HOME! 8 g :'. LIBRARY OF THE 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 3 2 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 Q f j t an d a pus h 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 i s 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 (1901258= 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; 'i-e <