bottled ale, &c., 268
Brackish water unfit for railway engines, 263
Bread heavy, 276
made with yeast, 276
Breath exhaled, 244
visible in winter, 217
Breathing difficult on a mountain, 255
previous to a storm, 255
BREEZE at watering places, 310
evening, 309
morning, 308
of islands, 309
speed of, 313
(_See wind._)
Bricks for cold feet, 173
Brick stoves, 174
Bricklayers cannot work in a frost, 359
cover new work with straw, 359
Brilliancy, 364
Brine retards boiling, 119
tested, 361
Broth cooled by breath, 247, 312
by convection, 247
by stirring, 247
Bubbles in tea, 419
of boiling water, 114
Bulk for bulk, 110
Burns cured, 157
Burning glasses, 2
Caloric, 1
Cambric handkerchiefs cool, 184
Cambridge, rain of, 340
CANDLES, 74
burn, 74
" blue, 148
cotton, not easily blown out, 79
easily blown out, 51, 78
and rekindled, 51, 55
extinguished, 79
flame hot, 75
" hollow, 76
" pointed, 77
" purple below, 76
" tends upwards, 77
" yellow, 76
gas of, 281
held at a door, 290
hottest _above_ the flame, 79
give light, 76
make glass damp, 78
need snuffing, 81
Palmer's, 80
prevent our seeing abroad, 378
reflected in a window, 379
rush, easily go out, 79
smoke, 81
spirt, 155
suddenly introduced give pain, 365
wax, need no snuffing, 81
Candlestick rags catch fire spontaneously, 58
Capillary veins, 84
Captain Ross, 414
Carbon, 33, 74
Carbonate of lime, 426
of soda, 426
CARBONIC ACID GAS, 37, 108, 249, 264
deleterious, 250, 264
in human bodies, 84
its presence detected, 264
CARBURETTED HYDROGEN GAS, 279, 280
Carpets warm, 169
Carriage wheels catch fire, 99
Carriage windows misty, 213
Casks charred, 73
Cart grease, 100
Cathedral aisles famous for echoes, 417
CATS in wet weather, 147
prowl by night, 367
rub their ears, 150
see in the dark, 367
wink before a fire, 367
Cattle uneasy in wet weather, 148
Caverns famed for echoes, 416
Ceilings sooty, 71
Cellars cold in summer, 256
warm in winter, 256
Cerebellum, 424
Cerebrum, 424
Chalk, 426
CHARCOAL, 72
bad conductor, 166
fire, 72
" deleterious, 265
purifies water, 72
removes the taint of meat, 72
Charring bread, 73
casks, 73
wood, 73
CHEMICAL ACTION, 30
Chestnuts crack when roasted, 104
not if slit, 105
Chimney pots, 71
CHIMNEYS SMOKE, if a room be too close, 61
remedy, 62
in vestries, valleys, 66
remedy, 67
in wind, 66, 111
if too long, 62, 116
" short, 62
" large, 69
remedy, 70
when the draught is slack, 63, 69
when the door is on the same side, 68
remedy, 68
when it needs repairing, 68
sweeping, 68
when two fires are in one room, 65
remedy, 65
China broken by hot water, 125
Choke damp, 264, 279
Church bells heard at a distance, 151
Churchyards smell offensively, 283
Chyle, 242
Cider, 269
Cinders, 43
iron, 43
will not blaze, 48
Cirro-cumulus clouds, 136
Cirro-stratus clouds, 134
Cirrus clouds, 134
Citizens pale, 243
Citric acid, 426
City air unhealthy, 253
Clean kettles, 186
Cleanliness connected with the dietary, 93
Clear day overcast, 304
Clear nights exhilarating, 144
Clocks heard, at a distance, 151, 413
Close rooms unhealthy, 253
Cloth collects but little dew, 208
Clothes gather damp in summer, 211
wet, 157
Clothing for workmen, 164
promotes warmth, 176
CLOUDS, 127
cause of, 129
classes of, 134
colour of, 132
compound, 136
" simple, 134
differ from fog, 128, 227
dissipated, 304
distance from the earth, 129
edges most luminous, 399
electrical, 131
fall in rainy weather, 337
float, 128
height of, 4, 120
highest and lowest, 130
intermediate, 135
light, 120
motion of, 133
red, 132, 399
round mountain tops, 137
thickness of, 130
" how ascertained, 130
vary in shape, 129, 130
" in colour, 133
where most abundant, 129
where least, 129
use of, 137
velocity of, 314
wind affects them, 129, 131
Coal gas, 280
mines explode, 281
Coals black, 403
COLD WEATHER affects the barometer, 328
makes us love fat, 90
" activity, 91
out of doors, 312
promotes hunger, 91
Collapsing, 289
Colour of clouds, 132, 133
Colours vary, 400
some warm, some cold, 187
Combining not mixing, 25
COMBUSTION, _see fire_, 33, 85
cause of, 36
elements of, 36
heat of, 37
increased by wind, 58
in the veins, 84
COMMUNICATION of HEAT, 164
Compound clouds, 136
Compression, 102
CONDENSATION, 98, 102
Condensed air, 289
CONDUCTION, 164
not absorption, 184
CONDUCTORS, best, 165
worst, 166
not absorbers, 185
of lightning, 22
dangerous, 24
CONVECTION, 219, 231
Convective currents, 245
cool broth, 247
cool iron, 247
Cooking vessels with wooden handles, 166
Cooper applies hot hoops, 122
Copper sonorous, 410
tarnishes, 259
COPPER-HOLE, 60
roars, 60
" not when the door is open, 60
Cornea, 388
Corns ache in wet weather, 256
Corpse cold, 95
Corrosive sublimates, 426
Cotton bales catch fire spontaneously, 57
handkerchiefs hot, 184
Countrymen ruddy, 243
Cowls, 67, 111
Crowds produce drowsiness, 251
head-ache, 249
vitiate air, 249
unhealthy, 250
Culinary vessels have wooden handles, 166
should be sooty, 71, 201
Cultivation promotes dew, 210
warmth, 160
Cumulo-stratus clouds, 136, 137
Cumulus clouds, 134, 135
Cup in a pie, 120
why full of juice, 124
Damp banisters, 217
beds, 158
house, 217
DANGER IN A STORM, 12
in attics and cellars, 16
a crowd, 18
theatre, &c., 19
before a fire, 15
near a tree, 12
river, 14
flocks and herds are exposed to, 19
those who bar shutters, 18
lean against a wall, 17
or carriage, 20
who ring bells, 15, 17
run, 15
Dark colours warm, 186
radiate heat, 197
Davy, Sir H., 281
Day-light produces hunger, 88
Dead bodies cold, 95
taller than living, 423
Deal snaps in fire, 107
Decanting liquor, 274
spirting, 274
Depression of spirits, 145
Descent in a diving bell painful, 146
Deserts hot and dazzling, 405
DEW deleterious, 220
differs from rain, 226
distilled after a hot day, 219
especially if the wind is westerly, 218
unequally, 207
in open places, 204
in valleys and hollows, 207
on clothes, 211
cultivated lands, 210
grass, 209
leaves, &c., 208
none beneath a tree, 204, 205
a flower awning, 205
hedge or wall, 205
none in a cloudy night, 204
in a windy night, 207
especially if easterly, 218
none on stones, cloth, 208
deserts, gravel, metal, rocks, wool, 209
Dew-drops round, 223
flattened, 223
roll on cabbages, 223
roses, 224
Digging promotes warmth, 161
Digestion, 91
Dinner covers, 202
Dirt warm, 93
Distant bells heard, 413
clocks, 151
objects appear small, 381, 382
sight, 390
spectacles for, 391
Distance makes things invisible, 384
Distilled vinegar, 426
Divers suffer pain, 255
Diving bell, 146
Doors swell and shrink, 151
Dogs uneasy in wet weather, 147
Dough, 274
set before a fire to rise, 276
Double concave glasses, 389
convex glasses, 391
Draining lands promote warmth, 160
DRAUGHT at a door, 314
key-hole, 314
window, 315
slack, 63, 64, 69
Dreams, 424
foolish things, 424
Drops of rain roll on dust, 155
Drowned men restored, 101
Drums, 411
DRY WOOD for kindling, 44
burns best, 107
snaps about, 107
Dryest months, 328
Dublin, rain of, 340
Duck dry in water, 224
Dunghills hot, 277
Dusty shoes hot, 194
Dyeing changes a colour, 401
Ear-trumpets, 415
EARTH, bad conductor, 181
cool in summer, 182
cracks by frost, 357
crumbles in spring, 358
warm in whiter, 131
Earth-fog, 221
Earthen tea-pots, 197, 198
set on a hob to draw, 198
East wind cold, 302
dry, 303
prevents dew, 218
Eat more in cold, 90
less in warm weather, 91
Echo, 416
Echoes, two or more, 418
EFFERVESCENCE, 269
soon subsides, 275
Egg cracked when boiled, 239
tested, 178, 239
ELECTRICITY affects the clouds, 131, 133
excited by friction, 29
felt at the elbow joints, 27, 29
hot, 3
of clouds, 4
positive & negative, 16
ENGLAND grows warmer and warmer, 160
WINDS of, 300
east dry, 302
morning at watering places, 310
most prevalent, 300
north cold, 312
north-east dry, 305
south rainy, 303
warm, 303
south-west rainy, 304
west rainy, 304
when highest, 301
lowest, 301
_See March wind._
Epsom salts, 426
Esquimaux love blubber, 92
Equatorial current, 298
ETHER, 47
boils, 119
used for freezing, 360
used for inflammation, scalds, burns, 157
European skin white, 191
EVAPORATION, 156
freezes, 360
EVENING CLOUDS, 132
grey, 140
red, 138, 399
EVENING RAINBOW, 141
Evergreens frost-bitten, 230
Ewers broken by frost, 349
EXPANSION by HEAT, 103
Extinguishers, 79
made of paper, 79
Eyes, two, 368
see single, 369
affected by blue glasses, 407
fire-light, 407
the sun, 407
Face soon scorched, 196
Fanning, 179, 313
Far sight, 390
spectacles for, 391
Farriers apply hot shoes, 123
Fat men swim best, 362
Feathers warm, 176
Feeling, 425
Feet cold before a fire, 53
wet dangerous, 157
FERMENTATION, 269
of dough, 276
Fender and fire-irons cold, 185
Fiddle-strings musical, 411
snap from wet, 339
Fine weather braces, 147
Finger feels cold when wet, 157
FIRE black and red, 38, 40
blazes, 39
not in frost, 48
burns blue, 148
cause of, 36
charcoal, 72
damp, 280
effect upon the eyes, 407
extinguished, 54
by water, 107
fiercest in winter, 49
out of doors, 50
grotesque figures in, 40
heat of, 280
how increased, 63
hot, 37
kindled at the bottom, 42
light dazzles, 366
lighted with paper and wood, 41
luminous, 46
poker draws up, 52
radiates heat, 196
red hot, 38
reflected on windows, 379
sun dulls it, 49
thaw dulls it, 50
wind intenses it, 51
_See combustion._
Fire-irons cold, 185
rust, 257
prevented, 258
Fishes ascend and dive, 363
seem nearer than they are, 388
cold, 94
FLAME of a CANDLE, 76
described, 77
blown out easily, 78
damp, 78
hollow, 76
hottest above, 79
pointed, 77
purple and yellow, 76
smokes, 81
Flame of a fire between the bars of a grate blue, 46
green, 45
yellow, 46, 47
Flannel warm, 94
used for foot-warmers, 173
Flash, _see lightning_
Flat beer, 273
improved, 273
Flavour discerned by the taste, 425
Flint and steel, 97
FLOWING WATER freezes slowly, 354
makes rough ice, 354
oscillates, 348
pure, 347
Flower awnings arrest dew, 205
purify air, 253
Flowers smell sweetest at night and before rain, 152
Flues blacked, 238
_See chimney._
Flutes, 412
Fly-poison, 422
FOGS, 225, 226
arrest sound, 413, 414
cause of, 129
differs from cloud, 128, 227
mist, 227
dispersed by wind, 228
by sun, 227
frozen, 231
in autumn, 228
in marshes, 226
valleys, 228
none in a frosty night, 227
Food converted to blood, 242
cooled by the breath, 312
Foot-prints frozen, 350
Foot-warmers, 173
Forked lightning, 5
dangerous, 5
Forests catch fire spontaneously, 102
France warmer than of yore, 162
FREEZING MIXTURES, 360
FRICTION (_see rubbing_), 98
excites electricity, 29
sets forests on fire, 102
Frogs cold, 94
FROST affects barometer, 329
sound, 414
braces, 147
breaks ewers, 349
tiles, stones, rocks, 350
pipes, 351
cracks earth, 357
expands water, 352
prevents fog, 227
warm, 356
Froth of beer, 269, 350
Frozen ruts and footprints, 350
Fruits cool the blood, 92
fall to the earth, 419
pleasant in summer, 92
Fuel for the body, 87
Fumigation for sick rooms, 421
FUR, bad conductor, 166
for clothing, 175
warm, 171
Furnaces of brick, 174
lined with clay, 174
Furr of kettles, 262
steam engines dangerous, 263
Gallery hot, 249, 316
Gas, 112
of candles, 281
Gauze wire of safety lamps, 282
prevents explosion, 282
German silver tarnishes, 260
German tinder, 102
Germany warmer than of yore, 162
Ghosts, 286
Gideon's miracle, 211
Ginger pop, 268
acid, 269
GLASSES broken by hot water, 125
covered with mist, 214
which soon subsides, 215
dulled by a hot hand, 215
by breath, &c., 215
_See spectacles._
Glass a reflector, 194
soon cools, 212
_See looking-glass._
Glauber salts, 426
Gloves, black kid, 188
Lisle thread, 188
Glow-worms glisten by night, 368
GOD'S WISDOM 182, 208, 210, 302, 308, 352, 357
Gold never tarnishes, 260
Goulard, 426
Grapes never ferment, 272
Grass promotes warmth, 161
collects dew, 209
Grate, _see stove_
Gravel collects no dew, 209
Gravity, 419
Gray morning, sign of a fine day, 140
GREASE liked in cold weather, 90
loathed in hot, 92
prevents rust, 258
used for wheels, 100
Green colour, 401
wood does not burn, 107
Grottoes famous for echoes, 416
Ground frost, 229
Growth promoted by moonlight, 220
Gulls fly to sea, 154
to land, 154
Gusty weather makes a smoky house, 71
HAIL, 331, 334
cause of, 335
accompanied with thunder, 335
falls in summer, 335
Hair, bad conductor, 166
covered with dew, 217
Halls famous for echoes, 417
Halo round the moon, 143
Hard work promotes hunger, 88
Hat covered with dew, 217
turned red at the seaside, 344
Hawks see near and far, 392
Hay-stacks catch fire spontaneously, 58
Haze round the sun, 143
moon, 143
affects sound, 414
Head aches in a crowd, 249
itches in wet weather, 150
Hearth-rug warm, 169
Hearth-stone cold, 169
hot, 170
HEAT, 1
and light, 47
affects barometer, 328
sound, 414
animal, 83, 85, 277
applied to the bottom of boilers, 234
effects of, 2, 4, 103
expands water, 352
from beaten iron, 95
LATENT, 31, 75, 96
of candles, 75
dunghills, 277
fire, 37, 277
lime, 278
radiates, 196
sources of, 2
Heavy bread, 160
Hills larger in a fog, 148
HOAR FROST, 228
not found on trees, 230
under shrubs, &c., 230
of frozen fog, 231
on clear nights only, 229
on grass, 229
tombstones, 189, 230
very partial, 229
HONEY-DEW, 220
ants fond of, 221
effects of, 221
injures plants, 221
Hot cloudy night oppressive, 144
Hot weather abates activity, 93
appetite, 90
love for grease, 92
Hottest place at church, 316
Hoops used red hot, 122, 123
Horse shoes fitted hot, 123
Horses strike fire, 98
snuff up air, 152
uneasy in dull weather, 148
Houses catch fire spontaneously, 56
smoke in valleys, 66
Hunger, 88
promoted by cold, 90
day-light, 88
singing, speaking, work, 88
_See appetite._
Hydrogen gas, 34, 74
ICE, 349
lighter than water, 349
grows thicker, 353
dissolved by snow, 357
melted by sun, 126
Ice-bergs famous for echoes, 417
Idiots, 424
IGNIS FATUUS, 285
cause of, 286
Impure water purified, 72
Indian mode of striking fire, 99
Inflammable air, 34, 74
Insensible perspiration, 213
Intermediate clouds, 135
IRON, bad conductor, 185
cinders, 43
contains latent heat, 96
cooled by air, 246
convection, 246
radiation, 246
matches, 96
rust, 257
when most common, 258
prevented, 258
sonorous, 410
stoves, 174
Ironing-box, 155
Islands equable in temperature, 311
subject to wind, 309, 311
Itching in wet weather, 150
Jack o'lanthorn, _see ignis fatuus_
Jet of flame through bars, 45
Juice of lemons, 426
Jungle of Hindostan fatal, 266
Kendal rainy, 340
Keswick rainy, 340
KETTLE boils over, 115
quickly when covered with soot, 186
slowly when clean, 186
when new, 186
bottom should be sooty, 200
cold when water boils, 200
inside white, 200
lid hot, 201
furr, 262
holder, 167
not full after boiling, 115
runs over, 233
through the spout, 115
sings, 113, 233
top bright, 200
Kindling wet, 43
Lakes which never freeze, 355
Lamps, 74
Argand, 83
smoke, 82, 83
spirit, 155
_See candle._
Lamp-glasses, 83
Land air cold, 224, 311
breeze unhealthy, 309
Laplanders clad in skin, 183
LATENT HEAT, 31, 75, 96
Laziness promoted by want of food, 89
by heat, 93
Lead tarnished, 259
LEAVES collect dew unequally, 208
green, 404
light green in spring, 404
in a pond, 419
pale in dark places, 403
promote cold, 161
yellow in autumn, 408
Lid of kettles, &c. hot, 201
Light bread, 276
LIGHT, 363
composed of various colours, 400
divided by a prism, 393
from a flint, 97
of candles, 76
fire, 46
sun, 363
reflected, 364
speed of, 364
sudden painful, 365
LIGHTNING, 3
balls, 6
barks and snaps trees, 27
comes from clouds, 16
from earth, 16
conductors, 22
dangerous, 24
follows dry weather, not wet, 28
forked, 5
fuses metal, 27
kills animals, 7
knocks down churches, 24
maims, 8
passes down the outside of a tree, 14
passes through the inside of animals, 14
purifies air, 27
rare in winter, 28
sheet, 6
summer, 11
common, 28
straight, 6
turns beer sour, 27
not old beer, 27
milk sour, 25
_See danger, safety._
Lilac steel rusts, 259
prevented, 259
LIME and water, 26, 30
burned, 278
hot, 277
purifies bins, 266, 421
sewers, 267, 421
Lime-wash for rooms, 422
Lincoln, rain of, 340
Linen cool wear, 183
dried, 160, 316
Linseed oil boils, 119
LIQUEFACTION, 126
LIQUIDS, 112
bad conductors, 172, 232
cooled, 235
Lisle thread gloves, 188
Liverpool, rain of, 340
LONDON FOG, 225
rain of, 340
Long flues, 110
grass promotes cold, 161
Log of wood, 2
two burn better than one, 44, 52
Looking-glass, 369
Lucifer matches, 284
Lunar caustic, 426
Mackarel scales, &c., 136
Macintosh prevents cold, 158
Madness from starvation, 86
Malt, 270, 272
Man a swimmer, 362
no bigger than a crow, 382
Manchester, rain of, 340
Magpies indicate weather, 153
Marble, 426
MARCH comes in like a lion, 306
goes out like a lamb, 306
dry good, wet bad, 306
flowers undesirable, 307
wind dry, 305
Marsh damp, 280
Marsupium, 392
Meat-covers, 202
MEAT liked in cold weather, 90
loathed in hot, 92
taint removed, 422
tainted by moonlight, 220
MECHANICAL ACTION, 95
Mercury of barometer bright, 260
concave, 325
convex, 325
its rise and fall, 325
METAL collects no dew, 209
feels colder than wood, 168
hotter than wood, 167
fused by fire, 127
by lightning, 27
good conductor, 165
handles burn, 166
reflectors, 193
tea-pots, 197
Milk soured by lightning, 25
Miners' danger, 283
prevented, 265
Mirror, 369
MIST arrests sound, 414
black, 144
cause of, 224
differs from cloud, 128
dew, 222
fog, 227
seems to rise, 222
vanishes at sunrise, 227
white, 144
Mixing not combining, 25
Money hot in a pocket, 168
Monsoon, 300
Months, driest, 328
wettest, 329
MOON, distance and size, 383
largest at horizon, 149, 378
reflected in water, 376
in a well, 374
seems flat, 383
larger than stars, 383
Moonlight makes plants grow, 220
taints meat, 220
MORNING breeze, 308
gray, 140
rainbow, 141
red, 139, 399
streaks, 132
MORTAR, 278
adhesive, 279
crumbles, 358
Motes in a sun-beam, 248
Mould hardened by sun, 163
Mouldiness prevented, 422
Mountains cold, 100, 195
collect rain, 338
famous for echoes, 417
impede respiration, 255
noiseless, 416
Muriate of soda, 426
Musical instruments, 411
flat, 412
Nails for matches, 96
Naves fitted on hot, 122
Near-sight, 388, 391
spectacles for, 389
Negative electricity, 66
Negroes, why black, 190
with black eyes, 190
New kettles boil slowly, 186
Night allays hunger, 88
exhilarating, 144
oppressive, 144
produces cold, 89
rainbow at, 141
Nimbus clouds, 137
Nitrate of silver, 426
Nitric acid, 28, 426
Nitrogen, 36
North wind cold, 302
dry, 303
North-east wind dry, 305, 320
November rainy, 308, 338
Oak attracts lightning, 257
Old people far-sighted, 390
hold objects at a distance, 392
lose their sensation, thought, volition, 425
lose their power of walking, 425
spectacles for, 391
Oil, 74
linseed, 119
of turpentine, 119
of vitriol, 426
One pot will not boil in another, 118
how to make it boil, 118
Oxalic acid, 426
copper, 259
iron, 257
OXIDE of lead, 259, 426
platinum, 261
potassium, 262
silver, 260
sodium, 262
Oxygen, 34
of air, 97
its use, 240
supports combustion, 240
sustains life, 240
Out-of-door work produces hunger, 89
Owls prowl at night, 367
see in the dark, 367
sleep all day, 367
Paleness, 243
Palmer's candles, 80
Paper burns, 41
not always, 44, 53
extinguishers, 79
puckers from wet, 339
used for kindling, 41
Papillæ, 425
Paris, plaster of, 426
rain of, 340
Parlours smell of smoke in summer, 71
Partition walls to arrest sound, 415
Pea-soup fog, 225
PERCUSSION, 95
Perspiration, 89
Petals, 402
Petrels, 154
Phosphate of lime, 284
Phosphorus, 283, 284
PHOSPHURETTED HYDROGEN GAS, 283
Piano-forte, 412
Pickle tested, 361
Pie with a cup, 120
full of juice, 121
Pin puts a candle out, 81
Pineal gland, 424
Pipes broken by frost, 351
Piston, 102
PLANTS collect dew, 208
deleterious in bedrooms, 405
grow out of walls, 316
Plaster of Paris, 426
of stoves falls away, 124
Plasterers cannot work in frost, 359
Platinum, 261
its use, 261
never tarnishes, 261
Plate warmer, 188, 193
Ploughing, promotes warmth, 161
Plumbago, 258
prevents rust, 258
Poison for flies, 422
Poker draws up fire, 52
cold, 172, 238
how to carry it when hot, 237, 238
rusts, 258
prevented, 258
Polar current, 298
Poor averse to cleanliness, 93
ventilation, 94
lazy, 89
Pores of wood, 106
Porter, froth of, 109
set before a fire, 109
stale, 275
Positive electricity, 16
Potatoes, green, 405
yellow, 404
Potassium, 262
burns in water, 262
Primrose, 402
Prisms divide light, 393
Pump handle cold, 168
water hard, 363
Purple steel rusts, 259
its rust prevented, 259
PUTREFACTION, 277, 278
Putrefying bodies smell, 284, 285
Quadrupeds swim, 362
RADIATION, 195
cools iron, 247
Radiators are absorbers, 197
Rags catch fire spontaneously, 58
Railway steamers, 218
RAIN, 331, 336
affected by wind, 337
after lightning, 11
arrests sound, 413
cause of, 326, 336
cools air, 159
differs from dew, 226
falls in drops, 336
fertilizing, 307, 337
from passing clouds, 336
heaviest in summer, 341
least at the poles, 342
melts salt, 346
sugar, 345
most in mountainous places, 338
most in winter, 341
near the equator, 341
not salt, 347
on dust, 223
prognostics of, 137
purifies air, 338
sudden change, 326
RAINBOW, 394, 397
colours reversed, 396
morning, 141
night, 141
two, 395
Rain drops, 336
vary in size, 337
Rain-water smells offensively, 345
soft, 344
stagnant, 347
Rainy months, 308
parts of England, 340
Rattling of kettle-lid, 116
Ray of light divided, 393, 400
Reading aloud produces hunger, 88
RED colour, 401
rose, 401
sky, 132, 399
sun-rise, 139
sun-set, 139
Reflected light, 364
REFLECTION of HEAT, 192, 370
REFLECTORS, 192
help the roast, 194
keep kitchen cool, 194
not absorbers, 192
should be clean and bright, 189, 192
should not be painted, 189
REFRACTION, 386, 394
Refrangible, 132
Retina, 388
Reverberation, 417
Rice for food, 93
RIVERS flow slowest at sides, 348
freeze unequally, 354
never frozen at bottom, 352
not wholly frozen, 353
shallow freeze fastest, 354
seem shallower than they are, 387
warm when frozen, 354
Roast apples, 105
soft, 106
chestnuts, 104
Road dark from a light room, 194
Rocks collect no dew, 209
broken by frost, 350
Room cooled, 159, 315
ventilated, 375
warmed by fire, 237
Rose red, 401
Ross Captain, 414
Rotting leaves promote cold, 161
Rubbing, 99
hands to warm them, 101
melts ice, 101
restores suspended animation, 101
_See friction._
Ruddiness, 243
Ruins famed for echoes, 416
Running, promotes warmth, 87
Running water freezes slowly, 354
makes rough ice, 354
oscillates, 348
promotes warmth, 87
pure, 347
Rush lights easily blown out, 79
extinguished by a pin, 81
RUST, 257
prevented, 258
when most troublesome, 258
SAFETY IN A STORM abroad, 20
at a slight distance from a tree, 20
best to be wet, 22
in a carriage, 20
in bed, 22
in-doors, 21
Safety lamp, 281, 282
Sailors rarely catch cold, 158
St. Bride's church destroyed by lightning, 24
SALT, 426
and snow cold, 357
and water, 31
bad for washing, 343
crackles in a fire, 44
dissolves ice, 357
by water, 346
especially hot water, 346
retards boiling, 118
white, 403
of lemons, 426
smelling, 426
water unfit for railway engines, 263
Sand dazzling, 405
Saturday's kettle boils fastest, 199
Saucepan boils best when black, 199
slowly when new, 199
lids should be clean and bright, 199
Scald cured, 157
Scum of fermentation, 272
Sea-beach healthy in the morning, 310
not healthy at night, 310
Sea before storm, 146
heaves and sighs, 146
not much heated by sun, 296
Sea-gulls, 154
Sea water easier to swim in than fresh, 360
rarely frozen, 355
gives cold, 158
salt, 346
Sea-waves, 312
Sedentary pursuits abate hunger, 90
SEEING in a glass, 369
into a dark street, 366
light room, 378
ourselves in a small mirror, 371
the same object, 365
when used to darkness, 366
Sensation destroyed, 424
of feeling, 425
of taste, 425
Sewers purified, 267
Shade cool, 183
Shadow in water, 371, 372
Shadow larger as the object approaches a light, 379
Sheen, 405
Sheep bleat, 148
Sheet lightning, 6
Sheets wet, 157
Ships out at sea, 385
Shirts of linen, 183
Shoes hot when dusty, 194
Sick rooms purified, 421
Sides of a pond covered with leaves, 419
Swimming, 112
SILVER meat-covers, 202
should not be chased, 202
tarnishes, 260
Simple clouds, 134
Singing of a kettle, 113
of boiling water, 233
produces hunger, 88
Single magpie unlucky, 153
Skin, black does not scorch, 191
white does, 191
itches, 150
Sleep elongates the body, 423
body feels not in, 425
dreams in, 424
ears hear not in, 423
eyes see not in, 423
mind wills not in, 424
tongue tastes not in, 423
Sleet, 332
Slit chestnuts, 105
Smelling salts, 426
SMELLS in wet weather, 152
of church-yards, 283
of putrefying bodies, 284
SMOKE, 39, 59
curls, 59
falls, 152
of fresh coals, 39
lamps diminished, 83
by a glass, 83
rises, 110
useful in cooking, 201
Smoky chimneys, 59
_See chimney._
Smoke-jacks, 112
SNOW, 331
arrests sound, 413
bad conductor, 333
cause of, 331
falls in winter, 332
not in summer, 334
like wool, 175
nourishes the earth, 333
on mountains, 334
soon melts beneath a hedge or wall, 206
use of, 332
warm, 332, 333
white, 334, 402
Snow and salt cold, 31, 357
Soap, 344
cleansing, 344
hard, soft, 344
yellow, 344
Soap-bubbles, 348, 398
change colour, 399
Soapy water bubbles, 348
Soda water, 268, 269
Sodium, 262
decomposes water, 262
Soft soap, 344
Solids, 112
Soot in summer, 71
on ceilings, 71
Sooty kettles, 186
SOUND, 409
affected by frost, 414
heat, 414
arrested by wet, 413
velocity of, 410
diminished by rarity of air, 416
heard best by night, 414
inaudible on mountains, 147
South wind rainy, 303, 320
warm, 303
South-west wind rainy, 304
Sparks from a fire, 106
a flint, 97
a horse-shoe, 98
Spectacles, 389
black, 408
blue, 407
for aged, 390
near sights, 389
Split bells, 411
Sponge swells when wet, 339
SPONTANEOUS COMBUSTION, 56, 57, 58, 85
Spoons become dull, 26
in water, 387
retard boiling, 117
Speaking promotes hunger, 88
Spring best late, 307
water cool, 182
sparkles, 269
Springs prevent freezing, 356
Sprinkling to cool rooms, 159
Stagnant water, 347
full of worms, 347
Stale beer, &c., _see beer_, 275
Stars distance and size of, 383
invisible by day, 368
seem flat, 384
seen in a well, 368, 374
seen on mountains, 376
twinkle, 406
Starvation, 86
produces madness, 86
STEAM, 127
engines burst, 236
invisible, 116, 235
of a kettle, 236
why visible, 117
what becomes of it, 117
STEEL and flint, 97
rusts, 259
prevented, 259
Stillness before a storm, 146
Stirring cools broth, &c., 247
Stockings difficult to draw on when wet, 340
STONES broken by frost, 350
cold, 169
collect no dew, 208
snap in fire, 108
unfit for fuel, 43
STORMS, 146
direction of, 28
places of danger in, 12
safety in, 20
Straw covered over brickwork, 359
over trees, 359
water-pipes, 359
Street dark from a light room, 194
STOVES crack, when lighted, 123
when cooling, 123
of bricks, 174
on a floor, 52, 237
rust, 257
not often, 258
prevented, 258
settings fall away, 124
warm a room, 237
Strata of air, 9
Stratus clouds, 135
Streets seem to meet at bottom, 381
watered, 159
Stucco peels off in frost, 358
Sublimates, 426
Sublimation, 426
Sudden light painful, 365
SUGAR at top of tea melts quickly, 421
left at the bottom of a cup melts slowly, 420
melted by water, 345
especially by hot water, 346
retards boiling, 118
stirred melts quickly, 420
white, 402
of lead, 426
Sulphate of lime, 426
magnesia, 426
soda, 426
zinc, 426
Sulphuric acid, 426
and water, 30
boils, 110
Summer allays hunger, 90
clothes for, 187
creates dislike of grease, 92
love of fruit, 92
lightning, 11
Sun-beams full of mites, 248
SUN affects eyes, 407
dazzles, 364
dulls fire, 40
largest at horizon, 149, 377
not seen in a well, 373
seems flat, 384
source of heat, 2
reflected in water, 375
Sun-rise red, 139
Sun-set gray, 140
red, 138
yellow, 139
Super-acetate of lead, 426
Swallows fly low, 152
Swan dry in water, 224
Swimmers sink, 361
Swimming, 262
Syrup boils, 119
Table salt, 426
Tainted meat cured, 72, 422
water, 72
Tallow, 74
Tarnish, 259
Tartar emetic, 426
Tartrate of potash, 426
Tarts have a cup inside, 120
full of juice, 121
TEA cooled by blowing, 248
by stirring, 247
in a saucer, 163
green deleterious, 423
poison for flies, 423
TEA-POT, bright metal, 197
tarnishes, 260
black earth, 197
preferred by some, 198
set on a hob, 198
Telescopes, 385
Tempest, 146
affects weather, 326
_See storms._
Thaumatrope, 406
THAW affects barometer, 329
cold, 320, 356
dulls fire, 50
Thermometer, 307
Thick clothing unhealthy, 164
THUNDER, 8
after lightning, 12
bolts, 11
deep growl, 10
irregular roar, 9
one crash, 8
rolling, 10
_See danger, safety, storm._
Tigers prowl by night, 367
sleep all day, 367
see in the dark, 367
Tiles broken by frost, 350
Timber charred, 73
Tin blowers, 70
foot-warmers, 173
reflectors, 193
_See reflectors._
Tinder blown, 97
Toast and water, 73
for the sick, 73
Tomb-stones frosted, 230
Tongs rust, 258
prevented, 258
Trade-winds, 198
Transparency, 405
Treble, 412
TREES barked by lightning, 29
collect dew, 208
covered with bass, &c., 359
look more distant in a fog, 148
promote warmth, 161
purify air, 253
shade of, cool, 183
Tumblers, _see glasses_
Twilight, 399
Two eyes, 368
see single, 369
Unslit chestnuts, 104
Use of barometers, 317
clouds, 137
smoke in cooking, 201
snow, 332
Valley chimneys smoke, 66
VAPORIZATION, 126, 127
Vapour of a carriage, 214
of a room, 212
of sea not salt, 163
Vats fatal, 265
Vegetable and animal life co-dependent, 244
Vegetables collect dew, 208
cool the blood, 92
Velocity of clouds, 314
light, 364
sound, 410
wind, 313
Vent peg, 273, 274
VENTILATION, 315
sought by the well-fed, 94
not by the ill-fed, 94
Verdigris, 426
Vertical sun, 293
Vestry chimneys smoke, 66
Violets blue, 402
Walls wet in winter, 216
Want connected with dirt, 93
Warm clothes, 187
some things more than others, 165
Wash-hand-basin, 171
Washing, water for, 275
should not be hard, 343
WATER, 38, 342
and lime, 30
and sulphuric acid, 30
ashes soften, 345
bad conductor, 171, 234
boiling, 119, 232, 234
bubbles, 114, 233
rattles, 116
runs over, 115, 233
sings, 233
cleans dirty linen, 344
cold, 177
converted to steam, 127, 343
cools slowly, 225
deep, freezes slowly, 356
dried up in summer, 162
expands by frost, 351
by heat, 351
extinguishes fire, 54, 107
flat when boiled, 275
fluid, 342
flowing, pure, 347
for washing, 275
freezes at the surface, 253
hard, 343
unfit for washing, 343
how preserved cool, 191, 202
hot, 191
heated, 232
intenses fire, 54
mixed with salt, boils slower, 119
not heated above boiling, 235
of a spring cool, 182
purified, 72
purifies bins, &c., 267
salt, bad for washing, 343
shallow, freezes fastest, 355
slackens flame, 55
soft, 344
best for washing, 345
sparkles, 269
stagnant, 347
full of worms, 347
stale, 275
swells with boiling, 114
will not bubble without soap, 348
warm when frozen, 354
Water pipes broken by frost, 351
covered with litter, 359
Watering plants by the saucer, 420
streets, 159
Waves, 312
Wax, 74
Wax candles need no snuffing, 81
Weather affected by tempests, 326
prognostics of, 137
told by barometer, 318
rules, 319
Weather toys, 339, 340
Well, moon seen in, 374
stars seen in, 368
sun not seen in, 373
West Wind promotes dew, 218
rainy, 304, 320
Wet clothes cold, 157
feet dangerous, 157
finger cold, 157
kindling, 43, 44
sheets, 158
summer, cold winter, 160
weather offensive, 145, 148
Wettest months, 329
Wheels catch fire, 99
greased, 100
kept cool by water, 162
Wheel-ruts frozen, 350
Wheelwright, 122
WHITE, 402
blisters, 190
body linen, 186
crust on clothes, 163
dresses for summer, 186
not fit for winter, 187
mist, 144
vitriol, 426
WICKS cotton, need snuffing, 81
have a knob when long, 80
not upright when long, 80
Palmer's wicks need no snuffing, 80
smoke, 82
_See candles._
Will o' the wisp, _see ignis fatuus_.
WIND, 287
affects barometer, 327
clouds, 129, 131
after lightning, 11
altered by clouds, 295
by seas, 295, 296
brings dry, 305
rain, 305
cause of, 287, 292
changes the shape of clouds, 132
cold, 117, 180, 312
dispels clouds, 131, 138
fog, 228
draws up fire, 51
dries linen, 316
feels hot sometimes, 181
in England, 300
increases clouds, 131, 138
makes barometer fall, 320
chimneys smoke, 66
of a morning, 308
of an evening, 309
prevents dew, 206
rate of travelling, 313
regular, 297
_See England, monsoon, north, south, west &c., trade-winds &c._
Winding passages famed for echoes, 417
Windows blazing with the sun, 372
not at noon, 372
covered with frost, 214
mist, 211
carriage, dull, 213
rattle, 418
Wine glasses, _see glasses_
Wine made without yeast, 271
Winter clothing, 187
promotes hunger, 90
WISDOM of GOD, 182, 208 210, 352, 357
WOOD burns, 41
spontaneously, 55
charred, 73
hot at one end, cold at the other, 165
ignited by friction, 99
kindling, 41
dry, 44
wet, 107
two logs burn best, 44, 52
sends forth sparks, 106
will not melt, 127
Wooden handles, 166
WOOL bad conductor, 166
collects no dew, 209
warm, 176, 333
Woollen clothing, 175
Work produces hunger, 88
Yeast, 271
makes light bread, 276
not used in wine, 271
Yellow flame gives best light, 47
soap, 344
sun-set sign of wet, 139
FINIS
JARROLD AND SONS, PRINTERS, NORWICH.
Transcriber's Notes:
Archaic and inconsistent punctuation and spelling retained.
Inconsistent question formats were regularized.
*** End of this LibraryBlog Digital Book "A Guide to the Scientific Knowledge of Things Familiar" ***
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