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Entered according to Act of Congress, In the year 1857, by
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District of New York.

CONTENTS.

PART I.

CHAP-TEE LAWS AND PROPERTIES OF MATTER. PAS«

I. "What we Know of Matter, and How we Know It . 3

II. Attraction . . 11

III. Weight . 19

IV. Motion 22

PART II.

APPLICATION OP THE LAWS AND PROPERTIES OP MATTER
TO THE ARTS.

I. How we apply Power 31

II. Strength of Materials 36

III. Application of Materials for Architectural and Structural

Purposes 38

IV. Principles of Architecture 41

PART III.

THE LAWS AND PHENOMENA OF FLUIDS.

I. "Water in Motion and at Rest 49

II. Specific Gravity » . . 62

III. Capillary Attraction 65

IV. The General Properties of Gaseous and Aeriform Bodies 67
V. The Atmosphere 69

VI. Atmospherical Phenomena 74

VII. The Pump and Barometer 97

VIII. Peculiarities of Climates 104

IV CONTENTS.

PART IV.
SOUND.

I. Origin and Transmission of Sound . . . . 114

II. Vocal arid Musical Sounds . . . . . . 120

in. Reflection of Sounds ,124

PART V.

HEAT.

I. Nature and Origin of Heat j 129

II. The Sun a Source of Heat 133

III. Other Sources of Heat besides the Sun ... 136

IV. How Heat is Communicated 143

V. The Phenomena of Dew 162

VI. Reflection, Absorption, and Transmission of Heat . 171
VII. Effects of Heat 176

PART VL

VENTILATION AND WARMING, COMBUSTION, RESPIRATION,
AND NUTRITION.

I. "Warming and Ventilation . . . . . . 204

II. Combustion 220

1IL Respiration and Nutrition ... . 233

PART VII.

LIGHT, AND HOW WE SEE.

I. Nature and Laws of Light 241

II. Structure of the Eye and the Phenomena of Vision . 262

PART VIII.

ELECTRICITY, GALVANISM, MAGNETISM, AND ELECTRO-
MAGNETISM.

I. Electricity 275

II. Galvanism 289

III. Magnetism 295

IV. Electro-Magnetism 299

PART IX.

FAMILIAR CHEMISTRY. 303

PREFACE.

THE design of the present volume is to furnish for the
use of schools and young persons, an elementary text-book
on the first principles of science. For this purpose, the
system of question and answer, which for certain classes
of pupils and for familiar instruction has proved emi-
nently popular, has been followed. The advantages of this
system are : — first, that it affords a most simple and easy
method of communicating useful and practical informa-
tion : — second, the question excites a feeling of curiosity in
the mind of the young student, which serves to fix the sub-
ject-matter more strongly in the memory : — and thirdly,
the form of question and answer imparts truth to the mind,
in a logical sequence of cause and effect, and by showing
how consequents in sciences are deduced from antecedents,
unconsciously trains and familiarizes the pupil to think and
reason according to the true spirit of inductive philosophy.

It is believed that the questions in the. present volume
are simple, practical, and expressed in the plainest language
that the subject allows. Engravings have also been used
to illustrate more clearly the most important topics treated
of.

As this work has been designed exclusively as an elemen-
tary book, the more abstruse and difficult departments of

M69927

V PREFACE.

physical science hare been passed over, or briefly noticed ;
such as the theory and application of the mechanical powers,
the polarization of light, crystallography, &c. Those who
are desirous of possessing a more complete and elaborate
work, arranged in the form of question and answer, — em-
bracing the whole subjects of Natural Philosophy, Organic
and Inorganic Chemistry, the applications of science to the
.Industrial Arts, Geology, *fcc., are referred to a work by the
'author of the present volume, entitled " Wells's Familiar
Science" and to u Wells's Natural Philosophy," in both of
which special reference is made to the application of the
principles of physical science to the useful arts and necessi-
ties of every-day life.

In the preparation of the " Science of Common Things "
especial care has been taken to render the facts and prin-
ciples given, full, complete, and accurate, and in strict con-
formity with the very latest results and researches of modern
science.

XEW TOEK, May, 1857.

SCIENCE OF COMMON THINGS.

PAET I

LAWS AND PROPERTIES OF MATTER.

CHAPTER I.

WHAT WE KNOW OF MATTER, AND HOW WE KNOW IT.
1 What is matter t

"We apply the term matter to any substance which
affects our senses.

& How do lee know that anything exists f

Because our senses give us evidence of the fact

3 What are the senses t

They are the instruments, or means, by which the
mind is enabled to know that matter exists and pos-
sesses certain properties.

4 How many senses are there f

Five ; hearing, seeing, smelling, tasting, and feeling.

5 Wsuld a person deprived of all sensation, be conscious of any mats-
rial existence f

He would not ; for all knowledge of the material
world is derived through the medium of the senses.

6 Is the impression transmitted to the mind by each organ of sensation,

different*

It is; each organ of sense is adapted to receive a
particular influence of matter ; and is designed to con-

SCIENCE OF COMMON THINGS.

Properties of matter Impenetrability.

vey to the mind immediate notice of some peculiar
action. This is the more noticeable, when we consider
that, however delicate its structure, each organ of
sense is wholly insensible to every influence except that
to which it is especially adapted ; thus, the eye is never
affected by sound, nor the ear by light.

7 What is meant by the term body ?

Any distinct portion of matter existing in, and oc-
cupying space.

8 What do we mean, when we speak of "he properties or qualities of a
body?

The powers belonging to the body, which are capa-
ble oif^xfeiting* In .'oiii* miad certain sensations.

Tlu- ]a4ftd£al; qualifies of matter are MAGNITUDE or

EXTENSION, IMPENETBABiLlTY, DIVISIBILITY, POROSITY, IN-
ERTIA, DENSITY, ELASTICITY, DUCTILITY, and MALLEABILITY.

10 What is magnitude f

The property of occupying space. It is impossible
to conceive of a portion of matter so minute as to have
no magnitude.

11 What do we mean by the term size of a body ?

The quantity of space a body occupies.

13 What is the surface of a body f

The external limits of its magnitude-
is What is the area of a body ?

The quantity of surface.

14 What is impenetrability f

That quality of matter which precludes the possibility
of two bodies occupying the same space at the same
time. "When bodies are said to be impenetrable, it is
therefore meant, that one cannot pass through another
without displacing some, or all, of the component parts
of that other.

There are many instances of apparent penetration ; but in all those, the
parts of the body which seem to be penetrated are only displaced. Thus,
if a needle be plunged into a vessel of water, all the water which pre-
viously filled the space into which the needle enters, will be displaced ;
and the level of the water will rise in the vessel to the same height as it

SCIENCE OF COMMON THINGS.

Divisibility of matter. Atoms. Particles.

would by pouring in so much more water as would fill the space occupied
by the needle.

15 Why witt water, or any other liquid, poured into a funnel, closely
inserted in the mouth of a bottle, or decanter, run over the sides f

Because the air filling the bottle, and having no
means of escape, prevents the fluid from entering the
bottle ; but if the funnel be lifted from the neck of the
bottle a little, so as to afford the air an opportunity to
escape, the water will then flow into the bottle in an
uninterrupted stream.

ie What is the figure of a body f

Its form or shape, as expressed by its boundaries or
terminating extremities.

17 What is meant by the divisibility of matter t

Its property, or capability of being divided.

18 Is matter capable of being divided into separate portions infinitely or
without limit f

So far as we are able to perceive with our senses, all
matter is capable of being divided into separate por-
tions without limit; yet the recent investigations of
chemistry have proved beyond a doubt, that there is
a point beyond which matter is no longer divisible.
Such a portion of matter as cannot be divided we call
an atom.

19 WJiai ffien is an atom of matter f

A particle so minute, as to admit of no division.
Atoms are conceived to be the first principles or com-
ponent parts of all bodies.

The extent to which matter can be divided and yet be perceived by
the senses, is wonderful.

An ounce of gold may be divided into four hundred and thirty-two
thousand million parts. Each of these parts will retain all the characters
and qualities which are found in the largest masses' of metal. It retains
its solidity, texture, and color; it resists the same agents, and enters into
combination with the same substances.

20 What is a particle of matter ?

The term particle is also used to express^ sra«Z£ com-
ponent parts of matter, but is generally applied to those
which are not too minute, to be discovered by obser-
vation.

SCIENCE OF COMMON THINGS.

Pores of a body. Compressibility. Density.

31 What are the pores of a body ?

No two particles of matter are supposed to be in
actual contact with each other; and the openings, or
interstitial spaces between these particles, are called
pores.

33 What is the reason that a sponge, apiece of tcood or metal, can, by
pressure, be made to occupy a smaller space than it did originally f

Because the particles of which the sponge, the piece
of wood or metal, are composed, are by pressure
brought more closely together, diminishing at the same
time the pores and the space the body occupies.

33 What then is compressibility ?

That quality of matter in virtue of which a body
allows its volume or size to be diminished, without
diminishing the number of atoms or material particles
of which it consists.

34 What reason have we for supposing that no two particles of matter
are in absolute contact f

Because all known bodies, whatever may be their
nature, are capable of having their dimensions reduced
without diminishing the amount of matter contained in
them ; hence the space by which the volume may be
diminished must, before diminution, consist of pores'.

35 What is density f

The proportion of the quantity of matter in a body to
its magnitude. Thus, if of two substances one contains
in a given space twice as much matter as the other, it
is said to be twice as dense.

36 What connexion is there between the density of a body and its
porosity ?

A body will be more or less dense according as its
particles are near to or remote from each other ; and
hence it is evident that the greater the density the less
the porosity, and the greater the porosity the less the
density.

37 Why do we caU lead heavy, and feathers light ?

Because the amount of matter contained in a quan-
tity of lead occupying a given space is much greater
than in a quantity of feathers capable of occupying the

SCIENCE OF COMMON THINGS. 11

Ductility. Malleability. Attraction.

much more dense than the diamond, yet the metal is
soft, while the diamond is the hardest body in nature.

56 When is a body said to be ductile ?

When it is capable of being drawn into wire. In
ductile substances the atoms seem to have no more
fixed relation of position than in a liquid, but yet they
cohere very strongly.

y 57 When is a body said to be malkabk f

When it is capable of being hammered or rolled into
thin plates. Bodies that are malleable are not always
ductile. Lead and tin may be hammered out into
very thin plates, but it is 'difficult, or impossible, to
draw out these metals into fine wire.

CIIAPTEE II.'

ATTRACTION.

58 What is attraction ?

It is the force manifested by the mutual approach or
cohesion of bodies.

59 Is all matter subject to the power of attraction ?

All matter is under the influence of attraction in
some of its forms. Every particle of matter attracts
every other particle, and is in turn itself attracted.

60 What is repulsion ?

It is the force manifest in the movement of bodies
from each other. Thus, if a piece of glass, having
been briskly rubbed, with a silk handkerchief, touch
successively two feathers, these feathers, if brought to-
gether, will move asunder.

61 What is cohesive attraction f

It is the force which holds together the atoms of

SCIENCE OF COMMON THINGS.

Adhesion. Examples of cohesion^ |

bodies. Cohesion acts only between particles of pat-
ter of the same kind, and at distances which are not
measurable, or, as they are termed, insensible distaaices.

63 What is adhesion ?

Adhesion is attraction between particles of matter
of different kinds acting at immeasurably small dis-
tances only, and uniting the dissimilar particles into
one mass.

63 Why is mortar used to fasten bricks together f

Because the adhesive attraction between the particles
of the brick and the particles of mortar is so strong,
that they unite to form one solid mass. j

64 Why is a bar of iron stronger than a bar of wood of the same size ?

Because the cohesion existing between the particles
of iron is greater than that existing between the par-
ticles of wood.

65 Why are the particks of a liquid more easily separated than those
of a solid ?

Because the cohesive attraction which binds together
the particles of a liquid is much less strong than that
which binds together the particles of a solid.

66 Why will a small needle, carefully laid upon the surface of water,
float f

Because its weight is not sufficient to overcome the
cohesion of the particles of water constituting the sur-
face ; consequently, it cannot pass through them and
sink.

6*7 If you drop water and laudanum from the same vessel why wiU
sixty drops of the water fill the same measure as one hundred drops of
laudanum ?

The cohesion between the particles of the two liquids
is different, being greatest in the water. Consequently,
the number of particles which will adhere together to
constitute a drop of water is greater than in the drop
of laudanum.

68 Why is the prescription of medicine by drops an unsafe method f

Because not only do drops of fluid from the same
vessel, and often of the same fluid from different ves-

SCIENCE OF COMMON THINGS. 13

Attraction of gravitation. Illustrations of gravitation.

jj differ in size, but also drops of the same fluid, to
the 'extent of a third, from different parts of the lip of
the same vessel.

69 Why is it difficult to pour water from a vessel which has not a pro-
jecting lip ?

Because, in consequence of the attraction between
the water and the sides of the vessel, the fluid has a
tendency to run down along the inclined outside of the
vessel, and not at once to fall perpendicularly.

7*O | What is the attraction of gravitation ?

W<$ apply the term "gravity," or the "attraction
of gravitation," to that tendency which every particle
of matter in the universe has to approach all other
matter. Terrestrial gravitation is the attraction of a
body towards the centre of the earth.

T'l In what respect does the attraction of gravitation differ from all other
attractive forces ?

Because it is the common property of all bodies ;
since everything to which we can attach the idea of
materiality is aftected more or less by gravitation.

7*3 Why does an appk loosened from the tree fall to the ground?

Because the earth attracts or draws it to itself.

7*3 Since all bodies are attracted towards the earth, how does it happen
that all smoke and some other forms of matter display the contrary pheno-
menon of ascending from it ?

Because the smoke is lighter than the air, bulk for
bulk, and floats upon it. It is unable to advance, how-
ever, in the most minute degree, without displacing or
thrusting downward portions of the atmosphere equal
to its own bulk.

7*4: Why does a cork pressed beneath the water rise and float on the
turf ace ?

Because the cork is lighter than an equal bulk of
water, and is pressed up and sustained by it in the
same manner that the particles of smoke are sustained
by the particles of air.

7*5 Why does a balloon rise in the air ?

Because it is filled with a gas which is lighter, bulk
for bulk, than the air.

SCIENCE OF COMMON THINGS.

All bodies attract each other. Feather and the earth.

76 How long witt smoke continue to float above the surface of the earth f

Until its particles, uniting, become heavier than the
air, when they descend in the form of small flakes of
soot.

77 Why do bubbles in a cup of tea range round the sides of the cup ?

Because the cup attracts them.

78 Why do att the little bubbles tend towards the large ones f

^ Because the large bubbles (being the superior masses)
attract them.

79 Why do the bubbles of a cup of tea follow a tea-spoon f

Because the tea-spoon attracts them.

SO Do all bodies attract each other equally f

They attract each other with forces proportioned to
their masses.

8 1 A feather falls to the ground by the influence of the earth's attraction.
Now, as all bodies attract each other, does the feather attract or draw up the
earth in any degree towards itself?

It does, with a force proportioned to its m-ass / but
as the mass of the earth is infinitely greater than the
feather, the influence of the feather is infinitely small,
and we are unable to perceive it.

83 What would be the consequence if the feather did not attract the
earth f

If any portion of the earth, however small, failed to
attract another portion, and not be itself attracted, the
axis of the earth would le immediately changed, involv-
ing an alteration of climate, and the place of the ocean
in its bed.

83 Why is it more dangerous to fall from, a lofty elevation than from a
low one ?

As the attraction of the earth varies inversely with
the square of the distance, the force with which a fall-
ing body will strike the ground will increase in propor-
tion to the height from which it has fallen.

84 In what direction does a body, when not supported, endeavor to fall ?

In a line drawn from its centre of gravity towards
the centre of the earth.

85 Is the attraction of the earth the same at att distances from its sur-
face or centre f

SCIENCE OF COMMON THINGS.

Centre of gravity.

Position in which a body can rest.

JVb ; the attraction of the earth for a body varies
inversely with the square of its distance from the 'centre.

86 How can this be illustrated ?

In the following manner : — If one body attracts an-
other with a certain force at the distance of one mile, it
will attract with four times the force at half a mile,
nine times the force at one-third of a mile, and so on in
like proportion. On the contrary, it will attract with
but one-fourth of the force at two miles, one-ninth of
the force at three miles, one-sixteenth of the force at
four miles, and so on as the distance increases.

87 What do we mean by the centre of gravity ?

That point in a body about which, if supported, the
whole body will balance itself.

88 When you balance a rod, a stick, or any other body, upon the finger,
where is the centre of gravity of the stick or body ?

It is the point upon which the body will remain at
rest, or upon which it is balanced.

89 In what position only can a body rest ?

Only when its centre of gravity is supported ; and
until this is accomplished the body will move, and con-
tinue to do so, until it settles into a position in which
the centre of gravity cannot sink lower.

0O Why does a person carrying a weight upon his back stoop forward ?

In order to bring the centre of gravity of his body
and the load over his feet.

Fig 1.

fifr 2.

16 SCIENCE OF COMMON THINGS.

Centre of gravity in man and animals.

If he carried the load in the position of A, Fig. 1, he would fall back-
wards, as the direction of the centre of gravity would fall beyond his
heels ; to bring the centre of gravity over his feet, he assumes the posi-
tion indicated by B, Fig. 2.

91 When a person carries a load upon his head, why is it necessary
to stand perfectly upright ?

In order tliat the centre of gravity may be over his
feet. i

Q& Why does a person in rising from a chair bend forward ?

When a person is sitting, the centre of gravity is
supported by the seat ; in an erect position, the centre
of gravity is supported by the feet / therefore, before
rising it is necessary to change the centre of gravity,
and by bending forward we transfer it from the chair
to a point over the feet.

93 Why does a quadruped, in walking} never raise loth feet on the same
side simultaneously f

Because, if it did, the centre of gravity would be un-
supported, and the animal would tend to fall over.

94 Why is a large turtle placed on its back unable to move f

Because the centre of gravity of the turtle is, in this
position, at the lowest point, and the animal is unable
to change it ; therefore it is obliged to remain at rest.

95 WJiy is it more difficult to overthrow a body Jiaving a broad base
than one resting upon a narrow basis f

Because a body cannot fall over, so long as a line
directed from the centre of gravity vertically towards
the surface upon which the body rests, falls within the
figure formed by the base of the body in question.

SCIENCE OF COMMON THINGS.

Stability of buildings.

Centre of gravity in walking.

Hence, tlie broader the base of a body, the more securely
it will stand.

Thus, in Fig. 3, the line directed vertically from the centre of gravity,
G, falls within the base of the body, and it remains standing ; but in Fig.
4 a similar line falls without the base, and the body consequently cannot
be maintained in an upright position, and must fall.

96 How long will a watt or tower stand securely ?

So long as the perpendicular line drawn through its
eentre of gravity falls within its base.

The celebrated leaning tower
pf Pisa, 315 feet high, which
inclines 12 feet from a per-
fectly upright position, is an
example of this principle. For
instance, the line in Fig. 5,
falling from the top of the
tower to the ground, and pass-
ing through the centre of gra-
vity, falls within the base, and
the tower stands securely. If,
however, an attempt had been
made to build the tower a lit-
tle higher, so that the perpen-
dicular line passing through
the centre of gravity would
have fallen beyond the base,
the structure could no longer
have supported itself.

Fig.5.

It increases the breadth of the base supporting the
body, and enables us to stand more securely.

98 Why do very fat people throw hack their head and shoulders when
they walk ?

In order that they may effectually keep the centre
of gravity of the body over the base formed by the
soles of the feet.

99 W?cy cannot a man, standing with his heels close to a perpendicular
watt, bend over sufficiently to pick up any object that lies before him on the
ground, without falling ?

Because the wall prevents him from throwing part
of his body backward, to counterbalance the head and
that must project forward.

18 SCIENCE OF COMMON THINGS.

Eope-dancing. How we learn to walk.

100 What is the reason that persons walking arm-in-arm shake and
jostle each other, unless they make the movements of their feet to correspond,
as soldiers do in marching ?

When we walk at a moderate rate, the centre of
gravity comes alternately over the right and over the
left foot. The body advances, therefore, in a waving
line; and unless two persons walking together keep
step, the waving motion of the two fails to coincide.

101 Where would the centre of gravity be in a wheel made entirely of
wood and of a uniform thickness ?

In the centre.

1OS Where would the centre of gravity be if a part of the rim of the
same wJieel were made of iron f

It would be changed to some point aside from the
centre of the wheel.

103 In what does the art of balancing or walking upon a rope consist?

In keeping the centre of gravity in a line over the
base upon which the body rests.

104 What is the base upon which the human body rests or is supported t

The two feet and the space included between them.

105 Why is it a very difficult thing for children to learn to walk ?

In consequence of the natural upright position of the
human body, it is constantly necessary to employ some
exertion to keep our balance, or to prevent ourselves
from falling, when we place one foot before the other.
Children, after they acquire strength to stand, are
obliged to acquire this knowledge of preserving the
balance by experience. When the art is once acquired,
the necessary actions are performed involuntarily.

106 Why do young quadrupeds learn to walk much sooner than chil-
dren f

Because a body is tottering in proportion to its great
altitude and narrow base. A child has a body thus
constituted, and learns to walk but slowly because of
this difficulty, (perhaps in ten or twelve months,) while
the young of quadrupeds, having a broad supporting
base, are able to stand and move about almost immedi-
ately.

107 Are aU the limbs of a tall tree arranged in such a manner, that tlie

SCIENCE OF COMMON THINGS. 10

How trees grow. Weight. *»

line directed from the centre of gravity is caused to fall within the base of the

tree?

Nature causes the various limbs to shoot out and
grow from the sides with as much exactness, in respect
to keeping the centre of gravity within the base, as
though they had been all arranged artificially. Each
limb growsj in respect to all the others, in such a man-
ner as to preserve a due balance between the whole. /

CHAPTEK III.

"WEIGHT.
1O8 What is weight f

Weight is the measure of the attraction of gravita-
tion, or, in other words, it is the measure of force with
which a body^ is attracted by the earth. Iti an ordi-
nary sense it is the quantity of matter contained in a
body, as ascertained by the balance.

1O0 To what is the weight of a tody proportional f

The weight of a body is always proportional to the
quantity of matter contained in it.

110 Why witt a ball of kad weigh more than a baU of cotton of the
same size ?

Because the quantity of matter contained in the ball
of lead is much greater than the quantity of matter
contained in the ball of cotton. The attraction of gra-
vitation being proportioned to the quantity of matter,
it follows that the lead ball will be drawn towards the
earth with a greater force (i. e. will weigh more) than
the ball of cotton.

111 A man of moderate weight upon the surface of the earth would
weigh two tons if transported to the surface of the sun : why would he weigh
more upon the surface of the sun than upon the surface of the earth f

20 SCIENCE OF COMMON THINGS.

TV hen a body weighs the most Systems of weights.

Because the attractive force of the sun, on account
of its greater magnitude, far exceeds the attractive
force of the earth.

11Q Why witt a mass of iron weigh less on the top of a high mountain
than at the level of the sea f

Because the force of the earth's attraction is less at the
top of the mountain than at the sea-level ; the attrac-
tion (and, therefore, the weight of a body) being greatest
at the surface of the earth, and decreasing upward, as
the square of its distance from the centre of the earth
increases.

A ball of iron, weighing a thousand pounds at the level of the sea,
~y would be perceived to have lost two pounds of its weight if taken to the
top of a mountain four miles high, a spring balance being used.

113 Where witt a body weigh the most on the surface of the earth ?

At the poles of the earth, for at these points the
attractive power is greatest.

It must be remembered that the earth is not a perfect sphere, but flat-
tened at the poles : consequently, the poles of the earth are nearer the
centre of attraction (i. e. the centre of the earth) than any other point on
its surface.

114 Where witt a body weigh the least on the earths surface f

At the equator, for there the attractive power is less ;
the surface at this point being the most distant from
the centre of the earth.

115 What would be the weight of a body carried to the centre of the
earth f

It would have no weight ; for the attraction of gra-
vitation acting equally in every direction, no eftect
would be produced ; and the body wrould be fixed as
if sustained by a number of magnetic points.

116 What two systems of weights are employed in tlie United States
and Great Britain f

Troy weight and avoirdupois weight.

117' What is Troy weight used for } and from whence does it derive its
name?

Troy weight is used for weighing gold and silver.
It derives its name from the ancient designation of
London, Troy Novant, or from Troyes, in France,
where it was first adopted in Europe. It has existed
in England from the time of Edward the Confessor.

SCIENCE OF COMMON THINGS. 21

Avoirdupois and grain weights. English, American, and French weights.

118 What is avoirdupois weight used for, and from whence does it
uerive its name ?

Avoirdupois weight is used for the weight of mer-
chandise other than the precious metals. It derives its
name from the French avoirs (averia\ goods or chat-
tels, and poids, weight.

11Q What is a grain weight f

A grain weight is the smallest measure of weight
made use of in the English system. By a law of Eng-
land enacted in 1286, it was ordered that 32 grains
of wheat, well dried, should weigh a pennyweight.
Hence the name grain applied to this measure of
weight. It was afterwards ordered that a pennyweight
should be divided into only 24 grains.

150 How do we make a grain weight for practical purposes f

By weighing a thin plate of metal of uniform thick-
ness, and cutting out, by measurement, such a propor-
tion of the whole as should give one grain. In this
way, weights may be obtained for chemical purposes,
which weigh only lTrVu1;h part of a grain.

151 What part of an inch is a line f

One-twelfth of an inch is designated as a line.

1SS Are tJie standards of weights and measures in the United States
tlie same as in Great Britain ?

They are essentially the same.

1S3 Where are the standards of weights and measures to be found in
the United States ?

At Washington, and at the capitals of the several
States of the Union ; sets having been furnished to
each State by the United States.

124 Are the weights and measures used in France the same as those of
the United States and England ?

No ; they are entirely different. Within a compa-
ratively recent time the French have reconstructed
their old system of weights and measures, and formed
another on an entirely new plan. The French system
is, at present, the best and most accurate system
existing.

SCIENCE OF COMMON THINGS.

Force. Motion. Friction.

CHAPTER IYc

MOTION.
135 What is force f

Force is whatever causes or opposes ike production
of motion in matter.

1SS What is motion f

It is the term applied to the phenomena of the
changing of place among bodies.

13 *7 What would be the state of things if no motion existed f

The universe would be dead. There would be no
rising and setting of the sun, no flow of water or of air
(wind), no sound, light, or animal existence.

128 The surface of the earth at the equator moves at the rate of about a
thousand miles in an hour : why are men not sensible of this rapid move-
ment of the earth f

Because all objects about the observer are moving in
common with him. It is the natural uniformity of the
undisturbed motion which causes the earth and all the
bodies moving together with it upon its surface to ap-
pear at rest.

120 How can you easily see that the earth is in motion f

By looking at some object that is entirely uncon-
nected with it, as the sun or the stars. We are here,
however, liable to the mistake that the sun or stars are
in motion, and not we ourselves with the earth.

ISO Does the sun really rise and set each day ?

The sun maintains very nearly a constant position ;
but the earth revolves, and is constantly changing its
position. Really, therefore, the sun neither rises nor
sets.

131 What do we mean by the term friction f

In mechanics, it signifies the resistance which a
moving body meets with from the surface on which it
moves.

SCIENCE OF COMMON THINGS. 23

Impossibility of perpetual motion. Centrifugal force.

132 Is it possible to construct any machine, w arrangement of matter^
which will perpetually continue in motion ?

It is not / because the operations of gravity, the re-
sistance of the medium through which the body moves ,
or the friction of the surfaces upon which the lody
rests, will, in a given time, destroy and terminate all
motion. In addition to this, all materials which we
employ in construction will, in the course of time, wear
out by use, or decay by natural agencies.

133 Do we know of any instances of perpetual motion in nature 1

Yes • the various planetary bodies belonging to the
solar system have been moving with undiminished
velocity for ages past ; and, unless prevented by the
agency which governs all nature, will continue to
move in the same manner for ages to come.

134 Why are horses obliged to make a much greater exertion to start a
carriage than afterwards to keep it in motion ?

Because when a carriage is once put in motion upon
a level road, with a determinate speed, the only force
necessary to sustain the motion is that which is suffi-
cient to overcome the friction of the road / but, at
starting, a greater expenditure of force is necessary,
inasmuch as not only the friction is to be overcome,
but the force with which the vehicle is intended to
move must be communicated to it.

135 What is centrifugal force?

It is that force which causes a revolving body to fly
from a centre.

136 Why does a stone, discharged from a sling, move forwards, when
the cord which retained it is loosened f

Because of the centrifugal force it- has acquired by
the whirling of the sling previous to the discharge.

137 Why do grindstones or wheels, in rapid motion, not unfrequenfty
'break and fly to pieces with great violence ?

Because the centrifugal force, generated by the rapid
revolving motion, overcomes the cohesion of the parti-
cles, and thus causes them to separate and fly from the
centre.

SCIENCE OF COMMON THINGS.

Illustrations of centrifugal force. Revolution of the earth.

133 Can almost all revolving bodies be broken by sufficient rotative
velocity ?

Yes; for the centrifugal force increases with the
rapidity of revolution, and finally becomes too strong
to be resisted by the cohesive force which binds the
particles of the body together.

13Q When a vessel containing water is whirkd
rapidly round, why does not the water fall out when the
vessel is upside down ?

Because the centrifugal force, tending
to make the water fly from the centre,
overcomes or balances the attraction of
gravitation, which tends to cause the
water to fall out.

In Fig. 6. the water contained in the bucket which
is upside down, has no support under it, and if the
bucket were kept still in its inverted position for a
single moment the water would fall out by its own
weight, or, in other words, by the attraction of gravi-
tation : but the centrifugal force, which is caused by
the whirling of the bucket in the direction of the
arrow, tends to drive the water out through the bot-
tom and side of the vessel, and as this last force is
equal to and balances the other, the water retains its
place, and not a drop is spilled.

How much faster would the earth be required
to revolve in order to make the centrifugal force equal to
the attraction of gravitation f

/Seventeen times faster, or in eighty-
four minutes, instead of twenty-four
hours : in this case all bodies at the
equator of the earth would be destitute
of weight.

141 What would be the consequence if the earth
revolved around its axis in less time than eighty-four
minutes ?

I Gravitation would be completely over-
_ powered, and all fluids and loose sub-
Fi« 6- stances would fly from the surface.

143 Why does a man or horse, in turning a corner rapidly, incline
inwards, or kan towards the corner t

Because the centrifugal force, produced by turning

SCIENCE OF COMMON" THINGS.

Action of centrifugal force in equestrian sports.

rapidly, tends to throw him away from, the corner y
therefore, he inclines inwards to counteract it.

143 Why does a horse in a circus ring lean towards the centre 1

When the horse moves rapidly around the circular
course, the centrifugal force generated, tends to throw
him over, outwardly, or away from the centre of the
ring ; and this tendency the animal counteracts, by
inclining his body in an opposite direction.

Fig. 7.

In all equestrian feats exhibited in the circus, it will be observed that
not only the horse but the rider inclines his body towards the centre,
Fig. 7, and according as the speed of the horse round the ring is increased,
this inclination becomes more considerable. "When the horse walks
slowly round a large ring this inclination of his body is imperceptible ; if
he trot there is a visible inclination inwards, and if he gallop he inclines
still more, and when urged to full speed he leans very far over on his
side, and his feet will be heard to strike against the partition which defines
the ring. The explanation of all this is, that the centrifugal force caused
by the rapid motion around the ring tends to throw the horse out of, and
away from, the circular course, and this he counteracts by leaning
inwards.

144 Why do water-dogs give a semi-rotary movement to their skin to
free themselves from water ?

Because in this way a centrifugal force is generated,
which causes the drops of water aaherent to them to
fly off.

26 SCIENCE OF COMMON THINGS.

Phenomena of jumping. Flying of birds. Flying and leaping.

145 Why does a person who is about to leap over a ditch or chasm first
make a run of a little distance ?

In order that the impetus he acquires in running
may help him in the jump.

140 Why is a standing leap always shorter than a running one f

Because in the running leap, in addition to the force
acquired by the contraction of the muscles, we have
added the force of the motion acquired by running.

147 Why do we kick against the door-post to shake the snow or dust
from our shoes ?

The forward motion of the foot is arrested by the
impact against the post ; but this is not the case with
respect to the particles of dust or snow, which are not
attached to the foot ; but the motion imparted to them
equally with the foot is continued, and causes them to
fly off.

148 Why do we beat a coat or carpet to expel the dust f

The cause which arrests the motion imparted to the
coat or carpet by the blow does not arrest the particles
of dust, and their motion being continued, they fly off.

149 Why can birds fly f

Because they have the largest bones of all animals
in proportion to their weight. Air-vessels also enable
them to blow out the hollow parts of their bodies,
when they wish to make their descent slower, rise
more swiftly, or float in the air. The muscles that
move the wings of birds downwards, in many instan-
ces, are a sixth part of the weight of the whole body ;
whereas those of a man are not, in proportion, one-
hundredth part so large.

It is an erroneous idea, still taught in many educational works, that
the bones of birds are hollow and filled with air. This is not the case.
Recent investigations have shown that the bones of birds, as a general
thing, are not more hollow than those of other animals, and do not con-
tain air.

150 Why does flying differ from leaping 1

Because flying is the continued suspension and pro-
gress of the whole body in the air, by the action of the
wings. In leaping, the body is equally suspended in

SCIENCE OF COMMON THINGS. 27

Action of birds in flying. Action and reaction.

the air; but the suspension is only momentary. In
flying3 on the contrary, the body remains in the air
and acquires a progressive motion by repeated strokes
of the wings on the surrounding fluid.

151 Why do birds stretch out their necks when flying f

In order that they may act as a wedge, dividing the
air and diminishing the resistance.

152 Why are the strongest feathers of birds in the pinions and tail f

Because when the wing is expanded, the pinion-
feathers may form, as it were, broad fans, by which
the bird is enabled to raise itself in the air and fly;
while its tail-feathers direct its course.

153 Why can a person safely skate with great rapidity over ice which
would not support his weight if he moved over it more slowly f

From the fact that time is required for producing
the fracture of the ice : as soon as the weight of the
skater begins to act on any point, the ice, supported by
the water, bends slowly under him ; but if the skater's
Velocity is great, he has passed off from the spot which
was loaded before the bending has reached the point
which would cause the ice to break.

154 It sometimes happens when persons are knocked down "by carriages
that the wheels pass over them with scarcely any injury, though if the weight
of the carriage had rested on the body, even for a few seconds, it would have
crushed them to death. What explanation can be given of this fact f

The wheel moves with such rapidity, that the weight
has not time sufficient to exert its full effect.

155 When two equal bodies meet, moving with equal velocities in oppo-
site directions, what will be the effect ?

They will both come to rest — for their motion being
equal and contrary, will be mutually destroyed.

150 When two persons strike their heads together, one being in motion
and the other at rest, why are both equally hurt f

Because, when bodies strike each other, action and
reaction are equal ; the head that is at rest returns the
blow with equal force to the head that strikes.

157 When an elastic batt is thrown against the side of a house with a
certain force, why does it rebound f

28 SCIENCE OF COMMON THINGS.

Examples of action and reaction. Laws of falling bodies.

Because the side of the house resists the ball with
the same force, and the ball, being elastic; rebounds.

158 When the same ball is thrown against a pane of glass with the
same force, it goes through, breaking the glass : why does it not rebound as
beforef

Because the glass has not sufficient power to resist
the full force of the ball : it destroys a part of the force
of the ball, but the remainder continuing to act, the
ball goes through, shattering the "glass.

159 Why did not the man succeed who undertook to make a fair wind
for his pleasure boat, by erecting an immense bellows in the stern, and blow-
ing against the sails f

Because the action of the stream of wind and the
reaction of the sails were exactly equal, and, conse-
quently, the boat remained at rest

160 If he had blown in a contrary direction from the sails, instead of
against them, would the boat have moved ?

It would, with the same force that the air issued from
the bellows-pipe.

161 Why cannot a man raise himself over a fence by pulling upon the
straps of his boots f

Because the action of the force exerted to raise him-
self, is exactly counteracted by the reaction of the force
which tends to keep him down.

163 Does a man, in rowing, drive the water astern with the same fores
that he impels the boat forwards t

He does : action and reaction being exactly equal.

163 Why is it more dangerous to leap from a, high window than from
a low table ?

Because the velocity of a falling ~body, and, conse-
quently, the force with which it will strike the ground,"
^ncrease8 with the distance through which it falls.

164 How far ivitt a, body fall, through the influence of gravity, in one
te.cond of time ?

Sixteen feet.

165 How far will it fall in two seconds f

Four times 16 feet, or 64 feet ; in three seconds it
will fall 144 feet ; in four, 256 ; in five seconds, 400
feet, and so on.

SCIENCE OF COMMON THINGS. 20

Pendulum. Common clock.

166 Will a mass of iron, weighing one hundred pounds, let fall from
an elevation, reach the ground any quicker than a mass weighing only one
pound, ktfall at the same time and from the same place f

No ; the lighter mass will fall with the same velocity,
and reach the ground as soon as the larger one.

Before the time of Galileo it was taught and believed, that if two
bodies of different weights were let fall from any height at the same mo-
ment, the heavier body would reach the ground as much sooner as ita
weight was greater than the smaller. Galileo, on the contrary, main-
tained that they would both strike the ground at the same time, and, as
his doctrine was generally disbelieved, he challenged his opponents to a
practical trial. The experiment was made from the top of the celebrated
leaning tower of Pisa, in the presence of a great concourse of people, and
resulted in the complete triumph of Galileo.

167 What is the rule by which the height from which a body falls may
be found, the time consumed in falling being known?

Multiply the square of the number of seconds of time
consumed in falling, ~by the distance which a body will
fall in one second.

168 If a stone is five seconds in falling from the top of a precipice, hoio
high is the precipice f

The square of five seconds is 25 ; this multiplied by
16, the number of feet a lody will fall in one second,
gives 400, the height of the precipice.

169 What is a pendulum ?

A pendulum is a heavy body, as a piece of metal,
suspended by a wire or cord, so as to swing backwards
and forwards.

170 When is a pendulum said to vibrate f

When it swings backwards and forwards ; and that
part of the circle through which it vibrates, is called
its arc.

17*1 What is a common clock f

Merely a pendulum, with wheel- work attached to it,
to record the number of vibrations, and with a weight
or spring, having force sufficient to counteract the re-
tarding effects of friction and the resistance of the air.

17S How long must a pendulum be to beat seconds 1

About 39 inches.

178 Why does a common clock go faster in winter than in summer t
2*

30 SCIENCE OF COMMON THINGS.

Length of pendulum affects the rate of a clock.

Because the pendulum-rod becomes contracted by
cold in winter, and lengthened by heat in summer.

174: Why does a change in the length of the pendulum cause a clock to
go faster or slower f

The number of vibrations which a pendulum makes
in a giyen time depends upon its length, because a
long pendulum does not perform its journey to and
from the corresponding points of its arc so soon as a
short one.

SCIENCE OF COMMON THINGS. 31

Application of power. What are machines ?

PART n.

APPLICATION OF THE LAWS AND PROPER
TIES OF MATTER TO THE ARTS.

CHAPTER I.

HOW WE APPLY POWEB.

175 What is a machine f

By a machine we understand a combination of me-
chanical powers adapted to vary the direction, applica-
tion, and intensity of a moving force, so (is to produce
a given result.

176 What is the difference between a machine and a tool ?

The difference between a machine and a tool is not
capable of very precise distinction. A tool is usually
'more simple than a machine : it is generally used by
hand, while a machine is generally moved by some
vther than human power.

177 Does a machine ever create power, or increase the quantity of
power or force applied to it?

A machine will enable us to concentrate or divide
any kind or quantity of force which we may possess,
but it no more increases the quantity of force than a
mill-pond increases the quantity of water flowing in
the stream.

178 From what sources do we derive advantages by the use of machines
and manufactures f

From the addition they make to human power ;
from the economy they produce of human time ; from
the conversion of substances apparently common and
worthless into valuable products.

32 SCIENCE OF COMMON THINGS.

Object of machinery. Perpetual motion. Sources of power.

179 How do machines make additions to human power f

They enable us to use the powers of natural agents,
as wind, water, steam; they also enable us to use ani-
mal power with greater effect, as when we move an
object easily with a lever, which we could not with the
unaided hand.

ISO How do machines produce economy of human time f
They accomplish with rapidity what would require
the hand unaided much time to perform. A machine
turns a gun-stock in a few minutes ; to shape it by
hand would be the work of hours.

181 How do machines convert objects apparently worthless into valuable,
products f

By their great power, economy, and rapidity of ac-
tion, they make it profitable to use objects for manu-
facturing purposes which it would be unprofitable or
impossible to use if they were to be manufactured by
hand. Without machines, iron could not be forged
into shafts for gigantic engines ; fibres could not be
twisted into cables ; granite, in large masses, could not
be transported from me quarries.

182 Why are so many attempts continually made to produce mechani-
cal engines which shatt generate perpetual motion f

Because the projectors do not understand the great
truth, that no form or combination of machinery can,
under any circumstances, increase the quantity of power
applied.

183 What is the object ef a machine f

To receive and distribute motion derived from an
external agent, since no machine is capable of generat-
ing motion or moving-power within itself.

184 What are the principal sources from whence power is obtained f

Men and animals, water, wind, steam, and gunpow-
der. The power of all these may be ultimately re-
solved into those of muscular energy, gravity, heat,
and chemical affinity.

185 Are there any other sources ofpotver ?

Yes ; magnetism, electricity, capillary attraction, etc. ;

SCIENCE OF COMMON THINGS 33

Muscular energy. Horse-power. Water-power.

but none of these are capable of being used practically
for the production of motion.

186 How is muscular energy exerted f

Through the contraction of the fibres which constitute
animal muscles. The bones act as levers to facilitate
and direct the application of this force, the muscles
operating on them through the medium of tendons, or
otherwise.

187 What animals possess the greatest amount of muscular power f

Beasts of prey. Some very small creatures, how-
ever, possess muscular power in proportion to their
bulk, incomparably greater than that of the largest
and greatest of the brute creation. Kflea, considered
relatively to its size, is far stronger than an elephant or
a lion.

188 In what method can a man exert the greatest active strength f

In pulling upwards from his feet : because the
strong muscles of the back, as well as those of the up-
per and lower extremities, are then brought advan-
tageously into action. Hence the action of rowing is
one of the most advantageous modes of muscular action.

189 What is'the estimate of the uniform strength of an ordinary man
for the performance of daily mechanical labor ?

That he can raise a weight of 10 pounds to the height
of 10 feet once in a second, and continue to labor for
10 hours in the day.

10O What is a " horse-power ?" We say a steam-engine is of a cer-
tain horse-power ; what is the meaning of the term ?

The measure of a" horse's power" adopted as a
standard for estimating the power of steam-engines, is
that he can raise a weight of 33,000 pounds to the
height of one foot in a minute.

191 What is the strength of a horse compared with that of man f

The force of one horse is considered to be equal to
that of five men.

193 What do we mean by " water-power f"

The power obtained by the action of water, — applied
generally to the circumference of wheels, which it

34: SCIENCE OF COMMON THINGS.

Water- wheels. Power of steam. Gunpowder.

causes to revolve, either by its weight^ by its lateral
impulse, or "by both conjointly.

Fig. 8. Fig 9.

The most common forms of water-wheels in use are the under-shot and
over-shot, or breast-wheels. In the under-shot wheel, Fig 8, a stream of
water strikes against the " float-boards " or paddles, placed so as to receive
the impulse of the water at right angles to the radii or spokes of the
wheel. In over-shot or breast- wheels, Fig. 9, the water is received in
cells or buckets on the top or side. In this case the wheel revolves
through the agency of the weight of the water.

103 Upon what does the power of steam depend t

Upon the tendency which water possesses to expand
into vapor when heated to a certain temperature.

194 What is gunpowder f

A solid explosive substance, composed of saltpetre or
nitre, sulphur, and charcoal, reduced to powder, and
mixed intimately with each other.

105 Upon what does the power of gunpowder depend f

When brought in contact with any ignited substance,
it explodes with great violence. A vast quantity of
gas, or elastic fluid, is emitted, the sudden production
of which, at a high temperature, is the cause of the
violent effects which this substance produces.

106 Is the power produced in the explosion of powder ever used for
propelling machinery regularly f

It is not, on account of its expensiveness and the sud-
denness and violence of its action. It is chiefly applied
to the throwing of shot and other projectiles, and the
blasting of rocks.

107' What is (he estimated force of gunpowder when exploded t

SCIENCE OF COMMON THINGS. 35

Properties of a gun. Range of cannon. Explosive substances.

At least 14,750 pounds upon every square inch of
the surface which confines it.

198 What are the essential properties of a gun ?

To confine the elastic fluid generated by the explo-
sion of the powder as completely as possible, and to
direct the course of the ball in a straight or rectilinear
path.

199 Why will a rifle send a ball more accurately than a musket, or
ordinary gun ?

The space produced by the difference of diameter
between the tall and the bore of the gun greatly di-
minishes the effect of the powder, by allowing a part
of the elastic fluid to escape before the ball, and also
permits the ball to deviate from a straight line. The
advantage of the rifle-barrel is chiefly derived from
the more accurate contact of the ball with the sides of
its cavity.

J3OO To what distance may a ball be thrown by a twenty-four pounder f

"With a quantity of powder equal to two-thirds the
weight of the ball, it may be thrown about four miles.

The effective range of a twenty-four pounder is, however much less
than this.

SOI How much further would the same ball go, were the resistance of
the air removed ?

About five times the distance, or twenty miles.

2OS Why is gunpowder always manufactured in little grains f

In order to cause it to explode more quickly, by faci'
litating the passage of the flame among the particles.*

2O3 By what terms are cannon of different sizes distinguished '?

By the weight of the hall which they are capable of
discharging. Thus, we have 68-pounders, 24-pounders,
18-pounders, and the lighter field-pieces, from 4 to
12-pounders.

J3O4 Are there any more explosive substances than gunpowder f

Yery many ; but all of them are too expensive or
dangerous for practical use.

SO5 By whom was gunpowder supposed to have been discovered f

It is generally agreed that gunpowder was used by

36 SCIENCE OF COMMON THINGS.

Strength of materials. Hollow tubes.

the Chinese many centuries, before the Christian era.
In Europe, its composition and properties were dis-
covered by Berthold Schwartz, a Prussian monk, ins
the twelfth century. It was first used in battle inl
1346.

CHAPTEE II.

STRENGTH OF MATERIALS.

SOQ When materials are employed for mechanical purposes, upon what
does their power or strength, apart from the nature of ti*e material, depend
for resisting external force?

Upon the shape of the material, its hearing, and the
nature of the force applied to it.

SO7 In what position witt a bar or learn sustain the greatest application
of force f

When it is strained in the direction of its length.

SOS What do we mean by stiffness of a material f

It is the resistance to the application of force tending
to bend it.

509 How much stiffer is a beam supported at both ends, than one of
hall the length firmly faced at only one end?

Twice as stiff.

510 In what form can a given quantity of matter be arranged so as to
oppose the greatest resistance to a bending force f

In the form of a hollow tube or cylinder.

511 Why are the bones of man and animals hollow and cylindrical f

Because in this form they can with the least weight
of material sustain the greatest force. In man and
animals, the hollow part of the bones is filled with an
oily substance called marrow.

SIS Why are the quills of birds hottow and empty of marrow t

SCIENCE OF COMMON THINGS. 37

Stems of grasses hollow. Limit to the size of ships.

In order that they may possess the greatest strength,
and by their lightness assist in flying.

213 Why are the stems of seeds and grain-bearing plants hollow tube? 1

Because this disposition of matter gives to the stalk
its greatest strength, enables it to resist the action of
*the wind, and sustain, without breaking, the ripened
ear of grain or seed.

314 Is a column with ridges projecting from it, stronger than one that
w perfectly smooth f

It is.

SIS Why is a hoUow tube of metal stronger than tfie same quantity of
metal as a solid rod f

. Because its substance standing farther from the
centre, has a greater power of resisting a bending
force.

S1G Of two bodies of similar shape, but of different sizes, which is pro-
portionably the weaker f

The larger. That a large body may have propor-
tionate strength to a smaller, it must have a greater
proportionate amount of material ; and beyond a cer-
tain limit, no proportions whatever will keep it to-
gether ; but it will fall in pieces by its own weight.

SIT* Why cannot trees attain an unlimited height of trunk f

Because, beyond a certain limit, the weight of the
material will overcome the supporting strength of the
material.

£18 Why is it impracticable to build ships beyond a certain size f

Because the weight of the timber and other materials
contained in them tends to cause them to fall apart.

In 1825, two vessels, the largest ever constructed, were built in Ca-
nada, of 10,000 tons burden. They were found to be weak from their
size alone, and were both lost on their first voyage.

SCIENCE OF COMMON THINGS.

Ce»enta. Quicklime. Whitewash.

CHAPTEE III.

APPLICATION OF MATERIALS FOB ARCHITECTURAL OR
STRUCTURAL PURPOSES.

210 What are cements?

Cements are for the most part soft or semi-fluid sub-
stances which have the property of becoming hard in
time, and cohering with other bodies to which they have
been applied.

22O Of what are the ordinary cements which are called mortars com-
posed f

Of quicklime, sand, and water.

{321 What is quicklime?

Quicklime is principally pure lime, and is obtained,
from the limestone rock, ordinary marble, or shellr,
which are composed of carbonate of lime, by calcina
tion. The effect of the burning is to drive on the car-
bonic acid, leaving the lime pure and uncombined.

J3SS What is slacked lime f

If quicklime obtained as above described be wet
with water, it instantly swells and cracks, becomes
exceedingly hot, and at length falls into a white, soft,
impalpable powder. This is denominated "slacked
lime.

223 What is ordinary whitewash f

A mixture of slacked lime with water.

224 Why should slacked lime intended for mortars be excluded from
the air, or used soon after it has been prepared f

Because if exposed to the air it absorbs carbonic
acid, and becomes converted again into its former con-
dition of carbonate of lime.

225 Why does mortar become hard after a few days f

A portion of the water evaporates, and the lime by
a sort of crystallization adheres to the particles of sand

SCIENCE OF COMMON THINGS. 39

Mortar. Htucco. Color of bricks.

and unites them together. The lime also gradually
becomes converted into carbonate of lime.

336 What sand is mest suitable for the formation of mortar f

That which is wholly silicious and is sharp / that is,
not having its particles rounded by attrition.

337* What are the proportions of lime and sand in good mortar f

The proportions are varied in different places : the
amount of sand, however, always exceeds that of the
lime. The more sand that can be incorporated with
the lime the better, provided the necessary degree of
plasticity is preserved.

338 What are water, hydraulic, or Roman cements f

Those which have the property of hardening under
water, and of consolidating almost immediately on be-
ing mixed.

330 To what cause do the water-cements owe their property of becoming
hard under water f

The cause is not satisfactorily known : all water-
cements contain a portion of burnt clay, which proba-
bly absorbs immediately all superabundant moisture
from the lime, and thus expedites its solidification.

This explanation is rendered more probable from the fact, that if the
clay is burnt sufficient to vitrify it or convert it into brick, it ceases to
form a water-cement.

330 What are the constituents of a water-cement f

Quicklime, sand or silica, and a proportion of clay.

331 What is stucco f

Stucco is composed of various ingredients, generally
of "plaster of Paris," sometimes ot white marble pul-
verized and mixed with plaster and lime.

333 What is terra-cotta f

Literally, baked clay, a name given to statues, archi-
tectural ornaments, vases, figures, etc., modelled of
potters'-clay and fine colorless sand, and afterwards
exposed to a most intense heat.

333 Why are bricks when burned usually of a red color ?

Because the iron contained in the clay is converted

4:0 SCIENCE OF COMMON THINGS.

Brides with straw. Tiles] Mastic.

by the heat into the red oxide of iron, and acts in this
state as red coloring material.

334 Why are the bricks manufactured at Chicago, and some other
parts of the Western country, of a white or yettow color f

Because the clay of which they are formed does not
contain sufficient iron to color them.

335 Why did the children of Israel in making bricks desire to mix
straw with the clay f

j, The bricks of the Egyptians were composed of clay
simply baked in the sun, and not burnt. By using
straw the clay was held together more firmly and the
brick rendered stronger.

336 Why are the Egyptians enabled to dispense with the process of
burning the bricks ?

The extreme dryness of the climate in which they
were used enable them to dispense with the burning.
Bricks from Egypt and Babylon, which have remained
exposed to the open air uninjured for two thousand
years, rapidly fall to pieces when transported to a
moist climate.

237 Why do we mix hair with mortar f

In order to render it more cohesive and stronger.

338 What are tiles f

Plates of burnt clay resembling bricks in composi-
tion and manufacture, and used for the coverings of
roofs or floors.

339 What is mastich or mastic t

The name given to those cements which contain ani-
mal or vegetable substances in composition. Mastich
used for the external decoration of houses often con-
tains oil and a preparation of lead.

340 What is putty?

Putty, used by glaziers in setting window-glass and
for other purposes, is composed of whiting and linseed-
oil, mixed and worked together. "Whiting is simply
common chalk ground and purified.

SCIENCE OF COMMON THINGS.

Principles of architecture. Properties of a good building.

CHAPTER

PRINCIPLES OF ARCHITECTURE
341 What is architecture ?

In its general sense it is the art of erecting buildings.
In modern use, this name is often restricted to the ex-
ternal forms or styles of building.

343 To what cause do the different varieties of architecture owe their
origin ?

To the rude structures which the climate or materials
of any country obliged its early inhabitants to adopt
for temporary shelter.

These structures with all their prominent features have been afterwards
kept up by their refined and opulent posterity. Thus the Egyptian style
of architecture had its origin in the cavern or mound; the Chinese archi-
tecture is modelled from the tent; the Grecian is modelled from the
wooden cabin ; and the Gothic from the boiver of trees.

343 What kind of shape is it most probable that the fa'st human habi-
tations assumed ?

We have every reason to believe that huts of a
conical form were first constructed.

344 Why?

First, on account of their being easily erected, and
as easily^ removed ; secondly, because their declivity
on all sides would cause the rain to run off; and,
thirdly, owing to their breadth at the base and their
gradually growing to a point at the top, they were
capable of resisting the ordinary force of the wind.

345 Are conical huts anywhere in use at the present time f

Yes ; we find them still used by the uncultivated in-
habitants of the South Sea Islands, by the American
Indians, by the Hottentots, the Kamskatschans, and
other uncivilized tribes.

346 What are the three chief properties of a good building f

Usefulness, strength, and beauty.

347* Ifrw are they to be attained f

SCIENCE OF COMMON THINGS.

Essentials for building. Pile.

Mortising.

The proper arrangement of the respective parts of
the building will insure its usefulness. Its strength
will principally depend on the walls being laid on a
good and firm foundation, of sufficient thickness at the
bottom, and standing perfectly perpendicular. And if
all the parts of a building correspond with each other,
and are handsome in themselves, then the architect
may rely on its beauty.

S4S What are the essential elementary parts of a "building f

Those which contribute to its support, indosure, and
covering.

J349 What is a pile?

A cylinder of wood or metal pointed at one extremity
and driven forcibly into the earth, to serve as a support
or foundation of some structure. It is generally used
in marshy or wet places, where a stable foundation
could not otherwise be obtained.

25O Why are long columns supporting great weights made smaller- at
the top than at the bottom f

Because the lower part of the column must sustain,
not only the weight of the superior party but also the
weight which presses equally on the ' whole column.
Therefore the thickness of the column should gradually
decrease from bottom to top.

251 In the construc-
tion of buildings various
terms are employed to de-
signate the method in
which the timbers are
fitted into each other: what
do we mean by mortising ?

Mortising is a
method of insertion
in which the pro-
jecting extremity
of one timber is
received into a perforation in another. (See Jig. 10.)

S32 Why are steep roofs, or those constructed with considerable incli-
nation, best adapted for houses in cold climates ?

In order that the snow may not be retained upon

Fig. 10.

SCIENCE OF COMMON THINGS.

Tenons. Scarfing. Tongueing. Arch.

them, which otherwise would be liable to injure the
building by its weight.

253 What is a mortise ?

The opening or hole cut in one piece of wood to
admit the projecting extremity of another piece.

254 What is a tenon?

The end of a piece of timber which is reduced in di-
mensions so as to be fitted into a mortise for fastening
two timbers together.

255 What is scarfing and interlocking t

It is that method of insertion in which the ends of
pieces overlay each other, and are indented together, so
as to resist longitudinal strain by extension, as in tie
bearers and the ends of hoops. (See fig. 11.)

256 What is tongueing and rabbeting f

It is that method of insertion in which the edges of
boards are wholly or partially received by channels in,
each other.

257 What is an arch t

It is a part of a structure or building suspended over
a hollow, and concave towards the area of the hollow.

253 Is it known at what time the arch was invented ?

It is not ; it does not appear to have been known to
the ancients.

259 Why is an arch capable of resisting a greater amount of pressure
than a horizontal or rectangular structure constructed of* the same ma-
terials f

Because the arrangement of the materials composing

44 SCIENCE OF COMMON THINGS.

Dovetailing. Construction of the skull. Egg-shells.

the arch is such, that the force which would break a
horizontal beam or structure is made to compress all the
^articles of the arch alike, and they are therefore in no
danger of being torn or overcome separately.

S6O What is meant by dovetailing?

It is a method of insertion in
which the parts are connected
~by wedge-shaped indentations,
which permit them to be sepa-
rated only in one direction. (See

F«. 12. """ ' J1^' *rv

SGI What beautiful application of the arch exists in the human struc-
ture ? ~

In the skull, protecting the brain. The materials
are here so arranged as to present the greatest strength,
with the least weight.

S6J3 Why is it difficult to break an egg by pressing directly upon its
ends ?

Because the shell of the egg is constructed on the
principle of the arch, and is therefore capable of re-
sisting great pressure.

SG3 Why is a dished or arched wheel of a carriage much stronger for
resisting all kinds of shocks than a flat wheel?

In an arched or dished wheel, the extremity of a
spoke cannot be displaced inwards, or towards the car-
riage, unless the rim of the wheel be enlarged, or all
the other spokes yield at the same time ; and it cannot
be displaced outwards, unless the rim be diminished,
or the other spokes yield in an opposite direction.

Now the rim, being strongly bound with a tire of iron, cannot suffer
either increase or diminution, and the strength of all the spokee is thus
conferred by it on each individually. In a flat wheel, a given degree of
displacement, outwards or inwards, of the extremities of a spoke, would
less affect the magnitude of the circumference, and therefore the rim of
such a wheel secures it much less firmly.

S64 Why are the fore wheels of carriages smaller than the hind
wheels ?

Because they facilitate the turning of the carriage.
The advantage of the wheel is proportioned to the mag-

SCIENCE OF COMMON THINGS. 45

Arch. Orders in architecture, Gothic structures.

nitude ; the smaller wheel having to rise a steeper
curve.

365 WJiat is an abutment f

The vertical wall which sustains the base, or " spring"
of an arch.

366 What is meant by an order in architecture f

By an architectural order, we understand a certain
mode of arranging and decorating a column, and the
adjacent parts of the structure which it supports or
adorns.

367 How many orders are recognised?

five: — the Doric, Ionic, and Corinthian, derived
from the Greeks; to these the Romans added two
others, known as the Tuscan and Composite.

368 How do pilasters differ from columns f

Only in their plan, which is square, as that of
columns is round : pilasters are attached to walls.

369 What is a portico f

A portico is a continued range of columns covered at
the top to shelter from the weather. The portico of the
temple at Palmyra was full four thousand feet long.

370 What are balusters?

Small columns, or pillars of wood, stone, <&c., used
in terraces or tops of buildings for ornament ; also to
support railing. When continued for some distance,
they form a balustrade.

371 WJieredidthe Gothic order of architecture originate?

Among the northern nations of Europe. After the
destruction of the Roman empire, it was introduced to
the exclusion of the Greek and Roman manner of
architecture. It seems particularly adapted to reli-
gious edifices.

373 What are the characteristics of the Gothic architecture f

Pointed arches, with greater height than breadth in
the proportions, with profuse ornament, chiefly de-
rived from an imitation of the leaves and flowerg of
plants.

4:6 SCIENCE OF COMMON THINGS.

Bad taste in architecture. Columns. Capitals.

— — — — : . .. . ' — — — . — . *

373 What is said to have been the model of the aisle of a Gothic cathe-
dral?

A group of tall trees, meeting at tlie top with, inter-
woven branches.

374 Ought architecture to be considered as a fine or a useful art f

As a useful art.

It is degrading the fine arts to make them entirely subservient to
utility. It is out of taste to make a statue of Apollo hold a candle, or a
line painting stand as a fireboard. Our houses are for use, and architec-
ture is therefore one of the useful arts. In building, we should plan the
inside first, and then the outside to cover it.

375 Why is it bad taste to construct a dwelling-house in the form of a
Grecian temple f

Because a Grecian temple was intended for external
worship, not as a habitation or a place of meeting.

370 Had the Goths, who plundered Rome, anything to do with the
invention of Gothic architecture f

No; the name was introduced abont two hundred
years ago as a term of reproach, to stigmatize the
edifices of the Middle Ages, which departed from the
purity of the antique models.

377 What is the facade of a building t

Its front.

278 What is a pedestal f

The lower part or base of the column ; a continued
base, on which a range of columns is erected, is called
a stylobate.

379 What is the base of a column f

The lower part, where it is distinct from the shaft.

380 What is the shaft f

The middle or longest part of the column.

381 What is the capital f

The upper or ornamental part resting on the shaft.
The height of a column is measured in diameters of
the column itself, always taken at the base.

383 What is the plinth f

This term is applied to the lower part of the pedestal,
or to any square projecting basis, such as those at the

SCIENCE OF COMMON THINGS.
Entablaturel Architrave. Frieze.

bottom of walls, and under the base of columns. The
lower part of the pedestal being called the plinth, the
middle part will be termed the die, and the upper
part the cornice of the pedestal. (See fig. 13.)

r Entablature

Column..

Stylobate or Pe-
destal.. ...

....Plinth.

283 What is the entablature f

The horizontal continuous portion which rests upon
the top of a row of columns.

S84 What is the architrave f

The lower part of the entablature.

What is the frieze t

4:8 SCIENCE OF COMMON THINGS.

Durability of building materials. Effect of the atmosphere on rocks.

The middle part of the entablature.

S86 What is the cornice f

The upper or projecting part of the entablature^
(For illustration of these different terms, see fig. 13.)

28*7 In selecting a stone for architectural purposes, how may we be able
to form an opinion respecting its durability and permanence?

By visiting the locality from whence it was obtained,
we may judge from the surfaces which have been long
exposed to me weather if the rock is liable to yield to
atmospheric influences, and the conditions under which
it does so.

" For example, if the rock be a granite, and it be very uneven and
rough, it may be inferred that it is not very durable; that the feldspar,
which forms one of its component parts, is more readily decomposed by
the action of moisture and frost than the quartz, which is another ingre-
dient ; and therefore that it is very unsuitable for building purposes.
Moreover, if it possesses an iron-brown or rusty appearance, it may be
set down as highly perishable, owing to the attraction which this metal
has for oxygen, causing the rock to increase hi bulk, and so disintegrate."

388 Why are the sandstones, termed freestones, ill adapted for the
external portions of exposed buildings f

Because they readily absorb moisture ; and in coun-
tries where frosts occur, the freezing of the water in
the wet surface continually peels off the external por-
tions, and thus, in time, all ornamental work upon the
stone will be defaced or destroyed.

389 Why do some species of rock become harder when taken from the
quarry and exposed to the atmosphere f

This quality, in some species of stone, arises from
the fact that the water contained in it, when forming
part of the natural rock, evaporates, and the stone,
becoming dryer, becomes harder.

390 Why do some stones, altlwugh hard when first quarried, become
friable, and fall to pieces, when exposed to the atmosphere '(

Because they contain clay or alumina in such a state
as to readily absorb moisture from the atmosphere ; and
through the agency of the moisture the particles lose
their cohesion and tall apart.

SCIENCE OF COMMON THINGS. 49

Laws and phenomena of fluids. Water in motion and at rest.

PAET III.

THE LAWS AND PHENOMENA OF FLUIDS,

S91 Into what two classes may all fluid substances "be divided?

Into liquids, as water, oil, molasses, etc. ; and into
gases, as common air, carbonic acid gas, oxygen, and
others.

J393 What designation do we give to those branches of science, which
treat of the laws and phenomena of liquids ?

Hydrostatics, which considers the laws and pheno-
mena of water and other liquids in a state of rest ; and
hydraulics, which considers the laws and phenomena
of liquids in motion.

S93 What designation do we give to that department of science which
treats of the laws and phenomena of gases, and other substances resembling
air ?

We apply the term Pneumatics to that department
of science which explains and illustrates those pheno-
mena which arise from the weight, pressure, or motion
of common air and other gaseous bodies.

CHAPTEE I.

WATER IN MOTION AND AT REST.

S94 When water or any other fluid is at rest, in what condition is its
surface ?

The surface of water at rest is always perfectly level.

SCIENCE OF COMMON THINGS.

Velocity of rivers.

How we make an aqueduct.

595 Why is the surface of a fluid at rest always kvel ?

Because the particles are equally attracted towards
the earth ly gravity, and are all equally and perfectly
movable among themselves.

596 How slight a declivity is sufficient to give a running motion to
water ?

Three inches to a mile in a smooth, straight channel,
gives a velocity of about three miles per hour. The
river Ganges, at a distance of 1800 miles from its
mouth, is only 800 feet above the level of the sea.

£97 On what principle are we enabkd to conduct water under ground
through irregular tubes ?

On the principle that water will always rise to an
exact level in different tubes, pipes, or vessels communi-
cating with each other.

If we connect together a
series of vessels, no matter
how various their shapes and
capacities, so that water may
rise from the main channel,
A B, into them, we shall find
upon pouring water into one
that it will rise to the same
Fig- 14. level in all the vessels.

The dependence of all arrangements for conveying water in aqueducts
under ground upon the principle, that water in closed tubes or vessels
rises to a uniform level, is clearly shown in Fig. 15 : a, a, a, represents
the water-level of a pond or reservoir upon elevated ground. From this
pond a line of pipe is laid, passing over a bridge or viaduct at d, and

Fig. 15.

under a river at c. The fountains, at &, 6, show the stream rising to it3
level in the pond, a, at two points of very different elevation.

S98 In what part of a river does the water flow most rapidly f

In the middle of the stream, at the surface. On the

SCIENCE OF COMMON THINGS. 51

Origin of springs. How water collects in wells.

sides and bottom the velocity is diminished by the
friction of the water against the banks, bars, etc.

S99 Wliat is the origin of springs 1

The water falling upon the earth sinks downwards
through the sand and porous materials, until an imper-
vious bed of clay or rock is reached. Here the water
accumulates, and finally bursts out at some point where
the impervious bed or strata comes to the surface in
consequence of a valley or excavation.

Suppose a (Fig. 16) to
be a gravel hill, and b
a strata of clay or rock,
impervious to water.
The fluid percolating
through the gravel
would reach the imper-
•~~ " vious strata, along

which it would run un-
til it found an outlet at c at the foot of the hill, where a spring would be
formed.

SOO Why does not the water ooze out everywhere along the line of June*
tion of the two formations — the gravel and the rock or clay — so as to form
one continuous land soak, instead of a few springs only, and these far distant
from one another ?

For two reasons : first, on account of rents and fis-
sures in the layers of rock, which act as natural drains •
secondly, the existence of inequalities in the surface
of the impermeable stratum, which lead the water, as
valleys do on the external surface of a country, into
certain low levels and channels.

3O1 Why does the water coUect in an ordinary well f

An ordinary well consists of an excavation continued
until a stratum or layer of clay or rock is reached that
is permanently saturated with water. They are not
commonly supplied by springs, but merely by the
draining of the , water which exists within the circuit
of a few yards into a cavity.

SOS Why do wells and springs fail oftentimes in dry weather f

Because they are supplied by the water fallina as
rain, which percolates from the surface of the earth.

52 SCIENCE OF COMMON THINGS.

Artesian wells.
SO3 What is an Artesian weU?

Water is sometimes obtained by Coring into the
earth with a species of auger, until a vein or sheet of
water is found, which rises to the surface through the
cylindrical excavation. Such excavations are called
Artesian wells, because the method was first invented
and employed at Artois, in France.

/(•; 3O4 How do you account for the water rising to the surface in Arte-
sian, and sometimes in ordinary wells ?

Strata which are pervious frequently alternate with
others which are not so ; or may form a basin, the
area of which is partially filled with clay, through
which water cannot pass ; in such a case it is obvious
that the bed of sand beneath the clay, fed by the rain
which descends on the uncovered margin of the basin,
must form a reservoir where the water will gradually
accumulate beneath the central layer of clay, through
which it cannot escape. If the bed of clay be pene-
trated by natural or artificial means, the water must
necessarily rise to the surface, and may even be thrown
up in a jet to an altitude which will depend on the
level of the fluid in the subterranean reservoir.

Fig. 17.

Thus, if a sandy stratum, a a (Fig. 17), acting as a filter, occupies an
inclined position between two other strata impervious to water, such
as clay, the water being absorbed by the superficial parts of the strata,
a» at a a (which may be of very great extent), will penetrate through its
whole depth, and, finding no egress below on account of the basin-like
form of the stratum, or from its resting at the lower termination upon a
compact rock, will accumulate. The porous strata, therefore, becomes a
reservoir tp a greater or less extent, and if, by boring through the super-
incumbent mass, we form an opening into the stratum, as at 6, the water

SCIENCE OF COMMON THINGS. 53

Effect of drainage upon springs. Pressure of water.

will rise in it, and flow over in a jet proportional to the height of the
water accumulated in the stratum from whence it flows.

305 What general effect does the cultivation and drainage of a country
have upon the springs ?

In a well cultivated and improved country the
springs are comparatively few in number and not con-
stant, While the face of a country is rough, the rain-
water remains long among its inequalities, slowly sink-
ing into the earth ,to feed the springs, or slowly run-
ning away from bogs and marshes towards the rivers ;
but in a well drained, country the water runs off quick-
ly, often producing dangerous floods.

SOS How is the pressure of water exerted?

Equally in all directions.

SOT* Does ivater, contained in a vessel, press with as great force against
t)ie sides and top as against the bottom ?

The pressure, in all directions, is the same

SOS What is the result if a corked empty bottle be lowered into the
ocean for a considerable depth ?

The cork is generally forced inwards at a given
depth, no matter in what direction the mouth of the
bottle may happen to point.

SOD Jf the cork is fastened immovably into the bottle, what will be the
effect?

The bottle will be crushed inwards by the pressure
before it reaches a depth of sixty feet.

S1O When a ship founders in shallow water, the wreck, on breaking to
pieces, generally comes to the surface and is cast upon the shore ; but when
a ship sinks in very deep water, it never rises : why is this f

The pressure of very deep water forces the water
into the pores of the wood, and makes it so heavy that
no part of the wreck is enabled to rise again.

311 Can you sink a cork so deep that it will riot rise to the surfact
ugain t

At a great depth the water forced by pressure into
the pores of the cork renders it so heavy that it cannot
rise.

313 What is the pressure of water expressed in numbers f

The pressure of water at any depth, whether on the
3*

SCIENCE OF COMMON THINGS.

What is water ? "What is hard water ?

sides of a vessel or on its bottom, or on any body im-
mersed in it, is nearly one pound on the square inch
for every two feet of depth.

313 What is water?

Water is a fluid composed of oxygen and hydrogen,
in the proportion of eight parts of oxygen to one part
of hydrogen.

314 Why is water fluid?

Because its particles are kept separate by latent
heat ; when a certain quantity of this latent heat is
driven out, water becomes solid, and is called ice.

By increasing its latent heat, the particles of water are again subdivided
into invisible steam.

315 Why is spring water generally called "hard water?",

Because it is laden with foreign matters, and will
not readily dissolve substances immersed in it.

316 What makes spring or well water geneartty hard ?

"When it filters through the earth, it becomes im-
pregnated with sulphate of lime, carbonate of lime,
carbonic acid, magnesia, and many other impurities,
from the earths and minerals with which it comes in
contact.

31 7 What is the cause of mineral springs ?

"When water trickles through the ground, it dissolves
some of the substances with which it comes in contact ;
if these substances are retained in solution, the water
will partake of their mineral character.

318 When is a mineral water called a chalybeate ?

When it contains iron, in some form, dissolved in it.

319 Mineral springs exist in all parts of our country : what is the
nature of the substances contained in them ?

The great majority of them are only impregnated
with iron, salt, or sulphur. Some few, however, con-
tain many different substances, as the mineral waters
of Saratoga.

3J3O Why are springs containing iron in large quantities beneficial to
tome invalids ?

Because the iron contained in the water acts as a

SCIENCE OF COMMON THINGS. 55

Purity of waters. Air in water. Do fishes breathe air?

ionic j that is, it strengthens and invigorates the sys-
tem.

331 What quantity of mineral matter is generally contained in com-
paratively pure natural waters ?

Any water which contains less than fifteen grains of
solid mineral matter in a gallon, is considered as com-
paratively pure. Some natural waters are known so
pure that they contain only gV th of a grain of mineral
matter to the gallon, but such instances are very rare.

Waters obtained from different sources may be classed as regards com.
parative purity as follows :

Rain water must be considered as the purest natural water, especially
that which falls in districts remote from towns or habitations; then
comes river water; next, the water of lakes and ponds; next, spring
waters ; and then the waters of mineral springs. Succeeding these, arc
the waters of great arms of the ocean into which immense rivers dis-
charge their volumes, as the water of the Black Sea, which is only
brackish ; then the waters of the ocean itself; then those of the Mediter-
ranean and other inland seas ; and last of all, the waters of those lakes
which have no outlet, as the Dead Sea, Caspian, Great Salt Lake of
Utah, etc. etc.

333 How much solid matter is ordinarily contained in a gallon of sea
water f

From twenty-two hundred to twenty-eight hundred
grains.

333 H<JW much solid matter is contained in a gallon of water from the
Dead Sea?

From eleven thousand to twenty-one thousand grains,
or nearly one-fourth part of its weight.

334 Does air exist in all natural waters f

It does : fishes and other marine animals are depend-
ent on the air which water contains for their existence.

335 Would absolutely pure water act as a poison to a fish f

The fish would die of suffocation in such water.

336 Where is the purest water to be found as a natural product f

The purest natural water that can be procured is-
obtained by melting freshly-fallen snow, or by receiv-
ing rain in clean vessels at a distance from houses.

337 Why is flowing water not liable to become stagnant?

Because its currents carry away all contaminating
substances to the sea.

56 SCIENCE OF COMMON THINGS.

Spring water sparkles. Eain water, why soft.

338 What makes water bubble and sparkle f

The air or gas contained in it.

339 Why does soapy water, especially, lullle 1

Because soap makes water tenacious, and prevents
the bubbles from bursting as soon as they are formed.

330 When soap-bubbks are blown from a pipe, why do they ascend f

Because they are filled with the warm air of the
lungs, which is lighter than cold air.

331 Why is water fresh from the well or fountain more sparkling and
refreshing than the same water after it has been for some lime exposed to
the air ?

All spring and well waters contain atmospheric air,
oxygen, and carbonic acid gases, dissolved in them.

The amount of these substances contained in water, depends upon its
temperature, cold water dissolving and retaining a larger quantity than
warm or tepid waters. When cold waters from springs or fountains are
exposed to the air, they become elevated in temperature, and the gases
contained in them escape, rendering the water flat and insipid. The
principal agent in imparting a sparkle and freshness to water is atmo-
spheric air, and not carbonic acid, as is often supposed and taught. The
quantity of carbonic acid present in ordinary spring waters is generally
inconsiderable.

333 Why is it difficult to wash with hard water f

Because the water contains saline matters, which
deprive the water of a part of its solvent power.

333 Why is it difficult to wash with soap in salt water ?

Because soap is insoluble in salt water.

334: Why does water clean dirty linen f

Because it dissolves the stains as it would dissolve salt.

335 Why does soap greatly increase the cleansing power of water f

Because many stains are of a greasy nature ; and the
alkali of the soap has the power of uniting with greasy
matters, and rendering them soluble in water.

336 Why is rain water soft f

Because it is not impregnated with earths and mine*
rals.

337 Why is it more easy to wash with soft water than with hard?

Because soft water ^^nites freely with soap and dis-
solves it ; in hard water the soap is either insoluble 01

SCIENCE OF COMMON THINGS. 57

Action of soap on water. The sea, why salt ?

becomes decomposed. The solvent power of water
increases also with its purity or softness.

333 When we wash with soap in water what chemical action takes
place ?

The soap is resolved into a fatty substance and an
alkali ; the alkali dissolves most of the organic sub-
stances which constitute the dirt which we wish to
remove, and the greasy matter effects by its lubricity
an easy washing away of the dissolved matter from
other substances.

330 Why do wood ashes render hard water soft ?

Because they contain a powerful alkali — potash,
which removes or neutralizes those impurities in the
water which rendered it hard and unfit for washing.

340 Why does sugar or salt give a flavor to water f

Because the sugar or salt (being separated into very
minute particles) floats about in the water, and mixes
with it intimately.

341 Why does hot water dissolve sugar and salt more readily than
cold water t

Because the heat of the water assists its solvent ac-
tion, and opens for the water a passage through the
particles of the substance.

343 Why is the sea salt ?

The sea has undoubtedly derived all its salt and
other soluble mineral substances by washings from
the land. The streams that have flowed into it for
ages have been constantly adding to its quantity, until
it has acquired its present condition.

343 Why is not rain water salt, although most of it is evaporated
from the sea f

Because salt will not evaporate, and therefore when
sea water is turned into vapor, its salt is left behind.

344 Is there more or less of salt in every spring, river, or lake ?

The saline condition of sea water is but an exagge-
ration of that of all ordinary lakes, rivers, and springs ;
they all contain more or less of salt, but their contents

58 SCIENCE OF COMMON THINGS.

Salt lakes. Effect of salt in the ocean. Mineral springs.

are continually changing and discharging themselvea
into the sea ; therefore the salt does not accumulate,

345 Is every lake into which rivers flow, and from which there ts no
outlet except by evaporation, a salt lake f

It is j and it is curious to observe that this condition
disappears when an artificial outlet is provided for such
waters.

Such lakes are the Dead Sea, the Caspian, the Sea of Aral, and the
Great Salt Lake of Utah, the saltness of all of which exceeds that of the
ocean.

346 What good purposes does the presence of so much salt in the ocean
subserve f

It depresses the freezing point of the water many de-
grees, thereby diminishing the dangerous facility with
which fields of ice are formed in the polar regions ; it
also aids in preventing the corruption of the water by
the accumulation of animal and vegetable remains.

347 What are the substances extracted from the earth which we find
in sea water ?

The most abundant substance is common salt ; next,
certain combinations of magnesia : then salts of lime,
with small proportions of potash, iron, iodine, and bro-
mine.

348 Are these substances found in most springs f

With the exception of iodine and bromine, they may
be found in small quantities in almost all springs and
rivers.

349 Are those substances which we caU impurities in water of any ser-
vice to animal or vegetable systems f •

They give to water its freshness and sparkling pro-
perties j pure distilled water is very disagreeable to
drink ; these substances are also generally beneficial to
the systems of plants and animals, and are absorbed by
them with the water.

350 Does water form part of the composition of most bodies f

It enters directly into the composition of nearly all
crystallizdble bodies and most organic compounds.

351 If the waters of the ocean were not agitated by winds, currents,
and tides, what would be the effect f

SrfENCE OF COMMON THINGS. 59

What are tides ? Cause of tides. High and low tides.

The water would become stagnant.

352 Will waier contaminated with animal and vegetdbk matter under
some circumstances purify itself f

Water contaminated with animal and vegetable mat-
ter, if kept for some time, undergoes a spontaneous
purification, losing its offensive odor and color, and
depositing more or less sediment. "Water, for the sup-
ply of ships, is well known to undergo this process of
purification by fermentation ; and the larger the quan-
tity of destructible matter suspended in it, the more
complete and rapid is its purification.

353 What is a tide f

A tide is a wave of tJie whole ocean, which is elevated
to a certain height, and then sinks, after the manner
of a common wave.

354 What te the cause of tides f

The attraction of the sun and moon upon the waters
of the ocean. The moon being nearest to the earth,
her attraction is six times greater, than that of the sun.
This attraction of the moon raises the waters of the
ocean as they come under her influence by the motion
of the earth on its axis.

355 How many tides are there in a day f

Two in every lunar day — a period of 24 hours 49

minutes.

350 What tides are the highest f

The spring tides.

357* Why are they higher than at other periods ?

Because the sun and moon are then in such a posi-
tion that they exert their influence together. For every
five feet of height in tide produced by the moon, the
influence of the sun adds one foot.

358 What are neap tides t

Low tid.es.

35Q Why are neap tides lower than other tides f

Because then the sun and moon have such positions
that their attractive influence is opposed to each other ;

60 SCIENCE OF COMMON THINGS.

Tide movements. Ebb a d flow. Sea waves.

and for every six feet of the moon's tide, the opposite
attraction of the sun takes away one foot.

36O How fast does the tide wave move f

The rate of movement of the tide wave depends
upon the nature and depth of the sea bottom. With a
depth of one fathom, its rate is eight miles per hour ;
and with one hundred fathoms, eighty miles per hour.

\ 361 Does the height of the same tide vary in different places f

The height of the tide in different places depends
much on the configuration of the land ; the same tide
may rise in one place three inches, and in another
place thirty feet.

36S At what period during the day is it high water t

"When the moon passes the meridian — that is, when
it is nearly vertical over the place — the sea is elevated
to the greatest extent, and it is said to be high water.

363 When is it low water f

"When the moon is upon the horizon, or about six
hours after high tide. As the moon passes the meri-
dian below the horizon, another elevation occurs, so that
we have the ebb and flow of the tide twice every day.

364 How much later does the tidal eHb and flow occur each day f

The time becomes later every day by about fifty
and a half minutes, which is the excess of a lunar day
above a solar one: 28-J- minutes of the former being
equal to 27^ minutes of the latter.

365 What is the cause of ordinary sea waves f

The wind, pressing unequally on the surface of the
sea, depresses one part more than another ; every de-
pression causes a corresponding elevation, and these
undulations are called waves.

It must be remembered that waves have no other than a vertical m,o-
tion, i.e. up and down. Any substance, as a buoy, floating on a wave,
is merely elevated and depressed alternately; it does not otherwise
change its place.

366 If waves are stationary, and only move up anddmon, why do they
seem to advance towards the shore f

This is an ocular deception. When a corkscrew is

SCIENCE OF COMMON THINGS. 61

Breakers. Spray of waves. Swr£

turned round, the thread appears to move forward ;
and the apparent onward motion of the waves of the
sea is a similar delusion.

367 What is the cause of breakers ?

The interference of rocks or rising ~banks^ in the sea
with the regular form of the wave, by which the out>
line or curve of the wave is broken.

368 What causes the spray of waves f

The wind driving the surface of the water from the
top of the wave, and scattering the small particles in
all directions.

369 What is the surf?

When the shore runs out very shallow for a great
extent, the breakers are distinguished by the name of
surf.

SVO What do we know concerning the magnitude and velocity of ocean
waves ?

On the Atlantic, during a storm, the waves rise to a
height of about forty-three feet above the hollow occu-
pied by the ship ; the total distance between the crests
of two large waves being 559 feet, which distance is
passed by the wave in about seventeen seconds of time.

371 With what velocity is it estimated that such storm waves as the
above described travel f

At the rate of about thirty-two miles per hour.

A wave is a /orw, and not a thing ; the form advances, but not the
substance of the waves.

3753 If a cock at the extremity of a pipe be suddenly closed while water
is running through, why is a noise and shock produced ?

Because the forward motion of the whole body of
the water contained in the pipe being instantly arrested,
and the momentum of a liquid being as great as that
of a solid, the water strikes the cock with as much force
as if it were a long bar of metal, or a rod of wood hav-
ing the same weight and velocity as the water. Then,
as a fluid presses equally in all directions, a leaden
pipe of great length may be widened, or even burst in
the experiment.

62 SCIENCE OF COMMON THINGS.

Why 1ce floats and iron sinks in water. Platinum and hydrogen.

CHAPTER II.

SPECIFIC GRAVITY".

373 Why does ice float upon water f

Because it is lighter than water.

374 Why does iron sink in water f

Because it is heavier than water.

37*5 If we put a piece of ice in alcohol, it sinks ; if we put a piece, of
iron upon quicksilver, it floats : why is this f

Because the ice is heavier than the alcohol, and the
iron is lighter than the quicksilver.

37*6 What do we mean, when we say that ice is lighter than iron ?

We mean that, taking equal bulks of each, the former
weighs less than the latter ; and when we say that
quicksilver is heavier than water, we mean that, in
equal volumes, as a pint, for instance, the quicksilver
has a greater weight than the water.

377 What, then, is specific gravity f

It is the weight of a body compared with the weight
of an equal bulk of water.

378 How does it differ from ordinary or absolute weight f

In absolute weight no regard is paid to the volume or
bulk of substances. In specific weight, a given bulk
or volume is compared with an equal volume or bulk
of water.

379 What body has the greatest specific weight f

Purified platina, which is 22 times heavier than an
equal bulk of water.

380 What substance has tlie smallest specific weight f

Hydrogen gas, which is 12,000 times lighter than an
equal bulk of water.

381 Why will an egg float in strong brine, and not in fresh water f

Because the solution of a solid in any liquid increases
its density, or its specific gravity : the addition of salt

SCIENCE OF COMMON THINGS. 63

Swimming in fresh and salt water. Unskilful swimmers.

to the water, renders the specific gravity of the brine
greater than that of fresh water, or of the egg.

383 How do cooks sometimes ascertain if their brine be salt enough for
pickling f

They put an egg into their brine. If the egg sinks,
the brine is not strong enough ; if the egg floats, it is.

383 Why witt an egg sink, if the brine be not strong enough for pick-
ling f

Because an egg will be the heavier ; but if as much
salt be added as the water can dissolve, an egg will be
lighter than the strong brine, and consequently float on
the surface.

384 Why is it more easy to swim in the sea than in a river ?

Because the specific gravity of salt water is greater
than that of fresh ; and, therefore, it buoys up the
swimmer better.

385 Why do persons sink in water when they are unskilful swimmers?

Because they struggle to keep their head out of water.

386 Explain how this is f

When our head is thrown back boldly into the water,
our mouth is kept above the surface, and we are able
to breathe ; but when the head is kept above the sur-
face of the water, the chin and mouth sink beneath it,
and the swimmer is suffocated.

This may be illustrated thus : — If a piece of wood be of such specific
gravity that only two square inches can float out of water, it is manifest,
that if two other inches are raised out, the two former inches must be
plunged in. The body (in floating) resembles this piece of wood. If
two square inches of our face float out of the water, we can breathe; but
if part of the back and crown of the head are raised above the water, the
lower part of the face will be depressed beneath it.

387 Why can quadrupeds swim more easily than man f

1. Because the trunk of quadrupeds is lighter than
water, and this is the greater part of them ; and

2. The position of a beast (when swimming) is a na-
tural one.

388 Why is it more difficult for a man to swim than for a beast f

1. Because his body is more heavy in proportion
than that of a beast ; and

64: SCIENCE OF COMMON THINGS.

How fishes ascend and descend in water. Life boats. Cream on milk.

2. The position and muscular action of a man (when
swimming) differ greatly from his ordinary habits ; but
beasts swim in their ordinary position.

389 Why can fat men swim more easily than spare men?

Because fat is lighter than water / and the fatter a
man is, the more buoyant will he be.

390 How are fishes able to ascend to the surface of water f

I Fishes have an air-bladder near the abdomen ; when
this air-vessel is distended, the fish increases in size
and (being lighter) ascends through the water to its
surface.

391 How are fishes able to dive in a minute to the bottom of a stream f

They compress the air in their air-bladder ; in conse-
quence of which their size is diminished, and they sink
instantly.

393 Why does the body of a drowned person rise and float upon the
surface several days after death ?

Because, from the accumulation of gas within the
body (caused by incipient putrefaction), the body be-
comes specifically lighter than water, and rises and
floats upon the surface.

393 How are life-boats prevented from sinking ?

They contain in their sides air-tight cells, or boxes
filled with air, wThich by their buoyancy prevent the
boat from sinking even when it is filled with water.

394 The slaves of the West Indies have a plan of stealing rum from a
cask, by inserting the long neck of a bottle, full of water, through the bung.
How are they enabled in this manner to obtain the rum ?

The rum is very much lighter than the water / and
as the heavy water falls out of the bottle into the cask,
the lighter rum rises to take its place.

395 Why does cream rise upon milk ?

Because it is composed of particles of oily or fatty
matter, which are lighter than the watery particles of
the milk.

396 Why do stale eggs fioat upon water?

Because, by keeping, air is substituted for a portion
of the water of the egg, which escapes.

SCIENCE OF COMMON THINGS. 65

Iron ships. Movement Of stores in water. Capillary attraction.

SOT* Why does not a vessel constructed of iron sink, as the iron is much
heavier than the water ?

Because the vessel is constructed in a concave form,
and is thus rendered buoyant. Every substance be-
comes lighter in water, in proportion to the amount of
water displaced. This is a law of nature: if it dis-
places less water than its weight in air, it sinks; if
more, it floats. The ship, being concave, displaces a
greater weight of water than the weight of the iron of
which it is composed in the air.

A thick piece of iron, weighing half an ounce, loses in water nearly
one-eighth jf its weight ; but if it is hammered out into a plate or vessel,
of such a size that it occupies eight times as much space as before, it then
loses its whole weight in water, and will float, sinking just to the brim.
If made twice as large, it will displace one ounce of water, consequently,
twice its own weight ; it will then sink to the middle, and can be loaded
with half an ounce weight before sinking entirely.

398 Why are stones, gravel, and sand so easily moved by waves and
currents ?

Because the moving water has only to overcome
about half the weight of the stone.

399 Why can a stone which, on land, requires the strength of two men
to lift it, be lifted and carried in water by one man f

Because the water holds up the stone with a force
equal to the weight of the volume of water it displaces.

CHAPTER III.

CAPILLARY ATTRACTION.

400 Why does water melt salt ?

Because very minute particles of water insinuate
themselves into the pores of the salt by capillary at-
traction, and force the crystals apart from each other.

401 Why does water melt sugar f

Because very minute particles of water insinuate

SCIENCE OF COMMON THINGS.

"Watering plants. Cotton lamp-wick.

Blotting paper absorbs ink.

fig. 18.

themselves into the pores of the sugar by capillary
attraction* and force the crystals apart from each
other.

4OS What is capillary attraction ?

The power which very minute
tubes possess of causing liquid to
rise in them above its level.

" Capillary," from the Latin word, " capil-
laris" (like a hair) ; the tubes referred to are
almost as fine and delicate as a hair. Water
ascends through a lump of sugar or «pieee of
sponger by capillary attraction.

N. B. The smaller the tube, the higher will
the liquid be attracted by it. Fig. 18 illus-
trates the manner in which water will rise in
tubes of different diameters.

403 Why is vegetation on the margin of a river more luxuriant than
in an open field ?

Because the porous earth on the bank draws up too-.
ter to the roots of the plants by capillary attraction.

404 Why do persons who water plants very often pour the water into
the saucer, and not over the plants ?

Because the water in the saucer is drawn up by the
mould (through the hole at the bottom of the flower-
pot), and is transferred to the stem and leaves of the
plant by capillary attraction.

405 Why is cotton best adapted for lamp-wicks f

Because the arrangement of the fibres of the cotton-
wick is such, that the whole forms a bundle of minute
tubes, in which the oil ascends and supplies the flame
by capillary attraction.

406 Why does blotting-paper absorb ink f

The ink is drawn up between the minute fibres of
the paper by capillary attraction.

407 Why will not writing or sized paper absorb ink f

Because the sizing, being a species of glue into
which writing papers are dipped, fills up the little in'
terstices or spaces between the fibres, ana in this way
prevents all capillary attraction.

408 How does a sponge absorb water t

SCIENCE OF COMMON THINGS. 67

Dry wood swells in water. Solution of substances. Liquids and gases.

The pores of the sponge constitute minute tubes in
which the water rises by capillary attraction.

409 Why does dry wood, immersed in water, swell 1

Because the water enters the pores of wood by capil-
lary attraction, and forces the particles further apart
from each other.

41 0 Why does sugar or salt give a flavor to water f

Because the sugar or salt (being separated into very
minute particles) floats about the water, and mixes
with it intimately.

411 Why does hot water dissolve sugar and salt more readily than cold
water f

Because the heat of the water assists its solvent ac-
tion, and opens for the water a passage through the
particles of the substance.

CHAPTEK IT.

THE GENERAL PROPERTIES OF AERIFORM OR GASEOUS
BODIES.

413 What is the difference between a liquid and a gas?

The distinction between liquids and those more elas-
tic fluids which wre term air, gas, vapor, steam, etc.,
depends principally on heat and pressure. Thus, wa-
ter, according to the addition or subtraction of heat,
may exist as a solid, ice ; as a liquid, wrater ; or as a
vapor, steam.

413 Under what pressure of the atmosphere is water converted into
steam ?

Tinder the ordinary pressure of the atmosphere, wa-
ter is converted into steam at 212 degrees, Fahrenheit's
thermometer ; if this pressure is increased, it requires

68 SCIENCE OF COMMON THINGS.

Varieties of gaseous bodies. Composition of the atmosphere. Air porous.

a proportionally higher temperature ; if this pressure
is diminished, the amount of heat required is propor-
tionably less.

414 How many kinds of aeriform or gaseous bodies exist in nature f

Those which, under common circumstances of tem-
perature and pressure, are always in a gaseous state,
as common air ; and those which become gases chiefly
at high temperature, as steam, or vapor of water.

415 Are all gases invisible or colorless like atmospheric air f

Some gases possess color, but the greater number
are colorless and invisible.

416 Of what is atmospheric air composed f

Principally of two gases, oxygen and nitrogen, mixed
together in the following proportion : viz. one volume
of oxygen to four of nitrogen.

It must not be forgotten that the air contains small quantities of other
gaseous substances also, as vapor of water, carbonic acid, and ammonia.

41 7* Do the particles of which atmospheric air and other gaseous bodies
are composed, appear to have any cohesion between themselves f

The ultimate particles of which air and other gases
are composed appear to be destitute of cohesion ; hence
air has a disposition not only to sink down and spread
out laterally, like liquids when unconfined, but also to
expand and rise upwards.

418 Is the air porous f

Yes ; in a very high degree.

419 How do we know this fact ?

Because air readily yields to pressure, and a great
bulk of it may be forced to occupy a very small space.

4SO Is air also impenetrable f

Yes ; beyond a certain limit it cannot be compressed.

431 How much lighter is steam than ordinary air f

Steam has but little more than half the weight of
atmospheric air ; and hence it rises and floats in the
air as a cork rises and floats in water.

SCIENCE OF COMMON THINGS. 69

What is the atmosphere ? Why mountains appear blue.

CHAPTEE Y.

THE ATMOSPHERE.

433 What do we understand by the atmosphere f

The thin transparent fluid which surrounds the earth
to a considerable height above its surface, and which,
by its peculiar constitution, supports animal life by
respiration, and is also necessary for the due exercise
of the vegetable functions.

433 Is the atmosphere invisible f

It is generally, but erroneously, so regarded. The
atmosphere is not invisible.

434 How can you prove that the atmosphere is not invisible f

Because when we look upwards into the firmament on
a clear day, the space appears of an azure or clear color.

This color belongs not to anything which occupies the space in which
the stars or other celestial objects are placed, but to the mass of .air
through which the bodies are seen.

435 Why do distant mountains appear Hue f

"Not because it is their color, but because it is the
color of the air through which they are seen.

-±36 Has air weight f

It has / as well as lead, stone, or any other material
substance.

437 How can this be readily proved?

By weighing a vessel filled with air, and the same
vessel after the air has been exhausted from it.

438 Can the existence of air be known by the sense of touch or feeling f

It can ; since it opposes resistance when acted upon,
and strikes with a force proportionate to the speed of
its motion.

438 Why do we always feel a breeze on the deck of a steamboat in
motion, even upon the calmest day t

Because our bodies forcibly displace the air as w$
are carried through it,

70 SCIENCE OF COMMON THINGS.

Height of the atmosphere. Weight of the atmosphere.

430 How are waves of the ocean produced ?

By the force of the air in motion, or wind striking
upon the surface of the water.

431 Could a bird fly in a space devoid of air, even if it could exist
without respiration ?

It could not ; as the bird rises simply by the resist-
ance of the particles of air to the beating of its wings.

/ 432 How do we know that air is elastic f

Because a volume of compressed air, the pressure
being removed, immediately restores itself to its origi-
nal bulk.

433 When is air said to be rarefied f

When a given quantity of air is caused to expand
and occupy a greater space, it is said to be rarefied.

"When a part of the air inclosed in any vessel is withdrawn, that which
remains, expanding by its elastic property, always tills the dimensions of
the vessel as completely as before. If nine-tenths were withdrawn, the
remaining one-teiith would occupy the same space that the whole did
formerly.

434 What is the height of the atmosphere above the surface of the earth f

It is supposed to be about 45 miles ; the zone or shell
of air which surrounds the earth to the height of nearly
21 miles from its surface, contains one-half of the
atmosphere ; and the remaining half being relieved of
this superincumbent pressure, expands into another
zone or belt of the thickness of 41 or 42 miles.

Some authorities suppose this last zone to have a much greater area.

435 What is the weight of air compared with that of water f

Water is about 840 times the weight of air, taken
l>ulkfor bulk.

430 What is the estimated weight of the whole atmosphere enveloping
tJie globe f

To the weight of a globe of lead sixty miles in dia-
meter.

437' As air has weight, and as the mass of it extends at least 45 miles
above the earths surface, what amount of pressure does it exert ?

At the level of the ocean the atmosphere exerts a
pressure of about 1 5 pounds for every square inch of
surface.

SCIENCE OF COMMON THINGS. 71

Pressure of air. Vacuum.

438 If the air were condensed, so as to occupy no more space than the
same weight of water, to how great an tkvation above the earth would it

extend ?

To an elevation of thirty-four feet.

439 In what direction is the pressure of the atmosphere exerted f

It is the nature of a fluid to transmit pressure in every
direction equally ; therefore the air presses upwards,
downwards, laterally, and obliquely, with the same
force.

440 How great a pressure is exerted by the air upon the body of a
man or animal having a surface of 2000 square inches f

Not less than 30,000 pounds, or about 15 tons.

441 Why is not the individual crushed beneath so enormous a load?

Because the atmosphere presses equally in all direc-
tions^ and our bodies are filled with liquids capable of
sustaining pressure, or with air of the same density as
the external air ; so that the external pressure is met
and counteracted by the internal resistance.

44S What would be- the effect upon a man or animal if at once
relieved of all atmospheric pressure ?

All the blood and fluids of the body would be forced
~by expansion to the surface, and the animal would burst.

443 What do we mean by a vacuum?

A space devoid of all matter ; in general, we mean
by a vacuum, a space devoid of air.

444 Can a perfect vacuum be produced artificially f

No ; but confined spaces may be deprived of air
sufficiently for all experimental or practical purposes.

445 Are there any instances of a vacuum in nature?

There is no positive certainty that the spaces which
exist between the various planets and other hea-
venly bodies, are occupied with any material sub-
stance.

446 Is the existence of air necessary to the production of sound?

It is ; in a vacuum there can be no sound ; and on
the top of high mountains, where the air is greatly
rarefied, as on Mont Blanc, the report of a pistol can
hardly be heard.

72 SCIENCE OF COMMON THINGS.

How flies walk on the ceiling. How we breathe.

447* Why is it often painful and difficult to breathe on a mountain-top f

Because, owing to the extreme rarity of the air on
the top of the mountain, a person, although expanding
his chest as much as usual, really takes in only half
as much air as he does when at the foot of the moun-
tain.

448 If the lips be applied to the back of the hand, and the breath drawn
in so as to produce a partial vacuum in the mouth, why will the skin be
drawn or sucked in f

Not from any force resident in the lips or the mouth
drawing the skin in, but from the fact that the usual
external pressure of air is removed, and that the pres-
sure from within the skin is suffered to prevail.

449 How is a boy enabled to lift a stone by means of the common
sucker ?

The sucker consists of a disk of moistened leather,
with a string by which it may be suspended with any
weight attached to it. If its smooth moist surface be
pressed so closely against the flat side of a stone or
other body that the air cannot enter between them, the
weight of the atmosphere pressing upon the upper sur-
face of the leather makes it adhere so strongly, that a
stone of weight proportioned to the extent of the disk
of leather may be raised by lifting the string.

450 How are flies and other small insects enabled to walk on ceilings
and surfaces presented downwards, or upon smooth panes of glass in an
upright position ?

Their feet are formed in such a manner that they
act as small air-pumps or suckers, excluding the air
between them and the surface with which they are in
contact ; and the atmospheric pressure keeps the animal
in position.

451 Why in breathing do we first draw in the breath, as it is termed?

Because by so doing we make an enlarged space in
the chest, and the pressure of the external atmosphere
forces the air in to fill it.

The air enters the lungs, not because they draw it in, but by the weight
of the atmosphere forcing it into an empty space.

453 How is the air caused to escape from the lungs f

Simply by means of its elasticity ; the lungs by

SCIENCE OF COMMON THINGS. 73

Why a jug gurgles. Air in water.

muscular action compress the air contained in them,
and give to it by compression a greater elasticity than
the air without. By the excess of the elasticity it is
propelled, and escapes by the mouth and nose.

453 Why does a bottle or jug gurgle when liquid is freely poured
from it ?

On account of the pressure of the atmosphere forcing
air into the interior of the bottle. In the first instance,
the neck of the bottle is filled with liquid, so as to stop
the admission of air. When a part has flowed out, and
an empty space is formed within the bottle, the atmo-
spheric pressure forces in a bubble of air through the
liquid in the neck, which, by rushing suddenly into the
interior of the bottle, produces the sound. .

454 How long will a lottle continue to gurgle ?

/So long as the neck continues to be choked with liquid.
But as the contents of the bottle are discharged, the -
liquid, in flowing out, only partially fills the neck ; and,
while a stream passes out through the lower half of the
neck, a stream of air passes in through the upper part.
The flow being now continued and uninterrupted, no
sound takes place.

455 Does air exist in water f

Water, and most liquids exposed to the air, absorb a
greater or less quantity r, which is maintained in them by
the pressure of the atmosphere acting on the surface.

456 Why is boiled water flat and insipid f

Because the agency of the heat expels the &ir which
the water previously contained.

457* Could fishes and other marine animals live in water deprived of
air ?

They could not, as they breathe the air contained in
the water.

458 Why do ale, porter, and cider froth, and champagne sparkle, when
uncorked and poured into an open vessel f

When these liquors are bottled, the air confined
under the cork is condensed, and exerts upon the sur-
face a pressure greater than that of the atmosphere.

SCIENCE OF COMMON THINGS.

Frothing of ale. Sparkling of champagne. Meteorology.

This has the effect of holding, in combination with the
liquor, air or gas which, under the atmospheric pressure
only, would escape. If any air or gas rise from the
liquor after being bottled, it causes a still greater con-
densation, and an increased pressure above its surface.
When the cork is drawn from a bottle containing liquor
of this kind, the air fixed in the liquid, being released
from the pressure of the air which was condensed under
the cork, instantly makes its escape, and, rising in
bubbles, produces effervescence and froth.

459 Why do bottles containing ale, cider, porter, &c., frequently
burst f

It is the nature of these liquids to produce gas or air
in considerable quantities, the elastic force of which
sometimes becomes greater than the cohesive strength
of the particles of matter composing the bottle, which
then necessarily gives way, or bursts.

460 Why does one kind of liquor froth, and another kind only sparkle, f

Those liquors only which are viscid, glutinous, or
thick, froth, because they retain the little bubbles of
air as they rise ; while a thin liquor, like champagne,
suffers the bubbles to escape readily.

CIIAPTEK VI.

ATMOSPHERICAL PHENOMENA.

461 What designation do we give to that department of science which
treats of the various phenomena of the atmosphere?

Meteorology.

463 How is the air heated f

In two ways ; either by the rays of the sun passing
through it, or by the heat communicated to it by the
earth.

SCIENCE OF COMMON THINGS; 75"

Air, how heated and cooled. Origin of winds.

463 In what manner is the air heated by the earth ?

The sun heats the earth, and the earth heats the air
resting upon it ; the air thus heated rises, and is suc-
ceeded by other air, which is heated in a similar way,
till the whole volume is warmed,

464 How is the air made cold?

The air resting on the earth is made cold by contact /
this cold air makes the air above it cold / and cold cur-
rents (or winds) cause the whole to mix together, until
all becomes of one temperature.

465 What effect is produced upon air "by cold f

It is condensed or compacted into a smaller compass ;
in consequence of which it becomes heavier, and de-
scends towards the ground.

466 Prove that the air is condensed ly cold.

Lay a bladder half full of air before a fire, till it has
become inflated ; if it be now removed from the fire$
the bladder will collapse again, because the air con-
denses into its former bulk.

467 What effects has heat upon air f

Heat rarefies or makes it lighter ; that is, a quantity
of air heated will occupy more space than the same
quantity which has been cooled.

468 What is wind f

"Wind is air put in motion.

460 What occasions- those movements of the air which we call wind?

The principal cause is the variation of temperature
produced by the alternation of day and night and the
succession of the seasons.

4"7O How can winds originate through variations of temperature f {

"When through the agency of the sun a particular
portion of the earth's surface is heated to a greater
degree than the remainder, the air resting upon it
becomes rarefied and ascends, while a current of cold
air rushes in to supply the vacancy. Two currents, the
one of warm air flowing out, and the other of cold air
flowing in, are thus continually produced ; and to these

76 SCIENCE OF COMMON THINGS.

"Wind always blows. Effect of mountains on winds.

movements of the atmosphere we apply the designation
of wind.

471 Does the wind always blow f

Yes ; there is always some motion in the air ; but the
violence of the motion is perpetually varying.

473 Does the rotation of the earth upon its axis affect the motion of
the air f

1 Yes, in two ways : 1. As the earth moves round its
axis, the thin movable air is left somewhat behind, and
therefore seems (to a stationary object) to be blowing
in the opposite direction to the earth's motion ; and

2. As the earth revolves, different portions of its sur-
face are continually passing under the vertical rays of
the sun.

473 When are the rays of the sun called vertical rays ?

When the sun is in a direct line above any place, his
rays are said to be "vertical " to that place.

474 When the sun is vertical, or nearly over head at any place, what
time of day is it at that place ?

Noon.

475 How does a change in the heat of air produce wind f

The air always seeks to preserve an equilibrium • so
cold air rushes into the void made by the upward cur-
rent of warm air.

470 Why does not the wind always blow one way, following the direc-
tion of the sun f

Because the direction of the wind is subject to per-
petual interruption from kills and valleys, deserts,
seas, &c.

477 How can hills or mountains affect or change the direction and course
of the wind ?

If a current of air, blowing from a particular direc-
tion, strike against the side of a mountain, it will neces-
sarily be deflected from a straight line, and must either
ascend the mountain, turn back, or assume a lateral
direction.

478 Why are those winds which llow over large continents or tracts
of land generally dry ?

SCIENCE OF COMMON THINGS. 7<

Velocity of winda. Force of winds.

Because in their passage they absorb very little water,
as they do not blow over large oceans.

479 Why do our "hands and lips chap in frosty and windy weather 1

Because a cold, dry wind absorbs moisture from the
surface of the skin ; and this action, in turn, causes the
skin to crack and inflame.

480 Would the wind blow regularly from east to west if all obstructions
were removed ?

Without doubt. If the whole earth were covered
with water, the winds would always follow the sun,
and blow uniformly in one direction.

481 Do winds ever blow regularly f

Yes, in those parts of the world which present a
large surface of water, as in the Atlantic and Pacific
Oceans.

483 With what velocity do winds move f

Every graduation exists in the speed of winds, from
the mildest zephyr to the most violent hurricane.

483 With what velocity does a wind which is hardly perceptible move f

With a velocity of about one mile per hour, and
with a perpendicular force on one square foot of *005
Ibs. avoirdupois.

484 In a gentle wind, what is the velocity and estimated pressure f

'From four to Jive miles per hour, and a force of "079
to 123 Ibs.*

485 In a very brisk wind, what is the velocity and pressure ?

From twenty to twenty -free miles per hour / force 1*9
to 3-07 Ibs.

4SQ What is the velocity and pressure of the wind in a storm t

From fifty to sixty miles per hour, with a pressure
of 7 to 12 Ibs.

487 In a hurricane, what is the estimated velocity and pressure f

From eighty to one hundred miles per hour> with a
varying force of 31 to 50 Ibs.

* In these estimates the pressure is computed per square foot in
pounds avoirdupois.

78 SCIENCE OF COMMON THINGS.

Movements of clouds. Trade winds and their location.

488 Why do we sometimes see clouds at one elevation moving in one
direction, and at anotfier elevation, at the same time, others moving in a
contrary direction ?

Because different currents of air exist at different
elevations, moving in different airections, with different
velocities.

In 1839, an English aeronaut, at the height of 14,000 feet, encountered
a current that bore him along at the rate of five miles per hour ; but,
upon descending to the altitude of 12,000 feet, he met with a contrary-
wind, blowing with a velocity of eighty miles per hour.

489 How is the force of the wind ascertained ?

By observing the amount of pressure that it exerts
upon a given plane surface perpendicular to its own
direction.

If the pressure plate acts freely upon spiral springs, the power of the
wind is denoted by the extent of their compression, and that weight will
be a measure of their force, the same as in weighing by the ordinary
spring-balance.

09 O What is an instrument for measuring the force of the wind called f

An Anemometer.

491 What are the constant winds which bloiv over the Atlantic and
Pacific Oceans called f

They are called " trade-winds"

493 Why are they called trade-winds f

Because they are very convenient to navigators who
have to cross the ocean, inasmuch as they always blow
in one direction.

493 In what direction do the trade-winds blow f

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

494 Do trade-winds blow from the north-east and south-east all Hie
year round 1

Yes, in the open sea; that is in the Atlantic and
Pacific oceans, for about 25° each side of the equator.

495 Where do the trade-winds blow with uniform force and constancy f

In many parts of the Pacific embraced within the
region of the trade-winds, a vessel may sail for a week
without altering the position of a sail or rope.

SCIENCE OF COMMON THINGS. 79

Cause of sea breezes. North and south winds.

406 Why does a sea breeze feel cool f

Because the sun cannot make the surface of the sea
so hot as the land ; therefore the air which blows from
the sea is cooler than the air of the land.

407 Why is there generally a fresh breeze from the sea during ihe
summer and autumn mornings f

Because land is more heated by the sun than the sea
is ; and the land air becomes hotter than that over the
sea ; in consequence of which the cooler sea air glides
inland to restore the equilibrium.

408 Why are ihe west winds in the Atlantic States generally dry?

Because they come over large tracts of land, and
therefore absorb very little water ; and being* thirsty,
they readily imbibe moisture from the air and clouds,
and therefore bring dry weather.

400 Why is the north wind generally coldf

Because it comes from the polar regions, over moun-
tains of snow and seas of ice.

500 Why are north winds generally dry ?

Because they come from colder regions, and being
warmed by the heat of our climate, absorb moisture
from everything they touch ; in consequence of which
they are generally dry.

501 Why are south winds generally warm f

Because they come over countries warmer than our
own, where they are much heated.

SOS Why are winds which blow over a vast body of water generally rainy f

Because they come laden with vapor ; if, therefore,
they meet with the least chill, some of the vapor is
deposited as rain.

SOS Why is there often an evening breeze during the summer months 9

Because the earth radiates heat at sunset, and the
air is rapidly cooled down by contact; this conden-
sation causes a motion in the air, called the evening
breeze.

SO4 Why do south winds often bring rain f

Because, coming from the torrid zone, they are much

80 SCIENCE OF COMMON THINGS.

Effect of the winds on the weather. Hurricanes.

heated, and absorb water very plentifully as they pass
over the ocean.

SOS How does this account for the rainy character of south winds f

As soon as they reach a cold climate they hecome
chilled, and can no longer hold all their vapor in sus-
pension ; in consequence of which some of it is deposited
as rain.

SOG Why are dry winds in the spring montJis desirable and advan*
tageous for agricultural operations f

They dry the soil saturated with the moisture ot
winter, 'break up the heavy clods, and fit the land for
the seed committed to it.

SOT* Why is a fine clear day sometimes overcast in a few minutes ?

Because some sudden change of temperature has
condensed the vapor of the air into clouds.

SO 8 Why are clouds sometimes dissipated very suddenly ?

Because some dry wind (blowing over the clouds)
imbibes their moisture, and carries it off in invisible
vapor.

0 O9 Why does wind sometimes Iring rain, and sometimes fine weather f

If the wind be colder than the clouds, it will condense
their vapor into rain / but if the wind is warmer than
the clouds, it will dissolve them and cause them to dis-
appear.

510 What is a hurricane f

The hurricane is a remarkable storm wind, peculiar
to certain portions of the world. It rarely takes its
rise beyond the tropics, and it is the only storm to
dread within the region of the trade-winds.

511 How are hurricanes especially distinguished from other kinds of
tempests f

By their extent, irresistible power, and the sudden
changes that occur in the direction of the wind.

S1J3 Do any particular portions of the tropics appear to be especially
visited with hurricanes ?

In the northern hemisphere, the hurricane most fre-
quently occurs in the regions of the West Indies ; in

SCIENCE OF COMMON THINGS. 81

What are hurricanes ? Breadth and velocity of hurricanes.

the southern hemisphere, it occurs in. the neighborhood
of the Mauritius.

513 Do the hurricanes occur at particular seasons f

The West Indian occur from August to October / the
Mauritian from February to April.

514 What have recent investigations shown the hurricanes to be?

Extensive storms of wind, which revolve round an
axis either upright • or inclined to the horizon ; while
at the same time the body of the storm has a progres-
sive motion over the surface of the ocean.

515 Illustrate more clearly the manner in which a hurricane moves f
It is the nature of a hurricane to travel round and

round as well as forward, much as a corkscrew tra-
vels through a cork, only the circles are all^^, and de-
scribed by a rotatory wind upon the surface of the water.

516 In ivhat direction would a ship revolving in the circles of a hurri-
cane find the wind ?

As the ship revolved, she wrould in turn find the
wind blowing from every point of the compass.

517 What is known concerning the distance travelled by hurricanes f

The distance traversed by these terrible tempests is
immense. The great gale of August, 1830, which oc-
curred at St. Thomas on the 12th, reached the Banks
of Newfoundland on the 19th, having travelled more
than three thousand nautical miles in seven days / the
track of the Cuba hurricane of 1844: was but little infe-
rior in length.

518 What is known of their progressive and rotary velocity f

Their progressive velocity is from seventeen to forty
miles per hour • but distinct from the progressive velo-
city is the rotary, which increases from the exterior
boundary to the centre of the storm, near which point
the force of the tempest is greatest, the wind sometimes
blowing at the rate of one hundred miles per hour.

519 How great is the breadth of the hurricane $

The surface simultaneously swept by these tremen-
dous whirlwinds is a vast circle varying from one hun-
dred to Jive hundred miles in diameter.

82 SCIENCE OF COMMON THINGS.

Tornadoes-~cause of. Eddies in water.

520 How great is the surface over whicJi they prevail ?

Mr. Redfield, of New York, lias estimated the great
Cuba hurricane of 1844 to have been not less than
eight hundred miles in breadth, and the area over
which it prevailed during its whole length was com-
puted to be two million four hundred thousand square
'miles — an extent of surface equal to two-thirds of that
of all Europe.

521 What curious fact have mariners noticed when in the centre or
vortex of the hurricane ?

An awful calm prevails, described as the lull of the
tempest, in which it seems to have rested only to
gather strength for greater efforts.

522 In what respect does a tornado differ from a hurricane f

Tornadoes may be regarded as hurricanes, differing
chiefly in respect to their continuance and extent.

523 How long do they usually last f

From fifteen to seventy seconds.

524 What is their extent f

Their breadth varies from &few rods to several hun-
dred yards, and the length of their course rarely ex-
ceeds twenty miles.

525 What phenomena generally attend them f

The tornado is generally preceded by a calm and
sultry state of the atmosphere, when suddenly the
whirlwind appears, prostrating everything before it.
Tornadoes are usually accompanied with thunder and
lightning, and sometimes showers of hail.

526 What is supposed to be the origin of tornadoes f

They are supposed to be generally produced by the
lateral action of an opposing wind, or the influence of
a brisk gale upon a portion of the atmosphere in repose.

527 How are the eddies or whirlpools produced which occur in water,
and which in their formation resemble some tornadoes f

Eddies or whirlpools are most frequently formed in
water when two streams flowing unequally meet, They
may be seen at the junction of two brooks or rivers.

SCIENCE OF COMMON THINGS. 83

Waterspouts. Why winds feel cool. What are clouds?

535 How are the whirlwinds which we frequently see at the corners of
streets in cities produced f

They are caused by a gust of wind sweeping round
a corner of a building, and striking the calm air be-
yond it.

530 What is a waterspout f

A waterspout is a whirlwind over the surface of
water, and differs from a whirlwind on land in the fact
that water is subjected to the action of the wind, instead
of objects on the surface of the earth.

530 Why does wind generally feel cold f

Because a constantly-changing surface comes in con-
tact with our body to draw off its heat.

531 What are the effects of wind noticed in the Arctic regions f

Arctic explorers inform us that in those regions, when
the thermometer ranges from 40° to 60° below zero,
the cold of the external air is easily endurable, provided
the air is calm and the individual exercises freely / but
if a wind arises at this temperature, the severity of the
cold becomes too great for human endurance.

533 If the winds should cease to blow over the ocean, what would be the
e/ectf

The water would undoubtedly become stagnant.
Tempests and hurricanes also exercise a beneficial effect
by agitating and purifying the atmosphere, and sweep-
ing from it the seeds of pestilence and contagion.

533 What are clouds f

Moisture evaporated from the earth^ and again par-
tially condensed in the upper regions of the air.

534 What is the difference between a fog and a cloud ?

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.

635 Why are clouds higher on a fine day f

Because they are lighter and more buoyant.

536 Why are clouds lighter on a fine day f

1. Because the vapor of the clouds is less condensed;
and

84: SCIENCE OF COMMON THINGS.

Why clouds float in the air. Height of clouds. Size of clouds.

2. The air itself (on a fine day) retains much of its
vapor in an invisible form.

537* Why do clouds float so readily in the air f

Because they are composed of very minute globules
(called vesicles), which (being lighter than air) float
like soap-bubbles.

538 Are att clouds alike f

No ; they vary greatly in density, height, and color.

530 What is the chief cause of fog and clouds f

During the daily process of evaporation from the
surface of the earth, warm, humid currents of air are
continually ascending ; the higher they ascend, the
colder is the atmosphere into which they enter ; and, as
they continue to rise, a point will at length be attained
where, in union with the colder air, their original
humidity can no longer be retained : a cloud will then
appear, which increases in bulk with the upward pro-
gress of the current into colder regions.

540 How do changes in the wind produce clouds f

If a cold current of wind blows suddenly over any
region, it condenses the invisible vapor of the air into
cloud or rain j but if a warm current of wind blows
over any region, it disperses the clouds by absorbing
their vapor.

541 What distance are the clouds from the earth f

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

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

542 What is the size of the clouds f

Some clouds are many square miles in surface, and
above a mile in thickness / while others are only a few
yards or inches.

543 How can persons ascertain the thickness of a cloud f

As the tops of high mountains are generally above
the clouds, travellers may pass quite through them into

SCIENCE OF COMMON THINGS. 85

Cause of the appearance of clouds. Color of clouds.

a clear blue firmament, when the clouds will be seen
beneath their feet.

544 Why do clouds, when not continuous over the whole surface of the
sky, appear jagged, rough, and uneven ?

The rays of the sun, falling upon different surfaces at
different angles, melt away one set of elevations, and
create another set of depressions ; the heat also which is
liberated from below in the process of condensation,
the currents of warm air escaping from the earth, and
of cold air descending from above, all tend to keep the
clouds in a state of agitation, upheaval, and depression.
Under their various influences the masses of vapor
composing the clouds are caused to assume all manner
of grotesque and fanciful shapes.

545 What effect have winds on the shape of clouds f

They sometimes absorb them entirely ; sometimes
increase their volume and density ; and sometimes
change the position of their parts.

546 How can winds absorb clouds altogether ?

Warm, dry winds will convert the substance of clouds
into invisible vapor, which they will carry away in
their own current.

54*7 How can winds increase the bulk and density of clouds f

Cold currents of wind wrill condense the invisible
vapor of the air, and add it to the clouds with which,
they come in contact.

54S Why is not the color of clouds always alike f

Because their size, density, and situation in regard to
the sun are perpetually varying, so that sometimes one
color is reflected and sometimes another.

549 Why do the clouds after sunset about the western horizon often
exhibit a beautiful crimson appearance ?

Because the red rays, of which the sun's light is in
part composed, are less refrangible than any of the
other colors. In consequence of this, they are not bent
out of their course so much as the blue and yellow rays,
and are the last to disappear.

For the same reason they are the first to appear in

86 SCIENCE OF COMMON" THINGS.

Eeft uigibility of light Red clouds at sunrise and sunset.

the morning when the sun rises, and impart to the
morning clouds red or crimson colors.

Fig. 19.

Let us suppose, as in^. 19, a ray oflight, proceeding from the sun, S,
to enter the earth's atmosphere at the point P. The red rays, which
compose in part the solar beam, being the least refrangible, or the least
deviated from their course, will reach the eye of a spectator at the point
A ; while the yellow and blue rays, being refracted to a greater degree,
will reach the surface of the earth at the intermediate points B and C.
They will, consequently, be quite invisible from the point A.

550 What, is meant by being " less refrongiblef'1

Being less able to be bent. Blue and yellow rays are
more easily bent below the horizon through the action
of the atmosphere, but red rays are not so much bent
down, and therefore we see them later in the evening.

551 What is the cause of a red sunset f

The vapor of the air not being actually condensed
into clouds, but only on ihe point of being condensed.

In the same manner, if light be transmitted through steam mingled
with air, and therefore on the verge of condensation, it assumes a deep
orange or red color.

552 Why is a red and lowering sky at sunrise an indication of a wet
day f

The red and lowering appearance of the morning sky?
which indicates foul weather, probably depends upon
such an excess of vapor being present in the whole
atmosphere that clouds are actually forming in the

SCIENCE OF COMMON THINGS. 87

Haziness of the Indian summer. When vapor forms clouds and fogs.

higher regions, or upon the point of condensation, which
the rising sun cannot disperse.

Hence our Lord's observation — " In the morning ye say, It will be foui
weather to-day, for the sky is red and lowering." (Matt. xvi. 3.)

553 Which is the most transparent, dry or moist air ?

Air moderately moist is more transparent than very
dry air.

554 What is the cause of the haziness of the atmosphere during that
portion of the autumn known as the " Indian Summer f "

It is undoubtedly due to several causes ; partially to
an excessive dryness of the atmosphere, and, in some
degree, to the prevalence of smoke in the air arising
from burning forests. But it is also a fact, ascertained
within a few years, that the constitution of the atmo-
sphere is changed in the autumn, and that solar light
at that season has less chemical influence than at any
other portion of the year.

555 Why does the sun seen through a fog appear red?

Because the red rays of light have a greater power to
pass through a thick, dense atmosphere than any of the
other colored rays.

556 Why does vapor sometimes form into clouds, and sometimes rest
upon the earth as mist or fog?

This depends on the temperature of the air. "When
the surface of the earth is warmer than the lower air,
the vapor of the earth (being condensed by the chill
air) becomes mist or fog. But when the lower air is
warmer than the earth, the vapor rises through the air,
and becomes cloud.

557* Why do clouds often hover around mountain peaks, when the
atmosphere elsewhere is clear and free from clouds 1

It is caused by the wind impelling up the sides of
the mountains the warm humid air of the valleys,
which in its ascent gradually becomes condensed by
the cold, and its excess of moisture becomes visible,
and appears as a cloud.

558 Why are windoios at night often covered with thick mist, and the
frames wet with standing water ?

Because the temperature of the external air always

88 SCIENCE OF COMMON THINGS.

Mist on windows. Insensible perspiration.

falls at sunset, and chills the window-glass with which
it comes in contact.

559 How does this account for the mist and water on a window f

As the warm vapor 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.

560 Does the glass of a ivindow cool down more rapidly than the air
of the room itself f

Yes ; because the air is kept warm by fires and by
the animal heat of the people in the room ; in conse-
quence of which the air of a room suffers very little
diminution of heat from the setting of the sun.

561 Whence arises the vapor of a room f

The air of the room always contains vapor ; vapor
also arises from the breath and insensible perspiration of
the inmates, from cooking and the evaporation of water.

563 What is meant by " the insensible perspiration f "

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 days of winter.

563 If the perspiration be both insensible and invisible, hoiu is it known
that there is any such perspiration ?

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

564 Why is a tumbler of cold water made quite dull with mist, when
brought into a warm room ?

Because the hot vapor of the room is condensed upon
the cold tumbler, with which it comes in contact, and
changes its invisible and gaseous form into that of dew.

565 Why does breathing on a glass make it quite dull f

Because the cold glass condenses the invisible vapor
contained in warm breath, and converts it into dew.

566 Why are the walls of a house covered with damp in a sudden
thaw?

Because the walls (being thick) cannot change their

SCIENCE OF COMMON THINGS. 89

Breath visible in cold weather. Difference between mist and fog.

temperature as fast as the air ; in consequence of which
they retain their cold after the thaw lias set in.

567 How does "retaining their cold" account for their being so wet?

As the vapor of the warm air touches the cold walls,
it is chilled and condensed into water, which either
sticks to the walls or trickles down in little streams.

568 Why is our breath visible in winter, and not in summer ?

Because the intense cold condenses its moisture into
visible vapor, but in summer the air is not cold enough
to do so.

569 Why are our hair and the brim of our hat often covered with lit-
tle drops of pearly dew in ivinter-time f

Because the vapor of the breath condenses as it comes
in contact with our cold hair or hat, and hangs there
in little dew-drops.

570 What are fogs f

Fogs are visible vapors that float in the atmosphere
near the surface of the earth.

571 What is the cause of fogs 1

They originate in the same causes as rain — the union
of a cool body of air with one that is warm and humid ;
when the precipitation of moisture is slight, fogs are
produced ; when it is copious, rains are the result.

573 What distinction is to be made between a mist and a fog ?

Mist is generally considered to be a fine rain, while
fog is vapor not sufficiently condensed to allow of its
precipitation in drops.

The term mist is also generally applied to vapors condensed on marshes,
rivers, and lakes, while the name fog is often applied to vapors condensed
on land, especially if those vapors are laden with smoke.

573 Why does not the fog become dew ?

Because the chill of the air is so rapid that vapor is
condensed faster than it can be deposited, and covering
the earth in a fog) prevents any further radiation of
heat from the earth.

574 When the earth can no longer radiate heat upwards, does it con-
tinue to condense the vapor of the air ?

Ko ; the air (in contact with the earth) becomes

90 SCIENCE OF COMMON THINGS.

When fogs occur. When vapor forms clouds and when fogs.

about equal in temperature with the surface of the
earth itself; for which reason the fog is not condensed
into dew, but remains floating above the earth as a
thick cloud.

57*5 This fog seems to rise higher and higher, and yet remains quite as
dense below as at first : explain the cause of this ?

The air resting on the earth is first chilled, and chills
the air resting on it ; the air which touches this new
layer of fog being also condensed, layer is added' to,
layer ; and thus the fog seems to be rising, when (in
fact) it is only deepening.

57*B Why are there not fogs every night f

Because the air will always hold in solution a cer-
tain quantity of vapor (which varies according to its
temperature) ; and, when the air is not saturated, it
may be cooled without parting with its vapor.

57"? Wften do fogs occur at night f

When the air is saturated with vapor during the
day. When this is the case, it deposits some of its
superabundant moisture in the form of dew or fog as
soon as its capacity for holding vapor is lessened by
the cold night.

578 Why is there very often a fog over marshes and rivers at night-
time ?

Because the air of marshes is almost always near
saturation • and therefore the least depression of tem-
perature will compel it to relinquish some of its moist-
ure in the form of dew or fog.

57*9 Why does vapor sometimes form into clouds, and sometimes rest
upon the earth as mist or fog 1

This depends on the temperature of the air. "When
the surface of the earth is warmer than the air, the
vapor of the earth (being condensed by the chill air)
becomes mist or fog. But, when the air is warmer
than the earth, the vapor rises through the air, and be-
comes cloud.

58O If cold air produces fog, why is it not foggy on a frosty morning f

1, Because less vapor is formed on a, frosty day ;

SCIENCE OF COMMON THINGS. 91

What is rain ? Why falls in drops.

and 2. The vapor is frozen upon the ground before it
ean rise from the earth, and becomes hoar-frost.

581 What is rain?

Rain is the vapor of the clouds or air condensed and
precipitated to the earth.

58J3 In what manner is the vapor of the air condensed so as to form
rain ?

i When two or more volumes of humid air differing
considerably in temperature unite, the several portions
in union are incapable of absorbing the same amount
of moisture that each could retain if they had not
united. The excess of moisture, if very great, is pre-
cipitated as rain ; if in slight amount, it appears as
clouds, fogs, or mists.

583 Upon what law does this condensation of vapor and formation of
rain depend f

Upon the law that the capacity of the air for moist-
ure decreases in a greater ratio than the temperature.

58*4 Why does rainfall in drops ?

Because the vapory particles in their descent attract
each other ; and those which are sufficiently near unite
and form into drops.

The size of the rain-drop is increased according to the rapidity with
which the vapors are condensed.

585 Why does not the cold of night always cause ram f

Because the air is not always near saturation ; and
unless this be the case, it will be able to hold its vapor
in solution, even after it is condensed by the chilly
night.

580 Why does a passing cloud often drop rain ?

Because the cloud (travelling about on the wind)
comes into contact with something that chills it;
and its vapor being condensed, falls to the earth as

58 T Can the air absorb moisture at all temperatures, and retain it in
an invisible state f

It can ; and this power of the air is termed its
capacity of absorption.

92 SCIENCE OF COMMON THINGS.

What is snow ? Cause of sleet.

588 How much moisture can a volume of air at 32° F. absorb f

An amount equal to the hundred and sixtieth part
of its own weight.

589 How does the capacity of air for moisture increase with the tem-
perature ?

Eor every 27 additional degrees of heat, the quantity
of moisture it can absorb at 32° is doubled. Thus a
body of air at 32° F. absorbs the 160th part of its own
weight; at 59° F. the 80th; at 86° F. the 40th; at
113° F. the 20th part of its own moisture. It follows
from this that, while the temperature advances in an
arithmetical series, the capacity is accelerated in geo-
metrical series. ,

590 In what situations is the air always saturated f

Over the ocean and upon the adjacent coasts.

591 Where is the absolute humidity of the atmosphere the greatest f

In the tropics, where the temperature of the air, and
its consequent capacity for moisture, is the greatest.

593 What is snow ?

The condensed vapor of the air frozen and precipi-
tated to the earth.

593 What is the cause of snow f

When the air is nearly saturated with vapor, and
is acted on by a current of air l>elow the freezing point,
some of the vapor is condensed, 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 its vapor fell on the floor in a shower of*now.

594 What is the cause of sleet ?

"When flakes of snow (in their descent) pass through
a bed of air above the freezing point, they partially
melt, and fall to the earth as half-melted snow, or
sleet.

595 How does snow prove beneficial to the earth in the cold season f

It keeps the surface of the earth warm, protects vege-
tation to a considerable extent from the cold, and acts
as a fertilizer.

SCIENCE OF COMMON THINGS. 93

How snow keeps the earth warm. Why snow is white.

596 Does snow Jceep the earth warm f

Yes, because it is a very bad conductor j in conse-
quence of which, when the earth is covered with snow,
its temperature very rarely descends below the freezing
point, even when the air is fifteen or twenty degrees
colder.

59 7 Why is snow a lad conductor of heat and cold f

Because air is confined among 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.

Why is there no snow in summer-time f

Because the heat of the air adjacent to the earth
melts it in its descent, and prevents it from reaching
the surface of the earth.

590 Why is snow white f

Because it is formed of an infinite number of very
minute crystals and prisms, which reflect all the colors
of the ravs of light from different points, and these
colors, uniting before they meet the eye, cause snow to
appear white.

The same answer applies to salt, loaf-sugar, etc.

GOO Under what circumstances does snow fall in large flakes, and when
in small f

The largest flakes are formed when the air abounds
with vapor, and the temperature is about 32° F. ; but
as the moisture diminishes, and the cold increases, the
snow becomes finer.

6O1 What is the snow flake composed off

Regular and symmetrical crystals, having a great
diversity of forms.

6 OS Do we see the same crystals in ice f

They exist in ice, but are so blended together that
their symmetry is lost in the compact mass.

6O3 How much more bulky is snow than water ?

The bulk of recently-fallen snow is ten or twelve times
greater than that of the water obtained by melting it

94: SCIENCE OF COMMON THINGS.

Red and green snow. "What is hail ? Meteorites.

GO4 Does snow ever occur of any other appearance than white?

Yes ; in the Arctic regions and on some mountains
it is red, and occasionally green.

6O5 What is the cause of these appearances 1

These singular hues are occasioned by little micro-
scopic plants, which germinate and live in the snow.
They consist of little globules from TTfTo- of an inch to
3-500 °f an inch. Each globule is divided into seven
or eight cells filled with a liquid, which gives a color
to the snow, and is sometimes green and sometimes red.

eoe What is 'hail?

Rain, which has passed in its descent through some
cold bed of air, and has been frozen into drops of ice.

GOT* What makes one bed of air colder than another f

It is frequently caused by electricity unequally dis-
tributed in the air.

60S How can electricity make air cold ?

Air, when electrified, is expanded, and expansion
produces cold.

6O9 Why does hail fall generally in summer and autumn f

Because the air is more highly electrified in summer
and autumn than in winter and- spring; and the vapors
in summer and autumn (being rarefied) ascend to more
elevated regions, which are colder than those nearer
the earth.

G1O Is the occurrence and formation of hail clearly understood?

It is not ; much information exists upon the subject,
but no theory has yet been formed which satisfactorily
accounts for all the facts which have been observed.

Gil What are meteorites f

Meteorites are solid, luminous bodies, which from
time to time visit the earth, moving with immense
velocity, and remaining visible but for a few moments.
They are generally accompanied by a luminous train,
and during their progress explosions are often heard.

61Q What is an aerolite f

The term aerolite is given to those stony masses of

SCIENCE OF COMMON THINGS. 95

Aerolites. Appearance. Composition.

matter which are sometimes seen to fall from the
atmosphere.

It is derived from the Greek words, acp (atmosphere), and Xi0<>? (a stone).
A meteor is distinguished from an aerolite by the fact that it bursts in
the atmosphere, but leaves no residuum except a vapor-like smoke ;
while the aerolite, which is supposed to be a fragment of a meteor, comes
to the ground.

613 What is the weight of those aerolites which have been known to fall
from the atmosphere ?

Their weights vary from a few ounces to several hun-
dred pounds, or even tons.

614 At what height in the atmosphere are meteors supposed to

appear f

Their height above the earth has been estimated to
vary from eighteen to eighty miles.

615 With what velocity do they move ?

The velocity of these bodies is somewhat more than
three hundred miles per minute, though one meteor of
immense size, wrhich is supposed to have passed within
twenty-five miles of the earth, moved at the rate of
twelve hundred miles per minute.

616 What is the value of such estimates ?

Owing to the short time the meteor is visible and its
great velocity, accurate observations cannot be made
upon it ; and all estimates respecting their distance,
size, etc., must be considered as only approximations
to the truth.

617 What is the general appearance of aerolites f

Most of them are covered with a Hack shining crust,
as if the body had been coated with pitch. When
broken their color is ash-grey, inclining to black.

Very many of the meteorites which have fallen at different times and
m different parts of the globe, resemble eacli other so closely, that they
would seem to have been broken from the same piece or mass of matter.

618 What is their composition ?

Great numbers of aerolites have been analysed, and
found to contain nineteen or twenty different elementary
substances. But for the most part they consist of malle-
able iron and niokel.

96 SCIENCE OF COMMON THINGS.

Meteoric iron. Origin of meteors. Shooting stars.

619 Do tJie aerolites resemUe in composition any other bodies upon the
surface of the earth f

They do not : malleable iron is rarely if ever found
in terrestrial substances / and metallic nickel does not
occur upon the surface of the earth naturally.

620 What is peculiar to the composition of meteoric iron t

It has a highly crystalline arrangement, so peculiar
that it is especially distinguished by it. This arrange-
ment .of its particles enables us to decide upon the
meteoric origin of masses of iron which are occasionally
found scattered up and down the surface of the earth.

621 Where have such masses been found?

In the south of Africa, in Mexico, /Siberia, and on
the route overland to California. Some of these masses
are of immense weight, and undoubtedly fell from the
atmosphere.

622 How are meteorites supposed to originate ?

four hypotheses have been advanced to account for
the origin of these extraordinary bodies : 1. That they
are thrown up from terrestrial volcanoes. 2. That they
are produced in the atmosphere from vapors and gases
exhaled from the earth. 3. That they are thrown from
lunar volcanoes. 4. That they are of the same nature
as the planets, either derived from them, or existing
independently.

623 Which of these hypotheses is regarded as most probabk ?

The fourth most fully explains the facts connected
with the appearance of meteorites, and the third like-
wise has some strong evidence in its favor.

624 In what respect do shooting stars differ from meteors ?

Their altitude and velocity are greater, they are far
more numerous and frequent, and are unaccompanied
by any sound or explosion. Their brilliancy is also
much inferior to that of the meteor / and no portion of
their substance is ever known to have reached the earth.

625 What do we know concerning their altitude f

Owing to their great number and frequency of occur-
rence, many careful observations have been made upon

SCIENCE OF COMMON THINGS. 97

Origin of shooting stars. Zodiacal light.

them ; their altitude is supposed to vary from six to
four hundred and sixty miles, the greatest number
appearing at a height of about seventy mites.

636 What is their supposed velocity ?

It is supposed to range from sixty to fifteen hundred
miles per minute.

637* Are meteors and shooting stars at all times equally abundant f

They are not • some may be seen every clear night,
but they appear to return at certain periodical epochs,
when they descend literally in showers.

638 What are the periods when they may be noticed most abundantly f

On the 9tk and Wth of August, and the 12^A and
13t/t of November.

They have also been noticed in unusual abundance on the 18th of Octo-
ber, the- 6th and 7th of December, the 2d of January, the 23d and 24th of
April, and from the 18th to the 20th of June.

639 Do the shooting stars appear to emanate from any particular part
of the heavens ?

The majority seem to start from a point in the con-
stellation Perseus, and undoubtedly far beyond the
limits of our atmosphere.

63O What is the zodiacal light f

It is a singular luminous appearance seen in the
horizon before sunrise and after sunset, most conspicu-
ously in the months of April and May.

Observations made during the year 1855 seem to conclusively prove
that the appearance known as the " zodiacal light " is occasioned by a
ring of nebulous matter encircling and pertaining to the earth.

CHAPTER YII.

THE PUMP AND BAROMETER.

631 Why, when we suck up a liquid with a tube or straiv, does th&
liquid rise to the mouth 1

One end of the tube being placed between the lips,

SCIENCE OF COMMON THINGS.

The common pump.

How constructed.

Pump valves.

the air is removed from the tube by the ordinary pro-
cess of inhaling, when the pressure of the atmosphere
compels the liquid to fill the space deserted by the air.

633 Through how great a length of tube could tve raise a liquid by
suction ?

About thirty-two feet.

633 Why can we not raise it above thirty-two feet f

Because the atmospheric pressure will only support
or balance a column of water or similar liquid of that
height.

634 How is the common pump constructed ?

The common pump consists of a
hollow tube, the lower part of which,
descending into the water, is called
the siiction-pipe, and the upper part, b
(Fig. 20), the barrel or cylinder • of a
spout, s, at the top of the cylinder ; of
an air-tight piston, which works up
and down in the cylinder ; and of two
valves, both opening upwards, one of
which, g, is placed at the top of the
suction-pipe, and the other, p, in the
piston.

635 How does the common pump operate f

When the piston is raised from the
bottom of the cylinder, the air above
it is drawn uj?, leaving a vacuum be-
low the piston ; the water in the well
then rushes up through the valve, g,
and fills the cylinder ; the piston is then forced down,
shutting the valve, g, and causing the water to rise
through the piston-valve, p ; the piston is then raised,
closing its valve, and raising the water above it, which
flows out of the spout, s.

636 What is a valve f

A valve, in general, is a contrivance by which water
or other fluid, flowing through a tube or^ aperture, is
allowed free passage in one direction, but is stopped in

Fig. 20.

SCIENCE OF COMMON THINGS. 99

Common suction-pump. Height water rises in common pump.

the other. Its structure is such, that, while the
pressure of fluid on one side has a tendency to close
it, the pressure on the other side has a tendency to
open it.

/tys. 21, 22, and 23 represent the various forms of valves used in
pumps, water-engines, etc.

Fig. at. Fig. 22. Fig. 53.

637 How can water be raised by the common suction-pump ?

As the action of this pump depends upon the pressure
of the atmosphere, water cannot be raised by it from a
depth of more than 34 feet below the upper valve, and
in practice a much shorter limit is usually assigned.

633 A tinman of Seville, in Spain, ignorant of the principles of science,
undertook to construct a suction-pump to raise water from a well sixty feet
deep ; when the machine was finished, he was confounded at discovering
that it had no power to raise water at all, and enraged at his disappoint-
ment, while some one was working the pump, he struck the suction pipe with
a hammer or axe so forcibly as to crack it, when, to his surprise and delight,
the water almost immediately began to flow, and he found he had attained
his purpose. How is this result to be accounted for ?

The explanation is as follows : the air pressed in
through the slit, or aperture of the suction-pipe, and
becoming mixed with the water in its ascent, formed a
compound fluid far lighter than water alone, and there-
fore acted upon more readily by the atmospheric pres-
sure ; and thus produced the phenomenon described.

639 How high can water be raised in the suction-pump by resorting t*
Hie expedient above described ?

About fifty-five feet, instead of thirty to thirty-four.

6*1O To whom is the invention oftJie common pump attributed ?

To Ctesibius, an Athenian engineer, who lived at
Alexandria, in Egypt, about the middle of the second
century before the Christian era.

100

SCIENCE OF COMMON THINGS.

Forcing-pump.

Construction of chain-pump.

Fig. 24.

641 When it is desired to raise ivater above thirty -four feet, as in fire-
engines, etc., how is it accomplished ?

By means of tliQ forcing-pump.

643 In what manner is the forcing-pump con-
structed ?

In the forcing-pump atmospheric
pressure plays but a small part. There
is no valve in the piston c (fig. 24),
but the water raised through the suc-
tion-pipe #, and the valve <?, is forced
by each depression of the piston -up
through the pipe e e, which is furnished
with a valve to prevent the return of
the fluid.

643 What is a chain-pump f

The chain-pump consists
of a tube or cylinder, the
lower part of which is im-
mersed in a well or reser-
voir, and the upper part
enters the bottom of a cistern
into which the water is to
be raised. A chain is carried
round a wheel at the top,
and is furnished at equal
distances with movable
bottoms, which fit water-
tight in the tube. As the
wheel revolves, they succes-
sively enter the tube, and
carry the water up before
| them, which is discharged
into the cistern at the top
of the tube.

Fig. 25 represents the construction
and arrangement of the chain-pump.

644 Under what Circumstances is
the chain-pump generally employed 1

When the height through which the water is to be

SCIENCE OF COMMON,, THINGS. t 101

Torricelli.

Why water rises 1& a p'lrip*

raised, is not very considerable, as in the case where
the foundations of docks, &c., are to be drained.

645 Who first ascertained and demonstrated the reason for the ascent
of water in a tube by suction, and in the common pump ?

Torricelli, a pupil of Galileo.

646 How was he led to his conclusions ?

He argued, that whatever be the cause which sus-
tained a column of water in a common pump, the mea-
sure of the power thus manifested must be the weight
of the column of water ; and consequently, if another
liquid be used, heavier or lighter, bulk for bulk, than
water, then the same force must sustain a lesser or
greater column of such liquid. By using a much
heavier liquid, the
column sustained
would necessarily be
much shorter, and
the experiment in
every way more
manageable.

Torricelli verified his con-
clusions in the following
manner : — He selected for
his experiment mercury,
the heaviest known liquid.
As this is 13£ times heavier
than water, bulk for bulk,
it followed that, if the force
imputed to a vacuum could
sustain 33 feet of water, it
would necessarily sustain
13£ times less, or about 30
inches, of mercury. Torri-
celli therefore made the fol-
lowing experiment, which
has since become memo-
rable in the history of
science : —

He procured a glass tube
(Fig. 26) more than 30
inches long, open at one
end, and closed at tho
other. Filling this tube
with meccunr, and appl}'-
ing his finger to the open Kg. 2«.

102

SCIENCE OF COMMON THINGS.

Pascal is experiment.

Invention of the barometer.

end, so as to prevent its escape, he inverted it, plunging the end into mer-
cury contained in a vessel. On removing the linger, he observed that the
mercury in the tube fell, but did not fall altogether into the cistern; it
only subsided until its surface was at a height of about 30 inches above
the surface of the mercury in the cistern. The result was what Torricelli
expected, and he soon perceived the true cause of the phenomenon. The
weight of the atmosphere acting upon the surface of the mercury in the
vessel, supports the liquid in the tube, this last being protected from the
pressure of the atmosphere by the closed end of the tube.

647 How was the fact that the column of mercury was sustained by the
pressure of the atmosphere further verified ?

By an experiment made by Pascal, in France. He
argued, that if the cause which sustained the column in
the tube was the weight of the atmosphere acting on
the external surface of the mercury in the cistern, then,
if the tube was transported to the top of a high moun-
tain, where a less quantity of atmosphere was above it,
the pressure would be less, and the length of the column
less. This was tried and found to be the case.

648 How did these experiments lead to the invention of the barometer f

It was noticed that when the ap-
paratus above described was kept
in a fixed position, the height of the
column fluctuated from day to day
within certain small limits. The
effect was of course to be attributed
to the variation in the weight of the
incumbent atmosphere, arising from
various meteorological causes.

This led to the use of the tube and cistern
of mercury, arranged in the manner before
described (Fig. 26), for determining the changes
in the atmosphere, and consequently the cha-
racter of the weather.

649 Explain more fully in what manner
the barometer can be used as a weather-glass ?

When air is moist, or filled with
vapor, it is lighter than usual, and
the column of mercury stands low ;
when air is dry and free from vapor,
it is heavier than usual, and the mer-
cury stands high. Thus the baro-

SCIENCE OF COMMON THINGS.

103

Wheel-barometer.

Use of barometer on land unreliable.

meter (by showing the variations in
the weight of the air) indicates the
changes of the weather also.

650 How is the common form of barometer,
called the wheel-barometer, constructed f

The barometer consists of a bent
tube, filled with mercury, as repre-
sented in Fig. 27, the column be-
ing sustained by the pressure of the
atmosphere upon the surface of the
mercury in the shorter arm, the end
of which is open. A small float of
iron or glass rests upon the mercury
in the shorter arm of the tube, and
is suspended by a slender thread,
which is passed round a wheel car-
rying an index. As the level of the
mercury is altered, and the weight
raised or lowered in the tube, the
index moves; and as the divisions
on the circumference of the circles
within which it moves are much
amplified, very slight changes are
easily read off.

Fig. 27 represents the internal structure of
the wheel-barometer, and Fig. 28 its external
appearance, or casing, with a thermometer
attached. Fjg «;8

651 Why is the ordinary use of the barometer on the land extremely
limited and uncertain?

The height of the mercury in the tube at any time
must depend partially upon the elevation of the place
of observation above the level of^ the sea ; and no correct
judgment can be formed relative to the density of the
atmosphere as affecting the state of the weather, with-
out reference to the situation of the instrument at the
time of making the observation. Therefore, no atten-
tion ought to be paid to the words, "fair, rain, change-
able" etc., frequently engraved on the plate of a baro-
meter, as they will be found no certain indications of

104 SCIENCE OF COMMON THINGS.

Difference between a thermometer and barometer. Peculiarities of climates.

the correspondence between the heights marked, and
the state of the weather.

653 What is the difference "between a thermometer and a barometer?

In a thermometer the mercury is sealed up from the
air ; and rises or falls as the varying temperature of
the air expands or contracts it ; but in a barometer the
mercury is left exposed (or open) to the air / and rises
or falls as the varying weight ot the air presses upon
the open column.

653 Why is the tube of a barometer left open f

That the air may press upon it freely ; and, as this
pressure varies, the mercury rises or falls in the tube.

654 Why does the mercury in the barometer rise at the approach of
fair weather ?

Because the air is becoming more dry^ and the drier
the air, and the more free it is from vapor, the greater
the pressure.

655 Why does the mercury sink at the approach of foul weather f

Because the air is laden with vapor or disturbed by
wind.

656 Why does vapor in the air cause the mercury to sink f

Because air containing vapor is lighter than dry
air ; and its pressure on the mercury is therefore less.

657 Why will there be no rain if the air be very dry f

Because dry air will absorb moisture, and not part
with it in rain.

CIIAPTEE YIII.

PECULIARITIES OF CLIMATES.
658 What do we mean by the term climate ?

By climate, we mean the condition of a place in
relation to the various phenomena of the atmosphere,

SCIENCE OF COMMON THINGS. 105

Mean daily temperature. Temperature varies with the altitude.

as temperature, moisture, etc. Thus, we speak of a
warm or cold climate, a moist or dry climate, etc.

659 What is meant by the mean daily temperature f

The mean or average temperature of the day is
found by observing the thermometer at fixed intervals
of time during the twenty-four hours, and then divid-
ing the sum of the temperatures by the number of
observations.

6 6O How is the mean annual temperature of a particular point ascer-
tained ?

By taking the average of all the mean daily tempe-
ratures throughout the year.

661 How does temperature vary with the latitude ?

The average annual temperature of the atmosphere
diminishes from the equator towards either pole.

663 Give examples of this variation ?

At the equator, in Brazil, the average annual tem-
perature is 84° Fahrenheit's thermometer ; at Calcutta,
lat. 22° 35' 1ST., the annual temperature is 78° F ; at
Savannah, lat. 32° 5' N., the annual temperature is
65° F. ; at London, lat. 51° 31' 1ST., the annual tempe-
rature is 50° F. ; at Melville Island, lat, 74° 47' 1ST., the
mean annual temperature is 1° below zero.

663 How does the temperature vary with the altitude above the earth's
surface ?

Temperature diminishes with the altitude. As a
general rule, a loss of heat occurs to the extent of one
degree F. for every 343 feet of elevation.

664 How does the gradual reduction of temperature as we ascend from
the surface of the earth affect the moisture of the air ?

In every latitude there is a point above the surface
of the earth where moisture, once frozen, always re-
mains congealed.

665 Why are tlie tops of very high mountains always covered with
snow ?

Because, at the great elevation of their summit, the
temperature of the atmosphere is so low that the con-
gealed moisture which falls upon them never melts.

106 SCIENCE OF COMMON THINGS.

What is a glacier f Icebergs. Line of perpetual snow.

600 What is a glacier f

The glacier only exists upon mountains whose sum-
mits are covered with perpetual snow. The snow upon
the higher parts becomes somewhat softened during
the summer, and in the winter is again hardened nearly
to ice. In the succeeding summer, the action of the
sun, and the internal heat of the earth, detach large
masses loaded with recently deposited snow into the
neighboring valleys, where, being accumulated, and
the crevices filled with snow or water which at Jast
hardens to ice, they form huge seas of ice, or a glacier /
in French, mers-de-glace.

667 Do the glaciers continue to increase year by year f

Very many of them do ; and in Switzerland many
valleys, once fertile, are now filled with glaciers. From
the bottom of the glacier streams of water constantly
issue, and it is from such sources that the rivers Rhine
and Rhone of Europe take their rise.

668 How are the gigantic icebergs formed which are found floating at
some seasons in the Atlantic ?

They are portions of great glaciers formed in the
northern regions, which become detached and float in
the sea.

669 How high are icebergs sometimes seen f

Sometimes exceeding 300 feet in height.

670 At what elevation above the surface of the earth, at the equator,
will water remain frozen ?

At an elevation of about 15,000 jjfrf&

671 At what elevation in the straits of Magellan will water remain
frozen f

At about 4000 feet.

673 What is the point where water remains frozen called t

The line of perpetual snow.

673 Why are not all places which lie under the same parallel of lati-
tude of the same temperature ?

Because various disturbing circumstances tend to vary
the mean temperature.

SCIENCE OF COMMON THINGS. 107

Effect of the sea on the climate. Of mountains on temperature. Natural soils.

6 7*4 W hat disturbing circumstances affect the temperature of particular
situations f

1. The elevation and form of the land ;

2. The proximity of the sea ^

3. Mountains, swamps, and forests;

4. The nature of the soil ; and

5. The prevalence of cold or warm winds.

67*5 What effect is produced on temperature by the configuration of
lands?

Islands and peninsulas are warmer than continents ;
bays and inland seas also tend to raise the mean tem-
perature.

6*76 What effect has the sea on temperature ?

In warm climates it tends to diminish the heat ; in
cold climates to mitigate .the cold.

677* What effect have mountains on temperature f

Chains of mountains which ward off cold winds, aug-
ment the temperature / but mountains which ward on
south and west winds, lower it.

G7*8 What effect has soil on temperature ?

A sandy soil, which is dry, is warmer than a marshy
soil, whicn is wet, and subject to great evaporation.

67*0 What is a natural soil?

Natural soils are merely decomposed parts of the sub-
jacent rocks, mixed with the decomposed portion of
vegetable substances which have grown or fallen upon
it, with some animal substances.

68O What is the name given to the vegetable and animal products
mixed with the mineral ingredients of a soil f

681 What beneficial effect do loose stones and" rocks have upon dry
porous soils ?

They retain moisture in the soil by preventing the
evaporation which would otherwise take place. In
high lands they serve to condense fogs and low clouds,
and thus add to the moisture of the subjacent soil.

G83 What countries are the most cloudy f

Those where the temperature and winds are most
variable, as Great Britain.

108 SCIENCE OF COMMON THINGS.

Where the most rain falls. How many rainy days in the year.

633 What countries are the least cloudy f

Those where the temperature and winds are least
variable, as Egypt.

634 Why are mountainous countries more rainy than flat ones?

Because the air (striking against the sides of the
mountains) is carried up the inclined plane, and brought
in contact with the cold air of the higher regions ; in
consequence of which its vapor is condensed and depo-
sited in rain.

635 When is the quantity of moisture in the air greatest, and when
least?

It is greatest in the summer months, and least in the
winter.

686 In what part of the world does rainfall most abundantly f

Near the equator / and the quantity of rain decreases
as we approach the poles.

637* How many inches of rain faU yearly at tlie city of Vera Cruz,
Mexico ?

About two hundred and seventy-eight inches.

633 How great a depth of rain, measured in inches, falls yearly in
London f

•About twenty-Jive inches

689 How do you account for the great amount of rain falling at Vera
Cruz f

Vera Cruz, situated within the tropics, is backed by
lofty mountains, whose summits are covered with per-
petual snow j against these the hot, humid air from
the sea is driven by the trade-winds, condensed, and its
excess of moisture is precipitated as rain.

690 In what latitudes do the greatest number of rainy days occur f

There are more rainy days in the temperate zones
than in the tropics, although the yearly quantity of
rain falling in the latter districts is much greater than
in the former.

691 About how many rainy days are there in a year in the northern
parts of the United States ?

About one hundred and thirty-four ; in the South-
ern States the number is somewhat less, being about
one hundred and three.

SCIENCE OF COMMON THINGS. 109

Ilain-gauge. "Wet and dry seasons of the tropics.

693 Why does it rain more- frequently in the temperate zones than in
the tropics f

Because the temperate zone is a region of variable
winds, and the temperature of the atmosphere changes
often ; while in the tropics the wind changes but rarely,
and the temperature is very constant throughout a great
part of the year.

693 How is the amount of rain measured f

By means of a rain-gauge.

694: How is this constructed ?

The best form consists of a cylindrical metal vessel
furnished with a float ; the rain falling into the vessel
raises the float, the stem of which is so graduated that
the increase in depth can be very accurately measured.

695 Why does it rain more upon the sea-coast than in the interior of
a country ?

Because the air adjacent to the ocean contains more
moisture than the air inland.

696 What is the average yearly fall of rain in the tropics and tempe-
rate zones ?

The average yearly fall of rain in the tropics is nine-
ty-five inches ; in the temperate zone only thirty-five.

The greatest rain-fall, however, is precipitated in the shortest time.
Ninety -five inches fall in eighty days on the equator, while 'at St. Peters-
burg the yearly rain-fall is but seventeen inches, spread over one hundred
and sixty-nine days. Again, a tropical wet day is not continuously wet.
The morning is clear ; clouds form about ten o'clock ; the rain begins at
twelve, and pours till about half-past four; by sunset the clouds are
gone, and the nights are invariably fine.

697* In the tropics, how are the seasons divided?

Into the wet or rainy, and the dry season.

698 Are there some countries entirely destitute of rain ?

In some parts of Egypt it never rains ; in Peru it
rains once, perhaps, in a man's lifetime.

Upon the table-land of Mexico, in parts of. Guatemala and California,
for the same reason, rain is very rare. But the grandest rainless districts
are those occupied by the great desert of Africa, extending eastward
over portions of Arabia and Persia to a desert province of the Belooches —
districts. farther continued in the heart of Asia over the great desert of
Gobi, the table-land of Thibet, and part of Mongolia. In all these are
five or six millions of square miles of land that never taste a shower.

110 SCIENCE OF COMMON THINGS.

Countries destitute of rain. Aunual amount of rain. Annual eva'poration.
6Q9 Why are these countries destitute of rain ?

The cause of this scarcity is to be sought for in the
peculiar conformation of the country.

In Peni, parallel to the coast, and at a short distance from the sea, is
the lofty range of the Andes, the peaks of which are covered with per-
petual snow and ice. The prevailing wind is an east wind, sweeping
from the Atlantic to the Pacific across the continent of South America.
As it approaches the west coast, it encounters this range of mountains,
and becomes so cooled by them that it is forced to precipitate its moist-
ure and passes on to the coast almost devoid of moisture. In Egypt and
other desert countries, the dry sandy plains heat the atmosphere to such
an extent that it absorbs moisture, and precipitates none.

7OO Are there some districts in which it may be said to always rain ?

In some portions of Guiana it rains for 'a great por-
tion of the year. The fierce heat of the tropical sun
fills the atmosphere with vapor, which returns to the
earth again in constant showers, as the cool winds of the
ocean flow in from the higher latitudes.

7*O1 How great a quantity of water is supposed to be annually precipi-
tated as rainf

The amount is calculated to exceed seven hundred
and sixty millions of tons

7*OJ3 Was this whole, amount raised by evaporation into the atmosphere f

Certainly ; the daily amount of water raised by
evaporation from the sea alone amounts to no less than
one hundred and sixty-four cubic miles, or about sixty
thousand cubic miles annually.

7*O3 What is the daily amount of evaporation from the sea between the
Cape of Good Hope and Calcutta f

During the months of October and November, it is
known to average three quarters of an inch daily from
the wrhole surface.

7*04 Is the climate of New England and the Northern United States
drier than that of England and Central Europe ?

It is / and this fact exercises an important influence
upon many professions and callings, tainters find that
their work dries quicker in New England than in Cen-
tral Europe. Cabinet-makers here are obliged to use
thicker glue, and watchmakers animal instead of vege-
table oil.

SCIENCE OF COMMON THINGS. Ill

Hail-storms, where most frequent. The moon and the weather.

7*O5 Why will not pianofortes made in England or Germany answer
for use in New England ?

Because the difference in the climate of these respec-
tive countries is so great, as respects moisture, that
the foreign instruments shrink, and quickly become
damaged.

7O 6 In what climates do hail-storms most frequently occur f

In temperate climates most frequently, and rarely
within the tropics.

707 In what localities in the temperate zones do hail-storms occur most
frequently 1

In the vicinity of high mountains, whose peaks are
always covered with ice and snow. The south of France,
which lies between the Alps and Pyrenees, is annually
ravaged by hail ; and the damage which it causes
yearly to vineyards and standing crops, is estimated at
upwards of nine millions of dollars.

Do the general meteorological changes which take place almost
daily, and which are designated as weather changes, occur in accordance
with certain fixed laws f

There is no reason to doubt that every change in the
weather is in strict accordance with some certain phy-
sical agencies, which are fixed and certain in their
operations.

7*09 Why can we not, then, with certainty determine and foretell the
character of the weather for any particular time ?

Because the laws which govern meteorological
changes are as yet imperfectly understood.

7*1O Is there any reason for supposing that the moon has any influence
upon the weather f

An examination of meteorological records, kept in
different countries through many years, proves conclu-
sively that the popular notions concerning the influence
of the lunar phases on the weather have no foundation
in any well established theory, and no correspondence
with observed facts.

7*11 Do meteorological records afford any support to the belief in tha
occurrence of rain at particular phases of the moon ?

There is some reason for supposing that rain falls

112 SCIENCE OF COMMON THINGS.

Effect of moonlight on animals and vegetables. Equinoctial storm.

more frequently about four days before full moon, and
less frequently about four or five days before new
moon, than at other parts of the month ; but this can-
not be considered as an established fact : in other
respects the changes of the moon cannot be shown to
have influenced in any way the production of rain.

713 Does the bright moonlight in any ivay hasten the putrefaction of
animal or vegetable substances ?

It is generally supposed to do so ; but the fact is,
that- on bright, clear nights, when the moon shines
brilliantly, dew is more freely deposited on these sub-
stances than 'at other times, and in this way putrefac-
tion may be accelerated. With this the moon has no
connexion.

713 Is there any foundation for the belief that the appearance of the
aurora borealis is followed by a change in tlie weather?

Meteorological registers conclusively showT that there
is no such connexion, and that the appearance of the
aurora is as often followed by fair weather as by foul.

714 Is there any truth in the traditional notion that a long and violent
storm usually accompanies the period of the equinoxes ?

The examination of weather-records for sixty-four
years shows that no particular day can be pointed out
in the month of September, (when the " equinoctial
storm " is said to occur) upon which there ever was, or
ever will be, a so-called equinoctial storm. The fact,
however, should not be concealed, that taking the ave-
rage of the five days embracing the equinox for the
period above stated, the amount of rain is greater than
for any other five days, by three per cent., throughout
the month.

715 Is there any reason for believing that cold and warm seasons alter-
nate?

Meteorological records, kept for eighty years at the
observatory of Greenwich, England, seem to show that
groups of warm years alternate with cold ones in such
a way as to render it most probable that the mean an-
nual temperatures rise and fall in a series of curves,
corresponding to periods of about fourteen years.

SCIENCE OF COMMON THINGS. 113

Can animals foretell changes in the weather ?

7*1(3 Is it probable that some animals and insects are able to foretell
changes in the weather before man can perceive any indications of the same ?

Of this fact there appears to be no doubt. Some
varieties of the land-snail only make their appearance
'before a rain. Some other varieties of land crustaceous
animals change their color and appearance twenty-four
hours before a rain.

7*17* What curious fact has been noticed in respect to the leaves of. trt™
indicating changes in the iveather ?

For a light, short rain, some' trees have been observed
to incline their leaves, so as to retain water / but for a
long rain, they are so doubled as to conduct the water
away.

7*18 What fact has also been noticed respecting the changes in springs
previous to a rain ?

The water of springs has been observed to rise and
flow out in greater volume previous to a rain.

Most, if not all, of the popular proverbs respecting changes in the wea-
ther, the influence of the moon, of frosts, auroras, and the like, when
tested by observation, will be found to be unsupported by facts, and
unworthy of the slightest credence.

7*19 Why will there be no rain if the air be very cold f

Because it is so muck condensed that it has already
parted with as much moisture as it can spare.

7*2O Have heat and cold any effect on the barometer f

No, not of themselves ; but as cold weather is gene-
rally either dry or rough, with northerly winds, the
mercury generally rises in cold weather ; and as warm
weather is often moist, or accompanied by southerly
winds, which bring vapor with them, therefore the mer-
cury often sinks in warm weather.

114: SCIENCE OF COMMON THINGS.

Production of sound. Drum of the ear.

PART IV.

SOUND.

CHAPTEK I.

ORIGIN AND TRANSMISSION OF SOUND.

How is sound produced f

Sound is heard when any sudden shock or impulse,
causing vibrations, is given to the air, or any other
body, which is in contact directly or indirectly with the
drum of the ear.

T22 What is the drum or tympanum of the ear ?

A thin membrane which closes the aperture of the
ear.

7*23 How do the vibrations of the air, striking upon the drum of the ear,
give us the sensation of sound ?

Behind the drum of the ear are various cavities and
tubes in the bone which form the side of the head, in
which the minute fibres of the auditory nerve are dis-
tributed. When the drum of the ear is made to vibrate
freely .by the action of the sonorous undulations of the
external air, the vibrations are communicated by the
action of minute bones, nmscles, and fluids contained in
the cavities of the ear, to the nerve, and from thence the
impressions are conveyed to the brain.

Fig. 29 is a perspective magnified view of the interior of the ear. The
several parts of the ear, and the progress of sound towards the nerve
which communicates the sensation to the brain, may, however, be best
illustrated by reference to Fig. 30 : —

1. There is external to the head a wide-mouthed tube, or ear-trumpet,
<$, for catching and concentrating the waves of sound. It is movable in

SCIENCE OF COMMON THINGS.

115

Construction of the ear.

Air not necessary to sound.

fig. 29.

Fig. 30.

many animals, so that they can direct it to the place from which the
sound comes.

2. The sound concentrated at the bottom of the ear-tube falls upon a
membrane stretched across the channel, like the parchment of an ordi-
nary drum, over the space called the tympanum, or drum of the ear, b,
and causes the membrane to vibrate. That its motion may be free,
the air contained within the drum has free communication with the
external air by the open passage, /, called the eustachian tube, leading to
the back of the mouth. A degree of deafness ensues when this tube is
obstructed, as in a cold ; and a crack, or sudden noise, with immediate
return of natural hearing, is generally experienced when, in the effort of
sneezing or otherwise, the obstruction is removed.

3. The vibrations of the membrane of the drum are conveyed further
inwards, through the cavity of the drum, by a chain of four bones (not
here represented on account of their minuteness), reaching from the
centre of the membrane to the oval door or window, leading into the
labyrinth e.

4. The labyrinth, or complex inner compartment of the ear, over which
the nerve of hearing is spread as a lining, is full of watery fluid ; and,
therefore, by the law of fluid pressure, when the force of the moving
membrane of the drum, acting through the chain of bones, is made to
compress the water, the pressure is felt instantly over the whole cavity.
The labyrinth consists of the vestibuk, e, the three semicircular canals, c,
imbedded in the hard bone, and a winding cavity, called the cochlea, d,
like that of a snail-shell, in which fibres, stretched across like harp-strings,
constitute the lyra. The separate uses of these various parts are. not yet
fully known. The membrane of the tympanum may be pierced, and the
chain of bones may be broken, without entire loss of hearing. — ARNOTT.

*7S4: Is air necessary to the production of sound ?

' No ; but most sounds owe their origin to the vibra-
tions of the air. Sound can be produced under water,
and all bodies are, in fact, more or less fitted to produce
the sound vibrations ; in many cases air is neither the
quickest nor the best conductor of sound.

735 Upon what does the loudness of sound conveyed by air depend f

Upon the density of the air ?

SCIENCE OF COMMON THINGS.

What is a sonorous body ? Sonorous vibrations. Bell metal.

Why does a bell rung in a receiver exhausted of air fail to produce
sound ?

Because no air is present to receive and transmit the
vibrations.

7*37* What is a sounding or sonorous body f

A body possessing both hardness and elasticity,
which, when struck, vibrates, and imparts to the air in
contact with it undulations corresponding to its vibra-

tions.

7*38 Why has the peculiar kind of motion in bodies which gives rise to
the sensation of sound, been termed vibration ?

Because a striking analogy may be traced between
the tremulous agitation which takes place among the
particles of a sounding body and the oscillations of a
pendulum.

7*30 How 'may the nature of sonorous
vibrations be illustrated f

By noticing the visible mo-
tions which occur on striking
or twitching a tightly extender
cord or wire. Suppose such a
cord, represented by the cen- Flg 31

tral line in Fig. 31, to be

forcibly drawn out to A, and let go ; it would immedi-
ately recover its original position by virtue of its elas-
ticity ; but when it reached the central point, it would
have acquired so much momentum as would cause it to
pass onward to a ; thence it would vibrate back in the
same manner to B, and back again to 5, the extent of
its vibration being gradually diminished by the resist-
ance of the air, so that it would at length return to a
state of rest.

7*30 Why are copper and iron sonorous, and not lead ?

Copper and iron are hard and elastic / but as lead
is neither hard nor elastic, it is not sonorous.

731 Of what is bell-metal made f

Of copper and tin in the following proportions : — In
every five pounds of bell-metal there should be one
pound of tin and four pounds of copper.

SCIENCE OF COMMON THINGS. 117

Solids transmit sound. The earth conducts sound. Sound vibrations.

73S Why is this mixture of tin and copper used for bell-metal ?

Because it is much harder and more elastic than any
of the pure metals.

733 Are. solids capable of transmitting sounds f

All solid bodies which possess elasticity have the
power of propagating or transmitting sounds.

734 What easy experiment illustrates the transmission of sound by
solids f

When a stick is held between the teeth at one ex-
tremity, and the other is placed in contact with a table,
the scratch of a pin on the table may be heard with
great distinctness, though both ears be stopped.

735 Does tfie earth conduct sound f

The earth often conducts sound, so as to render it
sensible to the ear, when the air fails to do so. It is
well known that the approach of a troop of horse can
be heard at a distance by putting the ear to the ground,
and savages practise this method of ascertaining the
approach of persons from a great distance.

73Q What purpose is subserved by tJie body of a stringed instrument t

The string of an instrument, when caused to vibrate,
communicates the vibrations to the matter composing
the body of the instrument and the surrounding air,
and thus a tone or musical note is produced and ren-
dered audible to the ear.

737 How are aerial vibrations or pulses communicated?

The air, encompassing sounding bodies on every side,
conveys the sensation of sound in all directions ; there-
fore the aerial vibrations, or, as they have been termed,
"pulses" must be communicated successively and ge-
nerally throughout the whole space within the limits
of which they are capable of affecting the ear.

738 To what have the sound vibrations or pulsations been compared?

To the waves spreading in concentric circles over
the smooth surface of water.

"When a stone is thrown into water, the liquid waves are propagated
not only directly forward from the centre, but if they encounter any obr
struction, as from a floating body, they will bend their course round the
sides of the obstacle, and spread out obliquely beycm4 it. So th,e undu.

118 SCIENCE OF COMMON THINGS.

Sound vibrations may be rendered visible. Telocity of sound.

lations of air, if interrupted in their progress by a high wall or other simi-
lar impediment, will be continued over its summit and propagated on the
opposite side of it.

739 When a sonorous body is struck, do all the particles of which it it
composed really move or vibrate ?

They do ; and the body itself, no matter how com-
pact and solid it may be, really changes its form with
each vibration.

740 How may the sound vibrations in a solid body be rendered visible f

By many simple contrivances — as by a ball hung by
a string to a bell, by pieces of paper placed on the
strings of a violin, or by sand placed upon the sound-
ing-board of a piano or any other stringed instrument.

741 How fast does sound travel f

About 13 miles in a minute, or 1142 feet in a second
of time.

Why is the flash of a gun fired at a distance seen long before th«
report is heard ?

Because light travels much faster than sound.

Light would go 480 times round the whole earth while sound is going
its 13 miles.

743 How is a knowledge of the velocity of sound made applicable to the
measurement of distances f

Suppose a flash of lightning to be perceived, and on
counting the seconds that elapse before the thunder is
heard, we find them to amount to 3£ ; then as sound
moves 1142 feet in a second, it will follow that the
thunder-cloud must be distant 1142 x 3£ = 3997 feet.

744 Why do windows rattle when carts pass by a house ?

1. Because glass is sonorous • and the air communi-
cates its vibrations to the glass, which echoes the same
sound ; and

2. The window-frame being shaken, contributes to
the noise.

"Window-frames are shaken, 1. By sound-waves striking against them.
2. By a vibratory motion communicated to them by the walls of the
house.

745 Why. is the sound of a bell stopped by touching the bell with our
finger f

Because the weight of our finger stops the vibratiima

SCIENCE OF COMMON THINGS. 119

How sound is obstructed. Sounds more distinct by night than by day.

of the bell ; and as soon as the bell ceases to vibrate, it
ceases to make sound-waves in the air.

7*46 Why does a split bell make a hoarse, disagreeable sound f

Because the split of the bell causes a double vibration /
and as the sound-waves clash and jar, they impede
each other's motion, and produce discordant sounds.

7*47' Why can persons, living a mile or two from town, hear the bells
of the town churches sometimes and not at others f

Because fogs, rain, and snow obstruct the passage of
sound ; but when the air is cold and clear, sound is
propagated more easily.

7*48 Why can we not hear sounds (as those of distant church bells') in
rainy weather so well as in fine weather ?

Because the falling rain interferes with the undula-
tions of the sound-waves, and breaks them up.

7*49 Why can we not hear sounds (as those of distant church bells) in
snowy weather so well as in fine ivealher?

Because the falling snow interferes with the undula-
tions of the sound-waves, and stops their progress.

7*5O Why can we not hear sounds (such as those of distant clocks) so
distinctly in a thick mist or haze as in a clear night ?

Because the air is not of uniform density when it is
laden with mist; in consequence of which the sound
waves are obstructed in their progress.

7*51 Why do we hear sounds better by night than by day?

1. Because night air is of more uniform density, and
less liable to accidental currents ; and.

2. Night is more still, from the suspension of business
and hum of men. Many sounds become perceptible
during the night, which during the day are completely
stifled, before they reach the ear, by the din and dis^
cordant noises of labor, business, and "pleasure.

7*53 Why is tlie air of more uniform density by night than it is by
dayf

Because it is less liable to accidental currents ; inas •
much as the breezes (created by the action of the sun's
rays) generally cease during the night.

753 How should partition walls be made, to prevent the voices in adjoin'
ing rooms from being heard ?

120 SCIENCE OF COMMON THINGS.

Best conductors of sound. Musical sounds. "What is a noise ?

The space between the laths should be filled with
shavings or sawdust ; and then no sound would ever
pass from one room to another.

7*54 Why should shavings or sawdust .prevent the. transmission of sound
from room to room ?

Because there would be several different media for
the sound to pass through ; and every change of medium
diminishes the strength of the sound- waves.

7*55 What solids are among the best conductors of sound f

Iron and glass ; sound is transmitted by them at the
rate of 17,500 feet, or more than 3 miles in a second ;
after these rank copper, several different kinds of wood,
silver, tin, &c.

CIIAPTEK II.

VOCAL AND MUSICAL SOUNDS.
7*50 What is a musical sound?

A musical sound is produced by regular undulations
or vibrations — a succession of sounds following each
other with perfect uniformity.

7*57* How does a noise differ from a musical sound f

A noise is the result of very irregular or disturbed
undulations or vibrations.

7*58 Do all persons hear sounds alike f

The faculty of hearing depends upon the construc-
tion and sensibility of the ear, and as this differs in dif-
ferent individuals, it is certain that all persons will not
hear sounds alike.

7*59 What is meant by the terms concord and discord f

When two tones or notes sounded together produce
an agreeable effect on the ear, their combination is

SCIENCE OF COMMON THINGS. 121

Scale of music. Sounds of Instruments. How birds sing.

called a musical concord ; when the effect is disagree-
able, it is called a discord.

7* GO What is the gamut or diatonic scale of music ?

It consists of seven notes, which are distinguished by
the seven first letters of the alphabet, or by the seven
syllables, do, re, mi, fa, sol, la, si.

7*61 Why do flutes, etc., produce musical sounds 1

Because the breath of the performer causes the air
in the flute to vibrate / and this vibration sets in mo-
tion the sound-waves of the air.

7*03 Why does a, fiddle-string give a musical sound f

Because the bow drawn across the string causes it to
vibrate ; and this vibration of the string sets in motion
the sound-waves of the air, and produces musical notes.

7*63 Why does a drum sound t

Because the parchment head of the drum vibrates
from the blow of the drum-stick, and sets in motion the
sound-waves of the air.

7*64 Why do pianofortes produce musical sounds ?

Because each key of the piano (being struck with the
finger) lifts up a little hammer which knocks against a
string / and the vibration thus produced sets in motion
the sound-waves of the air.

7*35 Why is an instrument flat when the strings are unstrung?

Because the vibrations are too slow / in consequence
of which the sounds produced are not shrill or sharp
enough.

7*©S Why do birds alone, of animals, produce musical notes f

Because they alone are gifted with a vocal organiza-
tion, which enables them to produce musical notes. In
other animals, the larynx is placed wholly at the
upper end of the windpipe ; but in birds it is sepa-
rated, as it were, into two parts, one placed at each
extremity.

7*67* Why cannot birds be so correctly said to sing as to whistle f

Because natural singing is an exclusive privilege of
man.

122 SCIENCE OP COMMON THINGS.

The windpipe. Larynx. What is coughing ?

768/71 the human system, what are the parts concerned in the produc-
tion of speech and music ?

They are the windpipe, the larynx, and the glottis.

769 What is the windpipe f

The windpipe is merely a cartilaginous canal through
which the air issues from the lungs.

770 What is the larynx f

The larynx is an enlarged continuation of the wind-
pipe, formed, like it, of cartilage or gristle, membrane,
and muscle y it is, however, more complicated, ter-
minating above in two lateral membranes which
approach near together, leaving an oblong, narrow
opening, called the glottis.

771 How is sound produced by the organs of voice ?

The air expired from the lungs, passes through tLe
windpipe and out at the larynx, through the opening-
of the membrane called the glottis. The vibration of
these membranes, caused by the passage of air, causes
sound.

77S How can the tones of the voice be made grave or acute f

By varying the tension of these membranes and the
size of the opening.

773 What is the force exerted by the healthy chest in blowing f

About one pound on the inch of its surface ; that
is to say, the chest can condense its contained air with
that force, and can therefore blow through a tube the
mouth of which is ten feet under the surface of water.

774 What is the vocal action of coughing ?

In coughing the top of the windpipe or the glottis is
closed for an instant, during which the chest is com-
pressing and condensing its contained air ; and on the
glottis being opened, a slight explosion, as it were, of
the compressed air takes place, and blows out any irri-
tating matter that may be in the air-passages.

775 Why does a popgun make a loud report when the paper bullet is
discharged from it?

Because the air confined between the paper bullet
and the discharging rod is suddenly liberated, and

SCIENCE OF COMMON THINGS 123

" What is sneezing? Laughing. Crying. Suffocation.

strikes against the surrounding air ; this makes a report
in the same way as when any two solids (such as your
hand and the table) come into collision.

77© What is sneezing f

Sneezing is a phenomenon resembling cough ; only
the chest empties itself at one effort, and chiefly
through the nose, instead of through the mouth, as in
coughing.

777 What is laughing!

Laughing consists of quickly repeated expulsions of
air from the chest, the glottis being at the time in a
condition to produce voice ; but there is not between
the expirations, as in coughing, a complete closure of
the glottis.

773 What is hiccough f

Hiccough is the stopping of the commencement of a
strong inspiration, by a sudden closing of the glottis.

779 What is crying ?

Crying differs from laughing almost solely in the
circumstance of the intervals between the gusts or expi-
rations of air from the lungs being longer. Children
laugh and cry in the same breath.

780 Why, in straining to lift weights, or to make any powerful bodily
effort, do we compress our breath ?

We shut up the air in the lungs in order to give
increased steadiness and firmness to the body.

781 When is a person suffocated?

When the windpipe becomes choked, or the supply of
air to the lungs is in any way cut off.

783 Why do birds sing comparatively louder -than man f

Because the strength of the larynx, and of the muscles
of the throat, in birds, is infinitely greater than in the
human race. The loudest shout of man is but a feeble
cry compared with that of the golden-eyed duck, the
wild goose, or even the woodlark.

783 How are winged insects generally found to produce sound f

Generally they excite sonorous vibrations by the

124: SCIENCE OF COMMON THINGS.

Bounds of Insects. Echoes. "Where echoes occur.

fluttering of their wings or other membranous parts of
their structure.

7 84 How do locusts produce sound f

They are furnished with an air-bladder, or a species
of bagpipe, placed under and rather behind their wings.

CHAPTEE III.

KEFLECnON OF SOUNDS.

785 What is an echo f

An echo is a reflection of sound.

786 Will you explain the manner in which an echo is produced f

When a wave or undulation of water strikes against
a smooth surface, it is reflected, or turned back, and
waves moving in an opposite direction are produced.
The same thing takes place with a sound-wave of air : we
hear first the sound proceeding directly from the sono-
rous body ; then, if the sound-wave strikes against a
proper surface, at a suitable distance, it is turned back,
and we hear a repetition of the sound. This repetition
we call an echo.

787* Are echoes often Tieard at sea or on extensive plains f

Yery rarely ; at sea or on an extensive plain there
are no surfaces to reflect sound. It sometimes happens,
however, that in these situations the clouds reflect sound.

788 In what places do echoes most frequently occur f

In caverns, large halls, valleys and mountainous
passes, the windings of long passages, etc.

789 Why are these places famous for echoes ?

Because the sound-waves cannot flow freely forward,
but continually strike against opposing surfaces, and
are turned back.

SCIENCE OF COMMON THING8. 125

Ancient fable of echo. Distance requisite to produce echo.

7*00 What beautiful fiction existed among the ancients relative to the
production of echo f

They. supposed that Echo was a nymph who dwelt
concealed among the rocks, and who repeated the
sounds she heard.

791 At what distance must the body reflecting the sounds be situated in
order to produce an echo f

It is requisite that the reflecting body should be
situated at such a distance from the source of sound,
that the interval between the perception of the original
and reflected sounds may ~b& sufficient to prevent them
from being blended together.

793 When the seunds become thus blended together, what is the effect
called ?

A resonance, and not an echo.

793 Why do not the watts of a room of ordinary size, produce an echo f

Because the reflecting surface is so near the source
of sound that the echo is blended with the original
sound / and the two produce but one impression on
the ear.

7*94 Why do very large buildings (as cathedrals) often reverberate the
voice of the speaker ?

Because the walls are so far off from the speaker,
that the echo does not get oack in time to blend with
the original sound ; and therefore each is heard sepa-
rately.

7*95 Why do some echoes repeal only one syllable ?

Because the echoing body is very near. The farther
the echoing body is oif, the more sound it will reflect :
if, therefore, it be very near, it will repeat but one syl
lable.

790 Why does an echo sometimes repeat two or more syllables f

Because the echoing body is far off ; and therefore
there is time for one reflection to pass away before an-
other reaches the ear.

All the syllables must be uttered before the echo of the first syllable \
reaches the ear : if, therefore, a person repeats 7 syllables in 2 seconds of \
time, and hears them all echoed, the reflecting object is 1142 feet distant ;
because sound travels 1142 feet in a second, and the words take one
second to go to the reflecting object, and one second to return.

126 SCIENCE OF COMMON THINGS.

Effect of surfaces on sound. Construction of halls for speaking.

797 What must be the conditions of the reflecting surface in order to
produce a perfect echo ?

The surface must be smooth and of some regular
form ; for the wave of sound rebounds, according to
the same law as a wave of water or an elastic ball, per-
pendicularly to the surface if it fall perpendicularly,
and if it fall obliquely^ on one side, it departs with an
equal degree of ooliquity on the other side.

798 What must be the effect of an irregular surface ?

An irregular surface must break the echo ; and if
the irregularity be very considerable, there can be no
distinct or audible reflection at all. For this reason an
echo is much less perfect from the front of a house
which has windows and doors, than from the plane
end, or any plane wall of the same magnitude.

799 Why have halls for music plane bare walls f

Because the hard plane walls reflect the sound regu-
larly, and increase the effect of the music.

800 Why are halls for speaking, theatres, churches, etc., generally
ornamented on the wall, and furnished with pittars, curtains, etc.

Because the ornaments , pillars, curtains, etc., form
irregular surfaces, which break up and destroy the
echoes and resonances.

801 Why is a thick curtain often placed behind a pulpit or speaking-
desk f

Because the material absorbs the sound, and by not
reflecting it avoids the production of echoes and reso-
nances.

If the room is not rery large, a curtain behind the speaker impedes
rather than assists his voice.

SOS What is a speaking trumpet f

A speaking trumpet is a hollow tube,, so constructed,

SCIENCE OF COMMON THINGS. 127

Construction of the speaking trumpet. Ear trumpet.

that the rays of sound (proceeding from the mouth
when applied to it), instead of diverging, and being
scattered through the surrounding atmosphere, are
reflected from the sides, and conducted forward in
straight lines, thus giving great additional strength to
i the voice. The course of the rajs of sound proceeding

Fig. 33.

from the mouth through this instrument, may be shown
by Fig. 33. The trumpet being directed to any point*
a collection of parallel rays of sound moves towards
such point, and they reach the ear in much greater
number than would the diverging rays which would
proceed from a speaker without such an instrument.

8O3 What is an ear trumpet f

An ear trumpet, Fig. 34, is in form and application
the reverse of a speaking trumpet, but
in principle the same. The, rays of
sound proceeding from a speaker, more
or less distant, enter the hearing trum-
pet, and are reflected in such a manner
as to concentrate the sound upon the
opening of the ear. Fig. 34 repre-
sents the form of the ear trumpet generally used by
deaf pei-sons. The aperture A is placed within the ear,
and the sound which enters at B is, by a series of
reflections from the interior of the instrument, concen-
trated at A.

SO ± Why do persons hold the hand concave behind the ear, in order to
hear more distinctly ?

Because the concave hand acts in some respects as
an ear trumpet, and reflects -the sound into the ear.

128 SCIENCE OF COMMON THINGS.

Sound lender in a church than on a plain. Haunted bouses.

805 Why does sound seem louder in a church or hatt than on a plain t

Because the sides of the building confine the sound-
waves, and prevent their spreading ; in consequence of
which their strength is greatly increased.

SOS How can most of the stories in respect to the so-called "haunted
houses'11 be explained ?

By reference to the principles which govern the
reflection of sounds. Owing to a peculiar arrangement
'of reflecting walls and partitions, sounds produced by
ordinary causes are often heard in certain localities at
remote distances, in apparently the most unaccountable
manner. Ignorant persons become alarmed, and their
imagination connects the phenomenon with some super-
natural cause.

SCIENCE OF COMMON THINGS. 129

What is heat and heat matter ?

PART V.

HEAT.

CHAPTER L

NATURE AND ORIGIN OF HEAT.
8O7 What is heat f

In ordinary language the term heat expresses the
sensation of warmth which we experience when any
portion of our body comes in contact with a substance
which is warmer than itself?

SOS Do we really know what heat is?

We do not ; we only know and study the effects
which it produces on matter.

SOS To what cause have different philosophers attributed the phenomenon
of heat?

Some have supposed the phenomenon of heat to be
merely a species of motion among the minute particles
of bodies generally, as sound is motion of another kind
among the same particles ; others have supposed that
heat arises from the presence of a pecuUa/r fluid or
ethereal kind of matter.

S1O Is it generally believed at the present time that heat is a material
substance ?

It was believed formerly that heat was a kind of
matter ; but now it is generally considered that heat
has no material existence.

811 What great fact is opposed to the idea that heat has a separate
material existence as a fluid ?

The fact that nature nowhere presents us, neither has
art ever succeeded in showing us, heat alone in a sepa-
rate state.

130 SCIENCE OF COMMON THINGS.

Heat has no weight How heat is measured. What is cold ?

SIS Has heat any perceptible weight?

No ; if we balance a quantity of ice in a delicate
scale, and then leave it to melt, the equilibrium will
not be in the slightest degree disturbed. If we substi-
tute for the ice boiling water or a red-hot iron, and leave
this to cool, there will be no difference in the result.

813 What important property distinguishes heat from all other agents
or substances in nature f

The property of passing through and existing in all
kinds of matter at ail times / heat is everywhere present,
and every body that exists contains it without known
limit.

814 Has ice heat ?

Yes, large quantities of it. Sir Humphrey -Davy, by
friction, extracted heat from two pieces of ice, and
quickly melted them, in a room cooled below the freez-
ing point, by rubbing them against each other.

815 How do we measure the quantity of heat in different bodies, or judge
of its effects ?

Only by the change in hulk or appearance which
different bodies assume, according as neat is added or
subtracted.

810 According to what law does heat diffuse or spread itself 'f

Heat diffuses or spreads itself among neighboring
bodies until all have acquired the same temperature /
that is to say, until all will similarly affect the thermo-
meter.

817* Why does a piece of iron thrust into burning coals become hoi
among them f

Because the heat passes from the coals into the iron
until the metal has acquired an equal temperature.

818 What is cold?

Cold is a relative term expressing only the absence
of heat in a degree ; not its total absence, for heat
exists always in all bodies.

810 When the hand touches a body having a higher temperature than
itself, why do we call it hot ?

Because on account of the law that heat diffuses

SCIENCE OF COMMON THINGS. 131

When is a body cold f What is fire ? Effects of heat.

itself among neighboring bodies until all have acquired
the same temperature, neat passes from the body of
higher temperature to the hand, and causes a peculiar
sensation, which we call warmth.

SSO Under what circumstances do we call a body cold f

When we touch a body having a temperature lower
than that of the hand, heat, in accordance with the above
law, passes out from the hand to the body touched, and
occasions the sensation which we call cold.

831 What, then, really are the sensations of heat and cold f

Merely degrees of temperature, contrasted by name
in reference to the peculiar temperature of the indivi-
dual speaking of them.

833 When is a body said to be incandescent or ignited f

When the body naturally incapable of emitting light
is heated to sufficient extent to become luminous.

833 What is flame?

Flame is ignited gas issuing from a burning body.

834 What is fire f

The appearance of heat and light in conjunction, pro-
duced by the combustion of inflammable substances.

835 What character was attributed to fire by the ancient philosophers f

They used the term fire as a characteristic of the
matter of heat, and regarded it as one of the four ele-
ments of nature.

83B Enumerate the general physical properties of heat.

It is invisible, without weight, with great tendency
to diffuse itself, and is absorbed by all bodies.

837 What are the principal effects of heat 1

Expansion, liquefaction, vaporization, and ignition.

838 What do we understand by the term caloric f

Caloric is a name often used to indicate the agent
which produces the sensation of warmth; since the term
" heat," as generally used, refers only to the sensation.

839 Is caloric equally distributed over the globe f

No ; at the equator the average temperature is

132 SCIENCE OF COMMON THINGS

Sources of heat. The sun a source of heat. Burning-glasses.

while at the poles it is believed to be about 13° below
zero.

" Average temperature" — that is, the mean or medium temperature.
"ZERO" — the point from which a thermometer is graduated; it is 32'
below freezing, Fahrenheit's thermometer.

83 O How many sources of heat are recognised to exist t

Six.

831 What are they f

1. The sun: 2. The interior of the earth • 3. Electri-
city ; 4^ Vital action ; 5. Mechanical action • 6. Che-
mical action.

CHAPTEE II

THE SUN A SOURCE OF HEAT-
83S What is the great natural source of heat f

The sun.

833 Why do burning-glasses set fire to substances submitted to their
power?

Because, when the rays of the sun
pass through the burning-glass, they
are bent towards one point, called
the^ " focus ;" in consequence of
_ . _ which the light and heat at this
~Fi*™35. point are very greatly increased.

Fig. 35 represents the manner in which a burning-glass concentrates
or bends down the rays of heat until they meet in a focus.

834 Do the rays of the sun ever set fire to natural substances without
the assistance of a burning-glass f

No ; the rays of the sun, even in the torrid zone, are
never hot enough to kindle natural substances, unless
concentrated by a "burning-glass.

835 Does the heat of the sun possess any different properties from arti-
ficial heat?

SCIENCE OF COMMON THINGS. 133

Heat of the sun. Cause of spring, summer, and winter.

The heat of the sun passes readily through glass,
whereas this property is possessed by artificial heat in
a very small degree.

836 What is the generally received opinion at present, in regard to the
actual temperature of the visible surface of the sun 1

That the temperature of its luminous coating is much
more elevated than any artificial heat we are able to
produce.

837 Why is the heat of the sun always greater in some portions of the
earth than at others ?

Owing to the position of the earth's axis, the rays of
the sun always fall more directly upon the central por-
tion of the earth than they do at the poles or extremities.

838 Upon what does the succession of spring, summer, autumn, and
winter, and the variations of temperature of the seasons, depend ?

Chiefly upon the position of the sun in relation to the
earth.

839 When do we experience the greatest amount of heat from the rays
of the sun f

When its rays fall most perpendicularly.

840 Why is the heat of the sun greatest at noon ?

Because for the day the sun has reached the highest
point in the heavens, and its rays fall more perpendicu-
larly than at any other time.

84:1 Why is it warmer in summer than in winter f

Because in summer the position of the sun is such
that its rays fall more perpendicularly than at any other
season. The sun is longer above the horizon in summer
than in winter, and consequently imparts the greatest
amount of heat.

843 Why is it colder in winter than in summer f

Because in winter the position of the sun is such that
its rays fall more obliquely upon the earth than at any
other season. The sun is also for a less time above the
horizon in winter than in summer, and consequently
imparts less heat.

843 Upon what does the heating power of the sun depend in a great
measure ?

134 SCIENCE OF COMMON THINGS.

Effect of the inclination of the sun's rays. Natural heat

Upon its altitude or height above the horizon / tlie
greater its altitude, the more perpendicularly will its
rays fall upon the earth, and the greater their heating
effect ; the less the altitude, the more obliquely will its
rays fall, and the less their heating effect.

844 Why should the difference in the inclination of the sun's rays fall-
ing upon the earth occasion a difference in their heating effect f

Because the more the rays are inclined, the larger
the space over which they fall.

Let us suppose A B C D, Fig. 36,
to represent a portion of the sun's
rays; and C D a portion of the
earth's surface upon which the rays
fall perpendicularly, and C F and
C E portions of the surface upon
which they fall obliquely. Now,

Fig. 36. it is obvious that the surfaces C F

and C E are greater than the
Burface C D ; and as the same amount of rays of light and heat fall upon
all the surfaces, it is clear that they will fall more densely upon the
smaller surface (i.e. that it will be warmer there) and more diffusely
over the inclined or oblique surface (where it will be colder).

845 What is the greatest natural heat ever observed f

On the west coast of Africa the thermometer (Fah-
renheit) has been observed as high as 108° in the
shade / Burckhardt, in Egypt, and Humboldt, in South
America, observed it at 117° F. ; and, in 181 9-, at Bag-
dad, the thermometer rose to 120° F. in the shade.

840 What is the lowest atmospheric temperature ever observed f

From 60° to 70° below the zero of Fahrenheit's ther-
mometer. This temperature has been observed by Dr.
Kane and other Arctic navigators.

84*7 What is the greatest artificial cold ever produced f

220° below zero, which temperature was attained by
Prof. Natterer. At this temperature, pure alcohol and
ether did not freeze.

848 What is the estimated temperature of the space above the earth's
atmosphere ?

58° below zero.

849 At what temperature does mercury freeze T

SCIENCE OF COMMON THINGS. 135

Extremes of temperature. Melting point of iron. Greatest artificial heat.

3S°-6 below zero.

850 At what temperature does fresh water freeze?

At 32° above zero.

851 At what temperature does salt or sea water freeze f

At 28° '5 above zero.

85S Why does it require a greater amount of cold to cause sea water to
congeal, than it does fresh water f

Because sea water contains salt and other substances
which tend to prevent congelation.

853 What is the average temperature at the equator 1

In America, 81°'5 ; in Africa^ 83°.

854 What is blood-heat, or the vital temperature of the human body t

98°.

855 At what temperature does alcohol boil f

Under the ordinary atmospheric pressure at 1T3°*5.

856 At what temperature does water boil T

Under the ordinary atmospheric pressure at 212°.

85*7 At what temperature does lead melt ?

At 594°.

858 At what heat does mercury boilf

At 661° under the common atmospheric pressure.

859 At ivhat temperature do brass, copper, silver, and gold melt ?

Brass at 1869° ; copper, 1996° ; silver, 1873° ; gold,
2016°.

860 At what temperature does cast-iron melt ?

At 2786°.

861 What is the greatest degree of artificial heat which we have been
enabled to measure f

A furnace heat of 3280° : at this heat wrought iron
and platinum did not melt.

136 SCIENCE OF COMMON THINGS.

Heat of the earth. Cause of earthquakes.

CHAPTEE III.

OTHER SOURCES OF HEAT BESIDES THE SUN.

862 How far below the surface of the earth does the influence of solar
heat extend ?

The depth varies from 50 to 100 feet / never, how-
ever, exceeding the latter distance.

863 How do we know that the earth is a source of heal f

Because we find as we descend into the earth and
pass beyond the limit of solar heat, that the tempera-
ture constantly increases.

864 At what rate does the temperature increase f

About one degree of the thermometer for every fifty
feet.

865 Supposing the temperature to continue to increase according to this
ratio, what would be its effects at different deptJis 1

At the depth of two miles water would be converted
into steam ; at four miles, tin would be melted ; at
five miles, leaa; and at thirty miles, almost every
earthy substance would be reduced to a fluid state.

866 To what cause may earthquakes and volcanoes be attributed f

Undoubtedly to the agency of the internal haat of
the earth.

867 What effect has the internal heat of the earth on the temperature
of the surface ?

JVo sensible effect: it has been calculated that it
affects the temperature of the surface less than ^V of a
degree of the thermometer.

868 WAy, if so great an amount of heat exist in the interior of the
earth, does it not appear more manifest upon the surface f

Because the materials of which the exterior strata or
crust of the earth is composed, do not conduct it to the
surface from the interior.

869 In what manner is electricity a source of heat?

When an electric current passes from one substance

SCIENCE OF COMMON THINGS. 137

Heat of electricity. Heat of chemical action.

to another, the substance which serves to conduct it is
very frequently heated ; but in what manner the heat
is produced, we have no positive information.

8 7O How great a degree of heat is electricity capable of generating f

The greatest known heat with which we are acquaint-
ed, is produced by the agency of the electric or gal-
vanic current. Ah1 known substances can be melted or
volatilized by it.

871 Has the heat generated by electricity been employed for any prac-
tical or economical purposes ?

Not to any great extent ; but for philosophical experi-
ments and investigations it has been made quite useful.

873 What is chemical action ?

We apply the term chemical action to those opera-
tions, whatever they may be, by which the weight, form,
solidity, color, taste, smell, and action of substances
become changed ; so that new bodies with quite different
properties are formed from the old.

873 How does chemical action become a source of heat ?

Many bodies, when their original constitution is
altered, either by the abstraction of some of their com-
ponent parts, or by the addition of other substances not
before in combination with them, evolve heat while the
change is taking place.

874 Explain by illustration what you mean.

"Water is cold, and sulphuric acid is cold ; but if these
two cold liquids be mixed together, they will produce
intense heat.

875 Why does cold water poured on lime make it intensely hot ?

Because heat is evolved by the chemical action which
takes place when the cold water combines with the lirne.

Heat is always evolved when a fluid is converted into a solid form.
Heat is always absorbed when a solid is changed into a liquid state. As
the water is changed from its liquid form when it is taken up by the lime,
therefore heat is given off.

87Q Where does the heat come from f

It was in the water and lime before, but was in a
latent state.

138 SCIENCE OF COMMON THINGS.

Heat in all bodies. What is latent heat? Heat in ice.

8*77* Was there heat in Hie cold water and lime before they were mixed
together f

Yes. All bodies contain heat.

878 Is there heat even in icef

Yes ; but it is latent (i.e. not perceptible to our
senses).

Latent, from the Latin word lateo (to lie hid).
87*9 Does cold iron contain heat ?

Yes ; everything contains heat ; but when a thing
feels cold, its heat is latent.

88O What is meant by latent heat ?

Heat not perceptible to our feelings. "When anything
contains heat without feeling the hotter for it, that heat
is called u latent heat.

S81 Does cold iron contain latent heat f

Yes ; and when a blacksmith compresses the particles
of iron by his hammer, he brings out latent heat ; and
this makes the iron red hot.

382 Why is the air in the spring, when the ice and snow are melting,
always very chilly and cold 1

Solid bodies, in passing to the liquid state, absorb heat
in large quantities ; when ice and snow are thawing,
they absorb heat from the air, in consequence of which
its temperature is greatly reduced.

883 Why does the weather always moderate on the fall of snow t

Bodies, in passing from the liquid to the solid state,
give out heat y snow is frozen water, and in its forma-
tion heat is imparted to the atmosphere, and its tem-
perature increased.

884 Why does the temperature of melting ice and snow never exceed
32°?

Because all the heat imparted to melting ice and
snow becomes insensible, until the liquefaction is com-
plete.

885 Can we be made to feel the heat of ice or snow f

Yes. Into a pint of snow put half as much salt ;
then plunge your hands into the liquid ; and it will feel
so intensely cold that the snow itself will seem warm in
comparison to it.

SCIENCE OF COMMON THINGS. 139

Salt and snow produce intense cold — reason of.

886 Are salt and snow really colder than snow ?

Yes, many degrees ; and by dipping your hand into
the mixture first, and into snow afterwards, the snow
will seem to be comparatively warm.

887 Why do salt and snow mixed together produce intense cold ?

The salt and ' snow are both solids ; when they are
mixed, the salt causes the snow to melt by reason of its
attraction for water, and the water formed dissolves
the salt : so that both pass from the solid to the liquid
condition, and a large quantity of heat is absorbed.
As this heat is derived from that which previously ex-
isted in the solids themselves in a sensible state, its
abstraction occasions a reduction of temperature.

888 How is heal produced by mechanical action f

1. By percussion / 2. By friction / and 3. By con-
densation.

88Q What is meant by percussion f

The shock produced by the collision of two bodies ;
as when a blacksmith strikes a piece of iron on his
anvil with his hammer.

00 O Why does striking iron make it red hot f

Because it condenses the particles of the metal, and
makes the latent heat sensible.

801 What is meant by friction f

The act of rubbing two things together, as the Indians
rub two pieces of wood together to produce fire.

80S How do savages produce fire by merely rubbing two pieces of dry
wood together ?

They take a piece of dry wood, sharpened to a point,
which they rub quickly up and down & flat piece till a
groove is made ; and the dust (collected, in this groove)
catches fire.

80S Why does the dust of the wood catch fire by rubbing f

Because latent heat is developed from the wood by
friction.

804 Do not carnage wheels sometimes catch fire f

Yes ; when the wheels are dry, or fit too tightly, or
revolve very rapidly.

140 SCIENCE OF COMMON THINGS.

Heat caused by friction. Use of greasing cart •wheels.

Fig. ST.

Fig. 37 represents an Indian explaining the method of kindling a fire
by the friction of two pieces of wood.

895 Why do wheels catch fire in such cases ?

Because the friction of the wheels against the axle-
tree disturbs their latent heat, and produces ignition.

896 What is the use of greasing cart wheels f

Grease lessens the friction ; and, because there is less
friction, the latent heat of the wheels is less disturbed.

89*7 Does a body ever cease to give out heat by friction f

No j however long the operation may be continued.

898 What conclusions respecting the nature of heat have philosophers
drawn from this fact ? •

That heat cannot be a material substance, but merely
& property of matter.

899 Why is it easier to produce heat from the friction of rough sur-
faces than smooth ones f

Because in the friction of rough surfaces certain par-
ticles are rubbed off, which, being small, are readily con-
densed, and made to evolve their latent caloric.

900 Why, when you rub a smooth metallic surface, as a button, for
example, against apiece qf plank, does the metal become more heated than the
wood?

Because the caloric is forced out of the wood, as it

SCIENCE OF COMMON THINGS.

How a friction match ignites. Temperature of living animals.

were, by the compression of its parts, and the button
receives most of the caloric, owing to a stronger attrac-
tion for it, than is possessed by the wood.

9O1 Why does a friction match, drawn over sandpaper or other rough
tubstance, ignite 1

When the match is drawn over sand paper, or other
rough substance, certain phosphoric particles are rub-
bed off, and being compressed between the match and
the paper, their heat is raised sufficiently high to ignite
them, and fire the match. If the match be drawn over
a smooth surface, the compression must be increased, for
the temperature of the whole phosphoric mass must be
raised in order to cause ignition.

0O3 What singular property have most living animal bodies f

The property of maintaining in themselves an equable
temperature, whether surrounded by bodies that are
hotter or colder than they are themselves.

9O3 Illustrate this fact.

The sailors of the Arctic exploring expedition during
the polar winter, while breathing air that froze mer-
cury, still had in them the natural warmth of 98° Fah-
renheit above zero ; and the inhabitants of India, where
the same thermometer sometimes stands 115° in the
shade, have their blood at no higher temperature.

SO 4 Do vegetables possess in any degree this property of maintaiitkiy
a constant temperature within their structure ?

Growing or fresh vegetables have this property to a
certain extent.

9O5 What, then, is vital heat?

^ The heat generated or excited by the organs of a
living structure.

©O6 What is the cause of vital or animal heat?

The cause of animal heat is not certainly known or
determined; it is supposed to be due to chemical
action, the result of respiration and nervous excitation.

907 Has {he, power of animals to preserve a peculiar temperature any
limits ?

Yes ; intense cold suddenly coming upon a man
7

14:2 SCIENCE OF COMMON THINGS.

Vital heat. Effect of climate on animals.

who has not sufficient protection, first causes a sensation
of pain, and then brings on an almost irresistible sleepi-
ness, which if indulged in proves fatal. A great excess
of heat also cannot long be sustained by the human
system.

©OS Does each species of animal appear to have a peculiar tempera-
ture?

Yes ; each species of animal and vegetable appears
to have a temperature natural and peculiar to itself,
and from this diversity different races are fitted for
different portions of the earth's surface.

©O9 What effect does the peculiarity of temperature have upon the dis-
tribution and location of animals and plants upon the earth's surface ?

The different species are confined and circumscribed
within certain districts, depending mainly on their re-
lations to heat. Thus, the orange-tree and the bird of
Paradise are confined to warm latitudes ; the pine-tree
and the Arctic bear, to those which are colder.

01O What curious fact in relation to a species of whale illustrates the
influence of temperature in defining locations ?

It has been ascertained that at least one species of
whale is precluded from migrating from the north to
the south, from its inability to live in the heated waters
of the equator.

©11 When animals or plants are removed from their peculiar and
natural districts to one entirely different, what changes take place f

They either cease to exist, or change their character
in such a way as to adapt themselves to the climate.

913 What curious illustrations do we find of this f

The wool of the northern sheep changes in the tropics
to a species of hair. The dog of the torrid zone is
nearly destitute of hair. Bees transported from the
north to the region of perpetual summer cease to lay up
stores of honey ^ and lose in a great measure their habits
of industry.

©IS How has nature provided for the protection of animals against the
modifications of temperature ?

By covering their bodies with &form of for. or hair,
or feathers, in the exact degree required, and to such

SCIENCE OF COMMON THINGS 143

Man only lives in all climates. Communication of heat.

an extent as to vary the covering in the same animal
according to the climate and season.

914 What one species of organized beings is fitted to live in all climates ?

jbfan alone is capable of living in all climates, and of
migrating freely to all portions of the earth.

CHAPTER IY.

HOW HEAT IS COMMUNICATED.

915 In what three ways may heat le communicated ?

By direct contact, by conduction and convection,
by radiation.

916 How may heat be communicated by contact f

"When a hot body touches a cold one, the heat passes
directly from one into the other, as when it enters a bar
of iron put into the fire, or the hand immersed in hot
water.

917* When is heat communicated by conduction f

When the heat travels from particle to particle of
the substance, as from the end of the iron bar placed
in the fire to that part of the bar most remote from the
fire.

91S When is heat communicated by radiation f

"When the heat leaps, as it were, from a hot to a cold
body through an appreciable interval of 'space, as when
a body is warmed by placing it before a fire removed
to a little distance from it.

919 In ivhat way does a heated body cool itself?

first, by giving off heat from its surface, either by
contact or radiation, or both conjointly / and, secondly,
by the heat in its interior passing from particle to par-
ticle by conduction through its substance to the surface.

SCIENCE OF COMMON THINGS.

How a cold body is heated. Good and bad conductors of heat.

930 In what manner does a cold body become heated ?

First, by heat passing into its surface either by con-
tact or radiation, or by both conjointly j and, secondly ^
by tbe heat at its surface passing from particle to par-
ticle through its interior portions by conduction.

931 Does heat pass through all bodies with tlie same velocity ?

No ; some substances oppose very little impediment
to its passage, while through others it is transmitted
slowly.

933 Into what two classes are bodies divided in respect to their conduc-
tion of heat ?

Into conductors and non-conductors / the former are
such as allow heat to pass freely through them ; the
latter comprise those which do not give an easy pas-
sage to it.

933 What are the best conductors of heat f

Dense, solid bodies, such as metals, glass, some varie-
ties of stone, etc.

934 What are the worst conductors of heat ?

All light and porous bodies ; such as hair, fur, wool,
charcoal, and so on.

935 Why do some things feel colder than otliers f

Principally because they are better conductors, and
draw off heat from our body much faster.

936 Why does a piece of wood blazing at one end not feel hot at the
other f

Because wood is so bad a conductor that heat does
not traverse freely through it ; hence, though one end
of a stick be blazing, the other end may be quite cold.

937 Why does hot metal feel more intensely warm than hot wool ?

Because metal gives out a much greater quantity of
heat in the same space of time • and the influx of heat
is, consequently, more perceptible.

933 Why does a poJcer, resting on a fender, feel colder than the hearth-
rug, which is farther off from the fire ?

Because the poker is an excellent conductor, and
draws heat from the hand much more rapidly than the
woollen hearth rug, which is a very bad conductor :

SCIENCE OF COMMON" THINGS. 145

Familiar illustrations of the conduction of'heat.

though both, therefore, are equally warm, the poker
seems to be the colder.

030 Why does a stone or marble hearth feel to the feet colder than a car-
pet or hearth-rug ?

Because stone and marble are good conductors ; but
woollen carpets and hearth-rugs are very ~bad conduc-
tors.

i 03O Why does the stone hearth make our feet cold f

As soon as the hearthstone has absorbed a portion
of heat from our feet, it instantly disposes of it, and
calls for ^ fresh supply ; till the hearthstone has be-
come of the same temperature as the foot placed upon it.

031 Do not also the woollen carpet and hearth-rug conduct heat from
the human body f

Yes ; but being very lad conductors, they convey
the heat away so slowly that the loss is scarcely per-
ceptible.

Yes ; everything in the room, except our bodies, is
really of one temperature / but some tilings feel colde*
than others, because they are letter conductors.

033 How long will the heartJistone feel cold to the feet resting on it ?

Till iliefeet and the hearthstone are bot/i of the same,
temperature • and then the sensation of cold in the
hearthstone will go off.

034 Why would not the hearthstone feel cold, when it is of the samf
temperature as our feet ?

Because the heat would no longer rush out of ou1
feet into the hearthstone, in order to produce equi'
librium.

035 Why are cooking vessels of ten furnished with wooden handles?

Because wood is not a good conductor like metal;
and therefore wooden handles prevent the heat of the
vessel from rushing into our hands to burn them.

Because paper and woollen are both very lad con-
ductors of heat, in consequence of which the heat of

146 SCIENCE OF COMMON THINGS.

Conducting power of water. Stoves and furnaces.

the kettle does not readily pass through them to the
hand.

Yes ; but though the kettle-holder became as hot as
the kettle itself, it would never feel so hot.

038 Why would not the kettle-holder feel so hot as the kettle, when loth
are of the same temperature.

Because it is a very lad conductor, and disposes of
its heat too slowly to be perceptible ; but metal (being
an excellent conductor) disposes of its heat so quickly,
that the sudden influx is painful.

039 When we plunge our hands into a basin of water, why does it pro-
duce a sensation of cold f

Because water is a better conductor than air ; and, as
it draws off the heat from our hands more rapidly, it
feels colder.

040 Why does the conducting power of water make it feel colder than
air?

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.

041 Is water a good conductor of heat ?

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

04S Why is water a bettei* conductor of heat than air 1

Because it is more dense / and the conducting power
of any substance depends upon its solidity, or the close-
ness of its particles.

043 How do you know that water is not a good conductor of heat ?

Because it may be made to boil at its surface, without
imparting sufficient heat to melt ice a short distance
below the surface.

044 Why are not liquors good conductors of heat f

Because the heat (which should be transmitted) pro-
duces evaporation, and flies off in the vapor.

045 // air is not a good conductor, how can we make use of it in
warming our houses by means of stoves and furnaces?

SCIENCE OF COMMON THINGS. 147

What renders clothing necessary ? Use of woollens and furs.

In the case of a stove or furnace, the air which is in
contact with the tire or the heated surface, first becomes
heated, expands, and rises ; cold air rushes in to supply
its place, is heated, and ascends in like manner, and
this interchange goes on until all the air in the room is
heated.

946 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 f

Because the air (which is cooler than our body) is
never at rest j and every fresh particle of air draws off
a fresh portion of heat.

947* How does the ceaseless change of air tend to decrease the warmth
of that part of the body devoid of clothing ?

Thus : the air (which cases the body) absorbs as
much heat as it can while it remains in contact ; being
then blown away, it makes room for a fresh coat of
air, which absorbs more heat.

948 Does the air which encases a body devoid of clothing become (by
contact) as warm as the body itself?

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.

949 Why do we feel colder in windy weather than in a calm day f

Because the particles of air pass over us more rapidly,
und every fresh particle takes from us some portion of
heat.

950 Why are woollens and furs used for clothing in cold weather?

Because they are very bad conductors of heat ; and
therefore prevent the warmth of the body from being
drawn off by the cold air.

951 Do not woollens and furs actually impart heat to the body f

No ; they merely prevent the heat of the body from
escaping.

953 Where would the heat escape to, if the body icere not wrapped in
wool or fur 1

The heat of the body would fly off into the air ; for
the cold air (coming in contact with our body) would

148 SCIENCE OF COMMON THINGS.

Why wool, hair, and feathers are warm. Icehouses.

gradually draw away its heat, till it was as cold as the
air itself.

953 What, then, is the principal use of clothing in winter-time?

1. To prevent the animal heat from escaping too
freely ; and

2. To protect the body from the external air (or wind),
which would carry away its heat too rapidly.

954 Why are ivool, fur, hair, and feathers such slow conductors of heat f

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

The warmest clothing is that which fits the body rather loosely, because
more hot air will be confined by a moderately loose garment than by one
which fits the body tightly.

955 How are whales,seals, and other iv arm-blooded animals that live in
the water protected against the cold f

They are enveloped, beneath the sJcin, with a thick
coating of " blubber" or fat, which, like fur, hair, and
feathers, is a non-conductor of heat, and serves to pro-
tect them in like manner.

95G Why are blankets and warm woollen goods always made with a
nap cr projection of fibres on the outside ?

Because the nap or fibres retain air among them,
which, from its non-conducting properties, serves to
increase the warmth of the material.

How does the covering of hair, wool, and feathers serve to keep ani-
mals cool in hot weatlier, as well as warm in cool weather ?

In warm w^eather the non-conducting medium will
not allow the heat to enter the \to&y from without : in
cold weather the heat of the body cannot escape from
within.

958 Why do we wrap up ice in flannel to Jceep it from melting f

Because the flannel, being a non-conductor, does not
allow the heat of the atmosphere to penetrate to the ice.

959 In the construction of icehouses, why do we line the walls and roof
with straw or sawdust %

Because these substances are bad conductors of heat,

960 Why is it good economy to furnish our houses in winter with double
windows t

SCIENCE OF COMMON THINGS. 149

Linen cooler than cotton. Influence of heat on the soil.

The air confined between the two surfaces of glass is
a non-conductor of heat, and equally opposes the escape
of caloric from within, or the penetration of cold air
from without.

Because linen is a much better conductor than cotton ;
and therefore (as soon as it touches the body) it draws
away the heat more rapidly, and produces a greater
sensation of cold.

Because the fine fibres of the cambric have a strong
capillary attraction for moisture, and are excellent con-
ductors of heat ; in consequence of which the moisture
and heat are abstracted from the face by the cambric,
and a sensation of coolness produced.

Because the coarse fibres of cotton have less capillary
attraction, and are very bad conductors; in conse-
quence of which the heat of the face would be increased
(rather than diminished^ by the use of a cotton hand-
kerchief.

]Nro ; it is a very "bad conductor of heat.

Because its particles are not continuous; and the
power of conducting heat depends upon the density of
matter.

966 Why is the soil (below the surface) warmer in winter than the sur-
face itself?

Because it is a ~bad conductor of heat ; and therefore
(although the ground be frozen) the frost rarely pene*
trates more than a few inches below the surface.

967* Why is the soil (below the surface) cooler in summer than the sur-
face itself 'f

Because it is a bad conductor of heat ; and therefore
(although the surface be scorched with the burning sun)

150 SCIENCE OF COMMON THINGS.

Coolness of spring water. Snow protects the soil from cold.

the intense heat cannot penetrate to the roots of the
plants and trees.

908 Show the wisdom of the Creator in making the soil a bad con-
ductor.

If the heat and cold could penetrate the soil deeply
(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.

909 Why is water from a spring always cool, even in summer f

Because the soil is so bad a conductor, that the burn-
ing rays of the sun can penetrate only a few inches below
the surface ; in consequence of which the springs of
water are not affected by the heat of summer.

97*O How does the non-conducting power of snow protect vegetabks from
the frost and cold f

It prevents the heat of the soil from being drawn off
by the cold air which rests upon it.

97*1 Why is snow a non-conductor of heat ?

Principally because it contains a large quantity of
air between its particles.

97*3 Why is it cool under a shady tree in a hot summer's day ?

1. Because the overhanging foliage screens off the
rays of the sun /

2. As the rays of the sun are warded off, the cir
(beneath the tree) is not heated by the reflection of the
soil; and

3. The leaves of the trees, being non-conductors,
also obstruct the transmission of heat.

97*3 Why does a metal spoon (left in a kettle) retard the process of
boiling f

Because the metal spoon (being an excellent con-
ductor) carries off the heat from the water , and (as
heat is carried off by the spoon) the water takes a
longer time to boil.

97*4 Why does paint preserve wood f

1. Because it covers the surface of the wood, and
prevents both air and damp from penetrating into the
pores ;

SCIENCE OF COMMON THINGS. 151

Cellars, why warm in winter and cool in summer.

2. Because paint (especially white paint), being a
bad conductor, preserves tlie wood of a more uniform
temperature ; and

3. Because it fills up the pores of the wood, and pre-
vents insects and vermin from harboring therein and
eating up the fibre.

97*5 Why are furnaces and stoves (inhere much heat is required) built
of porous bricks f

Because bricks are bad conductors, and prevent the
escape of heat / in consequence of which they are em?-
ployed where great heat is required.

0*76 Why do cellars feel warm in winter 1

Because the external air has not free access into them1 5
in consequence of which they remain almost at an even
temperature, which (in winter-time) is about 10 degrees
warmer than the external air.

97*7* Why do cellars fed cold in summer f

Because the external air has not free access into them ;
in consequence of which they remain almost at an even
temperature, which (in summer-time) is about 10 de-
grees colder than the external air.

97*8 Why do the Laplanders wear skins with the fur imvardsf

Because the dry skin prevents the wind from pene-
trating to their body ; and the air (between the hairs
of the fur) soon becomes heated by the body / in conse-
quence of which the Laplander in his fur is clad in a
case of hot air, impervious to the cold and wind.

97*9 In what respect is bark especially adapted as a covering for trees
and shrubs ?

Bark is composed of matter which is. very slowly per-
meable by heat, and, like hair and fur in animals, is es-
pecially adapted for securing the temperature necessary
tg vegetable life.

9SO What is the temperature of the sap of healthy trees during the
summer f

It is several degrees below that of the surrounding at-
mosphere.

981 What is the temperature of the sap of a healthy tree in tfie winter f

152 SCIENCE OF COMMON THINGS.

Temperature of trees. Flannels and furs not really warm.

Several degrees above that of the surrounding atmo-
sphere.

983 What occasions this difference between the temperature of the sap
of a tree and the temperature of the surrounding atmosphere 1

The vital action of the tree.

It is also a noticeable fact that sap drawn from a tree will freeze at the
same temperature as water, while the sap circulating in the tree, nnder
.the influence of vital agency, will not freeze until reduced seventeen degrees
below the freezing-point of water.

983 Why in a frozen pond or lake is the ice always thinner^ and often
entirely wanting, in those parts where springs exist upon the bottom 1

Because the spring water, coining from a point in
the earth below the influence of the frosts, is elevated
in temperature, and by imparting its heat prevents an
accumulation of ice upon the surface above.

984 Is there in reality any positive warmth in the materials of cloth-
ing?

No ; but we consider clothing warm or cool accord-
ing as it impedes or facilitates the passage of heat to or
from the surface of our bodies. The thick cloak which
guards a Spaniard against the cold of winter is also in
summer used by him as a protection against the direct
rays of the sun; and, while in temperate climates flan-
nel is the warmest article of dress, we cannot at the
same time preserve ice more effectually than by inclos-
ing it in its softest folds.

985 Does fine or coarse woollen cloth make the warmest clothing?

TliQfaier the cloth, the more slowly it conducts heat.
Fine cloths, therefore, are warmer than coarse ones.

98S Is silk a good conductor of heat f

~No ; it is a bad conductor of heat. Spun silk allows
the heat of the body to pass off more quickly than wool ;
but raw silk confines it more than wool.

987* Tlie sheets of a bed feel cold and the blankets warm. : is there any
difference in the respective temperature of these articles f

No ; the temperature of both the sheets and the blan-
kets is always exactly the same.

988 Why, then, does one feel colder than the other f

Sheets feel colder than the blankets because they are

SCIENCE OF COMMON THINGS. 153

Coolness and warmth of the air. Conduction of heat.

better conductors of heat, and carry off the heat more
rapidly from the body ; but when bjr the continuance
of the body between them they acquire the same tem-
perature, they will then feel even warmer than the
blankets.

989 In the summer a still, calm atmosphere feels warm, but if a wind
arises, the same atmosphere feels cold : has there been any real change of tem-
perature f

~No ; for a thermometer suspended under shelter and
in a calm place wrill indicate the same temperature as a
thermometer on which the wind blows.

990 Why do we then consider that the air has grown colder ?

Because the air in motion by the wind conducts off
the heat from our bodies faster than the same air at
rest.

991 What is meant by the convection of heat?

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
ascends.

993 Are liquids good conductors of heat f

"No ; liquids are bad conductors; and are therefore
made hot by convection.

993 Why are liquids bad conductors of heat ?

This peculiarity is referable to the mobility wrhich
subsists among the particles of all fluids, and to the
change in the size of the particles, which is invariably
produced by their change in temperature.

The constituent particles of solid bodies being incapable of changing
their material position and arrangement, the heat can only pass through
them, from particle to particle, by a slow process ; but when the particles
forming any stratum of liquid are heated, their mass, expanding, becomes
lighter, bulk for bulk, than the colder stratum immediately above it, and
ascends, allowing the superior strata to descend.

994 Explain hotu water is made hot.

"When the heat enters at the bottom of a vessel con-
taining water, a double set of currents is immediately
established, — one of hot particles rising towards the

154

SCIENCE OF COMMON THINGS.

How liquids are made hot.

Why water is agitated when boiling.

Fig. 38.

surface, and the other of colder particles
descending to the bottom. The portion of
liquid which receives heat from below is
thus continually mixed through the other
parts, and the heat is diffused by the mo-
tion of the particles among each other.

These currents take place so rapidly, that if a thermo-
meter be placed at the bottom and another at the top
of a long jar, the fire being applied below, the upper one
will begin to rise almost as soon as the lower one. The
movement of the particles of water in boiling will be
understood by reference to Fig, 38.

995 What common experiment proves that water is a bad conductor of
heat f

When a blacksmith immerses his red-hot iron in a
tank of water, the water which surrounds the iron is
made boiling hot, while the water not immediately in
contact with it remains quite cold.

If a tube nearly filled with water is
held over a spirit lamp, as in Fig. 39, in
such a manner as to direct the flame
against the upper layers of the water,
the water will be observed to boil at the
top, but remain cool below. If quicksil-
ver, on the contrary, be so treated, its
lower layers will speedily become heated.
The particles of mercury will communi-
cate the heat to each other, but the particles of water will not do so.

996 "Why is water in such continual ferment when it is boiling ?

This commotion is mainly produced by the ascend-
ing and descending currents of hot and cold water.

The escape of steam from the water contributes also to increase this
agitation.

997* How do these two currents pass each oilier f

The hot ascending current rises up through the centre
of the mass of water ; while the cold descending cur-
rents pass down by the metal sides of the kettle.

998 Why is heat applied to the bottom, and not to the top of the kettle ?

Because the heated water always ascends to the sur-
face^ heating the water through which it passes ; if,
therefore, heat were applied to the top of a vessel, the
water below the surface would be heated very slowly.

Fig. 39.

SCIENCE OF COMMON THINGS. 155

How to cool liquids. Boiling point of liquids.

999 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 of a kettle ?

The iron of a grate is an excellent conductor ; if,
therefore, 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.

1000 If you wish to cool liquids, where should the cold be applied f

To the top of th« liquid / because the cold portions
will always descend, and allow the warmer part to come
in contact with the cooling substance.

1001 Does boiling water get hotter by being kept on the fire ?

No ; not if the steam be suffered to escape.

1OOS Why does not boiling water get hotter if the steam be suffered to
escape f

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

1003 What is ebullition f

"When a liquid substance is heated sufficiently to
form steam, the production of vapor takes place princi-
pally at that part where the heat enters ; and when the
heating takes place not from above, but from the bot-
tom and sides, the steam as it is produced rises in bub-
bles through the liquid, and produces the phenomenon
of boiling or ebullition.

1004 What do we mean by the boiling point of a liquid ?

The temperature at which vapor rises with sufficient
freedom to cause the phenomenon of ebullition is called
the boiling point.

1005 Do att liquids boil at the same temperature f

No ; the boiling point occurs in different liquids at
very different temperatures.

1006 Why does milk 'boil over more readily than water f

Because the bubbles of milk, produced by the pro-
cess of boiling, are more tenacious than the bubbles of
water ; and these bubbles, accumulating and climbing
one above another, seon overtop the rim of the saucepan
and run over.

1007 Why does water simmer before it boils?

356 SCIENCE OF COMMON THINGS.

Simmering. "Why a kettle sometimes boils over.

Because 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 " sim-.
mering."

1008 What is meant by simmering }

A gentle tremor or undulation on the surface of the
water. When water simmers, tha bubbles collapse
beneath the surface, and the steam is condensed to water
again; but when water boils, the bubbles rise to the
surface, and the steam is thrown off.

1009 Why does boiling water swell?

Because it is expanded by the heat / that is, the heat
of the fire drives the particles of water farther apart
from each other, and (as they are not packed so closely
together) they take up more room / in other words, the
water swells.

1010 Why does boiling water bubble ?

Because the vapor (rising through the water) is
diffused, and forces up bubbles in its effort to escape.

All the air of water is expelled at the commencement of its boiling.

1011 Why does a kettle sometimes boil over f

Because the water is expanded by heat / if, therefore,
a kettle is filled with cold water, some of it must run
over as soon as it is expanded by heat.

1O1J3 But I have seen a kettle boil over, although it has not been fitted
full of water : how do you account for that?

If a fire be very fierce, the air and vapor are expelled
so rapidly, that the bubbles are very numerous, and
(towering one above another) reach the top of the kettle,
and fall over.

1013 Why is a pot (which was full to over/lowing while the water was
boiling hot) not full after it has been taken off the fire for a short time f

Because (while the water is boiling) it is expanded
by the heat, and fills the pot even to overflowing ; but
when it becomes cool, it contracts again, and occupies a
much less space.

1014 When steam pours out from the ''spout of a kettle, the stream
"begins apparently half an inch off Hie spout : why does it not begin close to
the spout f

SCIENCE OF COMMON THINGS. 157

Steam is invisible. Liquids become no hotter after boiling.

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.

1O15 Why is not all the steam invisible as well as that half inch ?

Because the invisible particles are condensed ly the
cold air, and, rolling one into another, look like a thick
mist.

1O1B What becomes of the steam, for it soon vanisJies f

After it has been condensed into mist, it is dissolved
by the air, and dispersed abroad as invisible vapor.

lOlT* And what becomes of the invisible vapor f

Being lighter than air, it ascends to the upper regions
of the atmosphere, where (being again condensed) it con-
tributes to form clouds.

1O1S Why do sugar, salt, &c., retard the progress of boiling f

Because they increase the density of water ; and
whatever increases the density of a fluid retards its
boiling.

1O19 Why can liquids impart no additional heat after they boil f

Because all additional heat is spent in making steam.
Hence wrater will not boil a vessel of water immersed in
it, because it cannot impart to it 212° of heat; but
"brine wTill, because it can impart more than 212° of heat
before it is itself converted into steam.

Ether . . boils at 100 degrees
Alcohol . . " 173| "
Water . . . l( 212 "
Water, with one- fifth salt,
boils at. . . 219 "

Syrup . . boils at 221 degrees.
Oil of turpentine 314 "
Sulphuric acid 472 "
Linseed oil " 640 "
Mercury . . " 656 "

Any liquid which boils at a lower degree, can be made to boil if im-
mersed in a liquid which boils at a higher degree. Thus a cup of ether
can be made to boil in a vessel of water ; a cup of water, in a vessel of
brine or syrup ; but a cup of water will not boil if immersed in ether, nor
a cup of syrup in water.

1OJ3O Is the boiling point of the same liquid always constant ?

Yes, under the same conditions / but it is liable to be
affected by various circumstances.

1OS1 What cause has a powerful influence in regulating the boiling
point of liquids f

The pressure of the atmosphere : if the pressure be

158 SCIENCE OF COMMON THINGS.

Influence of atmospheric pressure on the boiling point. How air is heated.

less than usual, then the boiling point of water and all
other liquids will be lower than usual ; if the pressure
increases, and the barometer rises, the temperature of
ebullition will be proportionably increased.

1OSS If the atmospheric pressure be entirely removed, or if water be
made to boil in a vacuum, at what temperature will ebullition commence ?

At a point 140° lower than in the open air.

1053 To what temperature can water exposed to the air be heated under
ordinary circumstances ?

To about 212° Fahrenheit ; at this temperature water
passes into steam or vapor.

1054 Can water be heated beyond 212° ?

Yes ; if subjected to sufficient pressure, it can be heated
to any extent without boiling. There is no limit to the
degree to which water may be heated, provided the
vessel is strong enough to confine the vapor ; but the
expansive force of steam is so enormous under these
circumstances, as to overcome the greatest resistance ,
which has ever been exerted upon it.

1055 Why does soup keep hot longer than boiling water f {

Because the grease and other ingredients floating irf
the soup retain the heat longer than the particles of
water, and, at the same time, by their viscidity or tena-
city, prevent the circulation of the heated particles.

lOSe How is air heated?

By " connective currents"

lOST* Explain what is meant by " convective currents"

When a portion of air is heated, it rises upwards in
a current, carrying the heat with it ; other colder air
succeeds, and (being heated in a similar wTay) ascends
also : these are called " convective currents."

" Convective currents" so called from the Latin words cumvectus (carried
with), because the heat is "carried with" the current.

1058 Is air heated by the rays of the sun f

"N6 ; air is not heated (to any very great extent) Inj the
action of the surfs rays passing through it.

1059 Why, then, is the air hotter on a sunny day than on a cloudy
one?

SCIENCE OF COMMON THINGS. 159

How hot substances are cooled. Blowing hot food cools it

Because 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, while its place is sup-
plied by colder portions, which are heated in turn also.

1030 If air be a bad conductor, why does hot iron become cold by expo-
sure to the airf

Because it is made cold — 1. By " convection ;" and
2. By " radiation."

1031 How is hot iron made, cold by convection ?

The air resting on the hot iron (being intensely heated)
rapidly ascends with the heat it has absorbed ; colder
air succeeding, absorbs more heat and ascends also ; and
this process is repeated till the hot iron is cooled com-
pletely down.

ICpSS How is broth cooled by being left exposed to the air f

It throws o&some heat by radiation • but it is mainly
cooled down by convection.

1033 How is hot broth cooled down by convection 1

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

1 The particles on the surface of the broth sink as they are cooled down,
and warmer particles rise to the surface, which gradually assist the cool-
ing process.

1034 Why are hot tea and broth cooled faster by being stirred about f

1. Because the agitation assists in bringing its hottest
particles to the surface •

2. As the hotter particles are more rapidly brought
into contact with the air, therefore cqnvection is more
rapid.

1035 How does bloiving hot food make it coolf

It causes the air (which has been heated by the
food) to change more rapidly F, and give place to fresh
cold air.

1036 If a shutter be closed in the daytime, the stream of light (pierc-
ing through the crevice) seems in constant agitation : why is this f

Because little motes and particles of dust (thrown into

160 SCIENCE OF COMMON THINGS.

Milk boila qv.lcker than water. Why stoves are not placed at top of the room.

agitation by the violence of the convective currents) are
made visible by the strong beam of light thrown into
the room through the crevice of the shutter.

1O37* Why does milk boil more quickly than tvater?

Milk is a thicker liquid than water, and consequently
less steam escapes through the thick liquid (milk) than
through the thin liquid (water) ; therefore the heat of
the whole mass of the milk rises more quickly.

1O3Q Why are fires placed near the floor of a room, and not towards
the ceiling ?

Because heated air always ascends. If, therefore,
the fire were not near the floor, the air of the lower
part of the room would be elevated in temperature very
slowly.

1039 Would not the air of the lower part of a room be heated equally
well if the fires were fixed higher up f

No ; the heat of a fire has a very little effect upon
the air 'below the level of the fire / and therefore every
fire should be as near to the floor possible.

1040 Our feet are very frequently cold when we sit close by a good fire :
explain the reason of this ?

As the air over the fire becomes heated and rises,
cold air rushes through the crevices of the doors and
windows, and 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.

104:1 What is meant by radiation of heat f

The emission of rays of heat in all directions.

"When the hand is placed near a hot body suspended in the air, a sen-
sation of warmth is perceived, even for a considerable distance. If the
hand be held beneath the body, the sensation will be as great as upon
the sides, although the heat has to shoot down through an opposing cur-
rent of air approaching it. This effect does not arise from the heat being
conveyed by means of a hot current, since all the heated particles have a
uniform tendencj^ to rise; neither can it depend upon the conducting
power of the air, because aerial substances possess that power in a very
low degree, while the sensation in the present case is excited almost on
the instant. This method of distributing heat, to distinguish it from heat
passing by contact or conduction, is called radiation.

1O4S How do we designate heat so distributed f

As radiant or radiated heat.

SCIENCE OF COMMON THINGS. 161

Radiation. Good and bad radiators.

1043 When is heat radiated from one body to another ?

When the two bodies are separated by a non-con-
ducting medium.

1044 On ivliat does radiation depend f

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.

1045 Does a fire radiate heat f

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

1046 Why does our face feel uncomfortably hot when we approach a
fire?

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

1047* Why does the fire heat the face more than it does the rest of the
body ?

Because the rest of the body is covered with cloth-
ing ; which (being a bad conductor of heat) prevents
the same sudden and rapid transmission of heat to the
skin.

1O48 Do those substances which radiate heat absorb heat also f

Yes. Those substances which radiate most also
absorb most heat ; and those which radiate least also
absorb the least heat.

1O4Q Does any thing else radiate heat besides the sun and fire f

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

1050 What things radiate heat the next best to the sun and fire f

All dull and dark substances are good radiators of
heat ; but all light and polished substa'nces are lad ra-
diators.

1051 What is meant by being a " bad radiator of heat ?"

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.

1O553 Why does snow (at the foot of a tree or wall) melt sooner than in
an open field ?

162 SCIENCE OF COMMON THINGS.

Utility of blackening stoves. Bright metal retains heat. Dew.

Because the tree or wall radiates heat into the snow
beneath, which melts it.

1053 Why sliould the flues (connected with stoves, etc.) be always black-
ened with black lead f

In order that the heat of the flue may be more readi-
ly diffused throughout the room. Black lead radiates
heat more freely than any other known substance.

1054 Would a metal pot serve to keep water hot if it were dull and
dirty f

'No ; it is the bright polish of the metal which makes
it a bad radiator ; it it were dull, scratched, or dirty,
the heat would escape very rapidly.

"Water in hot weather is also kept cookr in bright metal than in dull or
earthen vessels.

1055 Why are dinner-covers made of bright tin or silver?

Because li^ht-colored 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 es-
cape through the cover by radiation.

CHAPTER Y.

THE PHENOMENA OF DEW.
1O5B What is Dew f

Dew is the moisture of the air condensed by coming
in contact with bodies colder than itself.

1O57* Why is the ground sometimes covered with dew ?

Because the surface of the earth (at sunset) is made
so very cold by radiation, that the warm vapor of the
air is chilled by contact, and condensed into dew.

1O58 Why is the earth made colder than the air after the sun has set f

Because the earth radiates heat very freely, but the

SCIENCE OF COMMON THINGS. 163

Cause of dew. When most dew is deposited. Difference between dew and rain.

air does not ; in consequence of which the earth is
often five or ten degrees colder than the air (after sun-
set), although it may have been warmer than the air
during the whole day.

1O5Q Why is the surface of the earth generally warmer than the air
during the day t

Because the earth absorbs solar heat very freely, but
the air does not; in consequence of which it is often
many degrees warmer than the air during the day.

1O6O Why is the surface of the ground colder in a fine night than in a
cloudy one ?

Because on a fine, clear, starlight night, heat radiates
from the earth freely, and is lost in open space ; but
on a dull night, the clouds arrest the process of radi-
ation.

1OQ1 Why is dew deposited inost readily on a fine, clear night f

Because the surface of the ground radiates heat most
freely^ on a fine night, and (being cooled down by this
loss of heat) chills the vapor of the air into dew.

1O©S Why is there no dew on a dull, cloudy night?

Because 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 vapor
of the air into dew.

1OQ3 Why is a cloudy night warmer than a fine, clear night?

Because the clouds prevent the radiation of heat from
the earth ; in consequence of which the surface of the
earth remains warmer.

1OQ-1 How do clouds arrest or prevent the radiation of heat from the
earth?

The lower surfaces of the clouds turn hack the rays
of heat as they radiate or pass off from the earth, and
prevent their dispersion into space.

1065 What is the difference between dew and rain?

In dew, the condensation is made near the earth's
surface. In rain, the drops fall from a considerable
height.

1066 What is the cause of loth dew and rain f

SCIENCE OF COMMON THINGS.

Situations in which no dew is deposited.

Cold condensing the vapor of the air wlien near the
point of saturation.

1067* Why do mist and fog vanish at sunrise1}

Because the condensed particles are again changed
into invisible vapor by the heat of the sun.

1068 Why is dew most abundant in situations most exposed?

Because the radiation of heat is not arrested by
houses, trees, hedges, or any other thing.

1069 Why is there scarcely any dew under a leafy tree ?

1. Because the thick foliage of a tree arrests the radi-
ation of heat from the earth ; and

2. A leafy tree radiates some of its own heat towards
the earth • in consequence of which the ground under-
neath a tree is not sufficiently cooled down to chill the
vapor of the air into dew.

1070 Why is there never much dew at the foot of walls and hedges?

1. Because they act as screens to arrest the radiation
of heat from the earth ; and

2. They themselves radiate some portion of heat
towards the earth ; in consequence of which the ground
at the foot of walls and hedges is not sufficiently cooled
down to chill the vapor of the air into dew.

1O7*1 Why is there no dew on a windy night %

1. Because the wind evaporates the moisture as fast
as it is deposited ; and

2. It disturbs the radiation of heat, and thus dimi-
nishes the deposition of dew.

1O7*!3 Why are valleys and hollows often thickly covered with dew,
although they are sheltered f

Because the surrounding hills prevent the agitation
of the air, but do not overhang and screen the valleys
sufficiently to arrest the radiation from their surfaces.

1O7*3 Why does dew fatt more abundantly on some substances than on
others?

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

SCIENCE OF COMMON THINGS. 165

Plants requiring the most moisture condense the most dew.

107*4: Why are substances which radiate the heat most freely always
the most thickly covered with dew ?

Because they are the coldest substances, and there-
fore condense vapor most readily.

107*5 What kind of materials radiate heat most freely f

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.

1O7*6 Do the kaves of all plants radiate heat equally well?

No. Rough, woolly leaves (like those of a hollyhock)
radiate heat much more freely than hard, smooth po-
lished leaves, like those of the common laurel.

1O7*7* Show the wisdom of the Creator in making grass, the kaves of
trees, and all vegetables, excellent radiators of heat ?

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

1O7*S Will polished metal, smooth stones, and woollen doth readily col-
lect dew f

No. "While grass and 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.

1O7*9 Why would polished metal and woollen cloth le dry, while grass
and leaves are drencJied with deiv %

Because the polished metal and woollen cloth part
with their heat so slowly, that the vapor of the air is
not chilled into dew as it passes over them,

1OSO Why is a gravel walk almost dry wlien a grass-plat is covered
fliick with dew ?

Because grass is a good radiator, and throws off its
heat very freely ; but gravel is a very l>ad radiator,
and parts writh its heat very slowly. •

1O81 Is that the reason why grass is saturated with dew, and the gra-
vel is not f

Yes. When the vapor of warm air comes in contact
with the cold grass, it is instantly chilled into dew ; but

168 SCIENCE OF COMMON THINGS.

Dew on rocky and on fertile Boils. Dew most abundant after a hot day.

it is not so freely condensed as it passes over gravel,
because gravel is not so cold as the grass.

1O8S Why does dew rarely fall upon hard rocks and barren lands ?

Because 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 deposits upon them.

1O83 Why does dew fall more abundantly on cultivated soils than on
barren lands f

Because cultivated soils (being loose and porous)
very freely radiate by night the heat which they ab-
sorb by day ; in consequence of which they are much
cooled down, and plentifully condense the vapor of the
passing air into dew.

1OS4 Show the wisdom of the Creator in this arrangement f

Every plant and inch of land which needs the moist-
ure of dew is adapted to collect it ; but not a single
drop is wasted where its refreshing moisture is not
required.

1O85 When is dew most copiously distilled t

After a hot day in summer or autumn, especially if
the wind blows over a body of water.

1OSG Why is dew distilled most copiously after a hot day ?

Because the surface of the hot earth radiates heat
very freely at sunset, and (being made much colder
than the air) chills the passing vapor and condenses it
into dew.

108*7 Why is there less dew when the wind blows across the land, than
when it blows over a body of water ?

Because the winds which blow across the.Zan^ are
dry and arid / but those which cross the water are
moist and full of vapor.

1088 How does the dryness of the wind prevent dew-falls?

As winds (currents of air) which blow over the land
are very dry, they imbibe the moisture of the air ; in
consequence of which there is very little left to be con-
densed into dew.

1089 Why is meal very subject to faint on a moonlight niyhtt

SCIENCE OF COMMON THINGS. 167

Protection against frost. Cause of fog and mist.

Because it radiates heat very freely in a bright moon-
light night ; in consequence of which it is soon covered
with dew, which produces rapid decomposition.

1O0 O How do moonlight nights conduce to the rapid growth of plants f

Radiation is carried on very rapidly on bright moon-
light nights ; in consequence of which dew is very
plentifully deposited on young plants, which conduces
much to their growth and vigor.

1O91 Why is the air in immediate contact with the earth, on a clear
night, cooler than tlie air at a little distance from the surface f

Because it parts with its heat to the earth, which in
turn loses it by radiation.

1O93 How can a thin covering of bass, or even muslin, protect trees
from frost ?

Because any covering prevents the radiation of heat
from the tree ; and if trees are not cooled down by radi-
ation, the vapor of the air will not fe frozen as it comes
in contact with them.

Bass — a kind of matting used by gardeners.

1093 Why is the bass or canvas itself (which covers the tree) ahvays
drenched with deiv ?

Because it radiates heat both upwards and down-
wards j in consequence of which it is so cooled down
that it readily chills the vapor of the air into dew.

1094 What is the cause of mist or earth-fog ?

If the night has been very calm, the radiation of heat
from the earth has been very abundant ; in consequence
of which the air (resting on the earth) has been chilled,
and its vapor condensed into a thick mist.

1095 Why does not the mist become devj ?

Because the chill of the air is so rapid, that vapor is
condensedy^site/' than it can be deposited and (covering
the earth as a mist) prevents any farther radiation of
heat from the earth.

1096 When the earth can no longer radiate heat upwards, does it con-
tinue to condense the vapor of the air ?

No ; the air (in contact with the earth) becomes about
equal in temperature with the surface of the earth itself;

168 SCIENCE OF COMMON THINGS.

Mist and dew vanish at sunrise. No dew in cities.

for which reason the mist is not condensed into dew^ but
remains floating above the earth as a thick cloud.

1097* This mitt seems to rise higher and higher, and yet remains quite
as dense below as at first : explain the cause of this.

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 thus the mist seems to be rising, when (in
fact) it is only deepening.

1O08 Why do mist and dew vanish as the sun rises f

Because the air becomes warmer at sunrise, and ab-
sorbs the vapor.

1OS9 Can the dew properly be said to "fall?"

Kow ; dew is a\w&ys formed upon the surface of the
material upon which it is found, and does not fall from
the atmosphere.

1100 Does the color of an object influence the deposition of dew f

It does to a considerable extent.

1101 How can this be sliown f

If we take pieces of red, black, green, and yellow
glass, and expose them when the dew is condensing, we
shall find that moisture will show itself first on the
yellow and then on the green glass, but that none will
appear on the red or black glass. The same thing will
take place if we expose colored fluids in white glass
bottles.

11O3 Why is the deposition of dew rarely observed in the close and
sheltered streets of cities f

• Because there the objects are necessarily exposed to
each other's radiation, and an interchange of heat takes
place, which maintains them at a temperature uniform
with the air.

1103 When is dew converted into frost f \

If the temperature of the earth, or of the vessel, sink
to the freezing point or below, the moisture will be de-
posited as before ; but by freezing, it assumes the solid
Ibrm, and is called frost.

1104 Why is a deiv-drop round f

SCIENCE OF COMMON THINGS. 169

Why a dew-drop is round. AVhy a duck is not wet with water.

Because every part of it is equally balanced ; and
therefore there is no cause why one part of the drop
should be farther from the centre than another.

11O5 Why will dew-drops roll about cabbage plants, poppies, &c., with-
out wetting the surface ?

Because the leaves of cabbages and poppies are
covered with a very fine waxen powder, over which the
dew-drop rolls without wetting the surface, as a drop of
rain would over dust.

HO 6 Why does not a drop of rain wet the dust over which it rottsf

Because dust has no affinity for w^ater, and therefore
repels it.

HOT* Why can swans and ducks dive under water vnthout being wetted 1

Because their feathers are covered with an oily secre-
tion, which has no affinity for water, and therefore re-
pels it.

11O8 WJiat is tlie figure which water always assumes when unsupported,
or supported on a surface having little attraction for it?

The figure of a sphere. This figure becomes more or
less globular or spheroidal in its shape, as the attraction
of the substances upon which it is received increases or
diminishes ?

11O0 What is the form of a drop of rain when descending in the air?

A sphere.

±11O Why should drops of water, resting upon surfaces which have no
affinity for them, assume a spheroidal shape?

Because such surfaces not having so great an attrac-
tion for the drops of water as the particles of water have
for each other, the drops tend to preserve, as nearly as
possible, the spheroidal form which they would have
if entirely unsupported, as when falling as drops of
rain.

1111 Is dew ever formed upon the surface of water ?

The formation of dew upon ships which traverse the
vast solitudes of the ocean has never been noticed ; and
it has been ascertained by experiment that even a small
quantity of water gains no weight by exposure during
a single night.

170 SCIENCE OF COMMON THINGS.

No dew on the ocean. No dew falls on the human body.

Although dew dcx s not appear upon ships at a great distance from land,
it is freely deposited on the same vessels arriving in the vicinity of terra
firma. Thus, navigators who proceed from the Straits of Sunda to the
Coromandel coast, know that they are near the end of the voyage when
they perceive the ropes, sails, and other objects placed on the deck become
moistened with dew during the night.

1112 Why does not dew form upon the surface of water ?

Because whenever the aqueous particles at the sur-
face are cooled, they become heavier than those below
uiein, and sink, while warmer arid lighter particles rise
to the top. These, in their turn, become heavier, and
descend; and the process, continuing throughout the
night, maintains the surface of the water and the air at
nearly the same temperature.

1113 Is the temperature at which dew is deposited from the air always
the same ?

No ; when the air is saturated with moisture, a slight
reduction of temperature occasions a deposition of dew;
but when the air is very dry, a greater reduction of
temperature is necessary to condense its vapor.

1114 Why are the exposed parts of the human body never covered with
deiv?

Because the vital heat, varying from 96° to 98° Fah-
renheit, effectually prevents such a loss of warmth as is
necessary to its production.

1115 In what countries are the dews most copious and abundant ?

In tropical climates.

1116 What is the reason of this f

Because in those countries there is the greatest dif-
ference between the temperature of the day and that
of the night.

The development of vegetation is greatest in tropical countries, and a
great part of the nocturnal cooling is due to the leaves, which present to
the sky ?.T\ immense number of thin bodies, having large surface, well
adapted to -radiate heat.

SCIENCE OF COMMON THINGS. 171

Reflection of heat. What are rays of heat f

CHAPTER YI

REFLECTION, ABSORPTION, AND TRANSMISSION OF HEAT.

1117 What is meant by the reflection of heat f

Heat is said to be reflected when it is caused to re-
"bound or be thrown back from the surface of a reflect-
ing body.

1118 What are the best reflectors of heat f

All bright surfaces and light colors.

1119 Are good absorbers of heat good reflectors also ?

No ; those things which absorb heat best reflect heat
worst • and those which reflect heat worst absorb it best.

1130 Why are those things which absorb heat unable to reflect it f

Because if anything sucks in heat, as a sponge does
water, it cannot throw it off from its surface ; and if
anything throws off heat from its surface, it cannot
drink it in.

1131 Why are reflectors always made of light-colored and highly-
polished metal f

Because light-colored and highly-polished metal makes
the best of all reflectors.

If metal be such an excellent conductor of heat, how can it reflect
heat, or throw it off?

Polished metal is a conductor of heat only when that
heat is communicated by actual contact; but when-
ever heat falls upon bright metal in rays* it is reflected
back again, and the metal remains cool,.

1133 What is meant " by heat falling upon metal in rays" and not
" by contact ?"

If a piece of metal were thrust into a fire, it would
be in actual contact with the fire ; but if it were held
before a flre^ the heat of the fire would fall upon it in
rays.

1134 Why will a kettle be slower in boiling if the bottom and sides are
clean and bright f

172 SCIENCE OF COMMON THINGS.

Use of white dresses in summer. Coldness of high mountains.

Because bright metal does not absorb heat, but re-
flects it ; and (as the heat is thrown off from the sur-
face of 'bright metal by reflection) therefore a new ket-
tle takes a longer time to boil.

Reflects heat — that is, throws it off.

1135 Why do persons wear white dresses in summer-time f

Because white throws off the heat of the sun by re-
flection, and is a very bad absorbent of heat ; in con-
sequence of which wrhite dresses never become so hot
from the scorching sun as dark colors do.

1136 Why do persons not wear white dresses in winter-time ?

Because white will not absorb heat like black and
other dark colors ; and therefore white dresses are not
so warm as dark ones.

Why are shoes hotter for being dusty f

Because dull, dusty shoes will absorb heat from the
sun, earth, and air ; but shoes brightly polished throw
off the heat of the sun by reflection.

1138 Why do not the solar rays, even in the hottest day, melt the snow
upon the tops of high mountains, which are nearer to the sun than tlie kvel
portions of the earth ?

Because they only heat those bodies which can alt-
sorb their warmth, as the rough surface of the earth.
The snow is indeed struck by the rays of the sun, but
being a white and shining body, it reflects them, and
remains cold.

1139 Why does it always freeze on the top of a high mountain ?

1. Because air is heated by contact with the earth's
surface more than by solar rays which pass through it :
as a mountain-top affords very small surface for such
contact, it remains intensely cold ; and

2. When air flows up the side of a mountain, it ex-
pands from diminished pressure ; and consequently
absorbs heat from surrounding objects.

Karefied air can hold more latent heat than dense air can.

11SO What is the difference between conducting heat and absorbing
heat?

To conduct heat is to transmit it from one body to

SCIENCE OF COMMON THINGS. 173

Conduction of heat. How fanning cools.

another through a conducting medium. To absorb heat
is to suck it up, as a sponge sucks up water.

1131 Give me an example ?

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 wrould not conduct the heat to the other
end.

113S Are good conductors of heat good absorbers also f

No ; every good conductor of heat is a lad absorber
of it ; and no good absorber of heat can be a good con-
ductor also.

1133 Is iron a good absorber of heat f

No ; iron is a good conductor, but a very bad ab-
sorber of heat.

1134 If a piece of brown paper be submitted to the action of a burning-
glass it will catch fire much sooner than a piece of white paper would : ex-
plain the reason.

Because white paper reflects the rays of the sun. or
throws them back ; in consequence of which it appears
more luminous, but is not so much heated as dark
brown paper, which absorbs the rays, and readily be-
comes heated to ignition.

1135 How does the ceaseless change of air tend to decrease the warmth
of a naked body ?

The air (which cases the body) absorbs as much heat
from it as it can, while it remains in contact ; bein^
then blown away, it makes room for a fresh coat of
air, which readily absorbs more heat.

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

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.

1137* Why does fanning the face in summer make it cool f

Because the fan puts the air in motion, and makes
it pass more rapidly over the face ; and (as the tem-
perature of the air is usually lower than that of the

174 SCIENCE OF COMMON THINGS.

Wind generally feels cool Utility of black kettles.

liumtmface) each volume of air carries off some portion
of its heat.

1138 Does a fan cool the air f

No ; it makes the air hotter by imparting to it the
heat out of our face / but it cools our face by transfer-
ring its heat to the air.

1139 How does fanning the face increase the heat of the air f

By driving the air more rapidly over the human
body, and causing it, consequently, to absorb more heat.

1140 If fanning makes the air hotter, why can it make a person feel
cooler f

Because it takes the heat out of the face, and gives
it to the air.

Why does wind generally feel cool f

Because it drives the air more rapidly over our body,
and this rapid change of air draws off a large quantity
of heat.

114S Why does air absorb heat more quickly by being set in motion f

Because every fresh gust of air absorbs a fresh por-
tion of heat ; and the more rapid the succession of
gusts, the greater will be the quantity of heat absorbed.

1143 If the air were hotter than our body would the wind feel cool f

No ; the air would feel insufferably hot, if it were
hotter than our body.

1144 Why would the air feel intensely hot, if it were warmer than our
body f

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

1145 Is the air ever as hot as the human body f

In the extreme of summer the temperature of the
air sometimes exceeds the natural temperature of the
body ; and when that is the case, the heat is almost
insupportable.

1146 Why does a kettle boil faster when the bottom and sides are
fovered wiih soot f

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

SCIENCE OF COMMON THINGS. 175

Colors most suitable for dresses. Why a negro never sunburns.

1147* Why do we wear white linen and a black outer dress, if we want
to be warm f

Because the black outer dress quickly absorbs heat
from the sun ; and the white linen (being a bad absorb-
ent) abstracts no heat from the warm body.

1148 What colors are warmest for dresses?

For outside garments black is the warmest, and then
such colors as approach nearest to black (as dark blue
and green). White is the coldest color for external
clothing.

1149 Why are dark colors (for external wear) so much warmer than
light ones f

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

1150 How can you prove that dark colors are warmer than light ones ?

If a piece of black and a piece of white cloth 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.

The darker any color is, the warmer it is, because it is a better absorb-
ent of heat. The order may be thus arranged : 1, black (warmest of all) ;
2, violet ; 3, indigo ; 4, blue ; 5, green ; 6, red ; 7, yellow ; and 8, white
(coldest of all).

1151 Why does the black skin of a negro never sunburn or blister with
Hie hot sun?

Because the black color absorbs the heat, conveys it
below the surface of the skin, and converts it into sen-
sible heat and perspiration.

1153 Why does the white European skin blister and burn when
exposed to the hot sun f

Because white will not absorb heat ; and therefore the
hot sun rests on the surface of the skin^. and burns it.

1153 Why do most of the animals inhabiting the frigid zones have
white fur, hair, or feathers?

Because white radiates and absorbs but little heat.

1154 What relation exists between the power of bodies to absorb and
communicate heat?

Those bodies which absorb heat freely, also part with
it most rapidly / that is, they are sooner heated and
more speedily cooled than other bodies.

176 SCIENCE OF COMMON THINGS.

Temperature of scalding water. General effects of heat.

1155 At what temperature do metals burn when handled f

Metals cannot be handled when raised to a tempe-
ratnre of more than one hundred and twenty degrees.

1156 At what temperature does water scald 7

At one hundred and fifty degrees.

1157 To what extent can the human system sustain the influence of
heated air f

Workmen enter ovens, in the manufacture of moulds
of plaster of Paris, in which the thermometer stands
100° above the temperature of boiling water, and sustain
no injury.

If the person so entering a heated oven should hold next to his skin a
piece of metal, the latter would absorb heat with sufficient rapidity to
burn the surface with which it was in contact.

1158 Why is there so great a difference between the burning tempera-
ture of 'metals and air f

The metals absorb heat quickly, and part with it
freely ; the air absorbs heat very slowly, and does not
readily part with it.

1159 What class of bodies allow heat to pass freely through them,?

Transparent bodies of little density, as the air, the
various gases, etc., etc.

CHAPTEE VII.

EFFECT OF HEAT.
116 O What effect has heat upon substances generally f

It expands them, or enlarges their dimensions.

1161 Are the dimensions of every kind of matter regulated by heatf

They are; its increase, with few exceptions, separates
the particles of bodies to a greater distance from each
other, producing expansion, so that the same quantity

SCIENCE OF COMMON THINGS. 177

Form of bodies dependent on heat. Heat expands all matter.

of matter is thus made to occupy a larger space ; the
diminution of heat has an opposite effect.

The expansion of solids by heat is
clearly shown by the following experi-
ment, Fig. 40 : m represents a ring of
metal, through which, at the ordinary
temperature, a small iron or copper
ball, a, will pass freely, this ball being a
little less than the diameter of the ring.
If this ball be now heated by the flame
of an alcohol lamp, it will become so
far expanded by heat as no longer to
pass through the ring.

116J3 Is Hie form of bodies depend-
ent on heat ?

It is.

1163 Sow is this shown ?

By the increase of heat, solids are converted into
liquids, and liquids are dissipated into vapor ; by its
decrease, vapors are condensed into liquids, and these
become solid.

1164 If matter ceased to be influenced by heat, what would be the effect?

All liquids, vapors, and doubtless even gases, would
become permanently solid, and all motion on the sur-
face of the earth would be arrested.

1165 What are the three most apparent effects of heat, so far as relates
to the form and dimensions of bodies ?

Expansion, liquefaction, and vaporisation.

1166 Does heat expand air f

Yes ; if a bladder (partially filled with air) be tied
up at the neck, and laid before the fire, the air will
expand till the bladder bursts.

1167 Why will the air swell if the bladder be Md before the fire f

Because the heat of the fire will drive the particles
of air apart from each other, and cause them to occupy
more room than they did before.

116S Does heat expand all matter ?

Yes ; every thing (that man is acquainted with) is
expanded by heat.

1169 How can we prove that solids expand with heat f

178 SCIENCE OF COMMON THINGS.

Force of expansion. Ice, why lighter than water.

If we take the exact dimensions in length, breadth,
and thickness of any substance when cold, and measure
it again when strongly heated, it will be found to have
increased in every direction.

117*O Do bodies expand with the increase of heat, and contract upon its
withdrawal, with any degree of force f

Yes ; the force with which bodies contract and ex-
pand under the influence of heat is apparently iwesist-
ible, and is recognised as one of the greatest forces in
nature.

117*1 What peculiarity exists in the effect of heat upon the bulk of so^*
fluids ?

That at a certain temperature increase of heat causes
them to contract, and its diminution makes them ex-
pand.

117*3 What classes of liquids exhibit this peculiarity f

Those only which increase in bulk in passing from
the liquid to the solid state^ and this change is remarked
only within a few degrees of temperature above their
point of congelation.

117*3 What is a noted example of this exception to the general laios of
Jieat?

Water / ice swims upon the surface of water, and
therefore must be lighter, a convincing proof that wa-
ter in the act of freezing must expand.

117*4 Why is the ice produced ly the freezing of sea water ahvays
fresh and free from salt ?

Because water, in freezing, if in sufficient quantity
to allow freedom of motion to its particles, expels all
impurities and coloring matters.

117*5 If a solution of indigo be frozen, why will the ice formed be clear
and colorless f

Because the water in which the indigo was dissolved
expels all the blue coloring matter while freezing.

117*6 Why are blocks of ice generally filled with air-bubbles f

Because the water, during the act of freezing, expels
the air contained in it, and many of the liberated bub-
bles become lodged and imbedded in the thickening
fluid.

SCIENCE OP COMMON THINGS. 179

Cause of wcuthcr-worn rocks. Cause of icicles. "What is ice f

IIT* 7 Is the force created by the expansion of water in the act of freezing
very great?

Yes ; as an illustration the following experiment
may be quoted : Cast-iron bomb-shells, thirteen inches
in diameter and two inches thick, were filled with wa-
ter, and their apertures or fuse-holes firmly plugged
with iron bolts. Thus prepared, upon exposure to the
severe cold of a Canadian winter, about 19° below
" zero," at the moment the water froze, the iron plugs
were violently thrust out, and the ice protruded, and
in some instances the shells burst asunder, thus demon-
strating the enormous interior pressure to which they
were subjected by water assuming the solid state.

117*8 What is the principal cause of the rounded and weather-worn
aspect of some rocks, especially the limestone and sandstone rocks ?

The expansion of freezing water : water is absorbed
into their fissures and pores by capillary attraction,
and when it freezes during winter, it expands and de-
taches successive fragments, so that the original sharp
and abrupt outline is gradually rounded and softened
down.

117*9 Why, in the winter, do we let the water run to prevent its freezing
in the service pipe ?

Because the motion of the water prevents the crys-
tals of ice from forming or attaching themselves to the
sides of the pipe.

1180 Can a lens be made of ice capable of concentrating the rays of the
sun with sufficient intensity to inflame substances ?

Yes ; a burning-lens can be formed of transparent
ice, of power sufficient to produce effects nearly equal
to those of the glass lens.

1181 What is " ground ice," or " anchor ice ?"

Ice formed at the bottom of streams or rivers.

1183 Upon what does the formation of icicles depend ?

Upon the successive congelation of drops or slender
streams of water.

1183 What is ice t

Frozen water. "When the temperature of water un-

180 SCIENCE OF COMMON THINGS.

Expansion of water in freezing.

der ordinary circumstances is reduced to 32° of heat,
water will no longer remain in a fluid state.

118-4 Can water be cooled below 32°, under any circumstances, without
freezing f

If pure, recently-boiled water, be cooled very slowly
and kept very tranquil, its temperature may be low-
ered to 21° without the formation of ice ; but the least
motion causes it to congeal suddenly, and its tempera-
ture rises to 32°.

1185 Why is solid ice lighter than water ?

Because water expands by freezing ; and as its bulk
is increased, its specific gravity must be less.

Nine cubic inches of water become ten when frozen.

118S Why are earthen or porcelain water vessels apt to break in a
frosty night ?

Because the water in them freezes, and (expanding
by frost) bursts the vessels to make room for its increas-
ed volume.

1187 Why does it not expand upwards (like boiling water) and run
over?

Because the surface is frozen first ; and the frozen
surface acts as a plug , which is more difficult to burst
than the earthen vessel itself.

1188 Why do tiles, stones, and rocks often split in winter f

Because the moisture in them freezes, and (expand-
ing by frost) splits the solid mass.

1180 In winter-time, footmarks and wheel-ruts are often covered with
an icy netivork, through the interstices of which the soil is clearly seen : why
does the water freeze in the form of network f

Because it freezes first at the sides of the footprints ;
other crystals gradually shoot across, and would cover
the whole surface, if the earth did not absorb the water
before it had time to freeze.

110 O In winter-time, these footmarks and wheel-ruts are sometimes
covered with a perfect sheet of ice, and not an icy network : why is this f

Because the air is colder and the earth harder than
in the former case ; in consequence of which the entire
surface of the footprint is frozen over before the earth
has had time to absorb the water.

SCIENCE OF COMMON THINGS. 181

Water-pipes often burst in winter. Bottom of a river rarely frozen.

1191 Why is not the ice solid in these ruts ? — why is there only a very
thin film or network of ice ?

Because the earth absorbs most of the water, and
•leaves only the icy film behind.

1193 Why do water-pipes frequently burst in frosty weather?

Because the water in them freezes, and (expanding
by frost) bursts the pipes to make room for its increased
volume.

1193 Why does the earth crack in intense cold weather ?

The moisture in the soil in the act of freezing ex-
pands^ and forces the particles asunder. The disrup-
tion of the earth is frequently accompanied with a loud
sound.

1194 Does not water expand by heat as well as ly coldf

Yes ; it expands as soon as it is more than 42°, till it
boils / after which time it flies off in steam.

1195 When does water begin to expand from cold?

Yvrhen it is reduced to 40°. Water is wisely ordained
to be an exception to a very general rule : it contracts
till it is reduced to 40°, and then it expands till it

freezes.

The general rule is this : — That cold condenses and contracts the volume
of nearly everything; but .water is not contracted by cold when it freezes
(which it does at 32°).

1196 Why does water expand when it freezes $

The expansion of water at the moment of freezing is
attributed to a new and peculiar arrangement of its
particles. Ice is, in reality, crystallized water, and dur-
ing its formation the particles arrange themselves in
ranks and lines which cross each other at angles of 60°
and 120°, and consequently occupy more space than
when liquid. This may be seen by examining the sur-
face of water in a saucer while freezing.

1197' Why is the bottom of a river rarely frozen f

Because water ascends to the surface as soon as it be-
comes colder than 42°, aad (if it freezes) floats there till
it is melted.

1198 Show the wisdom of the Creator in this wonderful exception to a
general law.

182 SCIENCE OF COMMON THINGS.

Why -water freezes first at the surface. Why running water freezes slowly.

If ice were heavier than water it would sink, and a
river w^ould soon become a solid Hock of ice, which
could never be dissolved.

The general rule is, that all substances become heavier from condensa-
tion ; but ice is lighter than water.

1199 Why does not the ice on the surface of a river chill the water
beneath, and make it freeze f

1. Because water is a very bad conductor ', and is
heated or chilled by convection only ;

2. If the ice on the surface were to communicate its
coldness to the water beneath, the water beneath would
communicate its heat to the, ice. and the ice would in-
stantly melt / and

3. The ice on the surface acts as a shield, to prevent
the cold from penetrating through the river to freeze the
water below the surface.

1500 Why does water freeze at the surface first?

Because the surface is in contact with the air, and the
ftir carries away its heat.

1501 Why does the coat of ice grow tiiicker and thicker if the frost
continues f

Because the heat of the water (immediately below
the frozen surface) passes through the ice into the cold
air.

1SOS Why are not whole rivers frozen (layer ly layer) till they be-
come solid icef

Because water is so slow a conductor, that our frosts
never continue long enough to convert a whole river
into a solid mass of ice.

12O3 Why does not running water freeze as fast as still water f

1. Because the motion of the current disturbs the
crystals, and prevents their 'forming into a continuous
surface ; and

2. The heat of the under surface is communicated to
the upper surface by the motion of the water.

1SO4 When running water is frozen, why is the ice generally very
rough f

Because little flakes of ice are first formed and carried
down the stream, till they meet some obstacle to stop

SCIENCE OF COMMON THINGS. 183

Sea water is rarely frozen. How the depth of water influences freezing.

them ; other flakes of ice (impinging against them) are
arrested in like manner ; and the edges of the different
flakes overlapping each other, make the surface rough.

13O5 Why do some parts of a river freeze less tlian others ?

Because springs issue from the bottom, and (as they
bubble upwards) thaw the ice, or make it thin.

13O0 When persons fall into a river in winter-time, why does the water
feel remarkably warm 1

Because the frosty air is at least ten or twelve de-
grees colder than the water is.

The water below the surface is at least 42°, but the air 32°, or even
less. '

1207 Why is sea water rarely frozen 1

1. Because the mass of water is so great, that it re-
quires a very long time to cool the whole volume down
to forty degrees ;

2. The ebb and flow of the sea interfere with the
cooling influence of the air ; and

3. Salt water never freezes till the surface is cooled
down to twenty-seven degrees, or five degrees below the
freezing point of fresh water.

13O3 Why do some lakes rarely (if ever) freeze? f

1. Because they are very deep ; and

2. Because their water is supplied by

springs which
bubble from the bottom.

ISO 9 How does the depth of water influence its freezing 1

It is necessary that the whole volume of water should
be reduced to forty degrees before the surface will
begin to freeze ; and the deeper the water, the longer it
will be before the whole volume is thus reduced.

1310 Why do springs at the bottom of a lake prevent its freezing ?

Because they keep continually sending forth water
having a temperature above that of the mass of the
water, which prevents the lake from being reduced to
the necessary degree of coldness.

1311 It is more chilly in a thaw than in a frost : explain the reason
of this.

When froz3n water is thawed, it absorbs heat from

184 SCIENCE OF COMMON THINGS.

Why it is chilly during a thaw. Cause of hoar-frost.

the air, etc., to melt the ice ; in consequence of which
the heat of the air is greatly reduced.

1212 To what extent can the temperature be reduced by the liquefaction
of a mixture of the two solids, snow and salt ?

By means of a mixture of equal weights of common
salt and fresh snow (or pounded ice), a steady temper-
ature of nearly 40° below the freezing point of water
can be maintained for hours.

1213 How much heat is required to melt ice f

The conversion of a cube of ice, three feet on the
side, into water at 32°, would absorb all the heat pro-
duced by the combustion of a bushel of coal.

1214 Why does the frost of winter make the earth in spring loose and
friable f

Because the water absorbed by the earth in warm
weather, expanding by the frost, thrusts the particles
of earth apart from each other, and leaves a chink or
crack between.

1215 Show the wisdom of the Creator in this arrangement.

These cracks in the earth let in air, dew, rain, and
many gases favorable to vegetation.

1216 Why are delicate trees covered with straw in winter f

Because straw (being a non-conductor) prevents the
sap of the tree from being frozen.

1217 What is hoarfrost f

There are two sorts of hoarfrost : 1. Frozen dew ; and
2. Frozen fog.

1218 What is the cause of the ground hoarfrost, or frozen dew ?

Yery rapid radiation of heat from the earth ; in
consequence of which the surface is so cooled down,
that \\, freezes the dew condensed upon it.

1219 Why is hoarfrost seen only after a very clear night ?

Because the earth will not have thrown off heat
enough by radiation io freeze the vapor condensed upon
its surface, unless the night be very clear indeed.

1220 What is the cause of that hoarfrost which arises from frozen fog f

SCIENCE OF COMMON THINGS. 185

Where hoar-frost does not accumulate. Frostwork on windows.

The thick fog which invested the earth during the
night (being condensed by the cold frost of early morn-
ing) is congealed upon every object with which it comes
in contact.

1221 Why is there little or no hoarfrost under shrubs and shady trees f

1. Because the leafy top arrests the process of radi-
ation from the earth ; and

2. Shrubs and trees radiate heat towards the earth ;
and therefore the ground beneath is rarely cold enough
to congeal the little dew which rests upon it.

1SSS Why does hoarfrost very often cover the ground and trees, when
the water of rivers is not frozen ?

Because it is not the eifect of cold in the air, but
cold on the surface of the earth (produced by excessive
radiation), which freezes the dew condensed upon it.

1223 Why is the hoarfrost upon grass and vegetables much thicker
than that upon lofty trees ?

Because the air (resting on the surface of the ground)
is much colder after sunset than the air higher up • in
consequence of which more vapor is condensed and
frozen there.

1224 What is the cause of the pretty frostwork seen on bedroom win-
dows in winter-time?

The breath and insensible perspiration of the sleeper
(coming in contact wTith the ice-cold window) 2x0, frozen
by the cold glass, and, crystallizing, form those beautiful
appearances seen on a winter morning.

1225 Are all the figures of frostwork formed in accordance ivith certain
fixed laws ?

All these figures are limited ~by certain laws, and the
lines which bound them form among themselves no
angles but those of 30°, 60°, and 120°.

1226 If you fracture thin ice by allowing a pole or weighi to fall upon
it, will the lines of the fracture have anything of regularity ?

Yes ; the fracture will generally present a star with
six equidistant radii, or angles of 60°.

122 7 Why is a glass or earthen vessel apt to break when hot water is
poured into itf

Because the inside of the glass is expanded by the

186 SCIENCE OF COMMON THINGS.

Why glass breaks when placed in hot water. "Why a stove snaps.

hot water, and not the outside / so tlie glass snaps in
consequence of this unequal expansion.

•1338 Why is not the outside of the glass expanded by the hot water as
well as the inside ?

Because glass is a bad conductor of heat, and breaks
before the heat of the inner surface is conducted to the
outside.

1339 Why does a glass snap because the inner surface is hotter than
the outer ?

Because the inner surface is expanded, and not the
outer ; in consequence of which an opposing force is
created which breaks the glass.

1330 Why does a cooper heat his hoops red hot when he puts them on
a tub?

1. As iron expands by heat, the hoops will be larger
when they are red hot ; in consequence of which they
wTill fit on the tub more easily ; and

2. As iron contracts by cold, the hoops wrill shrink
as they cool down, and girt the tub with a tighter
grasp.

1331 Why does a wheelwright make the tire red hot which he fixes on
a wheel f

1. That it may^ on more easily • and

2. That it may girt the wheel more tightly.

1333 Why will the wheelwrights tire Jit the wheel more easily for beiny
made red hot f

Because it will be expanded by the heat, and (being
larger) will go on the wheel more easily.

1333 Why will the tire which has been put on hot girt the wheel more.
firmly ?

Because it will shrink when it cools down, and
therefore girt the wheel with a tighter grasp.

1334 Why does a stove make a crackling noise when afire is very hot?

Because it expands from the heat ; and the parts of
the stove rulbing against each other, or driving against
the bricks, produce a crackling noise.

1335 Why does a stove make a similar crackling noise when a large
fire is put out f

SCIENCE OF COMMON THINGS. 187

Why clocks go faster in summer than in winter.

Because the metal of the stove contracts, by reason
of a reduction of temperature, when the fire is extin-
guished.

1336 Why are the nails in almost all old houses loose and easily
drawn out ?

Because the iron expands in the summer, and con-
tracts in the winter, more than the stone or wood, and
thus the opening is gradually enlarged after a lapse of
time.

133*7 Why does a piano give a higher tone in a cold than in a warm
room f

Because in a cold room the strings are contracted
and tighter.

1333 Why do clocks go slower in summer and faster in winter?

Because the pendulums elongate in summer through
the effects of heat, and consequently vibrate slower ;
while in winter they contract, become shorter, and
vibrate more rapidly.

1339 Hoiu is this inequality in the rate of motion in timepieces obviated f

By what is called a compensating pendulum / that
is, one constructed of two metals, possessing different
expansive powers, in such a manner that the greater
expansion of one bar in one direction equals the less
expansion of other bars in a different direction, and
thus maintain an invariable length of the pendulum.

1340 Does wood expand under the influence of heat differently from
metal ?

Yes ; an iron bar expands and contracts equally in
all directions, but wood expands and contracts more in
breadth than in length.

134:1 Why will a person, buying oil, molasses, spirits, etc., by the mea-
sure, get a greater weight of the same material in the same measure in the
winter tiian in the summer ?

Because these liquids contract and occupy less space
in the winter than in summer ; consequently it requires
more of the same kind to fill the same space in winter
than in summer.

1343 How can heat be measured f

Only by its effects : since the magnitude of any body

188 SCIENCE OF COMMON THING?.

What is temperature ? Thermometers and pyrometers.

changes with the heat to which it is exposed ; and since,
when subject to the same calorific influences, it always
has the same magnitude, these dilatations and contrac-
tions, which are the constant effects of heat, may be
taken as the measure of the physical cause that pro-
duced them.

1343 What is the temperature of a body ?

It is the actual state of a body at any moment, deter-
mined by a comparison of its magnitude with the heat
to which it is exposed.

1344 What is a change of temperature f

The change in magnitude which a body suffers by
changes in the heat to which it is exposed.

1345 What are the instruments for measuring lieat called?

Thermometers and pyrometers.

1346 What is the difference between them f

A thermometer is used for measuring moderate tem-
peratures ; wrhile the pyrometer is chiefly applied to de-
termine the more elevated degrees of heat.

1347* What substances are best adapted for measuring the effects of
heat by their expansion and contraction f

Liquids, above all other substances.

1348 Why are liquids best adapted for this purpose f

Because in solids the direct expansion by heat is so
small as to be seen or measured with difficulty ; in air
or gases it is too extensive and too liable to be affected
by atmospheric pressure ; but liquids are free from both
disadvantages.

1349 What liquid is generally used for the construction of ordinary
thermometers f

Mercury or quicksilver.

035 O What metal is distinguished from aU others by its fluidity at
ordinary temperatures f

Mercury or quicksilver.

1351 Does mercury, like other metals, expand by heatf

It readily expands or contracts with every variation
of temperature.

SCIENCE OF COMMON THINGS. 189

Use of mercury in thermometers. How thermometers are constructed.

1353 Why is mercury preferable to all other liquids for the purposes
of the thermometer f

Because it 'boils at a higher temperature than, any
other liquid, except certain oils ; and, on the other
hand, it freezes at a lower temperature than all other
liquids, except some of the most volatile, such as ether
and alcohoL

Thus, a mercurial thermometer will have a wider range than any other
liquid thermometer. It is also attended with this convenience, that the
extant of temperature included between melting ice and boiling water-
stands at a considerable distance from the limits of its range, or its
freezing and boiling points.

1253 Of what does the mercurial thermometer consist f

The mercurial thermometer consists essentially of a
glass tube with a bulb at one extremity, and which,
having been filled with mercury at a certain tempera-
ture, introduced through the open end, has been her-
metically sealed while full, so that no air can after-
wards enter it.

As the tube and mercury in it gradually become cooled, the inclosed
fluid contracts, and consequently sinks, leaving above it a vacant space
or vacuum, through which it may again expand on the application of
heat.

1354 As thermometers are constructed of different dimensions and
capacities, how are they graduated to indicate the same temperature under
the same circumstances, as the freezing point, for example?

The thermometers are first immersed in melting snow
or ice. The mercury will be observed to stop in each
thermometer-tube at a certain height ; these heights
are then marked upon the tubes. Now it has been
ascertained that at whatever time and place the instru-
ments may be afterwards immersed in melting snow or
ice, the mercury contained in them will always fix itself
at the point thus marked. This point is called the
freezing point of water.

1355 How is the boiling point ascertained ?

It has been found that at whatever time or place the
instruments are immersed in pure water, when boiling,
provided the barometer stands at the height of thirty
inches, the mercury will always rise in each to a certain

190 SCIENCE OF COMMON THINGS.

Determination of the boiling and freezing points.

height. This, therefore, forms another fixed point on
the geometric scale, and is called the boiling voint.

1356 How are the intermediate points determined ?

In Fahrenheit's thermometer, the intervals on the
scale, between the freezing and boiling points, are
divided into 180 equal parts. This division is similarly
continued below the freezing point to the place 0, and
each division upwards from that is marked with the suc-
cessive number 1, 2, 3, etc. The freezing point will
now be the 32d division, and the boiling point will be
the 212th division. These divisions are called degrees,
and the boiling point will therefore be 212°, and the
freezing temperature, 32°.

1557 When and by wham was the thermometer invented ?

The thermometer was invented about the year 1600;
but, like many other inventions, the merit of its dis-
covery is not to be ascribed to one person, but to be
distributed among many.

1558 Why is the thermometer in general use in the United States,
England, and Holland, called Fahrenheit's thermometer '?

Because thermometers having a like graduation were
first manufactured by Fahrenheit, a Dutch philoso-
phical instrument-maker. The employment of mercury
as the most suitable fluid for the thermometer is also
usually attributed to him.

IS 5 9 How many kinds of tliermorneters
are in general use ?

Three : Fahrenheit's, Reau-
mur's, and the Centigrade ther-
mometer, or thermometer of
Celsius.

126O What constitutes the di/erence
letween these instruments f

The differences of graduation
between the freezing and boiling
points of water. Reaumur is
divided into eighty degrees, the
Centigrade into one hundred,
Fig 4L and Fahrenheit's into one hun*

SCIENCE OF COMMON THINGS.

191

Different varieties of thermometers.

Construction of pyrometers.

dred and eighty. According to Reaumur, water freezes
at 0°, and boils at 80° ; according to Centigrade, it
freezes at 0°, and boils at 100° ; and according to Fah-
renheit, it freezes at 32°, and boils at 212°; the last, very
singularly, commences counting not at the freezing
point, but 32° below it.

The differences between these instruments can be easily seen by refer-
ence to Fig. 41.

1261 In what countries are the Reaumur and Centigrade thermometers
generally used ?

fieaumur is in general use in Germany, and the
Centigrade in France / but for scientific purposes the
Centigrade is almost universally adopted.

12362 At what temperature does mercury freeze ?

At about 39° below the zero of Fahrenheit's thermo-
meter.

1263 How are degrees of cold more intense than this measured f

By using a thermometer filled with alcohol colored
red, as this fluid when pure does not congeal at 100°
Fahrenheit below zero.

1264 At what temperature does mercury boil f

At 660° Fahrenheit.

1265 How are temperatures greater than this determined f

By means of the expansion of solids • and instru-
ments founded upon this principle are commonly called
pyrometers.

Fig. 42.
Ihe construction of the pyrometer is represented in Fig. 42. A repre-

192 SCIENCE OF COMMON THINGS.

What is liquefaction 1 Why ice is melted by heat.

senta a metallic bar, fixed at one end, B, but left free at the other, and in
contact with the end of a pointer, K, moving freely over a graduated scale.
If the bar be heated by the flame of alcohol, the metal expands, and
pressing upon the end of the pointer moves it, in a greater or less degree.

13 GQ On what principle have pyrometers generally been constructed f

On the relative expansion of bars of iron, or some
other metal.

12Q7 Does a thermometer inform us how much heat any body con-
tains ?

No ; it merely points out a difference in the tem-
perature of two or more substances. All we learn by
the thermometer is whether the temperature of one
body is greater or less than that of another ; and if
there is a difference it is expressed numerically —
namely, by the degrees of the thermometer.

It must be remembered that these degrees are parts of an arbitrary
scale, selected for convenience, without any reference whatever to the
actual quantity of heat present in bodies.

1368 After the expansion of solids, when acted upon by heat, what
other effect is next observed ?

They change their original state, become liquid, or
melt. Many of them become soft before melting, so
that they may be kneaded ; for instance, wax, glass,
and iron ; in this condition, glass can be bent and
moulded like wax, and iron can be forged or welded.

13 B9 What is meant by liquefaction ?

The conversion of a solid into a liquid by the agency
of heat, as solid ice is converted into water by the heat
of the sun.

137O Why is ice melted by the heat of the sun f

Because, when the heat of the sun enters the solid
ice, it forces its particles asunder, till their attraction
of cohesion is sufficiently overcome to convert the solid
ice into a liquid.

13*71 Why are metals melted by the heat of fire f

Because, when the heat of the fire enters the solid
metal, it forces its particles asunder, till their attraction
of cohesion is sufficiently overcome to convert the solid
metal into a liquid.

SCIENCE OF COMMON THINGS. 193

What is a solution ? Why water dissolves sugar.

IS 7*3 When salt is mixed with water and disappears in the liquid,
what is said to have taken place ?

The salt is said to have dissolved in the water, and
.the liquid is now a solution of salt.

IS 73 What, then, w a solution f

A solution is the result of an attraction or affinity
between a solid and a fluid ; and when a solid disap-
pears in a liquid, if the compound exhibits perfect
transparency, we have an example of a perfect solution.

1374 When is a solution said to be saturated f

When the fluid has dissolved as much of the solid as
it is capable of doing, it is said to be saturated ; or, in
other words, the affinity or attraction of the fluid for
the solid continues to operate to a certain point, where
it is overbalanced by the cohesion of the solid ; it then
ceases, and the fluid, is said to be saturated.

1S75 What is the difference between a solution and a mixture f

A solution is a chemical union / a mixture is a mere
mechanical union of bodies.

IS 70 Why will water dissolve sugar f

Because there is attraction or affinity between the
particles of the water and the particles of the sugar.

1S77 What do we mean by affinity f

Affinity is that kind of attraction in virtue of which
bodies of a dissimilar character combine together into
a whole, which appears perfectly uniform to the senses,
even when assisted by powerful magnifying instruments.

1S7S Why will not water dissolve granite or metallic iron f

Because there is not sufficient affinity or attraction
between the particles of the water and those of the iron
or granite.

1379 Are there any liquids that have sufficient affinity to dissolve iron
and granite ?

Yes ; certain acids have so great an affinity for the
iron and granite that they are enabled to dissolve them.

1S8O Why will not water dissolve oil?

Because there is no affinity or attraction between the
particles of the two substances.

194: SCIENCE OF COMMON THINGS.

Vaporization. Why heat converts water into eteam.

IS 81 Why will alcohol and ether dissolve oil f

Because the attraction or affinity between the alco-
hol or ether and the oil is sufficient to enable them to
effect a solution.

1S8S What effect has heat upon the dissolving power of liquids!

In most cases the addition of heat to a liquid greatly
increases its solvent properties. Hot water will dissolve
much more sugar than cold water, and hot water will
also dissolve many things which cold water is unable
to affect.

1583 Why does not wood melt like metal ?

Because the heat of the fire decomposes the wood into
gas, smoke, and ashes, and the different parts separate
from each other.

1584 What is meant by vaporization?

The conversion of a solid or liquid into vapor / as
snow or water is converted into vapor by the heat of
the sun.

IS 85 Why is water converted into steam by the heat of the fire f

Because, when the heat of the fire enters the water,
it separates its substance into very minute particles,
which (being lighter than air) fly off from the surface
in the form of steam.

1S86 Why do doors swell in rainy weather ?

Because the air is filled with vapor, wrhich (pene-
trating into the pores of the wood) forces its particles
farther apart, and swells the door.

1SS7 Why do doors shrink in dry weather?

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

1SSS Why does a drop of water sometimes roll along a piece of hot
iron without leaving the least trace f

Because the bottom of the drop is changed into vapor,
which buoys the drop up, without allowing it to touch
the iron.

1SS9 Whydoesitrott?

SCIENCE OF COMMON THINGS. 195

Volatile substances. What is distillation ?

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

1290 Why does a laundress put a little saliva on aflat-iron to know if
it be hot enough ?

Because when the saliva sticks to the iron and is
evaporated, she knows it is not sufficiently hot ; but
when it runs along the iron, it is.

1291 Why is the flat-iron hotter if the saliva runs along it, than if it
adheres till it is evaporated?

Because when the saliva runs along the iron, the heat
is sufficient to convert the bottom q£ the drop into vapor •
but if the saliva will not roll, the iron is not sufficiently
hot to convert the bottom of the drop into vapor.

1292 To what substances do we apply the term " volatile ?"

To those which have a great tendency to assume the
gaseous form.

1293 To what substances do we apply the term "fixed," or "non-vola-
tile?"

To those in which the tendency to assume the gaseous"
form is small.

1294 Do vapors occupy much more space tlian the substances from which
they were produced f

They occupy a much greater space ; water, in passing
from its point of greatest density into vapor, expands to
sixteen hundred and ninety-six times its volume.

1295 Under what two heads does the subject of vaporization divide
itself?

Into ebullition and evaporation

1296 What is distillation?

A process by which one body is separated from an-
other by means of heat, in cases where one of the bodies
assumes the form of vapor at a lower temperature than
the other ; this first rises in the form of vapor, which is
received and condensed in a separate vessel.

1297* How is the process of simple distillation effected ?

A peculiar-shaped vessel called a retort (Fig. 43) is
half filled with a volatile liquid and heated ; the steam,
as it forms, passes through the neck of the retort into a

196 SCIENCE OF COMMON THINGS.

"Why distilled water Is Tery pure. Construction of a still.

glass receiver contained in a vessel filled with cold
watery and is then condensed.

Fig. 43.

1298 Why is water obtained in this manner by distillation purer than
spring water f

Because the non-volatile, earthy, and saline portions
contained in all spring waters do not ascend with the
vapor, but remain in the retort. By this means very
volatile bodies can be easily separated from less volatile
ones ; as brandy and alcohol from the less volatile
water which may be mixed with them.

1J390 When the vessel used for generating the vapor is very large, what
is it called f

A "still ;" and, for con-
densing the vapor, vats are
constructed, holding ser-
pentine pipes or " worms"
which present a greater
condensing surface than
if the pipe had passed di-
rectly through the vat.

To keep the coil of pipe cool, the

vats are kept filled with cold water.

Fig™ (See Fig. 44.)

In this figure a is a furnace, in

which is fixed a copper vessel to contain the fluid. Heat being applied,
the steam rises in the head 6, and passes through the worm d, which is
placed in a vessel of water, the refrigerator. The vapor thus generated is
condensed in its passage, and passes out as a liquid by the external pipe
into a receiver.

13OO What is the difference between drying by heat and distil'tmg f

SCIENCE OP COMMON THINGS. 197

What is evaporation ? Danger of wearing wet clothes.

In the one case, the substance vaporized, being of no
use, is allowed to escape or become dissipated in the
atmosphere ; while in the other, being the valuable
part, it is caught and condensed into the liquid form.

13O1 What is the vapor from damp linen ?

The vapor from damp linen, if caught, would be dis-
tilled water.

13OS What is evaporation 1

The conversion of a fluid into vapor.

"When vaporization takes place only from the surface of a body, either
because the heat has access to that part, or because the evolution of
vapor takes place through the medium of a gas or air already present, the
action can only be recognised by the diminution of the bulk of the body :
this phenomenon is called evaporation.

1303 What effects are produced by evaporation f

The substance vaporized absorbs heat from the body
whence it issues ; and the body, deprived of a portion
of its substance by evaporation, loses heat.

1304 If you wet your finger in your mouth, and hold it up in the air,
why does it feel cold ?

Because the saliva quickly evaporates, and (as it
evaporates) absorbs heat from the finger, making it feel
cold.

1305 If you lathe your temples ivith ether, cologne water, spirits, etc.,
why does it allay inflammation and feverish heat?

Because these liquids very rapidly evaporate, and (as
they evaporate) absorb heat from the burning head,
producing a sensation of cold.

1306 Why do we feel cold when we have wet feet or clothes f

Because the wet of our shoes or clothes rapidly eva-
porates, and (as it evaporates) absorbs -heat from our
body, which makes us feel cold.

ISO? Why do wet feet or clothes give us " cold?"

Because the evaporation absorbs heat so abundantly
from the surface of our body, that its temperature is
lowered below its natural standard ; in consequence of
which health is injured.

13O8 Why is it dangerous to skep in a damp bed?

Because the heat is continually absorbed from the
9*

198 SCIENCE OF COMMON THINGS.

Health injured by reducing the temperature of the body.

surface of our body to convert the damp of the sheets
into vapor ; in consequence of which our animal heat
is reduced 'below the healthy standard.

1309 Why is health injured when the temperature of the body is
reduced below its natural standard f

Because the balance of the circulation is destroyed.
Blood is driven away from the external surface by the
chill, and thrown upon the internal organs, which are
oppressed by this increase of Hood.

1310 Why do we not feel the same sensation of cold if we throw a
waterproof coat over our wet clothes f

Because water-proof coats (being air-tight) prevent
evaporation, and (as the wet cannot evaporate) no heat
is absorbed from our bodies.

1311 Why does sprinkling a hot room with water cool it f

Because the heat of the room causes a rapid evapora-
tion of the sprinkled water, and as the water evaporates,
it absorbs heat from the room, which cools it.

131J3 Why does watering the streets and roads cool them f

Because they part with their heat to promote the eva-
poration of the water spi^inkled on them.

1313 Why does a shower of rain cool the air in summer-time ?

Because the wet earth parts with its heat to promote
evaporation y and when the earth is cooled, it cools the
air also.

1314 Why is linen dried by being exposed to the wind f

Because the wind accelerates evaporation by removing
the vapor from the surface of the wet linen as fast as it
is formed.

1315 Why does draining land promote warmth,

Because abstracting water diminishes evaporation ;
in consequence of which less heat is withdrawn from the
earth.

1310 Why does cultivation increase'the warmth of a country f

A cultivated country is better drained, and laid open
to the rays of the sun. The forests being cut down,
the snow quickly disappears in the spring, and the
earth soon becomes dry.

SCIENCE OF COMMON THINGS. 199

Air cool after a rain. Production and nature of steam.

131V Why does bread after the lapse of a few days become dry and
stale f

Because the moisture contained in it evaporates ; the
particles then shrink, and the whole mass becomes
hard.

1318 Why is not the vapor of the sea salt f

Because the salt is always left behind in the process
of evaporation.

131O " AH the rivers run into the sea :" why is not the sea full f

Because the quantity of water evaporated from the
surface of the sea is equal to the quantity poured into
it by the rivers ; therefore the sea is never full.

13J3O Why is it frequently cooler after a rain f

Because water which falls from the atmosphere soon
returns to it in the form of vapor, carrying with it, in
the latent form, a large amount of heat taken from
every object, thus moderating the temperature of the
earth, and refreshing the animal and vegetable creations.

1331 Does evaporation take place from the surface of snow and ice f

Yes, to a very considerable extent, even when the
temperature of the air is below the freezing point.

13SS What is steam?

The vapor of boiling water.

1323 Is steam visible or invisible f

Steam is invisible; but when it comes in contact
with the air (being condensed into small drops) it in-
stantly becomes visible.

13S4 How do you know that steam is invisible f

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.

1325 Why is the steam invisible for half an inch t

Because the air is not able to condense it, 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*

200 SCIENCE OF COMMON THINGS.

Vapor of water always exists in air. White appearance of steam.

1336 Does air ever exist without steam or vapor of water ?

Air without steam (theoretically called dry air) is
not ~known to exist in nature, and is probably not pro-
ducible by art.

1337* Is the visible matter, popularly called steam, really true steam ?

By no means, and should be carefully distinguished
from steam proper, or the aeriform state of water. The
cloud or smoke-like matter alluded to is really not an
air or vapor at all, but a dust-like cloud of minute
bodies of liquid water, wafted by a current either of
true steam, or, more frequently, of mere moist air.

1338 Is it necessary to the production of steam that water should be
raised to the boiling temperature f

It is not / the surface of any watery liquid, about 20°
warmer than any superincumbent air (however warm
or cold that may be), rapidly gives off true steam, which
is invisible, but which no sooner mixes with colder air
than it is recondensed into water, and assumes the
forms of minute globules.

1339 What causes the visible white appearance of condensed steam f

The myriads of minute globules of water into which
the steam is condensed are separately invisible to the
naked eye, but each, nevertheless, reflects a minute ray
of white light. The multitudes of these reflecting
points, therefore, make the space through which they
are diffused appear like a cloudy body, more or less
white, according to their abundance.

1330 In what manner is the production of steam in boiling water first
manifested ?

, When steam begins to be produced, as in the process
of making water boil, and the heat overcomes the
atmospheric pressure on the surface, small bubbles are
formed, adhering slightly to the sides of the vessel.

1331 In what parts of the boiler will its development be most conspicu-
ous?

The bubbles are formed most rapidly at those points
against which the flame is most strongly directed.

1333 How much lighter is steam than water f

SCIENCE OF COMMON THINGS.

Different spaces occupied by steam and water. Pressure of steam.

About 1700 times ; because a quantity of water
yields nearly 1700 measures
of steam at 212° F.

Fig. 45 represents the comparative
volume of water and of steam.

1333 How much steam will a cubic
inch of water furnish 1

A cubic inch of water ex-
pands into about a cubic foot
of steam at 212° F., under the
ordinary atmospheric pres-
sure.

1334 Upon what does the power of ..
steam depend f

On the tendency which water possesses to expand
into vapor when heated to a certain temperature.

1335 What is the most important property of steam ?

Its elasticity or pressure. By virtue of this property,
when freed from the limits which confine it, steam will
dilate into any space to which it may have access.

133S Jf a quantity of pure steam be confined in a close vessel, in what
manner will its pressure be exerted ?

It will exert on every part of the interior of the vessel
a certain pressure directed outwards, and having a ten-
dency to burst the vessel.

1337* How great a pressure does steam, formed under ordinary cir-
cumstances, have to overcome before it can rise from the surface of the water ?

That of one atmosphere — -fifteen pounds on eveiy
square inch, or one ton on every square foot — a force
equivalent to the strength of six hundred horses.

1338 What happens when the temperature of 'steam generated under
ordinary pressures is reduced below 212° f1. f

It is immediately condensed into water.

1339 As steam sustains and elevates a weight occasioned by the pressure
of the atmosphere, of fifteen pounds per square inch, what takes place when
a column of steam is immediately condensed ?

The atmospheric weight will immediately fall writh a
force equal to that with which it was raised.

1340 How can steam be used to advantage for cooking vegetables, etc. f

202 SCIENCE OF COMMON THINGS.

"What is high-pressure steam ? What is a steam-engine ?

In cookery, if steam raised from boiling water be
allowed to pass through meat and vegetables, it will be
condensed upon their surfaces, imparting to them the
latent heat which it contained before its condensation,
thus cooking them as effectually as if they were im-
mersed in boiling water.

1341 What do we mean when we speak of high-pressure steam f

High-pressure steam is merely steam condensed, not
by withdrawal of heat, but by pressure, just as high-
pressure air is merely condensed air. To obtain a
double, triple, or greater pressure of steam, we must
have twice, thrice, or more steam under the same vo-
lume.

1343 Is high-pressure steam, escaping from a boikr heated to 300° or
more, hotter than low-pressure steam escaping from a boiler at 212° ?

No ; for the instant that high-pressure or condensed
steam escapes into the air, it immediately expands and
becomes low-pressure steam, and is greatly cooled down
by its expansion.

1343 Does high-pressure steam, acting in a boiler at a high tempera-
ture, exert a greater mechanical and chemical power than low-pressure
steam f

It does f high-pressure steam acting upon bones,
breaks up and dissolves the whole mass, extracting all
the glue and fat, when ordinary steam would dissolve
nothing.

In the Western States, where large quantities of lard are manufactured,
the whole hog is exposed to high-pressure steam, and the carcass reduced
in a short tune to a fat fluid mass.

1344 Can high-pressure steam be raised to a very elevated degree of
heat?

It can / in some of the methods lately introduced for
purifying oils, etc., the temperature of the steam, before
its application, is required to be sufficiently elevated to
enable it to melt lead.

1345 What is the steam-engine f

The steam-engine is a mechanical contrivance by
which coal, wood, or other fuel is rendered capable of
executing any kind of labor.

SCIENCE OF COMMON THINGS. 203

Mechanical force of steam. Comparison of steam power and animal power.

1346 What substance furnishes the means of calling the powers of coal
into activity ?

Water.

1347* How much water will two ounces of coal evaporate t

About a pint.

1348 How much steam will this produce f

Two hundred and sixteen gallons.

1340 How much mechanical force can this steam exert t

It can raise a weight of thirty-seven tons to the
height of one foot.

1350 What amount of force can a man exert when applying his
strength to the best advantage through the help of machinery f

It has been found by experiment, that a man work-
ing on a tread-mill continuously for eight hours, will
elevate one and a half millions of pounds to the height
of one foot.

1351 With how much coal will a well constructed steam-engine perform
the same labor ?

With the expenditure of a pound and a half.

1352 How much coal then would be equivalent to the average power of
an able-bodied man during his active life, supposing him to work for twenty
years at Hie rate of eight hours per day ?

The consumption of about four tons of coal would
evolve in a steam-engine fully as much power.

1353 The great pyramid of Egypt is five hundred feet high, and weighs
twelve thousand seven hundred and sixty millions of pounds. Herodotus
states that in constructing it one hundred thousand men were constantly
employed for twenty years. With how much coal could all the materials of
this pyramid be raised to their present position from the ground ?

With the expenditure of four hundred and eighty
tons of coal.

204: SCIENCE OF COMMON THINGS.

What Is ventilation ? Warming and ventilation of buildings.

PART VI.

.VENTILATION AND WARMING, COMBUSTION,
RESPIRATION, AND NUTRITION.

CHAPTEK I.

WARMING AND VENTILATION.

1354 What is ventilation f

Ventilation is the act or operation of causing air to
pass through any place, for the purpose of expelling
impure air and dissipating noxious vapors.

1355 What is the theoretical perfection of ventilation ?

To render it impossible for any portion of air to be
breathed twice in the same building.

1356 Upon what principle does the whole process of warming and ven-
tilating buildings depend ?

Upon the expansion and contraction of air, or, in
other words, upon the fact that air which has been
heated and expanded ascends, and air wrhich has been
deprived of heat, or has become contracted, descends.

1357f Is there an upward current of air always
rising from heated substances f

There is ; air made lighter by heat
ascends through colder strata, as a cork
(put at the bottom of a basin of water)
rises to the surface.

135S What simple experiment shows the exist*
ence of this upward current in an ordinary stove f

If we attach to the side of a heated
stovepipe a wire on which a piece of
paper cut in the form of a spiral may

SCIENCE OF COMMON THINGS. 205

Why a fire balloon rises. Where ventilation is perfect. Oxygen.

be suspended, as is represented in Fig. 46, the upward
current of hot air will immediately put the paper in
motion, and make it revolve rapidly around the wire.

1359 When a boy makes a fire-battoon, and sets fire to the cotton or
sponge (which has been steeped in spirits of wine), why is the balloon inflated f

Because the air of the balloon is expanded by the
heat of the flame, and fills the balloon to its utmost
capacity.

1360 Why does the balloon rise after it has been inflated by the expanded
air?

Because the same quantity of air is expanded to three
or four times its orig^nal volume ; and made so much
lighter, that even when all the paper, wire, and cotton
are added, it is still lighter than common air.

1361 In what situation is ventilation perfect ?

In the open air, because the breath, as it leaves the
body, is warmer and lighter than the surrounding fresh
air, and ascending is immediately replaced by an in-
gress of fresh air ready to be received by the next
respiration.

1363 Why is it desirable to avoid breathing the same air twice ?

Air which has been once respired, is unwholesome,
and not suited to supply the wants of the animal system.

1363 What are the elements of atmospheric air?

Oxygen and nitrogen mixed together, in the propor-
tion of seventy-nine parts of nitrogen and twenty-one
of oxygen.

1364 What is oxygen f

A gas, colorless, tasteless, and odorless ; it is heavier
than atmospheric air, and is a non-conductor of elec-
tricity.

1365 Is oxygen a substance existing in great abundance ?

Oxygen is the most abundant of all known substances ;
it constitutes at least one third of the solid mass of the
globe, eight-ninths of all water, and nearly one-fourth
part of the atmosphere ; it also exists in most organic
substances.

1366 Is oxygen ever found in a liquid or solid state f

206 SCIENCE OF COMMON THINGS.

Use of oxygen in the air. Nitrogen, its properties and us«s.

~No ; when pure it is only known in the gaseous state ;
all efforts to reduce it to a liquid or solid condition by
cold or pressure have completely failed.

1367 Of what use is oxygen in the atmosphere ?

It sustains animal life and supports combustion.

1368 If an animal were immersed in oxygen gas, would it continue to
live for a time?

It would ; at the same time animal life could not be
sustained for any great length of time in an atmosphere
of pure oxygen.

1369 What is meant when it is said that oxygen " sustains life f "

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

1370 What good does this inspiration of oxygen do f

1. It gives vitality to the blood ; and

2. It is the cause of animal heat.

1371 What is nitrogen f

An invisible gas existing largely in atmospheric air,
and in most animal and vegetable substances.

1372 What are its principal characteristics f

1. It is not combustible /

2. It does not support animal life ; and

3. It is the principal ingredient in the composition
of atmospheric air.

1373 What proportion of the air we breathe is composed of nitrogen f

About four -fifths of the air is nitrogen / the other
one-fifth is oxygen.

1374 Why is there so much nitrogen in the air f

The uses of nitrogen are in a great measure unknown.
It has been supposed to act as a diluent to the oxygen,
but it most probably serves some useful purpose in the
economy of animals and vegetables, the exact nature of
which has not been discovered.

1375 What would be the effect if the proportion of oxygen in the atmo-
sphere were increased f

The inflammability of most substances would be in-
creased, fires would burn out very quickly, and the

SCIENCE OF COMMON THINGS. 207

Carbonic acM gas. The composition of the air never varies.

functions of life would be called into such rapid action
as to soon exhaust the powers of the system.

1370 Are the two gases, oxygen and nitrogen, existing in tlie atmo-
sphere, chemically combined, or merely intermingled ?

They are merely mixed, and not combined with each
other.

1377' Does thv atmosphere always contain any other ingredients besides
oxygen and nitrogen f

There is always in the air, at all places, carbonic acid
gas, in variable proportions, and watery vapor, besides
the odoriferous matter of flowers and other volatile
substances.

1378 What is carbonic acid gas f

A gas formed by the union of carbon and oxygen ;
it used to be called fixed air. Its chemical com-
position is one atom of carbon united to two of
oxygen.

1379 Is the air collected on the tops of high mountains, over marshes
in hospitals, and over deserts, the same in character and composition f

It is not found to vary, but is the same in all regions
of the earth and at all altitudes.

1380 Are the component parts of air, oxygen, nitrogen, carbonic acid,
and watery vapors, of different specific gravities, or do they all differ in
weight ?

They are all different, carbonic acid gas being the
heaviest.

1381 Then, as we have before stated that they are merely mixed, and
not combined, why do they not arrange themselves in the order of their densi-
ties, and float one upon the other, as oil and water do when mingled f

Because of a wonderful principle or law of nature,
that when two gases of different weights or specific
gravities are mixed together, they cannot remain sepa-
rate, as fluids of different densities do, but diffuse them-
selves uniformly throughout the whole space which
both occupy.

1383 Carbonic acid is tiventy times heavier than hydrogen gas ; if we
fill the lower part of a tatt jar with carbonic acid, and the upper part with
kydrogen, will the two gases mix ?

After a few hours the two gases will be found equally

208 SCIENCE OF COMMON THINGS.

Carbonic acid gas in the atmosphere.

mingled, as much carbonic acid being at the top of the
jar as at the bottom.

13 S3 Does this law appear to be opposed to the principles of the law of
gravitation ?

It appears to be opposed to it ; the only exception we
are acquainted with in the natural world.

1384 How much carbonic acid is estimated to exist in the atmosphere f

I About one part in two thousand, by volume.

1335 If this were all collected in one layer over the surface of the earth,
how great a thickness would this layer or stratum have ?

About thirteen feet.

138Q Can we breathe carbonic acid?

No • the animal immersed in it dies instantly.

1387* If, then, this singular law of the diffusion of gases did not prevail,
would the surface of the earth be habitable ?

It would not; carbonic gas would fill up all the
valleys and lower levels, separating every hill and ele-
vation • by an invisible ocean of poisonous gas, as im-
passable as the barrier between the dead and the
living.

1388 Is it owing to this law that we are enabled to enjoy and perceive
at a distance the odor of a flower-garden, or the perfume which has been
opened in an apartment f

It is by this law that a vapor, arising by its own
elasticity from a volatile substance, is caused to extend
its influence and mingle with the surrounding atmo-
sphere, until its effects become so enfeebled by dilution
as to be imperceptible to the senses.

138Q If the oxygen and nitrogen of which our atmosphere is composed
were combined together, instead of being merely mingled, what would the
compound be ?

A most deadly poison.

1390 What gas is generated by a lighted candle or lamp ?

Carbonic acid gas — formed by the union of the carbon
of the oil or tallow with the oxygen of the air.

1391 Under what circumstances does carbon most readily unite with
oxygen ?

1. When its temperature is raised : thus, if carbon
be red hot, oxygen will most readily unite with it ;

SCIENCE OF COMMON THINGS. 209

Carbonic acid a poison. Crowded room unhealthy.

2. Carbon in. the Hood unites readily -with oxygen
during respiration ; and

3. Carbonic acid is formed in large quantities during
the chemical changes which we call fermentation.

1302 Js carbonic acid in any degree wholesome f

No / it is fatal to animal life, and (whenever it is
inhaled) acts like a narcotic* poison, producing drowsi-
ness, which sometimes ends in death.

1303 When persons commit suicide by building a charcoal fire in a
closed room, what occasions their death ?

The inhalation of carbonic acid, which is generated
by the combustion of the charcoal.

1304 How can any one know if a place be infested with carbonic acid
gasf

If a pit or well contain carbonic acid, a lighted 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.

1305 Why does a crowded room produce headache?

Because we breathe air vitiated by the crowd.

1306 Why is the air of a room vitiated by a crowd ?

Because it is deprived of its due proportion of oxy-
gen, and loaded with carbonic acid.

1307* How is the air of a room affected thus by a crowd ?

The elements of the air inhaled are separated in the
lungs ; the oxygen, incorporated in the blood, forms
carbonic acid ; and the carbonic acid (together with
the nitrogen) is thrown back again by the breath into
the room,

1308 Is all the nitrogen rejected by the lungs f

Yes ; all the nitrogen of the air is always expired.

1300 How much oxygen does afull-groivn person consume per hourf

It is calculated that an adult of average size absorbs

* A narcotic is a substance which, when used as a medicine, relieves
pain and produces sleep, but in poisonous doses produces death. Opium,
laudanum, tobacco, etc,, are narcotics.

210 SCIENCE OF COMMON THINGS

Air consumed by a person in an heur. Vegetation purifies the air.

about a cubic foot of oxygen per hour by respiration,
and consequently renders five cubic feet of air unfit for
breathing, since every five cubic feet of air contain one
cubic foot of oxygen. It is also calculated that two
wax or sperm candles absorb as much oxygen as an
adult.

1400 To keep tJie air of a room pure, how much fresh air should be
allowed to pass in per hour f

Five cubic feet for each person, and two and a half
cubic feet for each candle, should be allowed to pass in,
and an equal quantity to pass out.

1401 Why do persons in a crowded church feel drowsy f

1. Because the crowded congregation inhale a large
portion of the oxygen of the air, which alone can sus-
tain vitality and healthy action ; and

2. The air of the church is impregnated with carbonic
acid gas, which (being a strong narcotic) produces
drowsiness in those who inhale it.

14OS Why do persons who are much in the open air enjoy the best
health f

Because the air they inhale is much more pure than
the air of close and confined rooms.

1403 How does vegetation (trees and flowers] serve to purify the airf

1. Because trees and flowers absorb the carbonic
acid generated by the lungs of animals, putrid sub-
stances, and other obnoxious exhalations ; and

2. Trees and flowers restore to the air the oxygen
which man and other animals inhale.

1404 Why is the air of cities generally less pure than the air of the
open country f

1. Because there are more inhabitants to vitiate the
air;

2. The sewers, drains, bins, and filth of a city very
greatly vitiate the air ;

3. The streets and alleys prevent a free circulation ;
and

4. There are fewer trees to absorb the excess of car-
bonic acid gas, and restore the equilibrium.

SCIENCE OF COMMON THINGS. 211

* ,. •

Close rooms unhealthy. Carbon thrown off by the lungs.

1405 Why are persons who live in close rooms and crowded' cities
generally sickly f

Because the air they breathe is not pure, but is (in
the first place) defective in oxygen, and (in the second)
is impregnated with carbonic acid gas.

1406 Where does the carbonic acid of close rooms and cities com*
from ?

From the lungs of the inhabitants, the sewers, drains,
and other like places, in which organic substances are
undergoing decomposition.

1407 What becomes of the carbonic acid generated in crowded cities f

It is gradually diffused through the air, absorbed by
vegetation and by water, and wafted by the winds to
different localities.

1408 Does not this constant diffusion of carbonic acid affect the purity
of the whole air 1

No ; because it is wafted by the wind from place to
place, and absorbed in its passage by the vegetable world.

1409 What is choke damp ?

Carbonic acid gas accumulated at the bottom of wells
and pits, which renders them noxious, and often fatal to
life. It is called choke damp, because it chokes (or suf-
focates) every animal that attempts to inhale it.

It suffocates without getting into the lungs, by closing the glottis spas'
modicatty.

1410 Why is not this carbonic acid taken up by the air and diffused, as
it is in tities f

Because (being heavier than common air) it cannot
readily rise from the well or pit ; and no wind can get
to it to blow it away.

By the chemical law of diffusion, a portion of the carbonic acid which
accumulates at the bottom of wells and pits, is removed ; but in many
cases this abstraction is more than counterbalanced by an increased
supply.

1411 How much carbon in the form of carbonic acid passes through the
lungs of a healthy person every twenty-four hours f

The quantity would be very accurately represented
by a mass of charcoal of the weight of fifteen ounces.

The volume of carbon in the atmosphere, although it forms but one per
cent, of the carbonic acid existing in it, exceeds in amount all the carbon

212 SCIENCE OF COMMON THINGS.

Sources of carbonic acid. The air always in motion.

that is stored in the earth in the form of coal, or spread over its surface in
the form of animals or vegetables.

141S What are the chief sources of carbonic acid ?

Combustion, respiration of men and animals, the
decomposition of organic substances, and the exhalations
of volcanoes. Carbonic acid also exists in large quan-
tities in the atmosphere, in most waters, and combined
with minerals in a solid state, as in marble, which con-
sists of lime united to carbonic acid.

1413 From which of these sources is carbonic acid most likely to accu-
mulate to a noxious extent f

From the fermentation arid putrefaction of decaying
vegetable and animal matters.

1414 How can this accumulation of carbonic acid be prevented?

By throwing quicklime into places where such fer-
mentation ana putrefaction are going on.

1415 How will quicklime prevent the accumulation of carbonic acid?

Quicklime will absorb the carbonic acid, and produce
a combination called " carbonate of lime."

1416 Does not heavy rain, as well as quicklime, prevent the accumula-
tion of carbonic acidf

Yes ; an abundant supply of water will prevent the
accumulation of carbonic acid, by dissolving it.

1417 Is the external air always in motion?

Some portion of the atmosphere is always in motion.
Currents of warm air ascending, and currents of cold
air descending.

1418 7s the air of our rooms always in motion f

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 cold air flowing into the room.

1419 How do you know that there are these two currents of air in
wery occupied room f

If I hold a lighted candle near the crevice at the top
of the door, the flame will be blown outwards (towards
me hall) ; but if I hold the candle at the bottom of
the door, the flame will be blown inwards (into the
room).

SCIENCE OF COMMON THINGS. 213

Causo of air currents at windows and doors. What is a vacuum ?

This is not the case if a fire be in the room. When a fire is lighted,
an inward current is drawn through all the crevices.

1430 Why would the flame 'be blown outvjards (towards the hall) if a
candle be held at the top of the door ?

Because the air of the room being heated, and con-
sequently ratified, ascends, and (floating about the
upper part of the room) some of it escapes through the
crevice at the top of the door, producing a current of
air outwards (into the hall).

1431 Why would the flame be blown inwards (into the room) if the
candle be held at the bottom of the door ?

Because a partial vacuum is made at the bottom of
the room, as soon as the warm air of the room has
ascended to the ceiling or made its escape from the
room ; and the cold air from the hall ruslies under the
door to supply the void.

1433 What is meant by a partial vacuum being made at the bottom
of the room ?

It here signifies a place from which the air has been
taken / and a " partial vacuum" means a place from
which a part of the air has been taken away. Thus,
when the air near the floor ascends to the ceiling, a
partial vacuum is made near the floor.

1433 And how is the vacuum filled up again f

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

1434 Give me an illustration.

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
Jilled up by the water around.

1435 Show how this illustration applies.

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 the air
around.

1436 Why is a room (even without a fire) generally warmer than ifa

epsn air?

214

SCIENCE OF COMMON THINGS.

"Why smoke ascends the chimney.

What is the draught of a chimney ?

Because the air in a room is not subject to much
change, and soon partakes of the same temperature as
our bodies, when it no longer feels cold.

1437* Why do we generally feel colder out-of-doors than in-doorsf

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 por-
tion surrounds us, to absorb more heat.

1458 Why is there always a draught through the window crevices ?

Because 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 warm air up the chimney, etc.

1459 Why, when we kindle a fire in a stove or grate, does the smoke
ascend the chimney ?

When a fire is lighted to warm a room, the smoke
and other gaseous products of combustion, being lighter
than the air of the room, ascend, and soon fill the chim-
ney with a column of air lighter, bulk for bulk, than
a column of atmospheric air.

143O /s the column of light air in the chimney pressed up by a column
of equal size on the exterior of the chimney f

It is.

1431 What, then, is the draught of
a chimney f

It is the rate or speed with
which the column of cold air
outside the chimney pushes
up the column of warm air
inside the chimney, and this
draught will be strong and
effective just in the same
proportion as the column of
air in the chimney is kept
warm.

Fig. 47 represents a section of a
grate and chimney. C D represents
the light and warm column of air with-
in the chimney, and A B the cold and
heavy column of air outside the chim-

SCIENCE OF COMMON THINGS.

215

Use of chimneys.

Utility of long chimneys.

ney. The column A B being cold and heavy presses down, the column C
t) being light and warm rushes up, and the greater the difference between
the weight of these two columns, the greater will be the draught.

14353 IIow do chimneys quicken the ascent of hot air ?

By keeping a long column of it together. A column
of two feet high rises, or is pressed up, with twice as
much force as a column of one foot, and so in propor-
tion for all other lengths — just as two or more corks,
strung together and immersed in water, tend upwards
with proportionally more force than a single cork.

In a chimney where one foot in height of the column of hot air is one
or.r.ce lighter than the same bulk of external cold air, if the chimney be
one undred feet high, the air or smoke in it is propelled upwards with
a fore, of one hundred ounces.

143. To what is the draught of a chimney in all cases proportioned to f

With sufficient fire, to the length of the chimney.

1434 Why are the chimneys of large manufactories generally very
high ?

A long chimney causes a current
of air to pass through a fire very
rapidly, and at the same time very
uniformly. On these accounts, for the
fires of steam-engines, etc., long chim-
neys are preferred.

1435 When the temperature of the air in a room
and of the air outside are the same, will there be any
draught up the chimney ?

There will be no draught.

143 6 When there is no fire in stove or grate, and
the air of a room is warmer than the air outside, will
there be a circulation up and down the chimney?

In such cases there will generally bo
two currents, up and down the chim-
ney, especially if the doors and win-
dows of the room be tight. The warm
air of the room will ascend through the
chimney, and the cold air descend by
the side of it, two currents readily cir-
culating through one tube. The direc-
tion of the arrows, in Fig. 48, will show Fig. 48.

216 SCIENCE OF COMMON THINGS.

How to construct a chimney. Use of a cowl upon a chimney.

the lines of the current, descending the chimney and
circulating round the apartment.

143 7* Why does an apartment often smell disagreeably of soot in sum-
mer-time ?

Because the air in the chimney (being colder than
the air in the apartment) descends into the room, and
leaves a disagreeable smell of soot behind.

1438 How ought chimneys to be constructed?

A chimney should be constructed in such a way
that the flue or passage will gradually contract from the
bottom to the top, being widest at the bottom, and the
smallest at the top.

1439 Why is it expedient to construct a chimney in iliis manner f

At the base of the chimney, the hot column of air fills
the entire passage ; but as the hot air ascends it
gradually cools and contracts, occupying less space. If,
therefore, the chimney were of the same size all the
way up, the tendency would be, that the cold external
air would rush down to fill up the space left by the con-
traction of the hot column of air. This action would
still farther cool the hot air of the chimney and
diminish the draught.

14:40 Why will a long chimney smoke, unless the fire be pretty fierce f

Because the heat of the fire will not be sufncient to
rarefy all the air in the chimney.

1441 Why will the chimney smoke, unless the fire be fierce enough to
heat all the air in the chimney-flue f

Because the cold air (condensed in the upper part of
the flue) will sink from its own weight ; and sweep
the ascending smoke back into the room.

144S What is the use of a cowl upon a chimney-pot f

It acts as a screen, to prevent the wind from blowing
into the chimney.

1443 What harm would the wind do if it were to blow into a chim-
ney?

1. It would prevent the smoke from getting out ;
and

2. The cold air (introduced into the chimney by the

SCIENCE OF COMMON THINGS. 217

Use of a blower upon a grate. Hottest arid coolest portions of a room.

wind) would fall down the fiue, and drive the smoke
with it into the room.

1444 Why do some chimneys smoJce ?

Because fresh air is not admitted into a room as fast
as it is consigned by the fire ; in consequence of which
a current of air rushes down the chimney to supply the
deficiency, driving the smoke along with it.

1445 Why do Mowers, when placed before a grate, tend to kindle the
fire?

A blower is a sheet of iron that stops up the space
above the grate bars, and prevents any air from enter-
ing the chimney except that which passes through the
fuel and produces combustion. This soon causes the
column of air in the chimney to become heated, and a
draught of considerable force is speedily produced
through the fire. The increase of draught increases the
intensity of the lire.

1446 Which is the hottest part of a room ?

The upper part, near the ceiling. The warm air
being the lightest seeks the highest position.

1447 Which is the coolest part of a room f

The lowest part, near the floor. Cold air being dense
and heavy seeks the lowest position.

144S By which means is a room better ventilated, by opening the uppef
or the lower sash ?

A room is better ventilated by opening the upper
sash • because the hot vitiated air (which always as-
cends towards the ceiling) can escape more easily.

1449 What temperature is most proper for keeping an apartment in
a healthy and pleasant condition during the cold season f

From 65° to 70° F., with a free ventilation.

1450 How are houses and other buildings heated with hot air f

The fire is kindled in a furnace which is erected in
the cellar. This fire heats the air in contact with it in
the air-chainber, as it is called, and as heated air
always ascends, it is forced up into the different apart-
ments of the building.

218 SCIENCE OF COMMON THINGS.

What is smoke ? Open fireplaces 111 adapted for heating rooms.

1451 Which would prove the warmest upon a bed — a blanket, or an
oiled silk, or India-rubber air-tight covering f

The air-tight covering.

1453 Why do we not use oiled silk or India-rubber bed coverings in
the winter ?

Because they prevent ventilation, and, by shutting
in the insensible perspiration, soon produce dampness.

1453 What is smoke?

Small particles of carbon separated by combustion
from the fuel, but not consumed.

1454 Is there a circulation of the air through the bed coverings at
night?

Yes ; from every part of the bed-clothes immediately
over the person there is a constant outward oozing of
warm air, and an oozing inwards of cold air in lower
situations around.

1455 In what two ways is heat communicated to apartments by fires
kept in them ?

By radiation and immediate contact.

The first portion passes through the air in diverging lines with great
velocity. The second penetrates slowly through the substance of the
densest bodies. To enjoy the full effect of radiated heat, we mus,t be in
the presence or sight of the radiating object. To receive conducted heat,
we must be in contact, either directly or through some intervening me-
dium, with the body that imparts it.

1456 Does a person who sits by afire in the open air receive any heat
by conduction?

Very little; for the air which surrounds the fire
having nothing to confine it, ascends by its diminished
specific gravity as fast as it is warmed, and its place is
immediately supplied by strata of cold air from beneath.

1457 Will a person sitting beside a fire in the open air be exposed,
ipon the side of his body removed from the fire, to additional cold?

He will, because cold currents rush in from every
nde towards the fire.

1458 Why are open fireplaces ill adapted for the economical heating
")f apartments ?

In an open fireplace the air flows from the room to
the fire, becomes heated, and passes off directly into
the chimney, without having an opportunity of parting

SCIENCE OF COMMON THINGS. 219

Advantages of stoves over fireplaces. Disadvantages of stoves.

with its heat for any useful purpose. In addition to
this, a quantity of the air of the room, which has been
warmed by radiation, is uselessly carried away by the
draught.

1459 What are Vie advantages of a stove over an open fireplace ?

1. Being detached from the walls of the room, the
greater part of the heat produced by combustion is
saved. The radiated heat being thrown into the walls
of the stove, they become hot, and in turn radiate heat
on all sides to the room. The conducted heat is also
received by successive portions of the air of the room,
which pass in contact with the stove ;

2. The air being made to pass through the fuel, a
small supply is sufficient to keep up the combustion, so
that little need be taken out of the room ; and

3. The smoke, in passing off by a pipe, parts with
the greater part of its heat before it leaves the room.

1460 What are the disadvantages of stoves ?

Houses containing them are generally ill ventilated.
The air coming in contact with the hot metal surfaces
is rendered impure, which impurity is increased by the
burning of the dust and other substances which settle
upon the stove. The air is, in most cases, kept so dry
as to render it oppressive.

1461 Upon what principle are the common hot-air furnaces for warm-

A stove, having large radiating surfaces, is inclosed
in a chamber (generally of masonry). This chamber
is generally built with double walls, that it may be a
better non-conductor of heat. A current of air from
without is brought by a pipe or box, and delivered un-
der the stove. A part of this air is admitted to supply
the combustion ; the rest passes upwards in the cavity
between the hot stove and the walls of the brick cham-
ber, and, after becoming thoroughly heated, is con-
ducted through passages in which its lightness causes
it to ascend, and be delivered in any apartment of the
house.

220 SCIENCE OF COMMON THINGS.

Construction of furnaces. Combustion.

1463 In the construction and arrangement of a furnace for warming,
what two points are of special importance, so far as regards the economy of
fuel?

1. The perfect combustion of the fuel ; and

2. The best possible transmission of all the heat
formed, into the air that is to pass into the rooms of
the house.

1463 How is the first of these requisites obtained?

By having a good draught and a fire-box which is
broad and shallow, so that the coal shall form a thin
stratum ; by which arrangement the carbonic acid gas
will be freely formed, and pass off without a previous
production of an imperfectly burnt product.

1464 How is the second of these requisites attained ?

By providing a great quantity of surface in the form
of pipes, drums, or cylinders, through which the smoke
and hot gases must pass on their way to the chimney,
and to which their heat will be imparted, to be in turn
delivered to the cold and pure air of the rooms of the
house.

CIIAPTEE II.

COMBUSTION.

1465 What is combustion ?

Every species of combustion with which we are
familiarly acquainted is the rapid chemical union of the
oxygen of the air with a combustible body, attended
with the evolution of light and heat.

1466 flow may combustion, as we ordinarily see it, be regarded ?

It may be regarded as simply & process of oxidation.

1467* What do we mean by the term oxidation f

SCIENCE OF COMMON THINGS. 221

Matter not destroyed by combustion. Heat, how originated by combustion.

The combination of some substance with oxygen, — -
or the act of combining with oxygen.

1468 Js there not always an increase in weight during the combustion
of inflammable materials, rather than a loss f

The products of combustion always exceed the weight
of the original substance burned, by an amount equal
to the weight of the oxygen gas absorbed during the
combustion.

1469 What becomes of the oxidized products of combustion f

They for the most part combine with oxygen to form
gases and vapors. We apply to these products the
general term smoke.

147*0 What is an essential requisite to every process of combustion f

That there should be a free supply of air, and that
the products of combustion, or the smoke, should be
conducted off.

147*1 Why, when we burn a candle or a piece of wood in the air, does
there always seem to be a loss of matter f

Because the results of combustion in these cases are
either gases or vapors, the existence of which, not being
apparent to common observation, requires to be made
known by experiment.

Until nearly the close of the last century it was generally believed and
taught, that when a body was burned, something went out of it, — that it
lost weight. Lavoisier, a celebrated French chemist, overthrew this doc-
trine by burning a substance in connexion with an arrangement whereby
all the results or products of the combustion were saved. These on
being weighed showed a gain rather than a loss, the amount being equal
to the quantity of oxygen which had been absorbed from the air during
the process of combustion, by the burning substance itself.

147*3 How is heat evolved by combustion ?

By chemical action. As latent heat is liberated,
when water is poured upon lime, by chemical action,
so latent heat is liberated in combustion by chemical
action also.

147*3 What chemical action takes place in combustion f

The elements of the fuel combine with the oxygen of
the air.

147*4 What is the temperature required to induce the combination of
oxygen with any substance called ?

10*

222 SCIENCE OF COMMON THINGS.

The burning point — rust — flame — fire.

The burning point.

14*75 Is this point different for different substances f

It is ,' thus phosphorus will combine slowly at 77° F.,
but does not enter into rapid combustion until the tem-
perature is raised to 104° F. Charcoal burns slowly
below a red heat.

14*70 Is the quantity of heat given out, when a body combines slowly
with oxygen, the same as when it combines rapidly with it, the relative
quantities of the combining bodies remaining the same in both cases ?

The total quantity of heat given out is the same,
whether the combustion takes place slowly or quickly ;
but in the case of slow combustion, the heat is much
less intense, and often becomes insensible, because
during the long time occupied in combination the
greater part is carried away by conduction.

147"7 Is the quantity of light given out the same, whether the combus-
tion be rapid or slow ?

No : the quantity of light given out during the com-
bination of oxygen with a given quantity of a com-
bustible body varies greatly, according to the rapidity
of the combustion.

1478 What is rust f

The oxidation of iron in moist air.

14*79 When iron rusts in the air is heat given outf

Certainly ; but the process of rusting takes place so
slowly that the amount of heat given out at any one
time is imperceptible to our senses.

148 O What is flame f

Burning gas or vapor.

1481 What is fire?

Heat and light produced by the combustion of in-
flammable substances.

1483 What does the brightness or illuminating power of flame depend
fnf

It depends on the degree of heat in part, but mainly
on the presence or absence of solid particles in the
flame, which may act as radiating points.

1483 Are there solid particles in every illuminating flume t

SCIENCE OF COMMON THINGS. 223

W hen will a lamp smoke ? Benefit of glass chimney on lamp.

There are / and if we present a cold surface to the
flame, they become deposited on it in the form of soot.

1484 When we Say a lamp smokes, what do we mean *

That the solid parts of the flame are passing off in an
unconsumed state,

1485 When the flame burns properly, why does the smoke cease to be
emitted f

Because the solid particles of carbon constituting the
smoke are burned up, or are completely united with
oxygen, forming an invisible gas — carbonic acid.

1480 From what source is the carbon, constituting the illuminating par-
ticles in tiie one case and the soot in the other, derived?

It was originally a part of the burning or combustible
body,

148 7 When will a flame smoke f

When the supply of oxygen received from the air ig
insufficient to consume all the carbon which the heat
separates from the combustible body in the form of
soot.

1488 What benefit arises from surrounding aflame with a glass cylin-
der of chimney open at the bottom and top ?

When a flame burns without a chimney, the hot air
radiates in all directions ; but when it is surrounded
by a chimney, the hot air is confined within the walls
of the cylinder: consequently, the hot air will issue
rapidly from the top of the chimney, and cold air will-
enter equally fast at the bottom to replace it. In this
Way a constant current of fresh air is kept up through
the centre of the flame, causing a more perfect com-
bustion, and a brighter and stronger flame.

148Q Why in solar and astral lamps do we use a hollow or circular
wick?

In order that a current of air may rusn up through the
interior surface of the flame as well as aiong the exterior.

1490 What is fuel?

Any substance which serves as aliment or food for
'(ire. In ordinary language we mean by fuel the pecu-
liar substance of plants, or the products resulting from

224 SCIENCE OF COMMON THINGS.

"What is fuel — carbon — charcoal — soot ?

their decomposition, designated under the various names
of wood, peat, and coal.

1401 What are the constituents of wood?

Carbon, hydrogen, and oxygen, combined together,
make up the chief part of its bulk ; all wood also con-
tains water.

1403 What is hydrogen?

It is an inflammable gas, one of the elements of which
water is composed. The gas used in our streets is in
great part hydrogen. Hydrogen, when pure, has neither
taste nor odor.

1403 What are the peculiar characteristics of hydrogen gast

1. It is the lightest of all known substances ;

2. It will burn immediately on being ignited ; and

3. A lighted candle (immersed in this gas) will be
instantly extinguished.

1404 What is carbon f

A solid elementary substance, generally of a dark or
black color, well known under the forms of charcoal,
lampblack, coke, etc.

1405 What is charcoal?

"Wood which has been exposed to heat until it has
been deprived of all its gases and volatile parts.

1406 Can all animal and vegetable substances, by partial burning, be
converted into coal f

They can.

1407* In the charring of animal and vegetable substances, do we gene-
rate charcoal, or did it exist there before %

The carbon or coal existed there previously, though
in chemical combination with other bodies, which are
principally driven off by heat, as is apparent from the
fact that a charred body weighs much less than the
original substance ; animal and vegetable substances
consist, therefore, in part of coal.

1408 Wliatissoot?

Coal in a state of minute division, which is deposited
from the flame of bituminous or pit-coal, wood, oil,

SCIENCE OF COMMON THINGS. 225

How charcoal is prepared. "What is mineral coal.

resin, etc., when, during the combustion of these sub-
stances, there is an insufficient supply of air.

1499 How is charcoal prepared f

By charring wood in mounds or pits, covered with
turf or soil in such a way as to exclude in a great degree
the admission of air, and thus prevent complete com-
bustion.

1500 What is mineral or hard coal?

Coal is the product of a vast accumulation of vege-
table matter, deposited during a remote geological
period in beds or layers in the earth, and which, by the
action of pressure, heat, and other causes, has become
consolidated and hardened into its present form.

15 Ol How does the coal occur in the earth ?

In strata or layers, varying from a few inches to
several feet in thickness, inclosed between other strata
of limestone, clay, or iron ore.

15OS In what manner is it supposed that this great accumulation of
vegetable, material took place 1

The vegetable matter of which coal is composed is
supposed, by some, to have grown in immense swamps
or marshes. By others, the vegetable matter is sup-
posed to have been swept down ~by rivers, and deposited
at their mouths or estuaries in immense beds.

1503 Are such accumulations of vegetable matter, through the agency
of rivers, going on at the present day ?

At the present time the Red River of Texas is abso-
lutely choked up with a raft composed of trunks of
trees and other vegetable matter, many miles in extent,
and of unknown thickness. Other rivers of the South-
western United States bring down vegetable materials
annually, sufficient for the production of vast beds of
coal.

1504 How do we know that coal is all vegetable matter ?

Because in every coal mine we find the leaves,
trunks, and fruits of trees in immense numbers, many
of them in a most perfect state of preservation ; so
much eo, that the botany of the coal period can be

226 SCIENCE OF COMMON THINGS.

Difference between anthracite and bituminous coal.

studied with nearly as great ease and facility as the
botany of any given section of the present surface of
the earth.

1505 What occasions the difference between bituminous and anthracite
coal?

Bituminous coal contains a large amount of bitumen
and other pitchy volatile substances which readily
ignite and burn with smoke and flame. In anthracite
coal these substances have been driven out ; it is there-
fore a purer variety of carbon, and burns without smoke
or flame.

1506 Are the deposits of coal of very great extent f

They are ; mineral coal exists in all the great divi-
sions of the earth. The largest deposits of coal, how-
ever, occur, in the United States, in Pennsylvania and
the Yalley of the Mississippi.

1507 Why will not stones do for fuel as well as coal f

Because they contain no hydrogen, and little or no
carbon.

1508 Of what are oil, tallow, and wax composed t

Principally of carbon and hydrogen gas. The solid
part is carbon, the volatile part is hydrogen gas.

1509 At what period of the year does wood contain the greatest amount
of water ?

In the spring and summer, when the sap flows freely
and the influence of vegetation is the greatest.

1510 Why is wood generally cut in the winter season f

Because at that season there is but little sap in the
tissues, and the wrood is drier than at any other period.

1511 Why is it difficult to inflame coal or hard wood with the blaze of
a match f

Coal and hard wood on account of their density are
good conductors, and carry off the heat of the kindling
substance, so as to extinguish it, before they themselves
become raised to the temperature necessary for their
combustion.

1513 Why is it easy to ignite light fuel with a smatt blaze f

Light fuel being a slow conductor of heat kindles

SCIENCE OF COMMON THINGS. 227

Amount of water in green and dry wood. Weight of wood.

easily, and, from the admixture of atmospheric air in its
pores and crevices, burns out rapidly, producing a com-
paratively temporary, though often strong heat.

1513 In recently cut wood, what proportion of its weight is water ?

From one-fifth to one-half.

1514 After wood has been dried in the air for ten or twelve months,
how much water does it usually contain ?

From twenty to twenty-Jive per cent.

1515 Why do we call some woods hard, and others soft f

This distinction is grounded upon the facility with
which they are worked, and upon their power of pro-
ducing heat. Hard woods, as the oak, beech, wTafnut,
elm, and alder, contain in the same bulk more solid
fibre, and their vessels are narrower and more closely
packed than those of the softer kinds, such as pine,
larch, chestnut, etc.

1516 How many pounds avoirdupois are there in a cord of dry, hard
wood?

From forty-four hundred pounds in a cord of dry
hickory, to twenty-six hundred in a cord of dry, soft
maple.

151*7 What is the most valuable wood for fuel? ,

The varieties of hickory ; after that, in order, the
oak, the apple-tree, the white-ash, the dog-wood, and the
leech.

1518 What woods give out the least heat in burning f

The white-pine, white-birch, and poplar.

1519 Why is it unprofitable to burn green wood or wet coal f

It is a well-known law of heat that the evaporation
of liquids, or their conversion into steam, consumes or
renders latent a great amount of caloric. When green
wood or wet coal are added to the fire, they abstract
from it by degrees a sufficient amount of heat to con-
vert their, own" sap or moisture into steam before they
are capable of being burnt. As long as any consider-
able part of this fluid remains unevaporated, the com-
bustion goes on slowly, the fire is dull, and the heat
feeble.

228 SCIENCE OF COMMON THINGS.

Unprofitable to burn green wood. Chemical changes produced by combustion.

1530 Js there any truth in the remark often made " that it is economy
to burn green wood because it is more durable, and therefore in the end more
cheap ?"

No j it is true that the consumption of green wood
is less rapid than dry, but to produce a given amount
of heat, a far greater amount of fuel must be con-
sumed.

1531 Jn ordinary fuel, what three elements enter into the process of
combustion f

Hydrogen gas, carbon., and oxygen gas; the two
former in the fuel, and the latter principally in the air
which surrounds the fuel.

1533 What chemical changes in air and fuel are produced by com-
bustion ?

1. Some of the oxygen of the air, combining with the
hydrogen of the fuel, forms vapor of water ; and

2. Some of the oxygen of the air, combining with the
carbon of the fuel, forms carbonic acid gas.

1523 Why is there more smoke when fresh fuel is added than when the
fuel is red hot ?

Because more carbon and volatile matters are sepa-
rated from the fuel than can be reduced by combustion /
and the surplus flies off in smoke.

1534 Why is there so little smoke with a red-hot fir ef

Because the entire surface of the coals is in a state of
combustion ; and, as very little of the escaping carbon
remains unconsumed, there is but little smoke.

1535 When a coal fire is lighted, why are paper and wood laid at the
bottom, against the grate f

That the flame may ascend through the fuel to heat
it. If the fire were kindled from the top, the flame
would not come in contact with the fuel placed below.

1536 Why do we cover up afire with ashes or cinders to preserve it f

The covering of ashes or cinders protects the fire
from the action of the air, and when fuel is deprived of
air it ceases to burn.

1537 Why does afire burn so fiercely in windy weather ?

Because the air is rapidly changed, and affords
plentiful nourishment to the fire.

SCIENCE OF COMMON THINGS. 229

"Why water extinguishes a fire. Cause of the heat of a dunghill.

15SS Why does a pair of bellows aid in kindling afire ?

Because it drives the air more rapidly to theft-re, and
the plentiful supply of oxygen soon makes the tire burn
intensely.

15S9 Why does water extinguish a fire 1

1. Because the water forms a coating over the fuel,
which keeps it from the air ; and

2. The conversion of water into steam draws off the
heat of the burning fuel.

1530 Why does a Uast of air from a pair of bellows often extinguish a
red-hot coal of anthracite ?

Because the cold air absorbs the heat of the coal so
quickly that it extinguishes it.

1531 Why can you not light a candle or lamp with a match so long as
the sulphur on the end of it is burning f

The chemical reason for this well known fact is, that
the sulphurous acid, formed by combustion of sulphur
in the air, surrounds the wick, and abstracts the oxygen
from the air, by passing to a higher state of oxidation ;
and this heavy vapor hangs about the wick and excludes
the air.

153S Cannot wood be made to blaze without actual contact with fire?

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.

1533 Why will wood blaze, even if it does not touch the fire ?

Because the heat of the fire drives out the inflam-
mable gas of the wood, which gas is ignited by contact
with the red-hot coals.

1534 What causes the heat of fire 1

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.

1535 Whence does the heal of a dunghill arise f

As the strawy etc., of the dunghill decays, it under-

230 SCIENCE OF COMMON THINGS.

Benefit of stirring a dull fire. How to extinguish a chimney on fire.

goes fermentation, which produces carbonic acid gas /
and heat is evolved through a species of combustion.

153G On what does the intensity of fire depend ?

The intensity of fire is always in proportion to the
quantity of oxygen with which it is supplied.

1537 Why does stirring a dull fire serve to quicken it ?

Because it breaks up the compacted cinders and
coals, making a passage for the air into the very heart
of the fire.

1538 Why is the fiame of a candle extinguished when bloion by the
breath, and not made more intense, like a fire f

Because the flame of a candle is confined to a very
small wick, from which it is severed by the breath, and
(being unsupported) must go out.

1539 When a chimney with an open fireplace gets on fire, and burns so
as to endanger the house, how may it at once be extinguished?

By throwing a quantity of brimstone or sulphur into
the fire, and closing up the fireplace with a fireboard or
screen. The sulphurous acid soon fills the chimney, and
taking up all the oxygen from the contained air, ex-
tinguishes the fire. Even the fire, after it has extended
into the woodwork of the house, may be extinguished
by this simple method.

1540 Fire in a chimney may be also extinguished by closing the top of
thefiue with a damper : how does this extinguish the fire f

It cuts off the draught, and the carbonic acid gene-
rated by the combustion soon puts an end to the fire.

1541 What is meant by spontaneous combustion ?

Combustion produced without contact with fire or
flame.

1543 Give me an example of spontaneous combustion.

Oiled cotton and rags imbued with any drying oil,
when packed in mass in a barrel, take fire, after a time,
at ordinary temperatures. Mixed lampblack and lin-
seed-oil cake take fire at ordinary temperatures, if the
lampblack is in excess, or a portion of it is dry.

1543 What is generally the cause of spontaneous combustion ?

The absorption of oxygen. Porous bodies, that are

SCIENCE OF COMMON THINGS. 231

Why all flames are not equally luminous. Cause of the color of a fire.

at the same time bad conductors of heat, by the
absorption of oxygen may become red hot, and finally
burst into a flame.

1544 Is pine charcoal capable of taking fire at an extremely low tem-
perature ?

Porous bodies, like pine charcoal, when perfectly
dry, absorb oxygen rapidly from the air, and take fire
at a temperature below 212° Fahrenheit, or the boil-
ing-point of water.

This has been proved by actual experiment, a piece of light pine char-
coal taking fire on a surface of sheet iron, heated below the boiling-point
of water.

1545 Why are not all flames equally luminous t

In all flames, the light is mainly emitted from mi-
nute particles of matter, intensely heated, and floating
in the burning gas or vapor ; and hence a flame con-
taining few such particles, will emit but a feeble light,
even though its temperature is very great.

1546 Upon what fact does the production of artificial light depend ?

Upon the fact that at certain high temperatures all
matter becomes luminous.

3-547 In order that we may profitably use a combustible body for illu-
minating purposes, what is required of the products of the combustion f

That they should be volatile, and freely escape from
the immediate vicinity of the illuminating centre.

1548 The product of all the ordinary forms of combustion is a gas —
carbonic acid : what would have been the result if the product of every com-
bustion had been a permanent solid ?

The world would have been buried beneath its own
ashes.

1549 Why is the flame of an ordinary fire ydloto f

Because the heat is not sufficient to render the car-
bon white hot. Increase the intensity of combustion,
arid the color of the burning bodies or the flames rises
from red to yellow, and from yellow to white.

1550 A candle burns when lighted : explain how this is 1

The heat of the lighted wick decomposes the tallow
into its elementary constituents, hydrogen and carbon.
The hydrogen is nrst consumed as a gas by itself with

232 SCIENCE OF COMMON THINGS.

Phenomena of combustion in the flame of a candle.

an almost imperceptible light, but with a powerful
evolution of heat; this causes the carbon, simultane-
ously eliminated, to become incandescent and conse-
quently luminous.

1551 As more carbon is successively -eliminated, what becomes of it ?

The moment the incandescent floating carbon comes
to the edge of the flame, it finds the oxygen of the air,
unites with it, and becomes converted into the invisible
gas, carbonic acid, while its place is occupied immedi-
ately by another portion of solid carbon.

1553 What if there is not sufficient oxygen to consume the carbon 1

It then passes off as soot, and we say the candle

smokes.

1553 Where is the tallow or wax of a candle decomposed f

In the wick. The melted tallow or wax rises up the
wick by capillary attraction, and is rapidly decom-
posed by the heat of the flame.

1554 Of what three parts does the flame of every lamp or
candle consist ?

The flame of every lamp or candle consists
of three cones. The innermost cone (a, Fig.
49) consists of gaseous matter produced by the
decomposition of the tallow ; this is at a tem-
perature below redness. Around it is the lu-
minous cone (b\ consisting of burning hydro-
gen, in which the particles of carbon float at a
white heat ; and on the very outside (c), a
thin, hardly-perceptible veil in which carbon
is burning. The veil is of a blue color, most
plainly seen at the bottom of the flame.

1555 Which is the hottest part of thejlame f

The pale Hue flame ; this marks the point where
the combination of the oxygen, supplied from without,
with the combustible matter evolved from the interior
takes place.

155G Why does thejlame of a candle point upwards ?

Because it heats the surrounding air, which

SCIENCE OF COMMON THINGS. 233

Use of a hole in the top of a lamp. Use of ground glass lamp shades.

hot) rapidly ascends, driving the flame upwards at the
same time.

1557* Why does the hand, held above a candle, suffer more from heat
than when it is placed below the flame, or on one side of it t

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.

1553 Why is not the wick of a candle consumed f

The wick, although it is blackened by the heat, is
prevented from consuming, merely because it is sur-
rounded by inflammable vapor, so that the oxygen of
the atmosphere has no access to it.

1559 Why do att closed lamps require a small hole in the top f

To admit the air • otherwise the pressure of the
atmosphere will prevent the oil from ascending the
wick ; if the hole be obstructed, the oil will sometimes
overflow from the expansion of the confined air.

1560 Why do we use ground-glass globes for lamp shades ?

To relieve the eye from the glare of light. Ground-
glass shades have the effect to disperse the rays by the
numerous reflections and refractions wThich they occa-
sion ; until at length the light issues from all parts of
their surface, and it appears as though the glass itself
were the luminous body.

CHAPTER III.

RESPIRATION AND NUTRITION.
15 SI What is respiration?

The act of inhaling air into the lungs, and again
expelling it.

234: SCIENCE OF COMMON THINGS.

Combustion a form of respiration. Construction of the lungs.

1562 What is the object of drawing air into the lungs and again expel-
ling it ?

To oxidize the carbon and hydrogen of the blood.

1563 We receive into the lungs oxygen through the medium of the atmo-
sphere, mingled with nitrogen : what do we expel from the lungs f

The nitrogen returns unaltered ; the oxygen unites
with the carbon of the blood to form a gas — carbonic
acid, and with hydrogen to form the vapor of water.

1564 Are not these the same products of every ordinary form of com-
bustion f

They are ; therefore respiration or breathing is but
a form of combustion.

1565 It is estimated that a man receives into his system about eight
hundred pounds of oxygen from the atmosphere in a year, but his weight at
the end of the year has increased but little, or not at all : what becomes of all
this oxygen ?

No part of it remains in the 'body, but is given out
again, combined with carbon and hydrogen.

1566 How much carbon passes out of the system of an adult man by
the agency of respiration daily ?

About fifteen ounces.

1567 How is this great abstraction of material from the body made up T

By the food which we eat.

1568 What are the lungs ?

Lungs are made up of bloodvessels imbedded in a
fleshy substance which we denominate cellular tissue,
and expanded over the walls of a series of chambers or
cavities.

They are so situated in the thorax (or chest) that the air must enter
into them whenever the cavities of the thorax are enlarged. The process
of breathing is performed thus : When we INHALE, the thorax (or chest)
is expanded ; in consequence of which a vacuum is formed round the
lungs, and the heavy external air instantly enters (through the mouth and
throat) to supply this vacuum.

When we EXHALE, the thorax contracts again; in consequence of
which it can no longer contain the same quantity of air as it did before,
and some of it is necessarily expelled. When this expulsion of air takes
place, the lungs and muscular fibres of the windpipe and gullet contract in
order to assist the process.

1569 To what may the mechanism of the lungs in respiration be con*
pared ?

To the action of a bellows.

SCIENCE OF COMMON THINGS. 235

Necessity of cleanliness. Color of the blood.

157*0 Do we respire or absorb and expel oxygen in any oilier way than,
through the lungs ?

We breathe also in a degree through the pores of
the skin, absorbing oxygen and expelling carbonic acid.

157*1 Do extensive burns on the surface of tht body frequently produce
diseases of the lungs f

They do.

157*3 Why should extensive burns on the surface of the, body tend to
produce diseases of the lungs ?

While in a condition of health, the skin tranquilly
aids the lungs in the expulsion of carbonic acid from
the body ; but the portion of the skin which has been
scorched by an extensive burn, no longer being able to
perform that function, the lungs are obliged to assume
an extra duty, and suffer as a consequence of their
exertion.

157*3 //j by neglect of washing, we suffer the sJcin to become covered with
impurities, do we not disturb the healthy action of the system f

We do ; there is no better-established law of health,
than that the surface of the whole body should be kept
clean and free from all impurities.

157*4 If the carbon taken from the system through the agency of the
lungs be not t estored, what is the consequence ?

Starvation ensues.

157*5 How does the oxygen we inhale mingle with the blood?

The oxygen of the air is absorbed in the lungs by the
blood, and imparts to it a bright red color.

157*6 How does oxygen convert the color of blood into a bright red f

The coloring matter of the blood is formed by very
minute globules floating in it. The oxygen uniting
with these globules changes their color, to a bright red.
The blood contains iron, and this metal is supposed to
play an important part in the coloration of the blood.

157*7* What color is the blood before it is oxidized in the lungs ?

A dark purple ; the oxygen turns it to a bright red*

157* S Do plants respire as well as animals t

They do; and their leaves may be regarded as per-
forming for them similar offices as the lungs of animals.
They are the breathing organs of plants.

SCIENCE OF COMMON THINGS.

How water plants purify the water. Cause of animal beat.

1579 Js there any difference between the respiration of plants and
animals f

The process of respiration in plants is exactly the
reverse of that in animals. Animals absorb oxygen, and
give out carlo nic acid ; plants, on the contrary, absorb
carbonic acid, and return oxygen.

15SO It is estimated that the population of London adds to the atmo-
sphere daily. 4, 500,000 pounds of carbonic acid: how is this immense quan-
tity of deleterious gas removed from the atmosphere f

Principally through the agency of plants, which
absorb it.

1581 Do water-plants purify and free water from carbonic acid in the
same manner that land-plants purify the atmosphere ?

The respiration of fishes produces carbonic acid, and
anless this is removed from the water, animal life will
cease to exist in it. Water-plants absorb the carbonic
acid from the water, and restore the oxygen.

1583 During bright weather, the leaves of water-plants, it will be no-
ticed, are covered with little bubbks : what are these bubbles 1

Oxygen gas, liberated by the organs of the plant.

1583 It is good policy, in fountains and reservoirs of water, to free
them wholly from the presence of vegetable and animal organisms ?

It is not : they are both dependent on one another,
and the joint action of the two serves to keep the water
pure and wholesome.

1584 What is the cause of animal heat?

The oxygen of the atmosphere, received into the blood
in the lungs, and circulated throughout every part of
the animal body, acting upon the elements of the food,
is the chief source of animal heat.

1585 Why does oxygen received into the blood produce heat ?

Through the medium of the capillary vessels oxygen
absorbed from the atmosphere unites with carbon and
hydrogen. This union is a species of combustion, and
produces heat in the same manner as when oxygen
unites with fuel in an ordinary fire.

1586 What are the capillary vessels f

Minute bloodvessels or tubes as small as hairs run-

SCIENCE OF COMMON THINGS. 237

Why no heat In the hair. Two kinds of blood, venous and arterial.

ning all over the body ; they are called capillary from
the Latin word capillaris, " like a hair."

1537* Do these capillary vessels run all over the human body f

Yes. Whenever Hood flows from a wound, some
vein or vessel must be divided ; and as you can bring
blood from any part of the body by a very slight
wound, these little vessels must run through every part
of the human frame.

1588 How do hydrogen gas and carbon get into these very small
vessels ?

The food we eat is converted into blood, and blood
contains both hydrogen and carbon.

1580 Does this combustion, and the consequent production of animal
heat, take place in every part of the body ?

In the animal body, heat is produced only in those
parts to which arterial Hood, and with it the oxygen
absorbed in respiration, is conveyed.

1590 Why is there no heat developed in hair, wool, andfeaffiers f

Because they receive no arterial Hood, and therefore
in them no heat is developed.

1591 What two kinds of blood are tliere in the animal body ?

Arterial Hood and venous Hood.

159 S What is the difference between the two?

The arterial blood going from the lungs conveys the
oxygen which it has absorbed in the lungs to the capil-
lary vessels. In these the combustion takes place, and
the color of the blood changes from a bright to a dark
red color.

1593 What becomes of the blood after it has given up its oxygen to the
hydrogen and carbon in the capillary vessels f

It enters the veins, carrying with it the products of
combustion. The venous blood passes to the lungs,
throws off the products of combustion, absorbs more
oxygen, becomes converted into arterial blood, with
a renewal of color, and is again returned into the
system.

1594 What becomes of the carbonic acid gas formed in the human
blood ?

238 SCIENCE OF COMMON (THINGS.

Why a dead body is cold. "Why we perspire.

The lungs throw off almost all of it into the air, by
the act of respiration.

1595 Does the heat of the human body arise from the same cause as
the heat of fire ?

Yes, precisely. The carbon of the blood combines
with the oxygen of the air inhaled, and produces car-
bonic acid gas, which action developes heat.

; 1590 If animal heat is produced by combustion, why does not the
human body burn up like a coal or candle ?

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.

1597 If every bone, muscle, nerve, and organ is thus consumed by com-
bustion, why is not the body entirely consumed?

It would be so, unless the parts destroyed were per-
petually 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.

1598 What is the principal difference between the combustion of a fire
or lamp, and that of the human body ?

In the human body, the combustion is effected at a
much lower temperature, and is carried on more slowly,
than it is in a lamp or fire.

1599 Why is a dead body cold?

Because air is no longer conveyed to the lungs after
respiration has ceased ; and therefore animal heat is
no longer generated by combustion.

1600 Why do we perspire when very hot ?

The pores of the body are like the safety-valves of a
steam-engine ; when the heat of the body is very great,
some of the combustible matter of the blood is thrown
off in perspiration, and the heat of the body is thereby
reduced.

1601 Why does exercise make us warm ?

Because we inhale air more rapidly when we exer-
cise, and cause the blood to pass more rapidly through
the lungs in contact with it.

SCIENCE OF COMMON THINGS. 2S9

Starvation and its effects. Food the fuel of the body.

16OS Why does inhaling air rapidly make the body feel warm?

Because more oxygen is introduced into the body ;
in consequence of which the combustion of the blood is
more rapid, the blood itself more heated, and every
part of the body is made warmer.

16O3 When a man is starved what part of the body goes first f

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.

1QO4 Why does a man shrink when starved f

Because the capillary fires feed upon the human
body when they are not supplied with food-fuel. A
starved man shrinks just as a fire does when it is not
supplied with fuel.

1BO5 What is fuel of the body f

Food is the fuel of the ~body. The carbon of the
food, mixed with the oxygen of the air, evolves heat
in the same way that a fire or candle does.

16O0 Why does hard work produce hunger f

Because it produces quicker respiration ; by^ which
means a larger amount of oxygen is introduced into the
lungs, and the capillary combustion increased. Hun-
ger is the notice (given by our body) to remind us that
our food-fuel must be replenished.

16O7" Why do persons feel lazy and averse to exercise when they are
half-starved or ill fed f

Because desire for muscular action ceases when the
body is not supplied with nutritious food.

ISO 8 Why do we like strong meat and greasy food when the weather
is very cold ?

Because strong meat and grease contain large pro-
portions of carbon and hydrogen, which (when burned
in the blood) produce a larger amount of heat than any
other kind of food.

1SO0 Why are the Esquimaux so passionately fond of train oil and
whale blubber f

Because oil and blubber contain large quantities of
carbon and hydrogen, which are exceedingly combus-

240 SCIENCE OF COMMON THINGS.

Activity disagreeable in warm weather.

tible ; and as these people live in climates of intense
cold, the heat of their bodies is increased by the greasy
nature of their food.

1610 Why do we feel lazy and averse to activity in very hot weather 1

Because muscular activity inweases the heat of our
body by quickening respiration, and lessens our desire
for active exertion.

1611 How much more carbon do we throw off from the system by respi-
ration in winter than in summer f

Full one-eighth more.

SCIENCE OF COMMON THINGS. 241

What is light ? Light possesses no weight.

PAET VII.

LIGHT, AND HOW WE SEE.

CIIAPTEE I.

NATURE AND LAWS OF LIGHT.

ISIS Through what agency alone are we enabled to enjoy the sense of
sight f

Through the agency of light.

1613 What is light?

Light is now believed to be caused by the agitation,
vibration, or undulation of an elastic fluid which is sup-
posed to occupy and pervade all space. "We call this
supposed fluid ether, and its undulations or vibrations,
reaching the eye, affect the optic nerve, and produce
the sensation which we call light.

1614 What analogy is there between the eye and the ear f

The vibrations or undulations of the ether pass along
the space intervening between the visible object and
the eye in the same manner that the undulations of the
air, produced by a sounding body, pass through the
air between this body and the ear.

1615 If we collect a large quantity of light in one point by means of a
glass, and throw it upon the most sensitive balance, does it indicate any per-
ceptible weight f

It does not, in the slightest degree.

1616 What are the chief sources of light?

The sun, the stars, ftre or combustion, electricity, and
phosphorescence.

1617 With what velocity does light move through space 1

24:2 SCIENCE OF COMMON THINGS.

Velocity of light Why some surfaces are brilliant and others dull.

With a velocity of one hundred and ninety-two thou-
sand miles in a second of time.

1618 Does all light travel equally fast?

Yes ; the light of the sun, the light of a candle, or
the light from houses, trees, and fields.

1619 How long a time does it require for light to pass from the sun to
the earth f

Eight minutes and thirteen seconds.

102 O How much time is required for a ray of light to traverse the
space intervening between the nearest fixed stars and the earth f

More than three years ; and from the farthest nebulae
hundreds of years will be required.

1621 What, therefore, would be the consequence if one oj the remote
fixed stars were to-day " blotted from the heavens?"

Several generations of the earth would pass away
before the obliteration could be known to man.

1622 In wJiat manner do the moon and the planets give light f

They shine only by means of the surfs light, which
is reflected from their surfaces.

1623 Where does the light of houses, trees, and fields come from?

The light of the sun (or of some artificial light) is re-
flected from their surfaces.

1624 Why are some surfaces brilliant (like glass and steel) and others
dull, like lead ?

Those surfaces which reflect the most light are the
most brilliant / and those which absorb light are dull.

1625 How does the velocity of light compare with the speed of a loco-
motive ?

Light passes from the sun to the earth in about eight
minutes ; a locomotive engine, travelling at the rate
of a mile in a minute, would require upwards of one
hundred and eighty years to accomplish the same
journey.

1626 How does the light of the full moon compare with that of the sun?

It is estimated to be three hundred thousand times
weaker than sunlight.

1627 The velocity of light is demonstrated by observations on the
satellites of Jupiter. Witt you explain how this can be proved?

SCIENCE OF COMMON THINGS. 24:3

Velocity of light determined from observations on Jupiter's satellites.

The earth revolves around the sun in an orbit of
which the sun is the centre. We are able to calculate
the exact time when an observer standing in the centre
of the earth's orbit, — that is, in the sun, would see an
eclipse of Jupiter's satellite ; but as the earth moves
round the sun in its orbit, it is brought at one time
ninety-five million of miles nearer Jupiter than the sun
is, and at another time it is carried ninety-five millions
of miles further off. Now, when the earth is nearest
to Jupiter, the eclipse takes place eight minutes in
advance of the calculated time, and when it is ninety-
five millions of miles farther off, the eclipse occurs eight
minutes later than the calculated time. This delay is
occasioned by the fact, that in the one case the light
coming from the satellite to the earth has to traverse a
much greater distance than in the other ; and if the
light requires eight minutes, or 480 seconds, to move
over 95,000,000 of miles, it will require one second to
move over 197,000 miles, or, with more exact data,
192.000 miles in one second.

Fig. 50.

The explanation above given will be made clear by reference to the
following diagram, Fig. 50. S represents the sun, a b the orbit of the
earth, and T T' the position of the earth at different and opposite points
of its orbit. J represents Jupiter, and E, its satellite, about to be eclipsed
by passing within the shadow of the planet. Now the time of the com-
mencement or termination of an eclipse of the satellite, as stated from
calculation in tables, is the instant at which the satellite would appear to
enter or emerge from the shadow, if it could be seen by an observer from
the sun, S. If the transmission of light were instantaneous, it is obvious
that the light coming from Jupiter's satellite, E, would be seen at the
same moment at the points T^ Sand T'. But repeated observation shows

244 SCIENCE OF COMMON THINGS.

How a multitude of persons see the same object. Shadows.

that the eclipse takes place eight minutes earlier than the calculated
period when the earth is in the nearest point of its orbit, as at T, and
eight minutes later when she is in the opposite part of her orbit, as at 7",
the difference in the distance of these two points from Jubiter being
190,000,000, of miles.

1638 Why can a thousand persons see the same object at Hie same
time?

Because it throws off from its surface an infinite
number of rays in all directions ; and one person sees
one portion of these rays, and another person another.

16J39 Why can we not see the stars in the day-time f

Because the light of the sun is so powerful that it
eclipses the feeble light of the stars ; in consequence
of whicli they are invisible by day.

1Q3O In what manner is light propagated f

In right lines from every luminous point, every such
line being called a ray of light.

1631 Wliat do we mean by a pencil of
light?

A collection of radiating lines
or rays, as seen in Fig. 51.

163S What is darkness?

The absence of light.

1633 What is a shadow?

A shadow is the name given to the comparative
darkness of places or objects, which are prevented by
intervening things from receiving the direct rays of
some luminous body shining on the objects around.

1634 Why cannot we see through a crooked tube as well as through a
straight one ?

Because light moves only in straight lines.

1635 What is the philosophy of taking aim with a gun or arrow ?

In taking aim with a gun or arrow, we proceed upon
the supposition that light moves in straight lines, and
try to make the projectile go to the desired object as
nearly as possible by the path along which the lig/it
comes from the object to the eye.

1636 Why does a carpenter look along the edge of a plank to see if it
is straight ?

SCIENCE OF COMMON THINGS. 245

Mirrors. Reflection of light. Incidence and reflection.

If the edge be straight and uniform, the light from
all points of the edge will come to the eye regularly
and uniformly ; if irregularities, however, exist, they
will cause the light to be irregular, and the eye at
once notices the confusion and the point which occa-
sions it.

37* What is a mirror f

Any substance reflecting light. The term is gene-
rally applied to glass covered on the back with quiet
silver.

1038 When liglit falls upon a body, in what three ways may it dispose
of itself?

It may be reflected, refracted, or absorbed.

1039 What do we mean when we speak of light being reflected?

When a ray of light strikes against a surface, and is
caused to turn back or rebound in a direction different
from whence it proceeded, it is said to be reflected.

1040 Why do we see ourselves in a mirror f

Because the rays of light from our face strike against
the glass, and (instead or being transmitted) are reflect-
ed, or sent back again to our eye.

1041 Why are flie rays of light reflected by a mirror ?

Because they cannot pass through the impenetrable
metal with which the back of the glass is covered ; so
they rebound back, just as a marble would do if it were
thrown against a wall.

1043 When a marble is rotted towards a waU, what is the path
through which it runs called ?

The line of incidence.

1043 When a marbk, rebounds back again, what is the path it then
describes called?

The line of reflection. (See
Fig. 52.)

If A B be the line of incidence,
then B E is the line of reflection;
and vice versa.

1044 When the light of our face
goes to the glass, what is the path

rough which it goes catted ?

11*

246

SCIENCE OF COMMON THINGS.

Lines of incidence and reflection. Why images appear inverted in water.

The line of incidence.

1645 When the light of our face is reflected back again from the mir-
ror, what is this returning path called f

The line of reflection.

1646 What is the angle of incidence f

The angle between the line of incidence and the per-
pendicular.

1647 What is the angle of reflection ?

The angle between the line of reflection and the per-
pendicular. (See Fig. 52.)

Let F B C (Fig. 53) be any surface ; D B a perpendicular to it. If a
marble were thrown from E to B, and bounded back to A, then E B D
would be the angle of incidence, and DBA the angle of reflection.

1648 Why does the image of any object in water always appear in-
verted f

Because the angles of incidence being always equal
to the angles of reflection, the light of the object, reflect-
ed to our eyes from the surface of the water, comes to
us with the same direction as it would have done, had
it proceeded directly from an inverted object in the
water.

In Fig. 53, the light proceeding from the ar-
row-head, A, strikes the water at F, and is re-
flected to G and that from the barb, B, strikes
the water at E, and is reflected toG. A spec-
tator standing at G will see the reflected
lines, E G and F G, as if they proceeded di-
rectly from C and D. Now we always judge
of the position of an object according to the
direction in which the rays of light repre-
senting it come to the eye, and for this
reason the image of the arrow, A B, reflect-
ed from the surface of water, appears to be
located at C D. It is also plain that A (the more elevated object) will
strike the water, and be projected from it more perpendicularly than the
point B ; and therefore the image will seem inverted.

164O If we lay a looking-glass upon the floor, with its face uppermost,
and place a candle beside it, why will the image of the candle seen in the
mirror by a person standing opposite to the candle, seem as much below the
surface of the glass as the candle itself stands above the glass ?

Because the incident ray coming from the top of the
candle, strikes the surface of the glass, and is reflected

Fig. 53.

SCIENCE OF COMMON THINGS. 247

Why the image in a mirror seems behind the glass.

in the same direction that a ray of light would have
taken, had it really come from a candle situated as
much below the surface of the glass, as the first candle
was above the surface. This fact will be clearly shown
by referring to Fig. 54.

F,g. 54.

165O Why, when we look into a plane mirror (the common looking-
glass) does our image appear to be at the same distance behind the surface
of the glass, as we are before the surface f

Because the lines and angles of incidence being
always equal to the lines and angles of reflection, the
rays which proceed from each point of our body
before the mirror will, after reflection, proceed as if
they came from a point holding a corresponding posi-
tion behind the mirror ; — and therefore produce the
same effect upon the eye of an observer as if they
actually had come from
that point.

For this reason our reflec-
tion in a mirror seems to ap-
proach us as we walk towards
it, and to retire from us as we
retire.

The whole subject of the re-
flection of images being gene-
rally of difficult comprehen-
sion by most persons, Fig. 55
is introduced as a means of
further explanation.

Let A be a part of an
object placed before a looking-
glass M N. Let A B and A C
be two rays diverging from it,

and refl 3cted from B and C to

an eye at 0, After reflexion ' Fig 55,

248 SCIENCE OF COMMON THINGS.

Peculiarities of reflected light.

they will proceed as if they had issued from a point a as far behind
the surface of the looking-glass, as A is before it — that is to say, the dis-
tance A N will be equal to the distance a N. In seeing an object with
the eye, we fix upon its position according to the direction in which the
rays of light coming from it proceed, and do not take into account the
fact that the rays have been reflected from their original course.

1651 Is the same quantity of light reflected at all angles, or inclina-
tions ?

It is not : when the angle or inclination with which a
ray of light strikes upon a reflecting surface is great,
the amount of light reflected to the eye will be con-
siderable ; when the angle, or inclination is small, the
amount of light reflected will be diminished

1653 Why does a spectator, standing upon the bank of a river, see the
images of the opposite bank, and objects upon it reflected in the water, but
not the images of any near object ?

Because the rays of light coming from distant objects
strike the surface of the water very obliquely, and the
light reflected is sufficient to make a sensible impres-
sion upon the eye, while the light proceeding from
near objects strikes the water with little obliquity, and
the light reflected is not sufficient to make a sensible
impression upon the eye.

Tliis fact may be clearly seen by reference to Fig. 56.

Fig- 56.

Let S be the position of the spectator ; O and B the position of distant
objects. The rays O R and B R which proceed from them, strike the
surface of the water very obliquely, and the light which is reflected in
the direction R S is sufficient to make a sensible impression upon the
eye.

But in regard to objects such as A placed near the spectator, they are
not seen reflected, because the rays A R' which proceed from them strike
the water with but little obliquity ; and consequently, the part of their

SCIENCE OF COMMON THINGS.

240

Why windows blaze at sunset.

light which is reflected in the direction R' S, towards the spectator, is not
sufficient to produce a sensible impression upon the eye.

1653 Why do windows seem to blaze at sunrise and sunset f

Because glass is a good reflector of light, and the
rays of the sun (striking against the window-glass) are
reflected, or thrown back.

1054 On a lake of water the moon seems to make a path of light
towards the eye of the spectator, while ail the rest of the lake seems dark :
why is this ?

The reason of this appearance is that eveiy little
wave, in an extent perhaps of miles, has some part of
its rounded surface with the direction or obliquity
which, according to the required relation of the angles
of incidence and reflection, fits it to reflect the light to
the eye, and hence every wave in that extent sends its
momentary gleam, which is succeeded by others.

1S55 In a sheet of water at noon, the sun appears to shine upon only
one spot, and all the rest of the water seems dark : why is this f

Because the rays fall
at various degrees of
obliquity on the water,
and are reflected at
similar angles / but as
only those which meet
the eye of the spectator
are visible, all the water
will appear dark ex-
cept that one spot.

Here, of the rays S A, S B,
and S C, only the ray S C
meets the eye of the specta-
tor D. The spot C, therefore,
will appear luminous to the
spectator D, but no other spot of the water ABC.

1050 Why can we not see into the street or road when candle* are
lighted f

1. Because glass is a reflector, and throws the candle-
light lack into the room again ; and

2. The pupil of the eye (having become contracted
by the light of the room) is too small to collect rays

Fig. 67

250

SCIENCE OF COMMON THINGS.

When are shadows large, and when small ?

enough from the dark street to enable us to see
into ^t.

1657 Why do we often see the fire reflected in our windows in winter-
time f

Because glass is a good reflector, and the rays of the
fire (striking against the window-glass) are reflected
back into the room again.

1058 If the shadow of an object be thrown on a wall, the closer the object

is held to the candle, the larger
,.---|I will be its shadow : why is thisf

,,/"'' Because the rays of

light diverge (from the
flame of a candle) in
straight lines, like lines
drawn from the centre
of a circle.

Here the arrow A, held close
to the candle, will cast the
shadow B F on a wall ; while
~^\, V the same arrow, held at C,
"x» would cast only the little sha-

*.* dowDE-

1659 How do we judge of the position, distance, and size of an object f

We judge of the position and distance and size of an
object by the relative direction of lines drawn from the
object to the eye, and by the angle which the intersec-
tion of these lines makes with the eye. This angle is
called the angle of vision.

"""•— >

"~ti

Fig, 50.

The student will bear in mind that an angle is simply the inclination
of two lines without any regard to their length. Thus, in Fig. 59, the
inclination of the lines, caused by rays of light proceeding from A and B,

SCIENCE OF COMMON THINGS. 251

How we estimaUthe size and position of distant objects.

and from C and 7>, and meeting at the eye, forms an angle at the point
of intersection, which is the eye. This angle is the angle of vision. As
the inclination of the ines proceeding from A and B, and from C and Z>,
is the same, the angles will be equal, and the man and the bird will ap-
pear of the same size.

1660 Why does a man on the top of a mountain or church-spire seem
ti be no larger than a crow t

Because the angle made in our eye by the perpen-
dicular height of the man at that distance is no larger
than that made by a crow close by.

Let A B (Fig. 59) be a man on a distant mountain or spire, and C I) A
crow close by, the man will appear only as high as the line C D, which
is the height of the crow. For the same reason the trees and houses far
down a street or avenue appear smaller than those near by.

1661 Why does the moon appear to us so much larger than the stars,
though, in fact, it is a great deal smaller ?

Because the moon is very much nearer to us than any
of the stars.

Fig. 60.

Let A B represent a fixed star, and C D the moon. The angle of
vision, A G B, which the fixed star, A B, makes with the eye is evidently
less than the angle of vision, G G D, which the moon makes with the eye.
But we judge of the size of a body by the size of the angle, and therefore
the moon, which is nearest and makes the greatest angle of vision, ap-
pears the largest. A B, though much the larger body, will appear no
bigger than E F; whereas the moon (CD) will appear as large as the
line, 0 D, to the spectator, G.

The moon is 240,000 miles from the earth, not quite a quarter of a
million of miles. The nearest fixed stars are 20,000,000,000,000 (that is,
twenty billions).

1663 Why does the moon (which is a sphere) appear to be a fiat sur-
face f

Because it is so far off that we cannot distinguish any
difference between the length of the rays issuing from
'the edge and those which issue from the centre.

253 SCIENCE OF COMMON THINGS.

Why objects in the shade seem dark, t Telescopes.

The rays A D and C D
appear to be no longer
than the ray B 1) ; but if
all the rays seem of the
same length, the part B
will not seem to be nearer
to us than A and C ' ; and therefore ABO will look like a flat or straight
line. The rays A D and C D are 240,000 miles long. The ray B D is
238,910 miles long.

1603 An object in the shade is not so bright and apparent as an object
in the sun : why is it not f

Because objects in the shade are seen by reflected
light reflected ; that is, the light is twice reflected ;
and, as the rays of light are always absorbed in some
measure by every substance on which they fall, and
also scattered by irregular reflections, therefore in the
two reflections much light is lost, and the object is seen
with less distinctness.

Part of the rays are absorbed, and part are scattered in all directions
by irregular reflections ; so that rarely more than half are reflected, even
from the most polished metals.

1664 Why is it light when the sky is covered with thick clouds ?

Partially because the sun's light is transmitted
through the clouds, and partially on account of the
multiplied reflections of light in the atmosphere.

1665 What is the use of telescopes f

They gather together the rays of light, and a greater
number are thus brought to the eye.

1666 How can these rays be gathered together ?

Rays of light diverge — that is, spread out in all direc-
tions— from a luminous object. The number of these
diverging rays which will enter the eye is limited by
the size of the pupil. But before they reach the eye,
they may be received upon a glass lens of a convex
form, which will have the effect of collecting them into
a space less in magnitude than the pupil of the eye. If
the eye be placed where the rays are thus collected, all
the light will enter the pupil.

The light which produces vision, as will be more fully explained here-
after, enters the eye through a circular opening called the pupil, which is
the black circular spot surrounded by a colored ring, appearing in the

SCIENCE OF COMMON THINGS.

253

How telescopes assist the sight.

Fig. 62.

FiK.es.

centre of the front of the eye. Noy, as the rays of light proceeding from
an object diverge, or spread out, the number which will enter the eye will
be limited by the size of the pupil. At a great distance from an object,
as will be seen in Fig. 62, few rays will enter the eye ; but if, as in Fig.
63, we place before the eye a piece of glass, called a lens, so constructed
as to collect all the diverging rays together, the light will be concentrated
at one point, and in sufficient quantity to enable us to see distinctly.

1607 Why do telescopes enable us to see objects invisible to the naked
eyef

Because they gather together more luminous rays
from obscure objects than the eye can, and form a bright
image of them m the tube of the telescope, where by
means of lenses they are magnified.

1608 When a ship (out at sea) is approaching the shore, why do we
see the small masts before we see the bulky hull ?

Because the earth is round; and the curve of the sea
hides the hull from our eyes after the tall moists have
become visible.

Fig 64.

Here only that part of the ship above the line A C can be seen by the
gpectator, A ; the rest of the ship is hidden by the swell of the curve D E.

The diminution of the size of a ship seen at sea, owing to the convexity
of the earth and the distance of the observer, is also illustrated in Fig. 65k,

1669 What is meant by the rejraction of light?

Light traverses a given transparent substance, such as

254:

SCIENCE OF COMMON THINGS.

Refraction of light.

A stick partially in water seems broken.

Fig. 66-

Fig 65.

air, water, or glass, in a straight line, provided no
reflection occurs and there is no change of density in
the composition of the medium ; but when light passes
from one medium into another, or from one part of the
same medium into another part of a different density,
it is lent from a straight line, or refracted.

In Fig. 66, suppose n m to represent the sur-
face of water, and S 0 a ray of light striking
upon its surface. When this ray S O enters
the water, it will no longer pursue a straight
course, but will be refracted, or bent towards
the perpendicular line, A B, as in the case of S 0
H. The denser the water, or other fluid, may
be, the more the ray S O H will be refracted, or
turned towards A B.
167O Does air possess the property of refracting light f

Yes ; the more dense the air, the greater is its refrac-
tive power.

167f 1 Why does the part of a stick immersed in the water appear lent
or broken ?

The water and the air being of different densities,
the rays of light proceeding from the part of the stick
contained in the water are refracted, or caused to deviate
from a straight line as they pass from the water into
i the air ; consequently that portion of the
[stick immersed in the water will appear
to be lifted up, or to be lent in such a
manner as to form an angle with the part
| out of the water.

The bent appearance of the stick in water is repre-
|| sented in Fig. 67. For the same reason, a spoon in a
glass of water, or an oar partially immersed in water,
always appears beut.

SCIENCE OF COMMON THINGS. 255

Rivera deeper than they appear to be. Compound nature of white light.

167*8 Why does a river always appear more shallow than it really is 1

Because the light proceeding from the bottom of the
river is refracted as it emerges out of the water, and
causes the bottom to appear elevated.

167*3 How much deeper is a river than it seems to be?

About one-third. If, therefore, a river seems only
four feet deep, it is really six feet deep.

Many persons get out of their depth in bathing in consequence of this
deception.

The following simple experi-
ment illustrates the effect of re-
fraction:— Place a silver coin, i
m, at the bottom of a basin, Fig.
68. The rays, i *, proceeding to
the eye from the silver surface,
render the coin visible. The
point a, the eye, is then moved
farther back, so that the edge of
the basin obstructs the direct
rays, and of course the coin is
no longer seen. If an attendant
carefully pours water into the
basin, so that the object is not moved, it will presently, as the water rises
in the basin, become again visible. This arises from the refraction of the
rays by the water, the image, indeed, appearing at n instead of at m.

167*4 Is a ray of white light simple or compound?

Every ray of white light is compounded of other rays
of colored light.

1675 Into how many parts may a ray of light be divided f

Into three parts : blue, yellow, and red.

These three colors, by combination, make seven : 1, red ; 2, orange (or
red and yellow) ; 3, yettow ; 4, green (or yellow and blue) ; 5, blue ; 6, in-
digo (a shade of blue) ; and, 7, viokt (or blue and red).

1676 How is it known that a ray of light consists of several different
colors f

Because if a ray of light be cast upon a triangular
piece of glass (called a prism), it will be distinctly
divided into seven colors : 1, red ; 2, orange ; 3, yel-
low ; 4, green ; 5, blue ; 6, indigo ; and, 7, violet.

1677 Why does a prism divide a ray of light into various colors f

Because all these colors are refracted, or bent out of
their course differently. Red is refracted least, and
blue the most ; therefore, the blue ray will be bent to

256 SCIENCE OF COMMON THINGS.

Effects of a prism In separating the rays of light.

the top of the prism, and the red will remain at the
bottom.

Violet

Indigo.

Blue?

Green.

Yellow.

Orange.

Ked.

Fig. by.

This separation of a ray of solar light into different colors, by refraction,
is represented in Fig. 69. A ray of light, £ A, is admitted through an
aperture in a window-shutter into a darkened chamber, and caused to fall
on a prism, P. The ray thus entering would, if allowed to pass unob-
structedly, have moved in a straight line to the point K, on the floor of
the room ; but the prism being so placed that the ray may enter and quit
it at equal angles, it will be refracted in such a manner as to form on the
opposite side of the room an oblong image called the solar spectrum,
divided horizontally into seven colored spaces or bands of unequal extent,
succeeding each other in the order represented: red, orange, yellow, green,
blue, indigo, viokt.

1678 Are the colored rays, once separated and refracted from the
prism, capable of being analyzed by refraction again ?

They are not, and are hence designated as primary
colors.

1679 If the seven different colors as separated by the prism be again
collected together, what will they form ?

White light.

1G8O To what is the great brilliancy of the diamond and other precious
stones due ?

To their power of refracting light ; they are also
artificially cut in such a manner as to form a series of
prisms,, which separate the rays of light falling on
mem into their component colored rays.

1GS1 What is a rainbow f

The rainbow is a semicircular l>and or arc, composed

SCIENCE OF COMMON THINGS.

257

Production and explanation of the rainbow

of the different colors, generally exhibited upon the
clouds during the occurrence of rain in sunshine.

If we take a glass globe filled with water, and suspend it at a certain
height in the solar rays above the eye, a spectator standing with his back
to the sun will see the refraction and reflection of red light ; if, then, the
globe be lowered slowly, the observer retaining his position, the red light
will be replaced by orange, and this in its turn by yellow, and so on, the
globe at different heights presenting to the eye the seven primitive colors
iri succession. If now, in the place of the globe occupying different posi-
tions, we substitute drops of water, we have a ready explanation of the
phenomena of the rainbow.

Fig 70.

Let -A, B, and C be three drops of rain ; S A, S B, and S C, three rays
of the sun. £ A is divided into three colors ; the blue and yellow are
bent above the eye, D, and the red enters it.

The ray, S B, is divided into three colors ; the blue is bent above the
eye, and the red falls below the eye, D, but the yellow enters it.

The ray, S C, is also divided into the three colors. The blue (which is
bent most) enters the eye ; and the other two fall below it. Thus the
eye sees the blue of (7, and of all drops in the position of C; the yellow
of B, and of all drops in the position of B ; and the red of A, and of all
drops in the position of A ; and thus it sees a rainbow.

1683 What is the occasion of the rainbow f

The rainbow is produced by the refraction ana re-
flection of the solar rays in the drops oi falling rain.

1683 What are the conditions necessary in order that we may see a
rainbow f

The rainbow can be seen only when it rains, and in
that point of the heavens which is opposite to the sun.
It is necessary also that the sun should not have too

258

SCIENCE OF COMMON THINGS.

No two persons see the same rainbow. Formation of two rainbows at the same time

great an altitude above the horizon. Hence, within a
certain interval each day, no visible rainbows can be
formed, on account of the sun's high altitude above the
horizon.

1684 How do we know that the rainbow results from the decomposition
of the solar rays by drops of water 1

Because in the case of cascades and water-falls, the
\spray and the drops of moisture dispersed over the
igrass and the spiders -webs produce the same phenomena.

1635 Does every person see the same colors from the same drops?

No ; no two persons see the same rainbow.

To another spectator, the rays from S B (Fig. 70) might be red instead
of yellow ; the ray from S C, yellow ; and the blue might be reflected
from some drop below C. To a third person, the red may issue from a
drop above A, and then A would reflect the yellow, and B the blue, and
so on.

1686 Why are there often two rainbows at one and the same time f

The first, or primary bow, is formed by two refrac-
tions of the solar ray, and one reflection, tne rays of the
sun entering the drops at the top, and being reflected
to the eye from the bottom.

Thus in Fig. 71, the ray S A of the
primary rainbow strikes the drop at A,
is refracted or bent to B, the back part
of the inner surface of the drop ; it is
then refracted to C, the lower part of
the drop, when it is refracted again,
and so bent as to come directly to the
eye of the spectator.

The secondary, or outer bow, is pro-
duced, on the contrary, by two refrac-
tions and two reflections, the ray of
light entering the drops from the bot-
tom, and being reflected to the eye
from the top.

Thus in Fig. 72, the ray S B of the
secondary bow strikes the bottom of
the drop at B, is refracted to A, is then
reflected to C, is again reflected to D,
when it is again refracted or bent, till
it reaches the eye of the spectator.

1687 Why are the colors of the
second bow all reversed 1

jne. re. Because in one bow we sea

SCIENCE OF COMMON THINGS. 259

Colors in a soap-bubble. Origin of morning and evening twilight.

the rays which enter at the top of the rain-drops,
refracted from the bottom :

But in the other bow we see the rays which enter at
the bottom of the rain-drops (after two reflections)
refracted from the top.

The position and formation of the primary and secondary rainbows are
represented in Fig. 73. Thus in the formation of the primary bow, the
ray of light S strikes the drop n at a, is refracted to n &, thence to g, and
leaving the drop at this point, proceeds to the eyes of the spectator at 0.
In the formation of the secondary bow, the ray S' strikes the drop p at the
bottom at the point i, is refracted to rf, thence to/, and again to e, pro-
ceeding from the top of the drop, also to the eye of the spectator at 0.

The reason why the primary bow exhibits the stronger colors is, be-
cause the colors are seen after one reflection and two refractions ; but the
colors of the secondary (or upper) rainbow undergo two reflections and
two refractions.

Fig. 73.

1688 Why does a soap bubble exhibit such a variety of colors f
Because the thickness of the film through which the
rays pass is constantly varying.

1680 Why is a soap bubble so constantly changing its thickness t

Because the water runs down from the top to the
bottom of the bubble, till the crown becomes so thin as
to burst.

3 60O Wliat is the cause of morning and evening twilight f

When the sun is below the horizon, the rays which
strike upon the atmosphere or clouds are bent down

260

SCIENCE OF COMMON THINGS.

Lenses and their varieties.

What is a focus of light?

towards the earth, and produce a little light called twi-
light.

1691 What is a lens f

A piece of glass or other transparent substance,
bounded on both sides by polished spherical surfaces,
or on the one side by a spherical, and on the other by a
plane surface. Rays of light passing through it are
made to change their direction, and to magnify or
diminish the appearance of objects at a certain distance.

1603 Sow many varieties of lenses are generally recognised f

Two : convex and concave.

Fij?. 74.

Among convex lenses are the double convex A (Fig. 74) to which the
appellation lens was originally applied from its resemblance to a lentil-
seed (kns in Latin) being bounded by two convex spherical surfaces
whose centres are on opposite sides of the lens ; the plano-convex B,
having one side bounded by a plane surface, and the other by a convex
surface ; and the meniscus or concavo-convex C, bounded on one side by
a concave, and on the other by a convex surface.

There are also three principal varieties of concave glasses; as the
double concave D, bounded by two concave surfaces, forming portions of
spheres whose centres are on opposite sides of the lens; the plano-
concave E, bounded on one side by a plane, and on the other by a
concave surface ; and convexo-concave F, bounded by a convex surface
on one side, and by a concave one on the other.

1693 What is a focus of light f

"When rays of light continually approach each other,
as in moving to a point, they are said to converge, and
the point at which the converging rays meet is called
tliejocus.

1694 What sort of a lens is a common burn-
ing-glass ?

A double convex lens.

Fig. 75 represents the action of a double con-
vex lens in causing the rays of light to converge
and meet at a focus.
Figi 75. 1695 What are transparent bodies f

SCIENCE OF COMMON THINGS. 261

Opaque and transparent bodies. Absorption of light.

Those which do not irvterrupt the , passage of light,
or which admit of other bodies being seen through
them.

1606 When is a body said io be opaque ?

When it entirely prevents the passage of light.

1607 Is there any body perfectly transparent f

No ; some light is evidently lost in passing even
through space, and still more in traversing our atmo-
sphere.

160S Row much of Vie sun's light is supposed to be intercepted by the

atmosphere ?

It has been calculated that the atmosphere, when the
rajs of the sun ^>ass perpendicularly through it, inter-
cepts from one-fifth to one-fourth of their light; but
when the sun is near the horizon, and the mass of air
through which the solar rays pass is consequently
vastly increased in thickness, only one two hundred and
twelfth part of their light can reach the surface of the
earth.

1S00 Why is charcoal black f

Because it absorbs all the light which falls upon it,
and reflects none.

1*700 What becomes of the light which is absorbed?

This question cannot be satisfactorily answered. In
all probability it is permanently retained within the
substance of the absorbing body.

1*7O1 To what depth is light supposed to penetrate tJie ocean f

It is calculated that sea water loses all its transpa-
rency at the depth of seven hundred and thirty feet ;
but a dim twilight must prevail much deeper in the
ocean.

262 SCIENCE OF COMMON THINGS.

Structure of the eye. How the eye is moved.

CHAPTER II.

STRUCTURE OF THE EYE AND THE PHENOMENA OF VISION.
1*703 What is the structure of the human eye ?

In man the organ of vision consists of two hollow
spheres, each about an inch in diameter, filled with
certain transparent liquids, and deposited in cavities of
suitable magnitude and form in the upper part of the
front of the head on each side the nose.

±7O3 How is it that we are enabled to move the eye in various directions t

By means of muscles attached to different points of
its surface.

These are shown in Fig. 76. where the external bones of the temple
are supposed to be removed in order to render visible the muscular
arrangements. The muscle, 1, raises the eye-lid, and is constantly in
action while we are awake. During sleep, the muscle being in repose
and relaxed, the eye-lid falls and protects the eye from the action of light.
The muscle, 4, turns the eye upwards ; 5, downwards ; 6, outwards ; and
a corresponding one on the inside, not seen in the figure, turns it inwards.
No. 2 and 10 turn the eye round its axis. No. 11 is tue great optic

SCIENCE OF COMMON THINGS. 263

Eetina. Iris. Pupil. Cornea

nerve, which conveys the sensation to the brain. If this nerve were cut,
notwithstanding the eye might be in other respects perfect, the sense of
sight would be destroyed.

1704 Of what parts does the eye consist f

The eye is of globular form, and is composed of three
coats or membranes, called the sclerotic, the choroid,
and the retina; and three humors, denominated the
aqueous ', the crystalline, and the vitreous.

1705 What is meant by the " retina of the eye ?"

The network which lines the back of the eye is called
the retina ; it is composed of an expansion of the optic
nerve.

1706 What is that portion of the eye called ivhich in some persons is
blue, in others gray or hazel ?

It is called the iris.

17*O 7* In the centre of the iris is a circular "black opening : what is this
called 1

It is called the pupil. But this spot is not a black
substance, but an aperture, which appears black only
because the chamber within it is dark. It is properly
speaking the window of the eye, through which light
is admitted, which strikes on the retina.

17*O8 Does light admitted through the pupil to the retina produce vision ?

Yes, provided the light enter in sufficient quantity.

How by the arrangement of the several parts of the eye are we
enabled to see?

The rays of light falling upon the cornea, enter the
interior of the eye through the pupil, and by the joint
action of the cornea and crystalline lens are brought to
a focus at the back part of the eve, upon the retina.
Here an image is formed, and the impression it makes
is conveyed along the optic nerve to the brain.

17*1O What is meant "by Hie " cornea of the eye ?"

All the outside of the visible part of the eyeball.

Fig. 77 represents the interior construction of the eye. It is composed,
in the first place, of the cornea, a, a transparent membrane in front of the
globe of the eye. Next is the sclerotic coat, t, which joins on the cornea,
and upon which the external form of the eye depends. The cornea is
united to, or fixed in, the sclerotic coat, like the glass into the case of a
watch : d, c represents the iris, with an opening in it, forming the pupil

SCIENCE OF COMMON THINGS.

Explanation of near-sightedness.

Next in order is the aqueous humor, &, e, in the middle of which is the
iris, d, c. Behind the pupil we have the crystalline. lens, /, and then the
vitreous humor, A, filling all the interior of the ball of the eye. m indi-
cates the retina, which is an expansion of the optic nerve, n. k is the
choroid coat, a membrane interposed between the retina and the sclerotic
coat ; it terminates in form in a series of folds or filaments, #, called the
ciliary ligament or processes.

1711 Why are some persons near-sighted ?

Because the curvature of the cornea and the crystal-
line lens is too great, and the rays of light which form
the image are brought to a focus before they reach the
retina or the back part of the eye. The object, there-
fore, is not distinctly seen.

Fig. 79 represents the manner
in which the image is formed
upon the retina in the perfect eye.
The curvature of the cornea, s s,
and of the crystalline lens, c c, is
just sufficient to cause the rays
of light proceeding from the im-
age, e e, to converge to the right
focus, m, upon the retina.

Fig. 78 represents the man-
ner in which the image is formed
in the eye of a near-sighted per-
son. The curvature of the cor-
nea, s 5, and of the crystalline
lens, c c, is so great that the im-
age is formed at m m in advance
of the retina.

SCIENCE OF COMMON THINGS.

Explanation of far-sightedness.

What sort of glasses do near-sighted persons wear ?

If the cornea and crystalline lens be too convex (or
projecting), the person must wear double concave glasses
to counteract it.

17*13 What is meant by " double concave glasses ?"

Glasses hollowed-in on both sides.

1 714 Why are old people far-sighted ?

< Because the humors of their eves are dried up by age;
in consequence of which the cornea sinks in, or becomes
flattened.

17*15 Why does the flattening of the cornea prevent persons seeing
objects which are near ?

Because the cornea is too flat, and the image of ob-
jects is not completely formed when their rays reach the
retina / in consequence of which the image is imper-
fect and confused.

Fig. 80 represents the man-
ner in which the image is
formed in the eye, when the
cornea or crystalline lens is
flattened. The perfect image
would be produced at m m,
behind the retina, and, of

course, beyond the point ne- FJ ^

cessary to secure perfect vision.

17*16 What sort of spectacle-glasses are suitable for old people f

Double-convex glasses, or those which curve outwards
on both sides. These shorten the focus of the eye, and
produce an image upon the right point, the retina.

1717* Why do near-sighted persons bring objects close to the eye in order
to see them ?

Because the distance between the front and back of
the eye is so great, that the image of distant objects is
formed m front of the retina; but when objects are
brought near to the eye, their image is thrown farther
made to fall on the retina.

1718 Why do old people hold objects far off in order to see them better t

Because the distance between the front and back of
their eyes is not great enough / when, however, objects

266 SCIENCE OF COMMON THINGS.

Use of the e}rebrows and eyelashes.

are held farther off, it compensates for this defect, and
a perfect image is formed on the retina.

Birds of prey are enabled to adjust their eyes so as to see objects at a
great distance, and again those which are very near. The first is accom-
plished by means of a muscle in the eye, which enables them to flatten
the cornea by drawing back the crystalline lens ; and to enable them to
perceive distinctly very near objects, their eyes are furnished with a
flexible bony rim. by which the cornea is thrown forward at will, and the
eye thus rendered near-sighted.

1*710 Why do persons who are short-sighted in youth, gradually have
this failing corrected as they grow old ?

They are short-sighted because the cornea of the eye
is too globular ; but as age advances, the fluids are not
secreted as before, the eye becomes flattened, and
natural sight is again restored.

1730 What is the use of the eyebrows ?

The eyebrows defend the eyes from too strong a light,
and serve to turn away substances which might other-
wise fall into the eye.

1731 What is the use of the eyelashes?

The eyelashes guard the eye from danger, and pro-
tect it from dust or insects floating or flying in the atmo-
sphere.

17*33 Why is the eye pained by a sudden light f

Because the nerve of the eye is burdened with rays
before the pupil has had time to contract.

1733 What is the pupil of the eye ?

The circular black opening in front of the eye.

1734 Why does it give us pain if a bright light is brought suddenly
towards us at night-time ?

Because the pupil of the eye dilates very much in
the dark in order to admit more rays.

When therefore a light is brought suddenly before us, the enlarged
pupils overload the optic nerves with rays, which causes pain.

1735 Why can we bear the light Rafter a few moments f

Because the pupils contract again almost instantly,
and adjust themselves to the quantity of light which
falls upon them.

1736 Why can we see nothing when we leave a well-lighted room, and
go into the darker road or street ?

SCIENCE OF COMMON THINGS. 267

Vision in the light and in darkness. Cats — how see in the dark.

Because the pupil (which contracted in the bright
room) does not dilate instantaneously ; and the con-
tracted pupil is not able to collect rays enough from the
darker road or street to enable us to see objects before us.

IT'S? How does light cause the pupil of the eye to contract ?

The pupil of the eye is a round hole in the midst of
a movable muscular curtain or screen, called the iris.
"When too much light falls on the nervous retina at the
back of the eye, it irritates it ; and this irritation is
conveyed to the muscular rings composing the curtain
by small nervous fibres, causing them to contract.

17*38 Why do we see better when we get used to the dark f

Because the pupil dilates again, and allows more rays
to pass through its aperture.; in consequence of which
we see more distinctly.

17*39 If we look at the sun for a few moments, why do all oilier things
appear dark f

Because the nerve of the eye, by looking at the sun,
is so affected by the intensity of the light that it requires
a few moments to recover its former sensibility.

17*30 Why can we see the proper colors of every object again after a
few minutes f

Because the eye again recovers its sensibility, and
accommodates itself to the light around.

17*31 Why can tigers, cats, and owls see in the dark f

Because they have the power of enlarging the pupil
of their eyes so as to collect the scatterea rays of light ;
in consequence of which they can see distinctly when it
is not light enough for us to see anything at all.

17*33 Why is it that when we press slightly upon the ball of either eye,
while viewing an object, we see double? \

Because the pressure of the finger prevents the ball
of one eye from following the motion of the other, and
the axis of vision in each eye being different, we see
two images.

17*33 Do persons who squint see double 1

They do / but practice gives them p^ower of attending
to the sensation of only one eye at a time.

268 SCIENCE OF COMMON THINGS.

Cause of squinting. We see images and not objects themselves.

17*34 What is the cause of strabismus, or squinting ?

The inability of one eye to follow the motions of the
other ; this may arise from habit, imperfect power in
one eye, or some defect in the muscular movements.

17*35 Why, when the eye is violently struck or pressed upon, do we seem
to see light ?

Because the pressure communicated to the optic
nerve causes a violent and momentary sensation of
light.

17*3G When we say we see an object, what do we in fact do f

The mind is only taking cognizance of the picture or
impression made on the retina.

17*37* If the mind, in seeing an object, sees in reality only a picture
yainted on the back of the retina, how is it enabkd to judge of magnitudes,
distances, etc., the picture being on a comparatively fiat surface f

It is only by experience. " I see men as trees walk-
ing," said the man born blind, when restored to sight.

17*33 Would a person whose eyes, although perfect, had been covered up
from infancy to maturity, be able to see ? that is, comprehend any scene or
prospect on which he first opened his eyes ?

He would see the objects, but could no more under-
stand them than a child understands the printed page
on which it looks, although every word is clear and
distinct.

17*39 Do we see the same lines and surfaces of an object alike wicheach
eye?

"We do not.

We may convince ourselves that we do not, by placing two candles, fo?
example, in such & position, that when they are looked at with the right eye,
one is made to cover the other ; if now we close the right eye and look at
them with the left, the most remote candle will be no longer screened by
the front one, but will be seen about an inch to the left of it.

17*40 Why cannot we count the posts of a fence when wt are riding
rapidly in a railroad car ?

Every impression, according to the intensity of its
effects, remains for a certain length of time on the
retina, and a measurable period is necessary to produce
the impression. The light from each post falls upon
the eye in such rapid succession, that the different
images become confused and blended, and we do not
obtain a distinct vision of the particular parts.

SCIENCE OF COMMON THINGS. 269

Why the sun and moon seem larger on the horizon than overhead.

17*41 Why do the sun and moon seem larger at their rising and setting
than at any other time f »

The appearance is an illusion, in consequence of ter-
restrial objects being placed in close comparison with
them at one time, and not at the other.

1*74:3 Is this illusion an optical one, or a mental illusion t

A mental one, since the organs of vision do not pre-
sent to us a larger image of the moon or sun in the
horizon than in the zenith.

17*43 What do we mean by the horizon ?

The circle or line where the earth and sky appear to
meet.

1744 What do we mean by the zenith f

The point or part of the heavens immediately over-
head.

17*45 Is the moon nearer or farther from us when upon the horizon f

When the moon is on the horizon, it is about four
thousand miles farther from us than when in the zenith ;
its apparent diameter, therefore, instead of appearing
larger, ought to appear about a sixtieth part less.

17*46 Why are we so often mistaken in respect to the actual distance
of a conflagration at night ?

Light radiating from a centre rapidly weakens as the
distance from the centre increases, being, for instance,
only one-fourth part as intense at double the distance.
The eye learns to make these allowances, and by the
clearness and intensity of the light proceeding from the
object, judges with considerable accuracy of the com-
parative distance. But a fire at night appears uncom-
monly brilliant, and therefore seems near.

17*47* Why does the evening star rising over a hill-top appear as if
situated directly over the top of the eminence ?

Because we make brightness and clearness to depend
on contiguity, as it ordinarily "does ; and as the star is
bright, we unconsciously think it near us.

1748 What is the cause of colors t

The action of light.

1749 How is thit proved ?

12*

270 SCIENCE OF COMMON THINGS.

Color and its cause. Why are some bodies red and others white, black, &c. ?

In the dark, bodies have no color, and in the light
their colors may be altered by subjecting to certain mo-
difications the light by which they are rendered visible.
Thus a blue piece of cloth in a red light will appear red.

17*50 Why is it that we find it difficult to distinguish colors ~by candle-
light?

Because we have modified the light upon which the
full effect of the color depends.

17*51 What then is the true definition of color ?

The color of a substance is the effect of light on a
surface adapted to reflect its particular color.

17*53 Why do some things reflect one color, and some another f

Because the surface of things is so differently consti-
tuted, both physically and chemically.

17*53 Why is a rose red ?

Because the surface of a rose absorbs the Hue and
yellow rays of light, and reflects only the red.

17*54 Why are some things black f

Because they absorb all the rays of light, and reflect
none.

1755 Is black a color f

It is not / it is the absence of color.

17*56 Why are some things white f

Because they absorb none of the rays of light, but
reflect them all.

17*57* Why are clouds, snow, sugar, and salt white f

Because they reflect 'back unchanged the white light
which strikes upon them.

17*58 Why are not the crystals of frost and snow transparent like icef

The crystals of frost and snow are not solid, but they
contain air ; hence their brilliant whiteness : for the air
preventing the ready transmission of light through the
crystals, the rays are copiously reflected, from the mass
of crystals.

17*59 Why is the darkness of night diminished by the presence, of snow f

Because the snow reflects, instead of absorbing, like

SCIENCE OF COMMON THINGS* 271

Origin of color in leaves of trees. Why is the sky blue ?

the bare ground, the faint light that proceeds from the
sky.

176O Why are the leaves of plants green f

Because a peculiar chemical principle, called chloro-
phyl, is formed within their cells, which has the property
of absorbing the red rays, and of reflecting the blue and
yellow, which mixture produces green.

17G1 Why are leaves a light green in spring f

Because the chlorophyl is not fully formed.

17(33 Why do leaves turn brown in autumn f

Because the chlorophyl undergoes decay, and is not
replaced as it is in spring.

1763 Why do all things appear black in the dark f

In the dark there is no color, because there is no light
to be absorbed or reflected, and therefore none to be
decomposed.

Of course, in certain degrees of darkness, all objects are actually invi-
sible. The question refers to that peculiar degree of darkness when the
forms of objects may be seen, but not their hues.

1764 Why does the sky appear blue ?

Because the atmosphere absorbs the red and yellow
rays, and transmits the blue.

1765 Why does the sun most generally fade artificial colors f

Generally the loss of color arises from the oxidation
of the substances used in dyeing ; as tarnish and rust are
an oxidation of metals. Sometimes, however, the
ingredients of the dye are otherwise decomposed by the
sun ; and the color (which is due to a combination of
ingredients) undergoes a change as soon as the sun
deranges or destroys that combination.

1766 What remarkable correspondence is there between the geographical
position of a region, and the colors of its plants and animals f

In the tropics, where the sun shines longest and
brightest, the darkest green prevails over the leaves of
plants, the flowers and fruits are colored brightly, and
the plumage of the birds is of the richest description.

1767 What is the natural coloration exhibited -in temperate climates f

In temperate climates everything is of a more sub-

272 SCIENCE OF COMMON THINGS.

Colors in different regions of the earth. Contrasts of colors.

dued variety • the flowers are less bright ; the prevail-
ing tint of the birds is brown ; and the dresses of the
inhabitants are sombre.

IT'S 8 How is this corfespondence further exemplified in the Arctic and
Antarctic regions ?

Here there is little color in natural objects ; the few
flowers are white or yellow / and the animals are almost
uniformly Hack or white.

17*69 In what part of the ocean do we find the brightest shells and sea-
weeds ?

Near the shore, in shallow water, where the influence
of light is greatest.

17* 7*0 What fishes are distinguished for the brilliancy of their colors?

Those that swim near the surface; whereas those
which live at greater depths are gray, brown, and black.

17*7*1 What is the appearance of the sea-weeds and animals that live at
great depths of the ocean ?

They are nearly colorless.

17*7*3 Why is grass growing under a covering of a white or yellowish
white color f

Because it is secluded from the light, whose presence
and action is necessary for the production of the material
which imparts to it its green color.

17*7*3 Of the various rays composing solar light, which are the most
visible to the human eye ?

The yellow.

17*7*4 Which have the greatest heating effect f

The faint red rays.

17*7*5 Why does a dress composed of cloths of different colors, look well
much longer, although worn, than one of only a single color, the character of
the cloth in both instances being identical ?

It is owing to the effect of contrast between the
colors. If a dress is composed of cloths of two colors,
as red and green, orange and blue, yellow and violet,
they will mutually heighten the effect of each, and make
each portion appear to the best advantage.

17*7*0 Why will stains be less visible on a dress of different colors, than
on one composed of only a single color ?

Because there exists in general a greater contrast

SCIENCE OF COMMON THINGS.

Contrasts of colors In dress. Arrangement of bouquets.

among the various parts of the first-named dress, than
between the stain and the adjacent part, and this differ-
ence renders the stain less apparent to the eye.

177 7 Why can a coat, waistcoat, and pants of the same color be worn
with advantage together only when they are new f

Because as soon as one of them loses its freshness
from having been worn longer than the others, the
difference will increase by contrast.

1778 Give an illustration.

A pair of new black pants, worn with a vest of the
same color, which is old and rusty, will make the tinge
of the latter appear more conspicuous, and at the same
time the black of the pants will appear more brilliant.
White and other light-colored trowsers would produce
a contrary effect.

1779 What is the general law upon which the harmony of colors
depends ?

Every color when placed beside another color is
changed, appearing different from what it really is;
and it moreover equally modifies the colur with whicn
it is in proximity.

1780 What effect has rose-red upon a rosy complexion f

It causes it to lose some of its freshness.

1781 For fair complexions, deficient in rose, which color is most favor*
abkf

A delicate green.,.

17SS What effect has black drapery upon the color of the skin 1

It makes it appear whiter.

1783 What rule should be observed in the grouping of flowers and the
preparation of bouquets ?

"We must separate pink flowers from those that are
either scarlet or crimson ; orange, from orange yellow
flowers ; yellow flowers from greenish-yellow flowers ;
blue from violet-blue, red from orange, pink from violet ;
blue flowers from violet flowers.

1784 What is the optical effect of dark colors and black upon the size
of the figure f

2 74: SCIENCE OF COMMON THINGS.

Most conspicuous colors. Colors of animals adapted to their necessities.

It causes it to appear smaUer / therefore these colors
are most suitable for stout persons.

1785 What effect do white and light-colored dresses have upon the size
of the figure ?

They cause it to appear larger.

178Q What effect do large patterns in dress make f

They make the figure look shorter.

1787 What is the effect of narrow longitudinal stripes in dress t

They add to the apparent height of the figure.

1788 What is the effect of fwrizontal stripes ?

The effect of horizontal stripes is opposed to that of
longitudinal, and under every condition they are un-
graceful.

1789 What colors are most conspicuous in battle f

It has been found by numerous observations that red
is the most fatal color, and the least fatal is a light grey.

1790 What curious provision for the protection of animals does nature
appear to make ?

She appears to have adapted the color of the creature
to its haunts in such a way as tends to preserve it from
injury. Caterpillars and insects which feed on leaves
are generally of the color of the leaves. As long as
they remain still, it is almost impossible to distinguish
the grasshopper from the herbage on which it rests.

1791 What curious change is noticed in the color of animals inhabiting
the Arctic regions f

During the snows of winter, foxes, hares, and some
varieties of birds are white ; when the ground is free
from snow in summer, they are of a 'brown color.

SCIENCE OF COMMON THINGS. 275

What is electricity ? Means of exciting electricity.

PART VIII.

ELECTRICITY, GALVANISM, MAGNETISM, AND
ELECTRO-MAGNETISM,

CHAPTEE I.

ELECTRICITY.
1793 What is electricity t

Electricity is one of those imponderable agents that
appear to be diffused through all nature, existing in all
substances without affecting their volume or their tem-
perature, or giving any indication of its presence when
in a latent state. When, however, it is liberated from
this repose, it is capable of producing the most sudden
and destructive effects, or of exerting powerful influences
by a quiet and long-continued action.

1*793 How may electricity be called into activity f

By mechanical power, by chemical action, by heat,
and by magnetic influence.

17*94 What is the most ordinary way of exciting electricity f

By friction.

17*95 Do we know any reason why the means above enumerated should
develope electricity from its latent condition?

We are entirely ignorant upon this 'subject.

17*96 When you rub apiece of paper with India-rubber, why does it
adhere to the table f

Because tlie friction of the India-rubber against the
surface of the paper developes electricity, to which this
adhesiveness is mainly to be attributed.

17*97* Does electricity present any appearance by which it can be "known f

No ; electricity, like heat, is in itself invisible, though
often accompanied by both light and heat.

276 SCIENCE OF COMMON THINGS.

Electrified and non-electrified bodies.

17*93 When a substance, by friction or by any other means, acquires
the property of attracting other bodies, in what state is it said to be?

It is said to be electrified^ or electrically excited / and
its motion towards other bodies, or of other bodies to-
wards it, is ascribed to a force called electric attraction.

17*09 Does an electrified body exercise any other influence than an,
attractive onef

It does ; for it will be found that light substances,
after touching the electrified body, will recede from it
just as actively as they approached it before contact.
This is termed electric repulsion.

Thus, if we take a dry glass rod, rub it
well with silk, and present it to a light pith
ball, or feather, suspended from a support
by a silk thread, the ball or feather will be
attracted towards the glass, as seen at G,
Fig. 81. After it has adhered to it a mo-
ment, it will fly off, or be repelled, as P' from
G'. The same will happen if sealing-wax
be rubbed with dry flannel, and a like ex-
Fig. 81. periment made ; but with this remarkable
difference, that when the glass repels the

ball, the sealing-wax attracts it, and when the wax repels, the glass will
attract. These phenomena are examples of electrical attraction and
repulsion.

1800 What is a non-electrified body f

One that holds its own natural quantity of electricity
undisturbed.

1801 What happens when an electrified body touches one that is non-
electrified f

The electricity contained in the former is transferred
in part to the latter.

Thus, on touching the end of a suspended silk-thread with a piece of
excited wax, the silk will be excited, as will be shown by its moving
towards a book, piece of metal, or any other object placed near it.

18OS Do all bodies conduct or allow electricity to pass through them
equally well?

Although there is no substance that can entirely pre-
vent the passage of electricity, nor any that does not
oppose some resistance to its passage, yet it moves with
a much greater facility through a certain class of sub-
stances than through others. Those substances which

SCIENCE OF COMMON THINGS.

277

Conductors and non-conductors of electricity.

Electrical machines.

facilitate its passage are called conductors ; those that
retard or almost prevent it, are called non-conductors.

1803 What substances are good conductors of electricity ?

The metals, charcoal, the earth, water, and most fluids,
except oils, the human body, etc., are good conductors.

1804 What substances obstruct the passage of electricity, or are "non-
conductors ?"

Glass, resin, oil, silk, sulphur, dry air, etc., etc., are
non-conductors.

1805 What is an electrical machine f

An electrical machine is an arrangement by which
quantities of electricity can bexollected and discharged.

The electrical machine most usu-
ally employed consists of a large
circular plate of glass, see Fig. 82,
mounted upon a metallic axis, and
supported upon pillars fixed to a
secure base, so that the plate can,
by means of a handle, W, be turned
with ease. Upon the supports
of the glass, and fixed so as to
press easily but uniformly on the
plate, are four rubbers, marked r r
r r in the figure ; and flaps of silk,
s 5, oiled on one side, are attached
to these, and secured to fixed sup-
ports by several silk cords. "When
the machine is put in motion, these
flaps of silk are drawn tightly
against the glass, and thus the
friction is increased, and electricity
excited. The points p p collect
the electricity from the glass, and
convey it to the conductor, c, which is sup-
ported by the glass rod g.

Fig. 83 represents another form of an
electrical machine, constructed on similar
principles. S being a glass cylinder turn-
ing on an axis, Y the conductor, F the
rubber, A A supports.

1806 What is the theory of electricity
most generally adopted ?

The theory proposed by Dr.

ine tneory proposed by Ur.
Franklin: this supposes the ex-
istence of a single, imponderable

Fig, 83.

278 SCIENCE OF COMMON THINGS.

Positive and negative electricity. Velocity of electricity.

fluid, equally distributed throughout nature : every
substance being so constituted as to retain a certain
quantity of this agent. Any disturbance of the natural
state of a body produces evidences of electricity.

ISOT* Does electricity seem to exist in two different states or conditions f

It does ; and to designate these two conditions, the
terms positive and negative have been employed. Thus
a body which has an overplus of electricity is called posi-
tive, and one that has less than its natui^l quantity is
called negative.

ISO 8 Do light, heat, and electricity appear to have some properties in
common f

They do / each may be made, under certain circum-
stances, to produce or excite the other. All are so light,
subtle, and diffusive, that it has been found impossible
to recognise in them the ordinary characteristics of
matter. Some suppose that light, heat, and electricity
are all modifications of some common principle.

18O9 Why does the fur of a cat sparkle and crackle when rubbed with
the hand in cold weatlier ?

Because the friction between the hand and fur pro-
duces an excitation of negative electricity in the hand
and positive in the fur, and an interchange of the two
causes a spark, with a slight noise.

1S1O Why does this experiment work best in very cold weather ?

Because the air is then very dry, and does not convey
away the electricity as fast as it is excited ; if the air,
on the contrary, were moist, the electricity would be
conducted off nearly as fast as it was excited by friction,
and its effects would not therefore be so manifest.

1811 With what velocity is electricity transmitted through good conduc-
tors f

"With a velocity so great that the most rapid motion
produced by art appears to be actual rest when com-
pared to it. Some authorities have estimated that elec-
tricity will pass through copper wrire at the rate of two
hundred and eighty-eight thousand miles in a second
of time — a velocity greater than that of light. The

SCIENCE OF COMMON THINGS. 279

Principal agents in nature exciting electricity.

results obtained, however, by the United States Coast
Survey, with iron wire, show a velocity of from 15,000
to 20,000 miles per second. »

1813 What agents are undoubtedly the most active in producing and
exciting electricity in the operations of nature f

The light and heat of the suds rays.

1813 It has become the habit with many to ascribe to electricity the
agency of phenomena in the natural world, the cause of which may not be
apparent: is there any reason for this?

There certainly is not : electricity is diffused through
all matter, and is ever active, and many of its pheno-
mena cannot be satisfactorily explained ; but it is go-
verned, like all other forces of nature, by certain fixed
laws, and it is by no means a necessary agent in all the
operations of nature.

It argues great ignorance to refer without examination every mysteri-
ous phenomenon to the influence of electricity.

1814 Do some animals have the power of exciting electricity within
themselves f

There are certain animals which are gifted with the
extraordinary power of producing electncal phenomena
by an effort of muscular or nervous energy. Among
these the electrical eel and the torpedo are most re-
markable.

1815 How powerful a charge of electricity can the electrical eel send
forth when in full vigor f

Sufficient to knock down a man or stun a horse.

1810 Is the electricity generated by these animals the same as that occa-
sioned by tlie ordinary electrical machine ?

It is the same, and produces the same effects.

Do vital action and muscular movements in man and animals
give rise to electricity f

They do ; and it can be shown by direct experiment
that a person cannot even contract the muscles of the
arm without exciting an electrical action.

1818 Does change of form or state in bodies generally produce electrical
excitation ?

Change of form or state is one of the most powerful
methods of exciting electricity.

280 SCIENCE OF COMMON THINGS.

Lightning. Three forms of lightning.

Water, in passing into steam by artificial heat, or in evaporating by the
action of the sun or wind, generates large quantities of electricity. The
crystallization of solids from liquids, all changes of temperature, the
growth and decay of vegetables, are also instrumental in producing elec-
trical phenomena.

1S1Q What is lightning f

Lightning is accumulated electricity, generally dis-
charged from the clouds to the earth, but sometimes
from the earth to the clouds.

1S3O What causes the discharge of an electric cloud?

When a cloud overcharged with electric fluid ap-
proaches another which is undercharged, the fluid
rushes from the former into the latter, till both contain
the same quantity.

18J31 Is there any other cause of lightning besides the one just men-
tioned ;

Yes ; sometimes mountains, trees, and steeples will
discharge the lightning from a cloud floating near, and
sometimes the electricity passes from the earth, into
the clouds.

1833 How high are the lightning clouds from the earth?

Sometimes they are elevated four 01* five miles high,
and sometimes actually touch the earth with one of
their edges ; but they are rarely discharged in a thun-
der storm when they are more than seven hundred
yards above the surface of the earth.

1833 What is a thunder storm ?

The disturbance caused" in the air when successive
discharges of accumulated electricity take place.

1S34 Into how many kinds has lightning been divided ?

Three.

1835 What are they ?

The zig-zag lightning, sheet lightning, and hall light-
ning.

1836 Why is lightning sometimes forked ?

Because the lightning cloud is at a great distance ;
and the resistance of the air is so great that the electri-
cal current is diverted into a zig-zag course.

SCIENCE OF COMMON THINGS. 281

Sheet and heat lightning. Duration of a flash of lightning.

1837 How does the resistance of the air make the lightning zig-zag ?

As the lightning condenses the air in the immediate
advance of its path, it flies from side to side, in order
to pass where there is the least resistance.

18SS Why is the flash sometimes quite straight ?

Because the lightning cloud is near the earth, and as
the flash meets with very little resistance, it is not
diverted ; in other words, the flash is straight.

183Q What is sheet lightning?

Either the reflection of distant flashes not distinctly
visible or beneath the horizon, or else several flashes
intermingled.

1830 What other form does lightning occasionally assume ?

Sometimes the flash is globular, which is the most
dangerous form of lightning.

1831 Does a discharge produce a flash when it passes through good
conductors f

It does not, but passes quietly and invisibly.

1S3S What is heat lightning f

Sometimes it is the reflection in the atmosphere of
the lightnings of storms very remote, the storms them-
selves being so far distant that their thunders cannot
be heard. This phenomenon is also occasioned by the
play of silent flashes of electricity between the earth
and the clouds, the amount of electricity developed not
being sufficient to produce any other effects than the
mere flash of light.

1833 Why is lightning more common in summer and in autumn than
in spring and winter f

Because the heat of summer and autumn produces
great evaporation, and the conversion of water into
vapor always developes electricity.

1834 How long is the duration of a flash of lightning f

Arago has demonstrated that it does not exceed the
millionth part of a second.

1835 With ivhat velocity is lightning, or the electric fluid which gives
rise to its appearance, supposed to move f

282 SCIENCE OF COMMON THINGS.

Places dangerous in a thunder storm. How a tree influences lightning.

Not less than two hundred and fifty thousand miles
per second.

1836 Why does lightning sometimes kill men and leasts f

Because, when the electric current passes through a
man or beast, it produces so violent an action upon the
nervous system, that it destroys life.

1337* When is a person struck dead by lightning 1

Only when his body forms a part of the lightning's
path j that is, when the electric fluid (in its way to the
earth) actually passes through his body.

1838 Wliat places are most dangerous during a thunder storm f

It is very dangerous to be near a tree or lofty building.

1839 Why is it dangerous to be near a tree or lofty building during a
thunder storm f

Because a tall, pointed object (like a tree or spire)
will frequently discharge a lightning cloud ; and if any
one were standing near, the lightning might diverge
from the tree and pass through the fluids of the human
body.

1S4O How can a tree or spire discharge a lightning cloud f

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 this distance, it might no longer be too
far off to be discharged.

For example : If a lightning-cloud were seven hundred yards above the
, earth, it might be too far off to be discharged ; but a tree or spire fifty
yards high would make the cloud only six hundred and fifty yards off a
conductor ; in consequence of which the cloud might be instantly dis-
charged.

1841 What parts of a dwelling are most dangerous during a thunder-
storm f

The fireplace (especially if the fire be lighted). It is
also imprudent to sit close by the walls.

1843 Why is it dangerous to sit before afire during a thunder storm f

Because the heated air and soot are conductors of
lightning, especially when connected with such excel-
lent conductors as the stove, grate, or fire-irons.

1843 Why is it dangerous to lean against a wall during a thunder
storm f

SCIENCE OF COMMON THINGS. 283

Safest places in a thunder storm.

Because the electric fluid will sometimes run down
a watt, and (as the body of a person is a better conduc-
tor than a wall) would leave the wall and run.' down the
body.

184:4 Why is it dangerous to be in a crowd during a thunder storm f

For two reasons : 1. Because a mass of people forms
a better conductor than an individual', and

2. Because the vapor arising from a crowd increases
its conducting power.

1845 Why is the danger increased by the vapor which rises from a
crowd?

Because vapor is a conductor, and the more conduc-
tors there are, the greater the danger will be.

1846 If a person be abroad in a thunder storm, what place is the
safest ?

Any place about twenty or thirty feet from a tall
tree, building, or stream of water.

1847* Why would it be safe to stand twenty or thirty feet from a tall
tree during a thunder storm ?

Because the lightning generally chooses tall trees as
conductors, and we should not be sufficiently near the
trees for the lightning to diverge from them to us.

1848 Why is the middle of a room more safe than any other part of
it in a thunder storm ?

Because the lightning (if it should strike the room at
all) would come down the chimney or walls of the room;
and therefore the farther distant from these, the better.

184Q Why is a mattress, bed, or hearth-rug a good security against
injury from, lightning ?

Because they are all non-conductors ; and as lightning
always makes choice of the lest conductors, it would not
choose for its path such things as these.

1850 What is the safest thing a person can do to avoid injury from
lightning ?

Lie upon a led in the middle of a room. A led filled
with feathers is an excellent non-conductor.

1851 Is there not generally a greater apprehension of the danger from
lightning than experience would justify ?

The apprehension and solicitude respecting lightning

284: SCIENCE OF COMMON THINGS.

Lightning conductors. Their proper principle of construction.

are proportionate to the magnitude of the evils it pro-
duces, rather than the frequency of its occurrence. The
chances of an individual being killed by lightning are
infinitely less than those which he encounters in his
daily .walks, in his occupation, or even during his sleep
from the destruction of the house in which he lodges
by fire.

185S Why does the lightning in its course down a building generally
dart from point to point, and not follow a direct path ?

Because it always takes in its course the best conduc-
tors ; and will fly both right and left in order to reach
them.

1853 What is a lightning conductor f

A metal rod fixed in the earth, running up the whole
height of a building, and rising in a point above it.

185<b What metal is best, for this purpose f

Copper makes the best conductor.

1855 What is the use of a lightning conductor f

As metal is a most excellent conductor, lightning
(which makes choice of the best conductors) will run
down a metal rod rather than the walls of the building.

1856 Why should lightning conductors be pointed f

Because points conduct electricity away silently and
imperceptibly. •

Blades of grass, ears of corn, and other pointed objects serve to with-
draw electricity from the clouds.

1857* How far will the beneficial influence of a lightning conductor
extend f

It will protect a space all round four times the length
of that part of the rod which rises above the building.

1858 Give me an example.

If the rod rises two feet above the house, it will pro-
tect the building for (at least) eight feet all round.

1859 How can lightning conductors be productive of harm ?

If the rod be broken, the electric fluid (being obstruct-
ed in its path) will enter the building.

18BO Is there any other evil to be apprehended from a lightning rod f

Yes ; if the rod be not large enough to conduct the

SCIENCE OF COMMON THINGS. 285

Franklin's experiment with a kite. Identity of lightning and electricity.

whole current to the earth, the lightning will fuse the
metal and enter the building.

1861 By' whom was Uie identity of lightning and electricity first esta-
lliahed f

By Dr. Franklin, at Philadelphia, in 1752.

The manner in which this fact was demonstrated, was as follows:
Having made a kite of a large silk handkerchief stretched upon a frame,
and placed upon it a pointed iron wire connected with the string, he raised
it upon the approach of a thunder storm. A key was attached to the
lower end of the hempen string holding the kite, and to this one end of a
silk ribbon was tied, the other end being fastened to a post. The kite
was now insulated, and the experimenter for a considerable time awaited
the result with great solicitude. Finally, indications of electricity began
to appear on the string; and on Franklin presenting his knuckles to the
key, he raised an electric spark. The rain beginning to descend, wet the
string, increased its conducting power, and vivid sparks in great abun-
dance flashed from the key.

18 63 Why was the Me insulated when FranUin fastened tlie key to the
post with a silk ribbon ?

Because the silk was a non-conductor ', and would not
allow the electricity received upon the kite to pass off
by means of the string to the ground.

1863 Was this experiment one of great danger and risk ?

It was ; because the whole amount of electricity con-
tained in the thunder cloud was liable to pass from it,
by means of the string, to the earth, notwithstanding
the use of the silk insulator.

1864 If a lightning rod is made of iron, how large should it be f

•Not less than three-quarters of an inch in diameter.

1865 In what manner should the rod be erected ?

The rod should be continuous from the top to the bot-
tom, and an entire metallic communication should exist
throughout its whole length.

This law is violated when the joints of the several parts that form the
Conductor are imperfect and when the whole is loosely put together.

1866 How should tlie conductor be fastened to tfie building?

By wooden supports.

- If there are masses of metal about the building, as gutters, pipes, etc.,
these should be connected with the rod by strips of metal ; for unless this
is done the lightning may pass from the rod to the metal, and enter the
building^

28(5 SCIENCE OF COMMON THINGS.

Utility of lightning-rods. What is thunder ?

1867 How should the lower end of the rod be arranged ?

It should be divided into two or three branches, and
turned from the building.

The end of the rod ought to extend so far below the surface of the
ground as to reach earth that is permanently damp.

1868 Why is it a good plan to bury the end of the rod in powdered
charcoal f

Because it preserves the iron from rust, and facili-
tates the passage of the electricity.

1869 Have we any proof of the utility of lightning rods f

The experience of a hundred years has shown that
when all the necessary rules have been observed, the
protection is perfect, as far as human effort can avail.

187*0 Is a buikling more or less liable to be struck when furnished with
a good lightning conductor f

Lightning conductors do not, as many suppose, attract
the lightning towards the building on which they are
situated ; they simply direct its course, and facilitate
the passage of the fluid in the most direct way to the
earth, only when a discharge must inevitably occur.
There is no attraction, but the lightning takes the road
which offers the least resistance.

187*1 Are lightning conductors protective when even no visible discharge
takes place f

They are; they possess a very great preventive
power, and gradually and silently disarm the clouds by
conducting the electricity from them ; and this process
commences as soon as the cloud has approached a posi-
tion vertically over the rod.

18 7S What is thunder?

It is a certain noise proceeding apparently from the
clouds, which usually follows, after a greater or less
interval, the appearance of a flash of lightning.

187*3 How is it supposed to be occasioned?

The usual explanation offered is a sudden displace-
ment of the air produced by the electrical discharges in
which the lightning is evolved.

Others have supposed that the passage of the electric current creates a

SCIENCE OF COMMON THINGS. 287

What occasions the rolling of thunder ? Aurora- borealis.

vacuum, and that the air rushing in to fill it produces the sound. Any
explanation that has yet been ottered is not altogether satisfactory.

1374 What occasions the rotting of the thunder %

It has been ascribed to the effect of echo ; but the
true cause probably is, that the sound is developed by
the lightning in passing through the air, and conse-
quently separate sounds are produced at every point
through which the lightning passes.

187*5 Why is thunder sometimes one vast crash?

Because the lightning cloud is near the earth ; and
as all the vibrations of the air (on which sound depends)
reach the ear at the same moment, they seem like one
vast sound.

187*0 Why is the thunder generally heard several moments after the
/lash?

Because it has a long distance to travel. Lightning
travels nearly a million times faster than thunder ; if,
therefore, the thunder has a great distance to come, it
will not reach the earth till a considerable time after
the flash.

187"? Can we not tell the distance of a thunder cloud by observing the
interval which elapses betiveen the flash and the peal f

Yes ; the flash is instantaneous, but the thunder will
take a whole second of time to travel three hundred and
eighty yards ; hence, if the flash be five seconds before
thunder, the cloud is nineteen hundred yards off.

i. e. 380 x 5=1900 yards.

187*8 What is the aurora borealis or northern lights f

JLuminous appearances seen in the sky at night-time.
Sometimes streaks of blue, purple, green, red, etc., and
sometimes flashes of light, are seen.

187*9 What is the cause of the aurora borealis or northern lights ?

Electricity in the higher regions of the atmosphere
is undoubtedly an active agent in producing this pheno-
menon.

188O Is the aurora ever seen in other parts of the heavens than towards
the north f

In the northern hemisphere it always appears in the

288

SCIENCE OF COMMON THINGS.

Extent of the aurora. Height of the aurora. Appearance.

north) but in the southern hemisphere it appears in the
south : it seems to originate at or near the poles of the
earth, and is consequently seen in its greatest perfection
within, the arctic and antarctic circles.

1S81 What is known concerning the extent of the auroral

It is not local, but it is seen simultaneously at places
widely remote from each other, as in Europe and
America.

1883 What calculations "have been made respecting the height of the
aurora f

The height of the appearances varies from one to two
hundred miles / they sometimes appear within the
region of the clouds, and very near to the earth.

1883 Do the auroras appear at any particular seasons and times f

They appear more frequently in the winter than in
the summer, and are only seen at night.

Fig. 84.

The accompanying figure represents one of the most beautiful of the
auroral phenomena.

1884 Do they also occur in the day -time f

The aurora is known to affect the magnetic needle and

SCIENCE OF COMMON THINGS.

Aurora-borealis occurs In the day-time. TThat is galvanism ?

the telegraph ; and as the effects upon these instruments
are noticed by day as well as by night, there can be no
doubt of the occurrence of the aurora at all hours. The
intense light of the sun renders the auroral light in-
visible during the day.

1385 Of what utility are the auroral appearances in the polar regions ?

During the long polar night, when the sun is absent,
the aurora appears with a magnificence unknown in
other regions, and affords light sufficient for many of
the ordinary out-door employments.

CIIAPTEE II.

GALVANISM.

1886 What is galvanism ?

It is the production of electrical disturbance by chemi-
cal action.

1887* What is the most simple manner of illustrating the production of
this electricity?

If we place a piece of silver on the tongue, and a
piece of zinc underneath it, no effect will be produced
as long as the two metals are kept asunder ; but when
their ends are brought together, a distinct thrill will
pass through the tongue, a metallic taste will diffuse
itself, and, if the eyes are closed, a sensation of light
will be evident at the same moment.

1888 To what is this result owing f

To a chemical action developed the moment the two
metals touched each other.

The saliva of the tongue oxidizes a portion of the zmc, which excites
electricity, for no chemical action ever takes place without producing elec-
tricity. Upon bringing the ends of the two metals together, a slight
current passes from one to the other.

1889 By whom was the production of galvanic electricity first noticed t

290

SCIENCE OF COMMON THINGS.

How galvanic electricity was discovered.

By Galvani, professor of anatomy at Bologna, Italy,
in 1790.

Having occasion to dissect several frogs, he hung up their hind legs on
some copper hooks, until he might find^t necessary to use them for illus-
tration. In this manner he happened to suspend a number of the copper
hooks on an iron balcony, when, to his great astonishment, the limbs wero
thrown into violent convulsions.

189O On investigating the phenomena what did Galvani discover ?

He found that whenever the nerves of a frog's leg
were touched by one metal and the muscles by another,
convulsions took place on bringing the two different
metals in contact.

Fig. 85.

This is explained by reference to Fig. 85, which represents a frog's legs,
the upper part dissected in such a way as to exhibit the nerves of the legs-?.,
and a portion of the spinal marrow. If we now take two thin pieces of cop-
per and zinc. C z, and place one under the nerves, and the other in contact
with the muscles of the leg, we shall find that so long as the two pieces
of metal are separated, so long will the limbs remain motionless, but by
making a connection, instantly the whole lower extremities will be thrown
into violent convulsions, quivering and stretching themselves in a manner
too singular to describe. If the wire is kept closely in contact, these
phenomena are of momentary duration, but are renewed every time the

SCIENCE OF COMMON THINGS.

291

Construction of a galvanic battery.

Origin of the term "galvanism.''

Fig. 86.

contact is made and broken, Here, then, we have distinct evidence of
the presence of free electricity, developed apparently by simple contact.

1891 What is the simplest way of exciting a current of galvanic elec-
tricity f

By arranging a series of metal plates in a
pile, placing them in pairs, with a wet cloth
Between them, it berng necessary that one
of each pair should be more easily oxidized
than the other. The simple contact of these
plates will produce a feeble and continued
galvanic current.

Fig. 86 represents an arrangement of this character.

180S What is such an arrangement of plates for pro-
ducing electrical currents called f

A galvanic or voltaic battery.

1893 Why are the terms "galvanic" and "voltaic"
applied ?

They originated in honor of Galvani and
Volta, the Italian philosophers who first de-
veloped these phenomena of chemical electricity, and
the means of producing them.

1894 Are there many metals or other substances which, wlien brought
together, are capable of producing galvanic action f

The number is quite large ; among them we may
enumerate the following : zinc, lead, tin, antimony,
iron, brass, copper, silver, gold, platinum, Hack lead or
graphite, and charcoal.

1895 Witt any two of these brought together produce a galvanic current f

They will : but they possess the power in different
degrees ; and the more remote they stand from each
other in the order above given, the more decidedly will
the chemical electricity be developed.

Thus zinc and lead will produce a voltaic battery, but it will be much
less active than zinc and iron, or the same metal and copper, and this last
less active than zinc and platinum, or zinc and charcoal.

1896 Does galvanic or voltaic electricity appear to consist of two kinds,
positive and negative, as in ordinary electricity ?

It does ; positive electricity always flows from tlie
'metal which is acted upon most powerfully, and nega-
tive electricity from the other.

292

SCIENCE OF COMMON THINGS.

Poles of a battery. Means by which galvanic-electricity in quantity can be developed.
1897* What do we mean when we speak of a galvanic circuit ?

The connection of the two metals in the battery, so
that the positive and negative electricities can meet,
and flow in opposite directions.

1898 At what point in the circuit will the manifestations of electricity
be most apparenl ?

At the point where the two currents meet.

' 1899 What is meant by the poles of the battery ?

The two metals forming the elements of the battery
are generally connected by copper wires ; the ends of
these wires, or the terminal points of any other connect-
ing medium used, are called the poles of the battery.

Thus, when zinc and copper poles are used, the end of the wire con-
veying positive electricity from the zinc would be the pbsitive pole, and
the end of the wire conveying negative electricity from the copper plate
would be the negative pole. Faraday describes the poles of the battery
as the doors by which electricity enters into or passes out of the substance
suffering decomposition.

A very simple, and at the same time an active, galvanic circuit may be
formed by an arrangement as re-
presented in Fig. 87. C and Z are
thin plates of copper and zinc im-
mersed in a glass vessel containing
a very weak solution of sulphuric
acid and water. Metallic contact
is made by means of the" wires, X
and W, soldered to the plates, the
poles intersecting at Y. The cur-
rent of positive electricity, when
the circuit is closed, passes from
the zinc, through the liquid, to the
copper, and from the copper, along
the conducting wires, to the zinc,
as indicated by the arrows in the
figure. A current of negative elec-
tricity traverses the circuit also, Fig. 87.
from the copper to the zinc, in a
direction precisely reversed.

1900 By lohat chemical action can the greatest abundance of galvanic
electricity be developed ?

By the oxidation of metallic zinc by weak sulphuric
acid.

01 Ol The electricity developed by the action of a single pair of plates
immersed in acid water is very feeble : how can it be increased ?

By increasing the number of the plates and the quan-

SCIENCE OF COMMON THINGS

293

Different forms of galvanic batteries. Light and beat produced by galvanism.

tity of the liquid, we increase the intensity of the elec-
tricity developed.

Fig. 88.

Fig. 89.

Figs. 88 and 80 represent some of the most common forms of galvanic
batteries. In Fig. 88 two plates of zinc, z z, inclosing a piece of silver
between them, are immersed in a glass cylinder, Gr, containing acid ; S
and A represent the poles of the battery. In Fig. 89 the battery con-
gists of two concentric cups or cylinders of copper, C, and a cylinder of
zinc, Z, fitting between. The acid solution is poured into the spaces be-
tween the cylinders. Another form consists of an earthenware trough,
containing acid, in which alternate plates of copper and zinc are arranged,
and connected together by wires rising from each end of the trough.

19O3 What are the most ordinary effects produced by the developed
electricity of a large galvanic battery f

The production of sparks and brilliant flashes of
light, the heating and fusing of metals, the deflagration
of gunpowder and other inflammable substances, and
the decomposition of water, saline compounds, and
metallic oxides.

19 O3 How may the most splendid artificial light known be produced f

By fixing pieces of pointed charcoal to the wires
connected with opposite poles of a powerful galvanic
battery, and bringing them into contact.

19 O 4 Can intense heat be developed by the action of the galvanic bat-
tery as well as intense light ?

The greatest artificial heat man has yet succeeded in
producing has been through the agency of the galvanic
oattery.

19O5 What refractory substances c&n be fused by the aid of the gal'

vanic battery f

All the metals, including platinum, can be readily

294 SCIENCE OF COMMON THINGS.

Principles and processes of electro-metallurgy.

melted / quartz, sulphur, magnesia, slate, and lime are
liquefied ; and the diamond fuses, boils, and becomes
converted into coal.

19 OG What is ekctrotyping, or electro-metallurgy ?

It is the art or process of depositing, from a metallic
solution, through the agency of galvanic electricity, a
coating or film of metal upon some other substance.

19O7 Upon what principles is it accomplished f

The process is based on the fact, that when a galva-
nic current is passed through a solution of some metal,
as a solution of sulphate of copper (sulphuric acid and
copper), decomposition takes place / the metal is sepa-
rated in a metallic state, and attaches itself to the nega-
tive pole, or to any substance that may be attached to
the negative pole; while the acid or other substance
before in combination with the metal, goes to, and is
deposited on the positive pole.

In this way a medal, a wood-engraving, or a plaster cast, if attached
to the negative pole, may be covered with a coating of copper; if the
solution had been one containing silver or gold, the substance would
have been covered with a coating of silver or gold instead of copper.

19 OS How can the thickness of the deposits be regulated f

The thickness of the deposit, providing the supply
of the metallic solution be kept constant, will depend
on the length of time the object is exposed to the influ-
ence of the 'battery.

In this way, a coating of gold thinner than the thinnest gold-leaf can
be laid on, or it may be made several inches or feet in thickness, if
desired.

The process of electrotyping has been strikingly taken advantage of in
reproducing expensive engraved plates, as the map-plates of the Coast
Survey of the United States. The plate of the map, usually on copper, is
frequently the work of years under the hand of the engraver, the cost
being counted by thousands of dollars. If the plate, when finished, were
printed on directly, the pressure of the paper a few hundred times would
goon obliterate the faint lines of the engraving on the metal, and the plate
would soon become injured or spoiled. But now the original plate is
uever printed on. but an electrotype on copper is taken from it, at a very
email expense ; and this may be repeated almost indefinitely, thus afford-
mg fresh plates for printing whenever required.

SCIENCE OF COMMON THINGS. 295

Magnetism. Natural magnets. Where found.

CHAPTER III

MAGNETISM.

1909 Is there any connection "between magnetism and electricity f

There is every reason to believe that magnetism and
electricity are but modifications of one force.

10 1O What is a loadstone or a natural magnet f-

It is an ore of iron, known as the "protoxide of
iron" or " magnetic oxide of iron" which is capable
of attracting other pieces of iron to itself; and if sus-
pended freely by a thread, and left to take its own po-
sition, it will arrange itself so that its extremities will
point towards the north and south, poles of the earth.

1911 Are natural magnets rare ?

They are not • they are found in many places in the
United States. In Arkansas, especially, an ore of iron
possessing remarkably strong attractive powers is very
abundant.

The magnetic ore is usually of a dark
grey hue, and possesses but little me-
tallic lustre. Fig. 91. If a piece of this
ore be dipped in iron filings, or a number
of small needles, they will generally be
found collected and clinging together in
great quantities at two opposite extremi-
ties, as represented in the figure, whilst
the middle portion is nearly destitute.
The magnetic property, whatever it may F5B. 91.

be, seems therefore to be collected and act
with the greatest energy at two opposite extremes; these have been
termed poles.

1913 What is the origin of the terms " magnet" and " magnetism ?"

The loadstone or natural magnet was first found at
Magnesia, in Lydia, Asia, whence were derived the
names.

1913 Can a natural magnet communicate its attractive properties to
sther bodies by contact ?

It can, and that too without any apparent loss of
attractive strength.

296 SCIENCE OF COMMON THINGS.

Bodies capable of being magnetized. Induction. Magnetic needle.

1014 What bodies are capable of being magnetized by contact with
natural magnets ?

Iron and steel are the substances most susceptible of
tins influence, but brass, nickel, and cobalt can also
become magnets.

1015 Does the magnetism imparted to a piece of soft iron, or steel, by
contact with a natural magnet, remain permanent in their substances f

In the steel it does^ but the soft iron loses its power as
soon as it is removed from the magnet.

1016 Is it necessary that absolute contact should take. place between a
magnet and a pwcu of soft iron to render the latter a magnet 1

No, every piece of soft iron brought near a magnet
becomes by induction itself a magnet.

IS*!*? What dc you mean by induction ?

It is the production of like effects in contiguous bo-
iifs. In electricity or magnetism, it is the influence
exerted by an electrified or magnetized body through
a non-conducting medium without any apparent com-
munication of a current.

1018 What is meant by the directive power of the magnet f

It is that power which will cause a magnet, when
suspended freely, to constantly turn the same part to-
wards the north pole and the opposite part towards the
south pole of the earth.

1010 What are the poles of a magnet f

They are the ends of the magnet, and are denomi-
nated north and south poles, according as they point to
the north or south poles of the earth.

103O What are the poles of the earth ?

The extremities of the earths axis, or the points on
the surface of the globe through which the axis passes.

1031 What is a magnetic needle ?

Simply a bar of steel which is a
magnet, suspended in such a way
that it can freely turn to the north
or south.

1033 What is a mariner's compass f

It is a delicate steel lar or

Jig. 92-

SCIENCE OF COMMON THINGS. 297

The magnetic compass. ^Discovery and first use of the compass.

needle balanced upon & pivot placed beneath its centre
of gravity in such a way that it can turn horizontally
without obstruction. This needle is usually inclosed in
a box, upon the bottom of which is a card, with the
various points- — north, south, east, west, etc., etc.,
marked upon it.

Fig- 92.

Such a needle, if the box containing it be- placed on a level surface, will
generally be observed to vibrate more or less, till it settles in such a
direction that one of its extremities or poles will point towards the north,
and the other consequently towards the south. If the position of the box
be altered or reversed, the needle will always turn and vibrate again, till
its poles have attained the same direction as before.

1933 Does the compass needle always point exactly north and south ?

It does not / its natural direction is towards the north
and south poles, but it seldom points due north or

south.

1934 Who first discovered the fact that a magnet would invariably
point to the north -and the south, and made use of this knowledge in construct-
ing a ompass?

It is claimed to have been discovered by the Chinese:
it was known in Europe, and used in the Mediterranean,
in the thirteenth century.

1935 How were the compasses of that time constructed?

They were merely pieces of loadstone fixed to a cork,
which floated on the surface of water.

1936 Is the earth itself supposed to be a magnet?

It is undoubtedly a great magnet.

208 SCIENCE OF COMMON THINGS

How iron bars become magnetic. Horse-shoe magnets.

1937 Is iron under certain circumstances rendered magnetic by the
inductive action of tlie earth} s magnetism f

Most iron bars and rails, as the vertical bars of win-
dows, that have stood for a considerable time in a per-
pendicular position, will be found to be magnetic.

1938 If we suspend a bar of soft iron sufficiently long in the air, will it
assume magnetic properties ?

It will gradually become magnetic; and although
5vlien it is first suspended it points indifferently in any
direction, it will at last point north and south.

1939 How may a bar of iron, such as a kitchen poker, be made imme-
diately magnetic, without resorting to the use of other magnets f

If the bar devoid of magnetism is placed with one
end on the ground, slightly inclined towards the north,
and then struck one smart blow with a hammer upon
the upper end, it will immediately acquire polarity, and
exhibit the attractive and repellant Droperties of a
magnet.

1930 What is a horse-shoe magnet f

It is a magnetic bar bent into the form of a horse-shoe.

"When a piece of iron not magnetic is brought in
contact with a common magnet, it will be attracted
by either pole; but the most powerful attraction
takes place when both poles can be applied to the
surface of the piece of iron at once. The magnetic
bars are for this purpose bent into the shape of the
letter U, and are termed horse-shoe magnets.
Several of these are frequently joined together
with their similar poles in contact ; they then con-
stitute a magnetic battery, and are very powerful,
either for lifting weights, or charging other mag-
Fig. 93. nets. (See Fig. 93.)

1931 If we break a magnet across the middle, what happens f

Each fragment becomes converted into a perfect
magnet; the part which originally had a north pole
acquires a south pole at the fractured end, and the part
which originally had a south pole, gets a north pole.

1933 If we divide up a magnet to the extreme degree of mechanical fine-
ness possible, will the pieces possess magnetic powers f

Each fragment, however small, will be a perfect
magnet

SCIENCE OF COMMON THINGS. 299

Electro-magnetism. When and how discovered.

CHAPTER IY.

ELECTRO-MAGNETISM.
1933 What is electro-magnetism f

It is the magnetism developed through the agency
of electrical or galvanic action.

1034 What were the earliest phenomena observed which indicated a
relation between magnetism and electricity f

It was noticed that ship's compasses have their direc-
tive power impaired by lightning, and that sewing
needles could be rendered magnetic by electric dis-
charges passed through them.

1935 What discovery, made by Prof. Oersted of Copenhagen, esta-
blished beyond a doubt the connection of electricity and magnetism f

He ascertained that a magnetic needle placed near a
metallic wire connecting the poles of a galvanic battery
was compelled to change its direction, and that the new

direction it assumed was deter-
mined by its position in rela-
tion to the wire and to the di-
rection of the current trans-
mitted along the wire.

Thus, if, as in Fig. 94, a needle be in-
Fig. 94. closed in a wire not touching it at any

point, and a current of electricity pass

through the wire, the needle will be made to move in accordance with the
direction of the current

1036 What other important discovery was made about the same
time ?

It was found that if a piece of soft iron, not possessing
magnetic power sufficient to elevate a grain weight, be
placed within a coil of copper wire through which a
galvanic current is passing, it will become, through the
influence of the current, a powerful magnet ; and will,
so long as the current flows, sustain weights amount-
ing to many hundreds of pounds. (See figs. 95 and
96.)

300

SCIENCE OP COMMON THINGS.

Excitation of Magnetism. Morse's Magnetic Telegraph.

Fig. 94.

Fig. 95.

193*7 Is Hie magnetic power of the bar found to be wholly dependent on
(he existence of the current f

It is / the moment the current stops, the weights
fall away from the bar in obedience to the law of
gravity.

1933 How great weights have been lifted by magnets formed in this
manner 1

An electro-magnet constructed by Prof. Henry was
capable of elevating and sustaining about a ton weight.

1939 Upon what principle does the construction of the Morse magnetic
telegraph depend ?.

Upon the principle that a current of electricity circu-
lating about a bar of soft iron is capable of rendering it
a magnet.

The arrangement by which this principle is made available in the con-
struction and operation of the Morse magnetic telegraph will be under-
stood by reference to the accompanying diagram (Fig. 96), which repre-
sents the construction and arrangement of this form of telegraph. F and
E are pieces of soft iron surrounded by coils of wire, which are connected
at o and b with wires proceeding from a galvanic battery. When a cur-
rent is transmitted from a battery located one, two, or three hundred
miles, as the case may be, it passes along the wires and into the coils sur-
rounding the pieces of soft iron F and E, thereby converting them into
magnets. Above these pieces of soft iron is a metallic bar or lever, A,
supported on its centre, and having at one end the arm D, and at the
other a small steel point, o. A ribbon of paper, p h, rolled on the cylinder
B, is drawn slowly and steadily off by a train of clock-work, K, moved by
the action of the weight P on the cord C. This clock-work gives motion
to two metal rollers, G and H, between which the ribbon of paper passes,
and which, turning in opposite directions, draw the paper from the cylin-
der B. The roller H has a groove around its circumference (not repre-
sented in the engraving) above which the paper passes. The steel point,
9, of the lever, A, is also directly opposite this groove. The spring r pre-

SCIENCE OF COMMON THINGS.

301

Telegraph, magnetic, principles of.

Intelligence, how conveyed by.

Fig. 96.

vents the point from resting upon the paper when the telegraph is not in
operation.

1940 Why is it necessary, in conveying the telegraph wires, to support
them upon glass or earthen cylinders f

These are used for the purpose of insuring the perfect
insulation of the wires, since but for this the electricity
would pass down a damp pole to the earth, and be lost.

1941 Is there any truth in the idea that many persons have, that some
principle passes along the telegraphic wires when intelligence is transmitted ~?

This supposition is wholly erroneous ; the word cur-
rent, as something flowing, conveys a false idea, but we
have no other term to express electrical progression.

1943 How can we, gain an idea of what really takes place, and of the
nature of the influence transmitted ?

The earth and all matter are reservoirs of electricity ;
if we disturb this electricity at Boston by voltaic influ-
ence, its pulsations may be felt in New York. Suppose
the telegraphic wire were a tube, extending from
Boston to New York, filled with water. Now, if one
drop more is forced into it at Boston, a drop must fall
out at New York, but no drop was caused to pass from
Boston to New York. Something similar to this occurs
in the transmission of electricity.

302 SCIENCE OF COMMON THINGS.

"What is starch ? How manufactured ?

PART IX.

FAMILIAR CHEMISTRY.

1943 What is starch f

The name starch is given to a mealy substance which
is deposited in most vegetables at the time of ripening,
from the juices with which the cells of the plants are
filled.

1944 What common vegetable especially abounds in starch f

The potato ; which consists entirely of cells filled
with starch and water.

A cell is a little membranous bladder filled with a solid or fluid sub-
stance.

1945 Why does the laundress find it necessary to boil starch before
using it for stiffening linen, etc. f

The starch, consisting of little granules, is insoluble
in cold water ; but when acted upon by hot water,
the granules burst and allow their contents, which are
soluble, to become mingled with the water.

Starch is manufactured as follows : —

Potatoes, for example, from which most of the starch of commerce is
manufactured, after being pared, are grated to a pulp. This pulp is put
upon a sieve and stirred about, while at the same time a little stream of
water is made to flow upon it. A milkjr liquid runs through the sieve,
but the fibrous portion of the potato, the vegetable tissue, remains behind.
This liquid, after a short interval, deposits a white powder, which is the
starch. By the simple process of tearing up the vegetable tissue, and
removing the inclosed starch by washing, this substance may be procured
from a great variety of plants.

1946 Why do potatoes, beans, rice, and most of the common vegetables,
swell up when boiled with water f

Because the starch absorbs water at the boiling tern-

SCIENCE OF COMMON THINGS. 303

Composition of wheat flour. Acids. Alkalies.

perature, which causes the cells to swell, thereby giv-
ing to the vegetable a rounded appearance.

1947* What is the composition of wheat flour?

Starch is one of the principal constituents of wheat
flour, as well as of all other kinds of meal. The other
principal constituent is a grey, tough, viscous sub-
stance, called gluten.

1048 To what does paste, made of wheat or rye flour, owe its adhe~
siveness f

In some measure to the starch, but principally to the
gluten contained in it.

1949 Can starch be converted into gum. and sugar f

It can ; fruits and plants effect this change natu-
rally: we can also produce the change artificially by
chemical * rocesses.

50 SO Why are potatoes frozen and thawed sweet f

Because by the freezing action the starch of the po-
tato is in part converted into sugar.

1951 Why are apples, pears, grapes, etc., in their unripe state sour,
and in their ripe condition sweet ?

In the unripe fruits mentioned starch is present ; in
the ripe fruits it is absent • in the process of ripening
the starch is converted into sugar, and the fruit losing
its sour taste, becomes sweet.

1953 What are acids f

Acids are substances which excite the taste of sour-
ness when applied to the tongue ; they change the blue
juices of vegetables to red, and combine with alkalies
to form neutral compounds.

1953 What is an alkali?

An alkali is a body that possesses properties the
converse of those of an acid. It has a highly bitter,
acrid taste, changes the blue juices of vegetables green,
or the juices of vegetables which have been changed
red by an acid, back again to blue. Potash and soda
are the representatives of the alkalies.

3.954 When sulphur is burned in the air what is the product formed 1

Sulphurous acid.

304: SCIENCE OF COMMON THINGS.

Sulphuric, nitric, and muriatic acids. Sulphuretted hydrogen.

1955 What causes the suffocating odor of a lighted brimstone match ?

The sulphurous acid generated by the combustion
of the sulphur.

1956 What is sulphuric acid or oil of vitriol r

It is a compound of sulphur and oxygen, containing
one-third more oxygen than sulphurous acid.

1057 What is sulphuretted hydrogen f

, A gas formed by the union of sulphur and hydrogen.
llt possesses an offensive odor, and is very poisonous.

1953 How is sulphuretted hydrogen formed in nature f

Principally from the decomposition of animal $ub~
stances, as blood, flesh, hair, etc.

1959 Why does the yolk of an egg tarnish a silver spoon ?

Because it contains a little sulphur, which, at the
temperature of an egg just boiled, will decompose the
water or moisture upon the spoon, and produce sul-
phuretted hydrogen gas, which will tarnish silver.

Both the white and the yolk contain sulphur, but the latter the most
abundantly.

1960 What is it that makes an open or foul sewer so destructive of
health to any district in which it may be situated ?

The evolution of sulphuretted hydrogen. When in-
haled, it acts directly upon the blood, thickening it,
and turning it black.

1961 Why do surfaces painted with lead paints, in the vicinity of sew-
ers, soon turn black, or become discolored f

Through the action of sulphuretted hydrogen.

1963 What is nitric acid f

Nitric acid, or aqua-fortis, is a compound of five
parts of oxygen and one of nitrogen.

It is a liquid ; when pure, colorless, and highly corrosive ; it attacks al-
most all dead, unorganized substances, and destroys living tissues.

1963 What is muriatic, or, more properly, hydrochloric acid?

A compound of hydrogen and chlorine usually pre-
pared from salt. It is an acid much used in the arts.

1964 What is " lunar caustic ?"

A compound of nitric acid and oxide of silver.

1965 Why, when lunar caustic is applied to the flesh, does it burn and
destroy it ?

SCIENCE OF COMMON THINGS. 305

Tanning of hides to form leather. Vinegar Alcohol. Yeast.

Through the agency of the nitric acid contained in it.

196 6 Do plants produce acids f

Acids are formed in the vegetable kingdom in great
abundance / they especially exist in unripe fruits, im-
parting to them a sour taste.

Acids formed from mineral substances are called "mineral acids;''
acids formed by or from vegetable subsiunces are called " organic acids."

196*7 Why does tanning hides convert them into leather f

Hides are steeped in water, with ground bark of the
oak, hemlock, or other trees ; these barks contain large
quantities of tannic acid, which combines with the
skin of animals, and forms a combination which is in-
soluble in water and not subject to putrefaction — viz.
leather.

1968 What is ordinary vinegar ?

An acid, called acetic acid, and water.

I960 If wine or beer be imperfectly corked, why does it rapidly turn
sour?

Because air gets into the liquor, and the oxygen of
the air combining with the alcohol of the liquor pro-
duces acetic acid, or vinegar.

1970 What is alcohol?

Alcohol is the spirit existing in wine, beer, cider,
etc., obtained in the process of fermentation.

1971 What is a ferment ?

A ferment is a substance containing nitrogen in a
state of decomposition, which is able to excite fermen-
tation in solutions of sugar ; old cheese, putrefying
flesh, blood, etc., all of them are ferments.

1973 What is yeast?

We apply the term yeast to a particular species of,
ferment ; the foam of beer (or of some similar liquor),
produced by fermentation.

1973 Can you explain why it is that a body in a state of fermentation
or putrefaction should cause unlimited quantities of similar matter to pass
into the same state ?

e only know the f act : the reason we are ignorant
of. The most minute portion of milk, paste, juice of

306 SCIENCE OF COMMON THINGS.

Fruit, how preserved. Decay in wood.

grapes, flesh, or blood, in a state of fermentation or
putrefaction, causes fresh milk, paste, grape juice, flesh,
or blood, to pass into the same condition, when in con-
tact with them.

197*4: In storing or packing fruit for future use why is it necessary tc
Carefully remove every decayed specimen ?

Because the decayed portions of one specimen will
quickly communicate decay to the fresh fruit in contact
with it, and soon the whole mass of fruit will become
putrescent.

197*5 If in a vesssl, or any other structure, one Umber becomes decayed
what course ought to be adopted ?

It should be removed immediately, or the decompo-
sition once commenced will in time affect the whole
structure.

It sometimes happens that physicians, in dissection, are seriously poi-
soned by the slightest cut of a knife which has been used upon the dead
body. The knife introduces to the healthy blood, through the wound,
a minute portion of matter in the state of decomposition or putrefaction.
This acts as a ferment, and causes the healthy matter in contact with it
to pass into the same decomposed state. The action once commenced
rapidly extends, until the whole body becomes affected, and death ensues.
It is almost impossible to heal wounds of this character.

197*0 Why is it especially dangerous to eat fruit or meats partially
decayed f

Because the decayed portions of the substance eaten
are liable to induce the same condition in the healthy
organs of the stomach with which they may come in
con tact.

1£, 7*7* Why do fruit preserves frequently turn sour f

Because, owing to the action of some fermenting
substance present either in the fruits themselves or in
the air, the sugar used in preserving is converted into
alcohol,, and the alcohol into vinegar.

197*8 Why does the housewife scald her preserved fruits to prevent their
turning sour ?

Because fermenting substances and fermenting ac-
tion are destroyed by a boiling temperature.

197*9 Why do we keep preserves, beer, cider, or other substances liable
to turn sour, in a cool place ?

Because a depression of temperature arrests fermen*

SCIENCE OF COMMON THINGS. 30?

"What is ether ? Disinfecting agents.

tation, though it does not prevent its renewal when the
temperature is increased.

193O Wliat is ether t

Ether is a product obtained by distilling strong alco-
hol and sulphuric acid. The product is called sul-
phuric ether, but it does not contain sulphuric acid,
nor has it any sulphur in its composition.

j 1981 What are the properties of ether ?

It is an exceedingly volatile, inflammable body, pro-
ducing insensibility when inhaled, and readily dis-
solving all fatty and oily bodies.

1932 Why will etlier remove spots of oil, paint, or grease from gar*
ments?

Because it is a solvent for all greasy, oily matters.

1933 What are the best agents for depriving putrid and decaying
animal and vegetable substances of their offensive odo^s ?

Chloride of lime is the most effectual agent ; and
chloride of zinc and sulphate of iron (green vitriol) are
also exceedingly efficient. On a large scale, as in the
sanatory cleansing of towns, pulverized charcoal, burnt
clay, and quicklime, are to be recommended.

1984 What effect does the use of perfumes or the burning of pastiles
have upon offensive odors ?

They merely disguise the odor, but do not remove or
destroy it.

1935 By adopting what precautions may a person safely enter sick
rooms, or visit, without risk, the most dangerous receptacles of filth ?

By moistening a linen cloth with vinegar, and sprink-
ling over it finely-powdered chloride of lirne.

Air breathed through this, applied to the mouth and nostrils, will enter
the lungs charged with a minute quantity of chlorine, which will effec-
tually destroy any noxious vapors or miasms that escape from diseased
bodies, or from decaying animal and vegetable substances.

1980 What three conditions are requisite to produce putrefaction in
animal and vegetable substances ?

It is necessary that they should be exposed to the
combined influence of air, heat, and moisture.

1987 Why is a substance preserved from decay by drying, or by tin
exclusion of air from it?

308 SCIENCE OF COMMON THINGS.

How smoking preserves meat. What is albumen ?

Because by so doing we remove the moisture and air
essential to the process of decay.

19SS Why does the smoking of fish or flesh contribute to their pre-
servation f

Because the volatile matters of the smoke, such as
creosote, pyroligneous acid, and the like, effect a
species of chemical combination with the fibre of the
meat, and with the substances contained in the natural
juices of the flesh, which combinations are less liable
to decay than the substances themselves.

1989 What is albumen f

Albumen is an animal substance as well as vegetable.
It exists most abundantly, and in its purest natural
state, in the white of an egg, from whence it derives its
name (album ovi\ which is the Latin for the white of
an egg.

The serum or fluid portion of the blood (which, after exposure to the
air, is separated from tlie more solid part) the vitreous and crystalline
humors of the eye, the brain, the spinal marrow, and nerves, all contain
albumen.

1990 What is the yolk of an egg f

This also consists of albumen, but contains in addition
a yellow oil, which imparts to it its color.

1991 Why is meat tough which has been boiled too long f

Because the albumen becomes hard, like the white
of a hard-boiled egg.

The best way of boiling meat to make it tender is this: Put your joint
In very brisk boiling water; after a few minutes add a little cold water.
The boiling water will fix the albumen, which will prevent the water-
from soaking into the .meat, keep all its juices in,. and prevent the
muscular fibre from contracting. The addition of cold water will secure
the cooking of the inside of the meat, as well as of the surface.

1993 Why is meat always tough if it be put into the boiler before the
water boils f

Because the water is not hot enough to coagulate the
albumen between the muscular fibres of the meat,
which therefore runs into the water, and rises to the
surface as scum.

1993 Why -is Ute flash of old animals tough ?

SCIENCE OF COMMON THINGS, 309

What is a poison ? Arsenic. Certainty of its detection.

Because it contains very little albumen, and much,
muscular fibre,

1994 What is a poison f

A poison is any agent capable of producing a dan-
gerous effect upon anything endowed with life.

1995 In cases of poisoning by substances taken into the stomach, what
course should be pursued, in the absence ofmedioal •attendance?

The first step is to evacuate the stomach by means
of powerful emetics, and when vomiting has taken
place, warm water and the white of eggs may almost
always be given with advantage.

1996 Can poisons administered for criminal purposes be almost
certainly detected?

They can ; chemical science within the last few
years has made such advances, that the most minute
quantities of all the best known poisons can be detected
with certainty long after death.

There is no poison so liable and certain to be found as arsenic, and in
almost every case of poisoning with mineral poisons, science is enabled to
detect the substance, even when life has been extinct for years, and the
body nearly decomposed.

1997 What is arsenic?

Metallic arsenic is an exceedingly brittle metal, of a
steel-grey color. It vaporizes, when heated, with a
strong odor of garlic, a property not possessed by any
other metal.

The substance used as poison, and sometimes known as ratsbane, is
arsenious acid, a compound of arsenic and oxygen. Arsenious acid has
the form and appearance of a fine white powder.

1998 What is the best remedy in cases of poisoning with arsenic f

The hydrated peroxide of iron (iron rust)* is con-
gidered the best remedy.

1999 Is lead a poison ?

* The following is the best method for preparing this substance:
Take common copperas (sulphate of iron) four ounces ; dissolve in warm
water in a glass, or porcelain dish, and add a small quantity of sulphuric
&cid, and afterwards ammonia solution, so long as a dense red precipitate
is formed. This precipitate carefully strained off, and thoroughly washed
jn a filter with water, is hydrated peroxide of iron. So long as kept
jnoist, it may be preserved for a great length of time.

310 SCIENCE OF COMMON THINGS,

Lead pipes, how poison -water. Verdigris. Calomel.

Lead and nearly all its- compounds are dangerous and
secret poisons ; when received into the system, it fre-
quently remains dormant for years, and then suddenly
manifests itself in various- forms- of disease.

5000 What is the disease called "painters' colic f '

A disease to which- painters and others working in
lead are liable, in consequence of receiving- into their
system, imperceptibly, portions of lead.

5001 Is it dangerous to sleep in, or Ireathe the air of, a room newly
painted with paints containing lead ?

It is highly dangerous, since the air is filled with a
vapor of the lead compound used as paint.

5003 Why are some water s^ when conveyed through lead pipe,
poisonous ?

"Waters which are very pure and contain much oxygen
dissolved in them ; waters which contain nitric acid
compounds, such as those flowing from the vicinity of
barn-yards, manure heaps, and those which contain
common salt or organic matter, as water flowing from
swamps and fields ; waters containing soluble car-
Donates — all dissolve lead from the pipes through
which they may be made to pass Constant use of
such waters, in the process of time, will introduce suffi-
cient lead into the system to produce disease, which is
often attributed to other causes,

J2OO3 What is verdigris ?

Verdigris is a compound of copper, oxygen, and
acetic acid. This, and all the compounds of copper, are
very poisonous. The most efficacious antidotes for
poisoning with copper are, white of eggs and milk.

5004 What is calomel ?

It is a compound of two parts of mercury united to
one of chlorine, forming the sub-chloride of mercury.
The preparation commonly known in medicine as " blue
pill," is a preparation of mercury.

2OO5 What is corrosive sublimate f

A compound of mercury and chlorine united in equal
proportions, forming the perchloride of mercury.

SCIENCE OF COMMON THINGS. 311

Preservation of wood. Miasm. Contagion.

SOO6 Are loth these compounds, calomel and corrosive sublimate.

poisons f

They are / corrosive sublimate, especially, is a most
deadly poison. In case of poisoning by it, the most
effectual antidote is white of eggs.

SOOT* What is the process of preserving wood from decay, commonly
termed " kyanizing ? "

It consists in saturating the fibres of the wood with
a solution of corrosive sublimate.

Poisonous substances, and corrosive sublimate especially, have the pro»
perty of protecting animal and vegetable substances from decay. The
skins of stuffed birds and animals, and the plants of a herbarium, may be
protected from insects and decay, by washing them with a solution of cor-
rosive sublimate. It should not, however, be forgotten, that these sub-
stances by such treatment become themselves poisonous.

SOOS What is contagion ?

We apply the term contagion to that subtle matter
which proceeds from a diseased person or body, and
which communicates the disease to another person or
body.

Contagion differs from miasm in being the product of disease, arid in
reproducing itself.

J2OO9 What is miasm or miasmata ?

Miasm or miasmata is the product of the decay or
putrefaction of animal or vegetable substances, and
causes disease without being itself reproduced.

Contagion occasions disease in the same way that yeast excites fermen-
tation. Miasm often acts, by its chemical properties merely, as a poison.

SO1O Why are contagious diseases sometimes communicated to indi-
viduals who merely approach the vicinity of diseased persons, but do not come
in contact with or even see them ?

Because the air itself, which has been in contact with
the diseased persons, carries with it the seeds or germs
of infection, and thus communicates disease, sometimes
at great distances.

SOU Why are not all persons affected alike when exposed to similar
contagious diseases ?

Contagious matter is not capable of producing dis-
ease, unless a compound is present in the system capable
of being decomposed ly contact with the exciting body.

312 SCIENCE OF COMMON THINGS.

Susceptibility to contagion. Nutritive value of food.

SO1S What do we mean by susceptibility to contagion f

We mean that the blood of a person contains sub*
stances by the decomposition of which the exciting body
or contagion can be reproduced. If these substances
are not present, and if the system be perfectly healthy,
contagion will i'ail to produce disease.

J3O13 What is the relative nutritive value of the different kinds of meat
Us food f

The relative nutritive value of the different meats for
food is as follows : beef is the most nutritious / then
chicken, pork, mutton, and veal.

2014 What varieties offish are the most nutritious f

The haddock, the herring* the salmon, and the eel, in
order.

2015 What vegetable of ordinary consumption is tht most nutritious f

The cabbage.

INDEX.

ABSORPTION of light, 261

of heat, 172

Abutment, what is an, 45
Acetic acid, 305
Acids of plants, 305
Acid, what is an, 303
Action and reaction, explained, 28

illustrations of, 28
Adhesion, what is, 12
Adult, oxgyen respired by an, per hour,

209

Aerolites, general appearance of, 95

definition of, 94

velocity of, 95

weight of, 95.

Affinity, what is, 193

Air, always contains moisture, 91

in motion, 212

breathed twice unwholesome, 205
condensed by cold, 75
currents of. in an occupied room, 212
exists in all water, 55
expanded by heat, 75

proof of, 75
fresh, how much required per hour

for breathing, 210
heated, ascends, 204

how proved, 205
how ascends in chimneys, 215
how escapes from the lungs, 72
how heated and cooled, 74, 75
impenetrable, 68
in motion, why feels cool, 153

spring, why chilly, 138
necessary for the production of sound,

porous. 63

atmospheric composition of, 63

weight of, 00

how proved, 69
when rarefied, 70
A/Jbumen, in eggs, 308

Albumen, in meat, 308
what is, 308
Alcohol, what is, 305
tVlkali, what is, 303
Angle, definition of, 251
Animals, change of color in winter of, 274.
ector of arctic, 175
distribution of, 142
foretell changes in the weather,

113

the strongest, 33
Apples, unripe, why sour, 303

when sour and when sweet, 303
Aqueducts, principle of construction of, 50
Aqua-fortis, what is, 304
Architecture, defined, 41

origin of the varieties of, 41
Architrave, 47
Arsenic, poisoning by, 309

what is, 309"
Arch, what is, 43

when invented, 43
Ashes, how preserve a fire, 228
Atmosphere, amount of carbonic acid gas

in, 207
height of, 70
not invisible, 69
pressure of, 71
what is the, 69
Atom, what is, 5
Attraction, what is an, 11
Aurora borcalis, cause of, 287
height of, 288
occurs by day aa well as

by nisrht, 2S9
utility of, 2S9
what is, 2S7
where seen, 287
Avoirdupois weight, origin of, 20

Ball, elastic, why rebounds, 23

INDEX.

Balusters, what are, 45
Balloon, why rises in the air, 13
Bark, how especially adapted as a cover-
ing for trees, 157
Barometer, construction of, 102, 103

heat and cold no effect on, 113
how differs from a thermo-
meter, 104

how invented, 101, 102
tube, why left open, 104

iBuilding, properties of a good, 41
Buildings, principle of warming and von-

t; latins, 204

Burning'point, what is, 222
Burns on the skin affect respiration, 235

Calomel, what Is, 310

use of, for determining the Caloric, meaning of term, 181

state of the weather,
Base of a column, 46
Battery, galvanic, 291

/oles of, 292
in "~

Beams, strength

different positions.

Bed coverings, the warmest, 213

india-rubber, why not used Capital of a column, 46

for, 218

feather, safe place in a thunder storm,
2S3

Candle, why burns when lighted, 281
Cannon, distances to which they can send

a ball, 35

varieties of, 35

Capillary attraction defined, 65

vessels, action of, 237

what are they, 236

Carbon, more thrown off from the system

in winter than in summer, 240
what is, 224

Carbonic acid, sources of, 212
gas, 206

a poison, 207

Beer, why turns sour, 805

Bell, cracked, why discordant, 119

metal, composition of, 116

sound of, stopped by touching it, 118 where" found, 206

Bellows, use of in kindling a fire, 229 |Cat, fur of, why sparkles in cold weather,
Birds, how enabled to fly, 26 278

why stretch out their necks in fly- Cats, why see in the dark, 267

ing, 27
Black, the absence of color, not a color,

270

why some bodies are, 270
Blankets, why warm, 14S
Blood, arterial and venous, 237

color of, 237

how affected by oxygen, 205
Blowers, of grates, &c., use of, 217
Boats, life, how prevented from sinking,

Body, a, how far it can fall in one second,

Cellars, why cool in the summer, 151
warm in the winter, 151
Cement, definition of, 38
Cements, hydraulic, 39
Centrifugal force, 23

illustrations of, 23, 24
Chalybeate waters, 54
Champagne, why sparkles, 73
Charcoal, how made, 224, 225

what is, 224

why black, 261
Chemistry, familiar, 302

28 Children, why difficult to learn to walk,

what is a, 4 18

Boiling point, influence of atmospheric Chimney, fire in, how extinguished, 230

Chimneys, how quicken the ascent of hot

air, 215
of manufactories, why usually

very long, 215
principles of construction of,

pressure on, 157, 1S8
of a

liquid, 155
Bones, hollow cylinders, 37
Boots, why cannot a man raise himself by
pulling on the straps of, 23

Bottle, why gurgles, 73
Bottles of ale and cider, why frequently
burst, 74

216

smoke under what circumstan-
ces, 216

Bouquets, arrangement of flowers in, 273 Choke-damp, what is, 211

Breakers, what are, 61 j Church, crowded, persons in feel drowsy,

Breath, why visible in winter, and not in' 210

summer, 89 Circuit, galvanic, 292

Breathing on glass, why dulls it, 88 ! Cities, air >f, less pure than the country,

why difficult at a very high 210

elevation, 72 Cleanliness, necessity of, 233

Bricks, burned, why red, 39 jClimate, meaning of the term, 104

why used for lining stoves and fur- Climates, peculiarities of, 104

naces, 151 temperature of, coloration pecu-

Broth, cooled by convection, 159 liar to, 271

Bubbles, air, in ice, origin of, 178 '• Clock, common, what is a, 29

in a tea-cup, how attracted, 14 Clocks, why go faster in winter than ia
on leaves of water plants, what the summer, 30

are they, 236 Clothing, contains no warmth in itself;

eoap, why ascend, 56 | 152

INDEX*.

315

regetabl* De

Clothing, how makes us warm, 147

use of, 148

Clouds and fog, difference between, 80
Clouds, cause of their various shapes

appearances, 86
color of, 85

distance, above the earth, 84
size of, 84

sunset, why colored, 86
what are, 83
when high and low, 83
ffoai, anthracite, 225
bituminous, 225
deposits, extent of, 227
mineral, origin of, 225

produced from v

matter, 225
Cohesive attraction, 11

illustrations of, 12
Cold, greatest artificial, 134
natural, 134

how occasioned by wet clothes, 197
what is, 130
Color, does not exist in the dark, 270

influence of, on the deposition of

dew, 168

Colors, artificial, why fade in the sun, 271
dark, optical effects of, upon the

size of the figure, 273
iSght, effect of, 274
disadvantages of a dress of uniform,

most conspicuous in battle, 274
peculiar to arctic regions, 272
seven primary, 255
warmest for dresses, 175
Columns, why larger at the bottom than

at the top, 42

Combustion, a process of oxidation, 220
chemical action of, 221
essential requisites of, 221
spontaneous, illustrations of.

230

what is, 220
Compass, does not always point north and

south, 297
mariner's, 279

how constructed, 297
when discovered, 297
Compasses, ships', how affected by light-
ning, 299

Compressibility, 6
Concord «i«l -discord, what arc, 120
Contagion, susceptibility to, 810

what is, 811

Convection of h-eat, 153
Copper, poisonous effects of, 310
Cornea, effect of flattening, 265

of the eye, 263
Cornic<s, what is a, 47, 48
Corrosive-sublimate, what ts> 810
Coughing, what is, 122
Countries, least cloudy, 10S
most cloudy, 107
some, why destitute of rain,

110

Cowl, use of, upon a chimney, 216
Cream-, why rises upon milk, 64

Crying, what Is, 123

Cultivation, how increases the "warmth of

a country, 198
and Curtain, behind a pulpit, influence of on

sound, 126
Cylinder, strength of -a, 36

Dead body, whycold,238

Decay ift substances, how occasioned and

promoted, 806
Density, what is, 6
Diseases, when contagious, 811
Dew and rain, difference between, 163
Dew, cause of, 164

deposited most readily on cleat

nights, 163
does not fall, 168
does not form on exposed parts (#

the human body, reason of, 170
falls abundantly on cultivated soils,

none on a windy night, 164
none on cloudy nights, 163
phenomenon of, 162
rarely observed in cities, 168
when converted into frost, 163
when most copious, 166
why more abundant 0*1 some sub-
stances than others, 164
why rolls in drops on fcavcs, 169
Dewdrop, why round, 168 .
Diamond, cause of its brilliancy, 256
Disinfecting agents, 307
Distillation, how effected, 196

what is, 195
Divisibility of matter, 5
Doors, why shrink in dry weather, 199
swell in damp weather, 199
Dovetailing, what is, 44
Draining lands, promotes warmth, 198
Draught of air, occasion of, 214
a chimney, 214

stove, 214

v/hcn there is none, 215
Dress, arrangement of colors in, 272, 273
Presses, white^" why adapted for summer,

Drum, why sounds, 121

Drying and distilling, difference between^

1$6
Ducks, why not made wet with water,

169

Ductility, 11
Dust, how expelled from a crtat or carpet

by beating, 26
Dunghill, cause of the heat t>f, 229

Car, construction of, 115

drum of, 114
Sarthen vessels, why crack in cold we*

thcr, 180
Earth, heat of, 136

315

IHDEX,

Earth, how proved to be in motion, 22
poles of, 296
temperature of, influence on the

distribution of animals, 142
why made colder after sunset, 162
Earthquakes, probable cause of, 136
Ebullition, what is, 155
Ech6, distance necessary to produce, 125
what is, 124

why sometimes double, 125
how produced, 124
where heard in greatest perfection,

124

Edge, straight, 243
Eel, electrical, 279
Elastic bodies, what are, 8
Electricity, 275

and lightning, identity of, 285

how proved, 285 1 Figure, 5
connection of light and heat, | Filtration, principles of, 7

Exercise \vhy makes us xvarm, 238
Expansion by heat, 176

Falling bodies, laws of, 25

Fan, a, does not cool the air, 174

Fanning the face, why cools, 173

utility of, 174
Far-sightedness, cause of, 265

how remedied, 265

Fat people, why throw back their shoul-
ders, 17

Feathers, why called light, 6
Feather, how attracts the earth, 14
Ferment, what is a, 305
Fermentation, how induced by yeast, 305

278

conductors of, 276
galvanic, greatest quantity,

how excited, 292
galvanic of two kinds, posi-
tive and negative, 291
how called into action, 275
how excited by rubbing the

fur of a cat, 278
invisible, 275

natural agents active in pro-
ducing, "279
non-conductors of, 277"
of muscular action, 279
positive and negative, 278
produces heat, 136
velocity of, 278

Electric cloud, discharge of, 2SO
Electrical machines, how constructed, 277

repulsion, 276

Electrified and non-electrified bodies, 276
Electro-magnetism, what is, 299

when and how disj

covered, 299
metallurgy, 294

principles of, 294
Electrotype process, 294
Entablature, 47

Equinoxial storm, does it occur, 112
Esquimaux, why fond of oil and fat, 230
Ether, how removes grease, 307

what is, 307
Evaporation, daily amount from the sea,

110

effects of, 197
phenomena of, 195
Eye, human, structure of, 262
muscles of, 262
parts of, 263
retina of, 263

pained by sudden light, .266
pressure on, occasions the sensation

of light, 26S

Eyes, do not see alike with both, 263
Eyebrows, use of, 266
Eyelashes, use of, 266
Exertion, disagreeable in hot weather,
why, 240

Fire, benefit of stirring a dull, 230
caused by friction, 139
heat of, cause of, 229
intensity depends on what, 230
reflection of, in our windows, 250
what is, 222

why feels hot as we approach it, 161
whv placed near the floor of a room,

160
in the niirht, why difficult to judge of

the distance of, 269
places, open, advantages of, 219

not economical, 218
Flame, candle, hottest part of, 232
color of, 231

luminosity, depends on what, 222
of a lamp or candle, analysis of,

232
of a candle, why points upwards,

232

solid particles in, 222
what is, 222

when will it smoke, 223
Flames, why all not equally luminous, 231
Flues of stoves, why covered with black-
lead, 162
Flannel, how preserves ice from melting,

143
Fluids, laws and phenomena of, 49

two classes of, 49
Flying, how differs from leaping, 28
Force^ what is, 22
Food, hot, cooled by blowing, 159

the fuel of the body, 238
Fogs, cause of, 84

when and where occur, 90
why does not become dew, S9
Franklin's, Dr., theory of electricity, 277
Friction, what is, 22

action of in exciting electricity,

275

Frieze, in architecture, 47
Frost, hoar, what is, 187 ^.^

rare under trees and shrul

1S5
how a thin covering protects plants

from, 167 •
readers the earth friable, 184

INDEX.

317

Frost-work on windows, cause of, 185
Fruit, precautions to be used in packing,

306
Fuel, elements of, 228

perfect combustion of, bow attained,

220

Furnaces, hot air, how constructed, 219
Furs, why used for clothing, 147
Fumigation, 301

Galvanism, how discovered, 289

produced, 290

simple experiment illustrat-
ing, 290
what is, 289

Galvanl, discovers galvanic electricity, 290
Galvanic battery, ordinary effects of, 293
Gas, what is a, 8
Gases, law of diffusion of, 207

not all invisible, 68
Glacier, what is a, 106
Glaciers, where occur, 106
Glass, burning, a double convex lens, 260

ground for shades, use of, 233
Glasses, burning, 131
Gold, melting point of, 135
Gothic architecture, origin of, 45
Grain-weight, origin and construction of,

Grapes, ripe, why sweet, 303
Grass, grown in the dark, of a light color,

272

Gravitation, what is, 13
Gravity, centre of, 15

illustrations of the laws and prin-
ciples of, 15, 16

Oreasing carriage wheels, use of, 140
Greasy food, why relished in cold wea-
ther, 239
Green colors suited to fair complexions,

2T3
Grindstones, In rapid motion why often

burst, 23
Gun, essential properties of, 35

how we take aim with a, 244
Gunpowder, composition of, 34
power of. 34

when and how discovered,
35

Habitations, probable form of the

human, 41

Hail, what is, and how formed, 94
Hair, use of in mortar, 40.
Halls, for speaking, how constructed, 126
Hardness, what is~ 10
Headache, how produced by bad air, 209
Hearth-rugs, why feel warm, 145
stone, why feel cold, 145
Heat and cold, sensations of, 131

animal, cause of, 236

best conductors of, 144

Heat, effects on the dissolving power ol

liquids, 194
effects of, 131
effects of, on the bulk of some

liquids, ITS
expands all bodies, 176

illustrations of, 177
has no weight, 130
how communicated, 143

illustrations of, 4
how diffused, 130
how evolved by combustion, 221
how measured, 187
good absorbers of, not gooo* reflect-
ors, 171

greatest artificial, how produced, 293
greatest artificial, how measured,

134
illustrations of radiation of, 161,

162

In ice, 130
latent, what is, 138
occasioned by chemical action, il-
lustrations of, 137
of the sun, 132
produced by friction, 140
radiant, 160
rays of, 171
reflection of, 171
solar, extends below the earth's sur«

face how far, 136
sources of, 132

sun's differs from artificial, 133
velocity of transmission in different

substances, illustrations of,- 144
vital, illustrations of, 141
what is, 129

Health injured by reduction of the tempe-
rature of the body, 198
Height from which a body falls, how cal-
culated, 29

Hiccough, what is, 123
Hides, how converted into leather by tan-
ning, 305

Horizon, what is, 269
Horse-shoe magnets, 298
Horse-power, what is, 33
House, part most dangerous in a thunder

storm, 282

House, haunted, origin of stories concern-
ing, 128

Hurricane, what is a, 80, 81
Hurricanes, where prevail, 80
Huts, first form of human habitations,

Hydrochloric acid, 304
first Hydrogen gas, its properties, 224

the lightest of all bodies, 62
sulphuretted, 304
how formed, 304
what is, 224
Hydrostatics, definition of, 49

Ice, " anchor," what is, 179

318

INDEX.

Ice, fractures in regular Hues and aagles, Light, chief sources of, 241

186
heat of, 180
what is, 179

why floats upon water, 62
why melted by the sun, 196
Icebergs, height of, 106

how formed, 106
Illusions, optical, 269
Images all appear inverted in water, 246
Impenetrability, 4
Incandescence, what is, 181
Incidence, line and angle of, 246
Induction in magnetism, 296
Inertia, illustrations of, 10
Inertia, what is, 9

Insects, how occasion sounds, 123, 124
Instrument, stringed, use of the body ot,

117

Ionic order of architecture, 45
Iris of the eye, 263.
Iron, how made hot by striking, 139
meteoric, 96
where found, 96
why sinks in water, 62
•why stronger than wood, 12

Kettle, why heat is not applied at the top
of, 154

why sometimes boils over, 156
Kyanizing, what is, 311

Lakes, some never frozen, 183

Lamps, closed, use of a hole in the top,

233

gas generated by, 208
smokes, occasion of, 223
solar and astral, how constructed,

223
wicks, eottoa best adapted for,

Land, configuration of, effect on tempe-
rature, 107

Latent heat, what is, 189
Larynx, 122
Laundress, why boils starch, 802

how propagated, 244

intense, why causes pain to th«

eye, 266

most splendid artificial, how pro-
duced, 293

moves in straight lines, 244
of the sun, how much intercepted

by the atmosphere, 261
possesses no weight, 241
ray of, when reflected, 244, 245
refraction of, 2-54

the same quantity not reflected at
all angles, illustrations of thi»
principle, 248

velocity of, how estimated; illus-
trations of, 242, 243
what is, 241

white, composition of, 255
why, when it is cloudy, 252
zodiacal, 97
Lightning clouds, height above the earth,

280
conductors, best materials for,

284

different kinds of, 280
direction of a flash of, 281
does not follow a direct path,

284

heat, cause of, 281
how kills persons, 281
rod, what is a, 284
rods, how fastened to buildings,

285

how protect houses, 2S4
when productive of harnv,

284
why terminate in points,

284

sheet, 280
what is, 280
why most common in summer,

281

Lights, Northern, 287, 288
Lime, chloride of, 307
quick, 38

absorbs carhpnic acid, 212
slacked, 38
water poured on occasions heat,

how, 137
Linen handkerchief, why preferred to A

cotton one, 149

Linen, how dried by exposure to the air,
198

why touches
saliva, 195
Laughing, what is, 123
Lead, a poison, 310

why called heavy, 6
Leather, how made, 805

Leaves, of plants, how radiate heat, 165
of plants, why green, 271
why brown in autumn, 271
Lens, double convex, 260

what is a, 260

Lenses, different varieties of, 260
Li«ht, absorption of, 261

trtmcialt vn what depends, 231

flat-iron with! why cooler thnn cotton, 149

Liquefaction, 192
Liquid, what is a, 8
Liquids, how to cool, 155

impart no additional heat after
they boil, 157

Liquors, frothing, cause of, 74
Loadstone, what is a, 295

why so called, 295

Loudness, of sound, on what depend?., US
Lunar caustic, 304
Lungs, description of, 234

INDEX.

319

vantages of, 31

Machine and a tool, difference between, Mortar, why becomes hard, 33

31
rhat Is a, 31

,31

Machinery does not create power,
Magnet, directive power of, 296

what occurs when one is broken,

293
Magnets, horse-shoe, 293

how constructed, 297
natural, where found, 295
weights, great, lifted by, ?
Magnetism, communicated by contact,

295
connection with electricity,

295

Malleability, 11
Man alone capable of enduring all tempe-
ratures, 143
method in which he can exert the

greatest strength, 33
on a church spire, why scorns very

small, 251

shrinks when starved, 233
Maps, coast survey, how produced, 294
Mastich, or mastic, 40
Matches, how ignited by friction, 141
Materials, strength of, 36

illustrations of, 36
Matter defined, 3

evidence of its existence, 3

limits to the division of, 5

particle of, 5

properties of, 4

the strongest form in which it can

be arranged, 36, 37
Miasm, or miasmata, 311
Milk boils more readily than water, 155
Mirror, how we see ourselves in a, 245

why images appear behind a, 247

Moon, why seems a flat surface, 251

why seems larger than tho stare,

Mortare, composition of, 38

Mortising, what is, 42

Motion, 22

Mountains, distant, why appear

bluo,

high, why covered with snow,

105

Mountain tops, why cold, 172
Muriatic acid, 304
Muscular energy, how exerted, 33
Music, scale of, 121
Musical instruments, how occasion sound,

sounds, what are, 120

Nails in old houses, why loose, 187
Near-sightedness, cause of, 264

how remedied, 265
Needle, magnetic, 296
Negro's skin never blisters from the sun,

174

Nitric acid, 304

Nitrogen, its properties and uses, 205
what is, 205

Objects, how we judge of the sizo and

position of, 250
Ocean, colors of animals in, 272

depth to which light penetrates,

Odors, 307

Oersted, Prof., his discovery, 299

Mirrors, 245 Oil and water, why not mix, 193

Mist and fog, distinction between, 89 Opaque bodies, 261
Meat, how preserved by smoking, 303 Orders in architecture, 45

when tough, 303 'Owls, why see in the dark, 267

Medicines, prescription by drops unsafe, Oxygen, now much required per hour,

Mercury, freezes at what temperature,

191
of a barometer, why sinks in fine Oxidation, what is, 220

weather, 104
when freezes, 134
Metals, why melted by fire, 192
Meteorites, how supposed to originate, 96

what are, 94

Meteorology, what is, 74
Mist and fog, why vanish at sunrise, 164
Mist, on windows, cause of, 87

209

its properties and uses, 205
what is, 205

Paint, in tho vicinity of sowers, why dis-
colored, 304

how preserves wood, 152
Paints, lead, when dangerous, 310

Mixture and solution, difference between, Paper, blotting, why absorbs ink, 66

193
Moon, lisht of, seems to make a path in

'the water, 249
influence of, on the weather, 111

light, how occasions putrefaction, Pendulums, compensating, 187

112

why appears largo on the borkon,
269

writing, why will not absorb ink,

Paste, adhesiveness due to irhat, 303
Pedestal, what is a, 46

length of, that beats seconds,

29
what fa a, 29

320

INDEX.

Persons, why many. ROC the same object Rain, none if the air be dry, 104

at the same time, 244
Perpetual motion in nature, 23
instance of, 23
Perspiration, insensible, what is, S3

why caused by active exer-
tion, 239

Pilasters, what are, 45
Pile, what is a, 42

Pipes, lead, how affected by water, 310
water, why liable to burst in freez-
ing, 1S1

Pisa, leaning tower of, 17
Planets, how give light, 242
Plants, how purify the water, 236

respire as well as animals, 235
water, liberate oxygen, 236
Platina, the heaviest substance known,

Plastic bodies, what are, 9
Plinth of a column, 46
Pneumatics, what is, 49
Poison, what is a, 309
Poisoning, what to do in cases of, 309
Poles of a galvanic battery, 292
Pores of a body, 6
Portico, what is a, 45
Potatoes, frozen, why sweet, 303
Potato, starch constitutes the bulk of, 302
Posver, how we apply it, 31
horse, 33
of gunpowder, 34
sources of, 32
steam, 34
water, 33

Preserves, why turn sour, 306
Prism, how separates a ray of light, 255
Pump, chain, what is, 100
common, 98

forcing, construction of, 100
height to which water may be

raised by, 99
why water rises in, 100
Pupil of the eye, 263

contracts by a sudden

light, 266

Putrefaction, causes of, 307
Putty, what is, 40
Pyrometers, how constructed, 191

origin of, 91

water, why called soft, 56

where most abundant, 103

why cooler after, 199

why falls in drops, 91

yearly amount falling in different

parts of the earth, IDS
Rainbow, formation of, 257

when seen, 257
Rainbows at waterfalls, 253

double, when seen, 253

no two persons see the same,

253

Rain-gauge, what is a, 109
filed rays of light possess the greatest beak
! ing effect, 272
'Reflection, line and nnglc of, 246

of light, 24o

Reflectors of heat, what arc good, 171
RefraagibiUty, 86
Refraction of light, 254
Remedies for poisons, 309, 310
Repulsion, what is, 11
Resonance, what is, 125
Respiration a form of combustion, 234
object of, 234
what is, 233
Retina of the eye, 263
Retort, what is a, 195
.Rifle, advantages of, over a musket, 35
River, always seems more shallow than it

is,"255

bottom, rarely frozen, 181
part in which the water runs most

rapidly, 50
Rocks and stones retain moisture, 107

cause of their rounded and weather-
worn appearance, 179
why often split in cold weather,

ISO

Roman cement, 39
Room, air of. how affected by a current

209

coolest part of, 117
hottest part of, 217
Rose, why red, 270
SRust, what is, 222

Salt, how dissolves ice, 1S4
Qnadrrfpcd, never raises both feet on a, lakes, origin of, 5S

side at once, 17 utility of, in the ocean, 58

Quadrupeds, why swim easier than man,|Sand, best suited for mortar, 39

63
Quick lime, what is, 33

Radiators, good, of heat, 161
Radiation, 160

of heat, on what depends, 161
Rain drops, form of, 169

why spheres, 160
Low measured, 109

Savages, how hear by placing the ear closo

with ground, 117
Scarfing and interlocking, 43
Sea breeze, why cool, 79"

effect of, on temperature, 107

rarely freezes, Ib3

water, why freezes less readily than
fresh water, 135

why not full, 199

why salt, 47

vapor of, not salt, 199
Seasons, alternation of warm and cold, 112

INDEX.

321

Seeing, sense of, how exerted, 241 iBounds, when flat, 121

Senses, number of, 3 why seem louder in a church than

what are th'jy, 3 in a plain, 128

Sewers, foul, why destructive to health, Soup, why keeps hot longer than water,

Shade, why cool in the summer, 150 'Sparks of fire, what arc, 7

why objects seeui dark in, 252 Specific gravity defined, 62
Shadow, what is a, 244 iSpeetacles best suited for old people, 265

Shaft of a column, 46 Spoon, metal, how retards the boiling of a

Sheets of a bed why feel cold, and the kettle, 150

blankets wann, 152 why tarnisbod by the yolk of eggs,

Ship at sea, why the masts are seen before 304

the hull, 253 Spray of waves, cause of, 61

Ships, iron, why do not sink, 65 Springs, effect of drainage upon, 53

Sbces, hotter for being dusty, 172 Stones for building, bo\v" to estimate their

Skull, the form of the, embodies the prin- durability, 43

ciples of the arch, 44 building, action of the weather

Sight, difficult after leaving a lighted room on, 48

and going into the dark^"266 why lifted easier in water than on

Size, 4 land, 65

Skating swiftly over thin ice, effect of, 27 Stove, advantages over an open fireplace,
Skin, cleanliness essential to the healthy

action of, 237
Sky, why appears blue, 271
Sleet, what is, 92
Smoke, what is, 218

why ascends, 13

Smoking, how preserves meat, 808
Sneezing, what is, 123

Snow, at the foot of a wall, why melts Stucco, what is,

disadvantages of, 219

why crackles in cooling, 186

why crackles when a fire is kindled

in it, 1S6

Stones, why not suitable for fuel, 226
Straw, use of, in the Egyptian bricks, 40
Stripes, effect of, in dresses, 279

rapidly, 161
flake, how formed, 93
heat of, how shown, 138

Sucker, the common, 72

Suction, height to which water may bo

raised by, 98
how diminishes the darkness of 'Suffocation, how occurs, 123

night, 270 |Sugar and salt, how flavor water, 67

how protects the surface of the earth salt, &c., retard boiling, 157

in winter, 92, 93
melting absorbs heat, 138
various colors of, 94
what is, 92
why none in summer, 93

white, 93

Soap-bubble, origin of colors in, 259
Soap, utility of in washing, 57
SoiC a bad conductor of heat, 136
effects of on temperature, 107
Solid, what is a, S
Solution, what is a, 193

when saturated, 193
Sonorous bodies, what are, 116
Soot, smell of, why sometimes noticed in
a room, 216

of, 71

best conductors of, 120
how obstructed by fogs, rain, &c.,

119

how produced, 114
louder by night than by day, 119
not heard alike by all persons, 120
velocity of, 118
bounds, musical, what are, 120

origin and transmission of, 114
rejection of, 124
transmission of by solids, 117
vibrations, to what compared, 117
vibrations in solids, how rendered

visible, 118

Sulphur, product of when burned, 393

Sulphureous acid, 303

Sulphuric acid, 304

Summer, Indian, haziness of, 87

Sun, seen through a fog appears red, 87
the, a source of lu-at, 132
weight on the surface of, 19
why appears large on the horizon, 269

Sun's heat, why greater in some portions
of the earth than in others, 133

Sunbeam, motes floating in, what arc, ICO

Sunset, red, cause of, 86

Surf, what is, 61

Surfaces, some, why brilliant, 242
dull, 242

Swimmers, unskilful, why sink, 63

VJound, air necessary for the production Swimming why easier in salt than in fresh

water. 63
philosophy of, 63
Springs in ponds prevent freezing, 163
mineral, cause of, 54
origin of, 51

why cool in summer, 150
why often fail in dry weather, 51
Sprinkling a hot room how cools it, 198
Squinting, occasion of, 268

occasions double vision, 267
Starch, how manufactured, 302

may be converted into sugar, 303
what is, 302

why necessary to boil before using,
802

34*

322

INDEX.

Stars, shooting, 96 _

oacur periodicruly, 9T
why not visible in the daytime,

244 •
Starvation, process of, 239

what is, 235

Steam, bulk of, compared with water, 201
how much lighter than water,

200

engine, what is a, 202
high pressure, 202
how used for cookery, 202
invisible, 107
its elasticity, 201
lighter than air, 68
mechanical force of, 203

illustrations of, 203
parts of a boiler where first formed,

200

power of, on what depends, 201
visible appearance how caused,

200

what is true, 200
Stems of grain -plants, why hollow tubes,

Stick immersed in water, why seems bro-
ken, 254
Still, construction of, 191

Thunder, rolling of, cause of, 2S7

storm", places dangerous in, 282,

2S3

safest in, 233
what is a, 2SO
varieties of, 2S7
what is, 2S6
why heard after the lightning

is seen, 2S7
Tides, cause of, 59

when high and low, 59, 60
Toes, advantage of turning out the, io

walking, 17
Tornadoes, 82

phenomena generally attend-
ing, 82

Transparent bodies, what are, 260
Tree, centre of gravity in, 19

how discharges a lightning cloud,

2S2

Trees and flowers, how purify the air, 210
whv covered with straw in winter,

184

Tropics, rainy and dry seasons of, 109
Troy weight, origin of, 20
Trumpet, ear, construction of, 127

speaking, construction of, 127
Twilight, cause of~ 259

Telegraph, influence how transmitted by,
to convey intelligence, 301
magnetic, Morse's, principle

of, 300, 301
wire, why supported on glass,

301 '
Telegraphic current, what is meant by

301
Telescopss, construction and use of, 252,

253
why enable us to see

objects, 253
Temperature, effect of the sea on the, 107

soil on, 107

mean daily, what is, 106

varies with altitude, 105

latitude, 105

variation, examples of, 105
why all places have

same, 107
Temples, how cooled by ether, cologne,

water, &c., 197
Tenon, what is a, 43
Terra-cotta, what is, 39
Thaw, mo-e chilly than a frost, 183
Thermometer, centigrade, 191

Fahrenheit's, 190

Eeaumer's, 191

indicates difference of heat

only, 192
Thermometers and pyrometers, difference

of, 188

construction of, 189
different, 190
how graduated, 189
Thunder, cause of, 286

Vacuum, illustration of, 213

what is a, 71
Valves, pump, 93, 99
Vapor from damp linen, what is it, 197
in a room, origin of, 88
of the air, how condensed into rain

Vaporization, meaning of, 194
Vegetables, why swell in boiling water,

distant Vegetation, why luxurious on the margin

of a river, 66
Ventilation, in what situations is it perfect,

205

what is, 204

Vibration, what is a, 116
Vibrations, sonorous, how illustrated, 116
Vinegar, what is, 305
not the Vitriol, oil of, 304

Voice, organs of, 122

tones of, how altered, 122
Volatile substances, 195
Volcanoes, probable cause of, 136

Wall, a, when stands securely, 17
Walls, partition, construction of, to int«

cept sound, 119
Warming and ventilation, 204
Water, a bad conductor of heat, 146

at what elevation above the earth

remains frozen, 106
air in,
boiled, why flat and insipid, 73

INDEX.

323

Water, composition of, 54 I Wheels, carriage, why sometimes take

declivity sufficient to give fanning lire, 189

motion to, 50 fore, of carriages, why smaller

of, why rolls upon hot iron, than the hind, 44

of carriages, utility of greasing,

water, different kinds, 34
Whitewash, what is, 38
Wick of a candle, why not consumed,

233
Windpipe, what is the, 122

194

expands when freezing, 181
force of expansion in freezing, 179
hard, what is, 54

difficult to wash in, 56
bow extinguishes a fire, 229
hoAV heated, 153

hot, why hreaks glass, or earthen Windows, why blaze p.t sunset, 249

vessels, 185
in freezing, cracks earthen ves-
sels, 180

images in, appear inverted, 246
power, 33, 34
pressure of. 53

how exerted, 53
of mineral matter con-

tained in, 55
running, Avhy slow to freeze, 182
scalds at what temperature, 176
surface of, always level, 49
swells in boiling, 156
temperature ol'boiling, 135
what is the purest natural, 55
when affects lead pipes, 310
why a fluid, 54

why dissolves sugar and salt, 57
why freezes first at the surface,

182

why rises in a pump, 101
why sparkles, 56
why will not dissolve iron, 193

Waters, relative purity of, 55

Waterspout, what is a, 83

Waves, cause of, 60
spray of, 61
velocity of storm, 61

Well, ordinary, why water collects, 57

Wells, artesian, 52

why often covered with mist,

Wind, cause of, 75
Winds, force of, how measured, 78

high, difficult to walk against, 9

always blow, 76

effects of mountains, on the couira
of, 76

land, generally dry, 76

north, why cold, 79

south, why Avarm, 79

regular, 77

on" the direction of, 78

trade, 77

velocity of, 77
Wine, why sours on exposure to air, 305
Wood, constituents of, 224

green, unprofitable to burn, 227

hard and soft, 227

how preserved from decay, 811

"; profitable for f;i
kinds of, which impart the least

kinds most profitable for fuel, 227

heat in burning, 227
weight of a cord of, 227
why does not melt, 194
why generally cut in the winter,

why snaps when burning, 7
Wooden handles, why applied to cooking
vessels, 145

Winter, dark dresses most suitable for, Woollen kettle-holders, utility of, 145

172

Teast, what is, 305

Yellow, the color most visible, 272

Weather, action or. building materials,

48
Weather, animals foretell changes in, 113

moon's influence on, ill
Weight, how varies, 19, 20

proportional to what, 19

what is, 19

where a body has the greatest,

and least, 20
Weights and measures, English system of,

21 Zenith, what is the, 269

Weights and measures. French system of, Zero point of thermometer, how dele*

21 i mined, 190

Wheel, centre of gravity of, 18 ^Zodiacal light, 97

dished, or arched, stronger than a
flat, 44 i

Woollens, utility of as protectors against
cold, 147

zr.

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Full text of "The science of common things ; a familiar explanation of the first principles of physical science. For schools, families, and young students."

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