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UNIVERSITY OF CALIFORNIA.
Class
THE SCIENCES
A READING BOOK FOR CHILDREN
ASTRONOMY, PHYSICS — HEAT, LIGHT, SOUND,
ELECTRICITY, MAGNETISM — CHEMISTRY,
PHYSIOGRAPHY, METEOROLOGY
BY
EDWARD S. HOLDEN
GINN & COMPANY
BOSTON • NEW YORK • CHICAGO • LONDON
ENTERED AT STATIONERS' HALL
COPYRIGHT, 1902, BY
EDWARD S. HOLDEN
ALL RIGHTS RESERVED
68.10
tgftc
GINN & COMPANY • PRO-
PRIETORS • BOSTON ' U.S.A.
TO
MY YOUNG FRIEND
treble
190795
PREFACE
THE object of the present volume is to present chapters to be
read in school or at home that shall materially widen the outlook
of American school children in the domain of science, and of the
applications of science to the arts and to daily life. It is in no
sense a text-book, although the fundamental principles underlying
the sciences treated are here laid down. Its main object is to help
the child to understand the material world about him.
All natural phenomena are orderly; they are governed by law;
they are not magical. 1)hey are comprehended by some one ; why
not by the child himself ? It is not possible to explain every detail
of a locomotive to a young pupil, but it is perfectly practicable to
explain its principles so that this machine, like others, becomes a
mere special case of certain well-understood general laws.
The general plan of the book is to waken the imagination ; to
convey useful knowledge ; to open the doors towards wisdom. Its
special aim is to stimulate observation and to excite a living and
lasting interest in the world that lies about us. The sciences of
astronomy, physics, chemistry, meteorology, and physiography are
treated as fully and as deeply as the conditions permit ; and the les-
sons that they teach are enforced by examples taken from familiar
and important things. In astronomy, for example, emphasis is laid
upon phenomena that the child himself can observe, and he is
instructed how to go about it. The rising and setting of the stars,
the phases of the moon, the uses of the telescope, are explained in
simple words. The mystery of these and other matters is not magical,
VI PREFACE
as the child at first supposes. It is to deeper mysteries that his
attention is here directed. Mere phenomena are treated as special
cases of very general laws. The same process is followed in the
exposition of the other sciences.
Familiar phenomena, like those of steam, of shadows, of reflected
light, of musical instruments, of echoes, etc., are referred to their
fundamental causes. Whenever it is desirable, simple experiments
are described and fully illustrated,1 and all such experiments can
very well be repeated in the schoolroom.
Finally, the book has been thrown into the form of a conversation
between children. It is hoped that this has been accomplished
without the pedantry of Sandford and Merton (although it must be
frankly confessed that the principal interlocutor has his knowledge
very well in hand for an undergraduate in vacation time) or the sen-
timentality of other more modern books which need not be named
here. The volume is the result of a sincere belief that much can
be done to aid young children to comprehend the material world
in which they live and of a desire to have a part in a work so very
well worth doing.
EDWARD S. HOLDEN.
THE CENTURY CLUB,
. NEW YORK CITY, January, 1903.
l Illustrations have been reproduced from many well-known books, especially from the
reading books of Finch and Stickney, Frye's geographies, Davis' physical geography and
meteorology, Gage's text-books of physics, Young's text-books of astronomy, etc. To the
authors of these works the writer begs to express his sincere thanks.
CONTENTS
PREFACE
PAGE
V
INTRODUCTORY CHAPTER . . .
BOOK I. ASTRONOMY, — The Sci-
ence of the Sun, Moon, and
Stars
The Earth as a Planet ....
Distance of the Moon from the
Earth
Distance of the Sun from the
Earth
The Diameter of the Earth . .
Distance of the Sun from the
Earth .........
The Planets Mercury and Venus
The Planets Mars, Jupiter, Sat-
urn, Uranus, and Neptune
Distances of the Planets from the
Sun
How to make a Map that shows
the Sun and Planets . . .
Scale of the Map
Sizes of the Planets compared to
the Sun
The Solar System; the Sun and
Planets
Relative Sizes of the Planets
The Moons of the Planets . .
The Minor Planets; the Aster-
oids
Comets
The Stars . ....
9
9
ii
ii
12
14
16
16
17
i?
18
25
28
3°
32
32
32
Distances of the Stars . ... 32
What is a Planet ? 33
Phases of the Moon (New Moon,
Full Moon, etc.) 34
Number of the Stars .... 38
Clusters of Stars 39
The Pleiades 39
The Milky Way 41
Do the Stars have Planets as the
Sun does ? .42
Shooting Stars ; Meteors ; Fire-
balls 44
The Zodiacal Light 46
Nebulae 47
Rising and Setting of the Sun . 48
How the Sun appears to move
from Rising to Setting .
The Celestial Sphere . .
The Northern Stars . . ,
The Great Bear (the Dipper)
The Southern Stars . .
Time and Timekeeping
Telescopes 56
A Meridian Circle 57
The Lick Telescope . . . . 61
The Moon 62
Mountains on the Moon ... 62
Life on the Planets 64
The Planet Mars . . . . . . 64
The Planet Jupiter 64
Appendix (Statistics of the Solar
System) 66-70
49
49
5*
53
54
56
Vlll
CONTENTS
BOOK II. PHYSICS, — The Science
that explains Heat, Light,
Sound, Electricity, Magnetism 73
Solids and Liquids 73
Solids, Liquids, and Gases are
made up of Millions of Small
Particles 74
Heat makes Solids, etc., expand 74
Most Gases are Invisible ... 77
The Diving Bell 78
The Earth's Atmosphere ... 78
Balloons 80
Air is Heavy 81
Reservoirs, Fountains, and the
Water Supply of Cities . . 81
The Barometer 83
The Air presses about Fifteen
Pounds on Every Square Inch 84
How to measure the Heights of
Mountains 85
The Barometer is a Weather-
glass 86
United States Weather Bureau
Predictions 88
Thermometers ...... 88
Steam 90
The Steam Engine .... 91
The Locomotive 94
The Steamship 96
Light 96
The Sun's Rays travel in
Straight Lines 96
Shadows 101
Eclipses of the Sun and Moon 102
Reflection of Light . . . .104
Refraction of Light . . . .105
Prism; the Spectrum . . . 105
Lenses 106
Spectacles 107
PAGE
Sound no
Velocity of Sound and Light no
Sound is a Vibration . . .112
Musical Instruments (Bells,
Pianos, Violins, Organs,
Drums) 113
Reflection of Sound . . . .116
Echoes 116
Musical Notes 116
The Phonograph 117
Electricity 119
Apparatus needed . . . .119
Experiments 120
Benjamin Franklin's Kite . .123
Experiments 123
Electric Batteries 124
The Telegraph 125
Telegraphic Alphabet . . .127
Velocity of Electricity . . . 1 28
Magnetism 128
Experiments 129
Magnets 129
Natural Magnets (Lode-
stones) 133
Electro-Magnets . . . .133
Telegraph Instruments . . .133
Electric Bells 134
The Telephone 137
The Mariner's Compass . .138
The Electric Light . . . .140
The Dynamo 142
Electric Railways 143
Appendix 144-147
BOOK III. CHEMISTRY, — The Sci-
ence that teaches how to com-
bine Two Substances so as to
produce a Third Substance dif-
ferent from Either . . . .149
CONTENTS
IX
Physical Changes; Solutions . 150
Mixtures 150
Chemical Combinations . . -151
Chemistry (defined) 152
Chemical Affinity 152
Gunpowder 153
Bread Making 1 54
Composition of the Air . . .155
Oxygen 155
Nitrogen 155
Combustion 156
Hydrogen 157
Balloons 157
Water 157
Chemical Elements 158
Metals 158
Non- Metals 158
Chemical Compounds . . . .159
BOOK IV. METEOROLOGY, — The
Science of the Weather . .161
The Atmosphere ; the Colors of
Sunset and Sunrise . . . .161
Eruption of Krakatoa (1883) . 162
Twilight 163
Dust in the Atmosphere . . .163
The Rainbow 164
Halos 1 65
Fog and Clouds 165
Dew 167
Height of Clouds 167
Rain 168
Size of Raindrops 168
Hail, Snow, and Sleet . . . .168
The Snow Line (Line of Per-
petual Snow) 1 68
Snow Crystals 169
Uses of Snow 169
Irrigation of Farming Lands . 169
Frost 170
Rainfall 170
Rainfall and Crops 170
Winds 171
Wind Vanes 171
Force of the Wind . . . .171
Hurricanes 171
Causes of the Winds . . . 172
Land and Sea Breezes . . .174
Weather , . 174
The Seasons (Spring, Summer,
Autumn, Winter) . . . .175
Storms 175
Weather Predictions . . .176
United States Weather Bureau 176
Storm and Other Signals . .176
Value of Weather Predictions 178
Summer Thunderstorms . . 179
Lightning 180
Thunder 180
Distance of a Thunderstorm
from the Observer . . . 181
Lightning Rods 182
BOOK V. PHYSIOGRAPHY, — The
Science of the Land and of the
Sea 185
The Oceans 185
Depth of the Sea . -.. . . . 186
Soundings 186
The Sea Bottom . . . . .187
Dredging 187
Ooze 187
Fish 188
Phosphorescent Fish . . .188
Deep-Sea Fish . . . . . 189
Icebergs 189
Glaciers 191
Bowlders 191
CONTENTS
Pack-ice 191
Ice- Worn Rocks 192
Rivers and Streams . . . .193
Underground Water . . .193
Meandering Streams . . .194
Habits of Rivers 195
Canons 196
Flood Plains 197
Waterfalls 198
The Land 199
Changes in the Land . . .199
Mountains sculptured by
Rains 200
Sand Dunes 200
Waste of the Land . . . .201
Slow Motions of the Con-
tinents 202
Fossils 203
Sandstones 204
The Interior of the Earth . . 205
Stratified Rocks 205
Formation of Mountain
Ranges 205
The Oldest Mountains in
America 208
The Age of the Earth . . . 209
Age of Different Parts of
America 209
PACK
Age of Man on the Earth . .211
Flint Weapons 211
The Earliest Drawing . . .211
The First Plaything . . . .212
A Geyser 213
The Internal Heat of the Earth 214
Volcanoes 214
Teneriffe 214
Kilauea 215
Vesuvius 215
Herculaneum and Pompeii .215
Volcanoes in the United States 2 18
Old Lava Fields in Idaho,
Oregon, and Washington . 218
Earthquakes 218
Cause of Earthquakes . . . 219
The Charleston Earthquake
(1886) 219
The Mississippi Valley Earth-
quake (1811) 222
What to do during an Earth-
quake 222
Earthquake Detectors — how
to make them 222
The Lisbon Earthquake (1755) 223
Sea Waves 224
The United States Ship Wateree
at Iquique (1868) 224
THE SCIENCES
INTRODUCTORY CHAPTER
(To be read by the children who own this book)
LET me tell you how this book came to be written. Once
upon a time, not so very long ago, a lot of children were
spending the summer together in the country. Tom and
Agnes were brother and sister and were together all the day
long ; bicycling or playing golf in the morning, reading or
studying in the afternoon. The people who lived in the vil-
lage used to call them the inseparables because they were
always seen together during their whole vacation from June to
September.
Their cousins Fred and Mary always spent a part of every
summer with them ; and when they came there were four
inseparables, not two. The children liked the same games,
liked to read the same books, to talk about the same kind of
things, and so they got on very well together ; though some-
times the two boys would go off by themselves for a hard day's
tramp in the hills, or to shoot woodchucks, or for a very long
bicycle ride, leaving their sisters at home to play in the garden
with dolls, or to do fancywork and embroidery, or to play
tennis, or to read a book together. Tom was thirteen years
old then, and his sister Agnes was nine ; cousin Fred was ten
and his sister Mary was twelve.
i
2 THE SCIENCES
When the summer afternoons began to get very warm, in
July, a rule was made that the children should spend them in
the house, or on the wide, shady porch, or else under the trees
on the lawn, or in the garden. Golf, tennis, and wheeling had
to be done in the morning ; the afternoons were to be spent in
something different. Tom's father used to say that the proverb
All work and no play
Makes Jack a dull boy
was only half a proverb. It was just as true, he said, that
All play and no work
Makes Jack a sad shirk.
And so a part of every summer afternoon was given up to read-
ing some good book, or to study, or to work of some sort. The
two boys had their guns and wheels to keep thoroughly bright
and clean, and a dozen other things of the sort ; the two girls
had sewing to do ; and all of them, together agreed to keep the
pretty garden free from weeds.
Almost any afternoon you might see the four inseparables
tucked away in a corner of the broad piazza, each one busy
about something, and all talking and laughing — except, of
course, when one of them was reading, and the others paying
good attention. Tom's big brother Jack was at home from
college, and in the afternoons he was almost always on the
porch reading, or else on the green lawn lying under the trees ;
and Tom's older sisters, Mabel and Eleanor, were there too,
sewing, or embroidering, or reading, or talking together.
So there were two groups, the four children — the insepara-
bles— and the three older ones. When the children came to
something in their book that they did not quite understand,
Tom would call out to his big brother Jack to explain it to
INTRODUCTORY CHAPTER 3
them, and Jack would usually get up and come over to where
the children were and tell them what they wanted to know.
Almost every day there were conversations of the sort, and
explanations by some one of the older ones to the four
children. All kinds of questions would come up, like these :
FIG. i . THE PORCH
"Jack, tell us why a 'possum pretends to be dead when
he is only frightened and wants to get away."
"Jack, tell us why a rifle shoots so much straighter than a
shot-gun or a musket."
"Jack, what's the reason that a lobster hasn't red blood?"
or else :
" Eleanor, what is the difference between a fern and a tree ? "
"Is that coral bead made by an animal or an insect?"
"What is amber, anyway?" and so on.
THE SCIENCES
The children had no end of questions to ask, and Jack or
one of the older girls could generally answer them. When
they could not give a complete answer the dictionary was
brought out ; and if that was not enough, a volume of the
encyclopaedia. Sometimes the questions were talked over at
the dinner table and the whole family had something to say.
Tom's father had traveled a great deal and
could almost always tell the children some
real "true" story — something that had
happened to himself personally, or that he
had read.
The chapters in this book are conversa-
tions that the children had among them-
selves or with the older people. They are
written down here in fewer words than
those actually spoken, but the meaning is
the same.
When the children were talking about
electric bells, for instance, they actually
strung a wire from one end of the long
It costs about $1.10. The
two wires are to be fastened porch to the other, and put a real bell at
to the two screw posts in one en£ Qf jt and a push button and a
the picture — one at the . .
left-hand side, and one in battery at the other. In this book there
the middle, of the top of is a picture showing exactly what they
did ; but, after all, you cannot understand
an electric bell half so well by a picture as you can by the
real bell and the real wire.1 So when one of the children
who is reading this book comes to an experiment he must read
all that the book says about it, and understand it as well as he
1 Children should be careful to read the titles printed under each picture with
attention. The titles explain what the picture means.
FIG. 2. A CELL OF
DRY BATTERY
INTRODUCTORY CHAPTER 5
can. If he can get an electric battery, and a bell, and wire,
and a push button, then the picture in this book will tell him
exactly how to join them together; and when he has done this
and actually tried the experiment — and made it succeed — he
will know as much about electric bells as he needs to know.
If he cannot get the bell and the wire, and so forth, he can
probably see a bell of the sort somewhere ; and if he keeps his
eyes open and thinks about what he has read, he can certainly
understand how it works. Here is the battery always trying
to send out a stream of electricity along any wires joined to
the two screws at the top. Here is the wire, which is almost
Push
Button
Battery ' ' 1
'Bell
FIG. 3
a complete loop — almost but not quite. If the loop were con-
tinuous,— if the wire were all in one piece, — then the stream
of electricity would flow along the wire from the battery and
would ring the bell.
The use of the push button is to make the wire continuous
— to join the two ends of it so that the stream of electricity
can pass along it. When you have done this — when you have
joined the ends of the loop of wire — the bell rings, and only
then, which is just as it should be.
This book gives the pictures and the explanations. They
can be understood by paying attention ; and when they are
once understood a great number of things will be clear that
THE SCIENCES
all children ought to know, and that have to be learned some-
time. Why not now ? The sooner the better.
If you read what is written in the
book and perfectly understand it, that
is very well. If there is an experi-
ment to be tried, and you can get the
things to try it with, so much the bet-
ter. If you have any trouble in
understanding, ask some one — your
father, your mother, your teacher —
to explain to you. If you can find
another book — a dictionary or an
encyclopaedia — that describes the
same experiment, read that too.
Perhaps it will tell you what you
want to know, better, or more simply,
or more fully, or in a different way.
Then, finally, keep your eyes open to
actually see in the world the things
that are talked about in this book.
When you see them try to understand
them. Remember what you have
read here, and you will find that you
understand a good many things that
you see about you every day. Some-
body understands these things, —
push buttons, electric lamps, tele-
scopes, and so forth. Why should
FIG. 5. A PUSH BUTTON not you ? You can if you pay
it costs thirty cents. The two attention enough. The world is,
wires are fastened to two screws ' , . T . .
inside the push button. after all, your world. It belongs to
FIG. 4. AN ELECTRIC BELL
It costs seventy-five cents. The
wires are fastened to the two
screws at the bottom of the box.
INTRODUCTORY CHAPTER 7
you as much as it belongs to any one. The things in it can all
be explained and understood. It is everybody's business to
try to understand them at any rate. All these things concern
you. The more you know about them, the better citizen you
can be — the more useful to your country, to your friends, and
to yourself.
THE MOON
The moon, from a photograph taken with the great telescope of the Lick Observatory.
BOOK I
ASTRONOMY
THE SCIENCE OF THE SUN, MOON, AND STARS
The Earth as a Planet. — The children were looking at a map
of the world one fine afternoon and studying the way the land
and water are distributed, when Agnes said : " I never knew
before how little land there was on the earth. Why, there is
very much more water than land." "Oh, yes," said Tom,
"there's very much more water on the surface; but it's all
land at the bottom of the ocean. The sea is about three miles
deep, you know, and then you come to the ocean bottom, and
that is solid land again. The earth is nearly all rocks and soil ;
only a little of it is water, after all, but that little is on the
surface, of course, and that is why it shows."
Agnes. So the earth is almost all land ; if you dig down deep
enough, you would come to rocks, even below the oceans ?
• Tom. Yes, and if you went up high enough, you would
come to nothing. You would come to air first, and then by
and by to no air, and then you would come to just nothing —
to empty space.
Agnes. Well, it is n't quite empty, as you call it. There
are other globes in space. There are other planets, and the
sun and the moon, and there are simply thousands of stars.
So space is n't empty ; it is pretty full !
9
FIG. 6. AMERICA
FIG. 7. THE OLD WORLD
10
ASTRONOMY 1 1
Distance of the Moon and of the Sun from the Earth. Here
Tom's big brother Jack looked up from his book and said :
" Well, that depends on what you call full. It is 240,000 miles
from here to the moon, and the moon is the very nearest of all
the heavenly bodies to us. There is a good deal of empty
space between us and the moon, it seems to me."
Agnes. Two hundred and forty thousand miles ! Oh, Jack,
is that right?
Jack. Why, that is n't a beginning ; how far off do you sup-
pose the sun is ? It is 93,000,000 miles — millions this time,
FIG. 8
This picture shows the height of land on the earth compared to the depth of the sea. If
you could cut the earth through and through with a knife and look at one part only, it
would look something like the picture. All the shaded part \^\\ is land. The curved
line drawn all across the picture, near the top, is the curve of the surface of the oceans.
Part of one of the oceans is shown by the white space below this curved line and above
the floor of the ocean itself, — the shaded land. The curve of the ocean surface is con-
tinued across the picture underneath the mountains. If the surface of the earth were
all water, the bounding line would be this curve. From side to side of the picture is
about 350 miles. If the whole circle of the earth were drawn, it would be about eight
feet in diameter. That is the scale of the drawing.
not thousands ; and some of the planets are much farther off
yet, and every one of the stars is farther off still.
Agnes. Jack, tell us about it, will you ? We don't know,
and you do.
Jack. The very first thing you have to think about is the
size of the earth. How far is it through and through the
earth, Tom ? If you pushed a stick through the earth from
New York to China, how long would the stick be ?
12
THE SCIENCES
The Diameter of the Earth. — Tom. The geography says that
the diameter of the earth is 8000 miles ; so the stick would
FIG. 9. A BALLOON
Balloons carrying men have gone up more than five miles, and small balloons carrying
thermometers, etc., have been sent nearly ten miles high. The atmosphere of the earth
extends upwards a hundred miles or so, but beyond this there is no air — nothing but
empty space.
have to be 8000 miles long, — as long as from Cape Horn to
Hudson Bay, my teacher says.
ASTRONOMY
Jack. That 's about right. Suppose there were a railway
from Hudson Bay to Cape Horn, and express trains run-
ning on it at the rate of 40 miles an hour. Let us see how
long they would take to go the 8000 miles. They would go
FIG. 10. THE FULL MOON RISING IN THE EAST
40 miles in one hour, and 80 miles in two hours, and 960 miles
in a day — say 1000 miles a day. Well, they would take eight
days to go the 8000 miles, then. Now, suppose we could
build a railway to the moon. How long would an express train
take to go the distance ? Take your pencil, Tom, and cipher
it out.
THE SCIENCES
Tom. You said the distance from the earth to the moon
was 240,000 miles. If the train goes 1000 miles a day, it
would take 240 days. I don't need any pencil.
Jack. Sure enough ; and 240 days is eight months (8 x 30
= 240). It would take the train eight months to go from the
earth to the moon, then — eight whole
months, traveling night and day at forty
miles and more every hour.
Agnes. I should be nearly a year older
when I got there than when I started,
then.
Jack. Yes, and recollect that there are
no stations on the railway to the moon.
The moon is the heavenly body that is
nearest to us, so that space is pretty
nearly empty, after all.
Distance of the Sun from the Earth. —
Tom. How far did you say it was from
the earth to the sun — 93,000,000 miles ?
Jack. That's right. You will need your
pencil to figure out how long the express train would take to
go from the earth to the sun, Tom.
Tom. Yes, it is like this, is n't it ? The train goes
1000 miles in a day; then it will take 93,000 days to get to
the sun.
30)93000 days
12) 3100 months
258^ years
It would take 3100 months, that is more than 258 years, to
get to the sun. That 's a long journey ! You would have 258
birthdays on the road, Agnes.
FIG. ii. A SCHOOL
GLOBE
ASTRONOMY 15
Jack. Put it this way, Tom : 258 years ago takes you back
to the year 1643 (1901—258= 1643). The Pilgrims had been in
New England only twenty-three years in 1643, for they came
in 1620 (1643 — 1620 = 23). Suppose one of those Pilgrims
FIG. 12. THE PILGRIMS LANDING ON PLYMOUTH ROCK FROM THEIR SHIP,
THE " MAYFLOWER," DEC. 20, 1620
to have stepped on to the train at Plymouth Rock ; he would
have been traveling all these years, and he would only have
arrived at the sun a few years ago ; that is, if he had lived
to make the journey.
Tom. Two hundred and fifty-eight years !
1 6 ,THE SCIENCES
The Planets Mercury and Venus. — Jack. Yes, and nearly
all that space is empty too. There are only two planets
between the earth and the sun — Mercury and Venus.
Agnes. Venus, the evening star ?
Jack. Yes, Venus is the evening star sometimes. Venus
and Mercury are the only planets that the Pilgrim would pass
on the road from the earth to the sun. Space is rather empty,
is n't it ?
Agnes. Are n't there any stars in between the earth and
the sun, Jack ?
Jack. Not one ; the real stars are thousands and thousands
of times farther off. We call Venus the "evening star," but
Venus is not a star at all, but a planet. Let me tell you, so
that you can make a sort of picture of it all in your minds.
The sun is there in the middle of space and all the planets
move round him, just as the earth does. Nearest to the sun
is the planet Mercury, and then comes the planet Venus, and
then the planet Earth.
Agnes. That sounds queerly — " the planet Earth " — though
of course we know the Earth is a planet.
The Planets Mars, Jupiter, Saturn, Uranus, 1 and Neptune. —
Jack. Yes, exactly so. And then there are other planets
farther away from the sun than the earth ; Mars for one, and
then Jupiter, and then Saturn, and then Uranus, and then
Neptune. That is all we know of ; there may be more of
them. Neptune is thirty times as far from the sun as the
earth is. Here is a little table that I will write down for you
to keep. You need not memorize it, only recollect that
Mercury and Venus are nearer to the sun than we are, and
that all the others are farther away.
1 Pronounced u'ra-nus.
ASTRONOMY 17
DISTANCES OF THE PLANETS FROM THE SUN
The planet Mercury is 36 million miles from the sun
" Venus " 67 " " "
" Earth " 93 " " "
" Mars " 141 " " "
" Jupiter " 483 " " "
" Saturn " 886 " " "
" Uranus " 1782 " " "
" Neptune « 2791 " " "
Jupiter is five times, and Neptune is thirty times, as far from
the sun as the earth is.
Tom. Is n't there a map of all these planets that we
can see ?
Jack. No, and there 's a good reason why. Suppose you
tried to make a map of them, and suppose you took the dis-
tance from the Sun to the Earth on the map to be an inch.
Don't you see that the distance from the Sun to Neptune
would have to be thirty times one inch, and the page of your
book thirty inches wide — nearly a yard wide ?
Tom. Of course, no book has a page as big as that ; but
you might make little maps.
How to make a Map that shows the Sun and Planets. — Jack.
You and Agnes can make a map yourselves to-morrow morn-
ing, if you want to, when you go out for a walk, and I '11 tell
you how to do it.
Suppose you take the large globe in the library, that you
were looking at just now, to stand for the Sun. It is two feet
in diameter. Well, the diameter of the real Sun is 870,000
miles, and your map has to be made all to one scale. Every
step of yours is about two feet long, is n't it, Tom ? Try it.
Tom. Yes, my steps are almost exactly two feet long.
i8
THE SCIENCES
Jack. Well, remember to-morrow that every step you take
along the road to the village is really only two feet long, but
that it stands on the map for 870,000 miles.
Agnes. Are we going to make the map along the road ?
FIG. 13. THE ROAD TO THE VILLAGE
Jack. My dear, you have to do it that way ; your map is
going to be nearly a mile and a quarter long. You have to use
the whole country round to make it.
Agnes. Well, that is a map !
Tom. How shall we make it, Jack ?
Jack. You start, you know, with this globe in the house to
stand for the Sun. The globe is two feet in diameter, and the
real Sun is 870,000 miles in diameter.
Scale of the Map. — "So, recollect, every two feet on your
map is 870,000 miles. Every one of your steps, Tom, stands
for 870,000 miles.
ASTRONOMY 19
"You must take with you
a very small grain of canary-bird seed to stand for the planet Mercury ;
a very small green pea to stand for the planet Venus;
a common green pea to stand for the planet Earth;
a rather large pin out of Agnes' work box, and let its round head stand
for the planet Mars;
an orange to stand for the planet Jupiter;
a golf ball to stand for the planet Saturn;
a common marble to stand for the planet Uranus ;
a rather large marble to stand for the planet Neptune.
Sizes of the Planets compared to the Sun. — "If this globe,
two feet in diameter, stands for the Sun (which is really 870,000
miles in diameter), then a common green pea is just the right
FIG. 14
The sizes of the planets of the Solar System (the Sun's family) compared with each other.
h = Saturn; T/= Jupiter; tp= Neptune; & = Uranus; <f = Mars ; C= our Moon;
®= Earth; ?= Venus; $ = Mercury.
OF THE
UNIVERSITY
20 THE SCIENCES
size to stand for the Earth (which is really 8000 miles in
diameter) and an orange is just the right size to stand for
Jupiter, and so on. You are going to carry all the planets
off in your pocket, and when you have put them down in the
right places you have made your map."
Tom. How shall we know where to put them down ?
Jack. I will give you the right number of steps to take
between the Sun and every one of the planets. If one of
Tom's steps is 870,000 miles, then
Mercury (the canary seed) is 41 steps from the Sun (the globe at the
house) ;
Venus (the small pea) is 77 steps from the globe that stands for the Sun ;
Earth (the pea) is 107 " " « «
Mars (the pin's head) is 162 " " « «
Jupiter (the orange) is 555 " " " «
Saturn (the golf ball) is 1019 " " " "
Uranus (the small marble) is 2048 " " " "
ATeptune (the large marble) is 3208 " " " "
Those are the right distances, and you can make your map
to-morrow morning when you go for a walk. Recollect that
the globe in the house stands for the Sun. You are to walk
away from it along the road to the village until you 've taken 41
steps. Stop there and put down the canary seed to stand
for the planet Mercury. Then go on 36 steps more and you
will be 77 steps from the model of the Sun. This will be the
place to put the small green pea that stands for the planet
Venus ; then go on 30 steps more and you will be 107 steps
away from the Sun. This will be the place to put down the
green pea that stands for the Earth, and so on. The last
planet — Neptune — will be 3208 steps away from the house,
— about one and a fifth miles away.
ASTRONOMY 2 1
Agnes. I don't believe we can count such large numbers,
Jack ; we shall be sure to forget them and lose the count.
Jack. True enough, Agnes. Let me see if I can't make it
simpler for you. I will write down on a card all that you have
to remember, and we can make the numbers that you have to
count smaller. We can do it this way : instead of counting
the distances from the Sun to each planet, we will count the
number of steps between each planet and the next one ; this
way.
Here is the card that Jack wrote :
d d^^ld -id tf/0; 00$ Wl
/• / />
'i-e •£££<
<cz <£&€&£ d.-£-€i<
-e -cz-t.d'Z-ti'W'C'e
ff
€ttd=
4d ^- SS
-id
£e't ^t-o-
e a--e- -v- i-f-- . <t&
<td
i^td <t-a Cffle&trt&e -id 44 ' £0
22
THE SCIENCES
NOTE. — The numbers that are needed to make the map are obtained in this
way : If one step is 870,000 miles, then
The distance from the Sun to Mercury =
" « " Venus =
" " " Earth =
" " " Mars =
u u
Differen
4i ste
ps
—
77
36
107
30
162
55
555
393
1019
464
2048
|
1029
3208 '
1
1160
36,000,000 miles:
67,200,000 " =
92,900,000 " :
I4I,OOO,OOO " :
Jupiter = 483,000,000 " =
" " " Saturn = 886,000,000 " =
" " " Uranus = 1,782,000,000 " =
" " " Neptune= 2,791,000,000 " =
In the last column are the differences between the numbers just preceding; 77
less 41 is 36, 107 less 77 is 30, 162 less 107 is 55, and so on. If the model of the
planet Mercury must be 41 steps from the model of the Sun, and if the model of
the planet Venus must be 77 steps from the Sun, then the model of Venus must
be 30 steps away from the model of Mercury, and so on for the others.
When the next day came, Tom and Agnes set out to make
the map of the Sun and all the planets. The school globe
in the house stood for the Sun, and they carried the models
of the planets with them, as well as the card that showed how
far apart the planets were to be on the scale of their map.
Agnes kept the card in her hand and told Tom how many
steps he was to take. At the house she said : " Tom, you
must take 41 steps, and then stop." So Tom walked off,
counting his steps till he had made 41, and then he put down
the little canary seed that stood for the planet Mercury. The
globe in the library stood for the Sun ; this tiny seed stood
for the planet Mercury ; the distance from the globe to the
seed stood for the real distance of the real planet Mercury
from the real Sun. Thirty-six steps farther they put down the
small green pea that stood for the planet Venus ; and 30 steps
farther still they put down the green pea that was to stand for
the Earth.
Here they stopped for a minute to think about it all. This
little bit of a green pea was the huge Earth, very, very much
ASTRONOMY 23
smaller than the globe that stood for the Sun. They could
not even see the small green pea that stood for Venus, nor
the little seed that stood for Mercury, though they knew about
where they were, of course. There were no other planets in
the real space between the real Earth and the real Sun except
Mars
esi days
FIG. 15
A plan of the orbits of Mercury, Venus, the Earth, and Mars.
just those two, Mercury and Venus, and space was almost
empty, after all, as Jack had said, except for few, very few,
planets that were exceedingly far apart. " Why, we can't even
see the models of Mercury and Venus from here," said Agnes.
" No," said Tom, " but if they were shining things, as the
24 THE SCIENCES
planets are, we could see them. They ought to be painted
white so that the sunlight would make them glisten."
So the children went on putting the models down in the
road at the right distances apart. Agnes read the right num-
bers from the card, and Tom walked away counting his steps
years
Neptune
Uranus
A plan of the orbits of Mars, Jupiter, Saturn, Uranus, and Neptune. (The scale of this
drawing is much smaller than that of the preceding one.)
up to the thousands. He got rather tired of it, but they kept
on until finally all the models were put down at the right dis-
tances apart, and their map was made. By this time they were
nearly a mile and a quarter away from home, and they had
spent the whole morning in the work. But the work was not
ASTRONOMY 25
wasted. They really understood what they had been doing,
and realized, as very few people — even grown people — do,
how immensely large space is, and how few — very few —
planets there are to fill it.1
When the children came home that day there was a great
deal of talk about the map — the model — that they had made.
All the older people and some of the neighbors were interested
in it. They found their work had not been wasted and that
they had really learned something.
The Solar System; the Sun and Planets. — Jack told them
some interesting things about the sun and the planets. They
knew already, of course, that all the planets moved round the
sun in paths that were called orbits. The earth, for instance,
goes once round the sun every year, — every 365^ days. Every
one of the planets goes round the sun, too, in its own particular
orbit, in its own year. For instance,
Mercury goes round the Sun in 88 days = about 3 months
Venus " " 225 days = " 7 "
Earth " " 365 days = " 12 "
Mars " " 687 days = " 23 "
Jupiter " " 12 years
Saturn " " 29 years
Uranus " " 84 years
Neptune " " 165 years
Tom's father told them about one of the kings of Spain who,
long ago, used to play chess on a huge chessboard with real
living persons for chessmen. These men moved from square
1 It is strongly recommended that the teacher should make such a model of
the solar system as has just been described, with the aid of his pupils. If actually
made, it will lead to a true and living realization of the dimensions of the solar
system. No amount of mere class-room instruction can do this for young children.
26 THE SCIENCES
to square on the chessboard as the game went on ; and Tom's
father said that the map of the solar system with its eight
planets ought to have had eight little boys who would walk in
FIG. 17
In this picture the large circle stands for the sun. Each of the small dots stands for the
earth. The size of the dots and of the circle are in the right proportion. It would
take 109 earths in a row stretched across the disk of the sun to reach from edge to
edge. Count them.
circles round the model of the sun, carrying the models of the
planets in their hands. One boy would carry the canary seed
that stood for Mercury, and he would have to walk once round
his circle in three months ; another boy would carry the small
ASTRONOMY 2^
green pea that stood for Venus, and he would have to walk
around a larger circle once in seven months ; still another would
carry the green pea that stood for the Earth, and he would have
to walk around the circle of the Earth's orbit once in each year;
and so on for all the other planets. The boy that carried the
FIG. 1 8
Three drawings of Jupiter as seen in a telescope. The lower drawing shows Jupiter
with his four bright satellites. It is on a smaller scale than the others.
marble that stood for Neptune would not get all the way around
his circle for 165 years. "He would be quite grown up by
the time he got round, wouldn't he?" said Agnes. "Well,"
said Jack, " Papa' is right ; that is the real way to make the
model. The sun is in the middle. All the planets move round
him in circles; each one of the planets takes a different time
28 THE SCIENCES
to go once around its orbit. All of these planets together
make up the solar system, — the family of the sun."
Tom. Why do they call it the solar system, Jack ?
Jack. Just because it is the sun's system ; sol, in Latin,
means "the sun," and solar means " belonging to the sun." All
the planets go round the sun, and round nothing else. That 's
why. The sun is so much larger than any of the planets, or
than all of them put together for that matter, that it is the
sun's system.
Relative Sizes of the Planets. — "You see," said Jack, "that
the sun is very large indeed. He is as much larger than the
earth as the library globe is larger than a green pea. If all
the solar system were to shrink and shrink until the earth —
this huge earth — had shrunk to the size of one green pea, the
sun would still be as big as the globe in the library — it would
be two feet in diameter."
The real diameters of the sun and planets are :
The Sun is 866,400 miles in diameter
Mercury " 3,030 " "
Venus « 7,700
_, _ . I The smaller planets
The Earth " 7,918
The Moon " 2,162
Mars " 4,230 " "
Jupiter « 86,500 "
Saturn " 73,000
Uranus « 31,900 f The giant planets
Neptune " 34,800
"Oh !" said Agnes, "we left the Moon out of our model."
" So we did," said Tom ; "let us go this afternoon and stick
a pin in the ground to stand for the Moon, alongside of the
green pea that stands for the Earth."
FIG. 19
Drawings of the planet Saturn as seen in a telescope at different times. In the upper figure
\ve are looking at Saturn's rings edgewise, and they appear as a thin line. In the
next drawing we are looking down on the rings. In the third drawing -we are also
looking down on the rings.
29
30 THE SCIENCES
The Moons of the Planets. — "Well," said Jack, "that's all
right. Only you must choose a pin with a very small head.
And, while you are about it, you had better put in some more
pins, for several of the other planets have moons — satellites,
FIG. 20. THE STARLIT SKY
they are called — and they go around their planets just as the
Moon goes around the Earth. Mercury has no satellite that we
know of ; Venus has no satellite that we know of ; the Earth
has the Moon for satellite ; Mars has two very small satellites ;
FIG. 21. THE GREAT COMET OF i
32 THE SCIENCES
Jupiter has four large satellites about the size of our Moon, and
one extremely small one ; Saturn has eight satellites, one larger
than our Moon ; Uranus has four satellites ; Neptune has one
satellite almost the same size as our Moon."
The Minor Planets; the Asteroids. — "Yes, and at the same
time you might as well sprinkle about 500 grains of sand
in the space between Mars and Jupiter to stand for the 500
minor planets that they call asteroids. There are about 500 of
them known now, and, I 've no doubt, hundreds more not yet
discovered. When you read in the newspaper that a new
planet was discovered last night by some astronomer, that
means that another one of these minor planets has been found.
They find them by photography with a large telescope."
Comets. — " And, by the way, put in two or three thin wisps
of cotton wool somewhere to stand for comets. Comets are
mostly made out of shining gas — they are n't solid. But
they look a little like wisps of cotton wool, anyway."
Tom. Is that all ? Shall we put in anything else ?
Jack. That is all for the solar system, except clouds of very
little stones, almost like dust, that make the shooting stars or
meteors.
The Stars. — " What about the stars ? " said Agnes.
Jack. Oh, the stars are not part of the solar system, Agnes ;
they are millions and millions of miles outside of it ; the very
nearest star is thousands and thousands of times farther from
us than even the planet Neptune.
Tom. How far off are they, Jack, anyway ? Could we get
the nearest of the stars on our model ? Where would it be ?
In the next county ?
Distances of the Stars. — " Let me see," said Jack, "the
nearest star of all is 20,000,000,000,000 miles from the sun —
ASTRONOMY 33
twenty millions of millions of miles ! If you were to put it on
your map, it would have to be about 9000 miles from where we
are now — it would have to be somewhere in China."
Agnes. Is that the nearest star, Jack ?
Jack. Yes, the very nearest. If you should put another
school globe in the Chinese emperor's palace at Peking, that
would stand for the nearest star to our sun, which our school
globe in the library stands for. The sun is a star, and stars
are about of the same size. So a school globe may stand, for
any one of them.
Tom. Well, space is empty if planets and stars aren't any
closer than that. What is the difference between a planet
and a star, anyway ?
What is a Planet? — "The greatest difference," said Jack,
" is this : the stars shine by their own light, just as an electric
street lamp shines ; and the planets shine by light reflected
from the sun, just as a football would shine if you held it up
in the sunlight."
Tom. Do you mean that Venus and Jupiter do not shine by
their own light ?
Jack. I mean just that. Venus and Jupiter are two great
globes something like the earth, made out of rocks and soil,
with clouds all around them — clouds something like our clouds.
The sun shines on them, and they shine, and we see them. If
the sun were to stop shining on them, they 'd go out like a
candle.
Agnes. But, Jack, Venus shines at night, in the dark sky,
when the sun has stopped shining.
Jack. The sun has stopped shining on you and me at night
because the earth has turned round and we are in the earth's
shadow ; you know that. But all the while the sun is shining
34 THE SCIENCES
just the same. It is shining on the other side of the earth, where
it is daytime, and it is sending out sunbeams above the earth
and below it, everywhere and all the time. Some of these sun-
beams fall on Jupiter and Venus and make them bright, and
we see them. What we really see is the sun's brightness
reflected back to us, just as you might see an electric light at
night shining on a mirror. You might be in the dark yourself;
the electric light might be round the corner of the street, but
the mirror would be bright.
Tom. So planets are bright because the sun shines on them.
Why are stars bright then ?
Jack. Stars are bright just as the sun is bright. The sun
makes its own light as an electric lamp makes its own light.
The stars are like the sun. They shine by their own light.
Planets shine by borrowed light. They borrow their light from
the sun. If you were to go off and sit on the nearest star and
look at the solar system, you might see the sun in the middle
of it shining away all the time — all day and all night, too.
And if you could see our little group of eight planets wheeling
around it, they would be bright on the side nearest the sun
— on the side shined upon ; and be dark on the side away from
the sun. The sunlight cannot go through them. The sun can
shine only on that part of a planet that is turned towards it.
Phases of the Moon (New Moon, Full Moon, etc.). — "Don't
you know the moon is often only half bright, and sometimes
three-quarters bright, and so on ? Venus looks that way in a
telescope sometimes ; in a telescope you can see Venus like a
crescent moon — like a sickle. You do not see it like that
with your eye, because Venus is so bright that your eyes are
dazzled. You see the glare, and it looks like any other daz-
zling glare ; you do not see its true shape."
ASTRONOMY
35
Tom. You can't see the true shape of a sheet of tin that
the sun shines on; it looks just like a dazzle of light.
FIG. 22. THE NEW MOON SET-
TING IN THE WEST
FIG. 23. THE MOON IN THE
FIRST QUARTER
FIG. 24. FRED WATCHING THE FULL MOON RISE IN THE EAST
Jack. That is the way with the planets when you do not
use a telescope. Now the moon looks so large, and the light
from any part of it is so faint, that you can see its shape. It
36 THE SCIENCES
does not dazzle your eyes. They call those different shapes of
the bright part of the moon \te phases. Venus has phases, too.
The moon is a globe, you know, about 2000 miles in diameter.
One half of it is always turned towards the sun, and that half
of it is always bright, day and night. If we were on the sun,
we should always see the whole circle of the moon bright.
But we are on the earth, and the bright part of the moon is not
FIG. 25
A schoolroom experiment to show how the sun lights up half of every one of the planets, and
only half. The room should be darkened ; the lamp should have a ground-glass shade ;
the orange that stands for the earth or planet should be fastened by a knitting needle to
a pincushion. The pupils should see that half, and only half, of a globe (a planet, the
earth, the moon) is illuminated. They should also see that by going to different parts
of the room different portions (phases) of the illuminated part are visible. The phases
of the moon can be explained by this experiment. Half of the moon is lighted by the
sun ; all of the illuminated half that is turned towards the earth is seen bright ; the
moon moves round the earth and turns different parts to it at different times.
always turned towards us. We see only so much of the bright
part as is turned towards us — so much and no more.
Agnes. Sometimes we see the whole circle of the moon
bright — at/w// moon.
Jack. Yes, we see it so when the sun is setting in the west and
the moon rising in the east. The sun is shining full on the moon,
and the bright half of the moon is turned full towards us.
ASTRONOMY
37
Tom. When the moon is a sickle it is often in the west, not
far from the sun about sunset.
Jack. That is the phase we call new moon.
Tom. The moon goes round the earth, does n't it ?
FIRST I
• f
QUARTER •
IQUARTEH
FIG. 26
This picture shows why the moon's disk has different shapes at different times. The sun
is supposed to be far away in the direction of the top of the page. It shines on the
earth and lights half of it. It is night on the unlighted half of the earth. The moon
goes around the earth in its orbit in the direction of the arrow. Wherever the moon
is, one half of it is lighted — the half turned towards the sun. A person on the
earth sees one half of the moon — the half turned towards him. The little circles out-
side the orbit in the picture show the shape that the bright part of the moon will have
at new moon, full moon, etc.
38 THE SCIENCES
Jack. It goes round the earth once in every month. The
moon's month begins when the moon is a new moon. Every
night the bright part gets larger, and in about a week, a quarter
of a month, we see a quarter of the moon bright ; that is the
first quarter. Two weeks after the new moon the full moon
comes ; and a week later comes a moon that is only partly bright
again ; that is the third quarter. By and by, in four weeks,
comes another new moon, and so on forever.
Agnes. One of my storybooks says the old moons are cut up
to make stars out of. They would n't be bright enough, would
they ?
Jack. Not exactly. Stars are the brightest things there are
except the sun, which is the very brightest thing we know.
Agnes. There are faint stars, though — some that you can
scarcely see.
Tom. They are faint only because they are far off. If you
were near them, they would be bright like the sun.
Jack. That 's right. The stars are suns, and our sun is a
star. All of them are really very much alike, though the stars
do not look at all as the sun does. The sun looks large, and it
is hot, because it is close to us. The stars look small because
they are so far off, and we get no heat at all from them, though
we get light. You know you can see the light of a lamp much
farther than you can feel its heat.
Number of the Stars. — Agnes. There are thousands and thou-
sands of stars, Jack ; do you know how many there are ?
Jack. There are about 6000 stars that you can see with the
naked eye, not more; and you cannot see all those at once.
Probably you never see more than a couple of thousands at any
one time.
Agnes. Why, there seem to be many more than 2000.
ASTRONOMY
39
Jack. Well, my dear, the only way to know is to count them.
And the astronomers have counted them, and made maps that
show every one of them by a little dot. That is the way they
know how many there are. But if you take an opera glass, you
can see very many more ; and
if you take a telescope, you can
see thousands and thousands.
The largest telescopes that we
have will show perhaps a hun-
dred million stars. The bright-
est stars are nearest to us, and
the faint ones are very far away
indeed — inconceivably far, in
fact.
Tom. You said the nearest
star was as far away from the
sun on our map as New York
is from Peking. Are all the
stars as far apart as that ?
Are n't some of them close
together ?
Clusters of Stars. — Jack.
Well, there are some groups of
stars fairly close together; but
generally one star is about as
far from the star nearest to it
as our sun is from the nearest
star. If you were making a map of the whole universe, you
would begin by making a model of the solar system just as you
did yesterday. The library globe would stand for the sun,
which is one of the stars, you know. The nearest star to it
FIG. 27. THE GROUP OF STARS
CALLED THE PLEIADES
The six brightest stars can be seen with
the naked eye. To see the others a small
telescope must be used. The Pleiades
may be seen high up in the sky and to
the south of the point overhead about
10 P.M. December 21, about 9 P.M.
January 5, about 8 P.M. January 20,
every year. Or you may see them rising
to the north of the east point of your
horizon about 10 P.M. August 23, about
9 P.M. September 8, about 8 P.M. Sep-
tember 23.
40 THE SCIENCES
would be shown on the map by a globe set down at Peking,
8000 miles away from us, and 8000 miles from Peking there
would be another globe, and 8000 miles farther another one,
and so on. Every 8000 miles on your map there would be a
globe to stand for a star, and there would be at least a hundred
million globes on your map of the universe, because, you
know, the telescopes show us at least a hundred million stars.
Of course these stars are scattered all around us ; they are n't
«?
Sun
ft $ * ft 0 $ &
FIG. 28
The stars in space are arranged somewhat as in the picture. On the whole, no one of them
is nearer to any other one than the sun is to the nearest star, — 20,000,000,000,000 miles.
The Sun is just one out of a countless number of stars — one out of millions. No one
of the planets of the solar system can be seen from the nearest of the stars.
in a straight line one after another, but they are scattered all
over the surface of the night sky.
Agnes. The planets move around the sun ; do the stars
move around the sun, too ?
Jack. No, they are so far off from us that the sun has
nothing to do with them, nor they with the sun. The sun has
its own family of planets, and it is possible that the stars —
which are suns — have their own planets, too ; but we do not
know whether they have or not.
ASTRONOMY
Agnes. Why don't you know, Jack ?
Jack. Because the stars are so far away. We can see the
stars like bright shining points in the sky. They shine by
their own light and are bright. Now suppose any one of the
stars really had a family of planets around it. Those planets
FIG. 29
A photograph of a part of the Milky Way. Each little dot in the picture is a star, and there
are thousands of them even on one photographic plate. You can see the Milky Way like
a bright belt in the sky — a beH made of stars — overhead early in the evenings of
August and September or of November, December, and January, or parallel to the
northern horizon early in the evenings of April and May.
would shine by the light from that star, and they would be
faint, much too faint for us to see, even if the planets were
really there ; and the only way to know about stars and
planets is to see them ; you cannot touch them or hear them.
If you cannot see a planet it does not exist, so far as you know.
42 THE SCIENCES
Tom. Could n't a man on the nearest star, looking at our
sun, see the planets of our system, — Venus and Jupiter ?
Jack. No, indeed ; he would see our sun, but the light of our
planets would be too faint. He could not possibly see them.
Do the Stars have Planets as the Sun does ? — Tom. You
say you don't know whether the stars have planets round
them. What do you think about it ? Haven't you any idea?
• -
FIG. 30. THE STARLIT SKY
Jack. There is a great deal of difference between knowing
and thinking. I certainly do not know that the stars have
planets, for I have never seen them. But I do think that it is
very likely that they have families of planets, just as the sun
has. I think it is likely — very likely ; but I don't know.
ASTRONOMY
43
Tom. And do you think those planets, if there are any,
have people on them ? Are they inhabited as the earth is ?
Jack. That is a hard question. In the first place, it is not
certain that there are any planets around the stars, and then it is
a mere guess whether there could be inhabitants on them. That
is one of the questions we shall have to give up. It is too difficult.
FIG. 31. THE SHOWER OF SHOOTING STARS SEEN ON Nov. 13, 1866
The round dots stand for stars ; the arrows for the tracks of meteors that were seen.
Notice that nearly all the meteors radiated from a spot near the center of the picture.
Agnes. I am going to believe that every star has planets
round it, just as the sun has.
Jack. Well, that is reasonable enough. Very likely you are
right. Who knows ?
Agnes. And I am going to believe that some of these
planets round the stars have men on them.
44
THE SCIENCES
Jack. I can't say you're wrong ; I can't prove that you are
wrong. Who knows ? You can believe what you like about
it. Wait till we know more.
Shooting Stars ; Meteors ; Fireballs. — On the night of
August 10 the children stayed up late to watch the shooting
FIG. 32. THE GREAT METEOR THAT FELL IN CALIFORNIA IN 1894
stars that are regularly seen every year on that particular
night. On almost any night that is clear any one who will
ASTRONOMY
45
watch for an hour will see a dozen or more ; and the easiest
way to understand what they are like is to watch for them. In
the country, where the sky is dark and where there are no
electric lights, it is not hard to see them. In the city it is
not so simple ; the sky is too
bright and the street lamps
interfere too much. Any one
can see the stars. If one of
the stars should suddenly get
brighter and move quickly
away from its place and then
suddenly disappear, as if it
had been blown out like a
candle, it would look just as
the shooting stars do. The
real stars stay in the same
place night after night, year
after year, century after cen-
tury. They are called fixed
stars because they are fixed
in their places. The shoot-
ing stars are small pieces of
stone or iron that are mov-
ing about in space, as the
planets move. One of these
pieces comes near to the
earth and falls to the ground just as a stone falls. It moves
rapidly through the air and gets hot, as your hand will get hot
if you move it very rapidly to and fro on your desk. The
shooting star moves very fast and gets very hot indeed — hot
enough to burn. Usually the meteors (shooting stars) get so
FIG. 33. A METEORIC STONE THAT
FELL IN IOWA IN 1875
46 THE SCIENCES
hot in their flight through the air that they are quite burned
up before they reach the ground. Sometimes a piece of iron
falls and is picked up. The picture shows a piece of the
sort. Fig. 32 shows how such a meteor (a very large one
— much larger than a shooting star) looks as it is falling.
FIG. 34. THE ZODIACAL LIGHT
The best time to see it in the United States is in February, March, and April, in the early
evening, above the western horizon.
The Zodiacal l Light. — Space is full of such meteors, most
of them small, like dust. The sun shines on them, and you
can often see a triangle of faint light or glow, which is called
1 Pronounced zo-di'a-kal.
OF THE
OF
ASTRONOMY
47
the zodiacal light. If you live in the country, where the sky
is dark, be on the lookout for it. The street lamps of the city
make the sky entirely too bright for you to see it in towns.
Nebulae. — Nebula, in Latin, means a cloud ; and nebulae is the
plural. There are several spots in the sky that, even with the
FIG. 35. THE GREAT NEBULA IN ANDROMEDA, FROM A PHOTOGRAPH
MADE WITH A TELESCOPE (SEE FlG. 53)
naked eye, on a clear night look as if the stars in those spots were
covered with a thin veil of cloud. When these spots are looked
at with a telescope you see bright forms like those in the pictures
Figures 35 and 53, and they are, in fact, bright clouds of gas
and small particles of dust. They shine by their own light.
48
THE SCIENCES
Rising and Setting of the Sun. — Tom. We know that the
sun rises in the east every day —
Agnes. And goes across the sky and sets in the west.
Jack. Why does it ? Does the sun really move ?
Agnes. No ; the earth turns round and the sun stands still ;
but the sun seems to move.
Jack. The sun seems to move across the sky from rising to
setting every day ; the moon does the same thing ; each one of
the thousands of stars rises and then sets every night. There
are just two ways to explain these things. Either the earth
stands still and all these different heavenly bodies really move
around it — every one of them — in twenty-four hours, or the
FIG. 36. THE SETTING SUN
heavenly bodies stand still and the earth turns round on its
axis every day. The last explanation is the true one, as you know
very well, and so we have to say the sun appears to move from
ASTRONOMY
49
rising to setting (for the sun really does not move at all) ; and
we have to say the stars appear to move from rising to setting
(for the stars do not really move at all). It is the earth that
FIG. 37. THE WAY THE SUN SEEMS TO MOVE FROM RISING TO SETTING
The man in the picture is looking towards the south, and his arms are stretched out to the east
and to the west. If he stood there all day, he would see the sun rise above the horizon
in the east, gradually rise higher and higher and be highest at noon, just to the south,
and then decline towards the west and set in the west at the end of the day. The
dotted line shows the apparent motion of the sun. The picture was drawn at about
three o'clock in the afternoon. Why ? Because the sun in the picture is where the
real sun will be every day about three o'clock.
turns, and as it turns everything in the sky appears to move
from east to west.
The Celestial Sphere. — " Think of it in this way. You are
on a globe — the earth — that turns around every twenty-four
hours. Above you is the sky. It looks exactly as if it were
a hollow globe, and as if you were inside of it. In the night-
time the stars look like little shining marks fastened to the
hollow globe all around you. In the daytime the sun (and
sometimes the moon) seems to be fastened to the inside of the
hollow globe of the sky. We call the hollow globe of the sky
50 THE SCIENCES
the celestial sphere. You are in the middle of it, and you see
all the stars at night slowly moving from rising towards setting.
The celestial sphere is the surface of the sky to which the sun,
moon, and stars appear to be fastened. They look as if they were
fastened there, anyway. They all seem to be at the same distance."
FIG. 38. THE CELESTIAL SPHERE (THE HOLLOW GLOBE ON WHOSE
INNER SURFACE ALL STARS SEEM TO LIE)
The earth is supposed to be at O, and some stars at /, <?, r, s, /, t, /, u, v. You see the stars
as if they were all projected on the celestial sphere at P, Q, If, S, T, U, V. You think
of them as if they were all at the same distance from you.
Tom. They can't all be fastened to any one sphere, because
they are at very different distances from us. The sun .is very
much further away from us than the moon, and the stars are
much further off than the sun.
ASTRONOMY
Jack. True enough. If you will look at this picture I am
drawing, you will see how it is. You are supposed to be in the
middle of the celestial sphere at O. The earth is at O (Fig. 38),
FIG. 39
This picture shows the northern sky as it appears in the early hours of the evening every
August to people who live in the United States. If you face north, you see the
horizon * — the surface of the ground. Above that comes the sky with many stars in
it. Towards the west and pretty high up is the Dipper — the Great Bear (Ursa
Major). Two of its stars — the pointers — point at the north star — Polaris,2 it is
called. High in the east is Cassiopeia,3 a group that is sometimes called The Lady in
the Chair. Every child that owns this book should try to find these stars. They are
always there, in the north. If he looks in August they will be just as in the picture.
If he looks in other months the book must be turned a little. By taking a little pains
the book can be held so that the picture will look as the stars do.
1 Pronounced ho-ri'zon. 2 Pronounced po-la'ris. 3 Pronounced kas"i-o-pe'ya.
52 THE SCIENCES
and you are on it. All around you are stars, /, q, r, s, etc.
You see the star q along the line Oq — along the line that
joins your eye and the star. The line seems to pierce the
celestial sphere at Q, and you think the star q is really at Q.
In the same way you think the star r is at R, the star s at S,
and so forth. If there were really three stars, t, /, /, all in one
line, Ot, you would see only one star at T. All the stars seem
to be lying on the surface of some sphere, and all of them seem
equally far away.
Tom. That is true, I know. When I look at the stars at
night they certainly do seem to be all at one distance — just
like shining tacks driven into a darkish globe above my head
and all around me.
Agnes. And in the daytime the sun and, sometimes, the
moon seem to be the same way — shining circles fastened on
to a shining globe.
Jack. Of course there is n't any real globe there. It is only
an appearance. But it looks real, and we have a name for
the appearance because it is convenient to have names for
things we always see, or even for things that we always
think that we see.
Tom. You would have a model of the celestial sphere by
making a huge hollow globe as big as a barn and getting inside
of it.
Agnes. Yes, and by lining it with black velvet and driving
bright-headed tacks into the lining for stars ; only you would
have to drive them in the right places.
Jack. A model like that would be worth making, but it
would be expensive. We shall have to do with pictures
and flat maps. They will explain what we really see in
the sky.
ASTRONOMY
53
The next night Jack took the children out of doors. He made
them face towards the north ; the east was on their right hand,
the west on their left. First of all he showed them the Dipper
— the Great Bear (Ursa Major in Latin) — and the pointers.
The Dipper is made up of seven bright stars and is always
easy to find. Three of its stars make the handle, four make
the bowl, and two stars of ,gg^_—
the bowl are the pointers.
After you have found the
pointers it is easy to find
the polestar. Now if you
imagine a line drawn from
the polestar to the center
of the earth (under your
feet), that line will be the
axis of the earth. The
earth turns round that
line every day. Every
part of the axis itself
stands still, and every
point not in the axis
moves. The center of the
earth stands still while
the earth turns ; and Pola-
ris stands still. All the
parts of the earth not on the axis appear to move, and all the
stars except Polaris appear to move — they move from rising
to setting and back to rising again. The stars in the east
move upwards, then over the pole towards the west, and
then downwards (in the direction of the little arrows in
Figs. 39 and 40).
FIG. 40. THE DIPPER — THE GREAT BEAR —
AS IT APPEARS AT DIFFERENT TlMES
Sometimes it is above the pole, sometimes below it;
but if you lay a ruler on the picture, you will see
that the pointers always point to the north star —
Polaris.
54 THE SCIENCES
Jack kept the children out of doors till long after their bed-
time to let them see the stars rise higher and higher, but finally
they had to go to bed. They could not watch any longer.
On the next night Jack showed the children how the southern
stars appeared to move from rising to setting. He took them
FIG. 41
A photograph of a part of the northern sky near the pole. A camera was pointed at the
pole early in the evening and the plate was exposed all night and only shut off at day-
break. Each star moved about half of its course round the pole, and as it moved it
left a trail on the plate. All the trails in the picture are half circles. The star
Polaris is not exactly at the north pole of the heavens (though it happens to be pretty
near it). Its trail is the brightest one on the plate. The other stars left their trails, too.
ASTRONOMY 55
out into a large open field and made them face towards the
south. The east was on their left hand, the west on their
right hand, and the stars appeared to move from east to west,
— from rising towards setting — just as the sun does. The
FIG. 42
A photograph of a part of the southern sky, showing the trails of southern stars as they
moved across the plate from rising towards setting. This photograph, and the one like
it for the northern stars, prove that the stars really move with respect to the photo-
graphic plate. But it is not the stars that move. The plate moves with the earth as
the earth turns round its axis. The stars stand still.
apparent motion of all the stars — of the south stars as well as
of the north stars — is caused by one thing and one thing only.
The earth turns round on its axis underneath the starry sky.
56 THE SCIENCES
Time and Timekeeping. — We use the apparent motion of the
sun from rising to setting to give us the time. Watches and
clocks all over the world are now regulated by the sun. Long
ago the ancients used to tell their time by the stars. They
would say: "You must begin your journey when the Pleiades
are rising"; just as we might say: "I must take the train at
9 P.M." Groups of stars, like the Pleiades, were the moving
clock hands ; the dial was the celestial sphere. The stars moved
steadily across the dial, and their motion told the hour. The
sun moves regularly and steadily from rising to setting. When
it is highest up in the heavens and exactly south of any place
(a city, a town, any place), then it is noon at that particular
place. Twelve hours later it is midnight ; and twelve hours
later than midnight it is noon again — noon of the next day of
the week. A watch is a little machine arranged to drive a
steel hand round a dial in twelve hours. The hand is set so as
to mark XII o'clock at noon, and the machine is regulated so
that when the next noon comes the hand shall be at XII again.
To set our watches exactly, we must have a north and south
line. Astronomers have a particular kind of telescope set
exactly in the north and south line (the meridian), so that they
can observe the exact instant of noon. Their watches are
corrected so as to mark XII o'clock just at that moment; and
made to run so that when the next noon comes they will mark
XII o'clock again. They have other kinds of telescopes also,
especially made to examine distant planets and to discover
what is to be seen on their surfaces.
Telescopes. — The children were playing with a reading glass
that belonged to their father. Tom used it to light a match
with, and then to look at the wings of a fly, and noticed how
it magnified everything — how it made it look much larger.
ASTRONOMY
57
Then he said : "Jack, what is the difference between this
magnifying glass and a telescope ? Both of them magnify."
Jack. Well, the telescope magnifies very much more, for one
FIG. 43. A MERIDIAN CIRCLE
The eye end of the telescope is at M. The telescope is fastened to a horizontal axis which
lies in an east and west line, and the telescope always remains, therefore, in the meridian.
LL is a level by which the axis is made horizontal. The axis has two circles (Hand K)
fastened to it. These circles are divided into 360 degrees, and by them we can measure
the altitude (height) of any star.
58 THE SCIENCES
thing ; and a telescope is made up of more than one lens.
The burning glass has only one.
Jack took the burning glass and showed the children how to
use it to make an image (a picture) of the window on the wall,
as in Fig. 45.
Jack. You see that this glass makes an image of the window
on the wall. Suppose that we should cut a hole in the wall
just where the image is now. The image
would be there just the same, for if you
put a piece of white paper over the hole
the image would show on the paper as it
now does on the wall. Now suppose that
you were in the other room beyond the
wall and held another burning glass in
just the right place to magnify the image
in the hole. The second burning glass
magnifies everything it looks at ; well, you
could use it to magnify the image formed
by the first burning glass. If you did this,
you would have a telescope. Two lenses
FIG. 44. A READING combined so as to form a magnified image
GLASS, A MAGNIFY- of anv object make a telescope. One lens
ING LENS, OR A . . , .
BURNING GLASS alone ls not a telescope ; it is a magnify-
ing glass.
Agnes. Then a telescope must have two glasses ?
Jack. Yes, two at least ; the first glass forms an image of
the thing you are looking at — a picture of the window, for
instance. The second glass magnifies the image so that you
can see it better and see it larger. All opera glasses and
spyglasses have at least two lenses, usually more than
two.
ASTRONOMY 59
Tom. Here is a drawing of the great telescope of the Lick
Observatory (Fig. 46). Where are the two glasses there ?
Jack. One of them is at the upper end of the long steel
tube ; they call it the object glass, because it is nearest the
FIG. 45
If you hold a burning glass in a room, you can make it form an image (a picture) of the
window on the opposite wall. The image will be clear and distinct, but it will be upside
down, as you can prove by trying. Most lenses will need to be held nearer the wall
than that in the figure.
object you are looking at. The other glass is at the other end
of the tube ; they call it the eyepiece, because it is next your eye.
In the drawing you see a man looking through the eyepiece.
Agnes. But the telescope is inside a house, Jack. How can
the astronomer see anything ?
60 THE SCIENCES
Tom. Why, you know, Agnes, that there is a long window
in the dome that is opened when they want to look out to see
anything. The telescope looks out through the open window.
Agnes. What is the long tube for ?
Jack. It is principally to keep the object glass and the eye-
piece at exactly the right distance apart and to hold them
steadily where you want them.
Tom. The tube is on an iron stand, and you can go to the
top of the stand by a winding stairway. What are those big
circles at the top, Jack ?
Jack. The circles are fastened to the telescope, Tom, not to
the iron stand, you see ; and they are arranged to show the
latitude and the longitude of the particular star that the tele-
scope is pointed at.
Agnes. Do they know the latitudes and longitudes of stars ?
Jack. Yes, that is the way they point at them. If I tell you
to find on the map a town that has a latitude of 41° and a
longitude of 80°, you can find it, can't you ?
Agnes. Here is the map, and the town is Pittsburg.
Jack. Well, the astronomers have maps of the stars, and
they find the star they want by knowing its latitude and
longitude, and by pointing the telescope there.
Tom. But the star would be moving from rising to setting.
How do they manage to follow it ?
Jack. If you will look at the drawing of the telescope
(Fig. 46), you '11 see a piece of machinery in the top part of the
stand. It is really a powerful clock. That clock is arranged
so as to move the telescope towards the west exactly as fast as
the star moves toward the west. When you once have the star
in the telescope the clock keeps it there.
Agnes. How large is the object glass of the Lick telescope?
FIG. 46. THE GREAT TELESCOPE OF THE LICK OBSERVATORY
Its object glass is three feet in diameter, and it is nearly sixty feet long.
61
62
THE SCIENCES
Jack. The object glass is three feet in diameter, and the tube
is nearly sixty feet long, and the eyepiece is quite small — just
the size to be convenient for your eye to see through, Agnes.
Tom. How much can you magnify with a telescope like that ?
The Moon. — Jack. Well, you can arrange so as to magnify
more or less as you please. For instance, you can magnify
the moon about a thou-
sand times — you can see
the moon as if it were
a thousand times nearer
than it really is. How
far off did I tell you the
moon is ?
Tom. Two hundred
and forty thousand miles.
Jack. Then if the tele-
scope will make it seem
a thousand times nearer,
how far off will it seem
to be ?
Agnes. Two hundred
and forty miles.
Jack. That 's right, my
dear. The Lick telescope
will show you the moon
just as you would see it if you got within two hundred and
forty mi?es of it — just as if the moon were at Pittsburg and
you at Philadelphia.
Agnes. That does not seem to be very near.
Jack. Well, it is n't near ; but it is wonderful to do even so
well as that.
FIG. 47. MOUNTAINS ON THE MOON,
AS SEEN IN A TELESCOPE
ASTRONOMY
Tom. Then the planets, that are so much farther away than
the moon, cannot be seen anything like so well ?
Jack. No ; Mars, for instance, is 50,000,000 miles away
from us when we see it best, and so we never can make it
seem nearer to us than 50,000 miles. That is better than
nothing ; but it is n't very close, after all. It is really wonder-
ful that men have found
out so much as they have
about the planets when
you consider what the
difficulties are. The
smallest spot that can be
seen with distinctness on
the moon would contain
several acres ; and when
you come to looking at
a distant planet like Mars
a spot would have to be
fifty or sixty miles square
to be visible at all.
Tom. Then you might
see a city on the moon?
A city covers many acres.
r . _r FIG. 48. MOUNTAINS ON THE MOON,
Jack. You could see a AS SEEN IN A TELESCOPE
city on the moon if it
were there; or even a very large building like the Capitol at
Washington ; but there are no such cities or buildings on the
moon. Astronomers have looked for them thousands of times
without ever finding the slightest sign of any living thing.
Life on the Planets. — Agnes. Is there any sign of life on
the planets ?
64 THE SCIENCES
Jack. Not one; life of some sort may be there — plants,
trees, animals, or possibly men — but the telescope shows no
sign of life at all.
Tom. Not even on Mars ?
Jack. Not even on Mars — nowhere. Some people have
talked about land and water on Mars, calling parts of Mars
that are reddish, land, and parts that are bluish, water ; but
no one has any proof at all that the red parts are really land,
or the blue parts water.
Tom. I have read about canals in Mars.
Jack. Well, whatever they are, they are not canals. The
telescope shows narrow, straight, dark lines on the planet's
surface (see Fig. 49), and they were called canals because they
crossed the red parts of Mars that were called continents. But
the Lick telescope shows that the canals go across the oceans,
just as they go across the continents ; so that it is pretty
clear that the canals are not canals at all, and that we do not
know whether Mars has any water on its surface at all.
Tom. How is it about Jupiter ?
Jack. Jupiter looks as if it were a very hot planet ; like a huge
red-hot ball covered with clouds of steam. All of Saturn that we
can see seems to be clouds ; and the same is true for Uranus and
Neptune, and for Venus, too, for that matter. Mercury and
Mars have no clouds and probably little or no atmosphere at all.
All the others have atmospheres, but no one knows whether their
air is the right kind of air to breathe. It is very doubtful whether
any planet beside the earth is fit for men to live on.
Tom. Is there air on the moon ?
Jack. There is no air on the moon at all, nor any water
either; and it is so cold on the moon, and on Mars too, that
no man could possibly live there for an instant.
ASTRONOMY 65
Tom. Then there is n't any place in the whole universe where
we are really sure that men can live except just the earth ?
Jack. No. Men cannot live in the sun ; the sun is too hot.
Jupiter is too hot, also. Mercury and Mars have little or no
air. Venus, Saturn, Uranus, and Neptune are covered with
clouds, and we do not know what is underneath the clouds.
Men couldn't live in the stars ; they are like the sun — too
hot. And we do not know whether the stars have planets
FIG. 49
Drawings showing two hemispheres of the planet Mars. The narrow lines are what have
been called canals. The dark parts of the drawing should be colored blue and most
of the white parts reddish in order to make it look as Mars does.
round them or not ; very likely they have. If they have, some
of their planets may be fit for men to live on. Agnes says she
is going to believe it.
Agnes. Yes, I am. It makes the universe more interesting
to believe that there are people like ourselves everywhere, or
at least in many places.
Jack. Well, believe it, my dear. I half believe it myself ; but
there is no way to prove it, or to disprove it, for that matter.
APPENDIX
THE EARTH (0)
THE earth is a globe flattened at the poles. Its shortest diameter
(from pole to pole) is 7900 miles. Its longest diameter is 7927 miles. It
turns on its axis once daily. It moves in its orbit round the sun once in a
year of 365 days 5 hours 48 minutes 451 seconds. Its month (from new
moon to new moon) is about 29! days. The earth is 5^ times as heavy
as a globe of water of the same size. The sun weighs 333,000 times more
than the earth. The distance from the earth to the sun is 93,000,000
miles.
THE MOON (C)
The moon is 2163 miles in diameter. The moon weighs about 3!
times as much as a globe of water of the same size. The earth weighs
8 1 times as much as the moon. The distance from the moon to the earth
is 240,000 miles.
ECLIPSES OF THE SUN AND MOON
They are explained in Book II (Physics).
THE PLANET MERCURY (9)
Mercury is 3030 miles in diameter. It weighs about 3|- times as much
as a. globe of water of the same size. It goes once round the sun every
88 days. It is 36,000,000 miles distant from the sun — less than T% of
the earth's distance, therefore.
THE PLANET VENUS (9)
Venus is 7700 miles in diameter (about the size of the earth, therefore).
It weighs 4r% times as much as a globe of water of the same size. It goes
66
ASTRONOMY — APPENDIX
67
round the sun once every 225 days. It is 67,200,000 miles distant from
the sun — about T75 of the earth's distance, therefore.
THE PLANET MARS
Mars is 4230 miles in diameter. It weighs 4 times as much as a
globe of water of the same size. It turns once on its axis in 24 hours
FIG. 50
A rough drawing of the full moon.
37 minutes 22Tyff seconds. It goes round the sun once every 687 days. It
is 141,500,000 miles from the sun — about i| times the earth's distance,
therefore. It has two very small moons.
JUPITER
Jupiter is 86,500 miles in diameter. It weighs only ly^ times as much as
a globe of water of the same size. It turns once on its axis in 9 hours
68 THE SCIENCES
55 minutes. It goes round the sun once every IIT% years. It is 483,-
300,000 miles from the sun — about 5 times the earth's distance, therefore.
It has five moons. One of them is very small; the others much larger —
about the size of our own moon, or of the planet Mars.
THE PLANET SATURN (^7)
Saturn is made up of a globe with rings around it. The diameter of its
globe is 73,000 miles, It weighs only T7ff as much as a globe of water of the
same size. The globe turns on its axis every 10 hours 14 minutes 24 seconds.
It goes round the sun once every 29! years. It is 886,000,000 miles dis-
tant from the sun — about 9^ times the earth's distance, therefore.
The rings of Saturn are made up of a swarm of countless little moons.
The rings are about 28,000 miles wide and 168,000 miles in diameter, and
only about 100 miles thick. Saturn has eight moons — otie as large as
Mars, one about the size of our moon, and the rest smaller.
THE PLANET URANUS (£)
Uranus is 31,900 miles in diameter. It weighs only IT27 as much as a
globe of water of the same size. It goes round the sun once in 84 years.
It is 1,781,900,000 miles distant from the sun — about 19 times as far as
the earth, therefore. It has four rather small moons.
THE PLANET NEPTUNE
Neptune is 34,800 miles in diameter. It weighs only IT\J- times as much
as a globe of water of the same size. It goes round the sun once in
165 years. It is 2,791,600,000 miles distant from the sun — about 30 times
the earth's distance, therefore. It has one moon about the size, of our
own moon.
COMETS
A few comets belong to the family of the sun and move around him
as do the planets.
ASTRONOMY — APPENDIX
69
THE FIXED STARS
Stars are suns, immensely distant from our sun and from each other
except when they are grouped in clusters. Light, which travels nearly
200,000 miles in a second, takes 4 years to come to us from the nearest star.
The light from Polaris (the polestar) takes 47 years to reach the earth.
FIG. 51. THE TOTAL SOLAR ECLIPSE OF 1871 IN INDIA
The black circle is the disk of the moon ; behind it the sun's disk is hidden. The pale
white streamers are the sun's corona, or crown. The corona always surrounds the sun,
but is not visible every day because the streamers are so faint. Notice close to the
edge of the moon's disk a few brighter spots. These are flames of hydrogen — a gas
that is glowing as if it were white hot — in the sun's atmosphere.
70 THE SCIENCES
NEBULAE
Nebulae are masses of gas at about the same distance from the sun as
the stars are. They are of all shapes and sizes. Many of them are spiral
in shape — corkscrew shaped. If, as sometimes happens, a star burns up
it may turn into a nebula ; or, as sometimes happens, a nebula may solidify
and become a star. Perhaps our sun and all the planets were once a huge
nebula that cooled and solidified into separate globes.
FIG. 52.
A CLUSTER OF STARS IN THE CONSTELLATION OF
THE CENTAUR
Each white dot represents a star.
FIG. 53
Drawing of a large nebula (in Andromeda) as seen in a telescope. The white dots
are stars; the shining white cloud is the nebula. (See also Fig. 35.)
71
OF THE
UNIVERSITY
OF
BOOK II
PHYSICS
THE SCIENCE THAT EXPLAINS HEAT, LIGHT,
SOUND, ELECTRICITY, MAGNETISM
Solids and Liquids. — "What is the difference between a solid
and a liquid ? " said Tom one hot afternoon when the children
were all together on the porch, fanning themselves.
Mary. You can pick up a solid in your fingers, and you can-
not pick up a liquid — that's one difference.
Agnes. You mean you can pick up a piece of ice, and you
cannot pick it up when.it has melted into water?
Mary. Of course you can't.
Fred. Oh, yes, you can — and with that Fred took a lump of
sugar and put it in a teaspoon partly full of water. The sugar
took up the water, and Fred picked up the sugar and left the
spoon quite empty, saying : " Look at that ! I 've picked up a
liquid in my ringers. It 's magic."
Agnes. That is just foolish, Fred.
Fred. I know it — but it is magic. You said I could n't
do it.
Tom. It is n't fair, Fred ; you can pick up a sponge with
water in it, but you cannot pick the water up without the
sponge, nor the water without the sugar, either.
73
74
THE SCIENCES
Fred. All right. I was just playing. It is a kind of magic,
though.
Mary. Well, was n't I right ? A solid is a thing you can
pick up in your fingers, and a liquid is something you can't
pick up.
Tom. The real magic of it is that a piece of ice and a spoon-
ful of water are just the same thing. The same thing is differ-
ent at different times ; sometimes it is
ice, and sometimes water. I wonder why.
Let us ask Jack.
Jack. I think Mary's definition is a
pretty good one — a solid is a thing you
can pick up in your fingers. You can
change a solid into a liquid, if you want
to, by heating it. You can change a
piece of ice into water by letting it melt.
A little heat will do it.
Fred. How does heat do it, Jack ?
Solids, Liquids, and Gases are made up of
Millions of Small Particles. —Jack. Well,
you have to begin far off if you wish to
understand. The scientific men have
proved that all solids — and all liquids,
too — are made up of little particles
crowded close together. When you heat a solid the particles
are forced farther and farther apart.
Heat makes Solids, etc., expand. — "A piece of solid iron gets
larger when you heat it. When a blacksmith wants to fit a
new tire on a wheel he first heats it and puts it on ; then the
tire, as it gets cold again, shrinks tightly on the wheel and
stays where it was put."
FIG. 54
A solid, a piece of iron for
instance, is made up of
thousands and thousands
of little particles, each
one like every other one,
all crowded together, like
the lower part of the pic-
ture. When you heat a
solid the little particles
are forced farther apart,
so that by and by they
look like the upper part
of the picture. The solid
will get larger if you
heat it.
PHYSICS
75
" Every little particle of the tire has been forced apart by the
heat, and by and by the whole tire, which was in the first place
smaller than the wheel, grows large enough to slip over the
rim. Then the blacksmith slips it on and lets it cool. As it
cools, it shrinks and fits the rim tightly. The heat has loosened
the particles, you might say."
Agnes. How do you know the particles are farther apart
when the iron is hot ?
Jack. There are just so many particles in the cold iron to
begin with, Agnes — say ten millions of them, if you please.
And ypu haven't put any more particles in the tire, you know ;
FIG. 55
The right-hand picture shows a wheel ready to be fitted with a tire ; the middle picture
shows the tire heated in a fire. When the tire has expanded — grown large — enough
the blacksmith fits it on the wheel and lets it shrink tight by cooling.
you have simply heated it. But the tire really has grown
bigger — the proof is that it will slip over the rim of the wheel.
The same ten million little particles of the cold iron fill a larger
space than when they are cold ; so they must have been forced
farther apart somehow, you see. And the heat did it — noth-
ing else could have done it.
Mary. Suppose you had heated the iron more and more,
Jack. What then ?
76 THE SCIENCES
Jack. If you had put the iron in a furnace and kept on
heating it, you would have had a hot solid at first ; then it
would have become pasty, almost like dough, and by and by
it would become a liquid — it would flow like water. You
cannot try the experiment with iron, but you have often seen
the boys try it with lead when they are molding bullets for
their guns. Lead melts more quickly than iron.
Agnes. Yes ; they put the lead in a ladle and melt it, and
then pour it into molds and let it cool.
Jack. Iron is made up of one kind of small particles, and
lead is made up of another kind of particles ; and it takes less
heat to separate the lead particles. But heat does the same
thing always. It separates the particles farther, the more heat
you apply. First you have a solid, and then a liquid ; and if you
heat the liquid enough, you have a gas — iron gas, lead gas.
Tom. If you were to go on heating iron gas for a week,
what would you get ? something different from gas ?
Jack. No; you would get very hot iron gas and nothing
more. You can have matter in only three forms — solid, liquid,
gas — but you can turn one form into the other by heat or by
cold. Take ice, for instance.
Fred. Ice is solid. If you make it colder and colder, it is
nothing but ice — the north polar regions are ice and nothing
else.
Agnes. And if you heat ice, it becomes water.
Mary. And if you heat water in a teakettle, it becomes
steam.
Tom. And if you heat steam, Jack, more and more, is it
always steam ?
Jack. It is never anything else. It is simply very hot steam.
The boiler of a locomotive or of a steamship makes steam and
PHYSICS
77
nothing else. Solid, liquid, gas — that is all you can get. If
you cool a gas like steam enough, you will get a liquid ; and if
you cool a liquid enough, you will get a solid.
Most Gases are Invisible. — Mary. I have seen solids and
liquids ; but I am not sure I have ever seen gases.
Fred. Well, you have smelled them, anyway, from leaky gas
fixtures in the house, or when the match went out before you
could light the gas at the burner.
Mary. Oh, yes ; and of course
there is gas inside of the little
toy balloons. But I have never
seen gas.
Jack. Most gases cannot be
seen. They are invisible. Air
is invisible, but it is all around
us. If any one asked you to
prove that air was really all
around us, Mary, how would you
prove it ?
Mary. Why, I should say that
the wind was nothing but mov-
ing air.
Jack. That is a good way, my dear,
was n't blowing ; then what ?
Mary. I should wait till it did.
Jack. You could make an experiment to prove it this way.
Take an empty tumbler and hold it upside down. We call it
empty, but it is really full of air — of invisible air. Then take
a glass bowl half full of water and float a cork on it. Now
gently press the tumbler down over the cork (see the picture)
and see what you will see. If there were nothing in the tumbler
FIG. 56
A glass bowl partly filled with water, a
cork, and a glass tumbler are needed
to prove that the tumbler was filled
with air. This experiment should be
tried in the class room.
But suppose the wind
THE SCIENCES
-if the tumbler were really empty — then the water would
fill it full ; but you can see that the water rises only for a
certain distance, and no higher. There is air in the tumbler
still.
Tom. I can prove that there is air in the tumbler now.
Tip the tumbler sidewise a little while it is in the bowl
and the air will come out in
bubbles.
Fred. What becomes of
the air in the bubbles when
they come to the surface ?
Tom. Why, it just mixes
with the other air all around
us.
The Diving Bell. — Agnes.
The diving bell that men use
at the bottom of rivers is like
the tumbler, is n't it ?
The Earth's Atmosphere. —
Jack. The air is all around
us everywhere, for wherever
you go you find air to breathe.
Agnes. Not on the tops of mountains, Jack.
Jack. There is not so much air at the tops of mountains as
there is below, Agnes, but there is air. Men have climbed the
very highest mountains, and as they went up they found less
and less air. Birds fly nearly as high. The condor — a bird
like an eagle — flies high in the Andes of South America, and
balloons carrying men have gone five miles high. Balloons
without men have gone as high as ten miles, but the air is so
thin at that height that men could not breathe.
FIG. 57. BUBBLES OF AIR ESCAPING
FROM THE MOUTH OF A GOLDFISH
IN A GLOBE
FIG. 58
The diving bell is lowered by a chain from a ship, and air is pumped into it by the pipe
marked T in the picture. The whole diving bell is under wa,ter, but the water rises
no higher than its floor. The pressure of the air keeps it out. A diver goes down to
the bottom of the harbor and fastens ropes to whatever he wants to hoist to the sur-
face. He has a waterproof and air-proof suit of clothes, and air is pumped down for
him to breathe (through the small pipe in the picture). The foundations for the piers
of bridges can be laid by men working in this way.
79
80 THE SCIENCES
Mary. The air gets thinner and thinner as you go up.
Where does it stop, then ?
Jack. We do not know exactly ; but there is some air — a
very little — as high as sixty miles, because shooting stars
FIG. 59
The Himalaya Mountains are about five miles, and Mont Blanc, in the Alps, is about three
miles above the level of the sea. A balloon carrying men has gone up five miles and
very light balloons filled with gas have gone nearly ten miles above sea level.
begin to burn as high as that. They burn when they first meet
the air, about sixty miles above the ground.1
Balloons. — Tom. The balloon floats in the air because it is
lighter than the air, just as a chip floats on the water.
1 See Book I (Astronomy), Meteors, page 45.
PHYSICS
8l
Mary. If the balloon is lighter than the air, then the air
itself must be heavy ; for a balloon weighs a good deal, espe-
cially when it is carrying men.
Air is Heavy. — -Jack. Yes, the air is heavy, and there is a
simple way to prove it. /
Reservoirs, Fountains, and the Water Supply of Cities. — " If
you have a reservoir full of water and a fountain joined to
the reservoir by a pipe, the fountain will play as soon as the
All these glass vessels are joined together by the brass tube at the bottom. If you fill the
large jar at the left-hand side with water, all the other tubes will at once fill up to the
same level. The air presses on the water in the large jar and forces it up into the other
tubes and makes the little fountain play.
water is turned on, and the fountain will play as high l as the
water in the reservoir. That is because the air above the
reservoir is heavy and presses down on the water in it and
forces it up in the fountain. (See Fig. 61.) Now here is an
1 Or nearly as high ; the friction of the water in the pipe makes some difference.
FIG. 61. RESERVOIRS, FOUNTAINS, AND THE WATER SUPPLY OF CITIES
picture shows a lake which is the source from which the water is obtained. A dotted
line across the picture marks the level of the upper surface of the lake. An aqueduct
(water pipe) takes the water from the lake, carries it under the hill, under a pond, up
another hill, where there is a fountain, and delivers the water to the city reservoir.
From the city reservoir pipes conduct the water all over the city — to public fountains,
to the upper stories of houses, and so forth. Notice that all the fountains send their
jets to about the same height.
FIG. 62
The U-shaped tube is partly filled with water as in the right-hand picture. Air fills the rest
of both branches of the tube. Now tip the tube so that one branch of the tube shall be
completely filled with water — water on one side, air on the other. Then cover the
water side with your finger, as in the left-hand picture. You will see that the water
will stand at different heights on the two sides. There is air pressure on one side of
the tube and no air pressure on the other (your finger keeps the air out). The air
pressure keeps the water standing high. If you take your finger away and let the air
in, the water on both sides of the tube will stand at the same level on both sides.
(This experiment should be tried in the schoolroom.)
82
PHYSICS
experiment that we can try ourselves with this bit of glass tube
bent into the shape of a U.
" You see that the air must be heavy ; it must press down
with weight because it makes the fountain play (Fig. 61) and
keeps the water standing high (Fig. 62).
The Barometer.1 — " Instead of using water in the U-shaped
tubes, you can use any liquid — milk, kerosene oil, quicksilver.
It is convenient to use quicksilver
because it is heavy and because it is
so clean.2
" You need a hollow glass tube
about thirty-two inches long, closed
at one end, a lot of quicksilver, and
a flat basin of glass or china. Hold
the long tube with its open end
upwards. It is full of air. Make a
paper funnel and pour quicksilver
from a pitcher into the open tube,
slowly and carefully, until you have
quite filled it. As the quicksilver
goes in it will drive out the air, and
finally you will have a tube with no
, . . See the description in the text.
air in it — nothing but quicksilver.
You must handle it carefully because it is quite heavy. Now
put your finger over the open end of the long tube and turn
1 The barometer is an instrument to measure the weight — the pressure —
of the air. The name comes from two Greek words, one meaning " weight,"
and the other " to measure."
2 Quicksilver is a poison if taken in the mouth ; it is perfectly safe to handle
it unless there are open cuts on the hands and fingers. If it touches a gold ring,
however, it will cover the gold with a thin layer of quicksilver that will not wear
off for some time.
FlG. 63. HOW TO MAKE A
BAROMETER
84
THE SCIENCES
the tube swiftly upside down. (See the left-hand picture,
Fig. 63.) If you should now take your
finger away, all the quicksilver would fall
out. There would be nothing to support
it. But dip the open end of the long
tube in the basin of quicksilver, take
your finger away, and see what happens.
The quicksilver will fall in the tube a
little distance — a few inches — and
then it will stop. The air is pressing
on the quicksilver in the basin and is
pressing some of it up into the tube.
There is no air above the quicksilver in
the tube ; nothing is pressing downward
except the weight of the quicksilver in
the tube itself. The weight of the
quicksilver in the tube pressing down-
ward just balances tire pressure of the
air on the quicksilver in the basin. The
two pressures just balance each other."
The Air presses about Fifteen Pounds
on Every Square Inch. — Tom. The
height of the column of quicksilver in
the tube is about thirty inches.
Jack. Yes ; and if the tube were an
inch square, the column of quicksilver
in it (thirty inches high and an inch
square) would weigh fifteen pounds.
The air pressing on the basin keeps that
column standing. It keeps a weight of
fifteen pounds standing.
FIG. 64. A QUICKSILVER
BAROMETER READY FOR
USE
The long glass tube has a scale
of inches at the upper end ;
28, 29, 30, 31 inches are
marked, as well as the tenths
of inches. The basin of
quicksilver is at the bottom.
PHYSICS
Fred. That is what is meant by saying, the air presses
fifteen pounds on every square inch of your body, is n't it ?
Jack. It presses fifteen pounds on every square inch of the
whole world ; on your body, and on the ground, and on the water
— everywhere. It presses down and it presses up, too.
Tom. How does it press up? I see that it presses down.
Fred. The air must press up
or else a balloon would not rise.
Jack. That is one proof, and
here is another that you can try
for yourself. (See Fig. 65.)
How to measure the Heights of
Mountains. — "Now I want you
to say what would happen if I
had taken the barometer to the
top of a mountain."
Mary. The air is lighter at
the top of the mountain than
it is here, and does not press
down so much.
Tom. So the quicksilver in
the tube would not stand so
high ; it would not have so
much air pressure to balance.
Jack. Bravo ! that is just right. At the level of the ocean
all the air — the whole atmosphere — is above you, and it
presses fifteen pounds on every square inch of the ground.
The quicksilver stands thirty inches high. When you go up
about 1000 feet the air above you presses less because there is
less of it; you have left 1000 feet of it below you, and the
column of quicksilver is about twenty-nine inches high ; if you
FIG. 65
Fill (or partly fill) a tumbler with water and
press a stout piece of writing paper over
the top closely. Put the palm of your
hand over the paper and hold it on tightly.
Now quickly turn the tumbler upside
down and take away your hand from the
paper. (See the picture.) The pressure
of the air from below is so much greater
than the weight of the water, and of the
small amount of air in the tumbler, that
the paper will hold the water up. (This
experiment should be tried in the school-
room.)
86
THE SCIENCES
go up 2OOO feet, there is less air above you and the column is
about twenty-eight inches high, and so on.
Tom. So you could measure the height of a mountain by
noticing the height of the column of quicksilver in the tube ?
On high mountains the column
would be short.
Jack. That is right, and that
is the way the heights of moun-
tains are really measured. A
barometer measures the weight
of the air above you. The
higher you go the less air above
you and the less pressure on
the basin of the barometer.
The Barometer is a Weather-
glass. — Fred. Sometimes we
FIG. 66. AN ANEROID BAROMETER see in the newspapers a notice
(A BAROMETER WITHOUT QUICKSILVER) r storm
Aneroid is a Greek word that means " with- T21]rean oa Vo
out any liquid." Inside of the outer metal
case is a tightly sealed box containing no of low barometer Coming,
air. On this box the outside air presses, r^ jt happens that where
sometimes more, sometimes less. The
little box changes its shape under this storms are the air weighs less
pressure, and things are so arranged that ancj the barometer is low —
changes of pressure make a needle pointer . r ....
move around a dial. This form of barom- the Column of quicksilver IS
eter is very convenient for travelers and short. In fine weather the
air is heavy and presses down
more ; so the barometer is high and the column of quicksilver
is long. If you watch the quicksilver from day to day, you will
find this is the case, generally : when fine weather is coming
or is here the barometer is high; when storms are coming or
are here the barometer is low. So the barometer is a kind of
FIG. 67
A map made by the Weather Bureau one November morning. An area of low barometer
was near Omaha and it was moving towards Canada (in the direction of the curved
arrow). Wherever there are little dots observations had been taken and telegraphed
to Washington. The arrows through the dots fly with the wind — they point in the
direction of the wind's motion at each place. Where the dots are bkck it was raining ;
where they are square it was snowing ; where they are circles with white centers it was
cloudy. The full lines ( ) join all places where the barometer was at the same height,
as 30^, 30^5, 30, 29!% inches. The dotted lines ( ) join all the places where
the thermometer stood the same, as 70°, 60°, 50°, 40°, 30°, 20°, 10°, o°. There was
zero weather near the Rocky Mountains, while it was warm and cloudy east of the Alle-
ghenies. Northwest of the area of low barometer there was snow ; southeast of it there
88 THE SCIENCES
weatherglass. It tells you beforehand what kind of weather
is coming.1
Fred. And it tells ships at sea when to look out for storms.
United States Weather Bureau Predictions. — Jack. Every
day at a hundred places in the United States, in Cuba, and
so forth, the observers of the Weather Bureau notice how
their barometers are standing and telegraph to the central
Weather Bureau at Washington. There they make a weather
map of the whole country several times daily. If a storm is
traveling eastwards, it will show on the map by an area of low
barometer, as they call it. The barometer in the country round
Omaha will be low on Monday, for instance ; by Tuesday the
storm has traveled to Buffalo ; so the Weather Bureau tells
New York to look out for a storm on Wednesday.
Agnes. Well, I never knew before how that was done.
Thermometers.2— Fred. A thermometer has quicksilver in
it, too, but it is closed at both ends.
Tom. A thermometer is to measure how hot the air is. It
is different from a barometer ; that measures how heavy the
air is.
Jack. Yes, a thermometer measures how hot the quicksilver
in it happens to be by the height of the quicksilver in the glass
tube. If the quicksilver column is long, then the temperature
1 Barometers often have words engraved opposite points of their scales ; as :
30^ inches, set fair (meaning that the weather will be fair for some time);
30 inches, fair ; 2<)\ inches, change (meaning expect a change soon); 29, rain ;
28^, much rain ; 28, stormy. The weather is foretold by a change in the barome-
ter rather than by the actual height of the quicksilver. If the quicksilver is rising,
then the weather is changing towards fair ; if it is falling, then the weather is
changing towards stormy.
2 The word thermometer is from two Greek words, and it means " an instru-
ment to measure heat — temperature."
PHYSICS
89
100*
is high ; if the column is short, then the temperature is low.
The higher the temperature the longer is the quicksilver column.
Mary. It is like the iron tire of the cart wheel. (See
Fig. 55-) The hotter the fire, the b
longer the tire is.
Agnes. ^ By just putting my hand on
a thermometer I can make the quick-
silver mount up in the tube.
Tom. Jack, why do they make the
scale this way ? 32° is marked freezing,
and 212° is marked boiling.
Jack. A German named Fahrenheit l
invented the thermometer we use about
200 years ago. (See the right-hand
picture in Fig. 68.) He put his ther-
mometer into melting ice and made a
mark on the tube just where the quick-
silver stood ; and then into boiling
water and made a mark on the tube
where the quicksilver stood. It is too
complicated to tell you why he named
the first mark 32° and the second
212°, but anyhow he did so. The dis-
tance between his two fixed marks he
divided into 1 80 equal parts — degrees.
His thermometer was used in Eng-
land ; the Pilgrims brought it over to
America ; and we use it to-day. But
there is another scale of degrees — the centigrade2 (see the
left-hand picture in Fig. 68) — which was invented in France
1 Pronounced far'en-hlt. 2 Pronounced sen'ti-grad.
0*1*1—
-17.S*
FIG. 68. THE GLASS TUBES
OF Two THERMOMETERS
The tubes are closed at both ends,
are entirely empty of air, and
are partly filled with quicksilver.
90 THE SCIENCES
about a hundred years ago, that is used nearly everywhere in
Europe. On the centigrade thermometer the freezing point
is marked zero degrees (o°), and the boiling point of water
one hundred (100°) ; and the scale between o and 100 is divided
into equal parts. Zero of Fahrenheit's scale is 17^5- degrees
below zero of the centigrade scale. (See Fig. 68.)
Mary. Was Centigrade a man ?
Tom. Of course not; don't you see that centi means "one
hundred," and grade " degree " ?
Mary. Why, certainly ; I thought he might be a Frenchman
though.
Jack. If you put one of our thermometers into melting ice, it
will always mark 32° ; if you put it in boiling water, it will always
mark 212° ; and if you put the bulb of it in your mouth, it will
always mark about 98° — that is, unless you have a fever.
Fred. The doctor always takes my temperature with a little
thermometer when I am ill.
Tom. And if your temperature goes as high as 104°, he
looks very serious. The sign of being well is to have a tem-
perature of 98°, they say.
Steam. — Jack. If you took a teakettle and boiled the water
in it, the temperature of the boiling water would be 212°.
Inside the kettle there is water at the bottom, and above the
water there is steam. If we had a glass kettle, you could look
through the sides and you would see nothing at all above the
water. True steam is invisible ; but there is steam there all
the while. How do we know ?
Mary. We see the steam lift the lid of the kettle every now
and then.
Fred. I thought steam was visible. What is that cloud
coming out of the nozzle of the kettle ?
PHYSICS
Jack. That is water ; cooled steam ; water in small drops
like fog or clouds. The real invisible steam is inside, trying
to lift the lid and escape. If we fastened the lid down and
closed the nozzle, we
should have a little
steam engine.
The Steam Engine.
— Then Jack ex-
plained the working
of the steam engine
to the children in this
way. (See Fig. 70.)
F is the fire box ;
B is the boiler with
water in the bottom
of it, and steam at the
top; S is the steam
pipe that carries the
live steam over to
the valve chest VC.
There are two pipes
in the valve chest,
pipe M and pipe N,
and both pipes open
FIG. 69.
A TEAKETTLE WITH BOILING
WATER IN IT
It gives out clouds of what we call steam. The clouds are
really not steam, but steam cooled back into water. If
you hold an alcohol lamp under the cloud, the hot flame
will turn it back into steam and you will see no cloud
over the flame, because true steam is invisible. It is
there though, as you can tell by holding a cold spoon
over the invisible spot. The invisible steam will turn
into visible water (like fog or cloud) and gather in drops
on the spoon. (This experiment should be tried in the
schoolroom.)
from the valve chest
and run to the cylinder C. But things are so arranged that both
pipes M and N cannot be open at the same time. If N is open,
Mis shut (as in the picture). If Mis open, N must be shut.
The picture is drawn with the pipe N open. The live
steam rushes into the pipe N, fills it, and rushes into the
right-hand end of the cylinder C and presses against the piston
92 THE SCIENCES
head P. (The piston head is a large iron disk that fills up
the whole of the diameter of the cylinder.) The pressure of
the live steam moves the piston head P (to the left in the pic-
ture) to the other end of the cylinder C and pushes the piston
rod R against the crank G on the crank shaft A, and turns it.
You must imagine now that the piston head P is at the
FIG. 70
Drawing of part of a steam engine.
left-hand end of the cylinder C and that the live steam fills the
whole of the cylinder. Find the letter Rf in the picture. R1
is fastened to a slide valve Fat one end and to the crank shaft
at //", and things are so arranged that now the rod R' closes the
pipe N by which the steam came in and at the same time opens
the pipe M. The live steam is filling the valve chest VC all
PHYSICS 93
this time. It cannot get into the pipe A7" (which is now closed),
and so it rushes into the pipe M (which is now open) and
presses against the left-hand side of the piston head P (which
is now at the left-hand end of the cylinder C}. The piston
is now pushed back by the steam to where it started from
(just as in the picture), and the crank shaft A is turned still
more. When the piston gets back to where it started the pipe
M is closed and the pipe N is opened again (by the rod R') and
the piston head is moved to the left again, then to the right,
then to the left, and so on as long as the engine is running.
Every time the piston head P travels the length of the cylinder
C the crank G makes half a turn, and in this way the crank
shaft GA keeps on turning. W is a little pulley wheel fastened
to the crank shaft ; and if you put a leather belt on this pulley
wheel, you can carry the power of the engine wherever you
like. You can carry it as far as the belt goes and drive any
other machine — a lathe, a saw, a drill. W is a heavy fly
wheel fastened to the shaft A to keep the motion steady.
All this description of how an engine works is perfectly easy
to understand if you take one thing at a time and pay attention ;
but it is rather long, and you had better read it over again care-
fully with a pin in your hand to point with. The live steam starts
from the boiler B (put your pointer there) ; fills the valve
chest VC (put your pointer there) ; rushes through the pipe N
(point at it) ; presses against the piston head P (point at it) ;
drives the piston head to the left-hand end of the cylinder
(point at it) ; moves the stiff piston rod R so as to turn the
crank G (point at R and G). At this time the pipe N is
closed and the pipe M is open (point at A7" and M) ; the live
steam is all the while filling the valve chest VC (point there)
and cannot escape through the pipe N (which is closed) and
94
THE SCIENCES
now rushes through the pipe M (which is now open), and so
on. You must go through the whole description again and
again till you understand it.
The Locomotive. — Figs. 70 and 71 show just how steam
from a boiler can be made to turn a crank shaft (G in both
FIG. 71. A STATIONARY STEAM ENGINE
C, cylinder ; P, piston ; JR, piston rod. The reader should trace the course of the steam
(which enters through the pipe S) throughout a complete motion of the piston.
pictures) round and round. Suppose we put wheels on this
crank shaft and make the engine into a locomotive.
In Fig. 72 you should put your pointer on the sleepers,
the rail, the front wheels P, the front driving wheel, the fire
box A, the fuel grate R, the boiler G, the valve chest C,
the cylinder B (there is a separate picture of the cylinder above
the main picture), the smokestack E, the cowcatcher, the head-
light, the bell, the sand box M (the sand box is used to hold sand
to sprinkle on the rails when they are wet and slippery, so that
the driving wheels may not slide on the track), the whistle O,
and the cab. The to-and-f ro motion of the piston in the cylinder
96 THE SCIENCES
moves the driving wheels round ; the engine moves forward as
they move round, and the train follows the engine.
All steam engines work very much like the ones shown in
the pictures. You can see them at work in factories, on ships,
in locomotives, in automobiles — everywhere. With a machine
like this you can take a little water and a little coal and turn
FIG. 73. AN OCEAN STEAMSHIP
them into a power that will drive a locomotive sixty miles an
hour, or a great ship twenty-five miles an hour from New York
to Liverpool.
Light. — Jack. The very first thing to know about light is
that it travels in straight lines. You cannot see round a
corner, you know, though you can hear round a corner.
The room was darkened, and the sun's rays were let in through
a very small hole in a card and made an oval spot on the floor.
Tom took a newspaper, crumpled it up, and set it on fire in
PHYSICS 97
a coal hod, so that the room was partly filled with smoke and
dust. This made it easy to trace each little sunbeam along
its whole course, as the picture shows.
Fred. That spot on the floor looks like a picture of the sun.
Jack. It is a picture — an image — of the sun. It is oval
because the sunlight falls slanting on the floor. But take this
FIG. 74
The sun's rays travel in straight lines. (This experiment should be
tried in the schoolroom.)
large sheet of white pasteboard and hold it perpendicular to
the sun's rays and you will get a round image. You can get
a picture of the landscape outside by letting light in through
a small hole in the same way. (See Fig. 75.)
Mary. Well, I 'm sure I don't understand how you can get
a picture of out-of-doors by just letting light through a hole.
98
THE SCIENCES
Jack. It is the easiest thing in the world to understand when
it is explained ; but it is not so easy to understand it when you
see it the first time, as you have, Mary — when it is sprung on
you, as the boys say.
Fred. Well, Jack, how is it ? Explain it to us, now that
you have sprung it on us.
Jack. It all comes from light traveling in straight lines. Let us
begin with a simple case, and explain the harder one afterwards.
FIG. 75. A PICTURE OF THE LANDSCAPE FORMED INSIDE A DARK ROOM
(Camera obscura) BY LIGHT THAT PASSES THROUGH A VERY SMALL HOLE
This experiment ca n be tried in the schoolroom. The room should be quite dark. The hole
should be pierced in a sheet of cardboard or, better, a neat hole should be drilled in a
sheet of tin.
FIG. 76
The light of a candle travels in straight lines. Until you have the candle (C) and the two
holes (A and B} in the same straight line you cannot see the flame. (This experiment
should be tried in the schoolroom.)
FIG. 77
Some of the rays from three points of a candle flame are 'drawn in this picture. They fall
on a screen (a&) and make it bright. From every point of the flame there are such
rays. And there are many more than are drawn in the picture.
99
100 THE SCIENCES
The light of the candle (Fig. 76) travels in straight lines.
So does the light from every brilliant thing. Every point of
the sun and every part of a candle flame is always sending out
rays of light, and the rays go off in every possible direction.
If you take a pincushion shaped like a ball and stick it full of
pins so that the pins stand out all over it everywhere, that might
FIG: 78
In a dark room a candle shining through a pin hole will form its own image on a screen.
serve as a model of a brilliant point of a candle flame. Every such
point sends out rays of light in every direction — up, down, side-
wise. You "see " by the rays that happen to come your way.
Rays of light from the candle flame go out in every possible
direction. How do you know that, Tom ?
PHYSICS
101
Tom. Because you can see the candle flame no matter what
part of the room you are in. If you see it, you must get rays
from it.
Jack. Exactly ; now most of the rays from the flame light
up the card and the table and the walls of the room ; a few of
them — only a few — get through the hole in the card (Fig. 78).
Some ray from the top of the flame gets to the hole, goes
through it, and goes on till it meets the screen of white paste-
board. There it stops, and there you have an image of the
top of the flame. Some ray from the candle wick gets through
the hole and goes on to meet the screen and, when it meets
it, forms an image of the wick.
Some rays from each of the
other parts of the flame get
through the hole and make
images, so that finally an image
of the whole flame is shown
on the screen. The image of
the flame is built up of hun-
dreds of little separate images, FlG
The image of candle shining through a pin
hole is formed upside down on a screen,
and this drawing shows why.
you see.1
Agnes. The image of the
candle on the screen is upside
down, and so was the picture of the landscape (Figs. 75 and 78).
Jack. You can see why it was so from this drawing, Agnes.
Shadows. — "The shadow of any square or cube is bounded
by straight lines (Fig. 78), and this is another proof that
1 The reader should lay a straight edge (the edge of a card will do) on Fig. 78.
He will see that the wick, the hole, and the image of the wick are in one straight
line. Again, the top of the flame, the hole, and the image of the top of the flame
are in one straight line, and so on.
102 THE SCIENCES
light travels in straight lines. When the point of light is really
a point, or when it is only a small spot (as in the electric street
lamp) the edges of the shadow are sharp ; but when the
light comes from a large body like
the sun the true shadow (the umbra)
is bordered by a less dark shadow
(the penumbra). If you hold a piece
FlG- 8o of cardboard in front of a lighted
A point of light at A lights half of a candle in a dark room, you can see
globe at B, and B casts a shadow. the shadow of the cardboard on the
The electric street lamp casts a
shadow with sharp edges as in the wall. The shadow is made up of two
picture, because the light of an parts — tne ^ark center (\ht-umbra)
electric street lamp comes from a
very small spot -a point of light, and a less dark part (fat penumbra).
Move the cardboard till it is quite
near the wall and you will see the umbra get dark and sharp
and the penumbra almost disappear." l
Eclipses of the Sun and Moon. — Eclipses of the sun and moon
can be explained by Fig. 8 1 . The globe of the lamp stands for
the sun, the ball B for the earth, the ball C for the moon.
Suppose you were on the earth (B) inside the shadow of the
moon. (Take a pin and point out the place.) The sun would be
hidden from you if you were there ; the sun would be eclipsed
to you. An eclipse of the sun occurs for any place on the earth
when that place is in the moons shadow. (See Fig. 51.)
The moon revolves around the earth, you know. Take the
little ball C and suspend it on that side of the ball B which is
farthest from the lamp. It will be in the shadow of the ball B.
When the moon is in the shadow of the earth no light from
1 This experiment should be tried in the darkened schoolroom. When the
appearances are thoroughly understood a second candle should be lighted and
the shadows of the two made to overlap.
FIG. 8 1
A schoolroom experiment on shadows. The room must be dark and the lamp should have
a ground-glass globe. The ball B may be an orange fastened to a pincushion by a
knitting needle. The little ball C (a small ball of twine) can be suspended by a string
so as to cast a shadow on the globe B. Notice that the ball C has two shadows, a
dark central shadow (the umbra) and a less dark shadow around it (the penumbra).
The large brilliant globe of the lamp makes two shadows to C. (By a little thinking
you can see why.)
FIG. 82
A beam of light enters a dark room through a hole in the wall (A) and falls on a mirror at
B. It is reflected from the mirror upwards to form a spot on the ceiling at C. By put-
ting a pencil vertically at B, in the line £D, you will see that the ray of light AB
and the ray of light BC make the same angles with the pencil BD. That is, the angles
ABD and CBD are always equal to each other, no matter where the mirror may be.
103
104
THE SCIENCES
the sun can reach it, and it is eclipsed. An eclipse of the moon
occtirs whenever the moon is in the shadow of the eartJi.
Reflection of Light. — Jack. Light that falls on any surface is
reflected from it. That is the way we see the surface. The
sunlight falls on the ground
and is reflected up to our
eyes,
else we should not see
FIG. 83
the ground. A feather that
is floating in the air reflects
light to us, else we should
not see it. The moon float-
ing in the sky reflects the
sunlight to us, else we should
not see it.
Fred. The sun sends us its
own light though. We do
not see it by reflected light.
Jack. The sun, the stars, an
electric lamp, a candle, have
light of their own. They send
us light directly. The moon,
A ray of sunlight enters a dark room through ^ planets distant mountains
a hole in the wall, and it falls on water con-
tained in a box with glass sides (a box with and clouds, near-by houses
one glass side will do). The ray is bent and rQcks anj fieJds, reflect
(refracted) as soon as it enters the water. *
sunlight to us. If you could
shut off the sunlight, you would not see them.
Tom. The sunlight is shut off at night (at least it is shut off
from everything on the earth) and you do not see the moun-
tains and the houses then.1
1 The reasons why you see the moon and the planets at night are explained in
Book I (Astronomy), page 33.
PHYSICS
105
Refraction of Light. — Jack. Light always travels in straight
lines ; but when a ray of light that has been traveling along
one straight line in the air enters something different from air
— water or glass, for instance — it is bent (refracted) into
another line. This second line is straight, too ; but it is not
the same line as the first
one.
Water will bend a ray of
light, and so will glass. You
know what a prism is ? A
glass pendant to a chandelier
is a prism, for instance.
If you let sunlight pass
through a prism and then
fall on a sheet of paper, you
will get a beautiful spectrum
of all the colors of the rain-
bow. If a plate of glass or
a metal mirror is ruled with
fine parallel lines equally
distant, say 1000 or 10,000
to the inch, you can get a beautiful spectrum by laying it out
in the sunshine. The colors of mother-of-pearl are made in
this way. The inside of the oyster shell is made up of very
fine parallel ridges, and the light reflected from them is scat-
tered into a spectrum of colors. You can prove that it is
the ridges that make the colors by taking an impression of
the inside of the mother-of-pearl shell in wax. The wax
gives just the same colors. The scattering of sunlight by
raindrops in somewhat the same way has to do with forming
the rainbow.
FIG. 84
A straight stick partly out of water and partly
in the water looks as if it were bent just where
it enters the water. Of course it is not really
bent, but it looks so. Try the experiment
with a pencil in a shallow basin full of water.
106 THE SCIENCES
Lenses. — "Pieces of glass of certain shapes are called lenses. We
use them to make magnifying glasses, spectacles, microscopes,
telescopes. You children had better get some old spectacle
glasses and try experiments with them. (See Figs. 45, 88-90.)
FIG. 85
A glass prism is mounted, for convenience, on a stand ; but the experiment can be tried by
a prism held in the hand. The candle flame seen through the prism seems to be in a
different place from the real candle flame, because the rays of light sent out by the
flame are bent by the prism and when they come to the eye they seem to come from a
place where the real candle is not.
PHYSICS 107
" Two (or more) lenses used together make a telescope, you
know.1 Convex lenses concentrate the light that falls on them
(Fig. 89), and concave lenses disperse the light that falls on
FIG. 86
A beam of sunlight (white light) is separated by a prism into rays of violet, indigo, blue,
green, yellow, orange, and red, and most of the heat in the beam falls near the red end
of the spectrum. The heat rays are invisible.
FIG. 87. GLASS LENSES OF DIFFERENT SHAPES
The three to the left of the middle of the picture are convex lenses ; the other three
are concave lenses.
them. Persons who are nearsighted use concave lenses in their
spectacles, and persons who are farsighted use convex lenses."
1 See Book I (Astronomy), page 58.
FIG. 88
A convex lens in a dark room will make a sharp image of a candle flame on the wall
if the lens is at the right distance. (The distance to the wall must be different for
different lenses and can be found by trial.)
FIG. 89
A convex lens concentrates light falling on it to a focus (at F in the picture).
FIG. 90
A concave lens disperses light falling on it. (The light comes from F in the picture
and is dispersed by the lens.)
108
FIG. 91. A POWERFUL MICROSCOPE
The object to be examined is placed on the stand S and looked at through the long tube.
Light can be thrown on the object by the lens N or by the mirror M. The right-
hand picture shows the way the lenses are arranged in the tube. The eye is placed
near //, and there is one lens there, another at «, and three others at O (an enlarged
picture of these three is given at Z.). Such a microscope as this can be arranged so
as to magnify about 2000 times — to make things seem 2000 times larger.
109
HO THE SCIENCES
SOUND
Velocity of Sound and Light. — The children were sitting
on the porch one afternoon when they heard the church bell in
the village ringing.
Agnes. Listen to the bell ! how plainly you can hear it, and
yet it is nearly three miles away.
Mary. Two — three — four. It is four o'clock. The ham-
mer has just this moment struck the bell.
Fred. You mean the hammer struck the bell a moment ago,
and we have heard it this minute.
Mary. Why do you say that, Fred ? ,
Fred. You know that you do not hear the sound of a blow
when the blow is struck — not till afterwards. Have n't you
ever seen a gun fired by a man a mile away from you and then
waited to hear the sound ?
Mary. Why do you have to wait ?
Fred. Why, you know the light of the flash comes to you
instantly — the very minute the gun is fired; and it takes
time for the sound to travel. Let us ask Jack to tell us how
fast sound travels ; he is sure to know.
Jack. Light travels almost infinitely fast j1 but sound moves
much slower — about noo feet in a second. It takes sound
nearly five seconds to go a mile.
Mary. Do you mean, Jack, that we did n't hear the village
clock strike till fifteen seconds after it had really struck?
Jack. Yes ; the hammer struck the bell first and set it
vibrating ; then the air round the bell began to vibrate, and
the sound began to travel off in every direction — north, east,
1 The velocity of light is 186,330 miles in a second of time. Light travels
from the sun to the earth in 500 seconds, a little more than eight minutes.
PHYSICS 1 1 1
south, west. If you had been in the village, you would have
heard the bell the moment it was struck ; if you had been a mile
away, you would have heard it five seconds late ; and as we are
three miles away, we all heard it about fifteen seconds later.
FIG. 92. A CHURCH BELL
It is rung by the rope that you see on the left-hand side of the picture.
Tom. It is something like throwing a stone into a pond of
water. Little waves travel in every direction from the place
where the stone went into the pond.
112 THE SCIENCES
Jack. Yes ; and you remember that the waves get smaller
and smaller the farther they go. Sound is like that. The
vibrations of the air are powerful near the sounding bell, but
they get weaker and weaker as you go away from it.
Tom. So sound is a vibration is it, Jack?
Jack. There would be no sound unless there were some
vibration in the first place. But there wouldn't be any sound
FIG. 93
A wave of sound if it were visible, as it is not, would look something like the picture. Such
waves go out from a sounding bell in every direction. When they come to your ear you
hear the bell, but not before. Sound waves travel about noo feet in a second — a
mile in about five seconds.
unless there were some person to hear it. If there were a
mechanical piano playing at the north pole, by machinery,
there would be vibration of the strings — and of the air, too ;
but unless there were some one to hear it there would be no
sound, only vibration.
Tom. Well, usually there are persons to hear in our part of
the world. Are all the sounds we hear caused by vibrations ?
PHYSICS 113
Musical Instruments. — Jack. Yes ; let us take some sounds
we know about and see what makes them. In the first place
there is the bell. The hammer strikes it and makes it vibrate.
It is just the same with a piano ; the wire is struck and made
to vibrate. A violin string vibrates. In an organ pipe or in a
FIG. 94
A glass plate vibrates when a fiddle bow is drawn across its edge so that the plate makes a
sound. If you put a little clean dry sand on the plate, the sand will move so as to make
patterns (as in the cut). By drawing the bow at different places you can get different
patterns, especially if you lightly touch the plate with a lead pencil while the bow is
moving. Some of the patterns are shown in the next picture.
trumpet the air vibrates. When you speak or sing a couple of
elastic muscles in your throat vibrate. In a drum the parchment
vibrates when the drumsticks strike. Something always vibrates
first ; that, whatever it is, sets the air to vibrating, and the
vibration travels to where we happen to be and we hear a sound.
THE SCIENCES
Tom. How do you know that the bell vibrates ?
Jack. The next time you are in the village go up in the
clock tower when the clock is going to strike and hold a lead
pencil against the bell. You can/^/ the bell vibrate.
Here is a curious thing to think of. First the bell vibrates
and you can hear it for miles in every direction. Every
\
V — '
•*{•£***•
FIG. 95. PATTERNS MADE BY LOOSE SAND ON A VIBRATING
PLATE. (SEE FIG. 94.)
After the patterns have been made they can be preserved by carefully pouring varnish
on the plate and letting it dry.
particle in a very large sphere of air is set in motion. We
hear the sound at our house, miles away from the village. Now
the air that is set in motion weighs hundreds of tons, and it is
all moved by one stroke of the hammer on the bell.
PHYSICS 115
Tom. You can hear a locust chirping a quarter of a mile off.
I suppose he sets the whole air in motion, too.
Jack. That is a very good example. A small insect moves tons
and tons of air ; and a violin string, vibrating so little that you
can hardly see it move, stirs all the air in a great concert hall.
FIG. 96
A watch ticking in front of one mirror can be plainly heard through a tube placed in front
of another. If you take the second mirror away, you cannot hear it at all. The first
mirror acts as a speaking trumpet (a megaphone), and the second mirror acts as an ear
trumpet.
Sometimes when the organ is playing a low note in church
you can actually hear the air flutter and vibrate. The organ
makes a noise then, not music.
Mary. What is the difference between noise and music, Jack ?
Il6 THE SCIENCES
Jack. If the vibrations of a bell, a violin string, an organ
pipe — anything — come at even intervals, then they make a
musical note. If they come irregularly, the sound is usually a
FIG. 97. ECHOES
An echo is made by the reflection of sound from a wall, a rock, etc. The person who
speaks must be at least 100 feet away from the wall to get a good echo.
mere noise. Music is pleasant to hear, and noise is not. That
is the real difference.
Reflection of Sound. — Sound can be reflected somewhat as
light is, as the following experiment shows.
Musical Notes. — Mary. Are the sounds from my piano regular?
Jack. Yes ; perfectly regular. Each string vibrates regu-
larly just so many times in a second, no more and no less. The
middle C of your piano is a wire just long enough
to vibrate 261 times every second, and all of its
vibrations are alike.
The shorter a string is the quicker it vibrates, and you will
notice that the highest notes of your piano come from the
PHYSICS 1 1 7
shortest strings. It is the same with drums ; the small drums
give the highest notes, the large drums the lowest.
The phonograph is a machine for recording the vibrations of
the air that are made when a person speaks. He speaks into
a tube (F in Fig. 98) and sets the air into vibration. At
the small end of the tube is a little round thin metal plate that
moves up and down (slightly) as the air vibrates. The motions
of this little plate copy the vibrations of the air. On the lower
side of this thin plate is a sharp needle point. (See Fig. 99.)
FIG. 98. THE PHONOGRAPH
While the person is speaking the barrel (A), which is covered
with tin foil, is turned by the crank, and the little needle makes
marks on the tin foil. These marks are the record of the
human voice. Every vibration of the voice has left its mark
on the tin foil. If now we put a piece of tin foil so marked
into the machine and turn the barrel, what will happen ? As
each one of the marks in the tin foil passes underneath the small
needle the needle will move a little (if the mark in the tin foil is
shallow) or moves a little more (if the mark in the tin foil is
deep). The needle will move up and down for the tin foil just
as it formerly moved up and down for the voice. As the
Il8 THE SCIENCES
needle moves, so must the thin plate move ; and as the plate
moves and vibrates, so must the air above it move and vibrate,
and you will hear from the machine riow the very words you
spoke into it an hour ago, or a year ago, or twenty years ago,
whenever the record on the tin foil was made. You can keep
the tin foil and repeat the words whenever and wherever you like.
Tom. If the phonograph had been invented in Julius Caesar's
time, we might be able to hear his voice now, or George Wash-
ington's, or Lincoln's.
Jack. The records of the speeches
of some of the great men of to-day
actually have been preserved ; and
long after they are dead, so long as the
FlG little pieces of tin foil last, other peo-
ple will know exactly how they spoke.
Mary. It would be a fine thing for us to get Eleanor to sing
into a phonograph now, so that when we go home after vaca-
tion we could still hear her !
Jack. A wise man in England l once suggested that there
could be no worse punishment in a future life than to be forced
perpetually to hear all the foolish things you had said in this
life. It might not be a bad way to punish naughty boys and
girls in this world to shut them up in a room with phonographs
that would continually repeat the silly and foolish things they
had said.
Agnes, /think it would be dreadful, Jack. Nothing could
be worse.
Jack. Very well, my dear, you need not mind. The things
you say are always nice to hear. I was only trying to frighten
the boys.
1 Charles Babbage (born 1792, died 1871).
PHYSICS 119
ELECTRICITY
The children made some experiments in electricity which
any one of you can make too, if you like. You will need a few
things, most of which you can get at home or make for your-
self. A few you will have to buy (they do not cost much).
The principal things to get are : a couple of toy magnets, one
straight, one shaped like a horseshoe ; a piece of glass tube
(or a glass rod) about half an inch in diameter and eight or ten
inches long ; a piece of sealing wax about half an inch square
Copper
wire
Zinc
B
wire
FIG. 100
and about six inches long ; a rubber comb ; an old silk hand-
kerchief ; a piece of old flannel ; an ounce of sulphuric acid in
a bottle with a glass stopper (be careful not to get the acid on
your hands, and be sure that the bottle is labeled Sulphuric
Acid} ; an ounce of quicksilver in a bottle (be sure that the
quicksilver is labeled ; it is poisonous if swallowed) ; about
twenty feet or so of insulated copper wire (No. 18 annunciator
wire is the most handy to use) ; a piece of sheet copper about
three sixteenths of an inch thick, one and one half inches wide,
and five inches long; a piece of sheet zinc of the same size as
the copper. Take the copper sheet and the zinc sheet to a
plumber and have him solder a piece of copper wire (each
piece about twelve inches long) at A and B. After this is done
120 THE SCIENCES
take a large tumbler, fill it two-thirds full of water, pour
three tablespoonfuls of sulphuric acid in it (use an old kitchen
spoon for this purpose), dip the zinc plate in it, and leave it
there for a minute. Then take the zinc plate out, hold it
over a china plate, pour quicksilver on it, and rub the quick-
silver on to the surface of the zinc until it is all covered and
shining. (Do not empty the water and acid from the tumbler ;
you will need it by and by ; save it.) Now you have all the
things you need for your experi-
ments, but it is convenient to get
two dottble connectors (so called)
FIG. ioi like Fig. 101.
A double connector (so called) is a cylinder Jack. Before WC begin Our
of brass with two holes in it and with experiments with the things you
two screws. It is used to connect the ° J
ends of two wires and saves the trouble have Collected, tell me what yOU
of twisting the ends together, it is already know about electricity.
convenient, though not necessary.
You have heard it talked about.
Tell me what you have seen on your own account.
Agnes. Well, lightning is electricity, they say.
Mary. And electric bells ring by electricity, and some street
railways go by electricity.
Fred. And then there is the electric telegraph.
Tom. Yes, and the telephone, and the electric light.
Jack. All these things have to do with electricity. Let us
begin by making some lightning.
Agnes. Oh, Jack ! make lightning? It would be dangerous.
Tom. Agnes thinks Jack can make anything — even a
thunderstorm if he wants to.
Jack. Well, Agnes, the lightning we are going to make will
not be dangerous ; but I will put off making it for a little while
and begin with something else.
PHYSICS
121
Here is a lot of small pieces of tissue paper — they are
very light, you see — laid on the table. Now take the glass
rod, Agnes, and hold it over them. What happens?
FIG. 102
Little pieces of tissue paper (or light grains of sawdust) are attracted by a glass rod rubbed with
. a silk handkerchief (or by a piece of sealing wax or a rubber comb rubbed with flannel).
Agnes. Nothing happens at all.
Jack. Try the rubber comb, Mary.
Mary. Well, nothing happens.
Jack. Now, Agnes, rub the glass rod briskly with the silk
handkerchief ; and you, Mary, rub the comb with the flannel ;
and try again ; Agnes first.
Agnes. Why, Jack! the little pieces of paper rise up to meet
the glass. (See Fig. 102.)
Jack. Take the glass rod away, Agnes ; and now, Mary, try
with your comb.
122 THE SCIENCES
Mary. It is just the same thing; the little pieces of paper
rise up to meet the comb — it is like magic.
Jack. We have learned something, anyway. What have we
learned, Fred, so far ?
Fred. We have learned that if you rub a glass rod with silk,
the rod will attract pieces of paper as a magnet attracts pieces
of iron.
Tom. And that if you rub a piece of rubber1 with flannel,
the same thing happens.
Jack. That is very good so far. Now, Agnes, rub the glass
rod with the flannel, not the silk ; and Mary, rub the comb 2
with the silk, and both of you try once more. What
happens ?
Agnes. Nothing happens now.
Mary. Nothing happens when I try with the comb either.
Jack. Well, we have learned that to lift the little pieces of
paper with a glass rod you must rub the rod with silk, not
flannel ; and the comb with flannel, not silk. Glass rubbed
with silk is made electric — electrified, as they call it ; and
rubber (or sealing wax) rubbed with flannel is electrified.
When either glass or rubber is so electrified it will attract
little pieces of paper, or light grains of sawdust.
I want you all to try this experiment, too. Electrify the
glass rod and the comb and then hold them near your face.
What happens ?
Agnes. Why it tickles ! it feels as if there were a cobweb on
my cheek.
1 A piece of sealing wax rubbed with flannel will act just as the rubber comb
acts. Try it.
2 A piece of amber does the same thing. The Greek name for amber is elek-
tron, and we get the name " electricity " that way.
PHYSICS 123
Jack. Tom, take the glass rod and rub it smartly with the
silk. Now hold your knuckle close down to the tube. See
there is a little spark.
Tom. I felt it and I heard it, too.
Jack. Agnes, that spark was lightning and the crackling
noise was thunder, only they are not dangerous. Real light-
ning is just the same kind of thing as that little spark, -and
real thunder is just like the little noise the spark made. Per-
haps you know that in 1752 Benjamin Franklin sent a kite up
in the air during a thunderstorm and brought down some of
FIG. 103. A LONG ELECTRIC SPARK BETWEEN Two ELECTRIFIED BALLS
Lightning takes the shape of this spark. It is never a zigzag bolt made up of
straight lines, as it often seems to be.
the electricity that was in the clouds and proved that the light-
ning in the sky was exactly the same thing as the spark you
have just seen.
Now you children have seen the kind of electricity that
makes thunder and lightning. Let us make some of the kind
that they use in the telegraph. I want to make a current of
electricity that I can use to carry a message from New York
to San Francisco.
Now we shall need our tumbler of water with the acid in it
and the strips of copper and zinc. (See page 119.) Stand the
I24
THE SCIENCES
two strips upright in the tumbler and put some strips of wood
across the top of the tumbler to keep the zinc and copper apart.
They must not touch anywhere. When you have arranged this
all right so that everything will stay in place you have got a
battery, and if you join the two wires (see the picture, Fig. 104)
a current of electricity will flow
from the copper plate to the
zinc. I am going to prove it
to you.
Take the end of the wire
from the copper and put it on
one side of your tongue and
put the wire from the zinc on
the other side, and you '11 feel
a little current passing. The
current goes from the copper
through the wire, and through
A glass jar containing dilute sulphuric acid
with a plate of zinc and a plate of copper
your tongue to the zinc. Your
tongue connects the two wires.
in it (they must not touch each other) is Jf vou actually join the two
called an electric battery. If you join
the coppar (C) and the zinc (Z) plates by
a wire (Af), a current of electricity will
flow from C to Z through the wire; no
matter how long the wire is, the current
will still flow. It would flow (with a
wires, the current will be there
just the same. Feeling it with
your tongue proves that it is
there, and that is what I wanted
strong current) from New York to Boston. j.Q prove Jf yOU
batteries joined together,1 you would have a current twice as
strong. With many batteries joined together you would have
a current strong enough to travel over a wire as long as from
New York to Boston ; and that is the kind of electricity they
use in telegraphing.
1 The zinc of one battery to the zinc of the next one.
PHYSICS
The Telegraph. — "I understand how you send a current of
electricity from New York to Boston," said Tom ; "you have a
FIG. 105. A BATTERY OF FIFTEEN CUPS
Notice that the zinc qf one cup is connected to the copper of the next one, and so on.
At the ends there are two short wires marked + and — . If you join these to two
telegraph wires reaching to a distant town, a current of electricity will flow from + to
the distant town and back from the town to — . There would be a continuous circuit
of wire from + to the town, and back again to — . If you cut the circuit of wire any-
where and put the two ends of the wire to your tongue, you will feel the current.
That is a proof that the current is always there, in the wire. It is always flowing so
long as the battery is joined to the long loop, or circuit of wire.
battery at New York and a loop of wire — what you call a cir-
cuit — going to Boston and returning to New York, this way :
wire ^
Battery in
New York
Boston
wire
FIG. 1 06
126 THE SCIENCES
But I don't see how you make the signals. The current flows
through the wires quietly ; it makes no noise."
Fred. You have to put telegraph instruments — a key and so
forth — on the wire, don't you ?
Jack. Yes ; we can improve Tom's drawing by putting them
in, this way :
wire
Battery in
New, York
Telegraph Instrument
Telegraph Instrument in Boston
in New York
< wire
FIG. 107
The battery in New York is all the while sending a current
of electricity along the wire. It fills the whole of the wire
from New York to Boston and back again. It flows along
the wire and through the telegraph instruments at both places.
When you wish to talk to Boston you move your New York key
up and down, and the receiving instrument in Boston makes
little sounds, one sound for each motion of the New York key.
You can arrange an alphabet that way. For instance, three dots
( ) might be C, one dot (-) might be E, and two dots (- -) might
be /. You could spell .ice, for example, this way : - -, , - .
Fred. And Boston could talk to New York by dotting with
the Boston key, and New York would hear it.
Jack. That is exactly the way it is done. Go into a tel-
egraph office sometime and listen, and you will hear the
instruments clicking away. Sometimes they make dots and
PHYSICS
127
FIG. 108
This figure shows the way in which New York and Boston are connected by telegraph.
It is more complicated than the way described before, but the idea is the same.
The key at New York is marked K (the Kon the right-hand side) . If this key is tapped,
a signal goes over the wire to Boston and is received on a sounder there. (See the picture
of the sounder at the bottom of the cut.) In the same way signals made with the
Boston key are heard on the New York sounder.
sometimes longer sounds called dashes, and sometimes very
long dashes. The alphabet they use is :
TELEGRAPHIC ALPHABET
A
B
C
D
E
F
G
H
I
J
K
L
M
N
O
P
Q
R
S
T
u
V
W
X
Y
Z
&
t
p
TELEGRAPHIC
FIGURES
(
i
2
3
4
5
6
7
8
9
10
FIG. 109
128
THE SCIENCES
Velocity of Electricity. — " You children must remember," said
Jack, "that electricity travels at the same speed as light — it
travels 186,000 miles in a second. They once sent a message
from Cambridge through Canada to San Francisco, returning
by Omaha and Chicago, and it took only four seconds for the
message to go those
7000 miles. If the tele-
graph instruments had
been perfect, the mes-
sage would have gone
instantaneously. As it
was it did not take long."
MAGNETISM
Jack. Suppose we stop
talking about electricity
for a while and learn
something about mag-
nets. There is a magnet
in every telegraph
sounder, in every tele-
phone, and in every
dynamo, and I want you
to understand how they are used. But we will begin far off
and come to these complicated machines by and by. In the
first place, Fred, what is a magnet ?
Fred. A magnet is a piece of iron or steel that attracts other
pieces of iron.
Tom. Try your straight magnet on these iron filings,
Fred.
FIG. no
A straight magnet held in the hand will attract little
pieces of iron and will make each of them into mag-
nets, so that they will hold up other small pieces.
PHYSICS
129
Jack. There is a special thing to notice. A bar magnet
attracts iron filings, tacks, and so forth, at its ends, but not at
its middle. It is just the same
with a horseshoe magnet. Try it.
We have learned one thing.
Magnets of all shapes attract iron
filings, tacks, needles, and SO forth, A straight magnet — a bar me
to their ends, not to their centers. attracts iron filinss to its ends> but
,, , .. . ., , not to its middle part.
Here are four little piles of saw-
dust, of copper filings, of sand, and of coal dust. Try to pick
them up with your magnets.
Agnes. They do not move ; magnets
do not attract such things as sand.
Jack. No;
FIG. in
FIG. 112
magnets attract
iron and steel
nothing else.
you take a
A horseshoe magnet attracts iron
filings to its ends; but if you
try the curved part of the mag-
net on a needle, there is almost pile of CODDer
no attraction.
filings and iron
filings mixed together, the magnet will
pick up the iron filings and leave the
copper. Try the experiment and see for
yourself.
Tom. So it does. That is a way of FlG- "3- A HORSESHOE
,r MAGNET WITH AN IRON
sorting iron out of a pile. If some one BAR (AN ARMATURE)
told me to pick the iron filings out of ACROSS ITS ENDS
this pile by hand, it would take all day
to do it ; but with a magnet I can do it in five minutes.
Jack. See what the magnet will do through a pane of
glass. Lay a needle on a pane of glass held horizontally and
130
THE SCIENCES
put the magnet under the glass. You will see that the needle
moves over the glass as you move the magnet around.
Tom. So it does ; glass does not stop the attraction.
Jack. Try putting the needle on a sheet of writing paper or
on a piece of silk.
Tom. It is just the same; the needle moves when I move
the magnet.
Jack. So much is clear ; a magnet is made of iron; it attracts
iron and nothing else; it attracts it through silk, or paper,
or glass — through any-
thing.
These magnets that
you have been using
are manufactured.
They were made. Let
us make some more.
Agnes, have you got
any needles ?
Agnes. Here are some.
Jack laid the needles
on the table and rubbed
them with the horseshoe
magnet, as if he were
stroking them with it.1
He tried each needle on
the pile of iron filings,
and every one was able to lift up some filings just as the horse-
shoe magnet did. Then he took two of the needles and tied a
bit of silk about each, near its middle, and hung the silk from
1 Make all the strokes on all the needles in one direction, so as to have the needle
magnets all alike. Stroke all of them from eye end to point, or all from point to eye.
FIG. 114
Iron filings on a horizontal pane of glass will move
into a certain set of curves when yon hold a horse-
shoe magnet underneath the glass. (You must
tap the glass very gently with your finger tip.)
PHYSICS
two pencils (see Fig. 115), so that he had two little magnets,
like pendulums. Next he took the bar magnet — a straight
magnet — and tried some experiments with needle No. i (the
other needle was laid aside for the moment). The bar magnet
pencil ^••^•i -—^—tp—— pencil
silk
needle
no. i
silk
needle
no. 2
FIG. 115
had two ends of course ; one was the point, and the other
happened to be painted red.
point
red
FIG. 116
By trials with needle No. i he found :
1. That the point of the bar magnet attracted the point end
of needle No. i.
2. That the point of the bar magnet repelled the eye end of
needle No. i.
3. That the red end of the bar magnet repelled the point
end of needle No. i.
4. That the red end of the bar magnet attracted the eye end
of needle No. i.
Then he tried needle No. 2 and found just the same things
for it also.
132 THE SCIENCES
5. The point of the bar magnet attracted the point end of
needle No. 2 ;
6. — and repelled the eye end of No. 2.
7. The red end of the bar magnet repelled the point end
of No. 2 ;
8. • —and attracted the eye end of No. 2.
The next thing was to put aside the bar magnet and to try
the two needles together. He found :
9. That the two points of the needles repelled each other.
10. That their two eye ends repelled each other.
11. and 12. That the point end of either needle attracted the
eye end of the other.1
Tom. What is the explanation of all these experiments,
Jack ?
Jack. It is like this : just suppose there were two kinds of
magnetism in the bar magnet. We might call them point-end
magnetism and red-end magnetism, for want of better names.
Now when we made magnets out of these needles we put the
two kinds of magnetism into them. We put one kind into the
point ends of both needles and another kind into their eye
ends. Suppose we say that point-end magnetism, where-
ever it is found, will repel point-end magnetism ; and that
red-end magnetism, wherever found, will repel red-end mag-
netism ; and that point-end magnetism will attract red-end
magnetism, and vice versa, wherever they are found. Would not
that explain all that we have seen ?
Taking all the twelve cases one by one, the children found
that the explanation was right. Magnetism of the same name
repels ; magnetism of different name attracts. It is not easy
1 These experiments take some space to describe, but they are so interesting
that they should be tried in the schoolroom.
PHYSICS
133
to explain in simple words why this is so ; but any child who
will pay attention and make these simple experiments can
prove it.
Natural Magnets. — "These magnets were artificial; they
were manufactured," said Jack ; "but there are stones that are
magnetic to begin with. They were first found in Magnesia,
a town of Asia Minor, long ago, and the
ancients therefore called them magnets."
Mary. In the Arabian Nights, in " Sind-
bad the Sailor," there is a story of a whole
mountain made of magnets, so that when
a ship came that way the mountain pulled
all its iron nails out, and the ship broke to
pieces and sank.
Agnes. That is n't true, is it Jack ?
Jack. Certainly not, my dear ; it is one
of the big stories told by travelers. But
don't you recollect how they got past the
mountain with their ships ?
Mary. They built their ships with wooden
pins instead of nails and got safely past,
so the story says.
Electro-Magnets. — Jack. There is an-
other kind of magnet that I want you to know about. It is
made by a current of electricity from a battery passing through
a wire wrapped round a bar of soft iron. (See Fig. 1 17.)
You see now how a telegraph operator in New York
can make a click on the sounder in Boston. The bat-
tery current is flowing all the time except just at the
moment when the New York man lifts his key and breaks
the circuit.
FIG. 117
If wire be wrapped in a
spiral around a bar of
iron, and if a current of
electricity flow through
the wire, the bar be-
comes a magnet and
stays so as long as the
current is flowing, and
no longer.
134
THE SCIENCES
The electro-magnet of the sounder in Boston is a magnet so
long as the current flows, and stops being a magnet the
FIG. 118
Electro-magnets are often made of a core of soft iron bent into the shape of a horseshoe,
and wound with wire. The two ends of the wire go to the copper and zinc of a battery.
So long as the current flows the iron core is a magnet. When the current stops it is no
longer a magnet.
instant the current stops. Whenever the New York man lifts
his key the Boston sounder makes a click — a dot or a dash,
just as he chooses. In that way the message is spelled out.
Key in
New York
Bai
Sou ider
in Boston
tery
FIG. 119
Electric Bells. — "Now," said Jack, "it is easy to understand
how electric bells work. It is like a telegraph. In the first place
you must have a battery. We could make a battery by using
PHYSICS
135
several tumblers (like those described on page 124), but it is
more satisfactory to buy one cell of "dry "battery, so called.
FIG. 1 20. A TELEGRAPH KEY
FIG. 121. A REPEATING SOUNDER
FIG. 122. A CELL OF
DRY BATTERY
" We must run our
The coils of its magnets are vertical. Thearma- wire along the walls
tare is fastened to the horizontal ter which from one station to
moves as the armature moves and clicks against
the point of the little screw above it. another like this I "
wire
Push
Button
Battery
Bell
wire
FIG. 123
FIG. 124. A PUSH BUTTON
It is like a very simple telegraph key.
When you push it two ends of the wire
are connected so that the current from
the battery can flow to the bell and ring
it. Until the button is pushed the
circuit is broken and the current can-
not flow. If you should take away
the push button and join the ends of
the wire where it now is, the battery
current would flow continuously and
the bell would ring all the time.
FIG. 125. AN ELECTRIC BELL
When the push button is touched the cur-
rent from the battery flows along the
wire into the box and round the coils
shown in the picture. So long as the
current is flowing the soft iron inside
the coils is a magnet and attracts the
piece of iron which is -the hammer (K)
of the bell (T). But this piece is a vi-
brating spring and it keeps moving to and
fro and sounding the bell. The moment
that the push button is released the cur-
rent stops flowing and the bell stops
sounding.
136
FIG. 126. AN ELECTRIC-BELL OUTFIT
COMPLETE
It can be bought in this form with seventy-five
feet of wire and staples to fasten the wire for
about $2.75.
Grou.ntL Wire,
Line Wire.
FIG. 127. THE TELEPHONE
F is a handle ; turn it and the bell (G) will ring on your
telephone and also at the other end of the line. The
man you wish to talk to will hear it. He has another
instrument just like yours. Take down your tele-
phone (B) and put it to your ear. Speak into your
transmitter (C) and he will hear you in his tele-
phone. When he speaks into his transmitter you
will hear him in your telephone.
to Battery
137
138
THE SCIENCES
The Mariner's Compass. — "You know that a magnetized
needle points north and south," said Jack. " A compass needle
will point to the north no matter to what part of the earth you
FIG. 128. THE TELEPHONE
One view shows the telephone as it really is ; the other as it would look if it were split down
the middle so as to show what is inside. A is a long steel magnet wound with fine
wire (B). The ends of the spool of wire (B) are connected to the outside posts (D,D).
Close to the magnet yi(near B) there is a thin iron plate (EE) which vibrates so as to
copy the voice of the person speaking to you. That person speaks into his transmitter.
(See Fig. 127.) The vibrations of his voice make vibrations in the disk of his trans-
mitter ; these vibrations are sent along the telephone wire and come to your telephone ;
there they make the disk (BE ) of your telephone vibrate just ,as his voice vibrated ;
the disk (EE) makes the air in your telephone vibrate like the speaker's voice, and
you hear him speak.
take it. The reason is that a current of electricity is flowing
round and round the earth all the time and that any magnet
will always arrange itself at right angles to a current, if it can.
PHYSICS
139
The fact is so, and I am going to prove it." So Jack took
one of the little magnetized needles (Fig. 1 1 5) and let it
FIG. 129. THE MARINER'S COMPASS
swing freely. It swung so as to point to the north and
rested in that direction, thus :
->• North
FIG. 130
Then Jack took the two ends of the wire from his battery
and made them parallel to the needle, being careful not to
touch the ends together, this way:
> North
AB
Copper
Zinc
'
Battery
FIG. 131
140 THE SCIENCES
No current was flowing, and the needle remained as it was
before. Then he joined the ends A and B. A current flowed
through the wire, and immediately the needle moved round and
pointed west and not north (Fig. 132).
"You see," said Jack, "the needle moves so as to be perpen-
dicular to the direction of the current. A current is always
flowing round and round the earth from east to west. The sun
makes the current. The compass needle is always perpendicular
to the direction of the current, and that is why the mariner's
compass points to the north. It is a good thing for us that it
West
Copp.
er Zinc
Battery
FIG. 132
does so. Sailors can make long voyages and always know
which way is north whether the stars are shining or not.
They do not need the north star any more."
The Electric Light. — The first electric light was made about
a hundred years ago by using a battery of 3000 cells. (See
Fig. 105.) The wires from the ends of this immense battery
were brought close together, and the spark between the ends
did not come and go as lightning does, but was steady, like
our electric , street lamps. The current from so many cells
made a great heat as well as a brilliant light. The ends of the
wires were melted off where the light was produced, and they
o-w
'
H -»
.
•SS'S'.SS3';
^rc 3 ^rc
;s»*i
S 3 ; * § S
« °<S o^e-
6*8
?!
&B ^
iF^EfiiB
ss ^Hffli
„ ^H^ pjw'S1^ o rt.
l^eis.-^rg"
lll'llslg^
— . ^
" 0
141
142 THE SCIENCES
were obliged to use carbon ends (round sticks of coal dust or
coke) at the ends, just as we do to-day.
The Dynamo. — It is possible to make batteries of thousands
of cells, like those shown in Fig. 105, so powerful as to do the
work of electric lighting ; but it is very troublesome and
expensive. A much simpler and cheaper way to get the current
that is needed is to use a dynamo driven by a steam engine.
FIG. 136. A DYNAMO-ELECTRIC MACHINE
A belt from a steam engine is put on the wheel at the right of the picture and turns this
wheel very rapidly. The central part of the dynamo is a large stationary electro-magnet.
Fastened to the revolving wheel (and not visible in the picture) are a number of small
electro-magnets. When these small electro-magnets are revolved very rapidly in front
of the large magnet a strong current of electricity is made, and this current is carried
off on wires to where we wish to use it. It will light lamps or drive a street car, etc.
The steam engine is used to turn a set of little electro-
magnets in front of a larger magnet. When this is done a
current of electricity flows through two wires leading from the
machine, and these wires can be led to the place where we
want to use the current — to a distant part of the city to light
PHYSICS
143
lamps, or to drive electric cars. Lamps are lighted by letting
the current from the dynamo pass through them.
Electric Railways. — Street cars are driven in this way. Under-
neath each car is a dynamo (called a motor} fastened to the wheels.
FIG. 137. PART OF THE FRONT TRUCK OF A STREET CAR (SHOWING THE
WHEELS AND THE MOTOR BETWEEN THEM)
FIG. 138. AN ELECTRIC STREET RAILWAY
The power house with its dynamo (D) driven by a large steam engine is shown on the left-
hand side. From this dynamo a current goes out on an overhead wire (A*). A moving
trolley ( T) on each car takes the current to the motor. The motor turns the wheels
whenever the motorman turns the current on, and stops turning them whenever he shuts
the current off.
APPENDIX
SOME of the experiments that were tried by the children are given here.
Nearly all of them can be repeated in the schoolroom or by children at
home who will take the trouble. It is well worth while to do it, because
we learn so much more by really doing a thing than by merely talking or
reading about it. The teacher can readily buy or make the simple apparatus
described ; and, once made, it will serve for successive classes. Nearly
every child has a father, or an older brother, or a friend, who will help him
to make these experiments at home if they cannot be seen at school.
What Kind of Things Bodies are. — We need a convenient name for solids,
liquids, and gases ; let us call them bodies, and say that a piece of iron is
a solid body, a lake of water is a body of liquid, etc. When we think about
any body of this sort — a nugget of gold, for instance — we always think of
it as filling some space.
Extension. — All bodies are extended; they fill a space. Even a sponge
fills a space ; the holes in the sponge are full of air, and the air in a sponge
fills a space and has a shape of its own.
Impenetrability. — Where one body is, another body cannot be at the
same time. Putty is soft and can be molded into almost any shape, but
where the putty is, nothing else can be at the same time. It completely fills
its own space.
Divisibility. — Every body can be divided into two halves, and each of
those halves into halves again, and so on. If you will get from the
druggist a little piece of permanganate of potash (write the name down)
and put it into a hogshead of water, you will find that the whole of the water
has been colored red. Every drop of water that you take up in your hand
is red, and there are millions of drops in the hogshead. That means that
the little piece of permanganate of potash has been divided into millions
of smaller pieces, and that every single drop of water has several of
those small pieces in it ; for it takes more than one piece to color a whole
drop of water.
144
PHYSICS — APPENDIX 1 45
If you put a piece of musk no larger than a green pea (you can buy
musk from any druggist) in a room, it will scent the room and everything
in it, and it will keep on doing so for years and years. Leave a towel in
the room over night, and the next morning every thread of the towel
will smell of musk. You could go on leaving towels in the room for a
dozen years and taking them away after one night, and every thread of
every towel would show that the musk had been near it. That means that
every one of the threads of every one of the towels has several particles of
musk on it ; and it means that the original piece of musk (which seems
hardly to grow any smaller) has been divided into millions of little pieces.
Cohesion. — If you take two bars of soap and press them together under
a press, you can make one piece out of the two. That piece is held together
by a force that we call cohesion. All solids are held together by such a
force. One part of a lump of iron is held to the other parts by cohesion.
It requires a good deal of pulling to pull one part of an iron rail away from
the other parts (though it can be done). You can weld two pieces of iron
together (by heating) so that they become one piece.
If you stretch a solid body (or compress it) and then take away the
force that was stretching (or pressing) it, the body will usually spring back
to its first shape. A piece of india rubber stretched (or compressed) flies
back to its first shape as soon as you stop forcing it out of shape. A
bent steel knitting needle flies back into shape very quickly. India rubber,
steel, glass, and indeed most solid bodies, are elastic. If you strain them
a certain amount, they will spring back into shape like the springs of a
buggy. If you strain them too much, they sometimes lose their elasticity
like the springs of a farm wagon that has been used to carry very heavy
loads. Most solid bodies are elastic; all liquids are so.
Viscosity. — Did you ever see very cold molasses flowing from a spigot ?
It is viscous — a little like a solid and a little like a liquid at the same time.
Warm it, and it becomes like a liquid. Tar that is very hot acts like a
liquid ; as it cools it is viscous ; when it is perfectly cold it becomes a solid.
Water is not viscous ; it flows freely.
All Bodies are Heavy. — All bodies — solids, liquids, and gases — have
weight. A cubic inch of any solid is usually (not always) heavier than a
cubic inch of any liquid. Iron will sink in water, but wood will float on it.
Iron itself will float on quicksilver. The gases have weight. Air has
weight, for instance, as the barometer proves. (See page 84.)
146
THE SCIENCES
Hardness. — By a little trouble any child can get pieces of soapstone
(talc) (i), rock salt (2), fluor spar (4), feldspar (6), quartz (7). The numbers
1,2,4,6,7 denote the degree of hardness of these stones. The very hardest
stone is the diamond, whose hardness is 10. Rock salt (2) will scratch
soapstone (i) ; feldspar (6) will scratch fluor spar (4) ; quartz (7) will
scratch all of them and will scratch glass, too. You can write your name
on glass with a piece of pure quartz. A diamond will scratch every stone.
If you want to say how hard a stone is, you can give its hardness in a
number. Topaz is 8 ; it will scratch quartz but not diamond.
Ductility. — You can draw some metals out into long fine wires. These
are the ductile metals, lik'e gold, silver, iron, copper, etc. Glass can be
drawn out into fine threads by heating it. Gold can be hammered out into
leaves so thin that 30,000 of them, piled one above another, would be only
an inch high. If you were to press these leaves under a strong press,
they would go back into a gold plate by cohesion. (See page 145.) A body
is called malleable when it can be hammered out into thin sheets. Copper,
for instance, is very malleable.
Crystals. — Buy three ounces of alum at the druggist's and pound it
into a fine powder and put the powder into a tumbler full of very hot water,
stirring the alum in with a glass rod until all is dissolved. Then lay a bit
FIG. 139. How TO MAKE ALUM CRYSTALS
of stick across the mouth of the tumbler with a short string hanging down
into the water. (See Fig. 139.) Put the tumbler in a cool place and
look at it the next day and see the beautiful crystals of alum that have
formed. The hot water kept all the alum dissolved. As the water cooled,
PHYSICS — APPENDIX
H7
some alum was freed, and it formed into its own kind of crystal. Every-
thing has its particular way of crystallizing. Alum makes one kind of
crystal, quartz another.
You can buy some rock salt, some bichromate of potash, and some blue
vitriol at the druggist's also, and make crystals out of these substances,
FIG. 140. DIFFERENT FORMS OF SNOW CRYSTALS
just as you made the alum crystals. Each substance will crystallize in its
own way. You can save some of the best crystals in wide-mouthed glass
bottles, tightly corked, and begin to collect a cabinet of crystals for yourself.
Freshly fallen snow (that is, frozen water) makes crystals, as you can see
on a window pane in the winter time.
DIFFERENT FORMS OF CRYSTALS
• 148
BOOK III
CHEMISTRY
CHEMISTRY is the science that teaches how to combine two sub-
stances so as to produce a third substance different from either.
NOTE. — Many chemical experiments can be tried in the schoolroom ; but
a great number are not safe to try there, and many others require complicated
or expensive apparatus. Very many, again, are difficult to explain to children
who have had no formal teaching in chemistry. For these reasons the follow-
ing pages are devoted chiefly to simple and fundamental matters, omitting
details, which are instructive only when they are thoroughly understood.
The children bought at the druggist's small bottles of the
chemicals in the list below. Every bottle was labeled with
the right name, and they were warned not to get strong acids
on their hands or on their clothes.
A glass-stoppered bottle of sulphuric acid
" » " nitric "
" " " hydrochloric acid
" « " acetic acid (vinegar)
A cork-stoppered bottle with sulphur
" " " iron filings (or tacks)
" " " copper " (or tacks)
« K « zinc ic
" » " quicklime
" " " chalk crayons
« " " pieces of pure lead
" « " gunpowder
" " " oxyd of manganese
« « " sulphur matches
149
150 THE SCIENCES
Physical Changes ; Solutions. — " Let us take a pinch of this
common table salt," said Jack, "and put it in a tumbler of water.
What happens?"
Agnes. The water will dissolve the salt. You cannot see it
any more. It disappears.
Tom. It is there, though, in the tumbler; for the water
tastes salty when I wet my finger with it.
Jack. We can get all the salt back again if we want to, by
pouring the salted water on a flat dish and setting the dish on
a hot stove. The water will gradually go away, but our salt
will be left on the plate. The salt that you put in has not
been changed. It is the same salt. It is fit to use on the table,
and there is as much of it as there was at first. Now let us
try another experiment.
Mixtures. — "Here is some pure sulphur, and here are some
iron filings. Take a mortar and bruise the sulphur in it till it
is all in fine powder. Now mix the sulphur and the iron and
lay the mixture on this pane of glass. Can you boys tell me
of any way to separate the iron and the sulphur again, so that
you can make one little pile all sulphur and another all iron ?"
Fred. Why, I can take a magnet and pull all the iron filings
out with it and leave the sulphur.
Tom. That is one way ; but it is easier to blow on the pile,
and the light grains of sulphur will fly off and leave the heavier
iron.
Jack. That is a good way to separate the two things ; but
Fred's way is the better if you want to save the sulphur.
Well, the point is that when you mixed salt and water you
could get both of them back again — neither was altered ; and
when you mixed sulphur and iron you could get both back
again — neither was altered.
CHEMISTRY 1 5 I
•
I want to try a different kind of an experiment. I want to
mix two things together and to make a third thing different
from either one of them.
Tom. Like mixing a coat and a hat and getting a pair of
boots ?
Agnes. Oh, Tom, that is silly !
Jack. Well, it is rather funny ; and it is not quite so silly
as you think, Agnes, though of course it is absurd and impos-
sible the way Tom has said it. No ; I want to mix sulphuric
acid and iron, one a colorless liquid and the other a blackish
solid, and get some green crystals of a substance entirely
different from either of them.
Chemical Combinations. — Here Jack took some sulphuric acid
in a jar and dropped a few iron carpet tacks in it. In a little
while the tacks disappeared ; they combined with the acid, as
people say, and nothing but a colorless liquid was in the tum-
bler as before. This he poured into a flat china dish which he
put on the hot stove. In a little while all the liquid had dis-
appeared and there were left beautiful green crystals ; sulphate
of iron, or green vitriol, is the name of them.1 Then he
tried exactly the same experiment, using sulphuric acid and
copper carpet tacks, and on the plate there were left beautiful
blue crystals ; sulphate of copper, or blue vitriol, is the name of
them.
A little finely powdered quicklime combined with sulphuric
acid produces sulphate of calcium, or sulphate of lime (calcium
is another name for lime).
1 To make green vitriol take one part, by weight, of iron wire, or tacks, with two
parts of strong sulphuric acid in four parts of water and mix. If the mixture is
heated, the combination will be more rapid. Filter the resulting fluid, evaporate
it over a fire, and obtain the crystals.
152 THE SCIENCES
" Here," said Jack, "we have combined two things and in
each case made a third thing, quite unlike either of them."
Sulphuric acid + iron = sulphate of iron
" " + copper = " copper
" . " + lime = " lime l
Chemistry is the name of the science that is busy about
such combinations and the changes of one substance into
another.
"We have just made sulphate of lime," said Jack, "by com-
bining sulphuric acid and quicklime. Here is another way to
get it. This piece of chalk is made out of another acid
(a gas) combined with lime.
Carbonic acid gas + lime = carbonate of lime (chalk)
Chemical Affinity. — " It is as if the carbonic acid were a
soldier and the lime a prisoner. Sulphuric acid is a stronger
soldier than the other. If I pour diluted sulphuric acid on a
piece of chalk, the carbonic acid will fly off in gas and the sul-
phuric acid will take the lime prisoner in its turn, and we
shall have
Chalk + sulphuric acid = sulphate of lime.
" The carbonic acid has been driven off;
1 To make blue vitriol take one part, by weight, of copper wire, or tacks, with
ten parts of strong sulphuric acid (and no water). Mix and boil the acid until
gas rapidly escapes. Let it cool and carefully pour off the liquid. Add water to
what is left and evaporate it over a fire and obtain the crystals.
To make sulphate of lime take one part, by weight, of finely pulverized quick-
lime with two parts of strong sulphuric acid and four parts of water. No heat is
necessary. When the action ceases evaporate the liquid over a fire and obtain the
crystals. The teacher can repeat these experiments in the schoolroom after he
has himself performed them. Children should not undertake them.
CHEMISTRY 153
" Vinegar is an acid, too. It is called acetic acid. Take some
vinegar in the bottom of a tumbler and throw a little lump of
chalk into it. What happens ? You see the carbonic acid gas
flying off in bubbles. It leaves the lime, and the acetic acid
takes the lime prisoner.
Carbonic acid + lime = carbonate of lime (chalk)
Chalk + acetic acid = acetate of lime
"The carbonic acid has been driven off again.
" Chemists say that sulphuric acid has a stronger affinity for
(liking for, fondness for) lime than carbonic acid. It is just as
if the prisoner lime liked to be a prisoner of one acid better
than to be a prisoner of the other. Lead, for instance, likes
to combine with nitric acid better than to combine with
sulphuric acid, and so with other substances.
" Chemists study these likes and dislikes of the metals,
and make use of them. It is much easier and cheaper to get
sulphate of lime from carbonate of lime (chalk) by letting
sulphuric acid capture the lime than it is to take simple lime
and combine it directly with sulphuric acid."
Tom. What is the use of chemistry, Jack ? Is it to make
new substances cheaply ?
Jack. Partly that. The scientific use of it is to explain why
two things combine to make a third, and what is the best way
to make them do it (for there are many different ways). Its
practical use is to teach us how to make such things as gun-
powder, glass, soap, vinegar, cheese, leather, gas to burn in our
houses, bread to eat, and so forth.
Gunpowder, for instance, is a mixture of charcoal, sulphur, and
niter.1 It is a mixture, not a combination, until it is fired off.
1 Niter is a combination of potassium and nitric acid.
154 THE SCIENCES
Then it suddenly becomes a combination of all three substances,
and a great deal of gas is formed. The gas expands in the bar-
rel of the gun, and in expanding drives the bullet out. Chemists
have taught us how to make it in the best way. During our Revo-
lutionary War the powder was so poor that men were seldom killed
outright as far off as a hundred yards. Nowadays powder will
drive a bullet with force enough to kill at 2000 yards or more.
Tom. I have seen a book about Benjamin Franklin that says
he advised the Congress not to arm the soldiers in the Revolu-
tionary War with guns, but with bows and arrows, because they
could kill nearly as far off with arrows as with muskets and
because they could shoot much faster.
Jack. It sounds absurd nowadays, but it was not at all absurd
then. The muskets were better than bows and arrows, even
then, but not so very much better. The powder was especially
poor. Chemists would laugh at it nowadays.
Mary. What do chemists know about bread, Jack ? I think
the cook knows more than they do.
Jack. I have no doubt the cook can make bread better if you
give her the right kinds of flour and yeast, and so forth ; but
the chemist tells how to make the right kinds. She uses what
he has invented. There are dozens of different kinds of bread
for soldiers and sailors and invalids. They were invented by
chemists so as to be healthful, or to keep without spoiling on
long voyages. The cook could not do that. All the beautiful
dyes for silk and wool and cotton (different dyes for each kind of
stuff), all the paints, all the inks used for writing and printing,
and a thousand things of the sort were invented by chemists.
Why, chemists nowadays make indigo — by mixing carbon hydro-
gen, nitrogen, and oxygen in the right proportions — that is just
as good as the indigo that grows on the plant.
CHEMISTRY 155
Composition of the Air. — The air of the atmosphere is prin-
cipally made up of a mixture of two invisible gases called oxygen
and nitrogen. Both are invisible and so is the air^ the mixture
of the two. Water is a combination of oxygen and hydrogen.
Oxygen gas can be prepared by heating a mineral called oxyd
of manganese. It is made out of manganese combined with
oxygen. When the mineral is heated the oxygen goes off as a
gas and can be collected in a jar under water. (See Fig. 141.)
FIG. 141. PREPARATION OF OXYGEN GAS
Heat powdered oxyd of manganese in a test tube one-third full. The oxygen gas will be
driven off by the heat and can be collected over water in a jar turned upside down.
Afterwards slide a sheet of glass under the jar so as to close it and turn the jar right
side up till the gas is wanted for other experiments.
Nitrogen gas can be prepared by burning a bit of phosphorus
(not bigger than a green pea) under a glass containing air (air
is oxygen and nitrogen mixed). The phosphorus burns up all
the oxygen in the air and leaves only nitrogen.
In 100 pounds of air, 23 pounds are oxygen, and 77 pounds
are nitrogen. This is the air we breathe. If a live animal (a
mouse, for instance) is put into a glass jar that contains nitro-
gen and no oxygen, it dies. It is not the nitrogen that kills it,
but the lack of oxygen. To have life we must breathe ; to
156 THE SCIENCES
breathe there must be enough oxygen. Nitrogen helps plants
to live, but for men and animals there must be plenty of oxygen.
Combustion. — Combustion is burning. When a match burns
there is combustion. All combustion is the combination of
something with oxygen. When a match burns, the sulphur
on its head unites with the oxygen of the air about it. When
a coal fire burns, the coal unites with the oxygen of the air.
Combustion is rapid in the case of the match or of the coal, but
it is not always so quick. Sometimes it is slow. When iron
rusts, as we say, the iron of the outside layers combines with
the oxygen of the air and makes iron rust.1 Rusting is a sort of
slow fire without flame, and the iron rust that is left is the
ashes. By taking great pains we could even measure the heat
that is thrown off while the iron is rusting. A similar kind of
slow fire, without flame, takes place in our own body. Air is
breathed into our lungs and meets the blood there. The oxy-
gen of the air is carried to all parts of the body by the blood,
and our fat and food are actually burned (slowly and without
flame of course) in the body. That is the way the temperature
of the body is kept up to 98° when the air outside may be
down to zero.2
A very pretty experiment can be tried by lighting a match,
blowing it out, and then putting the glowing red end into a jar
of oxygen. The match instantly bursts into flame and burns
very brightly. Blow out the match and try the experiment
again. The match will burst into flame by itself, as it were,
so long as there is any oxygen left in the jar. Even the
diamond will burn in oxygen, though it cannot be burned in air.
1 Silver and gold do not rust, and that is why they are used for watch cases,
coins, and tableware — spoons and forks.
2 The average temperature of the healthy human body is between 98° and 99°.
OF THE
UNIVERSITY
OF
CHEMISTRY
157
Hydrogen gas can be prepared by putting some water and
a few scraps of zinc in a stoppered bottle (see Fig. 142) and by
adding hydrochloric acid, which is a combination of hydrogen
and chlorine.
Zinc + water I -f
hydrogen + chlorine I =
j water + chloride of zinc / + hydrogen
1 (these stay in the bottle) C (this goes over in the tube)
The hydrogen can be collected as the oxygen was before.
Water. — If hydrogen gas is burned in oxygen (the experi-
ment is not a safe one for the schoolroom), water is pro-
duced. Or, again, pure water can be separated by electricity
FIG. 142. PREPARATION OF HYDROGEN GAS
Put water and scraps of zinc into the stoppered bottle and add hydrochloric acid through
the straight funnel. The freed hydrogen gas will escape through the bent tube and can
be collected under water and kept for use in a jar. (Leave the jar upside down.) l
Hydrogen is one of the lightest of gases, and it is exactly suitable for the filling of balloons.
Fourteen cubic feet of hydrogen weighs only as much as one cubic foot of air. This
gas is expensive, however, and most balloons are filled with ordinary illuminating gas,
v/hich is much cheaper than hydrogen although not so good for the purpose.
into hydrogen and oxygen. These two gases, both invisible,
combine into water — a liquid; and ice — a solid — is nothing
but very cold water. That is, solid ice is made out of two gases.
1 None of these experiments are to be tried by children.
158 THE SCIENCES
Chemical Elements. — When a chemist sees a substance new
to him — a mineral, for instance — the first thing he tries to find
out is whether it is a combination of substances that he
knows already. For example, he finds that salt is made out
of chlorine (a gas) and sodium (a very light metal). Then he
tries to see if he can separate chlorine into any other two
substances ; he cannot do it, or, at any rate, chemists have not
done it so far. Neither have they separated sodium into any
simpler things. Substances that cannot be separated into
simpler substances are called elements. Here is a list of the
most familiar.
METALS
Aluminum Potassium
Calcium Quicksilver (a liquid metal)
Copper * Nickel
Gold Silver
Iron Tin
Lead Zinc
Sodium
NON-METALS
* Arsenic * Iodine
Carbon Nitrogen (a gas)
Chlorine (a gas) Oxygen (a gas)
Hydrogen (a gas) * Phosphorus
Sulphur
There are twenty-two elements named in this table. If all
known elements were included, there would be about seventy
names.
Every single thing on the earth that you can name is made
up of one, or two, or three, or more of these seventy elements;
and it is exceedingly interesting to remember that, so far as
we know, everything on the sun, the moon, and the planets is
made up in the same way.
CHEMISTRY 159
Some of the stars and some of the nebulae may have elements
unknown to our chemists, but the solar system — the sun,
the earth, and the planets — seem to be all of a piece. Ninety-
nine hundredths of all the matter in the solar system is made
up of the eighteen elements whose names are not marked with
an asterisk (*) in the table just preceding.
Chemical Compounds. — Nearly all the substances that we
handle are compounds, not elements.
Diamond is pure carbon.
The black lead of a lead pencil is nearly pure carbon.
Sugar is carbon, hydrogen, and oxygen.
Human hair is carbon, hydrogen, oxygen, nitrogen, and
sulphur.
Indigo is carbon, hydrogen, oxygen, and nitrogen.
Quinine is carbon, hydrogen, nitrogen, oxygen, and sulphur.
Air is a mixture of oxygen and nitrogen.
Water is oxygen and hydrogen.
Steel is iron, with some nickel, phosphorus, etc.
Wood is chiefly carbon, oxygen, hydrogen, and nitrogen.
Leather is chiefly carbon, oxygen, hydrogen, and nitrogen.
Human flesh is chiefly carbon, hydrogen, and oxygen, with
some sulphur, nitrogen, phosphorus, calcium, sodium, potassium,
and magnesium.
Fat is carbon, hydrogen, and oxygen.
Lean is carbon, hydrogen, oxygen, nitrogen, and sulphur.
Milk is water (oxygen and hydrogen), containing fat, etc.
(carbon, hydrogen, oxygen, nitrogen, and sulphur).
FIG. 143. DIFFERENT FORMS OF CLOUDS
a, cirrus; b, cumulus; c, stratus; d, nimbus (rain cloud).
160
BOOK IV
METEOROLOGY
THE SCIENCE' OF THE WEATHER
The Atmosphere ; the Colors of Sunset. ~ " I wonder why it
is," said Agnes, "that sunsets and sunrises are red. It is the
same sun at noon and at sunset, and the same sky ; but sunsets
are red, and the sky is never red at noon."
Jack. There are two main reasons, Agnes. In the first
place, we are looking at the sun through an air that is full of
dust ; and in the second place, the more dust you look through
the redder a thing looks that is beyond. At sunset (and sun-
rise) you see the sun through a greater thickness of air than
you do at noon.
Mary. I do not understand how that is.
Jack. Tom, see if you can explain it by a little drawing.
Tom. Is n't it like this ? When the sun is nearly overhead
at noon we see it through a less thickness of air than when it
is setting (or rising). (See Fig. 144.)
Jack. That is right. The greater the thickness of air the
more dust there is in it ; and, moreover, the more dust the
redder the sun looks.
Agnes. How do you know that, Jack ?
Jack. Well, you could try the experiment by pointing a long
wooden box filled with dusty air at the sun, and then by taking
161
162
THE SCIENCES
a box twice as long and doing the same thing. But the sim-
plest proof is this: In 1883 there was a huge volcanic erup-
tion of a mountain in Java, called Krakatoa. The whole air
for hundreds of miles round was darkened with the dust from
the volcano. The winds scattered this dust round the whole
earth, so that for two years afterwards all the sunsets in
Sun,
at noon.
•Sun, sett ing ^
FIG. 144
A person on the earth's surface at A sees the sun overhead at noon through a thickness of
air (AS), and the sun at sunset through a thickness of air (AC). AC is considerably
greater than AB.
Europe and America were very red indeed, much redder
than usual. There was an extra amount of dust in the air
at that time, and so the sunsets and sunrises were redder
than usual. It is the same thing in sand storms on deserts.
The sun looks red through them.
Fred. Suppose you should go up on a high mountain, what
then ?
METEOROLOGY 163
Jack. The higher up you go the less dust you look through.
If you are on Mount Washington in the White Mountains (5000
feet high), or on Mount Hamilton in California (4000 feet), the
sky looks very pure and blue, and if you go to the top of the
high Alps or on Pikes Peak (14,000 feet), the sky is a dark
violet color — it begins to look a little black even.
Fred. And in balloons ?
Jack. It is blacker yet. The less dust you are looking through
the whiter, or the bluer rather, the sun looks to you. If you were
quite outside the earth's atmosphere — on the moon, for instance
— the sun would not look yellow at all ; it would be bluish.
Mary. Where does the dust come from, Jack ?
Jack. Oh, from dusty plains, from smoke, the pollen of plants,
and from volcanoes. Just think of the millions of tons of coal
that are burned every winter.
Mary. Well, then, why doesn't the air become thick with
smoke by and by and stay so ?
Jack. See if you can answer that, Tom.
Tom. Is it because every rain storm carries the dust particles
down with the raindrops ? I have noticed that the air is clearer
after rain.
Jack. Yes, that is a good reason ; and a great part of the
dust falls on the ocean, too, and is lost in that way.
Twilight. — "If you will look out any evening half an hour
after sunset, you will see a faint arch in the sky in the west
that is a little brighter than the rest. That is the twilight
arch, and it is caused by the sun's rays reflected and scattered
from dust high up in our air. You had better look for it on
the next clear evening. It is easy to see.
Dust in the Atmosphere. — " One of the things that physicians
want to know is how pure the air is at any place — how free
1 64
THE SCIENCES
from dust. They put little plates of glass covered with sticky
varnish out of doors and then count the pieces of dust on
the glass with a microscope. High mountains and the snowy
arctic regions have the purest air of course ; but even there
there is a great deal more than you would think."
The Rainbow. — "Is the rainbow caused by dust, Jack? " said
Agnes ; "part of it is red."
Jack. No, Agnes ; that is different. You see all the colors
are in the rainbow, not red alone.
The white light from the sun is split up into colors by each
raindrop much as it would be by a glass prism, and then the
light is scattered by the different drops as light is scattered
FIG. 145. WHITE LIGHT ENTERING A RAINDROP is SPLIT UP
INTO COLORED LIGHTS
A white sunbeam enters a hollow raindrop, and its different colors are separated by the
water of the drop as they would be by a prism of glass. The white color is separated
into red, yellow, blue, and so forth, and is refracted by the drop down to the ground
where you are standing. (See Fig. 146.) You see the drops by these refracted colors —
red, yellow, blue — and all of these colors show in the rainbow.
METEOROLOGY
from mother-of-pearl shells. It is not very easy to explain in
simple words, but that is the main cause.
Halos. — "You have seen rainbows round the moon, haven't
you ? and halos — bright circles — round the moon ? They are
Sometimes two bows are seen. Both are formed in much the same way. The ordinary bow
is formed by sunlight that enters the top of the raindrops and is refracted to the eye.
The secondary bow is formed by sunlight that enters the bottom of the raindrops.
(Examine the picture carefully.) SSS'S' are rays from the sun ; HH' is the horizon.
The center of the bow is always exactly opposite to the sun from where you stand.
caused by little prisms of ice floating high up in the atmosphere,
which scatter the moonlight in a regular way."
Fog and Clouds. — "The air is full of dust that we can see,"
said Jack, " and it is full of the vapor of water that we cannot
1 66
THE SCIENCES
FIG. 147. A COMPLETE SOLAR HALO (parhelion, sundog)
Sometimes the complete halo is seen as in the picture, but more often only parts of it.
These halos are caused by light refracted from small prisms of ice in our atmosphere.
see, too. When I put a pan of water out of doors, Agnes,
what becomes of the water ? "
Agnes. It disappears somehow, if there is not much of it.
I don't know where it goes.
Tom. It evaporates ; it rises up into the air like a gas.
I suppose it is a gas.
Jack. Yes, it is a gas, like invisible steam. Real steam is
invisible, and water vapor is invisible. When the water vapor
in the air turns into visible water what do you see ?
METEOROLOGY 167
Agnes. Fogs and clouds and mist.
Mary. Yes, and rain and dew.
Jack. Mist and fog are made of millions and millions of
little drops of water.
Agnes. Why don't they fall down in rain, then, Jack ?
Water is heavy.
Jack. The drops are hollow, and they are very small and they
float in the air just as soap bubbles do.
Dew. — " When you breathe on a cold windowpane the
invisible water vapor in your breath," said Jack, " condenses on
the pane and makes a mist which is just like the dew that falls
at night. Take a tumbler of ice water and set it in a warm
room and you will see dew form on the outside of the tumbler.
The cold tumbler condenses the invisible water vapor just as
the cold water of a pond condenses the vapor of the air above
it into a fog or mist. The reason is because a cubic foot of
warm air can hold more water vapor than a cubic foot of cold
air. When you cool air, no matter how you do it, you squeeze
some of its water vapor out of it."
Tom. When the sun rises the fogs over ponds vanish. Is
that because all the air gets warmer and can hold more
vapor ?
Jack. Exactly so, and when all the air is warm you have no
clouds either. Clouds are a sure sign that the air where they
are is colder than the other air in the neighborhood.
Agnes. How high are the clouds, Jack ?
Jack. Oh, they are at very different heights. Why, don't
you know, Agnes, that you are sometimes in the very midst of
a rain cloud? The cirrus clouds (see Fig. 143) are sometimes
ten miles high, but usually less. They are probably made of
little ice crystals, for the air at that height is very cold indeed.
1 68 THE SCIENCES
The cumulus clouds are a mile high, or so. The stratus
clouds are the lowest.
Tom. If clouds are made of hollow water drops like soap
bubbles floating in the air, how is it that we ever have rain ?
Why don't the bubbles always float?
Jack. You have seen two soap bubbles come together and
burst? They become nothing but two heavy drops of water, or
even one drop, and the water falls. That is rain.
Rain. — " A little sphere of water that is not hollow is a good
deal heavier than the air, and a hollow sphere of water is often
lighter than air. There are millions of drops in a cloud, and
when they are blown about by winds they come into collision
and fall in rain.
Size of Raindrops. — "The next time it rains try to measure
the diameter of the raindrops. It is not very easy, but you
can find some way to do it. I leave it to you boys to invent a
way. The raindrops of a heavy pattering summer shower are
large — about a tenth of an inch in diameter. Fine rain is
made of drops one twentieth to one fiftieth of an inch in size."
Hail and Snow and Sleet. — "I suppose hail is nothing but
frozen rain," said Mary.
Agnes. And snow and sleet, too, for that matter.
Tom. Sleet is nothing but snow that is driven about by the
wind. In calm weather you get the little snow crystals ; but
when the wind blows, a dozen of them are blown into one and
they come down in little lumps of ice ; sleet, that is.
Jack. Or else the snow falls through a layer of rather warmer
air and is partly melted.
The Snow Line. — "The higher up you go," said Jack, "the
colder is the air, and by and by you come to a height above
which there is never rain, only snow. That is the line of
METEOROLOGY
169
perpetual snow. In our Rocky Mountains the snow line is about
1 3,000 feet or so. Above that height the snow never melts at
all, and you have snow mountains. In Alaska the snow line is
nearly at the level of the sea. That is one reason why Alaska
scenery is so impressive. A low snow line makes fine mountains.
Uses of Snow. — " If no snow fell in the winter time, seeds
would have a hard time to grow, as the ground would be frozen
FIG. 148. SNOW CRYSTALS
Notice that all snow crystals are six sided.
stiff ; but the snow fall covers it up like a blanket. The ground
is not frozen so very deep, and the seeds have a chance.
Irrigation. — " Snow has another great use. When it melts
in the spring the water can be used for irrigating arid lands.
We in the United States let our snow go mostly to waste.
We ought to save it in great reservoirs in the western and
southwestern states and let it out during the summer when it
is sadly needed. Nevada and Arizona and other states could
be made into gardens if people would take a little trouble."
Tom. That is something for the government to do. The
government must build the reservoirs, and the people will do
the rest.
THE SCIENCES
Frost. — " I suppose frost is nothing but frozen dew," said
Mary.
Jack. It is not quite that, Mary, though it looks so. The
dew does not fall first as water and then freeze ; but it really is
water vapor frozen in the air, and
it falls in fine spikelets of ice and
covers everything.
Rainfall. — " How much rain
falls in a year, Jack?" said Fred.
Jack. Fred, that is like asking
how long the nose of a man is.
Why, in some parts of the world
almost no rain falls — on the
deserts of Sahara and of Arizona,
for instance. The average rainfall
of the whole world is about thirty-
three inches in each year ; the
water would be about a yard deep
at the end of a year if all of it
The arrow points to the direction from were Saved if it did not get into
the soil. But there is an enormous
difference in rainfall at different
places. On the arid plains of
Arizona there are often less than
two inches a year. In some parts
of the Himalaya Mountains forty
once for all, so as to point north, feet of rain fall in a year,
east, south, west. Rainfall and Crops. — " Wheat
will not grow by itself where the rainfall is less than about
eighteen inches a year, unless there are plenty of fogs. In the
arid (dry) regions the farmers have to irrigate their crops."
FIG. 149. ONE FORM OF
WIND VANE
which the wind is coming. If you
should move the arrow so as to point
in any other direction and then let
go of it, you can see that the pressure
of the wind on the tail of the vane
would soon bring it back. A wind
vane put into a rapid stream of water
METEOROLOGY
171
Winds. — "A wind," said Jack, "is a current of air moving
near the surface of the earth. How can you tell which way
the. wind blows ? "
Mary. A wind vane will do that. (See Fig. 149.)
Force of the Wind. — "Here is a table," said Jack, "that
scientific men and sailors use to express the velocity of the
wind, or else its pressure on a square foot.
SCALE
DESCRIPTION
VELOCITY IN
MILES PER HOUR
PRESSURE IN POUNDS
PER SQUARE FOOT
O
Calm
0
O
I
Very light breeze
2
3
T017
2
Gentle breeze
7 or less
T2ijV or less
3
Fresh breeze
ii
T6o4o
4
Strong wind
1 8 or more
IT^ or more
5
High wind
27
3i6oV
6
Gale
36
6i&
7
Strong gale
45
10
8
Violent gale
58
17
9
Hurricane
76
29
10
Most violent hurricane
95
45
" You can describe a wind by using this little table. A wind
that blows about eighteen miles an hour — one that would carry
a feather or a little toy balloon about eighteen miles in sixty
minutes — is called/<?z/r (4). (See the first column of the table.)
Such a wind presses on every square foot of a -house nearly two
pounds. Hurricanes travel at the rate of seventy-six miles an
hour — faster than express trains — and press on every square
foot of houses nearly thirty pounds."
Agnes. And the houses are often blown down, too.
172 THE SCIENCES
Jack. They are n't built to resist such winds. We very seldom
have them in our part of the world, I 'm thankful to say.
Causes of the Winds. — " Whenever the surface of the earth
is warm," said Jack, "the air over that part rises and other air
N.POLE
FIG. 150. A MAP OF THE GENERAL WINDS OF THE EARTH
The arrows show their general direction. The dark spots mark places where there is
much rain. These winds blow over large regions of the earth. There are particular
winds over smaller regions ; but these are, of course, not shown on the map.
from a coWer place flows in to take its place. If you boys
build a bonfire, the air rises and the smoke rises with it.
Other air comes in to take its place, and if your fire was big
enough — if a city were burning — it would create a really
FIG. 151. DIAGRAM TO SHOW HOW WINDS ARISE
If any region (D) is warmer than near-by regions (C,C), the air over D is warmed and rises.
As it rises it cools, and the air near B,B moves downwards and inwards to take its place.
The air over a bonfire moves in this way, and we have a little local wind. The air over
a large part of the Mississippi valley may move in the same way for like reasons, and
then we have winds covering several states.
I. In January
II. In July
FIG 152. WINDS OF THE ATLANTIC OCEAN
The arrows show which way the winds blow. Charts like these are made for every ocean
and for each month, and sailing ships go by tracks where the winds are favorable.
173
174 THE SCIENCES
strong wind. The sun warms the hot regions of the earth,
near the equator, more than the arctic regions ; the hot air rises
and the cold arctic air flows southwards to take its place."
Tom. You have to add that the earth is turning round all
the time and so the winds do not flow straight to the equator
but in spirals.
Jack. The sun is warming the earth all day — land and
water, mountains and valleys ; and all night the heat from the
warmed places is rising up.
Land and Sea Breezes. — " The land gets warm more quickly
than the sea, so that all day the breeze blows from sea to land.
FIG. 153. THE SUN (S) SHINING ON THE EARTH ILLUMINATING AND
HEATING THE HEMISPHERE TURNED TOWARDS HIM
It is daytime in that hemisphere. As the earth revolves on its axis (NS) every twenty-four
hours both hemispheres are lighted and heated in turn.
At night the land gets cool sooner than the sea, so that all
night the breeze blows from land to sea. The next time you
go to the seashore see if this is not true. Of course there will
be other winds, too ; but every hot day you will notice the sea
breeze that springs up in the morning and blows till nightfall."
Weather. — " Weather depends upon a great many things,"
said Jack. " See if you children can tell me some of them."
METEOROLOGY 1 75
Agnes. Well, we have warm days and cooler nights because
the earth turns round. We are in the sun's rays in the day-
time and out of them at night. (See Fig. 153.)
Mary. And we have cold winters and warm summers because
— I don't believe I quite know why. Is it because the earth
is nearer to the sun in summer ?
Jack. No, the earth is a little nearer to the sun in Decem-
ber and January than it is in June and July — a little, though
FIG. 154. THE EARTH IN ITS PATH ROUND THE SUN
The earth is at A in December, at B in March, at C in June, at D in September. NS is
the earth's axis, and N is the earth's north pole (in all four positions). At A (December)
the arctic regions are dark. As the earth turns round on its axis a person at N is not
brought into the light. In the northern hemisphere in March the days are shorter
than the nights. As the earth turns a person anywhere in the northern hemisphere
is in the lighted half of the earth for a shorter time than in the dark. But in June
(C) a person in the northern hemisphere is longer in the light than in the dark — longer
in the region heated by the sun.
not much ; there is a different reason, Mary. (See Fig. 1 54.)
Storms. — " Our weather depends on the earth's turning on
its axis then," said Jack, " and on its motion round the sun.
Those causes are working all the time. Then there are storms that
1 76
THE SCIENCES
travel over the whole country from west to east l and others that
come up from the Gulf of Mexico along the Gulf Stream. These
storms reach us, and our weather on Thursday, we may say, depends
upon the weather some one else had on Monday. The Weather
Bureau in Washington gets reports of all the storms in the whole
country by telegraph several times a day and makes up a pre-
diction about the weather we are going to have. You see the
Weather Bureau predictions in the newspaper every day.2
Storm and Other Signals. — "Whenever you see a red flag with
a black center expect a storm. The triangular pennants tell
which way the wind will blow. (See the titles to the cuts.) A
N.E.
S.E.
N.W.
s.w.
FIG. 155. UNITED STATES WEATHER BUREAU STORM SIGNALS
square white flag predicts fair weather ; a square blue flag pre-
dicts rain or snow ; a flag half white and half blue predicts
local rain or snow storms. A square white flag with a black
center indicates that a cold wave is to arrive. If the black
pennant (No. 4) is hoisted above any flag, it means that the
weather is going to be warmer. If it is hoisted below any flag,
it means that the weather is going to be colder.3
1 See Book II (Physics), page 87. 2 Ibid., page 88.
3 These flags are displayed in all towns where there is an observing station of
the United States Weather Bureau, and children who live in such towns should
learn them by heart.
FIG. 156. HURRICANE SIGNAL
Great Lakes
On the coast
Easterly winds Westerly winds
FIG. 157. INFORMATION SIGNALS
On the Great Lakes a red pennant denotes easterly, a white pennant westerly, winds.
A red pennant at seacoast stations indicates a storm.
No. i, a square
white flag
Fair weather
No. 2, a square
blue flag
Rain or snow
No. 3, a square flag,
half white, half blue
Local rain or snow
No. 4, a triangular
black pennant
No. 5, a white flag
with a black center
Temperature Cold wave
FIG. 158. WEATHER SIGNALS
By a cold wave is meant a fall of temperature of at least 20° in twenty-four hours.
N.B. — In all the foregoing pictures a red flag is marked by vertical lines; a blue flag
by horizontal lines.
177
1 78 THE SCIENCES
" In some regions the Weather Bureau signals are given by
steam whistles. A long blast is sounded to attract attention,
then follow the signals for weather, and next those for temper-
ature. The signals for weather are long blasts ; those for
temperature are shorter.
" One long blast means ' expect fair weather.'
Two long blasts mean ' expect rain or snow.'
Three long blasts mean « expect local rains or snows.'
" One short blast means ' expect lower temperature.'
Two short blasts mean ' expect higher temperature.'
Three short blasts mean « expect a cold wave.'
" You have no idea how useful these weather predictions
are nor how many people read them and follow their indica-
tions. Think, about it a moment. Suppose there is a cold
wave far up in Winnipeg moving eastward. Often it makes
cold north winds in Texas — a * norther ' — and northers are
destructive to crops and to cattle. The whole of the United
States from the Mississippi River eastward to Maine and south-
ward to Florida is going to feel it, and every one is warned to
get ready. The railway people are all ready with snowplows ;
stock raisers herd their cattle into shelters and provide food for
them ; people who are shipping fruit, etc., on trains take warning
and wait ; orange growers in Florida light fires to protect their
trees ; ice companies prepare to get in their crop of ice ; house-
holders see that there is plenty of coal for their furnaces ; fire-
men take extra precautions about their hydrants. There are
millions of people who are affected in thousands of ways. The
government Weather Bureau warns them all, and every man
must look out for himself and for his business. That is the
way a government like ours should be, I think. It ought to do
friijffUfl
[pf*|ilr
r -w HE.?! --
S- 2^ 3* 3
i||i
^33"
i79
i8o
THE SCIENCES
the things that no single man can do — like this weather pre-
diction — and leave every man to take care of his own affairs
afterwards."
Lightning. — " The clouds in storms are electrified," said Jack,
"and lightning is electric sparks on a large scale exchanged
FIG. 160. THUNDER SQUALLS
A part of the preceding picture (within the space marked d b q in Fig. 159) is drawn on a
larger scale here. The first picture shows the thunderstorm as it moves across the
country at the rate of twenty to fifty miles an hour. This picture shows the thunder
squall as it reaches any particular place. The arrows indicate how the different winds
are blowing. If the two pictures are carefully studied, and especially if the reader will
compare them with the summer thunderstorms seen at his own home, they will explain
most of the appearances he sees.
between one cloud and another. Thunder is the crackle of the
spark echoed among the clouds and mountains. Sheet light-
ning is usually the reflection of distant forked lightning from
the surface of high clouds."
METEOROLOGY
181
Agnes. Thunder is the echo that we hear, and sheet lightning
is a kind of echo that we see.
Tom. How fast does lightning travel, Jack ?
Jack. Exactly as fast as light does — at the rate of 186,000
miles in a second — so that the duration of a lightning flash is
only a very small fraction of
a second. After the flash
comes the thunder. Do you
know how to tell how far
away a thunderstorm is?
Distance of a Thunderstorm
from the Observer. -- Tom.
You notice the flash of light-
ning and then count the num-
ber of seconds till you hear
the thunder ; I know that
much, but I forget the rest.
Jack. It 's like this. The
lightning flash and the thun-
der occur in the storm at
exactly the same moment.
You are far off from it. You see the flash the moment it occurs
because light travels so fast ; but as sound travels only 1 100 feet
in a second, it takes time for the sound of the thunder to reach
you. You have to multiply the number of seconds between
the time of the flash and the time of the thunder by noo,
and you '11 have the distance of the storm in feet.
FIG. 161. LIGHTNING FLASHES
The sound of the thunder is The storm is
heard after the flash by : distant :
Two seconds.
Three "
2200 feet.
3300 «
The sound of the thunder is
heard after the flash by :
Four seconds.
Five "
The storm is
distant :
4400 feet.
5500 " (about a mile).
It takes sound about five seconds to travel a mile.
1 82 THE SCIENCES
Lightning Rods. — " Some people say," said Fred, "that
lightning rods aren't of any use. How is it, Jack?"
Jack. Well, no lightning rods are so good that you can be
certain your house will not be struck. The government takes
the greatest pains to protect its powder magazines, but once in
a while they are struck. Still, a lightning rod really does
protect. It should be a good-sized copper rod that goes deep
down into the ground — far enough to reach moist earth—
and it should extend ten or twelve feet above the roof, and end
in a sharp point. Three or four good rods will protect an
ordinary house almost always. It is better to have them ; you
are safer.
i84
BOOK V
PHYSIOGRAPHY
THE SCIENCE OF THE LAND AND OF THE SEA
The Oceans. — The children were looking at a large globe
and talking about it. First they turned it so as to show the
water hemisphere, then so as to show the land hemisphere,
and then so as to show the two poles — arctic and antarctic.
(See the pictures, Figs. 6 and 7.)
Mary. I never quite understood before how much sea there
was and how very little land.
Tom. The books say that three quarters of the surface of
the earth are water, and this globe makes you believe it.
" You 'd believe it, if you ever made a long voyage by sea,"
said Tom's father. " Once I sailed straight west for a whole
month in the Pacific, from Peru to Tahiti, and at the end of the
month I was only halfway across to Australia. I knew all about
maps and globes, but I never realized how large the Pacific was
until that time. I 've had a respect for the mere size of it
ever since."
Tom. The Atlantic is large, too, but we don't think of
it as so very large because the steamers to England are
so very swift. They cross from New York to Liverpool in
six days.
185
i86
THE SCIENCES
Jack. There 's another thing. The Atlantic has cables across
it in many places and we read the telegrams from Europe in
the newspapers every day. That makes England seem near.
Mary. How deep is the sea, Jack ?
Jack. Oh, it is of very different depths in different places.
The Atlantic Ocean, on the average, is a little over two miles,
and the Pacific is deeper — about three miles. But you know
there are places where the sea is much
deeper — nearly six miles. Near our new
island of Guam in the Pacific there is a
spot 31,600 feet deep.
Fred. The highest mountains are about
five miles ; the sea is as deep as the moun-
tains are high. That is a way to remember.
Jack. Yes ; but you must remember,
too, that there is very much more area of
deep sea than of mountain regions, so you
could not fill up the sea by putting the
mountains in it. You would have to
borrow some land from another planet
to fill it up.
Depth of the Sea — " I suppose they
find the depth of the sea by sounding with
a weight on the end of a rope, don't they ?
— just as we do in a pond," said Fred.
Tom. They do not use rope ; they use
piano wire ; the rope would float — or at
least it would not sink as quickly as wire does.
Jack. Yes, they use miles of fine piano wire and a heavy
weight that drops off when it strikes the bottom. That makes
it easy to reel the wire in again.
FIG. 163. A DEEP-
SEA DREDGE
It is a large bag or scoop
for bringing up parts of
the ocean floor. Little
shells and so forth are
caught by the tassels.
PHYSIOGRAPHY
I87
Agnes. What is at the bottom of
the sea, Jack ?
Jack. Anywhere near the land
the sea bottom is covered with mud.
The rivers and the rains carry the
soil of the land far out to sea and
the ocean floor is covered with it.
Little pieces of the rocks of the
land are carried out to sea, and you
find the same rocks in this mud that
we have on the land. The Missis-
sippi or the Amazon river carries
its mud out to sea for hundreds of
miles. When you get very far from
land the dredge brings up a differ-
ent kind of rock. The little pieces
of rock in the sea bottom very far
from land have sharp angles. They
have not been rolled about by surf
and their corners are sharp like
crystals.
Besides these rocks the dredge
brings up the shells of little creatures
that live near the surface of the sea.
When they die their shells sink to
the bottom, and there are millions
and millions of them, so that a good
part of the ocean floor is covered
with a kind of ooze — they call it —
mostly made of these shells. Then
we find the bones of fishes, the teeth
|A«
«
«_0
n£M4
FIG. 164
A bit of the ocean floor from a region
within a few hundred miles of the
land. Notice that the fragments of
rock are rounded, which shows that
they have been washed by waves.
%&.»mm$
. ^ n v M. .jf^3 o /^ «K ' i
FIG. 165
A bit of the red clay of the floor of
the deep ocean far from shore.
Notice that the fragments of the
rock have sharp angles, which
proves that they have not been
rolled about by surf and do not
come from the washings of the
continents.
1 88
THE SCIENCES
of sharks, and things of that kind imbedded in the clay ; and
small pieces of ivory, too, with pieces of meteors which have
fallen into the sea. You see the ocean floor is made up of at
least three different things — the washings of the continents,
the red clay, and the ooze of shells and the like.
Tom. Then, of course, the
ocean is full of fish.
Jack. There are plenty of
fish near the surface. They
live where their food is, and
most of it is near the surface.
There are some fish in the
greatest depths, too, but the
living things there are mostly
crabs, starfish, shellfish, and
so forth. You know the sur-
face of the water is crowded
with jellyfish of all kinds.
The jellyfish are phosphor-
escent. They glow when they
are disturbed just as a sulphur
FIG. 1 66. A FLOATING JELLYFISH
match glows when you rub it
All the light at the bottom of
The sunlight does not go very
with your fingers in the dark.
the sea comes from jellyfish.
deep down.
Tom. How do you know there is any light at the bottom of
the sea, then ?
Jack. Because the deep-sea fish have eyes. If there were
no light whatever, all the fish would, in time, lose their eyes,
just as the fish in the Mammoth Cave have ; but many of the
deep-sea fish have eyes.
PHYSIOGRAPHY
189
Fred. There are fish — whales and so forth — near the sur-
face of the sea ; and there are starfish and crabs and shellfish
at the bottom. What is in between?
Jack. Almost nothing, Fred; just dark, quiet, cold water,
with no seaweed, no plants, no animals, and no fish. There is
no life there to speak of ; no light and no motion, for the
waves that we see on the surface do not go down very deep
either. The middle depths of the ocean are the most dreary
FIG.. 167. A DEEP-SEA FISH WITH EYES
FIG. 1 68. A DEEP-SEA SPIRULA, A KIND OF CUTTLEFISH
The real fish is just twice the size of the picture.
and the most monotonous places you can conceive of. The
arctic regions are gay compared to them !
Icebergs. — " How do you children suppose an iceberg is
formed ? " said Jack.
Mary. I suppose the sea water freezes and makes it.
Fred. That will not do, Mary. Don't you see that water
could not freeze high up in the air like that ?
Jack. Do any of you know ?
Tom. Icebergs break off from the ends of glaciers, they say.
FIG. 169. A FLOATING ICEBERG
Ice is a little lighter than water and it floats, therefore. About one seventh of an
iceberg' shows above the surface ; six sevenths are below.
FIG. 170. ICEBERGS BREAKING OFF FROM THE END OF MUIR GLACIER
IN ALASKA
190
PHYSIOGRAPHY
IQI
Glaciers. — "And glaciers are rivers of ice flowing slowly
down from the mountains," said Jack.
Agnes. Do they flow like rivers ?
Jack. They flow somewhat as rivers do ; yes, only very
much slower — a few hundred feet a year, for instance ; but
they often keep on till they reach the sea (see Fig. 170), and
there huge pieces break
off and form bergs.
Tom. Then the water
of icebergs is not salt ; it
is fresh.
Jack. Yes, it is rain
water that has fallen as
snow, you see.
Mary. But the sea
water does freeze, Jack,
does n't it ?
Jack. Certainly ; and makes the great ice fields that you have
read about.
Some of these fields are very thick, especially when they
have been packed together by tides and currents. When the
ice first freezes it is smooth, of course, but after it has been
packed it is horribly rough. It is often entirely too rough to
travel over, and that is the reason why it is so hard to get
to the north pole.
Tom. You go as far as you can in your ship, and then you
take dog sledges, and finally you come to ice too rough to travel
over. Is that it?
Jack. Yes ; the ice blocks are as big as houses and are
all piled together every which way, and a day's journey is often
only three or four miles.
FIG. 171. A BOWLDER OF ROCK THAT WAS
ONCE ON THE TOP OF A GLACIER
The glacier brought it from far away, and the rock
was left here when the glacier melted.
FIG. 172. A ROCK ON THE COAST OF MAINE THAT WAS ONCE UNDER A
GLACIER AND HAS BEEN WORN SMOOTH BY THE ICE
FIG. 173. THE BEGINNING OF A GLACIER HIGH UP IN THE MOUNTAINS
The snow of the peaks slides into and down the valleys and becomes ice by the pressure of the
tightly packed mass. If you pack a snowball very tight, it becomes nearly pure ice.
192
PHYSIOGRAPHY
193
Rivers and Streams. — " Did you children ever think of how
a drop of rain water gets from the mountains into the sea?"
said Jack. " It is worth while. Suppose you begin by thinking
of what happens when the rain falls on a plowed field. The
FIG. 174. A SHIP FROZEN IN AN ICE FIELD
next time there is a rain you must look carefully and see
exactly what takes place."
Underground Water. — " Part of the water soaks into the
ground, but most of it runs off in little streams," said Tom.
Jack. What becomes of the water that soaks into the ground,
Agnes ?
Agnes. Why, a good deal of it stays there. If you dig down,
the ground is always moist.
Jack. And when corn is planted in the field it gets a good
part of its water from the earth. You know there is a great deal
of water in Indian corn — in the ears and in the stalks ; so
some of last month's rain will be in the sweet corn you will eat
194
THE SCIENCES
next August. Now, what becomes of the water that does not
get into the ground but runs off ?
Fred. Some of it gets into the air as moisture and makes
fog and clouds.
Agnes. Yes, and those clouds may bring rain again.
Mary. But not on our field ; they will be far away the next
time it rains.
Fred. And most of the water runs off in little streams and
by and by gets into the brook.
Mary. And the brook carries it off to the river, and the
river to another river, and so on, till it gets to the sea.
FIG. 175.
LITTLE STREAMLETS OF RAIN WATER RUNNING OFF
PLOWED GROUND
Jack. Does the water ever flow uphill ?
Agnes. No, of course not.
Jack. Then it is downhill all the way from our field to the
sea. If you followed a drop of water in the brook, it would
always be traveling downhill, but it would not go straight.
Fred. I should think not ! No rivers are straight.
Jack. A river in Asia Minor, called the Maeander, was so full
of bends that it gave a name to that habit of rivers ; we call
them meandering rivers, and the bends meanders.
PHYSIOGRAPHY
195
Agnes. Can you say that rivers have habits, Jack ?
Jack. Why certainly, Agnes ; a habit is a custom, that is all.
It is a habit of rivers to flow downhill, to be crooked, to carry
little particles of sand and soil in their streams, to roll pebbles
FIG. 176. A MEANDERING BROOK
and stones along their beds, and so on ; it is a habit of rivers
to work — they are industrious.
Agnes. Oh, Jack — industrious !
Tom. Well, they are. They carry no end of soil and rocks
along in their course, and they work day and night, too.
Jack. You might almost think a river was alive if you
counted up all the different things it did, and you might
almost say a river had a purpose in life, just as a man has.
196
THE SCIENCES
(See the picture on page 184.)
NORTH CAROLINA __, /
Take the Colorado River, for instance ; its purpose is to get
to the sea in the best way possible, and it has industriously cut
a way through rocks till its canon is nearly a mile deep.
Some rivers actually steal.
Agnes. Oh, Jack ! what do
they steal ?
Jack. Well, for one thing,
they steal water from other
rivers and carry it away them-
selves. For instance, the
Savannah River has stolen a
lot of branches from the Chat-
tahoochee. (See Fig. 177.)
Then rivers are young and
middle aged and old, too ;
FIG. 177 torrents first, and then
The Chattahoochee River formerly owned the Steady-going, and by and by
waters quite up to the border of North Caro- Very mild and gentle J and
Una that now flow in the Chateuea and Tuea- • i , ,-\
you might say they are angry
loo basins into the Savannah River and so to J •> & J
the sea. It is quite likely that the Oconee when they are in flood. The
River will capture more of the Chattahoochee Yellow River in China has
waters in times to come.
drowned a million persons in
a year (1887); the Ganges is nearly as bad; and our own
Mississippi has terrible floods.
Fred. Anyhow they don't mean any harm, and they are
industrious ; they do the best they know how.
Jack. Industrious they certainly are. In the first place, the
water dissolves a great deal of rocky soil (just as water dissolves
sugar) and carries it along to a new place. Then a river carries
a great deal of sand and mud in its stream, and drops that, too,
when it can carry it no longer.
PHYSIOGRAPHY
197
Agnes. When does it drop the mud, Jack; when it gets tired ?
Jack. You might say so. While the river is flowing fast it
can carry a great deal of mud and sand ; as soon as it begins
to move slower some of this mud falls to the bottom.
Tom. If you want to get dirt out of a wash basin, you have
FIG. 178. THE TOWN OF EMS (PRUSSIA) BUILT ON THE NARROW
FLOOD PLAIN OF THE LAHN RIVER
to make the water move quickly. If it moves slowly, the dirt
begins to settle.
Jack. They say that the Mississippi carries mud enough every
year to make a range of hills a mile long, half a mile wide at
the bottom, and five hundred feet high; and the Nile brings
huge quantities of soil into lower Egypt. The flood plains of
such rivers are the most fertile parts of the world.
I98
PHYSIOGRAPHY
199
The Land. — "When people talk about the sea," said Jack,
" they speak about it as if it were always changing — they call it
* the restless sea ' ; and when they talk about the land they
speak as if the land never changed at all — * the everlasting
hills,' they say. Of course it is true that the hills and moun-
tains do not change much in your lifetime or in mine, and of
FIG. 180. A MOUNTAIN RANGE IN CALIFORNIA
The summits are covered with snow which, melting, forms the brooks and rivers ; rains model
the ravines. Every feature of this landscape has been formed by running water.
course it 's true that if you are at the seashore the waves are
never still for a moment ; but really and truly the land changes
more than the sea does, if you take the whole history of it.
The surface of the land is changing all the time."
Mary. I don't quite see how, Jack. I have been here all
summer. What changes have there been?
200 THE SCIENCES
Jack. You have seen the brook to-day. What color was the
water, Mary ?
Mary. Why, it was clear.
Jack. And yesterday, when it was raining so hard, what color
was it ?
Mary. It was muddy. Yes, I see; the rain from the ground
carried off some of the soil to the brook. It was not much,
though.
Jack. No, not much. But suppose you have a hundred
showers every year; in a hundred years there will be ten thou-
sand showers, and every shower will do some work and will carry
away some soil. In a hundred centuries there will be a million
FIG. 181. SAND MOUNTAINS (DUNES) IN THE RAINLESS DESERT OF
THE SAHARA
They are modeled by the wind. Along many seacoasts such dunes are to be found.
showers ; every one of them will do some work, and all of
them together will do a great deal. They will sculpture
mountains and level continents.
Mountains. — "Nearly all the mountains of the globe are
modeled by water. Wherever there is frost, too, great pieces
of rock break off and fall. The shapes of mountains in arid
countries like Arizona are modeled by the winds ; and then,
PHYSIOGRAPHY
2OI
you know, there are volcanoes, and they change their shape,
too. Everywhere the form of the land is changing."
Tom. If all this went on long enough, the earth would be flat.
Agnes. You might say more than that, Tom. You might
say that the rains would
make all the mountains flat,
and that the rivers would
carry everything to the sea.
Why does n't that happen,
Jack? Why isn't all the
land carried into the ocean ?
Why is n't the whole world
flat?
Jack. If you gave it time
enough, it would be, Agnes ;
but it would take a great
deal of time ! The books
say that the surface of a
whole continent might be
lowered an inch or so in a
century. North America
is, on the average, about
2000 feet (that is 24,000 inches) above the ocean, so you
see that it would take at least 24,000 centuries to level it —
at least 2,400,000 years. But long before that time other
things would happen to prevent. Some of the continents
are slowly rising out of the sea all the time, and it is the
elevation of whole countries that makes up for the washing
away of the land.
Tom. I never heard of that before, and I don't understand
it. What countries are rising now, for instance ?
FIG. 182. A CLIFF OF HARD ROCK
The sloping bank at its foot is made up of rock
that has fallen from the cliff.
2O2
THE SCIENCES
Jack. Well — Sweden is rising, slowly rising, two or three feet
in a century. And the northern coast of California is rising, and
many other coasts and regions, too. They say the coasts of
Alaska and of Peru have been raised more than a thousand feet.
Agnes. Aren't some regions sinking?
Jack. Yes, of course. If one region rises, others will sink.
They say the coasts of Massachusetts and of New Jersey are
now sinking about
two feet in a hundred
years; and there are
plenty of other places,
too, but I don't re-
member them now.
Agnes. But, Jack,
how can people pos-
sibly know that a
country is sinking, if
it moves as slowly as
that ? Two feet in
a hundred years —
why, how can they
tell ?
Jack. Well, it is not easy, but there are ways to do it. If
the sinking keeps on long enough, it is not hard to observe it.
For instance, there is a part of the German Ocean not far from
the mouth of the Thames where the whole coast has sunk.
They say you can even see the remains of buildings at the
bottom of the sea when the water is clear. Those were
English cities, and the land has sunk within a few hundred
years. We know the history of it, I believe. There is a very
good way to tell, though, what land has risen out of the ocean.
FIG. 183. FOSSIL SHELLS IMBEDDED
IN LIMESTONE
PHYSIOGRAPHY
203
Tom. What way, Jack ?
Jack. By seashells - — fossil seashells — found on land, even on
mountain tops. Suppose you should find, not one, but thousands
and thousands of seashells on the very top of a hill ; suppose that
the whole rock should be made of them. Well, would n't that
prove that that particular hill had once been under the sea ?
Tom. Yes, you could prove it that way.
Jack. Now suppose that all the hills for hundreds of miles
around were made of shells — of shells of animals that we know
FIG. 184. THE UPLAND OF NEW ENGLAND WITH MOUNT MONADNOCK
IN THE DISTANCE
cannot live on land, but absolutely must live in salt water —
would not that prove that the region had been under salt water
long ago ?
Tom. Yes, of course. Are there many regions like that?
Jack. Hundreds of them. And in some of them every bit
of the rock is filled with seashells. You know what sandstone
is, of course ?
204
THE SCIENCES
Tom. Yes, there is a lot of it here. Some of our hills are
all sandstone.
Jack. Well, sandstone is nothing but little grains of sand
cemented together to make rock; and many sandstones have
been formed under water — under salt water. A large river,
let us say, brings sand from the shore, and drops the sand
FIG. 185. A MOUNTAIN IN UTAH FILLED WITH RAVINES, EVERY ONE OF
WHICH HAS BEEN MODELED BY RUNNING WATER
grains on the sea bottom. In time the grains are cemented
together, and then you have layers of sandstone. By and by
something like a great slow earthquake happens, and the sand-
stone is lifted above the sea. It may be lifted, in time, very
high. Then you have layers of sandstone on land. The rains
come and wear it into ravines, and parts of it crack and fall, and
some of it is covered with soil by the washings of other rivers,
PHYSIOGRAPHY
205
and by and by trees and grass grow there, and you have a
country like the one we live in.
The earth is not solid down to its center, you know. We
live on the outside crust of it. That is solid, of course, and
it is about a hundred miles thick. Inside of that crust great
parts of the globe are red-hot rocks, like melted lava. It is as
if the continents and the oceans were resting on an inside globe
of melted rock. The heaviest parts are always pressing down,
and the crust is always being strained
and bent and cracked. Some parts
of the earth are sinking very slowly,
and other parts are slowly rising.
Wherever the crust moves you have
cracks, and when the cracks are large
you have long valleys and mountain
ridges. (See the picture, Fig. 188.)
Stratified Rocks. — " Are all moun-
tains made in that way, Jack ? " said
Tom.
Jack. Not exactly in that way, Tom.
You see it is like this : The crust of
the earth sometimes breaks one way,
and you have mountains like those in
the picture (Fig. 188) ; and sometimes
it does not break at all, but bends ; it may be pressed or
crumpled so slowly that it can yield without much breaking.
There is a way to prove this. Do you know what stratified
rock is ?
Tom. It is rock in layers — in strata.
Jack. Yes. Now we know that those layers were, in the first
place, horizontal. They were layers of sand on the bottom of the
FIG. 1 86
The earth's solid crust is about
100 miles thick ; the narrow line
in the picture would be more
than 100 miles thick if the diam-
eter of the circle were 8000
miles. Within the crust the
rocks are very hot — melted.
The pressures in the interior are
so great that the rocks, though
melted, do not flow like a liquid,
but are almost rigid, like a solid.
FIG. 187. MODEL TO SHOW HOW MOUNTAINS ARE MADE BY THE
CRACKING OF THE EARTH'S CRUST
FIG. 188. VIEW OF THE MOUNTAINS FORMED BY THE CRACKING OF THE
EARTH'S CRUST. (SEE FIG. 187.)
They are in southern Oregon and northern Nevada and California. The long lakes and
the streams lie in the direction of the cracks.
206
PHYSIOGRAPHY
207
sea, or perhaps they were layers of limestone with fossil shells
scattered through them. In the pictures (Figs. 182 and 189)
FIG. 189. A COLUMN OF STRATIFIED ROCK
The rock is made up of nearly horizontal layers. The softer rock between the column and
the cliff has been worn away by the waves in the course of thousands of years. Fig. 182,
preceding, shows a cliff of stratified rock — of rock arranged in layers.
they have been lifted up so as to keep the layers level ; but
there are places, many places, where the layers have been
crumpled like this:
(See also Fig. 190.)
208
THE SCIENCES
The crumpling makes the crust into mountains and valleys,
and you must always remember that just as soon as a moun-
tain is lifted up, it begins to be torn down again by the frosts,
the rains, the earthquakes. The older the mountain is, the
FIG. 190
Strata once horizontal are sometimes elevated and folded so as to make mountain ranges, as
in the picture, which shows such a case in Maryland. The Appalachian ridges in Penn-
sylvania (and the Jura Mountains in Switzerland) were made in this way.
more its first shape has been altered, and you can tell its age
in that way. (See Figs. 180 and 185.)
The oldest mountains in America are the Laurentian Hills,
near the St. Lawrence River, and the Green and Adirondack
mountains. The Green Mountains are about forty or fifty
million years old, the geologists say.
PHYSIOGRAPHY 209
Fred. What are the youngest mountains, Jack ?
Jack. The youngest in America are the Coast Ranges of the
Pacific slope. The books say they are about two or three
millions years old. Two million years is young for a moun-
tain. The Wasatch Mountains in Utah are middle aged.
The Age of the Earth. — " Do they know how old the earth
is ? " said Tom.
Jack. It is not known in the way you can say you know how
old a tree is after you have counted the number of rings in its
sawed-off stump ; but it is known in a way. Take these very
stratified rocks, for instance. They were formed under water
by sand which settled down on the ocean floor and slowly
cemented into rock. A layer a foot thick will be formed in
about 10,000 years, the geologists say. Then a layer 100 feet
thick might be formed in about a million years, and a layer
ten miles thick in about 500,000,000 years. There is good
reason to believe that the earth is at least as old as that, and
maybe older.1
Agnes. Five hundred million years ! I shall never be able
to realize that ! Why, I can't even understand what a million
years is.
Jack. You remember how you children made a model of the
solar system ? 2 It helped you to understand large numbers,
did n't it ? Well, you can do something of the same sort here.
Suppose that the next time you walk to the village you play
that every one of your steps counts for a year. When you
1 There is no part of the earth where we can see horizontal layers, one upon
another, ten miles thick ; but there are places where the layers, once horizontal
( ), have been tilted up (//////), so that we can now see their ends and be
sure that the original layers were at least ten miles in thickness.
2 See Book I (Astronomy), page 20.
210 THE SCIENCES
have taken 125 steps you have gone back 125 years, and that
will take you back to the time of the Revolutionary War
(1901 — 1776= 125); and when you have taken 1900 steps you
have gone back to the time of Christ. When you have walked
three miles you have gone back to the time when the first
pyramids were built. You would have to walk about twenty
miles, each step counting for a year, before you got back to the
time when human beings first came on the earth; and you would
have to walk two or three times round the earth before you got
back to the time when the first life appeared on the earth, and
much farther yet to get to the time when the earth was first
formed.
Mary. It is puzzling, but I think I understand it a little
better than I did before.
Jack. Well, my dear, suppose you remember what we have
said and think about it by and by. Recollect — a step stands
for a year ; you were born twelve years ago — twelve steps just
takes you out on to the lawn. The Pilgrims landed 281 years
ago — 281 steps down the road. You can put a peg here to
stand for the coming of the Pilgrims. Eight hundred and
thirty-five steps will take you to the landing of William the
Conqueror in England; put in a peg for him. A mile will take
you back to 600 years before Christ ; the city of Rome was
founded about that time. Two miles farther will represent
the time when the pyramids were built in Egypt ; and when
you have gone about twenty miles — a year to each step — you
will get back to the time that men first appeared on the earth.
That is far enough for now. The world was a very old world
when Man appeared on it ; it had a long history before he came.
There had been life long before his time, as we know by the
fossils, — shells, fishes, and animals ; and there was a long time,
PHYSIOGRAPHY 2 1 1
nobody knows how long, before that when the earth had no
life on it at all — no men, no animals, not even a plant.
Age of Different Parts of the Earth. — "I understand how
you can tell when the oldest seashells came," said Tom,
"because you would find their fossils in the oldest rocks — in
the rocks lowest down ; and if you find a fossil rhinoceros
higher up in the rocks than a fossil whale, you would say the
whale came first. But how about men ? Do they find fossil
skeletons of men ? "
Jack. Sometimes ; but more often they find arrowheads that
men have chipped out of flint, along with the fossils of animals.
For instance, there are caves where arrowheads and lanceheads
have been found along with the remains of animals, and where
it is plain that the caves were filled up by some accident soon
after the men had died ; those men and those animals lived at
the same time. Sometimes they find the bones of the animals
split open, so as to get the marrow out, and blackened
with fire.
Age of Man on the Earth. — " Well, that would prove that
the men used those very animals for food, would n't it ? "
said Fred.
Jack. Yes, and there is a more wonderful thing still. In one
of the very old caves they found bones carved with pictures of
reindeer. The man first killed the reindeer with his arrows,
and dragged him to his cave and cooked him with fire. Then
there was plenty of food in the house. The man felt secure
and happy; he had leisure to think and to enjoy himself. And
this drawing of a reindeer on a bone made by a half-naked
savage is the beginning of all the beautiful pictures in the world.
The man was, you may say, our ancestor ; and the drawing is
the ancestor of all the paintings of modern times.
212
THE SCIENCES
Tom. Some one ought to put up a monument to that man !
He was, the first artist — long before Pheidias and the Greeks.
Agnes. How long before, Jack ?
Jack. I knew you were going to ask me that, Agnes. I
was sure of it ! Well, at a guess, 10,000 years or, it may be,
1 5,000. It is not certain, like the date of the last eclipse, or the
time when Rome was founded. It is twenty miles, Agnes — a
year to a step — don't you remember ?
Agnes. Yes, I remember ; but I don't see how you can tell,
though.
Tom. Why, Agnes, if a man eats reindeer in order to live,
he must be at least as old as the reindeer, must n't he ?
Agnes. Of course.
Tom. And if the fossil reindeer are found in rocks that it
took 5000 years at least to make, then the man must have
lived at least 5000 years ago. That is the way they find out.
Jack. That is the way
they find out, — yes, Tom ;
but you must remember
that just about 5000 years
ago, in Egypt, men were
building palaces and tem-
ples and pyramids, writing
letters to each other, keep-
ing accounts, spinning and
weaving, painting, and
FIG. 191
making statues. You have
to go back at least 100,000
years to find the earliest men. Agnes, there is a place in
the West — Idaho or California, I forget which — where they
lately found something very like a doll ; it might have been
PHYSIOGRAPHY
213
an idol, but it looked like a doll. Now this doll was buried
in gravel that had been brought down by an old-time river.
No one knows exactly how long it took for the river to
bring down all the gravel that covered the place where the
doll was dropped by the man who had it, but it must have
taken thousands of years. Then,
long afterwards, the volcanoes near
by sent out rivers of lava, and thick
sheets of the lava poured out and
covered the old gravels and dried up
the old river. No one knows exactly
how many thousands of years it took
for the many sheets of lava to form
one above another ; but they were
more than half a mile thick — that
we know. Then came a new river
flowing across the lava, and it flowed
for so many thousand years that it
cut a deep groove for its bed in the
hard lava. Scientific men can make
a pretty good guess how long each of
these different things took. Some
men were sinking a deep well in the
valley of the new river the other day,
and in the well, deep down, they found
the doll. You see that we can make
a pretty good guess how long ago the doll was made by adding up
all the years that were required to deposit the gravel, and to make
the lava sheet, and for the river to cut its way in the lava.
Agnes. Yes, I see. I suppose that is certainly the oldest
doll in the whole world, though.
FIG. 192. A GEYSER SPOUT-
ING BOILING WATER WHICH
COMES FROM DEEP DOWN IN
THE EARTH
214
THE SCIENCES
The Internal Heat of the Earth. — " You were saying," said
Tom, "that the interior of the earth is made of melted rock.
I suppose you know that by the melted lava which comes from
volcanoes. Lava is melted rock."
Jack. Yes, it is known in that way : volcanoes pour out melted
rock. And then geysers send out hot water — boiling water
sometimes ; and in regions where there are no volcanoes we
FIG. 193. THE PEAK OF TENERIFFE IN THE CANARY ISLANDS
The mountain is 12,000 feet high, and its beautiful form has been shaped by the lava streams
flowing down from the crater. Notice that the rocks in the foreground form part of a
very much larger crater that was active in ancient times and is now extinct.
find that the deep wells always send out hot water — the
deeper the well, the hotter the water.
Fred. How deep are the deepest wells, Jack ?
Jack. There are some in Europe nearly a mile deep. They
are not dug, • you know, but are sunk by boring. There
are deep wells in America, too ; one in St. Louis is 3800 feet
deep — more than two thirds of a mile. The water from it has
a temperature of 105°. Boiling water is 212°, you know.
PHYSIOGRAPHY 215
Volcanoes. — " You know there are some splendid volcanoes
in Hawaii," said Jack; "papa' has seen them. One of them
especially is easy to visit — Kilauea,1 they call it. It is a great
lake filled with red-hot boiling lava that comes up from some
reservoir of lava deep in the ground. The lava is liquid rock.
Usually it does not flow over the rim of the crater, but sometimes
it overflows and sends great streams of red-hot lava all over the
country round about and even as far as the sea — fifty miles off.
FIG. 194
A volcano is built up somewhat as in the picture. Underneath it are old rocks in layers.
There is a reservoir of lava somewhere underneath them, and a pipe filled with lava
leading to the surface. (The lava is colored black in the picture.) When the lava overflows
it moves down the side of the mountain like a great river and covers up everything that
comes in its way. The upper end of the pipe is the vent, and the lake at the top is the
crater. There is often more than one vent. (See the little black lines in the picture
leading to different cones.)
" Vesuvius, near Naples, is the most famous volcano. You
know it buried two whole cities once — Herculaneum and
Pompeii." 2
Agnes. Tell us, Jack.
Jack. Pompeii was a kind of summer resort where the
Romans used to go for pleasure. It was a pretty little town
full of fine houses, temples, shops, and so forth, not far from
1 Pronounced ke'-lou-a'a.
2 Pronounced pom-pa'ye.
216 THE SCIENCES
the volcano of Vesuvius. Seventy-nine years after Christ
(A.D. 79) there was a great eruption, and the ashes began to
fall on the city. At first the people were not very much
frightened, but pretty soon things got worse and worse, and
they began to gather up their movables and to leave the city.
A great many of them got away, but hundreds and hundreds
were buried in the ashes and died there. The ashes kept on
falling for days, and the whole city was covered up. Almost
the same thing happened in Martinique in May, 1902. Just
imagine what might happen if there were a volcano near New
York, and if the city were to be covered up with a thick layer
of ashes and not even found again for more than a thousand
years !
Agnes. Not found for a thousand years !
Jack. Well, Pompeii was buried in A.D. 79, and it was not
until 1748 that people began to dig there and found the whole
city complete, just as it had been left a good deal more than a
thousand years before.
In a baker's shop, for instance, they found loaves of bread
all shriveled up, and perfumes and oil and jewelry in other
shops. The houses were filled with things that the people
used every day ; everything was just as before.
Agnes. But the people, Jack — were they found ? Were their
bodies found ?
Jack. Their bodies had mostly wasted away, Agnes ; they
found their skeletons. One man had come back after his
money, and other people after their jewels. The money and
jewels were found, and the bones of the persons near them.
In one place they found a picture of a watchdog with the
sign, Cave canem ; that means — what does it mean, Tom, in
English ?
PHYSIOGRAPHY
217
Tom. It means " Beware of the dog !"
Jack. Yes; as we should say "Look out for the dog!" A
very great deal of what we know about ancient pictures and
statues we learned from Pompeii.
Fred. If New York were buried and dug up a thousand years
from now, the people of that time would know how we lived.
FIG. 195
The picture shows the volcano of Vesuvius as it appears to-day, and in the foreground a part
of the city of Herculaneum after the layer of lava has been taken off. Herculaneum
was covered with thick ashy mud and was even better preserved than Pompeii, which
was buried in showers of ashes. Everything in it was found exactly as it was left —
shops, houses, temples, jewelry, tools.
Tom. If you went into a house, you would know just what
each room had been used for — the kitchen and the dining
2l8 THE SCIENCES
room and the bedrooms — and just what pictures we had liked
and hung on our walls, and what books we read, and everything
of that sort.
Mary. And they would know what games we played — tennis
and golf ; and they might find Agnes' dolls and mine.
Agnes. Just as we found the doll Jack told us about that
was buried under the lava in California.
Fred. Are there any volcanoes in the United States ?
Jack. There are plenty of mountains that are old worn-out
volcanoes, and a few that are still active. Mount Shasta, for
instance, in California, is an old volcano, and there are active
volcanoes in Alaska, Hawaii, and the Philippines. You children
ought to recollect, every time you look at a map, that a very
large part of three great states — Washington, Oregon, and
Idaho — is nothing but an old lava field. A good part of the
lava is 3000, even 4000 feet thick, and it covers thousands and
thousands of square miles. All that lava flowed from ancient
volcanoes, though it did not flow all at one time; for they
find the lava in layers with ashes and soil between, and in
some of the soil they find petrified tree trunks.
Tom. That shows the trees had time to grow between one
lava flow and the next one, does n't it ?
Jack. Yes, and it gives you an idea how long it took to
deposit all that thickness of lava. The doll I told Agnes
about was found in this very lava field.
Earthquakes. — "Do earthquakes come from volcanoes?" said
Fred.
Jack. There are always earthquakes wherever there are
active volcanoes, Fred. You can see that a volcano in eruption
which has energy enough to throw huge stones thousands of
feet into the air must shake all the ground near it by its
PHYSIOGRAPHY 219
explosions. All volcanoes make earthquakes, but very many
earthquakes are not caused by volcanoes.
Mary. What does cause them then, Jack ?
Jack. Suppose you lay a book flat on its side, Mary, and
imagine that the book is part of a layer of rock that was once
deposited at the bottom of the sea. Now take another book
and lay it flat on the first one. That stands for a second layer
of rock — perhaps a different kind of rock — lying over the
first layer. Now you know the crust of the earth is moving
slowly all the time, sometimes up, sometimes down. Sup-
pose both those layers of rock were lifted so that one end of
them was higher than the other. Tilt the books, Mary, and
keep tilting them, and see what happens.
Mary. Why, one book slides off the other.1
Jack. That is exactly what sometimes happens to great beds
of rock. They lie flat in the first place. Then they are slowly
tilted, and by and by one of them slides a little — a very little —
on the other. Ten million tons sliding only a little way —
an inch perhaps — will make a terrible shock that can be felt
for hundreds of miles around. The Charleston earthquake
was caused in just that way.
The geologists say that the layers of rock underneath South
Carolina lie one on another like the two books, and the earth-
quake was caused by the sliding of the layers. The rocks I am
talking about were deep underground, you know. When they
moved, the rest of the rocks moved, too, just as a pile of bricks
will slide when you move some of the bottom ones ; all of
them moved. A good part of Charleston was wrecked, you
know, and all the eastern part of the United States was shaken
1 The simple experiment should be tried in the schoolroom, choosing two
books with smooth covers.
22O
THE SCIENCES
more or less. Why, they even felt the shock at Boston, at
Toronto in Canada, at Chicago, at St. Louis, and at New
Orleans. The shock was not severe there, but it was felt.
FIG. 196. THE CHURCH OF SAINT AUGUSTINE IN MANILA, PHILIPPINE
ISLANDS, AFTER THE EARTHQUAKES OF JULY, 1880
Tom. Of course an earthquake is weaker and weaker the
farther you go away from the center of it.
PHYSIOGRAPHY
221
Jack. Yes ; like the little water waves in a pond when you
throw in a stone. That is a " waterquake," you might say.
You know the waves are larger and higher at the center, and
FIG. 197. VIEW OF PART OF CHARLESTON, S.C., WRECKED BY THE
EARTHQUAKE OF AUGUST, 1886
become smaller as they move out. All of South Carolina was
badly shaken, so that chimneys fell. The shocks were strong
enough to frighten people in Georgia, in Ohio, and in
222 THE SCIENCES
Pennsylvania, and they were felt as far as the Mississippi
River, and farther.
Mary. Were many people killed, Jack ?
Jack. Only a few, Mary. They ran out of their houses, and
lived in the parks for several days till the shocks were over.
Agnes. Oh, did the earthquake last for days ?
Jack. There were shocks every now and then for several
days, but only a few really severe ones. You see it took
several days for all those rocks underground to settle down and
be quiet. There was an earthquake in the Mississippi Valley
once (181 1) that lasted nearly a year. The people camped out
of doors for months and months.
Agnes. Might we have an earthquake here, Jack ?
Jack. Certainly, we might ; no one can tell. There are not
many earthquakes in the eastern part of the country, and those
that we have are usually light ; you need not be afraid of
them. If an earthquake comes, go out of doors and keep away
from houses — that is all. But there are earthquakes every-
where — light ones. You boys can prove it if you want to.
Fred. How can we prove it ?
Jack. Get some pieces of nice wood — red cedar, for
instance — and make two or three pyramids. (See Fig. 198.)
Then cut off a little of the top of each one of them, and stand
them upside down in a steady place — on the mantelpiece of a
room that is not used much, for example. When a slight earth-
quake comes — one too slight for you to feel perhaps — the
house will be shaken and the mantelpiece, too, and the pyramid
will fall on one of its sides. Try it.
The boys did try it. They made half a dozen pyramids
and cut off a little of the top of each one, and stood them
about in different places in the house and in the barn. They
PHYSIOGRAPHY 223
often would find one of them fallen on its side, and they
usually discovered that the housemaid, in dusting, had caused
that particular earthquake. But every few months they found
all the little pyramids thrown down, and most of them lying in
one direction ;*and then they knew that there had been a light
shock — too light for them to feel, but strong enough to over-
turn their " earthquake detectors," as they called them. The
FIG. 198. PYRAMID
direction in which the detectors lay on their sides showed the
direction in which the earthquake wave was moving — north
and south, for instance.
The Lisbon Earthquake. — "They say the Lisbon earthquake
was one of the very worst," said Tom ; " do you know about
that, Jack?"
Jack. It was one of the worst, certainly, because there was
not only an earthquake, but a great sea wave too. The people
ran out of their houses to take refuge in the churches, and then
the churches fell and crushed them. Many went to the wharves
224 THE SCIENCES
so as to be away from falling walls, and a huge wave from the
sea — eighty feet high, they say — rolled in and drowned
thousands of people.
Fred. A wave eighty feet high ! What made it, Jack? Was
it a part of the earthquake ?
Jack. No doubt the level of the sea bottom was changed some-
how, and the water rolled in like a great wall. That often occurs
in South American earthquakes. A strange thing happened
to one of our war vessels once. It was the Wateree, and she
was at anchor in the bay of Iquique1 in Peru (1868). All of
a sudden came a great wave from the sea and tossed the
ships about like boats, and it carried the Wateree far inland
and left her there high and dry. Think of it — one of our war
ships with all her guns and men (no one was hurt) high and
dry on land !
Fred. What did they do ? Could they get her off ?
Jack. No ; and so the government took away all her cannon
and everything that was valuable, and sold her to a Spanish
gentleman for a summer house !
Agnes. I think that 's funny. A man-of-war for a summer
house !
Jack. That is not the funniest part of it, Agnes. A few
years later there came another great sea wave, and it lifted up
the Wateree and carried her a long way farther inland, and
there she is now, a summer house for a different family.
1 Pronounced e-ke'ka.
UNIVERSITY OF CALIFORNIA LIBRARY
BERKELEY
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