A Guide to the Scientific Knowledge of Things Familiar
by Ebenezer Cobham Brewer · English · Gutenberg #40652 · 466,270 chars · public domain (US)
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Title: A Guide to the Scientific Knowledge of Things Familiar
Author: Ebenezer Cobham Brewer
Release date: September 3, 2012 [eBook #40652]
Most recently updated: October 23, 2024
Language: English
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*** START OF THE PROJECT GUTENBERG EBOOK A GUIDE TO THE SCIENTIFIC KNOWLEDGE OF THINGS FAMILIAR ***
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_.
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