A Guide to the Scientific Knowledge of Things Familiar Ebenezer Cobham Brewer 897 downloads.pdf

The Project Gutenberg eBook of A Guide to the Scientific
Knowledge of Things Familiar
This eBook is for the use of anyone anywhere in the United States and
most other parts of the world at no cost and with almost no restrictions
whatsoever. You may copy it, give it away or re-use it under the terms
of the Project Gutenberg License included with this eBook or online at
www.gutenberg.org. If you are not located in the United States, you
will have to check the laws of the country where you are located
before using this eBook.

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

Other information and formats: www.gutenberg.org/ebooks/40652

Credits: Produced by David Garcia, Marilynda Fraser-Cunliffe,
Matthew
Wheaton and the Online Distributed Proofreading Team at
http://www.pgdp.net (This file was produced from images
generously made available by The Internet Archive)

*** 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.
PAGE
I. The Sun a source of heat 2
II. Electricity a source of heat 3
Thunder and lightning 3-29
III. Chemical action a source of heat 30
III.—Combustion 36
IV.—Smoke and smoky chimneys 59
V.—Lamps and candles 74
VI.—Animal heat 83
VII. Mechanical action a source of heat 95
VII.—Percussion 95
VIII.—Friction 98
VIII.—Compression 102
IX. Effects of heat 103
X.—Expansion 103
XI.—Liquefaction 126
XI.—Vaporization (clouds) 127
XII.—Evaporation 156
XIII. Communication of heat 164
XIII.—Conduction 164
XIV.—Absorption 184
XV.—Reflection 192
XVI.—Radiation (dew) 195
XVII.—Convection (boiling) 231

PART II.—AIR.
XVIII. Air 240
Rust 257
Tarnish 259

XIX. Carbonic acid gas 264
Froth. Effervescence. Fermentation, &c. 269
XX. Carburetted hydrogen gas 279
Fire damp 280
Safety lamp 281
XXI. Phosphuretted hydrogen gas 283
Ignis fatuus 285
Ghosts 286
XXII. Wind 287
XXIII. Barometer 317
Ten special Rules 319
XXIV. Snow. Hail. Rain 331
XXV. Water 342
XXVI. Ice 349
Frost 357
Freezing mixtures 360
XXVII. Light 363
Reflection. Telescopes. Refraction 386
Spectacles 389
Rainbows 394
Colour 399
XXVIII. Sound 409
Ear trumpets 415
Echoes 416
XXIX. Miscellaneous 419
Attraction. Anti-putrescents. Sleep. Dreams. 424
Glossary 426
Index 427

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. 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 theair), 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 boils at 173-1/2 degs.
Water boils at 212 degs.
Water with one-fifth salt at 219 degs.
Syrup boils at 221 degs.
Oil of turpentine at 304 degs.
Sulphuric acid at 472 degs.
Linseed oil at 640 degs.
&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.

It is very manifest that the lines D C are shorter than the lines E C: if, therefore, A
be the earth, and D G E the boundary of the atmosphere round the earth, then the

rays M E C (at the horizon) will pass through more of the atmosphere, than the rays
S D C, which are more elevated.

Q. Why does the moon appear larger at her rising and setting, than
when above our heads?
A. Because the rays pass through more of the vapoury atmosphere
which surrounds the earth; and this vapoury atmosphere magnifies the
moon, just like a magnifying glass.

Q. Why do cats rub their ears when it is likely to rain?
A. Either because the air is full of vapour, and its humidity (piercing
between the hair of the cat) produces an itching sensation; or more
probably, because the air is overcharged with electricity.

Q. How can the electricity of air produce a sensation of itching?
A. If the air is overcharged with electricity, the hair of the cat is
overcharged also; and this makes her feel as if she were covered with
cobwebs.

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

Q. Why do our heads and skin itch before rain?
A. Probably because the air is overcharged with electricity; and,
therefore, a sensation (like that of cobwebs) irritates the skin, and
produces an itching.

Q. Why do we hear distant CLOCKS more distinctly when rain is near
at hand?
A. Because the air is filled with vapour, and water is a better
conductor of sound than dry air.

Q. Why do we hear church-bells further, just previous to rain?
A. Because the air is filled with vapour, and vapour is a better
conductor of sound than dry air.

Q. Why do doors swell, when rain is at hand?
A. Because the air is filled with vapour, which (penetrating into the
pores of the wood) forces the parts further apart, and swells the door.

Q. Why do doors shrink in dry weather?
A. Because the moisture is absorbed from the wood; and, as the
particles are brought closer together, the size of the door is lessened,
(or in other words, the wood shrinks).

Q. Why is the air filled with offensive smells previous to a coming
rain?

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

Q. Why do flowers smell sweeter and stronger just previous to rain?
A. Because the volatile parts (which constitute the perfume of flowers)
are laden with vapour; and (being unable to rise) are confined to the
lower regions of the air.

Q. Why do horses and other animals stretch out their necks, and snuff
up the air, just previous to a fall of rain?
A. Because they smell the odour of plants and hay, and delight to
snuff in their fragrance.

Q. Why does smoke fall when rain is at hand?
A. The air being less dense in wet weather, cannot buoy up smoke so
readily, as when more dry and heavy.

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

Q. Why do these insects seek the lower regions of the air in wet
weather, more than in fine weather?
A. Because they are forced downward, by some current of cold air
which drives them down.

Q. Why does a downward current of cold air bring rain?
A. Because it condenses the warm vapour; which then descends in
rain.

Q. The proverb says, “a single magpie in spring, foul weather will
bring:” why is this the case?
A. In cold stormy weather, one magpie alone will leave its warm snug
nest in search of food, while the other stays with the eggs or young
ones; but in fine mild weather (when their brood will not be injured by
cold) both the magpies will fly out together.

Q. Why is it unlucky for anglers to see a single magpie in spring?
A. Because when magpies fly abroad singly, the weather is cold and
stormy; but when both birds fly out together, the weather is warm and
mild, which is favourable for fishing.

Q. Why do sea gulls fly about the sea in fine weather?
A. Because they live upon fish, which are found near the surface of the
sea in fine weather.

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

Q. Why does the petrel always fly to the sea during a storm?
A. Because the petrel lives upon sea insects, which are always to be
found in abundance about the spray of swelling waves.
(The Petrel is a bird of the duck-kind, which lives in the open sea.
They run on the top of the sea, and are called Petrels, or rather Peter-
els, from “St. Peter,” in allusion to his walking on the sea, to go to
Jesus.)

Q. Why do candles and lamps spirt when rain is at hand?
A. Because the air is filled with vapour, and the humidity penetrates
the wick; where (being formed into steam) it expands suddenly, and
produces a little explosion.

Q. Why does a drop of water sometimes roll along a piece of hot iron
without leaving the least trace?
A. If the iron be very hot indeed, the bottom of the drop is turned into
vapour, before the drop can evaporate; and the vapour thus formed
buoys the drop up, without allowing it to touch the iron at all.

Q. Why does it roll?
A. The current of air (which is always passing over the heated
surface) drives it along.

Q. Why does a laundress put a little saliva on an ironing-box to know if
it be hot enough?
A. If the saliva sticks to the box and is evaporated, the box is not hot
enough; but if the saliva runs along the box, it is.

Q. Why is the box hotter if the saliva runs along the box, than if it
adheres to it till it is evaporated?
A. If the saliva runs along the box, the iron is hot enough to convert
the bottom of the drop of spittle into vapour; but if the saliva will not

roll, the box is not hot enough to convert the bottom of the drop of
spittle into vapour.

CHAPTER XII.
4.—EVAPORATION.

Q. What is meant by evaporation?
A. The dissipation of liquid by its being converted into vapour.

Q. What effects are produced by evaporation?
A. The liquid vaporized absorbs heat from the body whence it issues;
and the body deprived of the liquid by evaporation, loses heat thereby.

Q. If you wet your finger in your mouth, and hold it up in the air, why
does it feel cold?
A. The saliva quickly evaporates; and (as it evaporates) absorbs heat
from the finger, which makes it feel cold.

Q. If you bathe your temples with ether, why does it allay inflammation
and feverish heat?

A. Ether very rapidly evaporates; and (as it evaporates) absorbs heat
from the burning head, producing a sensation of cold.

Q. Why is ether better for this purpose than water?
A. Because it requires less heat to convert it into vapour; and
therefore it evaporates much more quickly.

(Ether is converted into steam with 104 degs. of heat, but water
requires 212 degs. of heat to convert it into steam.)

Q. Why does ether very greatly relieve a scald or burn?
A. Because it evaporates very rapidly; and (while it is converted into
vapour) carries off the heat of the burn.

Q. Why do we feel so cold when we have wet feet or clothes?
A. As the wet of our shoes or clothes evaporates, it keeps absorbing
heat from the body, which makes it feel cold.

Q. Why do wet feet or clothes give us “cold?”

A. Because the evaporation absorbs heat from the body so abundantly,
that it is lowered below its natural standard; and therefore health is
injured.

Q. Why is it dangerous to sleep in a damp bed?
A. Because the heat of the body is continually absorbed in converting
the damp of the sheets into vapour; and as heat is abstracted from the
body, its temperature is reduced below the healthy standard.

Q. Why do we not feel the same sensation of cold, if we throw a
macintosh over our wet clothes?

A. The macintosh prevents evaporation, because the steam cannot
escape through the air-tight fabric; and (as the wet cannot evaporate
from the clothes) no heat is absorbed from our bodies.

Q. Why do not sailors get cold, who are so often wet all day with sea-
water?

A. The salt of the sea retards evaporation; and (as the heat of the body
is drawn off very gradually) the sensation of cold is prevented.

Q. Why does sprinkling a hot room with water cool it?
A. The heat of the room causes a rapid evaporation of the sprinkled
water; and as the water evaporates, it absorbs heat from the room, and
cools it.

Q. Why does watering the streets and roads cool them?
A. The hot streets and roads part with their heat to promote the
evaporation of the water sprinkled on them.

Q. Why does a shower of rain seem to cool the air in summer-time?
A. The earth (being wet with the rain) parts with its heat to promote
evaporation; and as the earth is cooled, it cools the air also.

Q. Why is linen dried by being exposed to the wind?
A. The air (blowing over the linen) promotes evaporation, by
removing the vapour from the surface of the wet linen, as soon as it is
formed.

Q. Why is linen dried sooner in the open air, than in a confined room?
A. Because the particles of vapour are more rapidly removed from the
surface of the linen by evaporation.

Q. Why are wet summers generally succeeded by cold winters?
A. Because the great evaporation (carried on through the wet summer)
reduces the temperature of the earth lower than usual, and produces
cold.

Q. Why is england warmer than it used to be, when agues were so
common?
A. Because it is better drained and better cultivated.

Q. Why does draining land promote warmth?
A. Because it diminishes evaporation; in consequence of which less
heat is abstracted from the earth.

Q. Why does cultivation increase the warmth of a country?
A. 1st—Because hedges and belts of trees are multiplied;
2ndly—Because the land is better drained;
3rdly—Because the land is dug and ploughed; and
4thly—Because the vast forests are cut down.

Q. Why do hedges and belts of trees promote warmth?
A. Because they retard evaporation, by keeping off the wind.

Q. If belts of trees promote warmth, why do forests produce cold?
A. 1st—Because they detain and condense the passing clouds:
2ndly—They prevent the access of both wind and sun:
3rdly—The soil of forests is always covered with long damp grass,
rotting leaves, and thick brushwood: and
4thly—There are always many hollows in every forest full of stagnant
water.

Q. Why do long grass and rotting leaves promote cold?

A. Because they are always damp; and the evaporation which they
promote, is constantly absorbing heat from the earth beneath.

Q. Why do digging and ploughing help to make a country warm?
A. Digging and ploughing help to pulverize the soil, by admitting air
into it, and this increases its mean temperature.

Q. Why are France and Germany warmer now, than when the vine
would not ripen there?
A. Chiefly because their vast forests have been cut down; and the soil
is better drained and cultivated.

Q. What becomes of the water of ponds and tubs in summer-time?
A. Ponds and tubs in summer-time are often left dry, because their
water is evaporated by the air.

Q. How is this evaporation produced and carried on?
A. The air contains heat, and changes the surface of the water into
vapour; this vapour (blending with the air) is soon wafted away; while

fresh portions of air blow over the water, and produce a similar
evaporation; till the pond or tub is left quite dry.

Q. Why are the wheels of some machines kept constantly wet with
water?

A. To carry off the heat (arising from the rapid motion of the wheels)
by evaporation, as soon as it is developed.

Q. Why is mould hardened by the sun?
A. Because (when the moisture of the mould has been evaporated by
the sun) the earthy particles come into closer contact, and the mass
becomes more solid.

Q. Show the wisdom of god in this arrangement.
A. If the soil did not become crusty and hard in dry weather, the heat
and drought would penetrate the soil, and kill both seeds and roots.

Q. Why is tea cooled faster in a saucer than in a cup?

A. Because evaporation is increased by increasing the surface; and as
tea in a saucer presents a much larger surface to the air, its heat is
more rapidly carried off by evaporation.
(The subject of “convection” will be treated of in a future chapter, and
would scarcely be understood in this place.)

Q. Why is not the vapour of the sea salt?
A. Because the salt is always left behind, by the process of
evaporation.

Q. Why does a white crust appear (in hot weather) upon clothes
wetted by sea water?
A. The white crust is the salt of the water left on the clothes by
evaporation.

Q. Why does this white crust always disappear in wet weather?
A. In wet weather the moisture of the air dissolves the salt; and,
therefore, it no longer remains visible.

Q. Why should not persons, who take violent exercise, wear very thick
clothing?

A. When the heat of the body is increased by exercise, perspiration
reduces the heat (by evaporation) to a healthy standard: as thick
clothing prevents this evaporation, and confines the heat and
perspiration to the body, it is injurious to health.

CHAPTER XIII.
COMMUNICATION OF HEAT.

1.—CONDUCTION.

Q. How is heat communicated from one body to another?
A. 1. By Conduction. 2. By Absorption. 3. By Reflection. 4. By
Radiation: and 5. By Convection.

Q. What is meant by conduction of heat?
A. Heat communicated from one body to another, by actual contact.

Q. Why does a piece of wood (blazing at one end) not feel hot at the
other end?

A. Wood is a bad conductor of heat; and, therefore, heat does not
traverse freely through it: hence, though one end of a stick be blazing-
hot, the other end may be quite cold.

Q. Why do some things feel so much colder than others?
A. Principally because they are better conductors; and, therefore,
draw off the heat from our body (which touches them) so much faster.

Q. What are the best conductors of heat?
A. Dense solid bodies, such as metal and stone.

Q. Which metals are the most rapid conductors of heat?
A. Silver is the best conductor, then copper, then gold or tin, then iron,
then zinc, and then lead.

Q. What are the worst conductors of heat?
A. All light and porous bodies, such as hair, fur, wool, charcoal, and
so on.

Q. Why are cooking vessels so often furnished with wooden handles?

A. Wood is not a good conductor, like metal; and, therefore, many
vessels (which are exposed to the heat of the fire) have wooden
handles, lest they should burn our hands when we take hold of them.

Q. Why is the handle of a metal tea-pot made of wood?
A. As wood is a bad conductor, the heat of the boiling water is not so
quickly conveyed to the wooden handle, nor so quickly poured into the
hand by it, as when the handle is made of metal.

Q. Why would a metal handle burn the hand of the tea-maker?
A. As metal is an excellent conductor, the heat of the boiling water
rushes quickly into the metal handle, and into the hand that touches it.

Q. How do you know that a metal handle would be hotter than a
wooden one?

A. By touching the metal collar into which the wooden handle is
fixed: though the wooden handle is quite cold, this metal collar is
intensely hot.

Q. Why do persons use paper or woollen kettle-holders to take hold
of a kettle with?
A. Paper and woollen are both very bad conductors of heat; and,
therefore, the heat of the kettle does not readily pass through them to
the hand.

Q. Does the heat of the boiling kettle never get through the woollen or
paper kettle-holder?
A. Yes; but though the kettle-holder became as hot as the kettle itself,
it would never feel so hot.

Q. Why would not the kettle-holder feel so hot as the kettle, when it
really is of the same temperature?
A. Because (being a very bad conductor) it disposes of its heat so
slowly, that it is scarcely perceptible; but metal (being an excellent
conductor) disposes of its heat so quickly, that the sudden influx is
painful.

Q. Why then does hot metal feel so much more intensely warm than hot
wool?

A. Because it gives out a much greater quantity of heat in the same
space of time; and the influx of heat is, therefore, more perceptible.

Q. Why does money in our pocket feel so hot, when we stand before a
fire?

A. Metal is an excellent conductor; and, therefore, becomes rapidly
heated. For the same reason it becomes rapidly cold, when it comes in
contact with a body colder than itself.

Q. Why does a pump-handle feel intensely cold in winter?
A. As metal is an excellent conductor, when the hot hand touches the
cold pump-handle, the heat passes rapidly from the hand into the iron;
and this rapid loss of heat produces a sensation of intense coldness.

Q. Is the iron handle of the pump really colder than the wooden pump
itself?
A. No; every inanimate substance (exposed to the same temperature)
possesses the same degree of heat.

Q. Why then does the iron handle seem so much colder than the
wooden pump?

A. Merely because the iron is a better conductor; and, therefore,
draws off the heat from our hand much more rapidly than wood does.

Q. Why does a stone or marble hearth feel to the feet so much colder
than a carpet or hearth-rug?
A. Because stone and marble are good conductors, but woollen
carpets and hearth-rugs are very bad conductors.

Q. Why does the stone hearth make our feet cold?
A. As soon as the hearth-stone has absorbed a portion of heat from our
foot, it instantly disposes of it, and calls for a fresh supply; till the
hearth-stone has become of the same temperature as the foot placed
upon it.

Q. Do not the woollen carpet and hearth-rug, also, conduct heat from
the human body?

A. Yes; (but being very bad conductors) they convey the heat away so
slowly, that it is scarcely perceptible.

Q. Is the cold hearth-stone and warm carpet then of the same
temperature?

A. Yes; everything in the room is really of the same temperature; but
some feel colder than others because they are better conductors.

Q. How long will the hearth-stone feel cold to the feet resting on it?
A. Till the feet and the hearth-stone are both of the same temperature;
and then the sensation of cold in the hearth-stone will go off.

Q. Why would not the hearth-stone feel cold, when it is of the same
temperature as our feet?
A. Because the heat would no longer rush out of our feet into the
hearth-stone, in order to produce an equilibrium.

Q. Why does the hearth-stone (when the fire is lighted) feel so much
hotter than the hearth-rug?

A. The hearth-stone is an excellent conductor; and, therefore, parts
with its heat more readily than the woollen hearth-rug; which (being a
very bad conductor) parts with its heat reluctantly.

Q. Why does parting with heat rapidly make the hearth-stone feel
warm?

A. As the heat of the stone rushes quickly into our foot, it raises its
temperature so suddenly, that we cannot help perceiving the increase
of heat.

Q. Why does the non-conducting power of the hearth-rug prevent its
feeling so hot as it really is?
A. Because it parts with its heat so slowly and gradually, that we
scarcely perceive its transmission into our feet.

Q. When we plunge our hands into a basin of water, why does it
produce a sensation of cold?
A. Though the water (in which we wash) is really warmer than the air
of our bed-room; yet because it is a better conductor, it feels colder.

Q. Why does the conducting power of water make it feel colder than
the air, though in reality it is warmer?
A. Because it abstracts heat from our hands so rapidly, that we feel its
loss; but the air abstracts heat so very slowly, that its gradual loss is
hardly perceptible.

Q. Is water a good conductor of heat?
A. No; no liquid is a good conductor of heat; but yet water is a much
better conductor than air.

Q. Why is water a better conductor of heat than air?
A. Because it is less subtile; and the conducting power of any
substance depends upon its solidity, or the closeness of its particles.

Q. How do you know that water is not a good conductor of heat?
A. Because water may be made to boil at its surface, without
imparting sufficient heat to melt ice a quarter of an inch below the
boiling surface.

Q. Why are not liquids good conductors of heat?
A. Because the heat (which should be transmitted) produces
evaporation, and flies off in the vapour.

Q. Why does a poker (resting on the fender) feel so much colder than
the hearth-rug, which is further off the fire?
A. The poker (being an excellent conductor) draws heat from the hand
much more quickly than the rug, which is a bad conductor: and,
therefore, (though both are equally warm) the poker seems to be much
colder.

Q. Why are hot bricks (wrapped in cloth) employed in cold weather to
keep the feet warm?

A. Bricks are bad conductors of heat, and cloth or flannel still worse:
therefore a hot brick (wrapped in flannel) will retain its heat a very
long time.

Q. Why is a tin pan (filled with hot water) employed as a foot warmer?

A. Because polished tin (being a bad radiator of heat) keeps hot a very
long time; and warms the feet resting upon it.

Q. What is meant by being a “bad radiator of heat?”
A. To radiate heat is to throw off heat by rays, as the sun; a polished
tin pan does not throw off the heat of boiling water from its surface,
but keeps it in.

Q. Why is the tin foot-warmer covered with flannel?
A. 1st—To prevent the perspiration of the foot from taking off the
polish of the tin:
2ndly—Flannel is a very bad conductor; and, therefore, helps to keep
the tin hot longer: and
3rdly—If the feet were not protected, the conducting surface of the tin
would feel painfully hot.

Q. What harm would it be if the polish of the tin were injured by the
perspiration of our feet?
A. Polished tin throws off its heat very slowly; but dull, scratched,
painted, or dirty tin, throws off its heat very quickly: if, therefore, the

tin foot-warmer were to lose its polish, it would get cold in a much
shorter time.

Q. Why are furnaces and stoves (where much heat is required) built of
porous brick?
A. As bricks are bad conductors, they prevent the escape of heat: and
are, therefore, employed where great heat is required.

Q. Why are furnace doors, &c. frequently covered with a paste of clay
and sand?
A. Because this paste is a very bad conductor of heat; and, therefore,
prevents the escape of heat from the furnace.

Q. If a stove be placed in the middle of a room, should it be made of
bricks or iron?
A. A stove in the middle of a room should be made of iron; because
iron is an excellent conductor, and rapidly communicates its heat to
the air around.

Q. Why does the Bible say, that God “giveth snow like wool?”

A. As snow is a very bad conductor of heat, it protects vegetables and
seeds from the frost and cold.

Q. How does the non-conducting power of snow protect vegetables
from the frost and cold?
A. As snow is a bad conductor, it prevents the heat of the earth from
being drawn off by the cold air which rests upon it.

Q. Why are woollens and furs used in cold weather for clothing?
A. Because they are very bad conductors of heat; and, therefore,
prevent the warmth of the body from being drawn off by the cold air.

Q. Do not woollens and furs actually impart heat to the body?
A. No; they merely prevent the heat of the body from escaping.

Q. Where would the heat escape to, if the body were not wrapped in
wool or fur?
A. The heat of the body would fly off into the air; for the cold air
(coming into contact with our body) would gradually draw away its

heat, till it was as cold as the air itself.

Q. What then is the principal use of clothing in winter-time?
A. To keep the body air-tight; and prevent the external air (or wind)
from coming into contact with it, to absorb its heat.

Q. Why are beasts covered with fur, hair, or wool?
A. Because fur, hair, and wool are very slow conductors of heat; and
(as dumb animals cannot be clad like human beings) God has given
them a robe of hair or wool, to keep them warm.

Q. Why are birds covered with down or feathers?
A. Because down and feathers are very bad conductors of heat; and
(as birds cannot be clad like human beings) God has given them a
robe of feathers to keep them warm.

Q. Why are wool, fur, hair, or feathers such slow conductors of heat?

A. Because a great quantity of air lurks entangled between their
fibres; and air is a very bad conductor of heat.

Q. If air be a bad conductor of heat, why should we not feel as warm
without clothing, as when we are wrapped in wool and fur?

A. Because the air (which is cooler than our body) is never at rest;
and, therefore, fresh particles (perpetually passing over our body) keep
drawing off the heat little by little.

Q. Why does the ceaseless change of air tend to decrease the warmth
of a naked body?
A. Thus:—the air which cases the body absorbs as much heat from it
as it can, while it remains in contact; it is then blown away, and makes
room for a fresh coat of air, which does the same.

Q. Does the air (which encases a naked body) become by contact as
warm as the body itself?

A. It would do so, if it remained motionless; but as it remains only a
very short time, it absorbs as much heat as it can in the time, and
passes on.

Q. Why do we feel colder in windy weather, than in a calm day?
A. Because (in windy weather) the particles of air pass over us more
rapidly; and every fresh particle takes from us some portion of heat.

Q. Show the wisdom of God in making the air a bad conductor.
A. If air were a good conductor (like iron and stone) the heat would be
drawn so rapidly from our body, that we must be chilled to death.
Similar evils would be felt also by all the animal and vegetable world.

Q. Does not the bad conducting power of air enable persons to judge
whether an egg be new or stale?
A. Yes; touch your tongue against the shell at the larger end; if it feels
warm to the tongue, the egg is stale; if not, it is new-laid.

Q. Why will the shell of a stale egg feel warm to the tongue?
A. Between the shell and the “white of the egg” there is a small
quantity of air, which expands in a stale egg, from the shrinking of the
white.

Q. Why does the expansion of air (at the end of an egg) make it feel
warm to the tongue?

A. As air is a very bad conductor, the more air an egg contains, the
less heat will be drawn from the tongue when it touches the shell.

Q. Why do ladies fan themselves in summer, to make their faces cool?
A. The fan puts the air in motion, and makes it pass more rapidly over
their face; and (as the temperature of the air is always lower than that
of the human face) each puff of air carries off some portion of heat
from the face.

Q. Does fanning the air make the air itself cooler?
A. No; fanning makes the air hotter and hotter.

Q. Why does fanning the air increase its heat?
A. By causing the air continually to absorb heat from the human body
which it passes over.

Q. If fanning makes the air hotter, how can it make a person feel
cooler?

A. Fanning makes the air hotter, but the face cooler; because it keeps
taking the heat out of the face, and giving it to the air.

Q. Why is broth cooled by blowing it?
A. The breath causes a rapid change of air to pass over the broth; and
(as the air is not so hot as the broth) it keeps absorbing heat, and thus
makes the broth cooler and cooler.

Q. Would not the air absorb heat from the broth just as well without
blowing?

A. No; air is a very bad conductor; unless, therefore, the change be
rapid, the air nearest the surface of the broth would soon become as
hot as the broth itself.

Q. But would not the hot air part with its heat instantly to the
circumjacent air?

A. No; not instantly. Air is so bad a conductor, that it parts with its
heat very slowly: unless, therefore, the air be kept in continual motion,
it would cool the broth very slowly indeed.

Q. Why does wind generally feel cool?
A. Wind is only air in motion; and the more quickly the air passes
over our body, the more rapidly it absorbs the heat therefrom.

Q. Why does air absorb heat more quickly by being set in motion?
A. Because every fresh gust of air absorbs a fresh portion of heat; and
the more rapid the succession of gusts, the greater will be the quantity
of air absorbed.

Q. If the air were hotter than our body, would the wind feel cool?
A. No; if the air were hotter than our body, it would feel insufferably
hot.

Q. Why would the air feel intensely hot, if it were warmer than our
blood?

A. Because then the wind would add to the heat of our body, instead
of diminishing it.

Q. Is the air ever as hot as the human body?
A. Not in this country: in the hottest summer’s day, the air is always
10 or 12 degrees cooler than the human body.

Q. Is the earth a good conductor of heat?
A. No; the power of conducting heat depends upon the continuity of
matter; if the particles of which a thing is composed are not
continuous, they have very little power to conduct heat.

Q. Why is the earth (below the surface) warmer in winter than the
surface itself?
A. Because the earth is a bad conductor of heat; and, therefore
(although the ground be frozen) the frost never penetrates above an
inch or two below the surface.

Q. Why is the earth (below the surface) cooler in summer than the
surface itself?
A. Because the earth is a bad conductor of heat; and, therefore,
(although the surface be scorched with the burning sun) the intense
heat cannot penetrate to the roots of the plants and trees.

Q. Shew the wisdom of God in making the earth a bad conductor.
A. If the heat and cold could penetrate the earth (as freely as the heat
of a fire penetrates iron), the springs would be dried up in summer and
frozen in winter, and all vegetation would perish.

Q. Why is water from a spring so cool in summer?
A. As the earth is a bad conductor, the burning rays of the sun can
penetrate only a few inches below the surface; in consequence of
which, the springs of water are not affected.

Q. Why is it cool under a shady tree in a hot summer’s day?
A. 1st—Because the overhanging foliage screens off the rays of the
sun:

2ndly—As the rays of the sun are warded off, the air (beneath the
tree) is not heated by the reflection of the earth: and
3rdly—The leaves of trees, being non-conductors, allow no heat to
penetrate through them.

Q. Why do the laplanders wear skins, with the fur inwards?
A. The dry skin prevents the wind from penetrating to their body; and
as the fur contains a quantity of air between its hairs (which soon
becomes heated by the body) the Laplander is clad in a case of hot air,
impervious to the cold and wind.

Q. Why does a linen shirt feel colder than a cotton one?
A. Linen is a much better conductor than cotton; and, therefore, (as
soon as it touches the body) it more rapidly draws away the heat, and
produces a sensation of cold.

Q. Why is the face cooled by wiping the temples with a fine cambric
handkerchief?

A. The fine fibres of the cambric have a strong capillary attraction for
moisture; and are excellent conductors of heat: thus the moisture and
heat are both abstracted from the face, and a sensation of coolness is
produced.

“Capillary attraction,” i. e. the attraction of a thread or hair. The wick
of a candle is wet with grease, because the melted tallow runs up the
cotton from capillary attraction.

Q. Why would not a cotton handkerchief do as well?
A. The coarse fibres of cotton have much less capillary attraction, and
are nothing like such good conductors as linen: and, therefore, wiping
the face with a cotton handkerchief, increases the sensation of warmth.

CHAPTER XIV.
2.—ABSORPTION OF HEAT.

Q. What is the difference between conducting heat, and absorbing
heat?
A. To conduct heat, is to transmit it from one body to another through
a conducting medium: to absorb heat, is to suck it up, as a sponge
sucks up water.

Q. Give me an example.
A. Black cloth absorbs, but does not conduct heat: thus, if black cloth
be laid in the sun, it will absorb the rays very rapidly; but if one end of
the black cloth be made hot, it would not conduct the heat to the other
end.

Q. Are good conductors of heat, good absorbers also?
A. No; every good conductor of heat is a bad absorber of it; and no
good absorber of heat can be a good conductor also.

Q. Is iron a good absorber of heat?
A. No; iron is a good conductor, but a very bad absorber of heat.

Q. Why do the fender and fire-irons (which lie upon it) remain cold,
although they are before a good fire?
A. Because the metal fender and fire-irons have very little capacity for
absorbing heat; although they are soon made hot (by conduction),
when placed in contact with the hot fire or stove.

Q. Why does a kettle boil faster, when the bottom and back are
covered with soot?

A. The black soot absorbs heat very quickly from the fire, and the
metal conducts it to the water.

Q. Why will not a new kettle boil so fast as an old one?
A. Because the bottom and sides of a new kettle are clean and bright;
but in an old kettle are covered with soot.

Q. Why would the kettle be slower boiling, if the bottom and back
were clean and bright?
A. Bright metal does not absorb heat, but reflect it (i. e. throw the heat
back again); and as the heat is thrown off from the surface of bright
metal, therefore, a new kettle is longer boiling.

Q. Why do we wear white linen and a black outer dress, if we want to
be warm?
A. The black outer dress quickly absorbs heat from the sun, and
conveys it to the body; and the white linen (being a bad absorbent)
abstracts no heat from the warm body.

Q. Why do persons wear white dresses in summer time?
A. White throws off the heat of the sun by reflection, and is, therefore,
a very bad absorbent of heat; in consequence of which, it never
becomes so hot from the scorching sun as dark colours do.

Q. Why do not persons wear white dresses in winter time?

A. White will not absorb heat, like black and other dark colours; and,
therefore, white dresses are not so warm as dark ones.

Q. What colours are warmest for dresses?
A. For outside garments black is the warmest, and then such colours
as approach nearest to black (as dark blue and green). White is the
coldest colour for external clothing.

Q. Why are dark colours (for external wear) so much warmer than
light ones?

A. Because dark colours absorb heat from the sun more abundantly
than light ones.

Q. How can you prove that dark colours are warmer than light ones?
A. If a piece of black cloth and a piece of white were laid upon snow,
in a few hours the black cloth will have melted the snow beneath;
whereas the white cloth will have produced little or no effect upon it at
all.
N. B. The darker any colour is, the warmer it is, because it is a better
absorbent of heat. The order may be thus arranged:—1. Black

(warmest of all).—2. Violet.—3. Indigo.—4. Blue.—5. Green.—6.
Red.—8. Yellow: and 9. White (coldest of all).

Q. Why are black kid gloves so hot in summer time?
A. 1st—Because the black absorbs the solar heat: and
2ndly—The kid will not allow the heat of the hand to escape through
the glove.

Q. Why are lisle thread gloves so cool in summer time?
A. 1st—Because thread absorbs the perspiration of the hands: and
2ndly—It conducts away the heat of our hot hands.

Q. Are Lisle thread gloves absorbents of heat?
A. As Lisle thread gloves are generally of a grey or lilac colour, they
do not absorb solar heat.

Q. Why is a plate-warmer made of un-painted bright tin?

A. Bright tin reflects (or throws back) the heat, which issues from the
fire in rays; and (by reflecting the heat upon the meat) assists greatly
in roasting it.

Q. Why would not the tin reflector do as well if it were painted?
A. If the tin reflector were painted, it would be utterly spoiled,
because it would then absorb heat, and not reflect it at all. A plate-
warmer should be kept very clean, bright, and free from all scratches.

Q. Why should a reflector be kept so very clean and free from
scratches?

A. If a reflector be spotted, dull, or scratched, it will absorb heat,
instead of reflecting it; and, therefore, would be of no use whatsoever
as a reflector.

Q. Why does hoar-frost remain on tombstones, long after it has
melted from the grass and gravel-walks of a church-yard?
A. Tomb-stones being white, will not absorb heat, like the darker
grass and gravel; and, therefore, the white tombstones (being so much
colder) retain the hoar-frost after it has melted from other things.

Q. If black absorbs heat, why have those who live in hot climates
black skins, and not white skins (which would not absorb heat at all)?

A. Though the black skin of the negro absorbs heat more plentifully
than the white skin of a European, yet the blackness prevents the sun
from blistering or scorching it.

Q. How is it known that the black colour prevents the sun from either
blistering or scorching the skin?

A. If you put a white glove on one hand, and a black glove on the
other (when the sun is burning hot), the hand with the white glove will
be scorched, but not the other.

Q. Which hand will feel the hotter?
A. The hand with the black glove will feel the hotter, but it will not be
scorched by the sun; whereas the hand with the white glove (though
much cooler) will be severely scorched.

Q. Why does the black skin of a negro never scorch or blister with the
hot sun?

A. Because the black colour absorbs the heat,—conveys it below the
surface of the skin, and converts it to sensible heat and perspiration.

Q. Why does the white European skin blister and scorch when exposed
to the hot sun?
A. Because the white will not absorb the heat; and, therefore, the hot
sun rests on the surface of the skin, and scorches it.

Q. Why has a negro black eyes?
A. The black colour of a negro’s eyes defends them from the strong
light of the tropical sun. If a negro’s eyes were not black, the sun
would scorch them, and every negro would be blind.

Q. Why is water kept cooler (in summer time) in a bright tin pot, than
in an earthen one?
A. Because bright metal will not absorb the heat of the summer sun,
like an earthen vessel.

Q. Why is boiling water kept hot in a bright tin vessel longer, than in
an earthen one?
A. Because bright tin will not suffer the heat of the boiling water to
escape in rays, as an earthen vessel does.

CHAPTER XV.
3.—REFLECTION OF HEAT.

Q. What is meant by reflecting heat?
A. To reflect heat, is to throw it back in rays from the surface of the
reflecting body, towards the place from whence it came.

Q. What are the best reflectors of heat?
A. All bright surfaces, and light colours.

Q. Are good absorbers of heat good reflectors also?
A. No; those things which absorb heat best, reflect heat worst; and
those which reflect heat worst, absorb it best.

Q. Why are those things which absorb heat unable to reflect it?
A. Because if any thing sucks in heat like a sponge, it cannot throw it
off from its surface; and if any thing throws off heat from its surface, it

cannot drink it in.

Q. Why are reflectors always made of light-coloured and highly
polished metal?

A. Because light coloured and highly polished metal makes the best of
all reflectors.

Q. Why do not plate-warmers blister and scorch the wood behind?
A. Because the bright tin front throws the heat of the fire back again,
and will not allow it to penetrate to the wood behind.

Q. If metal be such an excellent conductor of heat, how can it reflect
heat, or throw it off?
A. Polished metal is a conductor of heat, only when that heat is
communicated by actual contact; but whenever heat falls upon bright
metal in rays, it is reflected back again, and the metal remains quite
cool.

Q. What is meant by “heat falling upon metal in rays,” and not “by
contact”?

A. If a piece of tin were thrust into a fire, it would be in actual contact
with the fire; but if it be held before a fire, the heat of the fire falls
upon it in rays.

Q. What is the use of the tin screen or reflector used in roasting?
A. The tin reflector throws the heat of the fire back upon the meat;
and, therefore, assists the process of roasting and helps to keep the
kitchen cool.

Q. How does a tin reflector tend to keep the kitchen cool?
A. Because it confines the heat to the hearth, and prevents it from
being dispersed throughout the kitchen.

Q. Why does a lamp glass diminish the smoke of a lamp?
A. As glass is a reflector, it reflects the heat of the lamp back upon the
flame; in consequence of which, less carbon escapes unconsumed (as
smoke).

Q. Why are shoes hotter for being dusty?

A. 1st—Because dust absorbs heat: and
2ndly—As it destroys the blackness of our shoes, it prevents them
from throwing off the heat of our feet in rays.

Q. Why can we not see into the road or street, when a candle is
lighted in a room?
A. Glass is a reflector; and, therefore, throws the rays of the candle
back into the room, and thus prevents our seeing into the road or
street.

Q. Why can persons in the dark street see into a room (lighted by a
candle or lamp)?
A. The pupil of the eye expands greatly, when persons are in the dark;
and, therefore, when any one in the dark street looks into a light room,
his dilated pupil sees every thing distinctly.

Q. Why does it always freeze on the top of a mountain?
A. Air is heated by the reflection of the earth, and not by the rays of
the sun; and, as there is no earth round a mountain-top to reflect heat,
therefore, it remains intensely cold.

CHAPTER XVI.
4.—RADIATION.

Q. What is meant by radiation?
A. Radiation means the emission of rays: thus the sun radiates both
light and heat; that is, it emits rays of light and heat in all directions.

Q. When is heat radiated from one body to another?
A. When the two bodies are separated by a non-conducting medium:
thus the sun radiates heat towards the earth, because the air comes
between (which is a very bad conductor).

Q. On what does radiation depend?
A. On the roughness of the radiating surface: thus if metal be
scratched, its radiating power is increased, because the heat has more
points to escape from.

Q. Does a fire radiate heat?

A. Yes; and because burning fuel emits rays of heat, therefore we feel
warm when we stand before a fire.

Q. Why does our face feel uncomfortably hot, when we approach a
fire?

A. Because the fire radiates heat upon the face; which (not being
covered) feels the effect immediately.

Q. Why does the fire catch the face more than the rest of the body?
A. The rest of the body is covered with clothing, which (being a bad
conductor of heat) prevents the same sudden and rapid transmission of
heat to the skin.

Q. Do those substances which radiate heat, absorb heat also?
A. Yes. Those substances which radiate most, also absorb most heat:
and those which radiate least, also absorb the least heat.

Q. Does any thing else radiate heat, besides the sun and fire?

A. Yes; all things radiate heat in some measure, but not equally well.

Q. What things radiate heat the next best to the sun and fire?
A. All dull and dark substances are good radiators of heat; but all
light and polished substances are bad radiators of heat.

Q. Why does a polished metal tea-pot make better tea than a black
earthen one?
A. As polished metal is a very bad radiator of heat, it keeps the water
hot much longer; and the hotter the water is, the better it “draws” the
tea.

Q. Why will not a dull black tea-pot make good tea?
A. Because the heat of the water flies off so quickly through the dull
black surface of the tea-pot, that the water is rapidly cooled, and will
not “draw” the tea.

Q. Do not pensioners, and most aged cottagers, prefer the little black
earthen tea-pot to the bright metal one?

A. Yes; because they set it on the hob “to draw;” in which case, the
little black tea-pot will make the best tea.

Q. Why will a black tea-pot make better tea than a bright metal one, if
it be set upon the hob to draw?
A. Because the black tea-pot will absorb heat plentifully from the fire,
and keep the water boiling hot: whereas, a bright metal tea-pot (set
upon the hob) would throw off the heat by reflection.

Q. Then sometimes a black earthen tea-pot is the best, and sometimes
a bright metal one?
A. Yes; when the tea-pot is set on the hob “to draw,” the black earth
is the best, because it absorbs heat: but when the tea-pot is not set on
the hob, the bright metal is the best, because it radiates heat very
slowly, and therefore keeps the water hot.

Q. Why does a saucepan which has been used, boil quicker than a new
one?

A. Because the bottom and back are covered with soot; and the black
soot rapidly absorbs the heat of the glowing coals.

Q. Why should the front and lid of a saucepan be clean and bright?
A. As they do not come in contact with the fire, they cannot absorb
heat; and (being bright) they will not suffer the heat to escape by
radiation.

Q. In what state should a saucepan be, in order that it may boil
quickly?

A. All those parts which come in contact with the fire should be
covered with soot, to absorb heat; but all the rest of the saucepan
should be as bright as possible, to prevent the escape of heat by
radiation.

Q. Why is it said that “Saturday’s kettle boils the fastest?”
A. Because on Saturday the front and top of the kettle are generally
cleaned and polished; but the bottom and back of the kettle are never
cleaned.

Q. Why should not the bottom and back of a kettle be cleaned and
polished?

A. Because they come in contact with the fire, and (while they are
covered with black soot) absorb heat freely from the burning coals.

Q. Why should the front and top of a kettle be clean and well
polished?
A. Because polished metal will not radiate heat; and, therefore, (while
the front and top of the kettle are well polished) the heat is kept in, and
not suffered to escape by radiation.

Q. Why is the inside of a kettle and saucepan white?
A. White will not radiate heat: if, therefore, the inside of a boiler be
white, the liquor in it is kept hot much longer.

Q. Why is the bottom of a kettle nearly cold, when the water is
boiling hot?

A. Black soot is a very bad conductor of heat; and, therefore, the heat
of the boiling water is some considerable time, before it gets through
the soot which adheres to the bottom of the kettle.

Q. Why is the lid of a kettle so intensely hot, when the water boils?
A. The bright metal lid of the kettle is an admirable conductor of heat;
and, therefore, the heat from the boiling water pours into our hand the
moment we touch it.

Q. Show the benefit of smoke in cooking.
A. The carbon of the fuel (which flies off in smoke) naturally blackens
all culinary vessels set upon the fire to boil, and thus renders them fit
for use.
(“Culinary vessels” are vessels used in kitchens for cooking, as
saucepans, boilers, kettles, &c.)

Q. How does smoke make culinary vessels fit for use?
A. If it were not for the smoke, (which gathers round a kettle or
saucepan) heat would not be absorbed, and the process of boiling
would be greatly retarded.

Q. Why is boiling water kept hot best in a bright metal pot?

A. Because bright metal being a bad radiator will not throw off the
heat of the boiling water from its surface.

Q. Why is water kept cold in summer-time in a bright metal pot, better
than in an earthen vessel?
A. Because bright metal will not absorb heat from the hot air, like an
earthen vessel; in consequence of which, the water is kept cooler.

Q. Why are dinner-covers made of bright tin or silver?
A. Light-coloured and highly-polished metal is a very bad radiator of
heat; and, therefore, bright tin or silver will not allow the heat of the
cooked food to escape through the cover by radiation.

Q. Why should a meat-cover be very brightly polished?
A. If the cover be dull or scratched it will absorb heat from the hot
food beneath it; and (instead of keeping it hot) will make it cold.

Q. Why should a silver meat-cover be plain, and not chased?

A. If the cover be chased, it will absorb the heat of the food covered
by it; and instead of keeping it hot, will make it cold by absorption.

Q. What is dew?
A. Dew is the vapour of the air condensed, by coming in contact with
bodies colder than itself.

Q. Why is the ground sometimes covered with dew?
A. The earth is more heated by solar rays than the air, during the day;
but at night, the earth parts with more heat than the air, and becomes
(in consequence) 5 or 10 degrees colder.

Q. How does the earth being colder than the air account for the
deposition of dew?
A. As soon as the air touches the cold earth, its warm vapour is
chilled, and condensed into dew.

Q. Why is the surface of the ground colder in a fine clear night, than
in a cloudy one?

A. On a fine clear star-light night, heat radiates from the earth freely,
and is lost in open space: but on a cloudy night, the clouds arrest the
process of radiation.

Q. Why is dew deposited only on a fine clear night?
A. Because, when the night is clear and fine, the surface of the ground
radiates heat most freely; and (being cooled down by this loss of heat)
chills the vapour of the air into dew.

Q. Why is there no dew on a dull cloudy night?
A. The clouds arrest the radiation of heat from the earth; and (as the
heat cannot freely escape) the surface is not sufficiently cooled down
to chill the vapour of the air into dew.

Q. Why is a cloudy night warmer than a fine one?
A. Because the clouds prevent the radiation of heat from the earth;
and, therefore, the surface of the earth remains warmer on a dull
cloudy night.

Q. Why is dew most abundant in situations most exposed?
A. Because the radiation of heat is not arrested by houses, trees,
hedges, or any other thing.

Q. Why is there scarcely any dew under a shady tree?
A. The shady head of the tree both arrests the radiation of heat from
the earth, and also radiates some of its own heat towards the earth;
and, therefore, the ground (underneath a tree) is not sufficiently cooled
down to chill the vapour of the air into dew.

Q. Why is there never much dew at the foot of walls and hedges?
A. 1st—Because the wall or hedge acts as a screen, to arrest the
radiation of heat from the earth: and
2ndly—The wall or hedge also radiates some portion of heat towards
the earth.

Q. How do these things prevent the deposition of dew?
A. As the ground (beneath a wall, tree, or hedge) is not cooled by the
radiation of heat, it remains of the same temperature as the air above

it; in consequence of which, the vapours of the air are not chilled by it
into dew.

Q. Why is there little or no dew beneath a flower-awning, although
that awning be open on all four sides?
A. 1st—Because the awning arrests the radiation of heat from the
ground beneath: and
2ndly—It radiates some of its own heat downwards; in consequence
of which, the ground beneath an awning is not sufficiently cooled
down to chill the vapour of air into dew.

Q. How can a thin covering of bass or even muslin protect trees from
frost?

A. Because any covering prevents the radiation of heat from the tree;
and if the tree be not cooled down by radiation, the vapour of the air
will not be frozen as it comes in contact with it.

Q. Why is the bass or canvass itself (which covers the tree) always
drenched with dew?

A. The bass or canvass covering radiates heat both upwards and
downwards; and is, therefore, so cooled down, that it readily chills all
the vapour of the air (which passes over it) into dew.

Q. Why does snow at the foot of a hedge or wall melt sooner, than in
an open field?
A. Because the hedge or wall radiates heat into the snow beneath,
which melts it.

Q. Why is there no dew after a windy night?
A. 1st—Because the wind evaporates the moisture, as fast as it is
deposited; and
2ndly—It disturbs the radiation of heat, and diminishes the deposition
of dew thereby.

Q. Why are VALLEYS & HOLLOWS often thickly covered with dew,
although they are sheltered?
A. The surrounding hills prevent the repose of air (in the valleys) from
being disturbed; but do not overhang and screen them, so as to arrest
their radiation.

Q. Why does dew fall more abundantly on some things than upon
others?

A. Because some things radiate heat more freely than others, and
therefore become much cooler in the night.

Q. Why are things which radiate heat most freely, always the most
thickly covered with dew?

A. Because the vapour of the air is chilled into dew, the moment it
comes in contact with them.

Q. What kind of things radiate heat most freely?
A. Grass, wood, and the leaves of plants, radiate heat very freely: but
polished metal, smooth stones, and woollen cloth, part with their heat
very tardily.

Q. Do the leaves of all plants radiate heat equally well?
A. No. Rough woolly leaves (like those of a holly-hock) radiate heat
much more freely, than the hard smooth polished leaves of a common
laurel.

Q. Shew the wisdom of God in making grass, the leaves of trees, and
all vegetables, excellent radiators of heat.

A. As vegetables require much moisture, and would often perish
without a plentiful deposit of dew, God wisely made them to radiate
heat freely, so as to chill the vapour (which touches them) into dew.

Q. Will polished metal, smooth stones, and woollen cloth, readily
collect dew?
A. No. While grass and the leaves of plants are completely drenched
with dew, a piece of polished metal, or of woollen cloth (lying on the
same spot) will be almost dry.

Q. Why would polished metal and woollen cloth be dry, while grass
and leaves are drenched with dew?
A. Because the polished metal and woollen cloth part with their heat
so slowly, that the vapour of the air is not chilled into dew as it passes
over them.

Q. Why is a gravel walk almost dry, when a grass plat is covered thick
with dew?

A. Grass, (being a good radiator) throws off its heat very freely; but
gravel (being a very bad radiator) parts with its heat very reluctantly.

Q. Is that the reason why grass is saturated with dew, and the gravel is
not?

A. Yes. When the vapour of warm air comes in contact with the cold
grass, it is instantly chilled into dew; but (as the gravel is not so cold
as the grass) the vapour of air is not so freely condensed as it passes
over the gravel.

Q. Why does dew rarely fall upon hard rocks and barren lands?
A. Rocks and barren lands are so compact and hard, that they can
neither absorb nor radiate much heat; and (as their temperature varies
but very little) very little dew distils upon them.

Q. Why does dew fall more abundantly on cultivated soils, than on
barren lands?

A. Because cultivated soils (being loose and porous) absorb heat
freely during the day, and radiate it by night; and (being much cooled
by the rapid radiation of heat) as the vapour of the air passes over
them, it is plentifully condensed into dew.

Q. Shew the wisdom of God in this arrangement.
A. Every plant and inch of land which needs the moisture of dew, is
adapted to collect it; but not a single drop even of dew is wasted,
where its refreshing moisture is not required.

Q. Shew the wisdom of God in making polished metal and woollen
cloth bad radiators of heat.

A. If polished metal collected dew as easily as grass, it could never be
kept dry, and free from rust. Again, if woollen garments collected dew
as readily as the leaves of trees, we should be often soaking wet, and
subject to constant colds.

Q. Shew how this affords a beautiful illustration of Gideon’s miracle,
recorded in the book of Judges, VI. 37, 38.
A. The fleece of wool (which is a very bad radiator of heat) was
soaking wet with dew: when the grass (which is a most excellent
radiator) was quite dry.

Q. Was not this contrary to the laws of nature?

A. Yes; and was, therefore, a plain demonstration of the power of God,
who could change the very nature of things at his will.

Q. Why do our clothes feel damp, after walking in a fine evening in
spring or autumn?

A. Because the vapour (condensed by the cold earth) lights upon
them, like dew.

Q. Why are windows often covered with thick mist, and the frames wet
with standing water?
A. The temperature of the external air always falls at sun-set, and
chills the window-glass, with which it comes in contact.

Q. How does this account for the mist and water on a window?
A. As the warm vapour of the room touches the cold glass, it is chilled
and condensed into mist; and the mist (collecting into drops) rolls
down the window-frame in little streams of water.

Q. Does the glass of a window cool down more rapidly than the air of
the room itself?
A. Yes; because the air is kept warm by fires, and the animal heat of
the people in the room; in consequence of which, the air of a room
suffers very little diminution of heat from the setting of the sun.

Q. Whence arises the vapour of a room?
A. 1st—The very air of the room contains vapour:
2ndly—The breath and insensible perspiration of the inmates increase
this vapour: and
3rdly—Hot dinners, the steam of tea, &c. contribute to increase it still
more.

Q. What is meant by “the insensible perspiration?”
A. From every part of the human body an insensible and invisible
perspiration issues all night and day; not only in the hot weather of
summer, but also in the coldest day of winter.

Q. If the perspiration be both insensible and invisible, how is it known
that there is any such perspiration?

A. If you put your naked arm into a clean dry glass cylinder, the
perspiration of your arm will soon condense on the glass, like mist.

Q. Why are carriage windows very soon covered with thick mist?
A. The warm vapour of the carriage is condensed the moment it
touches the cold glass, and covers it over with a thick mist.

Q. Why is the glass window cold enough to condense the vapour of
the carriage?
A. Because the inside of the carriage is much warmer than the outside,
and the glass window is made cold by contact with the external air.

Q. Where does the warm vapour of the carriage come from?
A. The warm breath and insensible perspiration of the persons riding
in the carriage, load the air of it with warm vapour.

Q. What is the cause of the pretty frost-work seen on bed-room
windows in winter-time?

A. The breath and insensible perspiration of the sleeper (coming in
contact with the ice-cold window) is frozen by the cold glass, and
forms those beautiful appearances seen in our bed-rooms in a winter
morning.

Q. Why is the glass of a window colder than the walls of a room?
A. Glass is a very excellent radiator; and, therefore, most rapidly
parts with its heat.

Q. Why is a tumbler of cold water made quite dull with mist, when
brought into a room full of people?
A. Because the hot vapour of the room (coming in contact with the
cold tumbler) is condensed upon it; and changes its invisible and
gaseous form for that of a thick mist.

Q. Why is a glass made quite dull, by laying a hot hand upon it?
A. The insensible perspiration of the hot hand is condensed upon the
cold glass, and thus made perceptible.

Q. Why are wine-glasses made quite dull when they are brought into a
room full of company?
A. The hot vapour of the room (coming in contact with the cold wine-
glasses) is condensed upon them, and covers them with vapour like
dew.

Q. Why does this misty appearance go off after a little time?
A. Because the glass becomes of the same temperature as the air of
the room, and will no longer chill the vapour which touches it, and
condense it into mist.

Q. Why is a wine-glass (brought out of a cellar into the air) covered
with a thick mist in summer-time?
A. The vapour of the hot air is condensed by the cold glass, and covers
it as a thick mist.

Q. Why does breathing on a glass make it quite dull?
A. Because the hot breath is condensed by the cold glass; and,
therefore, covers it with a thick mist.

Q. Why do walls stand thick with wet in a sudden thaw?
A. The walls (being thick) cannot change their temperature so fast as
the thin air can; and, therefore, they retain their cold after the thaw has
set in.

Q. How does retaining their cold account for their being so wet?
A. As the vapour of the warm air touches the cold wall, it is chilled
and condensed into water, which sticks to the wall, and sometimes
trickles down in little streams.

Q. Why does a thick well-built house contract more damp of this kind,
than an ordinary one?
A. Because the walls are much thicker; and (if the frost has penetrated
far into the bricks) it takes a long time to reduce them to the same
temperature as the air.

Q. Why are banisters, &c. damp after a thaw?

A. The wooden banister (being made of some very close-grained,
varnished wood) cannot change its temperature so fast as the air; and,
therefore, remains cold some time after the thaw has set in.

Q. How does this account for the banisters being damp?
A. The vapour of the warm air (coming in contact with the cold
banister) is chilled, and condensed into water upon it.

Q. Why is our breath visible in winter and not in summer?
A. In winter the coldness of the air condenses our breath into visible
vapour; but in summer the air is not cold enough to condense it into
visible vapour.

Q. Why are our hair and the brim of our hat often covered with little
drops of pearly dew in winter-time?
A. The breath (issuing from our mouth and nose) is condensed into
drops, as it comes in contact with our cold hair or hat; and (being
condensed) hangs there in little dew-drops.

Q. Why does the steam of a railway boiler often pour down, like fine
rain, when the steam is “let off?”
A. The steam from the steam-pipe (when the air is cold) is condensed
by contact with the chill air, and falls like fine rain.

Q. Why is there less dew when the wind is easterly, than when the wind
is westerly?
A. Easterly winds cross the continent of Europe, and, (as they pass
over land) are dry and arid; but westerly winds cross the Atlantic
Ocean; and (as they pass over water) are moist and full of vapour.

Q. How does the dryness of an eastern wind prevent dew-falls?
A. As the easterly winds are dry, they imbibe the moisture of the air;
and, therefore, there is very little left to be condensed into dew.

Q. How does the moistness of a western wind promote dew-falls?
A. As the westerly winds are saturated with vapour, they require a
very little reduction of heat to cause a copious deposition of dew.

Q. When is dew most copiously distilled?
A. After a hot day in summer or autumn, with the wind in the west.

Q. Why is dew distilled most copiously after a hot day?
A. Because the surface of the earth radiates heat very freely at sunset;
and (becoming thus much colder than the air) chills its vapour, and
condenses it into dew.

Q. Does not air radiate heat, as well as the earth and its various
plants?
A. No. The air never radiates heat, nor is the air itself made hot by the
rays of the sun.

Q. How is the air made hot or cold?
A. By convection of hot or cold currents.

Q. What is meant by “convection of hot and cold currents?”

A. The air (which is heated by the surface of the earth) ascends,
warming the air through which it passes. Other air (being warmed in a
similar way) also ascends, carrying heat; till all the air is made hot.

Q. Is the air made cold in a similar way?
A. Yes. The air resting on the earth is made cold by contact: this cold
air makes the air above it cold; and cold currents or winds shake the
whole together, till all becomes of one temperature.

Q. Why is meat very subject to taint on a moon-light night?
A. In a bright moon-light night, meat radiates heat very freely; and is,
therefore, soon covered with dew, which produces rapid
decomposition.

Q. Why do plants grow rapidly in moon-light nights?
A. In bright moon-light nights rapid radiation is carried on, and dew
is plentifully deposited on young plants, which conduces much to their
growth and vigour.

Q. Why is evening dew injurious to health?
A. Because the condensed vapours are always laden with noxious
exhalations from the earth: this is especially the case in marshy
countries.

Q. Is honey-dew a similar thing to dew?
A. No. Honey-dew is a sweet liquid shed by a very small insect (called
the aphis), and deposited in autumn on the under surface of favourite
leaves.

Q. Does honey-dew injure leaves, or do them good?
A. It injures them very much, because it fills the pores of the leaf with
a thick clammy liquid; and, therefore, prevents the leaf from
transpiring and absorbing.

Q. What effect has honey-dew upon the appearance of a leaf?
A. After a little time, the leaf (being smothered and starved) begins to
turn a dingy yellow.

Q. Are not ants very fond of honey-dew?
A. Yes; and they crawl up the loftiest trees, in order to obtain it.

Q. What is the cause of mist (or earth-fog)?
A. If the night has been very calm, a rapid radiation of heat has taken
place in the earth; in consequence of which, the air (resting on the
earth) is made so cold, that its vapour is chilled, and condensed into a
thick mist.

Q. Why does not the mist become dew?
A. Because the chill of the air is so rapid, that vapour is condensed
faster than it can be deposited; and (covering the earth in a mist)
prevents any further radiation of heat from the earth.

Q. When the earth can no longer radiate heat upwards, does it
continue to condense the vapour of the air?
A. No; the air (in contact with the earth) becomes about equal in
temperature with the surface of the earth itself; for which reason, the

mist is not condensed into dew, but remains floating above the earth
as a thick cloud.

Q. Why does this mist seem to rise higher and higher, and yet remain
quite as dense below as before?
A. The air resting on the earth is first chilled, and chills the air resting
on it; the air which touches this new layer of mist being also
condensed, layer is added to layer; and the mist seems to be rising,
when (in fact) it is only deepening.

Q. Why does mist and dew vanish as the sun rises?
A. Because the condensed vapour is again rarefied by the heat of the
sun, and separated into invisible particles.

Q. Why is a dew-drop round?
A. Because every part of the drop is equally balanced; and, therefore,
there is no cause why one part of the drop should be further from the
centre than another.

Q. Why is the dew-drop on a broad leaf sometimes flattened?

A. Whenever two or more drops of dew roll together, they make one
large spheroid (or flattened drop).

Q. Why will DEW-DROPS ROLL ABOUT CABBAGE-PLANTS,
POPPIES, &c. without wetting the surface?
A. The leaves of cabbages and poppies are covered with a very fine
powder; and the dew-drop rolls over this fine powder, as a drop of rain
over dust, without wetting the surface.

Q. Why does not the drop of rain wet the dust over which it rolls?
A. Because it is driven from grain to grain by capillary repulsion.

Q. Why does not the dew-drop wet the powder of the cabbage-plant?
A. Because it is driven from grain to grain by capillary repulsion.

Q. Why will dew-drops roll over roses, &c. without wetting their
petals?

A. The leaves of a rose contain an essential oil, which prevents them
from absorbing the dew immediately.

Q. Why can a swan or duck dive under water without being wetted?
A. Because their feathers are covered with an oily secretion, which
repels the water.

Q. What is the cause of mist?
A. When currents of air from land mix with currents of air from water,
the currents from the water are condensed into mist by the colder
currents blowing from the land.

Q. Why are the currents of air from the land colder than those
blowing over water?
A. Because the earth radiates heat very freely, and (being greatly
cooled down) cools the air also which comes in contact with it.

Q. Why is not the air, which passes over water, so cool as that which
passes over land?

A. Because water does not cool down at sun-set, so fast as the land
does; and, therefore, the air in contact with it is warmer.

Q. Why does not water cool down so fast as land?
A. 1st—Because the surface of water is perpetually changing, and as
fast as one surface is made cold, another is presented: and
2ndly—The moment water is made cold it sinks, and warmer portions
of water rise to occupy its place: therefore, before the surface of water
is cooled, the whole volume must be made cold; which is not the case
with land.

Q. What is the cause of a “pea-soup” london fog?
A. These fogs (which occur generally in the winter time) are
occasioned thus:—Some current of air (being suddenly cooled)
descends into the warm streets, preventing the rise of the smoke, and
forcing it back in a mass towards the earth.

Q. Why are there not always fogs every night?
A. Because the air will always hold in solution a certain quantity of
vapour, (which varies according to its temperature): and when the air

is not saturated with vapour, it may be condensed without parting
with it.

Q. Why are there ever fogs at night?
A. If the air be pretty well saturated with vapour during the day, as
soon as its capacity for holding vapour is lessened by the cold night, it
deposits some of the superabundant vapour in the form of dew or fog.

Q. Why is there very often a fog over marshes and rivers at night-
time?
A. The air of marshes is almost always near saturation; and, therefore,
the least depression of temperature, will compel it to relinquish some
part of its moisture in dew or fog.

Q. What is the difference between dew and rain?
A. In dew, the condensation is made near the earth’s surface:
In rain, the drops fall from a considerable height; but the cause of
both is the same, viz.—cold condensing the vapour of the air, when it
is near the point of saturation.

Q. Why does mist and fog vanish at sunrise?

A. Because the condensed particles are again changed into invisible
vapour, by the heat of the sun.

Q. What is the difference between a mist and fog?
A. Mist is generally applied to vapours condensed on marshes, rivers,
and lakes.
Fog is generally applied to vapours condensed on land, especially if
those vapours are laden with smoke.

Q. What is the reason why condensed vapour sometimes forms into
clouds, and sometimes into fog?

A. If the surface of the earth be hotter than the air, then the vapour of
the earth (being chilled by the cold air) becomes fog: but if the air be
hotter than the earth, the vapour rises through the air, and becomes
cloud.

Q. If cold air produces fog, why is it not foggy on a frosty morning?
A. 1st—Because less vapour is formed on a frosty day; and
2ndly—The vapour is frozen upon the ground before it can rise from
the earth, and becomes hoar-frost.

Q. Why are fogs more general in autumn than in spring?
A. In spring the earth is not so hot as it is in autumn. In autumn the
earth is generally warmer than the air; and, therefore, the vapour
(issuing from the earth) is condensed into fog by the chill air.

Q. Why are fogs more common in valleys than on hills?
A. 1st—Because valleys contain more moisture than hills: and
2ndly—They are not exposed to so much wind, (which dissipates the
vapour).

Q. How does wind dissipate fogs?
A. Either by blowing them away; or else by dissolving them into
vapour again.

Q. What is hoar-frost?
A. There are two sorts of hoar-frost: 1.—Frozen dew: and 2.—Frozen
fog.

Q. What is the cause of the ground hoar-frost, or frozen dew?
A. Very rapid radiation of heat from the earth; in consequence of
which, the surface is so cooled down, that it freezes the dew
condensed upon it.

Q. Why is hoar-frost seen only after a very clear night?
A. Unless the night has been very clear indeed, the earth will not have
thrown off heat enough by radiation, to freeze the vapour condensed
upon its surface.

Q. Why does hoar-frost very often cover the ground and trees, when
the water of rivers is not frozen?
A. Hoar-frost is not the effect of cold in the air, but the cold of the
earth (produced by excessive radiation); in consequence of which, the
dew (condensed upon it) is frozen.

Q. Why is the hoar-frost upon grass and vegetables much thicker than
that upon lofty trees?

A. Because the air (resting on the surface of the ground) is much
colder after sun-set, than the air higher up; in consequence of which,
more vapour is condensed and frozen there.

Q. Why is the air (resting on the surface of the earth) colder than that
in the higher regions?
A. Because the earth radiates more heat than the leaves of lofty trees;
and, therefore, condenses and freezes the vapour of the air more
rapidly.

Q. Why are evergreens often frost-bitten, when lofty trees are not?
A. Evergreens do not rise far above the surface of the earth; and (as
the air contiguous to the earth is much colder than that in the higher
regions) therefore, the low evergreen is often frost-bitten, when the
lofty tree is uninjured.

Q. Why are tomb-stones covered with hoar-frost, long after it has
melted from every object around?
A. White is a very bad absorbent of solar heat; and, therefore, the
white tomb-stone remains too cold to thaw the frost congealed upon its
surface.

Q. Why is there little or no hoar-frost under shrubs and shadowy
trees?

A. 1st—Because the leafy shrubs and trees arrest the process of
radiation from the earth: and
2ndly—Shrubs and trees radiate a little heat towards the earth; and,
therefore, the ground beneath is never cold enough to congeal the
little dew which rests upon it.

Q. What is the cause of that hoar-frost which arises from frozen fog?
A. The thick fog (which invested the earth during the night) is
condensed by the cold frost of early morning, and congealed upon
every object with which it comes in contact.

CHAPTER XVII.
5.—CONVECTION.

Q. What is meant by the convection of heat?
A. Heat communicated by being carried to another thing or place; as
the hot water resting on the bottom of a kettle, carries heat to the water
through which it passes. (see p. 246).

Q. Are liquids good conductors of heat?
A. No; liquids are bad conductors; and are, therefore, made hot by
convection.

Q. Why are liquids bad conductors of heat?
A. Because heat converts a liquid into steam, and flies off with the
vapour, instead of being conducted through the liquid.

Q. Explain how water is made hot?

A. The water nearest the fire is first heated, and (being heated) rises to
the top; other cold water succeeds, is also heated, and rises in turn;
and this interchange keeps going on, till all the water boils.

Q. Why is water in such continual ferment, when it is boiling?
A. This commotion is mainly produced by the ascending and
descending currents of hot and cold water.
The escape of air from the water contributes also to increase this
agitation.

Q. How do these two currents pass each other?
A. The hot ascending current passes close by the metal sides of the
kettle; while the cold descending current passes down the centre.

Q. Why does boiling water bubble?
A. The bubbles are portions of steam (formed at the bottom of the
vessel) which rise to the surface, and escape into the air.

Q. Why does a kettle run over, when the water boils?

A. As the heat insinuates itself between the particles of water, it drives
them asunder; and (as the particles of water are driven apart from
each other) the same vessel will no longer hold the expanded water,
and some runs over.

Q. Why does a kettle sing, when it is about to boil?
A. Water contains a great deal of air, which (being expanded by the
heat of the fire) escapes by fits through the spout of the kettle; which
sings in the same way as a trumpet does, when a person blows in it.

Q. Why does water boil?
A. Boiling is the effect of a more violent escape of air from the heated
water; when, therefore, the air is not permitted to escape, water will
never boil.

Q. Why is heat applied to the bottom, and not to the top of a kettle?
A. Because the heated water always ascends to the surface, heating
the water through which it passes: if, therefore, heat were applied to
the top of a vessel, the water below the surface would never be heated.

Q. As the lower part of a grate is made red-hot by the fire above, why
would not the water boil, if fire were applied to the top?
A. The iron of a grate is an excellent conductor; and, therefore, if one
part be heated, the heat is conducted to every other part: but water is a
very bad conductor, and will not diffuse heat in a similar way.

Q. How do you know that water is a bad conductor of heat?
A. When a blacksmith immerses his red-hot iron in a tank of water,
the water which surrounds the red-hot iron is made boiling hot, but the
water below the surface remains quite cold.

Q. If you wish to cool liquids, where should the cold be applied?
A. To the top of the liquid; because the cold portion will always
descend, and allow the warmer parts to come in contact with the
cooling substance.

Q. Does boiling water get hotter by being kept on the fire?
A. No; not if the steam be suffered to escape.

Q. Why does not boiling water get hotter, if the steam be suffered to
escape?

A. Because as fast as the water boils, it is converted into steam; and
the steam carries away the additional heat, as fast as it is
communicated.

Q. Is steam visible or invisible?
A. Steam is invisible; but when it comes in contact with the air (being
condensed into small drops) it instantly becomes visible.

Q. How do you know that steam is invisible?
A. If you look at the spout of a boiling kettle, you will find that the
steam (which issues from the spout) is always invisible for about half
an inch; after which, it becomes visible.

Q. Why is the steam invisible for only half an inch, and not either all
invisible or all visible?

A. The air is not able to condense the steam as it first issues from the
spout, but when it spreads and comes in contact with a larger volume
of air, the invisible steam is readily condensed into visible drops.

Q. Why is our breath visible in winter-time?
A. Because it is condensed by the cold air into small drops, which are
visible to the eye.

Q. Why do steam-engines sometimes burst?
A. Steam is very elastic; and this elasticity increases in a greater
proportion than the heat which produces it; unless, therefore, some
vent be freely allowed, the steam heaves and swells, till it bursts the
vessel which confined it.

Q. What becomes of the steam, after it has been condensed?
A. It is dissolved by the air, and forms a part of its invisible vapour.

Q. Is air a good conductor?

A. No; air is a very bad conductor, and is heated (like water) by
convection.

Q. How is a room warmed by a stove?
A. The air nearest the fire is made hot first; the cold air descends, is
heated also, and rises in turn; and this goes on, till all the air of the
room is warmed.

Q. Why are fires placed on the floor of a room, and not towards the
ceiling?

A. As heated air always ascends, if the fire were not near the floor, the
lower part of the air (which we want to be the warmest) would never
be benefited by the fire at all.

Q. If you take a poker out of the fire, and hold the hot end downwards,
why is the handle so intensely hot?
A. Because the hot end of the poker heats the air around it, and this
hot air (in its ascent) scorches the poker, and the hand which holds it.

Q. How should a red-hot poker be carried so as not to burn our
fingers?
A. With the hot end upwards; because then the air (heated by the
poker) would not pass over our hand to scorch it.

Q. Why is a poker (resting on the fender) cold; but if it leans against
the stove, intensely warm?
A. The poker is an excellent conductor; while, therefore, it rests
against the hot stove, the heat of the stove is conducted into the poker;
but when it rests on the fender, it does not come in contact with the
hot stove.

Q. Why does it feel so cold, when it rests on the fender?
A. Not being so warm as our hand, it imbibes the heat from it with
such rapidity, that our loss of heat is palpable, and produces the
sensation of coldness.

Q. Why are flues (which are carried through a church or room)
always blackened with black lead?
A. In order that the heat of the flue may be more readily diffused
throughout the room. Black lead radiates heat more freely than any

other known substance.

Q. Why do country people touch the thick end of an egg with their
tongue, to know if it be stale or not?

A. The thick end of an egg always contains a little air (between the
shell and the white); but, when the egg is stale, the white shrinks, and
the air expands.

Q. How can the tongue tell from this, whether the egg be stale or
fresh laid?

A. As air is a very bad conductor, if the egg be stale, it will feel much
warmer to the tongue, than if it be new-laid.

Q. Why will the big end of an egg feel warmer to the tongue, because it
contains more air?
A. As air is a bad conductor, it will draw off the heat of the tongue
very slowly, and, therefore, appear warm; but when there is only a
very little air in the egg (as the white is a pretty good conductor), the
heat of the tongue will be more rapidly drawn off, and the egg appear
colder.

Q. Why is the large end of an egg cracked, when put into a saucepan
to boil?
A. To let the air out; if the large end were not cracked, the air
(expanded by the heat) would enter the white of the egg, and give it an
offensive taste.

PART II.

AIR.

CHAPTER XVIII.

Q. Of what is atmospheric air composed?
A. Principally of two gases, oxygen and nitrogen; mixed together in
the following proportion: viz. 1 part of oxygen, to 4 parts of nitrogen.

Q. What are the uses of the oxygen of the air?
A. It is the oxygen of the air which supports combustion, and sustains
life.

Q. What is meant when it is said, that the oxygen of the air “supports
combustion?”

A. It means this; that it is the oxygen of the air which makes fuel burn.

Q. How does the oxygen of the air make fuel burn?

A. The fuel being decomposed (by heat) into hydrogen and carbon;
the carbon combines with the oxygen of the air, and produces
combustion.

Q. What does the combination of carbon and oxygen produce?
A. The carbon of the fuel combining with the oxygen of the air makes
carbonic acid gas. (see pp. 36, 37).

Q. What becomes of the hydrogen of the fuel?
A. Hydrogen (being very inflammable) burns with a blaze, and is the
cause of the flame which is produced by combustion. (see p.34).

Q. What becomes of the nitrogen of the air, amidst all these changes
and combinations?
A. The nitrogen of the air escapes, and is absorbed by the leaves of
grass, trees, and various other vegetables.

Q. What is meant when it is said, that oxygen “sustains life”?

A. It means this: if a person could not inhale oxygen, he would die.

Q. What good does this inspiration of oxygen do?
A. 1st—It gives vitality to the blood: and
2ndly—It is the cause of animal heat.

Q. How is food converted into blood?
A. After it is swallowed, it is dissolved in the stomach into a grey
pulp; it then passes into the intestines, and is converted by the “bile”
into a milky substance (called chyle).

Q. What becomes of the milky substance, called chyle?
A. It is absorbed by the vessels called “lacteals,” and poured into the
veins on the left side of the neck.

Q. What becomes of the chyle after it is poured into the veins?

A. It then mingles with the blood, and is itself converted into blood.

Q. How does the oxygen we inhale mingle with the blood?
A. The oxygen of the air mingles with the blood in the lungs, and
converts it into a bright red colour.

Q. What colour is the blood before it is oxydized in the lungs?
A. A dark purple. The oxygen turns it to a bright red.

Q. Why are persons so pale who live in close rooms and cities?
A. The blood derives its redness from the oxygen of the air inhaled;
but, as the air in close rooms and cities is not fresh, it is deficient in
oxygen, and cannot turn the blood to a beautiful bright red.

Q. Why are persons who live in the open air and in the country, of a
ruddy complexion?

A. As the blood derives its bright red colour from the oxygen of the air
inhaled, therefore, country-people (who inhale fresh air) are more
ruddy than citizens.

Q. Why is not the air in cities so fresh as that in the country?
A. Because it is impregnated with the breath of its numerous
inhabitants, the odour of its sewers, the smoke of its fires, and many
other impurities.

Q. How does the combination of oxygen with the blood produce animal
heat?

A. The principal element of the blood is carbon, which (combining
with the oxygen of the air inhaled) produces carbonic acid gas, (in the
same way as burning fuel.) (see pp.33,36).

Q. What becomes of the nitrogen of the air, after the oxygen enters the
blood?
A. The nitrogen is exhaled, and taken up by the leaves of trees and
other vegetables. (see p.35).

Q. Why does the vitiated air (after the oxygen has been absorbed)
come out of the mouth, and not sink into the stomach?

A. The vitiated air (being heated by the heat of the body) ascends
naturally, and passes by the heavier fresh air (which we inhale)
without obstruction or injury.

Q. If (both in combustion and in respiration) the oxygen of the air is
consumed, and the nitrogen rejected—Why are not the proportions of
the air destroyed?
A. Because the upper surface of vegetable leaves (during the day)
gives out oxygen and absorbs nitrogen, and thus the proper balance is
perpetually restored.

Q. Show how God has made animal and vegetable life dependent on
each other?
A. Animals require oxygen to keep them alive, and draw it from the air
by inspiration; the upper surface of leaves (all day long) gives out
oxygen, and thus supplies the air with the very gas required by man
and other animals.

Q. Do not animals exhale the very gas needed by vegetables?

A. Yes; animals reject the nitrogen of the air (as not suited to the use
of animal life), but vegetables absorb it, as it is the food they live on;
and thus the vegetable world restores the equilibrium of the air,
disturbed by man and other animals.

Q. Is air a good conductor?
A. No; air is a very bad conductor.

Q. How is air heated?
A. By “convective currents.”

Q. What are meant by “convective currents?”
A. When a portion of air is heated, it rises upward in a current,
carrying the heat with it: other colder air succeeds, and (being heated
in a similar way) ascends also; and these are called convective
currents.
(“Convective currents;” so called from the Latin words, cum-vectus
(carried with) because the heat is “carried with” the current.)

Q. Is air heated by the rays of the sun?
A. No; air is not heated (in any sensible degree) by the action of the
sun’s rays passing through it.

Q. Why then is the air hotter on a sunny day, than on a cloudy one?
A. On a fine day, the sun heats the surface of the earth, and the air
(resting on the earth) is heated by contact; as soon as it is heated it
ascends, and other air succeeding is heated in a similar way, till all is
heated by convection.

Q. If air be a bad conductor, why does hot iron get cold, by being
exposed to the air?

A. A piece of hot iron exposed to the air, is made cold—1st—By
“convection;” and
2ndly—By “radiation.”

Q. How is hot iron (exposed to the air) made cold by convection?
A. The air around the iron (being intensely heated by contact) rapidly
ascends, carrying some of its heat with it: other air succeeds, absorbs

more heat, ascends, and gives place to that which is colder; till the hot
iron is cooled completely down.

Q. How is hot iron cooled by radiation?
A. While the heat of the iron is being carried off by “convection,” it is
throwing off heat (on all sides) by radiation.

Q. What is meant by radiation?
A. Heat emitted (in all directions) from any surface, by innumerable
rays.

Q. Why is broth cooled by being left exposed to the air?
A. Hot broth throws off some heat by radiation; but it is mainly cooled
down by convection.

Q. How is hot broth cooled down by convection?

A. The air resting on the hot broth (being heated) ascends; colder air
succeeding absorbs more heat, and ascends also; and this process is
repeated, till the broth is made cool.

Q. Why is hot tea and broth cooled faster, for being stirred about?
A. 1st—The agitation assists the liquor in bringing its hottest particles
to the surface:
2ndly—The action of stirring agitates the air, and brings it quicker to
the broth or tea: and
3rdly—As the hottest particles are more rapidly brought into contact
with the air, therefore convection is more rapid.

Q. Why is hot tea, &c. cooled more rapidly by blowing it?
A. Because the heated air is blown more rapidly away; in consequence
of which, cold air more rapidly succeeds to absorb heat from the
surface of the tea or broth.

Q. If a shutter be closed in the day-time, the stream of light (piercing
through the crevice) seems in constant agitation. Why is this?
A. The air (in the sun-beam piercing through the shutter-crevice) is
more heated, than that in its neighbourhood; the convective current,

therefore, is distinctly seen, where little motes and particles of dust are
thrown into agitation by the violence of the current.

Q. Why is the gallery of a church or theatre hotter than the aisle or
pit?
A. The hot air ascends from the bottom to the top of the room, and
cold air (from the doors and windows) flies to the bottom to supply its
place.

Q. Why does a crowded room produce head-ache?
A. Because we breathe air vitiated by the crowd.

Q. How does a crowd vitiate the air of a room?
A. Whenever we breathe, the elements of the air are separated in the
lungs, some of the oxygen is absorbed by the blood, and some of it is
converted into carbonic acid gas, and exhaled with the nitrogen.

Q. Is all the nitrogen rejected by the lungs?

A. Yes; all the nitrogen of the air is always exhaled.

Q. What is carbonic acid gas?
A. As carbon has a very great affinity for oxygen, therefore, whenever
they are exposed to heat, they combine, and form carbonic acid gas (or
what is vulgarly called fixed air).

Q. Is carbonic acid gas wholesome?
A. No; it is quite fatal to animal life; and whenever it is inhaled, it acts
like a narcotic poison, (producing drowsiness which ends in death).

Q. Why is a crowded room unwholesome?
A. Because the oxygen of the air is either absorbed by the lungs, or
substituted for carbonic acid gas, which is a noxious poison.

Q. Mention the historical circumstances, so well known in connection
with the “Black Hole of Calcutta.”

A. In the reign of George II, the Raja (or Prince) of Bengal[12]
marched suddenly to Calcutta to drive the English from the country;

as the attack was unexpected, the English were obliged to submit, and
146 persons were taken prisoners.
[12] The Sur Raja, at Dowlat; a young man of violent passions, who had
but just succeeded to the throne. A. D. 1756.

Q. What became of these prisoners?
A. They were driven into a place about 18 feet square, and 15 or 16
feet in height, with only two small grated windows. 123 of the
prisoners died in one night; and (of the 23 who survived) the larger
portion died of putrid fevers, after they were liberated in the morning.

Q. Why were 123 persons suffocated in a few hours, from
confinement in this close hot prison-hole?
A. Because the oxygen of the air was soon consumed by so many
lungs, and its place supplied by carbonic acid exhaled by the hot
breath.

Q. Why do persons in a crowded church feel drowsy?
A. 1st—Because the crowded congregation inhale a large portion of
the oxygen of the air, which alone can sustain vitality and healthy
action: and
2ndly—The air of the church is impregnated with carbonic acid gas,
which (being a strong narcotic) produces drowsiness in those who

inhale it.

Q. Why did the captives in the black hole die sleeping?
A. 1st—Because the absence of oxygen quickly affects the vital
functions, depresses the nervous energies, and produces a lassitude
which ends in death: and
2ndly—The carbonic acid gas inhaled by the captives (being a
narcotic poison) would also produce drowsiness and death.

Q. Why do persons, who are so much in the open air, enjoy the best
health?

A. Because the air they inhale is much more pure.

Q. Why is country air more pure than the air in cities?
A. 1st—Because there are fewer inhabitants to vitiate the air:
2ndly—There are more trees to restore the equilibrium of the vitiated
air: and
3rdly—The free circulation of air keeps it pure and wholesome (in the
same way as running streams are pure and wholesome, while stagnant
waters are the contrary).

Q. Why does the scantiness of a country population render the country
air more pure?

A. Because the fewer the inhabitants, the less carbonic acid will be
exhaled; and thus country people will inhale pure oxygen, instead of
air impregnated with the narcotic poison, called carbonic acid gas.

Q. Why do trees and flowers help to make country air wholesome?
A. Because trees and flowers absorb the carbonic acid generated by
the lungs of animals, putrid substances, and other noxious exhalations.

Q. Why is the air of cities less wholesome than country air?
A. 1st—Because there are more inhabitants to vitiate the air:
2ndly—The sewers, drains, bins, and filth of a city, very greatly
vitiate the air:
3rdly—The streets and alleys prevent a free circulation: and
4thly—Besides all this, there are fewer trees to absorb the excess of
carbonic acid gas, and restore the equilibrium.

Q. Why are persons who live in close rooms and crowded cities,
generally sickly?

A. Because the air they breathe is not pure, but is both defective in
oxygen, and impregnated with carbonic acid gas.

Q. Where does the carbonic acid of close rooms and cities come from?
A. From the lungs of the inhabitants, the sewers, drains, and so on:
besides, trees and gardens are not numerous enough to absorb the
noxious gas as fast as it is generated.

Q. What becomes of the carbonic acid of crowded cities?
A. Some of it is absorbed by vegetables, and the rest is blown away by
the wind, and diffused through the whole volume of the air.

Q. Does not this constant diffusion of carbonic acid affect the purity
of the whole air?
A. No; because after it is thus diffused, it is carried to various lands,
and absorbed in its passage by the vegetable world.

Q. Why do persons who ascend in balloons feel intense pain in their
eyes and ears?

A. Because the air of the upper regions is more rarefied than the air
on the earth; and the air inside their bodies (seeking to become of the
same rarity) bursts through their eyes and ears, producing an intense
pain.

Q. Why is it often painful, and difficult to breathe, on a mountain top?
A. Because the pressure of air on the mountain top is not so great as
on the plain; and the air inside our bodies (seeking to become of the
same rarity) bursts through the pores of the body, and produces great
pain.

Q. Why do we feel oppressed just previous to a storm?
A. Because the air is greatly rarefied by heat and vapour; and the air
inside us (seeking to become of the same rarity) produces an
oppressive and suffocating feeling.

Q. Why do divers suffer great pain in their eyes and ears under water?
A. Because the air at the bottom of the sea is more dense than the air
on the surface; and while the air inside the diver’s body is settling into
the same density, he feels oppressed with pain, especially in the ears.

Q. Why is this pain felt especially about the ears of a diver?
A. The ear is fitted with a small membrane called the drum (or
tympanum), through which the dense air bursts, and the rupture very
often produces incurable deafness.

Q. Why do our corns ache just previous to rain?
A. Previous to rain, the density of air is greatly lowered (as every one
knows from the fall of the barometer); in consequence of an unequal
pressure, our feet swell; but the hard corn, not being elastic, is
painfully stretched and pressed.
(Some of this pain is due to electricity.)

Q. Why do cellars feel warm in winter?
A. As the external air has not free access into cellars, they remain at a
pretty even temperature, which (in winter time) is about 10 degrees
warmer than the external air.

Q. Why do cellars feel cold in summer time?
A. As the external air has not free access into cellars, they remain at a
pretty even temperature, which (in summer time) is about 10 degrees

colder than the external air.

Q. Why does lightning strike the oak-tree more frequently than any
other tree?

A. 1st—Because the grain of the oak, being closer than that of any
other tree, renders it a better conductor: and
2ndly—The sap of the oak contains a large quantity of iron in
solution, which is a most admirable conductor of lightning.

Q. Why does air rust iron?
A. The oxygen of the air combines with the surface of the iron, and
produces oxide of iron, which is generally called rust.
This rust is a species of combustion.

Q. Why does hot iron scale and peel off, when struck with a hammer?
A. The oxygen of the air very readily unites with the surface of the hot
iron, and forms a metallic oxide (or rust) which scales off when struck
with a hammer.

Q. Does iron rust in dry air?
A. No; iron undergoes no change in dry air.

Q. Why do stoves and fire-irons become rusty, in rooms which are not
occupied?

A. Because the air is damp; and moist air oxidizes (or rusts) iron and
steel.

Q. In what part of the year is it most difficult to keep stoves and fire-
irons bright?

A. In autumn and winter; because the capacity of the air for holding
water being on the decrease, its vapour is deposited on every-thing
with which it comes in contact.

Q. Why does greasing iron prevent its becoming rusty?
A. Because grease prevents the humidity of air from coming in
contact with the surface of the iron.

Q. Why do not stoves rust so frequently as pokers and tongs?
A. Because stoves are generally covered with plumbago, or black lead.

Q. What is plumbago, or black lead?
A. A mixture of charcoal and iron filings.
A most excellent varnish to prevent rust is made of 1 pint of fat oil
varnish, mixed with 5 pints of highly rectified spirits of turpentine,
rubbed on the iron or steel with a piece of sponge. This varnish may
be applied to bright stoves and even mathematical instruments,
without injuring their delicate polish.

Q. Why does ornamental steel (of a purple or lilac colour) rust more
readily than polished white steel?
A. Because the lilac tinge is produced by partial oxidation; and the
process which forms rust has, therefore, already commenced.

Q. How can lilac steel be kept free from rust?
A. By keeping it in a very dry place; for then no additional oxygen
will come in contact with it, to increase its amount of rust.

Q. Do any other metals (besides iron) combine rapidly with oxygen?
A. Yes; copper, lead, mercury, and even silver to some extent.

Q. Why does copper tarnish?
A. The tarnish of copper is caused by its oxidation; that is, the oxygen
of the air combines with the surface of the copper, and instead of
rusting it, covers it with a dark tarnish.

Q. Why does lead lose its brightness, and become dull and of a darker
hue, by being exposed to the air?
A. The vapour of the air combines with the lead, and oxidizes its
surface; but instead of becoming rusty, the surface becomes dull, and
of a darker colour.

Q. Why is it difficult to keep silver bright?
A. Because the vapour of the air oxidizes its surface, and tarnishes it.

Q. Why do silver tea-pots and spoons tarnish more quickly than silver
ore or bullion?
A. Because alloy (of some baser metal) is used to make it more hard
and lasting; and this alloy oxidizes more quickly than silver itself.

Q. Why does German silver turn a dingy yellow in a few hours?
A. German silver has a great affinity for oxygen, and shows its
oxidation by a sickly yellow tarnish, instead of rust.

Q. If quicksilver (or mercury) is tarnished like copper and lead,—Why
does it preserve its brilliancy in barometers and thermometers?
A. Because air is excluded from it, and no moisture comes in contact
with it to oxidize (or tarnish it).

Q. Is gold affected by the atmosphere?
A. Not readily: gold will never combine with oxygen of itself, (or
without aid).

Q. Which of the metals is capable of resisting oxidation altogether?
A. Plat’inum; in consequence of which, the graduated arcs of delicate
instruments for observation are made of plat’inum instead of any other
metal.

Q. Why is plat’inum used for the graduated arcs of delicate
mathematical instruments, instead of any other metal?
A. Because it will never oxidize; but retain its bright surface in all
weathers free from both rust and tarnish.

Q. Before plat’inum was discovered, which of the metals was
employed for the same purpose?
A. Gold.
Platinum, (a white metal), so called from “plata,” the Spanish word for
silver. It was first introduced into England by Mr. Wood, (A. D. 1749)
from South America.

Q. For what other scientific purposes is plat’inum now used?

A. For crucibles in which acids are employed, and for galvanic
batteries.

Q. Why are crucibles (in which acids are employed) made of
plat’inum?

A. Because the acid would act upon other metals, or upon glass, and
prevent the experimenter’s success.

Q. Which of the metals have the greatest affinity to oxygen?
A. Those called potassium and sodium.
Potassium and sodium derive their names from potash and soda.
Potassa is the oxide of potassium; and soda is the oxide of sodium.

Q. How is the affinity of potassium and sodium for oxygen shewn?
A. They decompose water the moment they are brought into contact
with it.

Q. What effect has potassium on water?

A. It catches fire the moment it is thrown into water, and burns with a
vivid flame, which is still further increased by the combustion of
hydrogen separated from the water.
(N.B. Water is composed of oxygen and hydrogen; and potassium
separates the two gases.)

Q. What effect has sodium on water?
A. It does not take fire as potassium does, but undergoes very rapid
oxidation.

Q. Is the furr of kettles an oxide?
A. No; the furr (or deposit of boiling water) is a precipitate of lime
and mineral salt, separated from the water by the process of boiling.

Q. Is not this furr of boiling water often dangerous?
A. Yes; especially in tubular boilers, such as those employed in
railways.

Q. Why is this furr especially troublesome in railway engines?

A. Because it is a bad conductor of heat; in consequence of which, it
hinders the evaporating effect of the fire, and prevents the economy of
fuel.

Q. Why is this furr especially dangerous in railway engines?
A. Because when it is deposited in the boilers, they are likely to
become over-heated; and then explosion will take place from the
sudden generation of highly elastic steam.

Q. Why cannot railway engines be fed with brackish water?
A. Because brackish water contains mineral salt, which makes a much
larger deposit of furr, than that which contains only vegetable matter.

CHAPTER XIX.
CARBONIC ACID GAS.

Q. What is choke damp?
A. Carbonic acid gas accumulated at the bottom of wells and pits,
which renders them noxious, and often fatal.

Q. Why is not this carbonic acid taken up by the air, and diffused, as
it is in cities?
A. Because (being heavier than common air) it cannot rise from the
well or pit; and no wind can get to it to blow it away.

Q. Is carbonic acid wholesome?
A. No; it is fatal to animal life, when inhaled through the mouth;
acting on the stomach, as a narcotic poison (i. e.. a poison which
produces death from drowsiness).

Q. How can any one know, if a place be infested with carbonic acid
gas?

A. If a pit or well contain carbonic acid, a candle (let down into it)
will be instantly extinguished. The rule, therefore, is this—Where a
candle will burn, a man can live; but what will extinguish a candle,
will also destroy life.

Q. Why does a miner lower a candle into a mine, before he descends?
A. Because the candle will be extinguished, if the mine contains
carbonic acid gas: but if the candle is not extinguished, the mine is
safe, and the man may fearlessly descend.

Q. Why are persons sometimes killed, by leaning over beer vats?
A. Vats (where beer has been made) contain a large quantity of
carbonic acid gas, produced by the “vinous fermentation” of the beer;
and when a man incautiously leans over a beer vat, and inhales the
carbonic acid, he is immediately killed thereby.

Q. Why are persons often killed, who enter beer vats to clean them?
A. Carbonic acid (being heavier than atmospheric air) often rests
upon the bottom of a vat: when, therefore, a person enters the vat, and

stoops to clean the bottom, he inhales the pernicious gas, which kills
him.

Q. Why are the jungles of Jarva and Hindostan so fatal to life?
A. Because vast quantities of carbonic acid are thrown off by
decaying vegetables; and (as the wind cannot penetrate the thick
brushwood to blow it away) it settles there, and destroys animal life.

Q. Why are persons sometimes killed by having a charcoal fire in
their bed-rooms?
A. When charcoal is burned, the carbon of the charcoal unites with
the oxygen of the air, and forms carbonic acid gas, which is a narcotic
poison.

Q. Why does the carbonic acid gas of a charcoal fire rise and disperse
itself about the room; whereas the carbonic acid gas of a beer vat
settles near the floor?

A. The carbonic acid gas of a charcoal fire is heated by the
combustion of the fuel, and rises; but the carbonic acid gas of a beer
vat is not heated, and, therefore, rests on the bottom of the vat.

Q. Why do persons throw lime into bins to prevent their offensive
smell, in summer time?

A. Bins contain large quantities of carbonic acid gas, which readily
combines with lime, and produces “carbonate of lime,” which is
entirely free from all offensive odour.

Q. Why do persons throw lime into sewers in summer time?
A. Sewers (like bins) contain large quantities of carbonic acid, which
readily combines with lime, and produces carbonate of lime; and thus
the offensive gas of the sewer is neutralized.

Q. Can carbonic acid be removed in any way besides by lime?
A. Yes; water thrown into a pit will disperse the carbonic acid.

Q. What effect has water on carbonic acid gas?
A. Water (under pressure) absorbs carbonic acid gas; and parts with it
(when the pressure is removed) in the form of effervescence.

Q. Why does aerated water effervesce, when the cork is removed?
A. While the cork was fastened down, the water absorbed the carbonic
acid; but the moment the pressure is removed (by taking out the cork)
the gas is given out with effervescence.

Q. Why does soda water effervesce?
A. Soda water contains 8 times its own bulk of carbonic acid gas,
which makes its escape in effervescence, the moment that the cork is
removed.

Q. Why does ginger pop fly about in froth, when the string of the cork
is cut?
A. All vinous fermentation produces carbonic acid gas. While the cork
is fast, the water of the liquor absorbs the carbonic acid; but the
moment that the pressure is removed, the gas is given off in
effervescence.

Q. Why does bottled ale froth, more than draught ale?

A. Because the pressure is greater in a bottle than in a tub which is
perpetually tapped: and effervescence is always produced in
proportion to the pressure.

Q. Why does bottled ale and porter become “lively” and frothy by
being set before the fire?
A. The heat of the fire expands the air (between the liquid and the
cork), and as this air expands, it presses the liquid down, which causes
effervescence.

Q. What produces the froth of bottled porter?
A. The carbonic acid gas, produced by its vinous fermentation; which
is absorbed by the liquor so long as the bottle is well corked, but is
given off in froth as soon as the pressure of the cork is removed.

Q. What gives the pleasant acid taste to soda water, ginger beer,
champagne, and cider?
A. The presence of carbonic acid, generated by fermentation, and
liberated by effervescence when the pressure of the cork is removed.

Q. Why does fresh spring water sparkle, when poured from one vessel
to another?
A. Because fresh spring and pump water contain carbonic acid; and it
is the presence of this gas which makes the water sparkle.

Q. What is the fermentation of beer and wine?
A. The production of carbonic acid gas and al’cohol.

Q. How is carbonic acid gas produced by fermentation?
A. Malt and fruit both contain sugar; and sugar consists of carbon,
oxygen, and hydrogen. In fermentation, a part of the carbon and
oxygen of the sugar escape, in the form of carbonic acid gas.
Carbonic acid gas is a compound of carbon and oxygen, in the
following proportions:—3 lbs. of carbon and 8 lbs. of oxygen will
form 11 lbs. of carbonic acid gas. Now, 100 lbs. of white sugar
contains 43 lbs. of carbon; 50 lbs. of oxygen; and 7 lbs. of hydrogen.

Q. How is al’cohol produced by fermentation?

A. The hydrogen of the sugar combines with the residue of the oxygen
and carbon to form “al’cohol.”

Q. What is al’cohol?
A. Al’cohol is the spirit of wine or beer, obtained by fermentation.
(100 gallons of alcohol consist of 38 gallons of oxygen; 43-1/2 of
carbon; 15 of hydrogen; and 3-1/2 of nitrogen.)

Q. Why is barley malted?
A. Because germination is produced by the artificial heat; and in
germination the starch of the grain is converted into sugar.

Q. How is barley malted?
A. The barley is moistened with water, and heaped up; by which
means, great heat is produced, which makes the barley sprout.

Q. Why is not the barley suffered to grow, as well as sprout?

A. Plants in the germ contain more sugar than in any other state; as
soon as the germ puts forth shoots, the sugar of the plant is consumed,
to support the shoot.

Q. How is barley prevented from shooting, in the process of malting?
A. The barley is put into a kiln as soon as it sprouts; and the heat of
the kiln checks or destroys the young shoot.

Q. Why is yeast put into beer to make it work?
A. Yeast supplies the beer with nitrogen, which is one of the
ingredients of alcohol.
Alcohol consists of oxygen, carbon, and hydrogen, (obtained from the
sugar of malt), and nitrogen, (obtained from yeast).

Q. Why is it not needful to put yeast into wine?
A. Because fruit contains carbon, hydrogen, oxygen, and nitrogen, in
the form of “gluten;” and, therefore, ferments spontaneously.
(Gluten is explained fully in the Appendix.—Turn to the word in the
Index.)

Q. Does not malt contain carbon, hydrogen, oxygen, and nitrogen, as
well as fruit?
A. No; the sugar of malt contains carbon, hydrogen, and oxygen, but
no nitrogen; in consequence of which, yeast (which contains nitrogen)
is added to the wort.

Q. Why do not grapes ferment while they hang on the vine?
A. 1st—Because the skin lets out the water of the pulp, which causes
the grapes to shrivel and dry up: and
2ndly—The skin prevents the admission of oxygen into the pulp, from
the air without.

Q. What is the froth or scum of fermented liquors?
A. Carbonic acid gas, which (being heavier than common air) settles
on the top of the liquor, in the form of scum.

Q. Why does a small piece of raw meat, or a few raisins improve flat
beer?

A. 1st—Because they supply it with nitrogen to form it into al’cohol.

2ndly—As the raw meat, &c. putrifies, it gives off carbonic acid gas
into the beer, which gives it “life.”

Q. Why is beer flat, if the cask be open too long?
A. Because too much of the carbonic acid gas (produced by
fermentation) is suffered to escape.

Q. How is the carbonic acid gas of beer generated?
A. The saccharine (or sugar) of the malt is converted by fermentation
into carbonic acid gas and alcohol.

Q. Why does beer turn flat, if the vent peg be left out of the tub?
A. Because the carbonic acid gas escapes through the vent hole.

Q. Why will not beer run out of the tub, till the vent peg is taken out?
A. When the tap is turned, air rushes through the tap into the bottom
of the tub, and holds the liquor in.
The upward pressure of air is illustrated by the

following simple experiment:—Fill a wine-glass with water; cover the
top of the glass with a piece of writing paper; turn the glass topsy
turvy, and the water will not run out. The paper is used merely to give
the air a medium sufficiently dense to act against.

Q. Why does the beer run freely, immediately the vent peg is taken
out?
A. As soon as the vent peg is taken out, air rushes through the vent
hole at the top of the tub,—presses the liquor down, and forces it
through the tap.

Q. Why does liquor flow reluctantly out of a bottle held upside down?
A. Because the upward pressure of the air prevents the liquor from
flowing out.

Q. Why should a bottle be held obliquely, in order to be emptied of its
liquor?
A. Because air will then flow into the bottle, and help the liquor out by
balancing the upward pressure.

Q. Why does wine (poured from a bottle quickly) spirt about without
going into the decanter?
A. The liquor fills the top of the decanter (like a cork), and leaves no
room for the air inside to escape; therefore, the decanter (being full of
air) refuses to admit the wine.

Q. Why is beer made stale, by being exposed to the air?
A. Because air absorbs its carbonic acid, which gave it “life.”

Q. Why is porter made stale, by being exposed to the air?
A. Because air absorbs its carbonic acid, which gave it “life.”

Q. Why does the effervescence of soda water and ginger beer so soon
go off?
A. Because air absorbs the carbonic acid, which produced the
effervescence.

Q. Why is boiled water flat and insipid?
A. Because the whole of the carbonic acid is expelled by boiling, and
absorbed by the air.

Q. Why does water become flat and insipid, after it has been drawn
some time?
A. Because air absorbs its carbonic acid; and when its carbonic acid
is absorbed, the water is flat and insipid.

Q. Why should spring water (used for washing) be exposed to the air?
A. Spring water contains carbonic acid; but (by being exposed to the
air) this carbonic acid is absorbed, and the water becomes more soft.

Q. Why does yeast make bread light?
A. Flour contains a small portion of saccharine matter (or sugar); and
the yeast (mixing with this) produces fermentation, as it does in
brewing.

Q. How does fermentation make the dough rise?
A. During fermentation, carbonic acid gas is evolved; but the sticky
texture of the dough will not allow it to escape, so it forces up little
bladders all over the dough.

Q. Why is dough placed before the fire?
A. 1st—Because the heat of the fire increases the fermentation: and
2ndly—It expands the gas which is confined in the little bladders; in
consequence of which, the bladders are blown up larger, and the
dough becomes lighter and more porous.

Q. Why is bread heavy, if the dough be removed from the fire?
A. Because the dough gets cold, and then the air in the bladders
condenses,—the paste falls,—and the bread is close and heavy.

Q. Whence does the heat of fire arise?
A. The carbon of fuel (when heated) combines with the oxygen of the
air, and produces carbonic acid gas: again, the hydrogen of the fuel

combining with other portions of oxygen, condenses into water; by
which chemical actions heat is evolved.

Q. Whence does the heat of our own body arise?
A. The carbon of the blood combines with the oxygen of the air
inhaled, and produces carbonic acid gas; which produces heat in a
way similar to burning fuel.

Q. Whence does the heat of a dunghill arise?
A. The straw, &c. of the dunghill undergoes fermentation as it decays:
the fermentation produces carbonic acid gas, and heat is evolved by a
species of combustion (as in the two former cases).

Q. What changes do vegetables undergo from putrefaction?
A. The hydrogen of the vegetables combines with the oxygen of the
air, and forms water: again, the carbon of the vegetables combines
with oxygen of the air, and forms carbonic acid gas. Putrefaction,
therefore, is only another species of combustion.

Q. What changes do animal bodies undergo from putrefaction?

A. The same as vegetables, with this addition—they give out
ammonia, sulphur, and phosphorus also; which causes the offensive
smell of putrefying animal bodies.

Q. Why is lime heated by a kiln?
A. All marl and chalk abound in carbonic acid; and (when heated by a
fire) the carbonic acid flies off in gas, producing great heat.

Q. What is mortar?
A. Lime mixed with sand and water.

Q. What is lime?
A. Lime-stone burnt produces lime.

Q. Why is the lime-stone burnt, in order to make it into lime?
A. The fire expels the carbonic acid, and converts the hard lime-stone
into a loose powder.

Q. Why does mortar become hard, after a few days?
A. Because the lime re-imbibes the carbonic acid of the air, which was
expelled by fire; and the loose powder again becomes as hard as the
original lime-stone.

Q. Why is mortar adhesive?
A. When the carbonic acid is expelled, the hard lime-stone is
converted into a loose powder, which (being mixed with sand and
water) becomes a soft and sticky plaster; but, as soon as it is placed
between bricks, it imbibes carbonic acid again, and hardens into lime-
stone.

CHAPTER XX.
CARBURETTED HYDROGEN GAS.

Q. What is choke-damp?
A. Carbonic acid gas accumulated at the bottom of wells and pits. It is
called choke damp, because it chokes (or suffocates) every animal that
inhales it. (see p. 264).

Q. What is marsh-gas or fire-damp?
A. Carburetted hydrogen gas accumulated on marshes, in stagnant
waters, and coal pits; it is frequently called “inflammable air.”

Q. What is carburetted hydrogen gas?
A. Carbon combined with hydrogen.

Q. How may carburetted hydrogen gas be procured on marshes?

A. By stirring the mud at the bottom of any stagnant pool, and
collecting the gas (as it escapes upwards) in an inverted glass vessel.

Q. What is coal gas?
A. Carburetted hydrogen extracted from coals, by the heat of fire.

Q. Why is carburetted hydrogen gas called fire-damp, or inflammable
air?
A. Because it very readily catches fire and explodes, when a light is
introduced to it.

Q. Why is carburetted hydrogen gas frequently called marsh gas?
A. Because it is generated in meadows and marshes from putrefying
vegetable substances. (See ignis fatuus, p. 285).

Q. What gas is evolved by the wick of a burning candle?

A. Carburetted hydrogen gas: that is, the carbon and hydrogen of the
tallow combine into a gas from the heat of the flame; and this gas is
carburetted hydrogen, or inflammable air.

Q. Why do coal-mines so frequently explode?
A. Because the carburetted hydrogen gas (which is generated in these
mines by the coals) explodes, when a light is incautiously introduced.

Q. How can miners see in the coal-pits, if they may never introduce a
light?

A. Sir Humphrey Davy invented a lantern for the use of miners, called
“the Safety Lamp,” which may be used without danger.

Q. Who was Sir Humphrey Davy?
A. A very clever chemist, born in Cornwall. (1778—1829).

Q. What kind of thing is the safety lamp?

A. It is a kind of lantern covered with a fine gauze wire, instead of
glass or horn.

Q. How does this fine gauze wire prevent an explosion in the coal
mine?
A. 1st—Because flame will never pass through fine gauze wire: and
2ndly—Though the wire get red-hot, it will not ignite the gas; for
carburetted hydrogen gas can be ignited only by flame.
(N. B. The interstices of the gauze wire must not exceed the 7th of an
inch in diameter.)

Q. Why will not flame pass through very fine wire-gauze?
A. Because the metal wire is a very rapid conductor of heat; and when
the flame of burning gas in the lamp reaches the wire gauze, the heat
(which is needful to produce flame) is conducted away by the wire,
and the flame is extinguished.

Q. Does the gas of the coal-pit get through the wire gauze into the
lantern?

A. Yes; but the inflammable gas ignites and burns inside the lamp: as
soon, however, as this is the case, the miner is in danger, and should
withdraw.

Q. Why is the miner in danger, if the gas ignites and burns in the
inside of the safety-lamp?

A. Because the heat of the burning gas will soon destroy the wire
gauze, and then the flame (being free) will set fire to the mine.

CHAPTER XXI.
PHOSPHURETTED HYDROGEN GAS.

Q. From what does the very offensive effluvia of church-yards arise?
A. From a gas called phosphuretted hydrogen; which is phosphorus
combined with hydrogen gas.

Q. What is phosphorus?
A. A pale amber-coloured substance, resembling wax in appearance.
The word is derived from two Greek words, which mean “to produce
or carry light.” (φῶς-φέρεινφῶς).

Q. How is phosphorus obtained?
A. By heating bones to a white heat; by which means the animal
matter and charcoal are consumed, and what is left is called
“phosphate of lime.”

Q. How is phosphate of lime converted into phosphorus?

A. It is reduced to powder, and mixed with sulphuric acid; which
(being heated and filtered) is converted into phosphorus.

Q. Of what are lucifer matches made?
A. Of phosphorus; and above 250 thousand lbs. of phosphorus are
used every year in London alone, merely for the manufacture of
lucifer matches.

Q. Why does a putrefying dead body smell so offensively?
A. From the phosphuretted hydrogen gas, which always arises from
putrefying animal substances.
The escape of ammonia and sulphur contributes also to this offensive
effluvia.

Q. What is the cause of the ignis fatuus, Jack o’Lantern, or Will o’the
Wisp?
A. This luminous appearance (which haunts meadows, bogs, and
marshes) arises from the gas of putrefying animal and vegetable
substances; especially decaying fish.

Q. What gases arise from these putrefying substances?
A. Phosphuretted hydrogen gas from putrefying animal substances:
and
Carburetted hydrogen, (or inflammable gas) from fermenting
vegetable matters.
Some persons erroneously think that the Aurora Borealis, or
Northern Lights, may be attributed to the same gases, burning in the
upper regions of the air.

Q. How are these gases ignited on bogs and meadows?
A. By the electricity of the air, the rays of the sun, some accidental
spark, the lamp of some traveller, or in some similar way.
And sometimes from the spontaneous combustion of some dung-
heaps, &c. in the locality.

Q. Why does an ignis fatuus or Will o’the Wisp fly from us when we
run to meet it?

A. When we run towards an ignis fatuus, we produce a current of air,
which drives the light gas forwards.

Q. Why does an ignis fatuus run after us, when we flee from it in
fright?
A. When we run away from the ignis fatuus, we produce a current in
the way we run, which attracts the light inflammable gas in the same
course.

Q. Is not a kind of Jack o’Lantern sometimes produced by an insect?
A. Yes; a swarm of luminous insects sometimes passes over a
meadow, and produces an appearance exactly like that of the ignis
fatuus.

Q. May this meteoric appearance be attributed to any other cause,
besides those mentioned?
A. Yes; if many horses, sheep, pigs, or oxen, are pastured on a
meadow, the animal vapour arising from them (strongly electrified by
the air) will ignite, and produce a luminous appearance.

Q. May not many ghost stories have risen from some ignis fatuus
lurking about church-yards?
A. Perhaps all the ghost stories (which deserve any credit at all) have
arisen from the ignited gas of church-yards lurking about the tombs, to

which fear has added its own creations.

CHAPTER XXII.
WIND.

Q. What is wind?
A. Wind is air in motion.

Q. What puts the air in motion, so as to produce wind?
A. The principal causes are the variations of heat and cold, produced
by the succession of day and night, and the four seasons.

Q. What effect has heat upon the air?
A. Heat rarefies the air, and causes it to expand.

Q. How do you know that heat causes the air to expand?
A. If a bladder half full of air (tied tight round the neck), were laid
before a fire, the heat of the fire would expand the air so much, that

the bladder would soon be entirely inflated; (in this case, the air in the
bladder is expanded to twice its original bulk, by the heat of the fire).

Q. What effect is produced upon air by rarefaction?
A. It causes the air to ascend through colder strata, as a cork (put at
the bottom of a basin of water) would ascend through the water.

Q. How do you know that rarefied air ascends?
A. When a boy sets fire to the cotton of his balloon, the flame heats
the air inside the balloon; and the air becomes so light, that it ascends,
and carries the balloon with it.

Q. What effect is produced upon air by cold?
A. Air is condensed by cold, or squeezed into a smaller compass; in
consequence of which, it becomes heavier, and descends towards the
ground.

Q. How do you know that air is condensed by cold?

A. After the bladder is fully inflated, (by lying before the fire), if it be
taken away from the fire, the bladder will collapse, and show that it is
not half full.

Q. What is meant by the bladder “collapsing?”
A. The skin will become wrinkled, shrivelled, and flabby, because
there is not sufficient air inside to fill it out.

Q. How do you know that condensed air will descend?
A. As soon as the cotton of the balloon is burnt out, the air inside
becomes cold again, and the balloon falls to the earth.

Q. Does the sun heat the air as it does the earth?
A. No; the air is not heated by the rays of the sun, because air (like
water) is a very bad conductor.

Q. How is the air heated?
A. By convection, thus:—The sun heats the earth, and the earth heats
the air resting upon it; the air thus heated rises, and is succeeded by

other air, which is heated in a similar way, till all is warmed by
“convective currents.”

Q. What is meant by “convective currents of air?”
A. Streams of air heated by the earth, which rise upwards and carry
heat with them, are called “convective currents” of hot air.

Q. Is the air in a room in perpetual motion, as the air abroad is?
A. Yes; there are always two currents of air in the room we occupy,
one of hot air flowing out of the room, and another of colder air
flowing into the room.

Q. How do you know, that there are these two currents of air in every
occupied room?
A. If I hold a lighted candle near the crevice at the top of the door, the
flame will be blown outward (towards the hall); but if I hold the
candle at the bottom of the door, the flame will be blown inwards
(into the room).

Q. Why would the flame be blown outwards (towards the hall), if the
candle were held at the top of the door?
A. Because as the air of the room is warmed by the fire, &c., it
ascends; and (floating about the upper part of the room) some of it
escapes through the crevice at the top of the door, and thus produces a
current of air outwards (into the hall).

Q. Why would the flame be blown inwards (into the room), if the
candle were held at the bottom of the door?
A. Because after the warm air of the room has ascended to the ceiling,
or made its escape into the hall, &c., a partial vacuum is made at the
bottom of the room; and cold air (from the hall) rushes under the door
to supply the void.

Q. What is meant by a “partial vacuum being made, at the bottom of
the room?”
A. A vacuum means a place from which the air has been taken: and a
“partial vacuum” means, a place from which a part of its air has been
taken away. Thus when the air on the floor ascends to the ceiling, a
partial vacuum is made on the floor.

Q. And how is the vacuum filled UP again?

A. It is filled up by colder air, which rushes (under the door, and
through the window crevices) into the room.

Q. Give me an illustration.
A. If I dip a pail into a pond and fill it with water, a hole (or vacuum)
is made in the pond as big as the pail; but the moment I draw the pail
out, the hole is filled up by the water around.

Q. Show how this illustration applies.
A. The heated air which ascends from the bottom of a room, is as
much taken away, as the water in the pail; and (as the void was
instantly supplied by other water in the pond) so the void of air is
supplied by a current from without.

Q. What is the cause of wind?
A. The sun heats the earth, and the earth heats the air resting upon it;
as the warm air ascends, the void is filled up by a rush of cold air to
the place, and this rush of air we call wind.

Q. Does the wind always blow?
A. Yes; there is always some motion in the air; but the violence of the
motion is perpetually varying.

Q. Why is there always some motion in the air?
A. As the earth is always turning round, the vertical rays of the sun are
always varying.

Q. What do you mean by “the vertical rays of the sun?”
A. The rays made at noon-day: when the sun is in a direct line above
any place, his rays are said to be “vertical” to that place.

Q. How are the vertical rays of the sun always varying?
A. Suppose the brass meridian of a globe to represent the vertical rays
of the sun; as you turn the globe round, different parts of it will pass
under the brass rim, in constant succession.

Q. And is it noon-day to the place over which the sun is vertical?
A. Yes; as each place passes under the brass meridian, it is noon-day
to one half, and mid-night to the other.

Q. Show how this rotation of the earth affects the air.
A. If we suppose the brass meridian to be the vertical sun, the whole
column of air beneath will be heated by the noon-day rays; that part
which the sun has left, will become gradually colder and colder; and
that part to which the sun is approaching, will grow constantly
warmer and warmer.

Q. Then there are three qualities of air about this spot?
A. Yes; the air over the place which has passed the meridian is
cooling: the air under the vertical sun is the hottest; and the air which
is over the place about to pass under the meridian, is increasing in
heat.

Q. How does this variety in the heat of air produce wind?

A. The air always seeks to preserve an equilibrium; so the cold air
rushes to the void, made by the upward current of the warmer air.

Q. Why does not the wind always blow one way, following the direction
of the sun?
A. Because the direction of the wind is subject to perpetual
interruptions from hills and valleys, deserts and seas.

Q. How can hills and mountains alter the course of the wind?
A. Suppose a wind, blowing from the north, comes to a mountain, as it
cannot pass through it, it must either rush back again, or fly off at one
side (as a marble when it strikes against a wall).

Q. Do mountains affect the wind in any other way?
A. Yes; many mountains are capped with snow, and the warm air is
condensed as it comes in contact with them; but as soon as the
temperature of the wind is changed, its direction may be changed also.
Suppose A B C to be three columns of air. A, the column of air which
is cooling down; B, the column to which the sun is vertical; and C, the
column which is to be heated next. In this case the cold air of A will
rush towards B C, because the air of B and C is hotter than A. But
suppose now C to be a snow-capped mountain. As the hot air of B

reaches C, it is chilled; and (being now colder than the air behind) it
rushes back again towards A, instead of following the sun.

Q. How can the ocean affect the direction of the wind?
A. When the ocean rolls beneath the vertical sun, the water is not
made so hot as the land; and (as another change of temperature is
produced) another obstacle is offered to the uniform direction of the
wind.

Q. Why is not the water of the sea made so hot by the vertical sun, as
the surface of the land?
A. 1st—Because the evaporation of the sea is greater than that of the
land:
2ndly—The waters are never still: and
3rdly—The rays of the sun strike into the water, and are not reflected
from its surface, as they are by land.

Q. Why does the evaporation of the sea prevent its surface from being
heated by the vertical sun?

A. As water absorbs heat by being converted into vapour; the surface
of the sea is continually losing heat by evaporation.

Q. How does the motion of the sea prevent its surface from being
heated by the vertical sun?

A. As one portion is heated it rolls away, and is succeeded by another;
and this constant motion prevents one part of the sea from being
heated more than another.

Q. How is the wind affected by the sea?
A. When air from the hot earth reaches the sea, it is often condensed,
and either rushes back again, or else its violence is very greatly
abated.

Q. Do clouds affect the wind?
A. Yes. As passing clouds screen the direct heat of the sun from the
earth, they diminish the rarefication of the air also: and this is another
cause why neither the strength nor direction of the wind is uniform.

Q. Would the winds blow regularly from east to west, if these
obstructions were removed?

A. Without doubt they would. If the whole earth were covered with
water, the winds would always follow the sun, and blow from east to

west. Their irregularity is owing to the interspersion of sea and land,
and the irregularities of the earth’s surface.

Q. Do winds never blow regularly?
A. Yes; in those parts of the world, where these obstructions do not
exist; as on the Atlantic and Pacific Ocean, the winds are pretty
uniform.

Q. What are the winds, which blow over the Atlantic and Pacific
Ocean, called?
A. They are called “Trade Winds.”

Q. Why are they called trade winds?
A. Because (as they blow uniformly in one direction) they are very
convenient to those who carry on trade by means of these oceans.

Q. In what direction do the trade winds blow?

A. That in the northern hemisphere blows from the north-east: that in
the southern hemisphere from the south-east.

Q. Why do they not blow from the full north and south?
A. Because the polar current, combining with the equatorial current,
give the wind a new direction.

Q. What is the cause of the equatorial current?
A. The rotation of the earth upon its axis.

Q. What is the cause of the polar current?
A. As the heat in the torrid zone is always greatest, and at the poles
the least, therefore a constant current of air rushes from the poles
towards the equator.

Q. How does the combination of these two currents give a new
direction to them both?

A. When these currents of air meet at the equator, they clash together,
and fly off in a new direction.

Q. Do trade winds blow from the north-east and south-east all the
year round?

A. Yes, in the open sea; that is, in the Atlantic and Pacific Oceans for
about 30 degs. each side of the equator.

Q. Do the trade winds blow uniformly from north-east and south-east
in the indian ocean?
A. No; nor yet in those parts of the Atlantic and Pacific which verge
on the land.

Q. Why do not the trade winds blow uniformly from north-east and
south-east in the indian ocean?
A. Because when Arabia, Persia, India, and China, are exposed to the
enormous heat of their summer sun, the air is so rarefied, that the
colder air from the south pole rushes towards these nations, and not to
the equator; in consequence of which, a south-west wind is produced
for six months of the year.

Q. How does it blow for the other 6 months?
A. When the sun has left the northern side of the equator for the
southern, then the southern part of the torrid zone is most heated; and
the cold air from the north (rushing towards the southern tropic) is
diverted to the north-east, where it continues for the other six months
of the year.

Q. What are the six-month trade winds called?
A. They are called monsoons; and blow from the north-east from
September to April, and from the south-west for the other six months
of the year.

Q. Have we any regular winds in England?
A. No; our island (having a continent on one side, and a sea on the
other) has a most variable climate.

Q. Have the winds in England no general direction throughout the
year?
A. We generally find that easterly winds prevail during the spring of
the year, and westerly winds are most common in the summer and
autumn.

S-West winds are most frequent in July and August. N-East winds in
January, March, April, May, June; and most seldom in July,
September, and December.

Q. When are the winds in England generally the highest?
A. The winds in December and January are generally the highest.
Those in February and November the next; and those in August and
September the least boisterous.

Q. Why are the winds of Europe generally highest in December and
January?
A. Because the sun is furthest south in those months; and (as the heat
in these northern regions rapidly decreases) the contrast between our
temperature and that of the torrid zone is greater in December and
January, than in any other two months throughout the year.

Q. Why does this contrast of heat increase the violence of the winds?
A. As the air always seeks to preserve an equilibrium, therefore the
greater the contrast, the more violent will be the rush of air to
equalize the two volumes.

Q. Why are the winds in Europe generally the most placid during the
months of September and August?
A. August and September are our warmest months, when we approach
nearer to the heat of the torrid zone than in any other two months;
therefore, the air (to and from the equator) moves with less velocity in
our northern hemisphere.

Q. Show the goodness and wisdom of God in the constant tendency of
air to equilibrium.
A. If the cool air of the polar regions did not rush into the torrid zone,
it would become so hot, that no human being could endure it. If (on
the other hand) the hot air from the torrid zone did not modify the
polar regions, they would soon become insufferably cold.

Q. Why are east winds in England generally dry?
A. Because, as they come over the vast continents of Asia and Europe,
they absorb very little water.

Q. Why does their imbibing so little water make them dry winds?

A. Being thirsty when they reach our island, they readily imbibe
moisture from the air and clouds; and, therefore, bring dry weather.

Q. Why is the north wind in England generally cold?
A. The north wind comes from the polar regions, over mountains of
snow, and seas of ice; in consequence of which, it is very cold.

Q. Why are north winds in England generally dry and biting?
A. As they come from regions colder than our own, they are warmed
by the heat of our island; and (as their temperature is raised) they
absorb moisture from every thing they touch; in consequence of
which, they are both dry and parching.

Q. Why is the south wind generally warm in England?
A. The south wind comes over the hot sandy deserts of Africa, and is
heated by the land it traverses.

Q. Why does the south wind often bring us rain?

A. The south wind (being much heated by the hot sands of Africa)
imbibes water very plentifully, as it passes over the Mediterranean Sea
and British Channel.

Q. Why does the saturation of the south wind cause rain?
A. As soon as it reaches our cold climate, it is condensed, and its
vapour is squeezed out (as water from a wet sponge).

Q. Why are west winds in England generally rainy?
A. The west winds come over the Atlantic Ocean, and are laden with
vapour: if, therefore, they meet with the least chill, some of the vapour
is squeezed out.

Q. Why is a fine clear day sometimes overcast in a few minutes?
A. Because some sudden change of temperature has condensed the
vapour of the air into clouds.

Q. Why are clouds sometimes dissipated quite as suddenly?
A. Because some dry wind (blowing over the clouds) has imbibed
their moisture, and carried it off in invisible vapour.

Q. Why does a south-west wind bring us rain?
A. As it comes from the torrid zone, and crosses the ocean, the hot
wind is laden with vapour; and as some of the heat escapes (as soon as
it reaches our northern island) the vapour is condensed, and
precipitated as rain.

Q. Why does a north-east wind rarely bring rain?
A. As it comes from a climate colder than our own, its capacity for
imbibing vapour is increased when it reaches our island; in
consequence of which, it dries the air, dispels the clouds, and
promotes evaporation.

Q. Why does wind sometimes bring rain, and sometimes fine weather?
A. If the wind be colder than the clouds, it will condense their vapour
into rain: if the wind be warmer than the clouds, it will dissolve them,

and cause them to disappear.

Q. Why are March winds dry?
A. Because they generally blow from the east or north-east; and,
therefore, sweep over the continent of Europe.

Q. What is the use of March winds?
A. They dry the soil (which is saturated with the floods of February),
break up the heavy clods, and fit the land for the seeds which are
committed to it.

Q. Why does “March come in like a lion?”
A. Because it comes in with blustering east winds, which are essential
to dry the soil, which would otherwise rot the seed committed to it.

Q. Why does “March go out like a lamb?”
A. Because the water (evaporated by the high winds) falls again in
showers to fertilize the earth, and breaks the violence of the winds.

Q. Why is it said that “A bushel of March dust is worth the king’s
ransom?”
A. Because it indicates that there has been a continuance of dry
weather; and unless March be dry, the seed will rot in the wet soil.

Q. Why is it said “A dry cold March never begs bread?”
A. Because the dry cold winds of March prepare the soil for seeds,
which germinate, and produce fruit in the autumn.

Q. Why is it said that “A wet March makes a sad autumn?”
A. Because, if March be wet, so much of the seed rots in the ground,
that the autumn crops are spoiled.

Q. Why is it said that “March flowers make no summer bowers?”
A. Because, if the spring be very mild, vegetation gets too forward,
and is pinched by the nightly frosts, so as to produce neither fruits nor
flowers.

Q. Why is it said “A late spring makes a fruitful year?”
A. Because if the vegetation of spring be backward, the frosty nights
will do no harm; for the fruits and flowers will not put forth their
tender shoots, till the nights become too warm to injure them.

Q. Why is it said that “April showers bring May flowers?”
A. Before seeds can germinate, three things are essential:—Darkness,
Heat, and Moisture. April showers supply the principal nourishment
on which seeds depend for existence.

Q. Does rain-water possess any fertilizing properties besides that of
mere moisture?
A. Yes; rain-water contains “ammonia,” to which much of its
fertilizing power may be attributed.
(Ammonia is a compound of nitrogen and hydrogen. Common
hartshorn is only ammonia and water.)

Q. Why has God made November a very rainy month?

A. Because the rain hastens the putrefaction of the fallen leaves, and
this makes the earth fertile.

Q. Why is there more rain from September to March than from March
to September?
A. From September to March, the temperature of the air is constantly
decreasing; on which account, its capacity for holding vapour is on
the decrease, and the vapour is precipitated as rain.

Q. Why is there less rain from March to September, than from
September to March?
A. From March to September, the temperature of the air is constantly
increasing; on which account, its capacity for holding vapour is on the
increase, and very little is precipitated as rain.

Q. Why is the rising sun in summer accompanied with a breeze?
A. Because the heat of the rising sun stops the radiation of heat from
the earth, and warms its surface.

Q. How does this warmth produce a breeze?
A. The air (resting on the earth’s surface) is warmed by contact,
ascends upwards, and colder air rushes in to fill up the void, which is
the cause of the morning breeze.

Q. Why is there often an evening breeze during the summer months?
A. The earth radiates heat at sun-set, and the air is cooled down
quickly by contact: this condensation causes a motion in the air, which
is the evening breeze.

Q. Why are tropical islands always subject to a sea-breeze every
morning (i. e.. a breeze blowing from the sea to the land)?

A. The solar rays are unable to heat the surface of the sea as they do
the earth; therefore, the air resting on the earth is more heated than
the air resting on the sea; and the colder sea air blows inland to
restore the equilibrium.

Q. Why is the land breeze unhealthy?

A. Because it is frequently loaded with exhalations from putrefying
animal and vegetable substances.

Q. Why is the sea breeze fresh and healthy?
A. Because it passes over the fresh sea, and is not laden with noxious
exhalations.
It is healthy, therefore, to walk on the sea-beach before ten o’clock in
the morning; but unhealthy after sun-set.

Q. Why is there generally a fresh breeze from the sea (in English
watering places) during the summer and autumn mornings?
A. As the land is more heated by the sun than the sea; therefore, air
resting on the land is hotter than air resting on the sea; in consequence
of which, cooler sea air glides inland, to restore the equilibrium.

Q. Why does the sea breeze feel cool?
A. As the sun cannot make the surface of the sea so hot as the surface
of the land; therefore, the air which blows from the sea, feels cooler
than the air of the land.

Q. Why are tropical islands subject to a land breeze every evening (i.
e.. a breeze blowing from the land towards the sea)?
A. The surface of land cools down faster (after sun-set) than the
surface of the sea: in consequence of which, the air of the cold land is
condensed, sinks down, and spreads itself into the warmer sea air,
causing the land breeze.

Q. Why is the land breeze cool?
A. As the surface of the land is cooled at sun-set quicker than the
surface of the sea; therefore, the seaman feels the air from the land to
be chill.

Q. Why is the temperature of islands more equable than that of
continents?

A. Because the water around the island absorbs the extreme heat of
summer, and gives out heat to mitigate the extreme cold of winter.

Q. Why does the sea round an island give out heat in winter?
A. Unless the sea be frozen (which is rarely the case), it is warmer
than the frozen land; and, therefore, the warmth of the sea air (mixing
with the cold land air) helps to mitigate the intense cold.

Q. Why are there waves in the sea?
A. The wind (acting on the surface of the sea) piles up ridges of water,
which leave behind an indentation: as the water on all sides rushes to
fill up this indentation, the disturbance spreads on all sides, and billow
rolls after billow.

Q. Why does wind in England generally feel cold?
A. Because a constantly changing surface comes in contact with our
body, to draw off its heat.

Q. Why is a room (even without a fire) generally warmer than the open
air?

A. As the air in a room is not subject to much change, it soon becomes
of the same temperature as our skin, and no longer feels cold.

Q. Why do we generally feel colder out-of-doors?
A. Because the air (which surrounds us) is always changing; and as
fast as one portion of air has become warmer by contact with our

body, another colder portion surrounds us to absorb more heat.

Q. Why are hot foods made cool by blowing them?
A. Blowing causes the air (which covers the hot food) to change more
rapidly; in consequence of which, the hot air is quickly blown away,
and gives place to fresh cold air.

Q. Why do ladies fan themselves in hot weather?
A. By the action of the fan, fresh particles of air are perpetually
brought in contact with the face, and every fresh particle of air
absorbs some heat from the skin.

Q. Does the fan cool the air?
A. No; it makes the air hotter, by imparting to it the heat out of our
face: but it cools the face blown upon, by transferring its heat to the
air.

Q. Is the air in summer time ever so hot as our bodies?

A. No, not in England. In the hottest day in summer, the air of
England is 15 or 20 degrees cooler than the human body.

Q. How fast does wind travel?
A. A gentle breeze goes at about the rate of 5 miles an hour. A high
wind from 20 to 60. A hurricane from 80 to 100 miles an hour.

Q. How is the velocity of winds ascertained?
A. By observing the velocity of the clouds, and by an instrument for
the purpose.
This instrument is called an Anemometer.

Q. How is the velocity of the clouds ascertained?
A. By observing the speed of their shadow along the ground; which is
found in a high wind to vary from 20 to 60 miles an hour.

Q. Why is there always a strong draught through the keyhole of a
door?

A. As the air of the room we occupy is warmer than the air in the hall,
therefore the cold hall air rushes through the keyhole into the room,
and causes a draught.

Q. Why is there always a strong draught under the door, and through
the crevice on each side?
A. The cold air rushes from the hall under the door, &c. into the room,
to supply the void caused in the room (by the escape of warm air up
the chimney, &c.)

Q. Why is there always a draught through the window crevices?
A. The external air (being colder than the air of the room we occupy)
rushes through the window crevices to supply the deficiency, caused
by the escape of air up the chimney, &c.

Q. Why is there more draught if you open the lower sash of a window,
than if you open the UPPER sash?
A. If the lower sash be open, the cold external air will rush more
freely into the room; but if the upper sash be open the heated air of the
room will rush out; and (of course) there will be less draught.

Q. By which means is the room better ventilated, by opening the lower
or the upper sash?
A. A room is better ventilated by opening the upper sash; because the
hot vitiated air (which always ascends towards the ceiling) can better
escape.

Q. By which means is a hot room more quickly cooled—By opening
the upper or the lower sash?
A. A hot room is cooled more quickly by opening the lower sash;
because the cold air can enter more freely by an under current, than by
one higher up.

Q. Why does wind dry damp linen?
A. Because dry wind (like a dry sponge) imbibes the particles of
vapour from the surface of the linen, as fast as they are formed.

Q. Which is the hottest place in a church, chapel, or theatre?
A. The gallery.

Q. Why is the gallery of all public places hotter than the lower parts
of the building?
A. Because the heated air of the room ascends, and all the cold air
(which can enter through the doors and windows) keeps to the floor,
till it has become heated.

Q. Why do plants often grow out of walls and towers?
A. Because sometimes the wind blows the seed there with the dust;
and sometimes birds (flying over) drop the seed which they had
formerly eaten.

CHAPTER XXIII.
BAROMETER.

Q. What is a barometer?
A. A weather-glass, or instrument to show the changes of the weather,
by marking the variations in the weight of air.

Q. What is a thermometer?
A. An instrument to show how hot or cold anything is.

Q. What is the difference between a thermometer and a barometer?
A. In a thermometer the mercury is sealed up from the air:
In a barometer the mercury is left exposed (or open) to the air.

Q. If the mercury of the thermometer be sealed up from the air, how
can the air affect it?

A. The heat of the air passing through the glass tube into the mercury,
causes it to expand more or less, and rise in the tube accordingly.

Q. Why is the tube of a barometer left open?
A. That the air may press upon it freely; and as this pressure is more
or less, the mercury rises or falls in the tube.

Q. How can weather be affected by the weight of the air?
A. When air is warm or moist, it is lighter than usual:
When it is cold or dry, it is heavier: and as a barometer marks whether
the air be light or heavy, it indicates these changes.

Q. How can you tell (by looking at a barometer) what kind of weather
it will be?
A. Because the mercury in the tube rises and falls, as the air becomes
lighter or heavier: and we can generally tell by the weight of the air,
what kind of weather to expect.

Q. Does the weight of the air vary much?

A. Yes; the atmosphere in England varies as much as one-tenth part
more or less.

Q. What is the chief use of a barometer?
A. To warn sailors how to regulate their ships, before squalls come
on.

Q. How can a barometer warn sailors to regulate their ships?
A. As the barometer will tell when wind, rain, or storm is at hand, the
sailor can make his ship trim before it overtakes him.

Q. Are there any rules which can be depended on?
A. Yes; there are ten special rules to direct us how to know the
changes of weather, by marking the mercury of a barometer.

Q. What is the 1ST SPECIAL RULE in regard to the barometer?

A. The barometer is highest of all during a long frost; and it generally
rises with a north-east wind.

Q. Why is the barometer highest of all during a long frost?
A. Because long frost condenses the air very greatly; and the more air
is condensed, the greater is its pressure on the mercury of the
barometer.

Q. Why does the barometer generally rise with a north-east wind?
A. Because north-east winds make the air both cold and dry: the air,
therefore, is both condensed, and without vapour.

Q. What is the 2ND SPECIAL RULE in regard to the barometer?
A. The barometer is lowest of all during a thaw which follows a long
frost: it generally falls with south and western winds.

Q. Why does the barometer fall lowest of all at the breaking up of a
long frost?

A. 1st—Because the air (which had been much dried by the frost)
absorbs the moisture of the fresh warm current of wind from the south
or south-west: and
2ndly—The air (which had been much condensed by the frost) is
suddenly expanded by the warm wind which is introduced.

Q. Why does the barometer fall very low with south and west winds?
A. Because south and west winds come heavily laden with vapour;
and vaporized air is lighter than dry air.

Q. What effect has wind on the mercury?
A. All winds make the barometer drop, except eastern winds: those
winds which blow from the south, and south-west make it drop the
lowest.

Q. Why do winds generally make the mercury of a barometer drop?
A. Wind is caused by a partial vacuum in some parts of the globe; and
as the air rushes in to supply this deficiency, its general pressure is
lessened, and the barometer falls.

Q. What is the 3RD SPECIAL RULE in regard to the barometer?
A. While the barometer stands above 30°, the air must be very dry or
very cold, or perhaps both, and no rain may be expected.

Q. Why will there be no rain if the air be very dry?
A. If the air be very dry it will absorb moisture, and not part with what
it has in rain.

Q. Why will there be no rain if the air be very cold?
A. If the air be very cold it is so much condensed, that it has already
parted with as much moisture as it can spare.

Q. What is the 4TH SPECIAL RULE in regard to the barometer?
A. When the barometer stands very low indeed, there is never much
rain, although a fine day will seldom occur at such times.

Q. What kind of weather will it be when the barometer is unusually
low?

A. There will be short heavy showers, with sudden squalls of wind
from the west.

Q. Why will there be very little rain if the barometer be unusually
low?

A. Because the air must be very warm, or very moist, or perhaps both.

Q. Why will there be little or no rain, if the air be very warm?
A. If the air be very warm it will have a tendency to imbibe more
moisture, and not to part with what it has.

Q. Why will there be little or no rain if the air be moist, and the
barometer remains very low?
A. If the air be ever so moist, rain will never fall till cold air has been
introduced to condense the vapour; and the moment that the cold air is
introduced, the barometer will rise.

Q. What is the 5TH SPECIAL RULE in regard to the barometer?
A. In summer-time (after a long continuance of fair weather) the
barometer will fall gradually for 2 or 3 days before rain comes; but if
the fall of the mercury be very sudden, a thunder-storm is at hand.

Q. What is the 6TH SPECIAL RULE in regard to the barometer?
A. When the sky is cloudless, and seems to promise fair weather, if the
barometer be low, the face of the sky will soon be suddenly overcast.

Q. What is the 7TH SPECIAL RULE in regard to the barometer?
A. Dark dense clouds will pass over without rain, when the barometer
is high; but if the barometer be low, it will often rain without any
gathering of clouds.

Q. What is the 8TH SPECIAL RULE in regard to the barometer?
A. The higher the barometer, the greater is the probability of fair
weather.

Q. Why is the barometer high in fine weather?
A. Because the air contains but very little vapour. The drier the air, the
higher does the mercury of the barometer rise.

Q. What is the 9TH SPECIAL RULE in regard to the barometer?
A. When the mercury is in a rising state, fine weather is at hand; but
when the mercury is in a sinking state, foul weather is near.

Q. Why does the mercury rise at the approach of fine weather?
A. Because the air is becoming more dry, and therefore its pressure is
greater.

Q. Why does the mercury sink at the approach of foul weather?
A. Because the air is laden with vapour, or disturbed by wind.

Q. Why does vapour in the air make the mercury sink?

A. Because vaporized air is lighter than dry air, and therefore its
pressure is less on the mercury of the barometer.

Q. What is the 10TH SPECIAL RULE in regard to the barometer?
A. If (in frosty weather) it begins to snow, the barometer generally
rises to 32°, where it remains as long as the snow continues to fall; if,
after this, the weather clear up, you may expect very severe cold.

Q. How can you know if the mercury of the barometer be rising?
A. If it be convex (i. e. higher in the middle than at the sides;) it is in a
rising state.

Q. How can you tell if the mercury of the barometer be about to fall?
A. If it be concave (i. e. hollow in the middle) it is in a falling state.

Q. Why is the mercury convex when it is rising?

A. The sides of the mercury rub against the glass tube, and are
delayed by it, so that the middle part rises faster than the sides.

Q. Why is the mercury concave when it is falling?
A. The sides of the mercury rub against the glass tube, and are
delayed by it, so that the middle part sinks faster than the sides.

Q. What effect does a thunder-storm produce on the weather?
A. Thunder is generally preceded by hot weather, and followed by cold
and showery weather.

Q. What effect does a sudden change produce on the weather?
A. A great and sudden change (either from hot to cold, or from cold to
hot) is generally followed by rain within 24 hours.

Q. Why is a sudden change from hot to cold followed by rain?

A. The cold condenses the air and its vapour; which, being condensed
and squeezed out, falls in rain.

Q. Why is a sudden change from cold to hot followed by rain?
A. Because the air is quickly saturated with moisture; and as soon as
night comes on, the temperature is lowered again, and some of the
abundant moisture falls in rain.

Q. Why is the air quickly saturated with moisture, when heat succeeds
rapidly from cold?
A. Because the evaporation (which was checked by the cold) is
carried on very rapidly, in consequence of the diminished pressure of
the air.
(N. B. The less the pressure of the air, the more rapidly it evaporates
moisture.)

Q. When does the barometer vary most?
A. In winter time.

Q. Why does the barometer vary more in winter than in summer time?
A. Because the difference of temperature between the torrid and
temperate zones is so great, that the state of the air is perpetually
disturbed by their mixing together.

Q. When does the barometer vary least?
A. In summer time.

Q. Why does the barometer vary less in summer than in winter time?
A. Because the temperature of our island is so nearly equal to that of
the torrid zone, that its state is not much disturbed by interchange of
currents.

Q. What effect has wind on the barometer?
A. North and east winds make the mercury rise; all other winds make
it sink; but south and west winds make it sink lower than any other
winds.

Q. Have heat and cold any effect on the barometer?
A. No, not of themselves; but because cold weather is generally either
dry, or rough with north-east winds, therefore the mercury rises in
cold weather; and because warm weather is often moist or fanned by
south-west winds, therefore, the mercury sinks.

Q. Why is the mercury of a barometer lower in the torrid than in the
frigid zones?

A. Because the warm air of the torrid zone contains much more
vapour than the condensed air of the frigid zone; and the moister the
air, the less is its pressure.

Q. In what months is the barometer highest?
A. In May and August; next to these, in June, March, September, and
April.

Q. In what months is the barometer lowest?
A. In November and February; then in October, July, December, and
January.

Q. What are the driest months?
A. March and June; then May and August; then April and November.

Q. What are the wettest months?
A. October and February; then July and September; then January and
December.

Q. Why is there less wet from March to August, than there is from
August to March?
A. Because the heat is constantly increasing; and the capacity of the
air to absorb and retain moisture increases likewise.

Q. Why is there more wet from August to March, than there is from
March to August?
A. Because the heat is constantly decreasing, and the capacity of the
air to retain moisture decreases also; so that (although it often rains)
yet the air is always on the point of saturation.

Q. Why does the mercury of a barometer rise in a frost?
A. Because frost condenses the air; and condensed air is heavier than
rarefied air.

Q. Why does the mercury of a barometer fall in a thaw?
A. Because the air is both warmer (or more rarefied), and also filled
with vapour.

Q. What does a sudden rise or fall of the barometer indicate?
A. If the rise be sudden, fine weather will not continue long:
If the fall be sudden, foul weather will not continue long.

Q. What sort of weather may we expect if the barometer be very
fluctuating?

A. If the mercury fluctuates much, the weather will be very
changeable and unsettled.
The fall of the barometer.
In very hot weather, the fall of the mercury denotes thunder.

Except in very hot weather, the sudden falling of the barometer
denotes high wind.
In frosty weather, the fall of the barometer denotes thaw.
If wet weather happens soon after the fall of the barometer, expect but
little of it.
In wet weather if the barometer falls, expect much wet.
In fair weather, if the barometer falls much and remains low, expect
much wet in a few days, and probably wind.
N. B. The barometer sinks lowest of all for wind and rain together,
next to that for wind (except it be an east or north-east wind).

The rise of the barometer.
In winter the rise of the barometer presages frost.
In frosty weather, the rise of the barometer presages snow.
If fair weather happens soon after the rise of the barometer, expect but
little of it.
In wet weather, if the mercury rises high and remains so, expect
continued fine weather in a day or two.
In wet weather, if the mercury rises suddenly very high, fine weather
will not last long.
N. B. The barometer rises highest of all for north and east winds; for
all other winds it sinks.

If the barometer be unsettled.

If the motion of the mercury be unsettled, expect unsettled weather.
If it stand at “much rain” and rise to “changeable,” expects fair
weather of short continuance.
If it stand at “fair” and fall to “changeable,” expect foul weather.
N. B. Its motion upwards indicates the approach of fine weather: its
motion downwards indicates the approach of foul weather.

CHAPTER XXIV.
SNOW. HAIL. RAIN.

Q. What is snow?
A. The condensed vapour of the air frozen, and precipitated to the
earth.

Q. What is the cause of snow?
A. When the air is nearly saturated with vapour, and condensed by a
current of air below freezing point, some of the vapour is squeezed
out, and frozen into snow.
A few years ago, some fishermen (who wintered at Nova-Zembla),
after they had been shut up in a hut for several days, opened the
window, and the cold external air rushing in, instantly condensed the
air of the hut, and the vapour (which was squeezed out) fell on the
floor in a shower of snow.

Q. Why does snow fall in winter time?

A. Because the sun’s rays are too oblique to heat the surface of the
earth; and (as the earth has no heat to radiate into the air) the air is
very cold.

Q. What is sleet?
A. When flakes of snow (in their descent) pass through a bed of air
above freezing point, they melt; and fall to the earth as half-melted
snow or sleet.

Q. What is the use of snow?
A. To keep the earth warm, and to nourish it.

Q. How can snow keep the earth warm?
A. Because it is a very bad conductor; in consequence of which, the
earth which is covered with snow, very rarely descends below freezing
point, even when the air is 15 or 20 degrees colder.

Q. Why is snow a bad conductor of heat and cold?

A. Because air is confined and entangled between the crystals, and air
is a very bad conductor; when, therefore, the earth is covered with
snow, it cannot throw off its heat by radiation.

Q. Tell me the words of the psalmist (cxlvii. 16.) respecting snow, and
explain what he means.
A. The Psalmist says—“The Lord giveth snow like wool:” and he
means not only that snow is as white as wool, but that it is also as
warm as wool.

Q. Why is wool warm?
A. Because air is entangled between the fibres of the wool, and air is a
bad conductor.

Q. Why is snow warm?
A. Because air is entangled between the crystals of the snow, and air
is a bad conductor.

Q. Why does snow nourish the earth?

A. Because it supplies it with moisture for a considerable time; which
penetrates slowly into the soil, and insinuates itself through every
clod, ridge, and furrow.

Q. Why is there no snow in summer time?
A. No snow reaches the general surface of the earth in summer time,
because the heat of the earth melts it in its descent.

Q. Why are some mountains always covered with snow?
A. 1st—Because the air is more rarefied; and rarefied air abstracts
heat which it holds in a latent state:
2ndly—As the mountain top is not surrounded by earth to radiate heat
into the air; therefore, the snow is not melted in its descent, but falls
on the mountain, and lies there.

Q. Why is snow white?
A. Snow is formed of an infinite number of very minute crystals and
prisms, which reflect all the colours of the rays of light; and these
colours uniting before they meet the eye, cause snow to appear white.

Q. What is hail?
A. Rain, which has passed in its descent through some cold bed of air,
and has been frozen into drops of ice.

Q. Why is one bed of air colder than another?
A. This is frequently caused by electricity in the air, unequally
distributed.

Q. Why is hail frequently accompanied with thunder and lightning?
A. 1st—Because the congelation of water into hail disturbs the
electricity of the air: and
2ndly—The friction (produced by the fall of hail) excites it still more.

Q. Why does hail fall generally in summer and autumn?
A. 1st—Because the air is more highly electrified in summer and
autumn: and
2ndly—The vapours (being rarefied) ascend to the more elevated
regions, where the cold is greater than it is nearer the earth.

Q. What two things are essential to cause HAIL?
A. Two strata of clouds having opposite electricities, and two currents
of wind. The lower cloud (being negative) is the one precipitated.

Q. What is rain?
A. The vapour of the clouds or air condensed, and precipitated to the
earth.

Q. Why is the vapour of the air or clouds precipitated?
A. When the air is saturated with vapour, if a cold current condenses
it, it is no longer able to hold all its vapour in solution, and some of it
is squeezed out, and falls as rain.

Q. Why does rain fall in drops?
A. The vapoury particles in their descent attract each other; and those
which are sufficiently near, unite and form into a drop.

Q. Why does not the cold of night always cause rain?
A. When the air is not near saturation (although condensed by the
chill of evening), it will still be able to hold its vapour in solution.

Q. Why does a passing cloud often drop rain?
A. Because the cloud (travelling about on the wind) comes into
contact with something that chills it; and its vapour being squeezed
out, falls to the earth as rain.

Q. Why are rain-drops sometimes much larger than at other times?
A. When the rain-cloud is floating near the earth, the drops are large,
because such a cloud is much more dense than one which is more
elevated.
The size of the rain-drop is increased according to the rapidity with
which the vapours are condensed.

Q. Does not wind sometimes increase the size of rain-drops?
A. Yes; by blowing two or more drops into one.

Q. Why do clouds fall in rainy weather?
A. 1st—Because the clouds are heavy with abundant vapour: and
2ndly—As the density of the air is diminished, it is less able to buoy
the clouds up.

Q. How do you know that the density of the air is diminished in rainy
weather?
A. Because the mercury of a barometer falls.

Q. Why is rain-water more fertilizing than pump-water?
A. Because it contains a compound of hydrogen and nitrogen (called
ammonia), which is a very excellent food for young plants.

Q. Why is November made by God to be a rainy month?
A. Because rain hastens the putrefaction of the fallen leaves by
causing fermentation.

Q. Why does rain purify the air?
A. 1st—Because it beats down the noxious exhalations collected in
the air, and dissolves them:
2ndly—It mixes the air of the upper regions with that of the lower
regions: and
3rdly—It washes the earth, and sets in motion the stagnant sewers and
ditches.

Q. Why are mountainous countries more rainy than flat ones?
A. The air (striking against the side of the mountains) is carried up the
inclined plane, and brought in contact with the cold air of the higher
regions, by which it is condensed, and its vapour squeezed out.

Q. Why does a sponge swell when it is wetted?
A. Because the water penetrates the pores of the sponge, and drives
the particles of the sponge further from each other; in consequence of
which, the bulk of the sponge is greatly increased.

Q. Why do fiddle-strings snap in wet weather?

A. Because the moisture of the air (penetrating the string) causes it to
swell; and (as the cord thickens) its tension is increased, and the string
snaps.

Q. Why does paper pucker when it is wetted?
A. Because the moisture (penetrating the paper) drives its particles
further apart; and (as the moisture is absorbed unequally by the paper)
some parts are more enlarged than others; in consequence of which,
the paper blisters or puckers.

Q. Why do the weather toys called capu’chins lift the cowl over the
figures in wet weather, and remove it in dry?
A. The cowl of the capu’chin is fastened to a piece of cat-gut. When
the weather is wet, the moisture swells the cat-gut and it is shortened,
by which means the cowl is pulled up; but in dry weather, the string is
loosened, and the cowl falls down.

Q. In another weather toy, the man comes out in wet weather, and the
lady in fine:—Why is this?

A. The two figures are attached to a piece of cat-gut in such a manner,
that when the cat-gut is shortened by moisture, it pulls the man out;
but when it is loose, the woman falls out by her own weight.

Q. Why are wet stockings difficult to pull on?
A. The moisture (by penetrating the threads of the stockings) causes
them to shrink in size.

Q. What is the most rainy spot in England?
A. Keswick (in Cumberland); and then Kendal (a market town in
Westmoreland).
(In Keswick, about 63 inches of rain fall in a year. In Kendal, 58;
Manchester, 38; Liverpool, 34; Dublin and Cambridge, 25; Lincoln,
24; London, 21; and in Paris, only 18.)

Q. In which part of the day does the most rain fall?
A. More rain falls by night than by day; because the cold night
condenses the air, and diminishes its capacity for holding vapour in
solution.

Q. Does more rain fall in summer or in winter time?
A. There are more rainy days from September to March; but heavier
rains between March and September.