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diff --git a/5726.txt b/5726.txt new file mode 100644 index 0000000..4b8d626 --- /dev/null +++ b/5726.txt @@ -0,0 +1,6342 @@ +Project Gutenberg's The Fairy-Land of Science , by Arabella B. Buckley + +Copyright laws are changing all over the world. Be sure to check the +copyright laws for your country before downloading or redistributing +this or any other Project Gutenberg eBook. + +This header should be the first thing seen when viewing this Project +Gutenberg file. Please do not remove it. Do not change or edit the +header without written permission. + +Please read the "legal small print," and other information about the +eBook and Project Gutenberg at the bottom of this file. Included is +important information about your specific rights and restrictions in +how the file may be used. You can also find out about how to make a +donation to Project Gutenberg, and how to get involved. + + +**Welcome To The World of Free Plain Vanilla Electronic Texts** + +**eBooks Readable By Both Humans and By Computers, Since 1971** + +*****These eBooks Were Prepared By Thousands of Volunteers!***** + + +Title: The Fairy-Land of Science + +Author: Arabella B. Buckley + +Release Date: May, 2004 [EBook #5726] +[Yes, we are more than one year ahead of schedule] +[This file was first posted on August 17, 2002] + +Edition: 10 + +Language: English + +Character set encoding: ASCII + +*** START OF THE PROJECT GUTENBERG EBOOK THE FAIRY-LAND OF SCIENCE *** + + + + + + + + + + + +The Fairy-Land of Science + +Arabella B. Buckley + + + + +TABLE OF CONTENTS + +Lecture I The Fairy-Land of Science; How to Enter It; + How to Use It; And How to Enjoy It +Lecture II Sunbeams, and the Work They Do +Lecture III The Aerial Ocean in Which We Live +Lecture IV A Drop of Water on its Travels +Lecture V The Two Great Sculptors - Water and Ice +Lecture VI The Voices of Nature, and How We Hear Them +Lecture VII The Life of a Primrose +Lecture VIII The History of a Piece of Coal +Lecture IX Bees in the Hive +Lecture X Bees and Flowers + + + +Week 1 + +LECTURE I + +HOW TO ENTER IT; HOW TO USE IT; AND HOW TO ENJOY IT + +I HAVE promised to introduce you today to the fairy-land of +science - a somewhat bold promise, seeing that most of you +probably look upon science as a bundle of dry facts, while fairy- +land is all that is beautiful, and full of poetry and +imagination. But I thoroughly believe myself, and hope to prove +to you, that science is full of beautiful pictures, of real +poetry, and of wonder-working fairies; and what is more, I +promise you they shall be true fairies, whom you will love just +as much when you are old and greyheaded as when you are young; +for you will be able to call them up wherever you wander by land +or by sea, through meadow or through wood, through water or +through air; and though they themselves will always remain +invisible, yet you will see their wonderful poet at work +everywhere around you. + +Let us first see for a moment what kind of tales science has to +tell, and how far they are equal to the old fairy tales we all +know so well. Who does not remember the tale of the "Sleeping +Beauty in the Wood," and how under the spell of the angry fairy +the maiden pricked herself with the spindle and slept a hundred +years? How the horses in the stall, the dogs in the court-yard, +the doves on the roof, the cook who was boxing the scullery boy's +ears in the kitchen, and the king and queen with all their +courtiers in the hall remained spell-bound, while a thick hedge +grew up all round the castle and all within was still as death. +But when the hundred years had passed the valiant prince came, +the thorny hedge opened before him bearing beautiful flowers; and +he, entering the castle, reached the room where the princess lay, +and with one sweet kiss raised her and all around her to life +again. + +Can science bring any tale to match this? + +Tell me, is there anything in this world more busy and active +than water, as it rushes along in the swift brook, or dashes over +the stones, or spouts up in the fountain, or trickles down from +the roof, or shakes itself into ripples on the surface of the +pond as the wind blows over it? But have you never seen this +water spell-bound and motionless? Look out of the window some +cold frosty morning in winter, at the little brook which +yesterday was flowing gently past the house, and see how still it +lies, with the stones over which it was dashing now held tightly +in its icy grasp. Notice the wind-ripples on the pond; they have +become fixed and motionless. Look up at the roof of the house. +There, instead of living doves merely charmed to sleep, we have +running water caught in the very act of falling and turned into +transparent icicles, decorating the eaves with a beautiful +crystal fringe. On every tree and bush you will catch the water- +drops napping, in the form of tiny crystals; while the fountain +looks like a tree of glass with long down-hanging pointed leaves. +Even the damp of your own breath lies rigid and still on the +window-pane frozen into delicate patterns like fern-leaves of +ice. + +All this water was yesterday flowing busily, or falling drop by +drop, or floating invisibly in the air; now it is all caught and +spell-bound - by whom? By the enchantments of the frost-giant +who holds it fast in his grip and will not let it go. + +But wait awhile, the deliverer is coming. In a few weeks or +days, or it may be in a few hours, the brave sun will shine down; +the dull-grey, leaden sky will melt before his, as the hedge gave +way before the prince in the fairy tale, and when the sunbeam +gently kisses the frozen water it will be set free. Then the +brook will flow rippling on again; the frost-drops will be shaken +down from the trees, the icicles fall from the roof, the moisture +trickle down the window-pane, and in the bright, warm sunshine +all will be alive again. + +Is not this a fairy tale of nature? and such as these it is +which science tells. + +Again, who has not heard of Catskin, who came out of a hollow +tree, bringing a walnut containing three beautiful dresses - the +first glowing as the sun, the second pale and beautiful as the +moon, the third spangled like the star-lit sky, and each so fine +and delicate that all three could be packed into a walnut shell; +and each one of these tiny structures is not the mere dress but +the home of a living animal. It is a tiny, tiny shell-palace +made of the most delicate lacework, each pattern being more +beautiful than the last; and what is more, the minute creature +that lives in it has built it out of the foam of the sea, though +he himself is nothing more than a drop of jelly. + +Lastly, anyone who has read the 'Wonderful Travellers' must +recollect the man whose sight was so keen that he could hit the +eye of a fly sitting on a tree two miles away. But tell me, can +you see gas before it is lighted, even when it is coming out of +the gas-jet close to your eyes? Yet, if you learn to use that +wonderful instrument the spectroscope, it will enable you to tell +one kind of gas from another, even when they are both ninety-one +millions of miles away on the face of the sun; nay more, it will +read for you the nature of the different gases in the far distant +stars, billions of miles away, and actually tell you whether you +could find there any of the same metals which we have on the +earth. + +We might find hundreds of such fairy tales in the domain of +science, but these three will serve as examples, and we much pass +on to make the acquaintance of the science-fairies themselves, +and see if they are as real as our old friends. + +Tell me, why do you love fairy-land? what is its charm? Is it +not that things happen so suddenly, so mysteriously, and without +man having anything to do with it? In fairy-land, flowers blow, +houses spring up like Aladdin's palace in a single night, and +people are carried hundreds of miles in an instant by the touch +of a fairy wand. + +And then this land is not some distant country to which we can +never hope to travel. It is here in the midst of us, only our +eyes must be opened or we cannot see it. Ariel and Puck did not +live in some unknown region. On the contrary, Ariel's song is + + "Where the bee sucks, there suck I; + In a cowslip's bell I lie; + There I couch when owls do cry. + On the bat's back I do fly, + After summer, merrily." + +The peasant falls asleep some evening in a wood and his eyes are +opened by a fairy wand, so that he sees the little goblins and +imps dancing around him on the green sward, sitting on mushrooms, +or in the heads of the flowers, drinking out of acorn-cups, +fighting with blades of grass, and riding on grasshoppers. + +So, too, the gallant knight, riding to save some poor oppressed +maiden, dashes across the foaming torrent; and just in the +middle, as he is being swept away, his eyes are opened, and he +sees fairy water-nymphs soothing his terrified horse and guiding +him gently to the opposite shore. They are close at hand, these +sprites, to the simple peasant or the gallant knight, or to +anyone who has the gift of the fairies and can see them. but the +man who scoffs at them, and does not believe in them or care for +them, he never sees them. Only now and then they play him an +ugly trick, leading him into some treacherous bog and leaving him +to get out as he may. + +Now, exactly all this which is true of the fairies of our +childhood is true too of the fairies of science. There are +forces around us, and among us, which I shall ask you to allow me +to call fairies, and these are ten thousand times more wonderful, +more magical, and more beautiful in their work, than those of the +old fairy tales. They, too, are invisible, and many people live +and die without ever seeing them or caring to see them. These +people go about with their eyes shut, either because they will +not open them, or because no one has taught them how to see. +They fret and worry over their own little work and their own +petty troubles, and do not know how to rest and refresh +themselves, by letting the fairies open their eyes and show them +the calm sweet picture of nature. They are like Peter Bell of +whom Wordsworth wrote:- + + "A primrose by a river's brim + A yellow primrose was to him, + And it was nothing more." + +But we will not be like these, we will open our eyes and ask, +"What are these forces or fairies, and how can we see them?" + +Just go out into the country, and sit down quietly and watch +nature at work. Listen to the wind as it blows, look at the +clouds rolling overhead, and waves rippling on the pond at your +feet. Hearken to the brook as it flows by, watch the flower-buds +opening one by one, and then ask yourself, "How all this is +done?" Go out in the evening and see the dew gather drop by drop +upon the grass, or trace the delicate hoar-frost crystals which +bespangle every blade on a winter's morning. Look at the vivid +flashes of lightening in a storm, and listen to the pealing +thunder: and then tell me, by what machinery is all this +wonderful work done? Man does none of it, neither could he stop +it if he were to try; for it is all the work of those invisible +forces or fairies whose acquaintance I wish you to make. Day and +night, summer and winter, storm or calm, these fairies are at +work, and we may hear them and know them, and make friends of +them if we will. + +There is only one gift we must have before we can learn to know +them - we must have imagination. I do not mean mere fancy, which +creates unreal images and impossible monsters, but imagination, +the power of making pictures or images in our mind, of that which +is, though it is invisible to us. Most children have this +glorious gift, and love to picture to themselves all that is told +them, and to hear the same tale over and over again till they see +every bit of it as if it were real. This is why they are sure to +love science it its tales are told them aright; and I, for one, +hope the day may never come when we may lose that childish +clearness of vision, which enables us through the temporal things +which are seen, to realize those eternal truths which are unseen. + +If you have this gift of imagination come with me, and in these +lectures we will look for the invisible fairies of nature. + +Watch a shower of rain. Where do the drops come from? and why +are they round, or rather slightly oval? In our fourth lecture +we shall se that the little particles of water of which the +raindrops are made, were held apart and invisible in the air by +heat, one of the most wonderful of our forces* or fairies, till +the cold wind passed by and chilled the air. Then, when there +was no longer so much heat, another invisible force, cohesion, +which is always ready and waiting, seized on the tiny particles +at once, and locked them together in a drop, the closest form in +which they could lie. Then as the drops became larger and larger +they fell into the grasp of another invisible force, gravitation, +which dragged them down to the earth, drop by drop, till they +made a shower of rain. Pause for a moment and think. You have +surely heard of gravitation, by which the sun holds the earth and +the planets, and keeps them moving round him in regular order? +Well, it is this same gravitation which is a t work also whenever +a shower of rain falls to the earth. Who can say that he is not +a great invisible giant, always silently and invisibly toiling in +great things and small whether we wake or sleep? + +*(I am quite aware of the danger incurred by using this word +"force", especially in the plural; and how even the most modest +little book may suffer at the hands of scientific purists by +employing it rashly. As, however, the better term "energy" would +not serve here, I hope I may be forgiven for retaining the much- +abused term, especially as I sin in very good company.) + +Now the shower is over, the sun comes out and the ground is soon +as dry as though no rain had fallen. Tell me; what has become of +the rain-drops? Part no doubt have sunk into the ground, and as +for the rest, why you will say the sun has dried them up. Yes, +but how? The sun is more than ninety-one millions of miles away; +how has he touched the rain-drops? Have you ever heard that +invisible waves are travelling every second over the space +between the sun and us? We shall see in the next lecture how +these waves are the sun's messengers to the earth, and how they +tear asunder the rain-drops on the ground, scattering them in +tiny particles too small for us to see, and bearing them away to +the clouds. Here are more invisible fairies working every moment +around you, and you cannot even look out of the window without +seeing the work they are doing. + +If, however, the day is cold and frosty, the water does not fall +in a shower of rain; it comes down in the shape of noiseless +snow. Go out after such a snow-shower, on a calm day, and look +at some of the flakes which have fallen; you will see, if you +choose good specimens, that they are not mere masses of frozen +water, but that each one is a beautiful six-pointed crystal star. +How have these crystals been built up? What power has been at +work arranging their delicate forms? In the fourth lecture we +shall see that up in the clouds another of our invisible fairies, +which, for want of a better name, we call the "force of +crystallization," has caught hold of the tiny particles of water +before "cohesion" had made them into round drops, and there +silently but rapidly, has moulded them into those delicate +crystal starts know as "snowflakes". + +And now, suppose that this snow-shower has fallen early in +February; turn aside for a moment from examining the flakes, and +clear the newly-fallen snow from off the flower-bed on the lawn. +What is this little green tip peeping up out of the ground under +the snowy covering? It is a young snowdrop plant. Can you tell +me why it grows? where it finds its food? what makes it spread +out its leaves and add to its stalk day by day? What fairies are +at work here? + +First there is the hidden fairy "life," and of her even our +wisest men know but little. But they know something of her way +of working, and in Lecture VII we shall learn how the invisible +fairy sunbeams have been buy here also; how last year's snowdrop +plant caught them and stored them up in it's bulb, and how now in +the spring, as soon as warmth and moisture creep down into the +earth, these little imprisoned sun-waves begin to be active, +stirring up the matter in the bulb, and making it swell and burst +upwards till it sends out a little shoot through the surface of +the soil. Then the sun-waves above-ground take up the work, and +form green granules in the tiny leaves, helping them to take food +out of the air, while the little rootlets below are drinking +water out of the ground. The invisible life and invisible +sunbeams are busy here, setting actively to work another fairy, +the force of "chemical attraction," and so the little snowdrop +plant grows and blossoms, without any help from you or me. + + + +Week 2 + +One picture more, and then I hope you will believe in my fairies. +From the cold garden, you run into the house, and find the fire +laid indeed in the grate, but the wood dead and the coals black, +waiting to be lighted. You strike a match, and soon there is a +blazing fire. Where does the heat come from? Why do the coals +burn and give out a glowing light? Have you not read of gnomes +buried down deep in the earth, in mines, and held fast there till +some fairy wand has released them, and allowed them to come to +earth again? Well, thousands and millions of years ago, those +coals were plants; and like the snowdrop in the garden of to-day, +they caught the sunbeams and worked them into their leaves. Then +the plants died and were buried deep in the earth and the +sunbeams with them; and like the gnomes they lay imprisoned till +the coals were dug out by the miners, and brought to your grate; +and just now you yourself took hold of the fairy wand which was +to release them. You struck a match, and its atoms clashing with +atoms of oxygen in the air, set the invisible fairies "heat" and +"chemical attraction" to work, and they were soon busy within the +wood and the coals causing their atoms too to clash; and the +sunbeams, so long imprisoned, leapt into flame. Then you spread +out your hands and cried, "Oh, how nice and warm!" and little +thought that you were warming yourself with the sunbeams of ages +and ages ago. + +This is no fancy tale; it is literally true, as we shall see in +Lecture VIII, that the warmth of a coal fire could not exist if +the plants of long ago had not used the sunbeams to make their +leaves, holding them ready to give up their warmth again whenever +those crushed leaves are consumed. + +Now, do you believe in, and care for, my fairy-land? Can you see +in your imagination fairy 'Cohesion' ever ready to lock atoms +together when they draw very near to each other: or fairy +'Gravitation' dragging rain-drops down to the earth: or the fairy +of 'Crystallization' building up the snow-flakes in the clouds? +Can you picture tiny sunbeam-waves of light and heat travelling +from the sun to the earth? Do you care to know how another +strange fairy, 'Electricity,' flings the lightning across the sky +and causes the rumbling thunder? Would you like to learn how the +sun makes pictures of the world on which he shines, so that we +can carry about with us photographs or sun-pictures of all the +beautiful scenery of the earth? And have you any curiosity about +'Chemical action,' which works such wonders in air, and land, and +sea? If you have any wish to know and make friends of these +invisible forces, the next question is + +How are you to enter the fairy-land of science? + +There is but one way. Like the knight or peasant in the fairy +tales, you must open you eyes. There is no lack of objects, +everything around you will tell some history if touched with the +fairy wand of imagination. I have often thought, when seeing +some sickly child drawn along the street, lying on its back while +other children romp and play, how much happiness might be given +to sick children at home or in hospitals, if only they were told +the stories which lie hidden in the things around them. They +need not even move from their beds, for sunbeams can fall on them +there, and in a sunbeam there are stories enough to occupy a +month. The fire in the grate, the lamp by the bedside, the water +in the tumbler, the fly on the ceiling above, the flower in the +vase on the table, anything, everything, has its history, and can +reveal to us nature's invisible fairies. + +Only you must with to see them. If you go through the world +looking upon everything only as so much to eat, to drink, and to +use, you will never see the fairies of science. But if you ask +yourself why things happen, and how the great God above us has +made and governs this world of ours; If you listen to the wind, +and care to learn why it blows; if you ask the little flower why +it opens in the sunshine and closes in the storm; and if when you +find questions you cannot answer, you will take the trouble to +hunt out in books, or make experiments to solve your own +questions, then you will learn to know and love those fairies. + +Mind, I do not advise you to be constantly asking questions of +other people; for often a question quickly answered is quickly +forgotten, but a difficulty really hunted down is a triumph for +ever. For example, if you ask why the rain dries up from the +ground, most likely you will be answered, "that the sun dries +it," and you will rest satisfied with the sound of the words. +But if you hold a wet handkerchief before the fire and see the +damp rising out of it, then you have some real idea how moisture +may be drawn up by heat from the earth. + +A little foreign niece of mine, only four years old, who could +scarcely speak English plainly, was standing one morning near the +bedroom window and she noticed the damp trickling down the +window-pane. "Auntie," she said, "what for it rain inside?" It +was quite useless to explain to her in words, how our breath had +condensed into drops of water upon the cold glass; but I wiped +the pane clear, and breathed on it several times. When new drops +were formed, I said, "Cissy and auntie have done like this all +night in the room." She nodded her little head and amused +herself for a long time breathing on the window-pane and watching +the tiny drops; and about a month later, when we were travelling +back to Italy, I saw her following the drops on the carriage +window with her little finger, and heard her say quietly to +herself, "Cissy and auntie made you." Had not even this little +child some real picture in her mind of invisible water coming +from her mouth, and making drops upon the window-pane? + +Then again, you must learn something of the language of science. +If you travel in a country with no knowledge of its language, you +can learn very little about it: and in the same way if you are to +go to books to find answers to your questions, you must know +something of the language they speak. You need not learn hard +scientific names, for the best books have the fewest of these, +but you must really understand what is meant by ordinary words. + +For example, how few people can really explain the difference +between a solid, such as the wood of the table; a liquid, as +water; and a gas, such as I can let off from this gas-jet by +turning the tap. And yet any child can make a picture of this in +his mind if only it has been properly put before him. + +All matter in the world is made up of minute parts or particles; +in a solid these particles are locked together so tightly that +you must tear them forcibly apart if you with to alter the shape +of the solid piece. If I break or bend this wood I have to force +the particles to move round each other, and I have great +difficulty doing it. But in a liquid, though the particles are +still held together, they do not cling so tightly, but are able +to roll or glide round each other, so that when you pour water +out of a cup on to a table, it loses its cuplike shape and +spreads itself out flat. Lastly, in a gas the particles are no +longer held together at all, but they try to fly away from each +other; and unless you shut a gas in tightly and safely, it will +soon have spread all over the room. + +A solid, therefore, will retain the same bulk and shape unless +you forcibly alter it; a liquid will retain the same bulk, but no +the same shape if it be left free; a gas will not retain either +the same bulk or the same shape, but will spread over as large a +space as it can find wherever it can penetrate. Such simple +things as these you must learn from books and by experiment. + +Then you must understand what is meant by chemical attraction; +and though I can explain this roughly here, you will have to make +many interesting experiments before you will really learn to know +this wonderful fairy power. If I dissolve sugar in water, though +it disappears it still remains sugar, and does not join itself to +the water. I have only to let the cup stand till the water +dries, and the sugar will remain at the bottom. There has been +no chemical attraction here. + +But now I will put something else in water which will call up the +fairy power. Here is a little piece of the metal potassium, one +of the simple substances of the earth; that is to say, we cannot +split it up into other substances, wherever we find it, it is +always the same. Now if I put this piece of potassium on the +water it does not disappear quietly like the sugar. See how it +rolls round and round, fizzing violently with a blue flame +burning round it, and at last goes off with a pop. + +What has been happening here? + +You must first know that water is made of two substances, +hydrogen and oxygen, and these are not merely held together, but +are joined to completely that they have lost themselves and have +become water; and each atom of water is made of two atoms of +hydrogen and one of oxygen. + +Now the metal potassium is devotedly fond of oxygen, and the +moment I threw it on the water it called the fairy "chemical +attraction' to help it, and dragged the atoms of oxygen out of +the water and joined them to itself. In doing this it also +caught part of the hydrogen, but only half, and so the rest was +left out in the cold. No, not in the cold! for the potassium and +oxygen made such a great heat in clashing together that the rest +of the hydrogen became very hot indeed, and sprang into the air +to find some other companion to make up for what it had lost. +Here it found some free oxygen floating about, and it seized upon +it so violently, that they made a burning flame, while the +potassium with its newly found oxygen and hydrogen sank down +quietly into the water as potash. And so you see we have got +quite a new substance potash in the basin; made with a great deal +of fuss by chemical attraction drawing different atoms together. + +When you can really picture this power to yourself it will help +you very much to understand what you read and observe about +nature. + +Next, as plants grow around you on every side, and are of so much +importance in the world, you must also learn something of the +names of the different parts of a flower, so that you may +understand those books which explain how a plant grows and lives +and forms its seeds. You must also know the common names of the +parts of an animal, and of your own body, so that you may be +interested in understanding the use of the different organs; how +you breathe, and how your blood flows; how one animal walks, +another flies, and another swims. Then you must learn something +of the various parts of the world, so that you may know what is +meant by a river, a plain, a valley, or a delta. All these +things are not difficult, you can learn them pleasantly from +simple books on physics, chemistry, botany, physiology, and +physical geography; and when you understand a few plain +scientific terms, then all by yourself, if you will open your +eyes and ears, you may wander happily in the fairy-land of +science. Then wherever you go you will find + + "Tongues in trees, books in the running brooks + Sermons in stones, and good in everything." + +And now we come to the last part of our subject. When you have +reached and entered the gates of science, how are you to use and +enjoy this new and beautiful land? + +This is a very important question for you may make a twofold use +of it. If you are only ambitious to shine in the world, you may +use it chiefly to get prizes, to be at the top of your class, or +to pass in examinations; but if you also enjoy discovering its +secrets, and desire to learn more and more of nature and to revel +in dreams of its beauty, then you will study science for its own +sake as well. Now it is a good thing to win prizes and be at the +top of your class, for it shows that you are industrious; it is a +good thing to pass well in examinations , for it show that you +are accurate; but if you study science for this reason only, do +not complain if you find it full, and dry, and hard to master. +You may learn a great deal that is useful, and nature will answer +you truthfully if you ask you questions accurately, but she will +give you dry facts, just such as you ask for. If you do not love +her for herself she will never take you to her heart. + +This is the reason why so many complain that science is dry and +uninteresting. They forget that though it is necessary to learn +accurately, for so only we can arrive at truth, it is equally +necessary to love knowledge and make it lovely to those who +learn, and to do this we must get at the spirit which lies under +the facts. What child which loves its mother's face is content +to know only that she has brown eyes, a straight nose, a small +mouth, and hair arranged in such and such a manner? No, it knows +that its mother has the sweetest smile of any woman living; that +her eyes are loving, her kiss is sweet, and that when she looks +grave, then something is wrong which must be put right. And it +is in this way that those who wish to enjoy the fairy-land of +science must love nature. + +It is well to know that when a piece of potassium is thrown on +water the change which takes place is expressed by the formula K + +H2O = KHO + H. But it is better still to have a mental picture of +the tiny atoms clasping each other, and mingling so as to make a +new substance, and to feel how wonderful are the many changing +forms of nature. It is useful to be able to classify a flower and +to know that the buttercup belongs to the Family Ranunculaceae, +with petals free and definite, stamens hypogynous and indefinite, +pistil apocarpous. But it is far sweeter to learn about the life +of the little plant, to understand why its peculiar flower is +useful to it, and how it feeds itself, and makes its seed. No one +can love dry facts; we must clothe them with real meaning and love +the truths they tell, if we wish to enjoy science. + +Let us take an example to show this. I have here a branch of +white coral, a beautiful, delicate piece of nature's work. We +will begin by copying a description of it from one of those +class-books which suppose children to learn words like parrots, +and to repeat them with just as little understanding. + +"Coral is formed by an animal belonging to the kingdom of +Radiates, sub-kingdom Polypes. The soft body of the animal is +attached to a support, the mouth opening upwards in a row of +tentacles. The coral is secreted in the body of the polyp out of +the carbonate of lime in the sea. Thus the coral animalcule +rears its polypidom or rocky structure in warm latitudes, and +constructs reefs or barriers round islands. It is limited in +rage of depth from 25 to 30 fathoms. Chemically considered, +coral is carbonate of like; physiologically, it is the skeleton +of an animal; geographically, it is characteristic of warm +latitudes, especially of the Pacific Ocean." This description is +correct, and even fairly complete, if you know enough of the +subject to understand it. But tell me, does it lead you to love +my piece of coral? Have you any picture in your mind of the +coral animal, its home, or its manner of working? + +But now, instead of trying to master this dry, hard passage, take +Mr. Huxley's penny lecture on 'Coral and Coral Reefs,' and with +the piece of coral in your hand try really to learn its history. +You will then be able to picture to yourself the coral animal as +a kind of sea-anemone, something like those which you have often +seen, like red, blue, or green flowers, putting out feelers in +sea-water on our coasts, and drawing in the tiny sea-animals to +digest them in that bag of fluid which serves the sea-anemone as +a stomach. You will learn how this curious jelly animal can +split itself in two, and so form two polyps, or send a bud out of +its side and so grow up into a kind of "tree or bush of polyps," +or how it can hatch little eggs inside it and throw out young +ones from its mouth, provided with little hairs, by means of +which they swim to new resting-places. You will learn the +difference between the animal which builds up the red coral as +its skeleton, and the group of animals which build up the white; +and you will look with new interest on our piece of white coral, +as you read that each of those little sups on its stem with +delicate divisions like the spokes of a wheel has been the home +of a separate polyp, and that from the sea-water each little +jelly animal has drunk in carbonate of lime as you drink in sugar +dissolved in water, and then has used it grain by grain to build +that delicate cup and add to the coral tree. + +We cannot stop to examine all about coral now, we are only +learning how to learn, but surely our specimen is already +beginning to grow interesting; and when you have followed it out +into the great Pacific Ocean, where the wild waves dash +restlessly against the coral trees, and have seen these tiny +drops of jelly conquering the sea and building huge walls of +stone against the rough breakers, you will hardly rest till you +know all their history. Look at that curious circular island in +the picture, covered with palm trees; it has a large smooth lake +in the middle, and the bottom of this lake is covered with blue, +red, and green jelly animals, spreading out their feelers in the +water and looking like beautiful flowers, and all round the +outside of the island similar animals are to be seen washed by +the sea waves. Such islands as this have been build entirely by +the coral animals, and the history of the way in which the reefs +have sunk gradually down, as the tiny creatures added to them +inch by inch, is as fascinating as the story of the building of +any fairy palace in the days of old. Read all this, and then if +you have no coral of your own to examine, go to the British +Museum and see the beautiful specimens in the glass cases there, +and think that they have been built up under the rolling surf by +the tiny jelly animals; and then coral will become a real living +thing to you, and you will love the thoughts it awakens. + +But people often ask, what is the use of learning all this? If +you do not feel by this time how delightful it is to fill your +mind with beautiful pictures of nature, perhaps it would be +useless to say more. But in this age of ours, when restlessness +and love of excitement pervade so many lives, is it nothing to be +taken out of ourselves and made to look at the wonders of nature +going on around us? Do you never feel tired and "out of sorts," +and want to creep away from your companions, because they are +merry and you are not? Then is the time to read about the +starts, and how quietly they keep their course from age to age; +or to visit some little flower, and ask what story it has to +tell; or to watch the clouds, and try to imagine how the winds +drive them across the sky. No person is so independent as he who +can find interest in a bare rock, a drop of water, the foam of +the sea, the spider on the wall, the flower underfoot or the +starts overhead. And these interests are open to everyone who +enters the fairy-land of science. + +Moreover, we learn from this study to see that there is a law and +purpose in everything in the Universe, and it makes us patient +when we recognize the quiet noiseless working of nature all +around us. Study light, and learn how all colour, beauty, and +life depend on the sun's rays; note the winds and currents of the +air, regular even in their apparent irregularity, as they carry +heat and moisture all over the world. Watch the water flowing in +deep quiet streams, or forming the vast ocean; and then reflect +that every drop is guided by invisible forces working according +to fixed laws. See plants springing up under the sunlight, learn +the secrets of plant life, and how their scents and colours +attract the insects. Read how insects cannot live without +plants, nor plants without the flitting butterfly or the busy +bee. Realize that all this is worked by fixed laws, and that out +of it (even if sometimes in suffering and pain) springs the +wonderful universe around us. And then say, can you fear for +your own little life, even though it may have its troubles? Can +you help feeling a part of this guided and governed nature? or +doubt that the power which fixed the laws of the stars and of the +tiniest drop of water - that made the plant draw power from the +sun, the tine coral animal its food from the dashing waves; that +adapted the flower to the insect and the insect to the flower - +is also moulding your life as part of the great machinery of the +universe, so that you have only to work, and to wait, and to +love? + +We are all groping dimly for the Unseen Power, but no one who +loves nature and studies it can ever feel alone or unloved in the +world. Facts, as mere facts, are dry and barren, but nature is +full of life and love, and her calm unswerving rule is tending to +some great though hidden purpose. You may call this Unseen Power +what you will - may lean on it in loving, trusting faith, or bend +in reverent and silent awe; but even the little child who lives +with nature and gazes on her with open eye, must rise in some +sense or other through nature to nature's God. + + + +Week 3 + +Lecture II Sunbeams and How They Work + +Who does not love the sunbeams, and feel brighter and merrier as +he watches them playing on the wall, sparkling like diamonds on +the ripples of the sea, or making bows of coloured light on the +waterfall? Is not the sunbeam so dear to us that it has become a +household word for all that is merry and gay? and when we want to +describe the dearest, busiest little sprite amongst us, who wakes +a smile on all faces wherever she goes, do we not call her the +"sunbeam of the house"? + +And yet how little even the wisest among us know about the nature +and work of these bright messengers of the sun as they dart +across space! + +Did you ever wake quite early in the morning, when it was pitch- +dark and you could see nothing, not even your own hand; and then +lie watching as time went on till the light came gradually +creeping in at the window? If you have done this you will have +noticed that you can at first only just distinguish the dim +outline of the furniture; then you can tell the difference +between the white cloth on the table and the dark wardrobe beside +it; then by degrees all the smaller details, the handles of the +drawer, the pattern on the wall, and the different colours of all +the objects in the room become clearer and clearer till at last +you see all distinctly in broad daylight. + +What has been happening here? and why have the things in the room +become visible by such slow degrees? We say that the sun is +rising, but we know very well that it is not the sun which moves, +but that our earth has been turning slowly round, and bringing +the little spot on which we live face to face with the great +fiery ball, so that his beams can fall upon us. + +Take a small globe, and stick a piece of black plaster over +England, then let a lighted lamp represent the sun, and turn the +globe slowly, so that the spot creeps round from the dark side +away from the lamp, until it catches, first the rays which pass +along the side of the globe, then the more direct rays, and at +last stands fully in the blaze of the light. Just this was +happening to our spot of the world as you lay in bed and saw the +light appear; and we have to learn today what those beams are +which fall upon us and what they do for us. + +First we must learn something about the sun itself, since it is +the starting-place of all the sunbeams. If the sun were a dark +mass instead of a fiery one we should have none of these bright +cheering messengers, and though we were turned face to face with +him every day we should remain in one cold eternal night. Now +you will remember we mentioned in the last lecture that it is +heat which shakes apart the little atoms of water and makes them +gloat up in the air to fall again as rain; and that if the day is +cold they fall as snow, and all the water is turned into ice. +But if the sun were altogether dark, think how bitterly cold it +would be; far colder than the most wintry weather ever known, +because in the bitterest night some warmth comes out of the +earth, where it has been stored from the sunlight which fell +during the day. But if we never received any warmth at all, no +water would ever rise up into the sky, no rain ever fall, no +rivers flow, and consequently no plants could grow and no animals +live. All water would be in the form of snow and ice, and the +earth would be one great frozen mass with nothing moving upon it. + +So you see it becomes very interesting for us to learn what the +sun is, and how he sends us his beams. How far away from us do +you think he is? On a fine summer's day when we can see him +clearly, it looks as if we had only to get into a balloon and +reach him as he sits in the sky, and yet we know roughly that he +is more than ninety-one millions of miles distant from our earth. + +These figures are so enormous that you cannot really grasp them. +But imagine yourself in an express train, travelling at the +tremendous rate of sixty miles an hour and never stopping. At +that rate, if you wished to arrive at the sun today you would +have been obliged to start 171 years ago. That is, you must have +set off in the early part of the reign of Queen Anne, and you +must have gone on, never, never resting, through the reigns of +George I, George ii, and the long reign of George III, then +through those of George IV, William IV, and Victoria, whirling on +day and night at express speed, and at last, today, you would +have reached the sun! + +And when you arrived there, how large do you think you would find +him to be? Anaxagoras, a learned Greek, was laughed at by all +his fellow Greeks because he said that the sun was as large as +the Peloponne-sus, that is about the size of Middlesex. How +astonished they would have been if they could have known that not +only is he bigger than the whole of Greece, but more than a +million times bigger than the whole world! + +Our world itself is a very large place, so large that our own +country looks only like a tiny speck upon it, and an express +train would take nearly a month to travel round it. Yet even our +whole globe is nothing in size compared to the sun, for it only +measures 8000 miles across, while the sun measures more the +852,000. + +Imagine for a moment that you could cut the sun and the earth +each in half as you would cut an apple; then if you were to lay +the flat side of the half-earth on the flat side of the half sun +it would take 106 such earths to stretch across the face of the +sun. One of these 106 round spots on the diagram represents the +size which our earth would look if placed on the sun; and they +are so tiny compared to him that they look only like a string of +minute beads stretched across his face. Only think, then, how +many of these minute dots would be required to fill the whole of +the inside of Fig. 4, if it were a globe. + +One of the best ways to form an idea of the whole size of the sun +is to imagine it to be hollow, like an air-ball, and then see how +many earths it would take to fill it. You would hardly believe +that it would take one million, three hundred and thirty-one +thousand globes the size of our world squeezed together. Just +think, if a huge giant could travel all over the universe and +gather worlds, all as big as ours, and were to make first a heap +of merely ten such worlds, how huge it would be! Then he must +have a hundred such heaps of ten to make a thousand world; and +then he must collect again a thousand times that thousand to make +a million, and when he had stuffed them all into the sun-ball he +would still have only filled three-quarters of it! + +After hearing this you will not be astonished that such a monster +should give out an enormous quantity of light and heat; so +enormous that it is almost impossible to form any idea of it. +Sir John Herschel has, indeed, tried to picture it for us. He +found that a ball of lime with a flame of oxygen and hydrogen +playing round it (such as we use in magic lanterns and call oxy- +hydrogen light) becomes so violently hot that it gives the most +brilliant artificial light we can get - such that you cannot put +your eye near it without injury. Yet if you wanted to have a +light as strong as that of our sun, it would not be enough to +make such a lime-ball as big as the sun is. No, you must make it +as big as 146 suns, or more than 146,000,000 times as big as our +earth, in order to get the right amount of light. Then you would +have a tolerably good artificial sun; for we know that the body +of the sun gives out an intense white light, just as the lime- +ball does, and that , like it, it has an atmosphere of glowing +gases round it. + +But perhaps we get the best idea of the mighty heat and light of +the sun by remembering how few of the rays which dart out on all +sides from this fiery ball can reach our tiny globe, and yet how +powerful they are. Look at the globe of a lamp in the middle of +the room, and see how its light pours out on all sides and into +every corner; then take a grain of mustard-seed, which will very +well represent the comparative size of our earth, and hold it up +at a distance from the lamp. How very few of all those rays +which are filling the room fall on the little mustard-seed, and +just so few does our earth catch of the rays which dart out from +the sun. And yet this small quantity (1/2000-millionth part of +the whole) does nearly all the work of our world. (These and the +preceding numerical statements will be found worked out in Sir J. +Herschel's 'Familiar Lectures on Scientific Subjects,' 1868, from +which many of the facts in the first part of the lecture are +taken.) + +In order to see how powerful the sun's rays are, you have only to +take a magnifying glass and gather them to a point on a piece of +brown paper, for they will set the paper alight. Sir John +Herschel tells us that at the Cape of Good Hope the heat was even +so great that he cooked a beefsteak and roasted some eggs by +merely putting them in the sun, in a box with a glass lid! +Indeed, just as we should all be frozen to death if the sun were +sold, so we should all be burnt up with intolerable heat if his +fierce rays fell with all their might upon us. But we have an +invisible veil protecting us, made - of what do you think? Of +those tiny particles of water which the sunbeams draw up and +scatter in the air, and which, as we shall see in Lecture IV, cut +off part of the intense heat and make the air cool and pleasant +for us. + + + +Week 4 + +We have now learnt something of the distance, the size, the +light, and the heat of the sun - the great source of the +sunbeams. But we are as yet no nearer the answer to the +question, What is a sunbeam? how does the sun touch our earth? + +Now suppose I with to touch you from this platform where I stand, +I can do it in two ways. Firstly, I can throw something at you +and hit you - in this case a thing will have passed across the +space from me to you. Or, secondly, if I could make a violent +movement so as to shake the floor of the room, you would feel a +quivering motion; and so I should touch you across the whole +distance of the room. But in this case no thing would have +passed from me to you but a movement or wave, which passed along +the boards of the floor. Again, if I speak to you, how does the +sound reach you ear? Not by anything being thrown from my mouth +to your ear, but by the motion of the air. When I speak I +agitate the air near my mouth, and that makes a wave in the air +beyond, and that one, another, and another (as we shall see more +fully in Lecture VI) till the last wave hits the drum of your +ear. + +Thus we see there are two ways of touching anything at a +distance; 1st, by throwing some thing at it and hitting it; 2nd, +by sending a movement of wave across to it, as in the case of the +quivering boards and the air. + +Now the great natural philosopher Newton thought that the sun +touched us in the first of these ways, and that sunbeams were +made of very minute atoms of matter thrown out by the sun, and +making a perpetual cannonade on our eyes. It is easy to +understand that this would make us see light and feel heat, just +as a blow in the eye makes us see starts, or on the body makes it +feel hot: and for a long time this explanation was supposed to be +the true one. But we know now that there are many facts which +cannot be explained on this theory, though we cannot go into them +here. What we will do, is to try and understand what now seems +to be the true explanation of the sunbeam. + +About the same time that Newton wrote, a Dutchman, named +Huyghens, suggested that light comes from the sun in tiny waves, +travelling across space much in the same way as ripples travel +across a pond. The only difficulty was to explain in what +substance these waves could be travelling: not through water, for +we know that there is no water in space - nor through air, for +the air stops at a comparatively short distance from our earth. +There must then be something filling all space between us and the +sun, finer than either water or air. + +And now I must ask you to use all you imagination, for I want you +to picture to yourselves something quite as invisible as the +Emperor's new clothes in Andersen's fairy-tale, only with this +difference, that our invisible something is very active; and +though we can neither see it nor touch it we know it by its +effects. You must imagine a fine substance filling all space +between us and the sun and the starts. A substance so very +delicate and subtle, that not only is it invisible, but it can +pass through solid bodies such as glass, ice, or even wood or +brick walls. This substance we call "ether." I cannot give you +here the reasons why we must assume that it is throughout all +space; you must take this on the word of such men as Sir John +Herschel or Professor Clerk-Maxwell, until you can study the +question for yourselves. + +Now if you can imagine this ether filling every corner of space, +so that it is everywhere and passes through everything, ask +yourselves, what must happen when a great commotion is going on +in one of the large bodies which float in it? When the atoms of +the gases round the sun are clashing violently together to make +all its light and heat, do you not think they must shake this +ether all around them? And then, since the ether stretches on +all sides from the sun to our earth and all other planets, must +not this quivering travel to us, just as the quivering of the +boards would from me to you? Take a basin of water to represent +the ether, and take a piece of potassium like that which we used +in our last lecture, and hold it with a pair of nippers in the +middle of the water. You will see that as the potassium hisses +and the flame burns round it, they will make waves which will +travel all over the water to the edge of the basin,, and you can +imagine how in the same way waves travel over the ether from the +sun to us. + +Straight away from the sun on all sides, never stopping, never +resting, but chasing after each other with marvellous quickness, +these tiny waves travel out into space by night and by day. When +our spot of the earth where England lies is turned away from them +and they cannot touch us, then it is night for us, but directly +England is turned so as to face the sun, then they strike on the +land, and the water, and warm it; or upon our eyes, making the +nerves quiver so that we see light. Look up at the sun and +picture to yourself that instead of one great blow from a fist +causing you to see starts for a moment, millions of tiny blows +from these sun-waves are striking every instant on you eye; then +you will easily understand that his would cause you to see a +constant blaze of light. + +But when the sun is away, if the night is clear we have light +from the starts. Do these then too make waves all across the +enormous distance between them and us? Certainly they do, for +they too are suns like our own, only they are so far off that the +waves they send are more feeble, and so we only notice them when +the sun's stronger waves are away. + +But perhaps you will ask, if no one has ever seen these waves not +the ether in which they are made, what right have we to say they +are there? Strange as it may seem, though we cannot see them we +have measured them and know how large they are, and how many can +go into an inch of space. For as these tiny waves are running on +straight forward through the room, if we put something in their +way, they will have to run round it; and if you let in a very +narrow ray of light through a shutter and put an upright wire in +the sunbeam, you actually make the waves run round the wire just +as water runs round a post in a river; and they meet behind the +wire, just as the water meets in a V shape behind the post. Now +when they meet, they run up against each other, and here it is we +catch them. Fir if they meet comfortably, both rising up in a +good wave, they run on together and make a bright line of light; +but if they meet higgledy-piggledy, one up and the other down, +all in confusion, they stop each other, and then there is no +light but a line of darkness. And so behind your piece of wire +you can catch the waves on a piece of paper, and you will find +they make dark and light lines one side by side with the other, +and by means of these bands it is possible to find out how large +the waves must be. This question is too difficult for us to work +it out here, but you can see that large waves will make broader +light and dark bands than small ones will, and that in this way +the size of the waves may be measured. + +And now how large do you think they turn out to be? so very, +very tiny that about fifty thousand waves are contained in a +single inch of space! I have drawn on the board the length of an +inch, and now I will measure the same space in the air between my +finger and thumb. Within this space at this moment there are +fifty thousand tiny waves moving up and down. I promised you we +would find in science things as wonderful as in fairy tales. Are +not these tiny invisible messengers coming incessantly from the +sun as wonderful as any fairies? and still more so when, as we +shall see presently, they are doing nearly all the work of our +world. + +We must next try to realize how fast these waves travel. You +will remember that an express train would take 171 years to reach +us from the sun; and even a cannon-ball would take from ten to +thirteen years to come that distance. Well, these tiny waves +take only seven minutes and a half to come the whole 91 millions +of miles. The waves which are hitting your eye at this moment +are caused by a movement which began at the sun only 7 1/2 +minutes ago. And remember, this movement is going on +incessantly, and these waves are always following one after the +other so rapidly that they keep up a perpetual cannonade upon the +pupil of your eye. So fast do they come that about 608 billion +waves enter your eye in one single second.* I do not ask you to +remember these figures; I only ask you to try and picture to +yourselves these infinitely tiny and active invisible messengers +from the sun, and to acknowledge that light is a fairy thing. +(*Light travels at the rate of 190,000 miles, or 12,165,120,000 +inches in a second. Taking the average number of wave-lengths in +an inch at 50,000, then 12,165,120,000 X 50,000 = +608,256,000,000,000.) + +But we do not yet know all about our sunbeams. See, I have here +a piece of glass with three sides, called a prism. If I put it +in the sunlight which is streaming through the window, what +happens? Look! on the table there is a line of beautiful +colours. I can make it long or short, as I turn the prism, but +the colours always remain arranged in the same way. Here at my +left hand is the red, beyond it orange, then yellow, green, blue, +indigo or deep blue, and violet, shading one into the other all +along the line. We have all seen these colours dancing on the +wall when the sun has been shining brightly on the cut-glass +pendants of the chandelier, and you may see them still more +distinctly if you let a ray of light into a darkened room, and +pass it through the prism as in the diagram (Fig. 7). What are +these colours? Do they come from the glass? No; for you will +remember to have seen them in the rainbow, and in the soap- +bubble, and even in a drop of dew or the scum on the top of a +pond. This beautiful coloured line is only our sunbeam again, +which has been split up into many colours by passing through the +glass, as it is in the rain-drops of the rainbow and the bubbles +of the scum of the pond. + + + +Week 5 + +Till now we have talked of the sunbeam as if it were made of only +one set of waves of different sizes, all travelling along +together from the sun. These various waves have been measured, +and we know that the waves which make up red light are larger and +more lazy than those which make violet light, so that there are +only thirty-nine thousand red waves in an inch, while there are +fifty-seven thousand violet waves in the same space. + +How is it then, that if all these different waves making +different colours, hit on our eye, they do not always make us see +coloured light? Because, unless they are interfered with, they +all travel along together, and you know that all colours, mixed +together in proper proportion, make white. + +I have here a round piece of cardboard, painted with the seven +colours in succession several times over. When it is still you +can distinguish them all apart, but when I whirl it quickly round +- see! - the cardboard looks quite white, because we see them all +so instantaneously that they are mingled together. In the same +way light looks white to you, because all the different coloured +waves strike on your eye at once. You can easily make on of +these card for yourselves only the white will always look dirty, +because you cannot get the colours pure. + +Now, when the light passes through the three-sided glass or +prism, the waves are spread out, and the slow, heavy, red waves +lag behind and remain at the lower end R of the coloured line on +the wall (Fig. 7), while the rapid little violet waves are bent +more out of their road and run to V at the farther end of the +line; and the orange, yellow, green, blue, and indigo arrange +themselves between, according to the size of their waves. + +And now you are very likely eager to ask why the quick waves +should make us see one colour, and the slow waves another. This +is a very difficult question, for we have a great deal still to +learn about the effect of light on the eye. But you can easily +imagine that colour is to our eye much the same as music is to +our ear. You know we can distinguish different notes when the +air-waves play slowly or quickly upon the drum of the ear (as we +shall see in Lecture VI) and somewhat in the same way the tiny +waves of the ether play on the retina or curtain at the back of +our eye, and make the nerves carry different messages to the +brain: and the colour we see depends upon the number of waves +which play upon the retina in a second. + +Do you think we have now rightly answered the question - What is +a sunbeam? We have seen that it is really a succession of tiny +rapid waves, travelling from the sun to us across the invisible +substance we call "ether", and keeping up a constant cannonade +upon everything which comes in their way. We have also seen +that, tiny as these waves are, they can still vary in size, so +that one single sunbeam is made up of myriads of different-sized +waves, which travel all together and make us see white light; +unless for some reason they are scattered apart, so that we see +them separately as red, green, blue, or yellow. How they are +scattered, and many other secrets of the sun-waves, we cannot +stop to consider not, but must pass on to ask - + +What work do the sunbeams do for us? + +They do two things - they give us light and heat. It is by means +of them alone that we see anything. When the room was dark you +could not distinguish the table, the chairs, or even the walls of +the room. Why? Because they had no light-waves to send to your +eye. But as the sunbeams began to pour in at the window, the +waves played upon the things in the room, and when they hit them +they bounded off them back to your eye, as a wave of the sea +bounds back from a rock and strikes against a passing boat. +Then, when they fell upon your eye, they entered it and excited +the retina and the nerves, and the image of the chair or the +table was carried to your brain. Look around at all the things +in this room. Is it not strange to think that each one of them +is sending these invisible messengers straight to your eye as you +look at it; and that you see me, and distinguish me from the +table, entirely by the kind of waves we each send to you? + +Some substances send back hardly any waves of light, but let them +all pass through them, and thus we cannot see them. A pane of +clear glass, for instance, lets nearly all the light-waves pass +through it, and therefore you often cannot see that the glass is +there, because no light-messengers come back to you from it. +Thus people have sometimes walked up against a glass door and +broken it, not seeing it was there. Those substances are +transparent which, for some reason unknown to us, allow the ether +waves to pass through them without shaking the atoms of which the +substance is made. In clear glass, for example, all the light- +waves pass through without affecting the substance of the glass; +while in a white wall the larger part of the rays are reflected +back to your eye, and those which pass into the wall, by giving +motion to its atoms lose their own vibrations. + +Into polished shining metal the waves hardly enter at all, but +are thrown back from the surface; and so a steel knife or a +silver spoon are very bright, and are clearly seen. Quicksilver +is put at the back of looking-glasses because it reflects so many +waves. It not only sends back those which come from the sun, but +those, too, which come from your face. So, when you see yourself +in a looking-glass, the sun-waves have first played on your face +and bounded off from it to the looking-glass; then, when they +strike the looking-glass, they are thrown back again on to the +retina of your eye, and you see your own face by means of the +very waves you threw off from it an instant before. + +But the reflected light-waves do more for us than this. They not +only make us see things, but they make us see them in different +colours. What, you will ask, is this too the work of the +sunbeams? Certainly; for if the colour we see depends on the +size of the waves which come back to us, then we must see things +coloured differently according to the waves they send back. For +instance, imagine a sunbeam playing on a leaf: part of its waves +bound straight back from it to our eye and make us see the +surface of the leaf, but the rest go right into the leaf itself, +and there some of them are used up and kept prisoners. The red, +orange, yellow, blue, and violet waves are all useful to the +leaf, and it does not let them go again. But it cannot absorb +the green waves, and so it throws them back, and they travel to +your eye and make you see a green colour. So when you say a leaf +is green, you mean that the leaf does not want the green waves of +the sunbeam, but sends them back to you. In the same way the +scarlet geranium rejects the red waves; this table sends back +brown waves; a white tablecloth sends back nearly the whole of +the waves, and a black coat scarcely any. This is why, when +there is very little light in the room, you can see a white +tablecloth while you would not be able to distinguish a black +object, because the few faint rays that are there, are all sent +back to you from a white surface. + +Is it not curious to think that there is really no such thing as +colour in the leaf, the table, the coat, or the geranium flower, +but we see them of different colours because, for some reason, +they send back only certain coloured waves to our eye? + +Wherever you look, then, and whatever you see, all the beautiful +tints, colours, lights, and shades around you are the work of the +tiny sun-waves. + +Again, light does a great deal of work when it falls upon plants. +Those rays of light which are caught by the leaf are by no means +idle; we shall see in Lecture VII that the leaf uses them to +digest its food and make the sap on which the plant feeds. + + + +Week 6 + +We all know that a plant becomes pale and sickly if it has not +sunlight, and the reason is, that without these light-waves it +cannot get food out of the air, nor make the sap and juices which +it needs. When you look at plants and trees growing in the +beautiful meadows; at the fields of corn, and at the lovely +landscape, you are looking on the work of the tiny waves of +light, which never rest all through the day in helping to give +life to every green thing that grows. + +So far we have spoken only of light; but hold your hand in the +sun and feel the heat of the sunbeams, and then consider if the +waves of heat do not do work also. There are many waves in a +sunbeam which move too slowly to make us see light when they hit +our eye, but we can feel them as heat, though we cannot see them +as light. The simplest way of feeling heat-waves is to hold a +warm iron near your face. You know that no light comes from it, +yet you can feel the heat-waves beating violently against your +face and scorching it. Now there are many of these dark heat- +rays in a sunbeam, and it is they which do most of the work in +the world. + +In the first place, as they come quivering to the earth, it is +they which shake the water-drops apart, so that these are carried +up in the air, as we shall see in the next lecture. And then +remember, it is these drops, falling again as rain, which make +the rivers and all the moving water on the earth. So also it is +the heat-waves which make the air hot and light, and so cause it +to rise and make winds and air-currents, and these again give +rise to ocean-currents. It is these dark rays, again, which +strike upon the land and give it the warmth which enables plants +to grow. It is they also which keep up the warmth in our own +bodies, both by coming to us directly from the sun, and also in a +very roundabout way through plants. You will remember that +plants use up rays of light and heat in growing; then either we +eat the plants, or animals eat the plants and we eat the animals; +and when we digest the food, that heat comes back in our bodies, +which the plants first took from the sunbeam. Breathe upon your +hand, and feel how hot your breath is; well, that heat which you +feel, was once in a sunbeam, and has travelled from it through +the food you have eaten, and has now been at work keeping up the +heat of your body. + +But there is still another way in which these plants may give out +the heat-waves they have imprisoned. You will remember how we +learnt in the first lecture that coal is made of plants, and that +the heat they give out is the heat these plants once took in. +Think how much work is done by burning coals. Not only are our +houses warmed by coal fires and lighted by coal gas, but our +steam-engines and machinery work entirely by water which has been +turned into steam by the heat of coal and coke fire; and our +steamboats travel all over the world by means of the same power. +In the same way the oil of our lamps comes either from olives, +which grow on trees; or from coal and the remains of plants and +animals in the earth. Even our tallow candles are made of mutton +fat, and sheep eat grass; as so, turn which way we will, we find +that the light and heat on our earth, whether it comes from +fires, or candles, or lamps, or gas, and whether it moves +machinery, or drives a train, or propels a ship, is equally the +work of the invisible waves of ether coming from the sun, which +make what we call a sunbeam. + +Lastly, there are still some hidden waves which we have not yet +mentioned, which are not useful to us either as light or heat, +and yet they are not idle. + +Before I began this lecture, I put a piece of paper, which had +been dipped in nitrate of silver, under a piece of glass; and +between it and the glass I put a piece of lace. Look what the +sun has been doing while I have been speaking. It has been +breaking up the nitrate of silver on the paper and turning it +into a deep brown substance; only where the threads of the lace +were, and the sun could not touch the nitrate of silver, there +the paper has remained light-coloured, and by this means I have a +beautiful impression of the lace on the paper. I will now dip +the impression into water in which some hyposulphite of soda is +dissolved, and this will "fix" the picture, that is, prevent the +sun acting upon it any more; then the picture will remain +distinct, and I can pass it round to you all. Here, again, +invisible waves have been at work, and this time neither as light +nor as heat, but as chemical agents, and it is these waves which +give us all our beautiful photographs. In any toyshop you can +buy this prepared paper, and set the chemical waves at work to +make pictures. Only you must remember to fix it in the solution +afterwards, otherwise the chemical rays will go on working after +you have taken the lace away, and all the paper will become brown +and your picture will disappear. + +And now, tell me, may we not honestly say, that the invisible +waves which make our sunbeams, are wonderful fairy messengers as +they travel eternally and unceasingly across space, never +resting, never tiring in doing the work of our world? Little as +we have been able to learn about them in one short hour, do they +not seem to you worth studying and worth thinking about, as we +look at the beautiful results of their work? The ancient Greeks +worshipped the sun, and condemned to death one of their greatest +philosophers, named Anaxagoras, because he denied that it was a +god. We can scarcely wonder at this when we see what the sun +does for our world; but we know that it is a huge globe made of +gases and fiery matter and not a god. We are grateful for the +sun instead of to him, and surely we shall look at him with new +interest, now that we can picture his tiny messengers, the +sunbeams, flitting over all space, falling upon our earth, giving +us light to see with, and beautiful colours to enjoy, warming the +air and the earth, making the refreshing rain, and, in a word, +filling the world with life and gladness. + + + +Week 7 + +LECTURE III The Aerial Ocean in Which We Live + +Did you ever sit on the bank of a river in some quiet spot where +the water was deep and clear, and watch the fishes swimming +lazily along? When I was a child this was one of my favourite +occupations in the summertime on the banks of the Thames, and +there was one question which often puzzled me greatly, as I +watched the minnows and gudgeon gliding along through the water. +Why should fishes live in something and be often buffeted about +by waves and currents, while I and others lived on the top of the +earth and not in anything? I do not remember ever asking anyone +about this; and if I had, in those days people did not pay much +attention to children's questions, and probably nobody would have +told me, what I now tell you, that we do live in something quite +as real and often quite as rough and stormy as the water in which +the fishes swim. The something in which we live is air, and the +reason that we do not perceive it, is that we are in it, and that +it is a gas, and invisible to us; while we are above the water in +which the fishes live, and it is a liquid which our eyes can +perceive. + +But let us suppose for a moment that a being, whose eyes were so +made that he could see gases as we see liquids, was looking down +from a distance upon our earth. He would see an ocean of air, or +aerial ocean, all round the globe, with birds floating about in +it, and people walking along the bottom, just as we see fish +gliding along the bottom of a river. It is true, he would never +see even the birds come near to the surface, for the highest- +flying bird, the condor, never soars more than five miles from +the ground, and our atmosphere, as we shall see, is at least 100 +miles high. So he would call us all deep-air creatures, just as +we talk of deep-sea animals; and if we can imagine that he fished +in this air-ocean, and could pull one of us out of it into space, +he would find that we should gasp and die just as fishes do when +pulled out of the water. + +He would also observe very curious things going on in our air- +ocean; he would see large streams and currents of air, which we +call winds, and which would appear to him as ocean-currents do to +us, while near down to the earth he would see thick mists forming +and then disappearing again, and these would be our clouds. From +them he would see rain, hail and snow falling to the earth, and +from time to time bright flashes would shoot across the air- +ocean, which would be our lightning. Nay even the brilliant +rainbow, the northern aurora borealis, and the falling stars, +which seem to us so high up in space, would be seen by him near +to our earth, and all within the aerial ocean. + +But as we know of no such being living in space, who can tell us +what takes place in our invisible air, and we cannot see it +ourselves, we must try by experiments to see it with our +imagination, though we cannot with our eyes. + +First, then, can we discover what air is? At one time it was +thought that it was a simple gas and could not be separated into +more than one kind. But we are now going to make an experiment +by which it has been shown that air is made of two gases mingled +together, and that one of these gases, called oxygen, is used up +when anything burns, while the other nitrogen is not used, and +only serves to dilute the minute atoms of oxygen. I have here a +glass bell-jar, with a cork fixed tightly in the neck, and I +place the jar over a pan of water, while on the water floats a +plate with a small piece of phosphorus upon it. You will see +that by putting the bell-jar over the water, I have shut in a +certain quantity of air, and my object now is to use up the +oxygen out of this air and leave only nitrogen behind. To do +this I must light the piece of phosphorus, for you will remember +it is in burning that oxygen is used up. I will take the cork +out, light the phosphorus, and cork up the jar again. See! as +the phosphorus burns white fumes fill the jar. These fumes are +phosphoric acid which is a substance made of phosphorous and the +oxygen of the air together. + +Now, phosphoric acid melts in water just as sugar does, and in a +few minutes these fumes will disappear. They are beginning to +melt already, and the water from the pan is rising up in the +bell-jar. Why is this? Consider for a moment what we have done. +First, the jar was full of air, that is, of mixed oxygen and +nitrogen; then the phosphorus used up the oxygen making white +fumes; afterwards, the water sucked up these fumes; and so, in +the jar now nitrogen is the only gas left, and the water has +risen up to fill all the rest of the space that was once taken up +with oxygen. + +We can easily prove that there is no oxygen now in the jar. I +take out the cork and let a lighted taper down into the gas. If +there were any oxygen the taper would burn, but you see it goes +out directly proving that all the oxygen has been used up by the +phosphorous. When this experiment is made very accurately, we +find that for every pint of oxygen in air there are four pints of +nitrogen, so that the active oxygen-atoms are scattered about, +floating in the sleepy, inactive nitrogen. + +It is these oxygen-atoms which we use up when we breathe. If I +had put a mouse under the bell-jar, instead of the phosphorus, +the water would have risen just the same, because the mouse would +have breathed in the oxygen and used it up in its body, joining +it to carbon and making a bad gas, carbonic acid, which would +also melt in the water, and when all the oxygen was used, the +mouse would have died. + +Do you see now how foolish it is to live in rooms that are +closely shut up, or to hide your head under the bedclothes when +you sleep? You use up all the oxygen-atoms, and then there are +none left for you to breathe; and besides this, you send out of +your mouth bad fumes, though you cannot see them, and these, when +you breathe them in again, poison you and make you ill. + +Perhaps you will say, If oxygen is so useful, why is not the air +made entirely of it? But think for a moment. If there was such +an immense quantity of oxygen, how fearfully fast everything +would burn! Our bodies would soon rise above fever heat from the +quantity of oxygen we should take in, and all fires and lights +would burn furiously. In fact, a flame once lighted would spread +so rapidly that no power on earth could stop it, and everything +would be destroyed. So the lazy nitrogen is very useful in +keeping the oxygen-atoms apart; and we have time, even when a +fire is very large and powerful, to put it out before it has +drawn in more and more oxygen from the surrounding air. Often, +if you can shut a fire into a closed space, as in a closely-shut +room or the hold of a ship, it will go out, because it has used +up all the oxygen in the air. + +So, you see, we shall be right in picturing this invisible air +all around us as a mixture of two gases. But when we examine +ordinary air very carefully, we find small quantities of other +gases in it, besides oxygen and nitrogen. First, there is +carbonic acid gas. This is the bad gas which we give out of our +mouths after we have burnt up the oxygen with the carbon of our +bodies inside our lungs; and this carbonic acid is also given out +from everything that burns. If only animals lived in the world, +this gas would soon poison the air; but plants get hold of it, +and in the sunshine they break it up again, as we shall see in +Lecture VII, and use up the carbon, throwing the oxygen back into +the air for us to use. Secondly, there are very small quantities +of ammonia, or the gas which almost chokes you in smelling-salts, +and which, when liquid is commonly called "spirits of hartshorn." +This ammonia is useful to plants, as we shall see by and by. +Lastly, there is a great deal of water in the air, floating about +as invisible vapour or water-dust, and this we shall speak of in +the next lecture. Still, all these gases and vapours in the +atmosphere are in very small quantities, and the bulk of the air +is composed of oxygen and nitrogen. + +Having now learned what air is, the next question which presents +itself is, Why does it stay round our earth? You will remember +we saw in the first lecture, that all the little atoms of a gas +are trying to fly away from each other, so that if I turn on this +gas-jet the atoms soon leave it, and reach you at the farther end +of the room, and you can smell the gas. Why, then, do not all +the atoms of oxygen and nitrogen fly away from our earth into +space, and leave us without any air? + +Ah! here you must look for another of our invisible forces. +Have you forgotten our giant force, "gravitation," which draws +things together from a distance? This force draws together the +earth and the atoms of oxygen and nitrogen; and as the earth is +very big and heavy, and the atoms of air are light and easily +moved, they are drawn down to the earth and held there by +gravitation. But for all that, the atmosphere does not leave off +trying to fly away; it is always pressing upwards and outwards +with all its might, while the earth is doing its best to hold it +down. + +The effect of this is, that near the earth, where the pull +downward is very strong, the air-atoms are drawn very closely +together, because gravitation gets the best of the struggle. But +as we get farther and farther from the earth, the pull downward +becomes weaker, and then the air-atoms spring farther apart, and +the air becomes thinner. Suppose that the lines in this diagram +represent layers of air. Near the earth we have to represent +them as lying closely together, but as they recede from the earth +they are also farther apart. + +But the chief reason why the air is thicker or denser nearer the +earth, is because the upper layers press it down. If you have a +heap of papers lying one on the top of the other, you know that +those at the bottom of the heap will be more closely pressed +together than those above, and just the same is the case with the +atoms of the air. Only there is this difference, if the papers +have lain for some time, when you take the top ones off, the +under ones remain close together. But it is not so with the air, +because air is elastic, and the atoms are always trying to fly +apart, so that directly you take away the pressure they spring up +again as far as they can. + + + +Week 8 + +I have here an ordinary pop-gun. If I push the cork in very +tight, and then force the piston slowly inwards, I can compress +the air a good deal. Now I am forcing the atoms nearer and +nearer together, but at last they rebel so strongly against being +more crowded that the cork cannot resist their pressure. Out it +flies, and the atoms spread themselves out comfortably again in +the air all around them. Now, just as I pressed the air together +in the pop-gun, so the atmosphere high up above the earth presses +on the air below and keeps the atoms closely packed together. +And in this case the atoms cannot force back the air above them +as they did the cork in the pop-gun; they are obliged to submit +to be pressed together. + +Even a short distance from the earth, however, at the top of a +high mountain, the air becomes lighter, because it has less +weight of atmosphere above it, and people who go up in balloons +often have great difficulty in breathing, because the air is so +thin and light. In 1804 a Frenchman, named Gay-Lussac, went up +four miles and a half in a balloon, and brought down some air; +and he found that it was much less heavy than the same quantity +of air taken close down to the earth, showing that it was much +thinner, or rarer, as it is called;* and when, in 1862, Mr. +Glaisher and Mr. Coxwell went up five miles and a half, Mr. +Glaisher's veins began to swell, and his head grew dizzy, and he +fainted. The air was too thin for him to breathe enough in at a +time, and it did not press heavily enough on the drums of his +ears and the veins of his body. He would have died if Mr. +Coxwell had not quickly let off some of the gas in the balloon, +so that it sank down into denser air. (*100 cubic inches near the +earth weighed 31 grains, while the same quantity taken at four +and a half miles up in the air weighed only 12 grains, or two- +fifths of the weight.) + +And now comes another very interesting question. If the air gets +less and less dense as it is farther from the earth, where does +it stop altogether? We cannot go up to find out, because we +should die long before we reached the limit; and for a long time +we had to guess about how high the atmosphere probably was, and +it was generally supposed not to be more than fifty miles. But +lately, some curious bodies, which we should have never suspected +would be useful to us in this way, have let us into the secret of +the height of the atmosphere. These bodies are the meteors, or +falling stars. + +Most people, at one time or another, have seen what looks like a +star shoot right across the sky, and disappear. On a clear +starlight night you may often see one or more of these bright +lights flash through the air; for one falls on an average in +every twenty minutes, and on the nights of August 9th and +November 13th there are numbers in one part of the sky. These +bodies are not really stars; they are simply stones or lumps of +metal flying through the air, and taking fire by clashing against +the atoms of oxygen in it. There are great numbers of these +masses moving round and round the sun, and when our earth comes +across their path, as it does especially in August and November, +they dash with such tremendous force through the atmosphere that +they grow white-hot, and give out light, and then disappear, +melted into vapour. Every now and then one falls to the earth +before it is all melted away, and thus we learn that these stones +contain tin, iron, sulphur, phosphorus, and other substances. + +It is while these bodies are burning that they look to us like +falling stars, and when we see them we know that hey must be +dashing against our atmosphere. Now if two people stand a +certain known distance, say fifty miles, apart on the earth and +observe these meteors and the direction in which they each see +them fall, they can calculate (by means of the angle between the +two directions) how high they are above them when they first see +them, and at that moment they must have struck against the +atmosphere, and even travelled some way through it, to become +white-hot. In this way we have learnt that meteors burst into +light at least 100 miles above the surface of the earth, and so +the atmosphere must be more than 100 miles high. + +Our next question is as to the weight of our aerial ocean. You +will easily understand that all this air weighing down upon the +earth must be very heavy, even though it grows lighter as it +ascends. The atmosphere does, in fact, weigh down upon land at +the level of the sea as much as if a 15-pound weight were put +upon every square inch of land. This little piece of linen +paper, which I am holding up, measures exactly a square inch, and +as it lies on the table, it is bearing a weight of 15 lbs. on its +surface. But how, then, comes it that I can lift it so easily? +Why am I not conscious of the weight? + +To understand this you must give all your attention, for it is +important and at first not very easy to grasp. you must +remember, in the first place, that the air is heavy because it is +attracted to the earth, and in the second place, that since air +is elastic all the atoms of it are pushing upwards against this +gravitation. And so, at any point in air, as for instance the +place where the paper now is as I hold it up, I feel no pressure +because exactly as much as gravitation is pulling the air down, +so much elasticity is resisting and pushing it up. So the +pressure is equal upwards, downwards, and on all sides, and I can +move the paper with equal ease any way. + +Even if I lay the paper on the table this is still true, because +there is always some air under it. If, however, I could get the +air quite away from one side of the paper, then the pressure on +the other side would show itself. I can do this by simply +wetting the paper and letting it fall on the table, and the water +will prevent any air from getting under it. Now see! if I try to +lift it by the thread in the middle, I have great difficulty, +because the whole 15 pounds' weight of the atmosphere is pressing +it down. A still better way of making the experiment is with a +piece of leather, such as the boys often amuse themselves with in +the streets. This piece of leather has been well soaked. I drop +it on the floor and see! it requires all my strength to pull it +up. (In fastening the string to the leather the hole must be +very small and the know as flat as possible, and it is even well +to put a small piece of kid under the knot. When I first made +this experiment, not having taken these precautions, it did not +succeed well, owing to air getting in through the hole.) I now +drop it on this stone weight, and so heavily is it pressed down +upon it by the atmosphere that I can lift the weight without its +breaking away from it. + +Have you ever tried to pick limpets off a rock? If so, you know +how tight they cling. the limpet clings to the rock just in the +same way as this leather does to the stone; the little animal +exhausts the air inside it's shell, and then it is pressed +against the rock by the whole weight of the air above. + +Perhaps you will wonder how it is that if we have a weight of 15 +lbs. pressing on every square inch of our bodies, it does not +crush us. And, indeed, it amounts on the whole to a weight of +about 15 tons upon the body of a grown man. It would crush us if +it were not that there are gases and fluids inside our bodies +which press outwards and balance the weight so that we do not +feel it at all. + +This is why Mr. Glaisher's veins swelled and he grew giddy in +thin air. The gases and fluids inside his body were pressing +outwards as much as when he was below, but the air outside did +not press so heavily, and so all the natural condition of his +body was disturbed. + +I hope we now realize how heavily the air presses down upon our +earth, but it is equally necessary to understand how, being +elastic, it also presses upwards; and we can prove this by a +simple experiment. I fill this tumbler with water, and keeping a +piece of card firmly pressed against it, I turn the whole upside- +down. When I now take my hand away you would naturally expect +the card to fall, and the water to be spilt. But no! the card +remains as if glued to the tumbler, kept there entirely by the +air pressing upwards against it. (The engraver has drawn the +tumbler only half full of water. The experiment will succeed +quite as well in this way if the tumbler be turned over quickly, +so that part of the air escapes between the tumbler and the card, +and therefore the space above the water is occupied by air less +dense than that outside.) + +And now we are almost prepared to understand how we can weigh the +invisible air. One more experiment first. I have here what is +called a U tube, because it is shaped like a large U. I pour +some water in it till it is about half full, and you will notice +that the water stands at the same height in both arms of the +tube, because the air presses on both surfaces alike. Putting my +thumb on one end I tilt the tube carefully, so as to make the +water run up to the end of one arm, and then turn it back again. +But the water does not now return to its even position, it +remains up in the arm on which my thumb rests. Why is this? +Because my thumb keeps back the air from pressing at that end, +and the whole weight of the atmosphere rests on the water at the +other end. And so we learn that not only has the atmosphere real +weight, but we can see the effects of this weight by making it +balance a column of water or any other liquid. In the case of +the wetted leather we felt the weight of the air, here we see its +effects. + +Now when we wish to see the weight of the air we consult a +barometer, which works really just in the same way as the water +in this tube. An ordinary upright barometer is simply a straight +tube of glass filled with mercury or quicksilver, and turned +upside-down in a small cup of mercury. The tube is a little more +than 30 inches long, and though it is quite full of mercury +before it is turned up, yet directly it stands in the cup the +mercury falls, till there is a height of about 30 inches between +the surface of the mercury in the cup, and that of the mercury in +the tube. As it falls it leaves an empty space above the mercury +which is called a vacuum, because it has no air in it. Now, the +mercury is under the same conditions as the water was in the U +tube, there is no pressure upon it at the top of the tube, while +there is a pressure of 15 lbs. upon it in the bowl, and therefore +it remains held up in the tube. + + + +Week 9 + +But why will it not remain more than 30 inches high in the tube? +You must remember it is only kept up in the tube at all by the +air which presses on the mercury in the cup. And that column of +mercury now balances the pressure of the air outside, and presses +down on the mercury in the cup at its mouth just as much as the +air does on the rest. So this cup and tube act exactly like a +pair of scales. The air outside is the thing to be weighed at +one end as it presses on the mercury, the column answers to the +leaden weight at the other end which tells you how heavy the air +is. Now if the bore of this tube is made an inch square, then +the 30 inches of mercury in it weigh exactly 15 lbs, and so we +know that the weight of the air is 15 lbs. upon every square +inch, but if the bore of the tube is only half a square inch, and +therefore the 30 inches of mercury only weigh 7 1/2 lbs. instead +of 15 lbs., the pressure of the atmosphere will also be halved, +because it will only act upon half a square inch of surface, and +for this reason it will make no difference to the height of the +mercury whether the tube be broad or narrow. + +But now suppose the atmosphere grows lighter, as it does when it +has much damp in it. The barometer will show this at once, +because there will be less weight on the mercury in the cup, +therefore it will not keep the mercury pushed so high up in the +tube. In other words, the mercury in the tube will fall. + +Let us suppose that one day the air is so much lighter that it +presses down only with a weight of 14 1/2 lbs. to the square inch +instead of 15 lbs. Then the mercury would fall to 29 inches, +because each inch is equal to the weight of half a pound. Now, +when the air is damp and very full of water-vapour it is much +lighter, and so when the barometer falls we expect rain. +Sometimes, however, other causes make the air light, and then, +although the barometer is low, no rain comes, + +Again, if the air becomes heavier the mercury is pushed up above +30 to 31 inches, and in this way we are able to weigh the +invisible air-ocean all over the world, and tell when it grows +lighter or heavier. This then, is the secret of the barometer. +We cannot speak of the thermometer today, but I should like to +warn you in passing that it has nothing to do with the weight of +the air, but only with heat, and acts in quite a different way. + +And now we have been so long hunting out, testing and weighing +our aerial ocean, that scarcely any time is left us to speak of +its movements or the pleasant breezes which it makes for us in +our country walks. Did you ever try to run races on a very windy +day? Ah! then you feel the air strongly enough; how it beats +against your face and chest, and blows down your throat so as to +take your breath away; and what hard work it is to struggle +against it! Stop for a moment and rest, and ask yourself, what +is the wind? Why does it blow sometimes one way and sometimes +another, and sometimes not at all? + +Wind is nothing more than air moving across the surface of the +earth, which as it passes along bends the tops of the trees, +beats against the houses, pushes the ships along by their sails, +turns the windmill, carries off the smoke from cities, whistles +through the keyhole, and moans as it rushes down the valley. +What makes the air restless? why should it not lie still all +round the earth? + +It is restless because, as you will remember, its atoms are kept +pressed together near the earth by the weight of the air above, +and they take every opportunity, when they can find more room, to +spread out violently and rush into the vacant space, and this +rush we call a wind. + +Imagine a great number of active schoolboys all crowded into a +room till they can scarcely move their arms and legs for the +crush, and then suppose all at once a large door is opened. Will +they not all come tumbling out pell-mell, one over the other, +into the hall beyond, so that if you stood in their way you would +most likely be knocked down? Well, just this happens to the air- +atoms; when they find a space before them into which they can +rush, they come on helter-skelter, with such force that you have +great difficulty in standing against them, and catch hold of +something to support you for fear you should be blown down. + +But how come they to find any empty space to receive them? To +answer this we must go back again to our little active invisible +fairies the sunbeams. When the sun-waves come pouring down upon +the earth they pass through the air almost without heating it. +But not so with the ground; there they pass down only a short +distance and then are thrown back again. And when these sun- +waves come quivering back they force the atoms of the air near +the earth apart and make it lighter; so that the air close to the +surface of the heated ground becomes less heavy than the air +above it, and rises just as a cork rises in water. You know that +hot air rises in the chimney; for if you put a piece of lighted +paper on the fire it is carried up by the draught of air, often +even before it can ignite. Now just as the hot air rises from +the fire, so it rises from the heated ground up into higher parts +of the atmosphere. and as it rises it leaves only thin air +behind it, and this cannot resist the strong cold air whose atoms +are struggling and trying to get free, and they rush in and fill +the space. + +One of the simplest examples of wind is to be found at the +seaside. there in the daytime the land gets hot under the +sunshine, and heats the air, making it grow light and rise. +Meanwhile the sunshine on the water goes down deeper, and so does +not send back so many heat-waves into the air; consequently the +air on the top of the water is cooler and heavier, and it rushes +in from over the sea to fill up the space on the shore left by +the warm air as it rises. This is why the seaside is so pleasant +in hot weather. During the daytime a light sea-breeze nearly +always sets in from the sea to the land. + +When night comes, however, then the land loses its heat very +quickly, because it has not stored it up and the land-air grows +cold; but the sea, which has been hoarding the sun-waves down in +its depths, now gives them up to the atmosphere above it, and the +sea-air becomes warm and rises. For this reason it is now the +turn of the cold air from the land to spread over the sea, and +you have a land-breeze blowing off the shore. + +Again, the reason why there are such steady winds, called the +trade winds, blowing towards the equator, is that the sun is very +hot at the equator, and hot air is always rising there and making +room for colder air to rush in. We have not time to travel +farther with the moving air, though its journeys are extremely +interesting; but if, when you read about the trade and other +winds, you will always picture to yourselves warm air made light +by the heat rising up into space and cold air expanding and +rushing in to fill its place, I can promise you that you will not +find the study of aerial currents so dry as many people imagine +it to be. + +We are now able to form some picture of our aerial ocean. We can +imagine the active atoms of oxygen floating in the sluggish +nitrogen, and being used up in every candle-flame, gas-jet and +fire, and in the breath of all living beings; and coming out +again tied fast to atoms of carbon and making carbonic acid. +Then we can turn to trees and plants, and see them tearing these +two apart again, holding the carbon fast and sending the +invisible atoms of oxygen bounding back again into the air, ready +to recommence work. We can picture all these air-atoms, whether +of oxygen or nitrogen, packed close together on the surface of +the earth, and lying gradually farther and farther apart, as they +have less weight above them, till they become so scattered that +we can only detect them as they rub against the flying meteors +which flash into light. We can feel this great weight of air +pressing the limpet on to the rock; and we can see it pressing up +the mercury in the barometer and so enabling us to measure its +weight. Lastly, every breath of wind that blows past us tells us +how this aerial ocean is always moving to and fro on the face of +the earth; and if we think for a moment how much bad air and bad +matter it must carry away, as it goes from crowded cities to be +purified in the country, we can see how, in even this one way +alone, it is a great blessing to us. + +Yet even now we have not mentioned many of the beauties of our +atmosphere. It is the tiny particles floating in the air which +scatter the light of the sun so that it spreads over the whole +country and into shady places. The sun's rays always travel +straight forward; and in the moon, where there is no atmosphere, +there is no light anywhere except just where the rays fall. But +on our earth the sun-waves hit against the myriads of particles +in the air and glide off them into the corners of the room or the +recesses of a shady lane, and so we have light spread before us +wherever we walk in the daytime, instead of those deep black +shadows which we can see through a telescope on the face of the +moon. + +Again, it is electricity playing in the air-atoms which gives us +the beautiful lightning and the grand aurora borealis, and even +the twinkling of the starts is produced entirely by minute +changes in the air. If it were not for our aerial ocean, the +stars would stare at us sternly, instead of smiling with the +pleasant twinkle-twinkle which we have all learned to love as +little children. + +All these questions, however, we must leave for the present; only +I hope you will be eager to read about them wherever you can, and +open your eyes to learn their secrets. For the present we must +be content if we can even picture this wonderful ocean of gas +spread round our earth, and some of the work it does for us. + +We said in the last lecture that without the sunbeams the earth +would be cold, dark, and frost-ridden. With sunbeams, but +without air, it would indeed have burning heat, side by side with +darkness and ice, but it could have no soft light. our planet +might look beautiful to others, as the moon does to us, but it +could have comparatively few beauties of its own. With the +sunbeams and the air, we see it has much to make it beautiful. +But a third worker is wanted before our planet can revel in +activity and life. This worker is water; and in the next lecture +we shall learn something of the beauty and the usefulness of the +"drops of water" on their travels. + + + +Week 10 + +LECTURE IV. A DROP OF WATER ON ITS TRAVELS + +We are going to spend an hour to-day in following a drop of water +on its travels. If I dip my finger in this basin of water and +lift it up again, I bring with it a small glistening +drop out of the body of water below, and hold it before you. Tell +me, have you any idea where this drop has been? what changes it +has undergone, and what work it has been doing during all the +long ages that water has lain on the face of the earth? It is a +drop now, but it was not so before I lifted it out of the basin; +then it was part of a sheet of water, and will be so again if I +let it fall. Again, if I were to put this basin on the stove till +all the water had boiled away, where would my drop be then? Where +would it go? What forms will it take before it reappears in the +rain-cloud, the river, or the sparkling dew? + +These are questions we are going to try to answer to-day; and +first, before we can in the least understand how water travels, +we must call to mind what we have learnt about the sunbeams and +the air. We must have clearly pictured in our imagination those +countless sun-waves which are for ever crossing space, and +especially those larger and slower undulations, the dark heat- +waves; for it is these, you will remember, which force the air- +atoms apart and make the air light, and it is also these which +are most busy in sending water on its travels. But not these +alone. The sun-waves might shake the water-drops as much as they +liked and turn them into invisible vapour, but they could not +carry them over the earth if it were not for the winds and +currents of that aerial ocean which bears the vapour on its +bosom, and wafts it to different regions of the world. + +Let us try to understand how these two invisible workers, the +sun-waves and the air, deal with the drops of water. I +have here a kettle (Fig. 18, p. 76) boiling over a spirit-lamp, +and I want you to follow minutely what is going on in it. First, +in the flame of the lamp, atoms of the spirit drawn up from below +are clashing with the oxygen-atoms in the air. This, as you know, +causes heat-waves and light-waves to move rapidly all round the +lamp. The light-waves cannot pass through the kettle, but the +heat-waves can, and as they enter the water inside they agitate +it violently. Quicker, and still more quickly, the particles of +water near the bottom of the kettle move to and fro and are +shaken apart; and as they become light they rise through the +colder water letting another layer come down to be heated in its +turn. The motion grows more and more violent, making the water +hotter and hotter, till at last the particles of which it is +composed fly asunder, and escape as invisible vapour. If this +kettle were transparent you would not see any steam above the +water, because it is in the form of an invisible gas. But as the +steam comes out of the mouth of the kettle you see a cloud. Why +is this? Because the vapour is chilled by coming out into the +cold air, and its particles are drawn together again into tiny, +tiny drops of water, to which Dr. Tyndall has given the +suggestive name of water-dust. If you hold a plate over the steam +you can catch these tiny drops, though they will run into one +another almost as you are catching them. + +The clouds you see floating in the sky are made of exactly the +same kind of water-dust as the cloud from the kettle, and I wish +to show you that this is also really the same as the invisible +steam within the kettle. I will do so by an experiment +suggested by Dr. Tyndall. Here is another spirit-lamp, which I +will hold under the cloud of steam - see! the cloud disappears! +As soon as the water-dust is heated the heat-waves scatter it +again into invisible particles, which float away into the room. +Even without the spirit-lamp, you can convince yourself that +water-vapour may be invisible; for close to the mouth of the +kettle you will see a short blank space before the cloud begins. +In this space there must be steam, but it is still so hot that +you cannot see it; and this proves that heat-waves can so shake +water apart as to carry it away invisibly right before your eyes. + +Now, although we never see any water travelling from our earth up +into the skies, we know that it goes there, for it comes down +again in rain, and so it must go up invisibly. But where does the +heat come from which makes this water invisible? Not from below, +as in the case of the kettle, but from above, pouring down from +the sun. Wherever the sun-waves touch the rivers, ponds, lakes, +seas, or fields of ice and snow upon our earth, they +carry off invisible water-vapour. They dart down through the top +layers of the water, and shake the water-particles forcibly +apart; and in this case the drops fly asunder more easily and +before they are so hot, because they are not kept down by a great +weight of water above, as in the kettle, but find plenty of room +to spread themselves out in the gaps between the air-atoms of the +atmosphere. + +Can you imagine these water-particles, just above any pond or +lake, rising up and getting entangled among the air-atoms? They +are very light, much lighter than the atmosphere; and so, when a +great many of them are spread about in the air which lies just +over the pond, they make it much lighter than the layer of air +above, and so help it to rise, while the heavier layer of air +comes down ready to take up more vapour. + +In this way the sun-waves and the air carry off water everyday, +and all day long, from the top of lakes, rivers, pools, springs, +and seas, and even from the surface of ice and snow. Without any +fuss or noise or sign of any kind, the water of our earth is +being drawn up invisibly into the sky. + +It has been calculated that in the Indian Ocean three-quarters of +an inch of water is carried off from the surface of the sea in +one day and night; so that as much as 22 feet, or a depth of +water about twice the height of an ordinary room, is silently and +invisibly lifted up from the whole surface of the ocean in one +year. It is true this is one of the hottest parts of the earth, +where the sun-waves are most active; but even in our +own country many feet of water are drawn up in the summer-time. + +What, then, becomes of all this water? Let us follow it as it +struggles upwards to the sky. We see it in our imagination first +carrying layer after layer of air up with it from the sea till it +rises far above our heads and above the highest mountains. But +now, call to mind what happens to the air as it recedes from the +earth. Do you not remember that the air-atoms are always trying +to fly apart, and are only kept pressed together by the weight of +air above them? Well, so this water-laden air rises up, its +particles, no longer so much pressed together, begin to separate, +and as all work requires an expenditure of heat, the air becomes +colder, and then you know at once what must happen to the +invisible vapour, -- it will form into tiny water-drops, like the +steam from the kettle. And so, as the air rises and becomes +colder, the vapour gathers into the visible masses, and we can +see it hanging in the sky, and call it clouds. When these clouds +are highest they are about ten miles from the earth, but when +they are made of heavy drops and hang low down, they sometimes +come within a mile of the ground. + +Look up at the clouds as you go home, and think that the water of +which they are made has all been drawn up invisibly through the +air. Not, however, necessarily here in London, for we have +already seen that air travels as wind all over the world, rushing +in to fill spaces made by rising air wherever they occur, and so +these clouds may be made of vapour collected in the +Mediterranean, or in the Gulf of Mexico off the coast of America, +or even, if the wind is from the north, of chilly +particles gathered from the surface of Greenland ice and snow, +and brought here by the moving currents of air. Only, of one +thing we may be sure, that they come from the water of our earth. + +Sometimes, if the air is warm, these water-particles may travel a +long way without ever forming into clouds; and on a hot, +cloudless day the air is often very full of invisible vapour. +Then, if a cold wind comes sweeping along, high up in the sky, +and chills this vapour, it forms into great bodies of water-dust +clouds, and the sky is overcast. At other times clouds hang +lazily in a bright sky, and these show us that just where they +are (as in Fig. 19) the air is cold and turns the invisible +vapour rising from the ground into visible water-dust, so that +exactly in those spaces we see it as clouds. Such clouds form +often on warm, still summer's day, and they are shaped like +masses of wool, ending in a straight line below. They are not +merely hanging in the sky, they are really resting upon a tall +column of invisible vapour which stretches right up from the +earth; and that straight line under the clouds marks +the place where the air becomes cold enough to turn this +invisible vapour into visible drops of water. + + + +Week 11 + +And now, suppose that while these or any other kind of clouds are +overhead, there comes along either a very cold wind, or a wind +full of vapour. As it passes through the clouds, it makes them +very full of water, for, if it chills them, it makes the water- +dust draw more closely together; or, if it brings a new load of +water-dust, the air is fuller than it can hold. In either case a +number of water-particles are set free, and our fairy force +"cohesion" seizes upon them at once and forms them into large +water-drops. Then they are much heavier than the air, and so they +can float no longer, but down they come to the earth in a shower +of rain. + +There are other ways in which the air may be chilled, and rain +made to fall, as, for example, when a wind laden with moisture +strikes against the cold tops of mountains. Thus the Khasia Hills +in India which face the Bay of Bengal, chill the air which +crosses them on its way from the Indian Ocean. The wet winds are +driven up the sides of the hills, the air expands, and the vapour +is chilled, and forming into drops, falls in torrents of rain. +Sir J. Hooker tells us that as much as 500 inches of rain fell in +these hills in nine months. That is to say, if you could measure +off all the ground over which the rain fell, and spread the whole +nine months' rain over it, it would make a lake 500 inches, or +more than 40 feet deep! You will not be surprised that the +country on the other side of these hills gets hardly any rain, +for all the water has been taken out of the air before +it comes there. Again for example in England, the wind comes to +Cumberland and Westmorland over the Atlantic, full of vapour, and +as it strikes against the Pennine Hills it shakes off its watery +load; so that the lake district is the most rainy in England, +with the exception perhaps of Wales, where the high mountains +have the same effect. + +In this way, from different causes, the water of which the sun +has robbed our rivers and seas, comes back to us, after it has +travelled to various parts of the world, floating on the bosom of +the air. But it does not always fall straight back into the +rivers and seas again, a large part of it falls on the land, and +has to trickle down slopes and into the earth, in order to get +back to its natural home, and it is often caught on its way +before it can reach the great waters. + +Go to any piece of ground which is left wild and untouched you +will find it covered with grass weeds, and other plants; if you +dig up a small plot you will find innumerable tiny roots creeping +through the ground in every direction. Each of these roots has a +sponge-like mouth by which the plant takes up water. Now, imagine +rain-drops falling on this plot of ground and sinking into the +earth. On every side they will find rootlets thirsting to drink +them in, and they will be sucked up as if by tiny sponges, and +drawn into the plants, and up the stems to the leaves. Here, as +we shall see in Lecture VII., they are worked up into food for +the plant, and only if the leaf has more water than it needs, +some drops may escape at the tiny openings under the +leaf, and be drawn up again by the sun-waves as invisible vapour +into the air. + +Again, much of the rain falls on hard rock and stone, where it +cannot sink in, and then it lies in pools till it is shaken apart +again into vapour and carried off in the air. Nor is it idle +here, even before it is carried up to make clouds. We have to +thank this invisible vapour in the air for protecting us from the +burning heat of the sun by day and intolerable frost by night. + +Let us for a moment imagine that we can see all that we know +exists between us and the sun. First, we have the fine ether +across which the sunbeams travel, beating down upon our earth +with immense force, so that in the sandy desert they are like a +burning fire. Then we have the coarser atmosphere of oxygen and +nitrogen atoms hanging in this ether, and bending the minute sun- +waves out of their direct path. But they do very little to hinder +them on their way, and this is why in very dry countries the +sun's heat is so intense. The rays beat down mercilessly, and +nothing opposes them. Lastly, in damp countries we have the +larger but still invisible particles of vapour hanging about +among the air-atoms. Now, these watery particles, although they +are very few (only about one twenty-fifth part of the whole +atmosphere), do hinder the sun-waves. For they are very greedy of +heat, and though the light-waves pass easily through them, they +catch the heat-waves and use them to help themselves to expand. +And so, when there is invisible vapour in the air, the sunbeams +come to us deprived of some of their heat-waves, and we +can remain in the sunshine without suffering from the heat. + +This is how the water-vapour shields us by day, but by night it +is still more useful. During the day our earth and the air near +it have been storing up the heat which has been poured down on +them, and at night, when the sun goes down, all this heat begins +to escape again. Now, if there were no vapour in the air, this +heat would rush back into space so rapidly that the ground would +become cold and frozen even on a summer's night, and all but the +most hardy plants would die. But the vapour which formed a veil +against the sun in the day, now forms a still more powerful veil +against the escape of the heat by night. It shuts in the heat- +waves, and only allows them to make their way slowly upwards from +the earth - thus producing for us the soft, balmy nights of +summer and preventing all life being destroyed in the winter. + +Perhaps you would scarcely imagine at first that it is this screen +of vapour which determines whether or not we shall have dew upon +the ground. Have you ever thought why dew forms, or what power has +been at work scattering the sparkling drops upon the grass? +Picture to yourself that it has been a very hot summer's day, and +the ground and the grass have been well warmed, and that the sun +goes down in a clear sky without any clouds. At once the heat- +waves which have been stored up in the ground, bound back into the +air, and here some are greedily absorbed by the vapour, while +others make their way slowly upwards. The grass, especially, gives +out these heat-waves very quickly, because the blades, being very +thin, are almost all surface. In consequence of this they part +with their heat more quickly than they can draw it up from the +ground, and become cold. Now the air lying just above the grass is +full of invisible vapour, and the cold of the blades, as it +touches them, chills the water- particles, and they are no longer +able to hold apart, but are drawn together into drops on the +surface of the leaves. + +We can easily make artificial dew for ourselves. I have here a +bottle of ice which has been kept outside the window. When I +bring it into the warm room a mist forms rapidly outside the +bottle. This mist is composed of water-drops, drawn out of the +air of the room, because the cold glass chilled the air all round +it, so that it gave up its invisible water to form dew-drops. +Just in this same way the cold blades of grass chill the air +lying above them, and steal its vapour. + +But try the experiment, some night when a heavy dew is expected, +of spreading a thin piece of muslin over some part of the grass, +supporting it at the four corners with pieces of stick so that it +forms an awning. Though there may be plenty of dew on the grass +all round, yet under this awning you will find scarcely any. The +reason of this is that the muslin checks the heat-waves as they +rise from the grass, and so the grass-blades are not chilled +enough to draw together the water-drops on their surface. If you +walk out early in the summer mornings and look at the fine cobwebs +flung across the hedges, you will see plenty of drops on the +cobwebs themselves sparkling like diamonds; but underneath on the +leaves there will be none, for even the delicate cobweb has been +strong enough to shut in the heat-waves and keep the leaves warm. + +Again, if you walk off the grass on to the gravel path, you find +no dew there. Why is this? Because the stones of the gravel can +draw up heat from the earth below as fast as they give it out, +and so they are never cold enough to chill the air which touches +them. On a cloudy night also you will often find little or no dew +even on the grass. The reason of this is that the clouds give +back heat to the earth, and so the grass does not become chilled +enough to draw the water-drops together on its surface. But after +a hot, dry day, when the plants are thirsty and there is little +hope of rain to refresh them, then they are able in the evening +to draw the little drops from the air and drink them in before +the rising sun comes again to carry them away. + +But our rain-drop undergoes other changes more strange than +these. Till now we have been imagining it to travel only where +the temperature is moderate enough for it to remain in a liquid +state as water. But suppose that when it is drawn up into the air +it meets with such a cold blast as to bring it to the freezing +point. If it falls into this blast when it is already a drop, +then it will freeze into a hailstone, and often on a hot summer's +day we may have a severe hailstorm, because the rain-drops have +crossed a bitterly cold wind as they were falling, and have been +frozen into round drops of ice. + +But if the water-vapour reaches the freezing air while it is still +an invisible gas, and before it has been drawn into a drop, then +its history is very different. The ordinary force of cohesion has +then no power over the particles to make them into watery globes, +but its place is taken by the fairy process of "crystallization," +and they are formed into beautiful white flakes, to fall in a +snow-shower. I want you to picture this process to yourselves, for +if once you can take an interest in the wonderful power of nature +to build up crystals, you will be astonished how often you will +meet with instances of it, and what pleasure it will add to your +life. + +The particles of nearly all substances, when left free and not +hurried, can build themselves into crystal forms. If you melt +salt in water and then let all the water evaporate slowly, you +will get salt-crystals; -- beautiful cubes of transparent salt +all built on the same pattern. The same is true of sugar; and if +you will look at the spikes of an ordinary stick of sugar-candy, +such as I have here, you will see the kind of crystals which +sugar forms. You may even pick out such shapes as these +from the common crystallized brown sugar in the sugar basin, or +see them with a magnifying glass on a lump of white sugar. + +But it is not only easily melted substances such as sugar and +salt which form crystals. The beautiful stalactite grottos are +all made of crystals of lime. Diamonds are crystals of carbon, +made inside the earth. Rock-crystals, which you know probably +under the name of Irish diamonds, are crystallized quartz; and +so, with slightly different colourings, are agates, opals, +jasper, onyx, cairngorms, and many other precious stones. Iron, +copper, gold, and sulphur, when melted and cooled slowly build +themselves into crystals, each of their own peculiar form, and we +see that there is here a wonderful order, such as we should never +have dreamt of, if we had not proved it. If you possess a +microscope you may watch the growth of crystals yourself by +melting some common powdered nitre in a little water till you +find that no more will melt in it. Then put a few drops of this +water on a warm glass slide and place it under the microscope. As +the drops dry you will see the long transparent needles of nitre +forming on the glass, and notice how regularly these crystals +grow, not by taking food inside like living beings, but by adding +particle to particle on the outside evenly and regularly. + + + +Week 12 + +Can we form any idea why the crystals build themselves up so +systematically? Dr. Tyndall says we can, and I hope by the help +of these small bar magnets to show you how he explains it. These +little pieces of steel, which I hope you can see lying +on this white cardboard, have been rubbed along a magnet until +they have become magnets themselves, and I can attract and lift +up a needle with any one of them. But if I try to lift one bar +with another, I can only do it by bringing certain ends together. +I have tied a piece of red cotton (c, Fig. 21) round one end of +each of the magnets, and if I bring two red ends together they +will not cling together but roll apart. If, on the contrary, I +put a red end against an end where there is not cotton, then the +two bars cling together. This is because every magnet has two +poles or points which are exactly opposite in character, and to +distinguish them one is called the positive pole and the other +the negative pole. Now when I bring two red ends, that is, two +positive poles together, they drive each other away. See! the +magnet I am not holding runs away from the other. But if I bring +a red end and a black end, that is, a positive and a negative end +together, then they are attracted and cling. I will make a +triangle (A, Fig. 21) in which a black end and a red end always +come together, and you see the triangle holds together. But now if +I take off the lower bar and turn it (B, Fig. 21) so that two red +ends and two black ends come together, then this bar actually +rolls back from the others down the cardboard. If I were to break +these bars into a thousand pieces, each piece would still have two +poles, and if they were scattered about near each other in such a +way that they were quite free to move, they would arrange +themselves always so two different poles came together. + +Now picture to yourselves that all the particles of those +substances which form crystals have poles like our magnets, then +you can imagine that when the heat which held them apart is +withdrawn and the particles come very near together, they will +arrange themselves according to the attraction of their poles and +so build up regular and beautiful patterns. + +So, if we could travel up to the clouds where this fairy power of +crystallization is at work, we should find the particles of +water-vapour in a freezing atmosphere being built up into minute +solid crystals of snow. If you go out after a snow-shower and +search carefully, you will see that the snow-flakes are not mere +lumps of frozen water, but beautiful six-pointed crystal stars, so +white and pure that when we want to speak of anything being +spotlessly white, you say that it is "white as snow." Some of +these crystals are simply flat slabs with six sides, others are +stars with six rods or spikes springing from the centre, others +with six spikes each formed like a delicate fern. No less than a +thousand different forms of delicate crystals have been found +among snowflakes, but though there is such a great variety, yet +they are all built on the six-sided and six-pointed plan, and are +all rendered dazzlingly white by the reflection of the light from +the faces of the crystals and the tiny air-bubbles built up within +them. This, you see, is why, when the snow melts, you have only a +little dirty water in your hand; the crystals are gone and there +are no more air-bubbles held prisoners to act as looking-glasses +to the light. Hoar-frost is also made up of tiny water-crystals, +and is nothing more than frozen dew hanging on the blades of grass +and from the trees. + +But how about ice? Here, you will say, is frozen water, and yet +we see no crystals, only a clear transparent mass. Here, again, +Dr. Tyndall helps us. He says (and as I have proved it true, so +may you for yourselves, if you will) that if you take a +magnifying glass, and look down on the surface of ice on a sunny +day, you will see a number of dark, six-sided stars, looking like +flattened flowers, and in the centre of each a bright spot. These +flowers, which are seen when the ice is melting, are our old +friends the crystal stars turning into water, and the +bright spot in the middle is a bubble of empty space, left +because the watery flower does not fill up as much room as the +ice of the crystal star did. + +And this leads us to notice that ice always takes up more room +than water, and that this is the reason why our water-pipes burst +in severe frosts; for as the water freezes it expands with great +force, and the pipe is cracked, and then when the thaw comes on , +and the water melts again, it pours through the crack it has +made. + +It is not difficult to understand why ice should take more room; +for we know that if we were to try to arrange bricks end to end +in star-like shapes, we must leave some spaces between, and could +not pack them so closely as if they lay side by side. And so, +when this giant force of crystallization constrains the atoms of +frozen water to grow into star-like forms, the solid mass must +fill more room than the liquid water, and when the star +melts, this space reveals itself to us in the bright spot of the +centre. + +We have now seen our drop of water under all its various forms of +invisible gas, visible steam, cloud, dew, hoar-frost, snow, and +ice, and we have only time shortly to see it on its travels, not +merely up and down, as hitherto, but round the world. + +We must first go to the sea as the distillery, or the place from +which water is drawn up invisibly, in its purest state, into the +air; and we must go chiefly to the seas of the tropics, because +here the sun shines most directly all the year round, sending +heat-waves to shake the water-particles asunder. It has been +found by experiment that, in order to turn 1 lb. of water into +vapour, as much heat must be used as is required to melt 5 lbs. +of iron; and if you consider for a moment how difficult iron is +to melt, and how we can keep an iron poker in a hot fire and yet +it remains solid, this will help you to realize how much heat the +sun must pour down in order to carry off such a constant supply +of vapour from the tropical seas. + +Now, when all this vapour is drawn up into the air, we know that +some of it will form into clouds as it gets chilled high up in +the sky, and then it will pour down again in those tremendous +floods of rain which occur in the tropics. + +But the sun and air will not let it all fall down at once, and +the winds which are blowing from the equator to the poles carry +large masses of it away with them. Then, as you know, it will +depend on many things how far this vapour is carried. Some of it, +chilled by cold blasts, or by striking on cold mountain tops, as +it travels northwards, will fall in rain in Europe and Asia, while +that which travels southwards may fall in South America, +Australia, or New Zealand, or be carried over the sea to the South +Pole. Wherever it falls on the land as rain, and is not used by +plants, it will do one of two things; either it will run down in +streams and form brooks and rivers, and so at last find its way +back to the sea, or it will sink deep in the earth till it comes +upon some hard rock through which it cannot get, and then, being +hard pressed by the water coming on behind, it will rise up again +through cracks, and come to the surface as a spring. These +springs, again, feed rivers, sometimes above- ground, sometimes +for long distances under-ground; but one way or another at last +the whole drains back into the sea. + +But if the vapour travels on till it reaches high mountains in +cooler lands, such as the Alps of Switzerland; or is carried to +the poles and to such countries as Greenland or the Antarctic +Continent, then it will come down as snow, forming immense snow- +fields. And here a curious change takes place in it. If you make +an ordinary snowball and work it firmly together, it becomes very +hard, and if you then press it forcibly into a mould you can turn +it into transparent ice. And in the same way the snow which falls +in Greenland and on the high mountains of Switzerland becomes +very firmly pressed together, as it slides down into the valleys. +It is like a crowd of people passing from a broad thoroughfare +into a narrow street. As the valley grows narrower and +narrower the great mass of snow in front cannot move down +quickly, while more and more is piled up by the snowfall behind, +and the crowd and crush grow denser and denser. In this way the +snow is pressed together till the air that was hidden in its +crystals, and which gave it its beautiful whiteness, is all +pressed out, and the snow-crystals themselves are squeezed into +one solid mass of pure, transparent ice. + +Then we have what is called a "glacier," or river of ice, and +this solid river comes creeping down till, in Greenland, it +reaches the edge of the sea. There it is pushed over the brink of +the land, and large pieces snap off, and we have "icebergs." +These icebergs - made, remember, of the same water which was +first draw up from the tropics - float on the wide sea, and +melting in its warm currents, topple over and over* (A floating +iceberg must have about eight times as much ice under the water +as it has above, and therefore, when the lower part melts in a +warm current, the iceberg loses its balance and tilts over, so as +to rearrange itself round the centre of gravity.) till they +disappear and mix with the water, to be carried back again to the +warm ocean from which they first started. In Switzerland the +glaciers cannot reach the sea, but they move down into the +valleys till they come to a warmer region, and there the end of +the glacier melts, and flows away in a stream. The Rhone and many +other rivers are fed by the glaciers of the Alps; and as these +rivers flow into the sea, our drop of water again finds its way +back to its home. + +But when it joins itself in this way to its companions, from whom +it was parted for a time, does it come back clear and transparent +as it left them? From the iceberg it does indeed return pure and +clear; for the fairy Crystallization will have no impurities, not +even salt, in her ice-crystals, and so as they melt they give back +nothing but pure water to the sea. Yet even icebergs bring down +earth and stones frozen into the bottom of the ice, and so they +feed the sea with mud. + +But the drops of water in rivers are by no means as pure as when +they rose up into the sky. We shall see in the next lecture how +rivers carry down not only sand and mud all along their course, +but even solid matter such as salt, lime, iron, and flint, +dissolved in the clear water, just as sugar is dissolved, without +our being able to see it. The water, too, which has sunk down +into the earth, takes up much matter as it travels along. You all +know that the water you drink from a spring is very different +from rain-water, and you will often find a hard crust at the +bottom of kettles and in boilers, which is formed of the +carbonate of lime which is driven out of the clear water when it +is boiled. The water has become "hard" in consequence of having +picked up and dissolved the carbonate of lime on its way through +the earth, just in the same way as water would become sweet if +you poured it through a sugar-cask. You will also have heard of +iron-springs, sulphur-springs, and salt-springs, which come out +of the earth, even if you have never tasted any of them, and the +water of all these springs finds its way back at last to the +sea. + +And now, can you understand why sea-water should taste +salt and bitter? Every drop of water which flows from the earth +to the sea carries something with it. Generally, there is so +little of any substance in the water that we cannot taste it, and +we call it pure water; but the purest of spring or river-water +has always some solid matter dissolved in it, and all this goes +to the sea. Now, when the sun-waves come to take the water out of +the sea again, they will have nothing but the pure water itself; +and so all these salts and carbonates and other solid substances +are left behind, and we taste them in sea-water. + +Some day, when you are at the seaside, take some extra water and +set it on the hob till a great deal has simmered gently away, and +the liquid is very thick. Then take a drop of this liquid, and +examine it under a microscope. As it dries up gradually, you will +see a number of crystals forming, some square - and these will be +crystals of ordinary salt; some oblong - these will be crystals +of gypsum or alabaster; and others of various shapes. Then, when +you see how much matter from the land is contained in sea-water, +you will no longer wonder that the sea is salt; on the contrary, +you will ask, Why does it not grow salter every year? + +The answer to this scarcely belongs to our history of a drop of +water, but I must just suggest it to you. In the sea are numbers +of soft-bodied animals, like the jelly animals which form the +coral, which require hard material for their shells or the solid +branches on which they live, and they are greedily watching for +these atoms of lime, of flint, or magnesia, and of other +substances brought down into the sea. It is with lime and magnesia +that the tiny chalk-builders form their beautiful shells, and the +coral animals their skeletons, while another class of builders use +the flint; and when these creatures die, their remains go to form +fresh land at the bottom of the sea; and so, though the earth is +being washed away by the rivers and springs it is being built up +again, out of the same materials, in the depths of the great +ocean. + +And now we have reached the end of the travels of our drop of +water. We have seen it drawn up by the fairy "heat," invisible +into the sky; there fairy "cohesion" seized it and formed it into +water-drops and the giant, "gravitation," pulled it down again to +the earth. Or, if it rose to freezing regions, the fairy of +"crystallization" built it up into snow-crystals, again to fall +to the earth, and either to be melted back into water by heat, or +to slide down the valleys by force of gravitation, till it became +squeezed into ice. We have detected it, when invisible, forming a +veil round our earth, and keeping off the intense heat of the +sun's rays by day, or shutting it in by night. We have seen it +chilled by the blades of grass, forming sparkling dew-drops or +crystals of hoar-frost, glistening in the early morning sun; and +we have seen it in the dark underground, being drunk up greedily +by the roots of plants. We have started with it from the tropics, +and travelled over land and sea, watching it forming rivers, or +flowing underground in springs, or moving onwards to the high +mountains or the poles, and coming back again in glaciers and +icebergs. Through all this, while it is being carried +hither and thither by invisible power, we find no trace of its +becoming worn out, or likely to rest from its labours. Ever +onwards it goes, up and down, and round and round the world, +taking many forms, and performing many wonderful feats. We have +seen some of the work that it does, in refreshing the air, +feeding the plants, giving us clear, sparkling water to drink, +and carrying matter to the sea; but besides this, it does a +wonderful work in altering all the face of our earth. This work +we shall consider in the next lecture, on "The two great +Sculptors - Water and Ice." + + + +Week 13 + +LECTURE V. THE TWO GREAT SCULPTORS - WATER AND ICE. + +In our last lecture we saw that water can exist in three forms:-- +1st, as an invisible vapour; 2nd, as liquid water; 3rd, as solid +snow and ice. + +To-day we are going to take the two last of these +forms, water and ice, and speak of them as sculptors. + +To understand why they deserve this name we must first consider +what the work of a sculptor is. If you go into a statuary yard +you will find there large blocks of granite, marble, and other +kinds of stone, hewn roughly into different shapes; but if you +pass into the studio, where the sculptor himself is at work you +will find beautiful statues, more or less finished; and you will +see that out of rough blocks of stone he has been able to cut +images which look like living forms. You can even see by their +faces whether they are intended to be sad, or thoughtful, or +gay, and by their attitude whether they are writhing in pain, +or dancing with joy, or resting peacefully. How has all this +history been worked out from the shapeless stone? It has been +done by the sculptor's chisel. A piece chipped off here, a +wrinkle cut there, a smooth surface rounded off in another place, +so as to give a gentle curve; all these touches gradually shape +the figure and mould it out of the rough stone, first into a +rude shape and afterwards, by delicate strokes, into the form of +a living being. + +Now, just in the same way as the wrinkles and curves of a statue +are cut by the sculptor's chisel, so the hills and valleys, the +steep slopes and gentle curves on the face of our earth, giving +it all its beauty, and the varied landscapes we love so well, +have been cut out by water and ice passing over them. It is true +that some of the greater wrinkles of the earth, the lofty +mountains, and the high masses of land which rise above the sea , +have been caused by earthquakes and shrinking of the +earth. We shall not speak of these to-day, but put them aside as +belonging to the rough work of the statuary yard. But when once +these large masses are put ready for water to work upon, then +all the rest of the rugged wrinkles and gentle slopes which make +the country so beautiful are due to water and ice, and for this +reason I have called them "sculptors." + +Go for a walk in the country, or notice the landscape as you +travel on a railway journey. You pass by hills and through +valleys, through narrow steep gorges cut in hard rock, or +through wild ravines up the sides of which you can hardly +scramble. Then you come to grassy slopes and to smooth plains +across which you can look for miles without seeing a hill; or, +when you arrive at the seashore, you clamber into caves and +grottos, and along dark narrow passages leading from one bay to +another. All these - hills, valleys, gorges, ravines, slopes, +plains, caves, grottos, and rocky shores - have been cut out by +the water. Day by day and year by year, while everything seems +to us to remain the same, this industrious sculptor is chipping +away, a few grains here, a corner there, a large mass in another +place, till he gives to the country its own peculiar scenery, +just as the human sculptor gives expression to his statue. + +Our work to-day will consist in trying to form some idea of the +way in which water thus carves out the surface of the earth, and +we will begin by seeing how much can be done by our old friends +the rain-drops before they become running streams. + +Everyone must have noticed that whenever rain falls on soft +ground it makes small round holes in which it +collects, and then sinks into the ground, forcing its way +between the grains of earth. But you would hardly think that the +beautiful pillars in Fig. 24 have been made entirely in this way +by rain beating upon and soaking into the ground. + +Where these pillars stand there was once a solid mass of clay and +stones, into which the rain-drops crept, loosening the earthly +particles; and then when the sun dried the earth again cracks +were formed, so that the next shower loosened it still more, and +carried some of the mud down into the valley below. But here and +there large stones were buried in the clay, and where this +happened the rain could not penetrate, and the stones +became the tops of tall pillars of clay, washed into shape by the +rain beating on its sides, but escaping the general destruction +of the rest of the mud. In this way the whole valley has been +carved out into fine pillars, some still having capping-stones, +while others have lost them, and these last will soon be washed +away. We have no such valleys of earth-pillars here in England, +but you may sometimes see tiny pillars under bridges where the +drippings have washed away the earth between the pebbles, and +such small examples which you can observe for yourselves are +quite as instructive as more important ones. + +Another way in which rain changes the surface of the earth is by +sinking down through loose soil from the top of a cliff to a +depth of many feet till it comes to solid rock, and then lying +spread over a wide apace. Here it makes a kind of watery mud, +which is a very unsafe foundation for the hill of earth above +it, and so after a time the whole mass slips down and makes a +fresh piece of land at the foot of the cliff. If you have ever +been at the Isle of Wight you will have seen an undulating strip +of ground, called the Undercliff, at Ventnor and other places, +stretching all along the sea below the high cliffs. This land +was once at the top of the cliff, and came down by succession of +landslips such as we have been describing. A very great landslip +of this kind happened in the memory of living people, at Lyme +Regis, in Dorsetshire, in the year 1839. + +You will easily see how in forming earth-pillars and causing +landslips rain changes the face of the country, but +these are only rare effects of water. It is when the rain +collects in brooks and forms rivers that it is most busy in +sculpturing the land. Look out some day into the road or the +garden where the ground slopes a little, and watch what happens +during a shower of rain. First the rain-drops run together in +every little hollow of the ground, then the water begins to flow +along any ruts or channels it can find, lying here and there in +pools, but always making its way gradually down the slope. +Meanwhile from other parts of the ground little rills are +coming, and these all meet in some larger ruts where the ground +is lowest, making one great stream, which at last empties itself +into the gutter or an area, or finds its way down some grating. + +Now just this, which we can watch whenever a heavy shower of rain +comes down on the road, happens also all over the world. Up in +the mountains, where there is always a great deal of rain, +little rills gather and fall over the mountain sides, meeting in +some stream below. Then, as this stream flows on, it is fed by +many runnels of water, which come from all parts of the country, +trickling along ruts, and flowing in small brooks and rivulets +down the gentle slope of the land till they reach the big stream, +which at last is important enough to be called a river. +Sometimes this river comes to a large hollow in the land and +there the water gathers and forms a lake; but still at the lower +end of this lake out it comes again, forming a new river, and +growing and growing by receiving fresh streams until at last it +reaches the sea. + +The River Thames, which you all know, and whose course you will +find clearly described in Mr. Huxley's 'Physiography,' drains in +this way no less than one-seventh of the whole of England. All the +rain which falls in Berkshire, Oxfordshire, Middlesex, +Hertfordshire, Surrey, the north of Wiltshire and north-west of +Kent, the south of Buckinghamshire and of Gloucestershire, finds +its way into the Thames; making an area of 6160 square miles over +which every rivulet and brook trickle down to the one great river, +which bears them to the ocean. And so with every other area of +land in the world there is some one channel towards which the +ground on all sides slopes gently down, and into this channel all +the water will run, on its way to the sea. + +But what has this to do with sculpture or cutting out of valleys? +If you will only take a glass of water out of any river, and let +it stand for some hours, you will soon answer this question for +yourself. For you will find that even from river water which +looks quite clear, a thin layer of mud will fall to the bottom +of the glass, and if you take the water when the river is +swollen and muddy you will get quite a thick deposit. This shows +that the brooks, the streams, and the rivers wash away the land +as they flow over it and carry it from the mountains down to the +valleys, and from the valleys away out into the sea. + +But besides earthly matter, which we can see, there is much +matter dissolved in the water of rivers (as we mentioned in the +last lecture), and this we cannot see. + +If you use water which comes out of a chalk country you will find +that after a time the kettle in which you have been in the habit +of boiling this water has a hard crust on its bottom and sides, +and this crust is made of chalk or carbonate of lime, +which the water took out of the rocks when it was passing +through them. Professor Bischoff has calculated that the river +Rhine carries past Bonn every year enough carbonate of lime +dissolved in its water to make 332,000 million oyster-shells, +and that if all these shells were built into a cube it would +measure 560 feet. + + + +Week 14 + +Imagine to yourselves the whole of St. Paul's churchyard filled +with oyster-shells, built up in a large square till they reached +half as high again as the top of the cathedral, then you will +have some idea of the amount of chalk carried invisibly past +Bonn in the water of the Rhine every year. + +Since all this matter, whether brought down as mud or dissolved, +comes from one part of the land to be carried elsewhere or out +to sea, it is clear that some gaps and hollows must be left in +the places from which it is taken. Let us see how these gaps are +made. Have you ever clambered up the mountainside, or even up +one of those small ravines in the hillside, which have generally +a little stream trickling through them? If so, you must have +noticed the number of pebbles, large and small, lying in patches +here and there in the stream, and many pieces of broken rock, +which are often scattered along the sides of the ravine; and +how, as you climb, the path grows steeper, and the rocks become +rugged and stick out in strange shapes. + +The history of this ravine will tell us a great deal about the +carving of water. Once it was nothing more than a little furrow +in the hillside down which the rain found its way in a thin +thread-like stream. But by and by, as the stream carried down +some of the earth, and the furrow grew deeper and wider, the sides +began to crumble when the sun dried up the rain which had soaked +in. Then in winter, when the sides of the hill were moist with the +autumn rains, frost came and turned the water to ice, and so made +the cracks still larger, and the swollen steam rushing down, +caught the loose pieces of rock and washed them down into its bed. +Here they were rolled over and over, and grated against each +other, and were ground away till they became rounded pebbles, such +as lie in the foreground of the picture (Fig. 25); while the grit +which was rubbed off them was carried farther down by the stream. +And so in time this became a little valley, and as the stream cut +it deeper and deeper, there was room to clamber along the sides of +it, and ferns and mosses began to cover the naked stone, and small +trees rooted themselves along the banks, and this beautiful little +nook sprang up on the hill-side entirely by the sculpturing of +water. + +Shall you not feel a fresh interest in all the little valleys, +ravines, and gorges you meet with in the country, if you can +picture them being formed in this way year by year? There are +many curious differences in them which you can study for +yourselves. Some will be smooth, broad valleys and here the +rocks have been soft and easily worn, and water trickling down +the sides of the first valley has cut other channels so as to +make smaller valleys running across it. In other places there +will be narrow ravines, and here the rocks have been hard, so +that they did not wear away gradually, but broke off and fell in +blocks, leaving high cliffs on each side. In some places you +will come to a beautiful waterfall, where the water has tumbled +over a steep cliff, and then eaten its way back, just like a saw +cutting through a piece of wood. + +There are two things in particular to notice in a waterfall like +this. First, how the water and spray dash against the bottom of +the cliff down which it falls, and grind the small pebbles +against the rock. In this way the bottom of the cliff is +undermined, and so great pieces tumble down from time to time, +and keep the fall upright instead of its being sloped away at the +top, and becoming a mere steam. Secondly, you may often see +curious cup-shaped holes, called "pot-holes," in the rocks on the +sides of a waterfall, and these also are concerned in its +formation. In these holes you will generally find two or three +small pebbles, and you have here a beautiful example of how water +uses stones to grind away the face of the earth. These holes are +made entirely by the falling water eddying round and round in a +small hollow of the rock, and grinding the pebbles which it has +brought down, against the bottom and sides of this hollow, just as +you grind round a pestle in a mortar. By degrees the hole grows +deeper and deeper and though the first pebbles are probably ground +down to powder, others fall in, and so in time there is a great +hole perforated right through, helping to make the rock break and +fall away. + +In this and other ways the water works its way back in a +surprising manner. The Isle of Wight gives us some good +instances of this; Alum Bay Chine and the celebrated Blackgang +Chine have been entirely cut out by waterfalls. But the best +know and most remarkable example is the Niagara Falls, in +America. Here, the River Niagara first wanders through a flat +country, and then reaches the great Lake Erie in a hollow of the +plain. After that, it flows gently down for about fifteen miles, +and then the slope becomes greater and it rushes on to the Falls +of Niagara. These falls are not nearly so high as many people +imagine, being only 165 feet, or about half the height of St. +Paul's Cathedral, but they are 2700 feet or nearly half-a-mile +wide, and no less than 670,000 tons of water fall +over them every minute, making magnificent clouds of spray. + +Sir Charles Lyell, when he was at Niagara, came to the conclusion +that, taking one year with another, these falls eat back the +cliff at the rate of about one foot a year, as you can easily +imagine they would do, when you think with what force the water +must dash against the bottom of the falls. In this way a deep +cleft has been cut right back from Queenstown for a distance of +seven miles, to the place where the falls are now. This helps us +a little to understand how very slowly and gradually +water cuts its way; for if a foot a year is about the average of +the waste of the rock, it will have taken more than thirty-five +thousand years for that channel of seven miles to be made. + +But even this chasm cut by the falls of Niagara is nothing +compared with the canyons of Colarado. Canyon is a Spanish word +for a rocky gorge, and these gorges are indeed so grand, that if +we had not seen in other places what water can do, we should +never have been able to believe that it could have cut out these +gigantic chasms. For more than three hundred miles the River +Colorado, coming down from the Rocky Mountains, has eaten its way +through a country made of granite and hard beds of limestone and +sandstone, and it has cut down straight through these rocks, +leaving walls from half-a-mile to a mile high, standing straight +up from it. The cliffs of the Great Canyon, as it is called, +stretch up for more than a mile above the river which flows in +the gorge below! Fancy yourselves for a moment in a boat on this +river, as shown in Figure 27, and looking up at these gigantic +walls of rock towering above you. Even half-way up them, a man, +if he could get there, would be so small you could not see him +without a telescope; while the opening at the top between the +two walls would seem so narrow at such an immense distance that +the sky above would have the appearance of nothing more than a +narrow streak of blue. Yet these huge chasms have not been made +by any violent breaking apart of the rocks or convulsion of an +earthquake. No, they have been gradually, silently, and steadily +cut through by the river which now glides quietly in the wider +chasms, or rushes rapidly through the narrow gorges at their feet. + +"No description," says Lieutenant Ives, one of the first +explorers of this river, "can convey the idea of the varied and +majestic grandeur of this peerless waterway. Wherever the river +turns, the entire panorama changes. Stately facades, august +cathedrals, amphitheatres, rotundas, castellated walls, and rows +of time-stained ruins, surmounted by every form of tower, +minaret, dome and spire, have been moulded from the cyclopean +masses of rock that form the mighty defile." Who will say, after +this, that water is not the grandest of all sculptors, as it +cuts through hundreds of miles of rock, forming such magnificent +granite groups, not only unsurpassed but unequalled by any of +the works of man? + +But we must not look upon water only as a cutting instrument, for +it does more than merely carve out land in one place, it also +carries it away and lays it down elsewhere; and in this it is +more like a modeller in clay, who smooths off the material from +one part of his figure to put it upon another. + +Running water is not only always carrying away mud, but at the +same time laying it down here and there wherever it flows. When +a torrent brings down stones and gravel from the mountains, it +will depend on the size and weight of the pieces how long they +will be in falling through the water. If you take a handful of +gravel and throw it into a glass full of water, you will notice +that the stones in it will fall to the bottom at once, the grit +and coarse sand will take longer in sinking, and lastly, the fine +sand will be an hour or two in settling down, so that the water +becomes clear. Now, suppose that this gravel were sinking in the +water of a river. The stones would be buoyed up as long as the +river was very full and flowed very quickly, but they would drop +through sooner than the coarse sand. The coarse sand in its turn +would begin to sink as the river flowed more slowly, and would +reach the bottom while the fine sand was still borne on. Lastly, +the fine sand would sink through very, very slowly, and only +settle in comparatively still water. + +From this it will happen that stones will generally lie near to +the bottom of torrents at the foot of the banks from which they +fall, while the gravel will be carried on by the stream after it +leaves the mountains. This too, however, will be laid down when +the river comes into a more level country and runs more slowly. +Or it may be left together with the finer mud in a lake, as in +the lake of Geneva, into which the Rhone flows laden with mud +and comes out at the other end clear and pure. But if no lake +lies in the way the finer earth will still travel on, and the +river will take up more and more as it flows, till at last it +will leave this too on the plains across which it moves +sluggishly along, or will deposit it at its mouth when it joins +the sea. + + + +Week 15 + +You all know the history of the Nile; how, when the rains fall +very heavily in March and April in the mountains of Abyssinia, +the river comes rushing down and brings with it a load of mud +which it spreads out over the Nile valley in Egypt. This annual +layer of mud is so thin that it takes a thousand years for it to +become 2 or 3 feet thick; but besides that which falls in the +valley a great deal is taken to the mouth of the river and there +forms new land, making what is called the "Delta" of the Nile. +Alexandria, Rosetta, and Damietta, are towns which are all built +on land made of Nile mud which was carried down ages and ages ago, +and which has now become firm and hard like the rest of the +country. You will easily remember other deltas mentioned in books, +and all these are made of the mud carried down from the land to +the sea. The delta of the Ganges and Brahmapootra in India, is +actually as large as the whole of England and Wales, (58,311 +square miles.) and the River Mississippi in America drains such a +large tract of country that its delta grows, Mr. Geikie tells us, +at the rate of 86 yards in year. + +All this new land laid down in Egypt, in India, in America, and +in other places, is the work of water. Even on the Thames you +may see mud-banks, as at Gravesend, which are made of earth +brought from the interior of England. But at the mouth of the +Thames the sea washes up very strongly every tide, and so it +carries most of the mud away and prevents a delta growing up +there. If you will look about when you are at the seaside, and +notice wherever a stream flows down into the sea, you may even +see little miniature deltas being formed there, though the sea +generally washes them away again in a few hours, unless the +place is well sheltered. + +This, then, is what becomes of the earth carried down by rivers. +Either on plains, or in lakes, or in the sea, it falls down to +form new land. But what becomes of the dissolved chalk and other +substances? We have seen that a great deal of it is used by river +and sea animals to build their shells and skeletons, and some of +it is left on the surface of the ground by springs when the water +evaporates. It is this carbonate of lime which forms a hard crust +over anything upon which it may happen to be deposited, and then +these things are called "petrified." + +But it is in the caves and hollows of the earth that this +dissolved matter is built up into the most beautiful forms. If +you have ever been to Buxton in Derbyshire, you will probably +have visited a cavern called Poole's Cavern, not far from there, +which when you enter it looks as if it were built up entirely of +rods of beautiful transparent white glass, hanging from the +ceiling, from the walls, or rising up from the floor. In this +cavern, and many others like it,*(See the picture at the head of +the lecture.) water comes dripping through the roof, and as it +falls carbonate of lime forms itself into a thin, white film on +the roof, often making a complete circle, and then, as the water +drips from it day by day, it goes on growing and growing till it +forms a long needle-shaped or tube-shaped rod, hanging like an +icicle. These rods are called stalactites, and they are so +beautiful, as their minute crystals glisten when a light is +taken into the cavern, that one of them near Tenby is called the +"Fairy Chamber." Meanwhile, the water which drips on to the +floor also leaves some carbonate of lime where it falls, and this +forms a pillar, growing up towards the roof, and often the hanging +stalactites and the rising pillars (called stalagmites) meet in +the middle and form one column. And thus we see that underground, +as well as aboveground, water moulds beautiful forms in the crust +of the earth. At Adelsberg, near Trieste, there is a magnificent +stalactite grotto made of a number of chambers one following +another, with a river flowing through them; and the famous Mammoth +Cave of Kentucky, more than ten miles long, is another example of +these wonderful limestone caverns. + +But we have not yet spoken of the sea, and this surely is not +idle in altering the shape of the land. Even the waves +themselves in a storm wash against the cliffs and bring down +stones and pieces of rock on to the shore below. And they help +to make cracks and holes in the cliffs, for as they dash with +force against them they compress the air which lies in the joints +of the stone and cause it to force the rock apart, and so larger +cracks are made and the cliff is ready to crumble. + +It is, however, the stones and sand and pieces of rock lying at +the foot of the cliff which are most active in wearing it away. +Have you never watched the waves breaking upon a beach in a +heavy storm? How they catch up the stones and hurl them down +again, grinding them against each other! At high tide in such a +storm these stones are thrown against the foot of the cliff, and +each blow does something towards knocking away part of the rock, +till at last, after many storms, the cliff is undermined and large +pieces fall down. These pieces are in their turn ground down to +pebbles which serve to batter against the remaining rock. + +Professor Geikie tells us that the waves beat in a storm against +the Bell Rock Lighthouse with as much force as if you dashed a +weight of 3 tons against every square inch of the rock, and +Stevenson found stones of 2 tons' weight which had been thrown +during storms right over the ledge of the lighthouse. Think what +force there must be in waves which can lift up such a rock and +throw it, and such force as this beats upon our sea-coasts and +eats away the land. + +Fig. 28 is a sketch on the shores of Arbroath which I made some +years ago. You will not find it difficult to picture to +yourselves how the sea has eaten away these cliffs till some of +the strongest pieces which have resisted the waves stand out by +themselves in the sea. That cave in the left-hand corner ends in a +narrow dark passage from which you come out on the other side of +the rocks into another bay. Such caves as these are made chiefly +by the force of the waves and the air, bringing down pieces of +rock from under the cliff and so making a cavity, and then as the +waves roll these pieces over and over and grind them against the +sides, the hole is made larger. There are many places on the +English coast where large pieces of the road are destroyed by the +crumbling down of cliffs when they have been undermined by caverns +such as these. + +Thus, you see, the whole of the beautiful scenery of the sea - +the shores, the steep cliffs, the quiet bays, the creeks and +caverns - are all the work of the "sculptor" water; and he works +best where the rocks are hardest, for there they offer him a +good stout wall to batter, whereas in places where the ground is +soft it washes down into a gradual gentle slope, and so the +waves come flowing smoothly in and have no power to eat away the +shore. + +And now, what has Ice got to do with the sculpturing of the land? +First, we must remember how much the frost does in breaking up +the ground. The farmers know this, and always plough after a +frost, because the moisture, freezing in the ground, has broken +up the clods, and done half their work for them. + +But this is not the chief work of ice. You will remember how we +learnt in our last lecture that snow, when it falls on the +mountains, gradually slides down into the valleys, and is pressed +together by the gathering snow behind until it becomes moulded +into a solid river of ice (see Fig. 29, Frontispiece). In +Greenland and in Norway there are enormous ice-rivers or glaciers, +and even in Switzerland some of them are very large. The Aletsch +glacier, in the Alps, is fifteen miles long, and some are even +longer than this. They move very slowly - on an average about 20 +to 27 inches in the centre, and 13 to 19 inches at the sides every +twenty-four hours, in the summer and autumn. How they move, we +cannot stop to discuss now; but if you will take a slab of thin +ice and rest it upon its two ends only, you can prove to yourself +that ice does bend, for in a few hours you will find that its own +weight has drawn it down in the centre, so as to form a curve. +This will help you to picture to yourselves how glaciers can adapt +themselves to the windings of the valley, creeping slowly onwards +until they come down to a point where the air is warm enough to +melt them, and then the ice flows away in a stream of water. It is +very curious to see the number of little rills running down the +great masses of ice at the glacier's mouth, bringing down with +them gravel, and every now and then a large stone, which falls +splashing into the stream below. If you look at the glacier in the +Frontispiece, you will see that these stones come from those long +lines of stones and boulders stretching along the sides and centre +of the glacier. It is easy to understand where the stones at the +side come from; for we have seen that damp and frost cause pieces +to break off the surface of the rocks, and it is natural that +these pieces should roll down the steep sides of the mountains on +to the glacier. But the middle row requires some explanation. Look +to the back of the picture, and you will see that this line of +stones is made of two side rows, which come from the valleys +above. Two glaciers, you see, have there joined into one, and so +made a heap of stones all along their line of junction. + +These stones are being continually, though slowly, conveyed by +the glacier, from all the mountains along its sides, down to the +place where it melts. Here it lets them fall, and they are +gradually piled up till they form great walls of stone, which +are called moraines. Some of the moraines left by the larger +glaciers of olden time, in the country near Turin, form high +hills, rising up even to 1500 feet. + +Therefore, if ice did no more than carry these stone blocks, it +would alter the face of the country; but it does much more than +this. As the glacier moves along, it often cracks for a +considerable way across its surface, and this crack widens and +widens, until at last it becomes a great gaping chasm, or +crevasse as it is called, so that you can look down it right to +the bottom of the glacier. Into these crevasses large blocks of +rock fall, and when the chasm is closed again as the ice presses +on, these masses are frozen firmly into the bottom of the +glacier, much in the same way as a steel cutter is fixed in the +bottom of a plane. And they do just the same kind of work; for +as the glacier slides down the valley, they scratch and grind the +rocks underneath them, rubbing themselves away, it is true, but +also scraping away the ground over which they move. In this way +the glacier becomes a cutting instrument, and carves out the +valleys deeper and deeper as it passes through them. + +You may always know where a glacier has been, even if no trace of +ice remains; for you will see rocks with scratches along them +which have been cut by these stones; and even where the rocks +have not been ground away, you will find them rounded like those +in the left-hand of the Frontispiece, showing that the glacier- +plane has been over them. These rounded rocks are called "roches +moutonnees," because at the distance they look like sheep lying +down. + +You have only to look at the stream flowing from the mouth of a +glacier to see what a quantity of soil it has ground off from +the bottom of the valley; for the water is thick, and coloured a +deep yellow by the mud it carries. This mud soon reaches the +rivers into which the streams run; and such rivers as the Rhone +and the Rhine are thick with matter brought down from the Alps. +The Rhone leaves this mud in the Lake of Geneva, flowing out at +the other end quite clear and pure. A mile and a half of land +has been formed at the head of the lake since the time of the +Romans by the mud thus brought down from the mountains. + +Thus we see that ice, like water, is always busy carving out the +surface of the earth, and sending down material to make new land +elsewhere. We know that in past ages the glaciers were much +larger than they are in our time; for we find traces of them +over large parts of Switzerland where glaciers do not now exist, +and huge blocks which could only have been carried by ice, and +which are called "erratic blocks," some of them as big as +cottages, have been left scattered over all the northern part of +Europe. These blocks were a great puzzle to scientific men till, +in 1840, Professor Agassiz showed that they must have been brought +by ice all the way from Norway and Russia. + +In those ancient days, there were even glaciers in England; for +in Cumberland and in Wales you may see their work, in scratched +and rounded rocks, and the moraines they have left. Llanberis +Pass, so famous for its beauty, is covered with ice-scratches, +and blocks are scattered all over the sides of the valley. There +is one block high up on the right-hand slope of the valley, as +you enter from the Beddgelert side, which is exactly poised upon +another block, so that it rocks to and fro. It must have been +left thus balanced when the ice melted round it. You may easily +see that these blocks were carried by ice, and not by water, +because their edges are sharp, whereas if they had been rolled +in water, they would have been smoothed down. + +We cannot here go into the history of that great Glacial Period +long ago, when large fields of ice covered all the north of +England; but when you read it for yourselves and understand the +changes on the earth's surface which we can see being made by +ice now, then such grand scenery as the rugged valleys of Wales, +with large angular stone blocks scattered over them, will tell +you a wonderful story of the ice of bygone times. + +And now we have touched lightly on the chief ways in which water +and ice carve out the surface of the earth. We have seen that +rain, rivers, springs, the waves of the sea, frost, and glaciers +all do their part in chiselling out ravines and valleys, and in +producing rugged peaks or undulating plains - here cutting through +rocks so as to form precipitous cliffs, there laying down new land +to add to the flat country - in one place grinding stones to +powder, in others piling them up in gigantic ridges. We cannot go +a step into the country without seeing the work of water around +us; every little gully and ravine tells us that the sculpture is +going on; every stream, with its burden of visible or invisible +matter, reminds us that some earth is being taken away and carried +to a new spot. In our little lives we see indeed but the very +small changes, but by these we learn how greater ones have been +brought about, and how we owe the outline of all our beautiful +scenery, with its hills and valleys, its mountains and plains, its +cliffs and caverns, its quiet nooks and its grand rugged +precipices, to the work of the "Two great sculptors, Water and +Ice." + + + +Week 16 + +Lecture VI + +THE VOICES OF NATURE AND HOW WE HEAR THEM + +We have reached to-day the middle point of our course, and here +we will make a new start. All the wonderful histories which we +have been studying in the last five lectures have had little or +nothing to do with living creatures. The sunbeams would strike +on our earth, the air would move restlessly to and fro, the +water-drops would rise and fall, the valleys and ravines would +still be cut out by rivers , if there were no such thing as life +upon the earth. But without living things there could be none of +the beauty which these changes bring about. Without plants, the +sunbeams, the air and the water would be quite unable to clothe +the bare rocks, and without animals and man they could not +produce light, or sound, or feeling of any kind. + +In the next five lectures, however, we are going to learn +something of the use living creatures make of the earth; and to- +day we will begin by studying one of the ways in which we are +affected by the changes of nature, and hear her voice. + +We are all so accustomed to trust to our sight to guide us in +most of our actions, and to think of things as we see them, that +we often forget how very much we owe to sound. And yet Nature +speaks to us so much by her gentle, her touching, or her awful +sounds, that the life of a deaf person is even more hard to bear +than that of a blind one. + +Have you ever amused yourself with trying how many different +sounds you can distinguish if you listen at an open window in a +busy street? You will probably be able to recognize easily the +jolting of the heavy wagon or dray, the rumble of the omnibus, +the smooth roll of the private carriage and the rattle of the +light butcher's cart; and even while you are listening for these, +the crack of the carter's whip, the cry of the costermonger at +his stall, and the voices of the passers-by will strike upon you +ear. Then if you give still more close attention you will hear +the doors open and shut along the street, the footsteps of the +passengers, the scraping of the shovel of the mud-carts; nay, if +he happen to stand near, you may even hear the jingling of the +shoeblack's pence as he plays pitch and toss upon the pavement. +If you think for a moment, does it not seem wonderful that you +should hear all these sounds so that you can recognize each one +distinctly while all the rest are going on around you? + +But suppose you go into the quiet country. Surely there will be +silence there. Try some day and prove it for yourself, lie down +on the grass in a sheltered nook and listen attentively. If +there be ever so little wind stirring you will hear it rustling +gently through the trees; or even if there is not this, it will +be strange if you do not hear some wandering gnat buzzing, or +some busy bee humming as it moves from flower to flower. Then a +grasshopper will set up a chirp within a few yards of you, or, if +all living creatures are silent, a brook not far off may be +flowing along with a rippling musical sound. These and a hundred +other noises you will hear in the most quiet country spot; the +lowing of the cattle, the song of the birds, the squeak of the +field-mouse, the croak of the frog, mingling with the sound of +the woodman's axe in the distance, or the dash of some river +torrent. And beside these quiet sounds, there are still other +occasional voices of nature which speak to us from time to time. +The howling of the tempestuous wind, the roar of the sea-waves in +a storm, the crash of thunder, and the mighty noise of the +falling avalanche; such sounds as these tell us how great and +terrible nature can be. + +Now, has it ever occurred to you to think what sounds is, and how +it is that we hear all these things? Strange as it may seem, if +there were no creature that could hear upon the earth, there +would be no such thing as sound, though all these movements in +nature were going on just as they are now. + +Try and grasp this thoroughly, for it is difficult at first to +make people believe it. Suppose you were stone-deaf, there would +be no such thing as sound to you. A heavy hammer falling on an +anvil would indeed shake the air violently, but since this air +when it reached your ear would find a useless instrument, it +could not play upon it. and it is this play on the drum of your +ear and the nerves within it speaking to your brain which make +sound. Therefore, if all creatures on or around the earth were +without ears or nerves of hearing, there would be no instrument +on which to play, and consequently there would be no such thing +as sound. This proves that two things are needed in order that +we may hear. First, the outside movement which plays on our +hearing instrument; and, secondly, the hearing instrument itself. + +First, then, let us try to understand what happens outside our +ears. Take a poker and tie a piece of string to it, and holding +the ends of the string to your ears, strike the poker against the +fender. You will hear a very loud sound, for the blow will set +all the particles of the poker quivering, and this movement will +pass right along the string to the drum of your ear and play upon +it. + +Now take the string away from you ears, and hold it with your +teeth. Stop your ears tight, and strike the poker once more +against the fender. You will hear the sound quite as loudly and +clearly as you did before, but this time the drum of your ear has +not been agitated. How, then, has the sound been produced? In +this case, the quivering movement has passed through your teeth +into the bones of your hear, and from them into the nerves, and +so produced sound in your brain. And now, as a final experiment, +fasten the string to the mantelpiece, and hit it again against +the fender. How much feebler the sound is this time, and how +much sooner it stops! Yet still it reaches you, for the movement +has come this time across the air to the drums of your ear. + +Here we are back again in the land of invisible workers! We have +all been listening and hearing ever since we were babies, but +have we ever made any picture to ourselves of how sound comes to +us right across a room or a field, when we stand at one end and +the person who calls is at the other? + +Since we have studied the "aerial ocean," we know that the air +filling the space between us, though invisible, is something very +real, and now all we have to do is to understand exactly how the +movement crosses this air. + +This we shall do most readily by means of an experiment made by +Dr. Tyndall in his lectures on Sound. I have here a number of +boxwood balls resting in a wooden tray which has a bell hung at +the end of it. I am going to take the end ball and roll it +sharply against the rest, and then I want you to notice carefully +what happens. See! the ball at the other end has flow off and +hit the bell, so that you hear it ring. Yet the other balls +remain where they were before. Why is this? It is because each +of the balls, as it was knocked forwards, had one in front of it +to stop it and make it bound back again, but the last one was +free to move on. When I threw this ball from my hand against the +others, the one in front of it moved, and hitting the third ball, +bounded back again; the third did the same to the fourth, the +fourth to the fifth, and so on to the end of the line. Each ball +thus came back to its place, but it passed the shock on to the +last ball, and the ball to the bell. If I now put the balls +close up to the bell, and repeat the experiment, you still hear +the sound, for the last ball shakes the bell as if it were a ball +in front of it. + +Now imagine these balls to be atoms of air, and the bell your +ear. If I clap my hands and so hit the air in front of them, +each air-atom hits the next just as the balls did, and though it +comes back to its place, it passes the shock on along the whole +line to the atom touching the drum of your ear, and so you +receive a blow. But a curious thing happens in the air which you +cannot notice in the balls. You must remember that air is +elastic, just as if there were springs between the atoms as in +the diagram, Fig. 31, and so when any shock knocks the atoms +forward, several of them can be crowded together before they push +on those in front. Then, as soon as they have passed the shock +on, they rebound and begin to separate again, and so swing to and +fro till they come to rest. meanwhile the second set will go +through just the same movements, and will spring apart as soon as +they have passed the shock on to a third set, and so you will +have one set of crowded atoms and one set of separated atoms +alternately all along the line, and the same set will never be +crowded two instants together. + +You may see an excellent example of this in a luggage train in a +railway station, when the trucks are left to bump each other till +they stop. You will see three or four trucks knock together, +then they will pass the shock on to the four in front, while they +themselves bound back and separate as far as their chains will +let them: the next four trucks will do the same, and so a kind of +wave of crowded trucks passes on to the end of the train, and +they bump to and fro till the whole comes to a standstill. Try +to imagine a movement like this going on in the line of air- +atoms, the drum of your ear being at the end. Those which are +crowded together at that end will hit on the drum of your ear and +drive the membrane which covers it inwards; then instantly the +wave will change, these atoms will bound back, and the membrane +will recover itself again, but only to receive a second blow as +the atoms are driven forwards again, and so the membrane will be +driven in and out till the air has settled down. + +This you see is quite different to the waves of light which moves +in crests and hollows. Indeed, it is not what we usually +understand by a wave at all, but a set of crowdings and partings +of atoms of air which follow each other rapidly across the air. +A crowding of atoms is called a condensation, and a parting is +called a rarefaction, and when we speak of the length of a wave +of sound, we mean the distance between two condensations, or +between two rarefactions. + +Although each atom of air moves a very little way forwards and +then back, yet, as a long row of atoms may be crowded together +before they begin to part, a wave is often very long. When a man +talks in an ordinary bass voice, he makes sound-waves from 8 to +12 feet long; a woman's voice makes shorter waves, from 2 to 4 +feet long, and consequently the tone is higher, as we shall +presently explain. + +And now I hope that some one is anxious to ask why, when I clap +my hands, anyone behind me or at the side, can hear it as well or +nearly as well as you who are in front. This is because I give a +shock to the air all round my hands, and waves go out on all +sides, making as it were gloves of crowdings and partings +widening and widening away from the clap as circles widen on a +pond. Thus the waves travel behind me, above me, and on all +sides, until they hit the walls, the ceiling, and the floor of +the room, and wherever you happen to be, they hit upon your ear. + + + +Week 17 + +If you can picture to yourself these waves spreading out in all +directions, you will easily see why sound grows fainter at the +distance. Just close round my hands when I clap them, there is +a small quantity of air, and so the shock I give it is very +violent, but as the sound-waves spread on all sides they have +more and more air to move, and so the air-atoms are shaken less +violently and strike with less force on your ear. + +If we can prevent the sound-wave from spreading, then the sound +is not weakened. The Frenchman Biot found that a low whisper +could be heard distinctly for a distance of half a mile through a +tube, because the waves could not spread beyond the small column +of air. But unless you speak into a small space of some kind, +you cannot prevent the waves going out from you in all +directions. + +Try and imagine that you see these waves spreading all round me +now and hitting on your ears as they pass, then on the ears of +those behind you, and on and on in widening globes till they +reach the wall. What will happen when they get there? If the +wall were thin, as a wooden partition is, they would shake it, +and it again would shake the air on the other side, and so anyone +in the next room would have the sound of my voice brought to +their ear. + +But something more will happen. In any case the sound-waves +hitting against the wall will bound back from it just as a ball +bounds back when thrown against anything, and so another set of +sound-waves reflected from the wall will come back across the +room. If these waves come to your ear so quickly that they mix +with direct waves, they help to make the sound louder in this +room than you would in the open air, for the "Ha" from my mouth +and a second "Ha" from the wall come to your ear so +instantaneously that they make one sound. This is why you can +often hear better at the far end of a church when you stand +against a screen or a wall, then when you are half-way up the +building nearer to the speaker, because near the wall the +reflected waves strike strongly on your ear and make the sound +louder. + +Sometimes, when the sound comes from a great explosion, these +reflected waves are so strong that they are able to break glass. +In the explosion of gunpowder in St. John's Wood, many houses in +the back streets had their windows broken; for the sound-waves +bounded off at angles from the walls and struck back upon them. + +Now suppose the wall were so far behind you that the reflected +sound-waves only hit upon your ear after those coming straight +from me had died away; then you would hear the sound twice, "Ha" +from me and "Ha" from the wall, and here you have an echo, "Ha, +ha." In order for this to happen in ordinary air, you must be +standing at least 56 feet away from the point from which the +waves are reflected, for then the second blow will come one-tenth +of a second after the first one, and that is long enough for you +to feel them separately.* Miss C. A. Martineau tells a story of +a dog which was terribly frightened by an echo. Thinking another +dog was barking, he ran forward to meet him, and was very much +astonished, when, as he came nearer the wall, the echo ceased. I +myself once knew a case of this kind, and my dog, when he could +find no enemy, ran back barking, till he was a certain distance +off, and then the echo of course began again. He grew so furious +at last that we had great difficulty in preventing him from +flying at a strange man who happened to be passing at the time. +(*Sound travels 1120 feet in a second, in air of ordinary +temperature, and therefore 112 feet in the tenth of a second. +Therefore the journey of 56 feet beyond you to reach the wall +and 56 feet to return, will occupy the sound-wave one-tenth of +a second and separate the two sounds.) + +Sometimes, in the mountains, walls of rock rise at some distance +one behind another, and then each one will send back its echo a +little later than the rock before it, so that the "Ha" which you +give will come back as a peal of laughter. There is an echo in +Woodstock Park which repeats the word twenty times. Again +sometimes, as in the Alps, the sound-waves coming back rebound +from mountain to mountain and are driven backwards and forwards, +becoming fainter and fainter till they die away; these echoes are +very beautiful. + +If you are now able to picture to yourselves one set of waves +going to the wall, and another set returning and crossing them, +you will be ready to understand something of that very difficult +question, How is it that we can hear many different sounds at one +time and tell them apart? + +Have you ever watched the sea when its surface is much ruffled, +and noticed how, besides the big waves of the tide, there are +numberless smaller ripples made by the wind blowing the surface +of the water, or the oars of a boat dipping in it, or even rain- +drops falling? If you have done this you will have seen that all +these waves and ripples cross each other, and you can follow any +one ripple with you eye as it goes on its way undisturbed by the +rest. Or you may make beautiful crossing and recrossing ripples +on a pond by throwing in two stones at a little distance from +each other, and here too you can follow any one wave on to the +edge of the pond. + +Now just in this way the waves of sound, in their manner of +moving, cross and recross each other. You will remember too, +that different sounds make waves of different lengths, just as +the tide makes a long wave and the rain-drops tiny ones. +Therefore each sound falls with its own peculiar wave upon your +ear, and you can listen to that particular wave just as you look +at one particular ripple, and then the sound becomes clear to +you. + +All this is what is going on outside your ear, but what is +happening in your ear itself? How do these blows of the air +speak to your brain? By means of the following diagram, Fig. 33, +we will try to understand roughly our beautiful hearing +instrument, the ear. + +First, I want you to notice how beautifully the outside shell, or +concha as it is called, is curbed round so that any movement of +the air coming to it from the front is caught in it and reflected +into the hole of the ear. Put your finger round your ear and +feel how the gristly part is curved towards the front of your +head. This concha makes a curve much like the curve a deaf man +makes with his hand behind his ear to catch the sound. Animals +often have to raise their ears to catch the sound well, but ours +stand always ready. When the air-waves have passed in at the +hole of your ear, they move all the air in the passage, which is +called the auditory, or hearing, canal. This canal is lined with +little hairs to keep out insects and dust, and the wax which +collects in it serves the same purpose. But is too much wax +collects, it prevents the air from playing well upon the drum, +and therefore makes you deaf. Across the end of this canal, a +membrane or skin called the tympanum is stretched, like the +parchment over the head of a drum, and it is this membrane which +moves to and fro as the air-waves strike on it. A violent box on +the ear will sometimes break this delicate membrane, or injure +it, and therefore it is very wrong to hit a person violently on +the ear. + +On the other side of this membrane, inside the ear, there is air, +which fills the whole of the inner chamber and the tube, which +runs down into the throat behind the nose, and is called the +Eustachian tube after the man who discovered it. This tube is +closed at the end by a valve which opens and shuts. If you +breathe out strongly, and then shut your mouth and swallow, you +will hear a little "click" in your ear. This is because in +swallowing you draw the air out of the Eustachian tube and so +draw in the membrane, which clicks as it goes back again. But +unless you do this the tube and the whole chamber cavity behind +the membrane remains full of air. + +Now, as this membrane is driven to and fro by the sound-waves, it +naturally shakes the air in the cavity behind it, and it also +sets moving three most curious little bones. The first of the +bones is fastened to the middle of the drumhead so that it moves +to and fro every time this membrane quivers. The head of this +bone fits into a hole in the next bone, the anvil, and is +fastened to it by muscles, so as to drag it along with it; but, +the muscles being elastic, it can draw back a little from the +anvil, and so give it a blow each time it comes back. This anvil +is in its turn very firmly fixed to the little bone, shaped like +a stirrup, which you see at the end of the chain. + +This stirrup rests upon a curious body which looks in the diagram +like a snail-shell with tubes coming out of it. This body, which +is called the labyrinth, is made of bone, but it has two little +windows in it, one covered only by a membrane, while the other +has the head of the stirrup resting upon it. + +Now, with a little attention you will understand that when the +air in the canal shakes the drumhead to and fro, this membrane +must drag with it the hammer, the anvil, and the stirrup. Each +time the drum goes in, the hammer will hit the anvil, and drive +the stirrup against the little window; every time it goes out it +will draw the hammer, the anvil, and the stirrup out again, ready +for another blow. Thus the stirrup is always playing upon this +little window. Meanwhile, inside the bony labyrinth there is a +fluid like water, and along the little passages are very fine +hairs, which wave to and fro like reeds; and whenever the stirrup +hits at the little window, the fluid moves these hairs to and +fro, and they irritate the ends of a nerve, and this nerve +carries the message to your brain. There are also some curious +little stones called otoliths, lying in some parts of this fluid, +and they, by their rolling to and fro, probably keep up the +motion and prolong the sound. + +You must not imagine we have explained here the many intricacies +which occur in the ear; I can only hope to give you a rough idea +of it, so that you may picture to yourselves the air-waves moving +backwards and forward in the canal of your ear, then the tympanum +vibrating to and fro, the hammer hitting the anvil, the stirrup +knocking at the little window, the fluid waving the fine hairs +and rolling the tiny stones, the ends of the nerve quivering, and +then (how we know not) the brain hearing the message. + +Is not this wonderful, going on as it does at every sound you +hear? And yet his is not all, for inside that curled part of the +labyrinth, which looks like a snail-shell and is called the +cochlea, there is a most wonderful apparatus of more than three +thousand fine stretched filaments or threads, and these act like +the strings of a harp, and make you hear different tones. If you +go near to a harp or a piano, and sing any particular note very +loudly, you will hear this note sounding in the instrument, +because you will set just that particular string quivering, which +gives the note you sang. The air-waves set going by your voice +touch that string, because it can quiver in time with them, while +none of the other strings can do so. Now, just in the same way +the tiny instrument of three thousand strings in your ear, which +is called Corti's organ, vibrates to the air-waves, one thread to +one set of waves, and another to another, and according to the +fibre that quivers, will be the sound you hear. Here then at +last, we see how nature speaks to us. All the movements going on +outside, however violent and varied they may be, cannot of +themselves make sound. But here, in the little space behind the +drum of our ear, the air-waves are sorted and sent on to our +brain, where they speak to us as sound. + + + +Week 18 + +But why then do we not hear all sounds as music? Why are some +mere noise, and others clear musical notes? This depends +entirely upon whether the sound-waves come quickly and regularly, +or by an irregular succession of shocks. For example, when a +load of stones is being shot out of a cart, you hear only a long, +continuous noise, because the stones fall irregularly, some +quicker, some slower, here a number together, and there two or +three stragglers by themselves; each of these different shocks +comes to your ear and makes a confused, noisy sound. But if you +run a stick very quickly along a paling, you will hear a sound +very like a musical not. This is because the rods of the paling +are all at equal distances one from another, and so the shocks +fall quickly one after another at regular intervals upon your +ear. Any quick and regular succession of sounds makes a note, +even though it may be an ugly one. The squeak of a slate pencil +along a slate, and the shriek of a railway whistle are not +pleasant, but they are real notes which you could copy on a +violin. + +I have here a simple apparatus which I have had made to show you +that rapid and regular shocks produce a natural musical note. +This wheel (Fig. 34) is milled at the edge like a shilling, and +when I turn it rapidly so that it strikes against the edge of the +card fixed behind it, the notches strike in rapid succession, and +produce a musical sound. We can also prove by this experiment +that the quicker the blows are, the higher the note will be. I +pull the string gently at first, and then quicker and quicker, +and you will notice that the note grows sharper and sharper, till +the movement begins to slacken, when the note goes down again. +This is because the more rapidly the air is hit, the shorter are +the waves it makes, and short waves give a high note. + +Let us examine this with two tuning-forks. I strike one, and it +sounds D, the third space in the treble; I strike the other, and +it sounds G, the first leger line, five notes above the C. I +have drawn on this diagram (Fig. 35), an imaginary picture of +these two sets of waves. You see that the G fork makes three +waves, while the C fork makes only two. Why is this? Because +the prong of the G fork moves three times backwards and forwards +while the prong of the C fork only moves twice; therefore the G +fork does not crowd so many atoms together before it draws back, +and the waves are shorter. These two notes, C and G, are a fifth +of an octave apart; if we had two forks, of which one went twice +as fast as the other, making four waves while the other made two, +then that note would be an octave higher. + +So we see that all the sounds we hear, - the warning noises which +keep us from harm, the beautiful musical notes with all the tunes +and harmonies that delight us, even the power of hearing the +voices of those we love, and learning from one another that which +each can tell, - all these depend upon the invisible waves of +air, even as the pleasures of light depend on the waves of ether. +It is by these sound-waves that nature speaks to us, and in all +her movements there is a reason why her boice is sharp or tender, +loud or gentle, awful or loving. Take for instance the brook we +spoke of at the beginning of the lecture. Why does it sing so +sweetly, while the wide deep river makes no noise? Because the +little brook eddies and purls round the stones, hitting them as +it passes; sometimes the water falls down a large stone, and +strikes against the water below; or sometimes it grates the +little pebbles together as they lie in its bed. Each of these +blows makes a small globe of sound-waves, which spread and spread +till they fall on your ear, and because they fall quickly and +regularly, they make a low, musical note. We might almost fancy +that the brook wished to show how joyfully it flows along, +recalling Shelley's beautiful lines:- + + "Sometimes it fell + Among the moss with hollow harmony, + Dark and profound; now on the polished stones + It danced; like childhood laughing as it went." + +The broad deep river, on the contrary, makes none of these +cascades and commotions. The only places against which it rubs +are the banks and the bottom; and here you can sometimes hear it +grating the particles of sand against each other if you listen +very carefully. But there is another reason why falling water +makes a sound, and often even a loud roaring noise in the +cataract and in the breaking waves of the sea. You do not only +hear the water dashing against the rocky ledges or on the beach, +you also hear the bursting of innumerable little bladders of air +which are contained in the water. As each of these bladders is +dashed on the ground, it explodes and sends sound-waves to your +ear. Listen to the sea some day when the waves are high and +stormy, and you cannot fail to be struck by the irregular bursts +of sound. + +The waves, however, do not only roar as they dash on the ground; +have you never noticed how they seem to scream as they draw back +down the beach? Tennyson calls it, + +"The scream of the madden'd beach dragged down by the wave;" and +it is caused by the stones grating against each other as the +waves drag them down. Dr. Tyndall tells us that it is possible +to know the size of the stones by the kind of noise they make. +If they are large, it is a confused noise, when smaller, a kind +of scream; while a gravelly beach will produce a mere hiss. + +Who could be dull by the side of a brook, a waterfall, or the +sea, while he can listen for sounds like these, and picture to +himself how they are being made? You may discover a number of +other causes of sound made by water, if you once pay attention to +them. + +Nor is it only water that sings to us. Listen to the wind, how +sweetly it sighs among the leaves. There we hear it, because it +rubs the leaves together, and they produce the sound-waves. But +walk against the wind some day and you can hear it whistling in +your own ear, striking against the curved cup, and then setting +up a succession of waves in the hearing canal of the ear itself. + +Why should it sound in one particular tone when all kinds of +sound-waves must be surging about in the disturbed air? + +This glass jar will answer our question roughly. If I strike my +tuning-fork and hold it over the jar, you cannot hear it, because +the sound is feeble, but if I fill the jar gently with water, +when the water rises to a certain point you will hear a loud +clear note, because the waves of air in the jar are exactly the +right length to answer to the note of the fork. If I now blow +across the mouth of the jar you hear the same note, showing that +a cavity of a particular length will only sound to the waves +which fit it. do you see now the reason why pan-pipes give +different sounds, or even the hole at the end of a common key +when you blow across it? Here is a subject you will find very +interesting if you will read about it, for I can only just +suggest it to you here. But now you will see that the canal of +your ear also answers only to certain waves, and so the wind +sings in your ear with a real if not a musical note. + +Again, on a windy night have you not heard the wind sounding a +wild, sad note down a valley? Why do you think it sounds so much +louder and more musical here than when it is blowing across the +plain? Because air in the valley will only answer to a certain +set of waves, and, like the pan-pipe, gives a particular note as +the wind blows across it, and these waves go up and down the +valley in regular pulses, making a wild howl. You may hear the +same in the chimney, or in the keyhole; all these are waves set +up in the hole across which the wind blows. Even the music in +the shell which you hold to your ear is made by the air in the +shell pulsating to and fro. And how do you think it is set +going? By the throbbing of the veins in your own ear, which +causes the air in the shell to vibrate. + +Another grand voice of nature is the thunder. People often have +a vague idea that thunder is produced by the clouds knocking +together, which is very absurd, if you remember that clouds are +but water-dust. The most probable explanation of thunder is much +more beautiful than this. You will remember from Lecture III +that heat forces the air-atoms apart. Now, when a flash of +lightning crosses the sky it suddenly expands the air all round +it as it passes, so that globe after globe of sound-waves is +formed at every point across which the lightning travels. Now +light, you remember, travels so wonderfully rapidly (192,000 +miles in a second) that a flash of lightning is seen by us and is +over in a second, even when it is two or three miles long. But +sound comes slowly, taking five seconds to travel half a mile, +and so all the sound-waves at each point of the two or three +miles fall on our ear one after the other, and make the rolling +thunder. Sometimes the roll is made even longer by the echo, as +the sound-waves are reflected to and fro by the clouds on their +road; and in the mountains we know how the peals echo and re-echo +till they die away. + +We might fill up far more than an hour in speaking of those +voices which come to us as nature is at work. Think of the +patter of the rain, how each drop as it hits the pavement sends +circles of sound-waves out on all sides; or the loud report which +falls on the ear of the Alpine traveller as the glacier cracks on +its way down the valley; or the mighty boom of the avalanche as +the snow slides in huge masses off the side of the lofty +mountain. Each and all of these create their sound-waves, large +or small, loud or feeble, which make their way to your ear, and +become converted into sound. + +We have, however, only time now just to glance at life-sounds, of +which there are so many around us. Do you know why we hear a +buzzing, as the gnat, the bee, or the cockchafer fly past? Not +by the beating of their wings against the air, as many people +imagine, and as is really the case with humming birds, but by the +scraping of the under-part of their hard wings against the edges +of their hind legs, which are toothed like a saw. The more +rapidly their wings move the stronger the grating sound becomes, +and you will now see why in hot, thirsty weather the buzzing of +the gnat is so loud, for the more thirsty and the more eager he +becomes, the wilder his movements will be. + +Some insects, like the drone-fly (Eristalis tenax), force the air +through the tiny air-passages in their sides, and as these +passages are closed by little plates, the plates vibrate to and +fro and make sound-waves. Again, what are those curious sounds +you may hear sometimes if you rest your head on a trunk in the +forest? They are made by the timber-boring beetles, which saw +the wood with their jaws and make a noise in the world, even +though they have no voice. + +All these life-sounds are made by creatures which do not sing or +speak; but the sweetest sounds of all in the woods are the voices +of the birds. All voice-sounds are made by two elastic bands or +cushions, called vocal chords, stretched across the end of the +tube or windpipe through which we breathe, and as we send the air +through them we tighten or loosen them as we will, and so make +them vibrate quickly or slowly and make sound-waves of different +lengths. But if you will try some day in the woods you will find +that a bird can beat you over and over again in the length of his +note; when you are out of breath and forced to stop he will go on +with his merry trill as fresh and clear as if he had only just +begun. This is because birds can draw air into the whole of +their body, and they have a large stock laid up in the folds of +their windpipe, and besides this the air-chamber behind their +elastic bands or vocal chords has two compartments where we have +only one, and the second compartment has special muscles by which +they can open and shut it, and so prolong the trill. + +Only think what a rapid succession of waves must quiver through +the air as a tiny lark agitates his little throat and pours forth +a volume of song! The next time you are in the country in the +spring, spend half an hour listening to him, and try and picture +to yourself how that little being is moving all the atmosphere +round him. Then dream for a little while about sound, what it +is, how marvellously it works outside in the world, and inside in +your ear and brain; and then, when you go back to work again, you +will hardly deny that it is well worth while to listen sometimes +to the voices of nature and ponder how it is that we hear them. + + + +Week 19 + +LECTURE VII THE LIFE OF A PRIMROSE + +When the dreary days of winter and the early damp days of spring +are passing away, and the warm bright sunshine has begun to pour +down upon the grassy paths of the wood, who does not love to go +out and bring home posies of violets, and bluebells, and +primroses? We wander from one plant to another picking a flower +here and a bud there, as they nestle among the green +leaves, and we make our rooms sweet and gay with the tender and +lovely blossoms. But tell me, did you ever stop to think, as you +added flower after flower to your nosegay, how the plants which +bear them have been building up their green leaves and their +fragile buds during the last few weeks? If you had visited the +same spot a month before, a few (of) last year's leaves, +withered and dead, would have been all that you would have found. +And now the whole wood is carpeted with delicate green leaves, +with nodding bluebells, and pale-yellow primroses, as if a fairy +had touched the ground and covered it with fresh young life. And +our fairies have been at work here; the fairy "Life," of whom we +know so little, though we love her so well and rejoice in the +beautiful forms she can produce; the fairy sunbeams with their +invisible influence kissing the tiny shoots and warming them into +vigour and activity; the gentle rain-drops, the balmy air, all +these have been working, while you or I passed heedlessly by; +and now we come and gather the flowers they have made, and too +often forget to wonder how these lovely forms have sprung up +around us. + +Our work during the next hour will be to consider this question. +You were asked last week to bring with you to-day a primrose- +flower, or a whole plant if possible, in order the better to +follow out with me the "Life of a Primrose." (To enjoy this +lecture, the reader ought to have, if possible, a primrose- +flower, an almond soaked for a few minutes in hot water, and a +piece of orange.) This is a very different kind of subject from +those of our former lectures. There we took world- +wide histories; we travelled up to the sun, or round the earth, +or into the air; now I only ask you to fix your attention on one +little plant, and inquire into its history. + +There is a beautiful little poem by Tennyson, which says - + + "Flower in the crannied wall, + I pluck you out of the crannies; + Hold you here, root and all, in my hand, + Little flower; but if I could understand + What you are, root and all, and all in all, + I should know what God and man is." + +We cannot learn all about this little flower, but we can learn +enough to understand that it has a real separate life of its +own, well worth knowing. For a plant is born, breathes, sleeps, +feeds, and digests just as truly as an animal does, though in a +different way. It works hard both for itself to get its food, +and for others in making the air pure and fit for animals to +breathe. It often lays by provision for the winter. It sends +young plants out, as parents send their children, to fight for +themselves in the world; and then, after living sometimes to a +good old age, it dies, and leaves its place to others. + +We will try to follow out something of this life to-day; and +first, we will begin with the seed. + +I have here a packet of primrose-seeds, but they are so small +that we cannot examine them; so I have also had given to each +one of you an almond-kernel, which is the seed of the almond- +tree, and which has been soaked, so that it splits in half +easily. From this we can learn about seeds in general, and then +apply it to the primrose. + +If you peel the two skins off your almond-seed (the +thick, brown, outside skin, and the thin, transparent one under +it), the two halves of the almond will slip apart quite easily. +One of these halves will have a small dent at the pointed end, +while in the other half you will see a little lump, which fitted +into the dent when the two halves were joined. This little lump +(a b, Fig. 37) is a young plant, and the two halves of the +almond are the seed leaves which hold the plantlet, and feed it +till it can feed itself. The rounded end of the plantlet (b) +sticking out of the almond, is the beginning of the root, while +the other end (a) will in time become the stem. If you look +carefully, you will see two little points at this end, which are +the tips of future leaves. Only think how minute this plantlet +must be in a primrose, where the whole seed is scarcely larger +than a grain of sand! Yet in this tiny plantlet lies hid the +life of the future plant. + +When a seed falls into the ground, so long as the earth is cold +and dry, it lies like a person in a trance, as if it were dead; +but as soon as the warm, damp spring comes, and the busy little +sun-waves pierce down into the earth, they wake up the plantlet +and make it bestir itself. They agitate to and fro the particles +of matter in this tiny body, and cause them to seek out for +other particles to seize and join to themselves. + +But these new particles cannot come in at the roots, +for the seed has none; nor through the leaves, for they have not +yet grown up; and so the plantlet begins by helping itself to +the store of food laid up in the thick seed-leaves in which it +is buried. Here it finds starch, oils, sugar, and substances +called albuminoids, -- the sticky matter which you notice in +wheat-grains when you chew them is one of the albuminoids. This +food is all ready for the plantlet to use, and it sucks it in, +and works itself into a young plant with tiny roots at one end, +and a growing shoot, with leaves, at the other. + +But how does it grow? What makes it become larger? To answer this +you must look at the second thing I asked you to bring - a piece +of orange. If you take the skin off a piece of orange, you will +see inside a number of long-shaped transparent bags, full of +juice. These we call cells, and the flesh of all plants and +animals is made up of cells like these, only of various shapes. +In the pith of elder they are round, large, and easily seen (a, +Fig. 39); in the stalks of plants they are long, and lap over +each other (b, Fig. 39), so as to give the stalk strength to +stand upright. Sometimes many cells growing one on the top of +the other break into one tube and make vessels. But whether +large or small, they are all bags growing one against the other. + +In the orange-pulp these cells contain only sweet juice, but in +other parts of the orange-tree or any other plant +they contain a sticky substance with little grains in it. This +substance is called "protoplasm," or the first form of life, for +it is alive and active, and under a microscope you may see in a +living plant streams of the little grains moving about in the +cells. + +Now we are prepared to explain how our plant grows. Imagine the +tiny primrose plantlet to be made up of cells filled with active +living protoplasm, which drinks in starch and other food from +the seed-leaves. In this way each cell will grow too full for +its skin, and then the protoplasm divides into two parts and +builds up a wall between them, and so one cell becomes two. Each +of these two cells again breaks up into two more, and so the +plant grows larger and larger, till by the time it has used up +all the food in the seed-leaves, it has sent roots covered with +fine hairs downwards into the earth, and a shoot with beginnings +of leaves up into the air. + +Sometimes the seed-leaves themselves come above the ground, as in +the mustard-plant, and sometimes they are left empty behind, +while the plantlet shoots through them. + +And now the plant can no longer afford to be idle and +live on prepared food. It must work for itself. Until now it has +been taking in the same kind of food that you and I do; for we +too find many seeds very pleasant to eat and useful to nourish +us. But now this store is exhausted. Upon what then is the plant +to live? It is cleverer than we are in this, for while we cannot +live unless we have food which has once been alive, plants can +feed upon gases and water and mineral matter only. Think over the +substances you can eat or drink, and you will find they are +nearly all made of things which have been alive: meat, +vegetables, bread, beer, wine, milk; all these are made from +living matter, and though you do take in such things as water +and salt, and even iron and phosphorus, these would be quite +useless if you did not eat and drink prepared food which your +body can work into living matter. + +But the plant as soon as it has roots and leaves begins to make +living matter out of matter that has never been alive. Through +all the little hairs of its roots it sucks in water, and in this +water are dissolved more or less of the salts of ammonia, +phosphorus, sulphur, iron, lime, magnesia, and even silica, or +flint. In all kinds of earth there is some iron, and we shall see +presently that this is very important to the plant. + +Suppose, then, that our primrose has begun to drink in water at +its roots. How is it to get this water up into the stem and +leaves, seeing that the whole plant is made of closed bags or +cells? It does it in a very curious way, which you can prove for +yourselves. Whenever two fluids, one thicker than the other, +such as treacle and water for example, are only separated by a +skin or any porous substance, they will always mix, the thinner +one oozing through the skin into the thicker one. If you tie a +piece of bladder over a glass tube, fill the tube half-full of +treacle, and then let the covered end rest in a bottle of water, +in a few hours the water will get in to the treacle and the +mixture will rise up in the tube till it flows over the top. Now, +the saps and juices of plants are thicker than water, so, directly +the water enters the cells at the root it oozes up into the cells +above, and mixes with the sap. Then the matter in those cells +becomes thinner than in the cells above, so it too oozes up, and +in this way cell by cell the water is pumped up into the leaves. + +When it gets there it finds our old friends the sun-beams hard at +work. If you have ever tried to grow a plant in a cellar, you +will know that in the dark its leaves remain white and sickly. +It is only in the sunlight that a beautiful delicate green tint +is given to them, and you will remember from Lecture II. that +this green tint shows that the leaf has used all the sun-waves +except those which make you see green; but why should it do this +only when it has grown up in the sunshine? + +The reason is this: when the sunbeam darts into the leaf and sets +all its particles quivering, it divides the protoplasm into two +kinds, collected into different cells. One of these remains +white, but the other kind, near the surface, is altered by the +sunlight and by the help of the iron brought in by the water. +This particular kind of protoplasm, which is called "chlorophyll," +will have nothing to do with the green waves and throws them back, +so that every little grain of this protoplasm looks green and +gives the leaf its green colour. + +It is these little green cells that by the help of the sun-waves +digest the food of the plant and turn the water and gases into +useful sap and juices. We saw in Lecture III. that when we +breathe-in air, we use up the oxygen in it and send back out of +our mouths carbonic acid, which is a gas made of oxygen and +carbon. + +Now, every living things wants carbon to feed upon, but plants +cannot take it in by itself, because carbon is solid (the +blacklead in your pencils is pure carbon), and a plant cannot +eat, it can only drink-in fluids and gases. Here the little +green cells help it out of its difficulty. They take in or +absorb out of the air carbonic acid gas which we have given out +of our mouths and then by the help of the sun-waves they tear +the carbon and oxygen apart. Most of the oxygen they throw back +into the air for us to use, but the carbon they keep. + +If you will take some fresh laurel-leaves and put them into a +tumbler of water turned upside-down in a saucer of water, and +set the tumbler in the sunshine, you will soon see little bright +bubbles rising up and clinging to the glass. These are bubbles +of oxygen gas, and they tell you that they have been set free by +the green cells which have torn from them the carbon of the +carbonic acid in the water. + +But what becomes of the carbon? And what use is made of the water +which we have kept waiting all this time in the leaves? Water, +you already know, is made of hydrogen and oxygen, but perhaps +you will be surprised when I tell you that starch, sugar, and +oil, which we get from plants, are nothing more than hydrogen +and oxygen in different quantities joined to carbon. + +It is very difficult at first to picture such a black thing as +carbon making part of delicate leaves and beautiful flowers, and +still more of pure white sugar. But we can make an experiment by +which we can draw the hydrogen and oxygen out of common loaf +sugar, and then you will see the carbon stand out in all its +blackness. I have here a plate with a heap of white sugar in it. +I pour upon it first some hot water to melt and warm it, and then +some strong sulphuric acid. This acid does nothing more than +simply draw the hydrogen and oxygen out. See! in a few moments a +black mass of carbon begins to rise, all of which has come out of +the white sugar you saw just now. *(The common dilute sulphuric +acid of commerce is not strong enough for this experiment, but +pure sulphuric acid can be secured from any chemist. Great care +must be taken in using it, as it burns everything it touches.) You +see, then, that from the whitest substance in plants we can get +this black carbon; and in truth, one-half of the dry part of every +plant is composed of it. + +Now look at my plant again, and tell me if we have not already +found a curious history? Fancy that you see the water creeping +in at the roots, oozing up from cell to cell till it reaches the +leaves, and there meeting the carbon which has just come out of +the air, and being worked up with it by the sun-waves into +starch, or sugar, or oils. + +But meanwhile, how is new protoplasm to be formed? for without +this active substance none of the work can go on. Here comes +into use a lazy gas we spoke of in Lecture III. There we thought +that nitrogen was of no use except to float oxygen in the air, +but here we shall find it very useful. So far, as we know, +plants cannot take up nitrogen out of the air, but they can get +it out of the ammonia which the water brings in at their roots. + +Ammonia, you will remember, is a strong-smelling gas, made of +hydrogen and nitrogen, and which is often almost stifling near a +manure-heap. When you manure a plant you help it to get this +ammonia, but at any time it gets some from the soil and also +from the rain-drops which bring it down in the air. Out of this +ammonia the plant takes the nitrogen and works it up with the +three elements, carbon, oxygen, and hydrogen, to make the +substances called albuminoids, which form a large part of the +food of the plant, and it is these albuminoids which go to make +protoplasm. You will notice that while the starch and other +substances are only made of three elements, the active protoplasm +is made of these three added to a fourth, nitrogen, and it also +contains phosphorus and sulphur. + +And so hour after hour and day after day our primrose goes on +pumping up water and ammonia from its roots to its leaves, +drinking in carbonic acid from the air, and using the sun-waves +to work them all up into food to be sent to all parts of its +body. In this way these leaves act, you see, as the stomach of +the plant, and digest its food. + +Sometimes more water is drawn up into the leaves than can be +used, and then the leaf opens thousands of little mouths in the +skin of its under surface, which let the drops out just as drops +of perspiration ooze through our skin when we are overheated. +These little mouths, which are called stomates (a, Fig. 42) are +made of two flattened cells, fitting against each other. When +the air is damp and the plant has too much water these lie open +and let it out, but when the air is dry, and the plant wants to +keep as much water as it can, then they are closely shut. There +are as many as a hundred thousand of these mouths under one +apple-leaf, so you may imagine how small they often are. + +Plants which only live one year, such as mignonette, the sweet +pea, and the poppy, take in just enough food to supply their +daily wants and to make the seeds we shall speak of presently. +Then, as soon as their seeds are ripe their roots begin to +shrivel, and water is no longer carried up. The green cells can +no longer get food to digest, and they themselves are broken up by +the sunbeams and turn yellow, and the plant dies. + +But many plants are more industrious than the stock and +mignonette, and lay by store for another year, and our primrose +is one of these. Look at this thick solid mass below the primrose +leaves, out of which the roots spring. (See the plant in the +foreground of the heading of the lecture.) This is really the +stem of the primrose hidden underground, and all the starch, +albuminoids, &c., which the plant can spare as it grows, are +sent down into this underground stem and stored up there, to lie +quietly in the ground through the long winter, and then when the +warm spring comes this stem begins to send out leaves for a new +plant. + + + +Week 21 + +We have now seen how a plant springs up, feeds itself, grows, +stores up food, withers, and dies; but we have said nothing yet +about its beautiful flowers or how it forms its seeds. If we +look down close to the bottom of the leaves in a primrose root +in spring-time, we shall always find three or four little green +buds nestling in among the leaves, and day by day we may see the +stalk of these buds lengthening till they reach up into the open +sunshine, and then the flower opens and shows its beautiful pale- +yellow crown. + +We all know that seeds are formed in the flower, and that the +seeds are necessary to grow into new plants. But do we know the +history of how they are formed, or what is the use of the +different parts of the bud? Let us examine them all, and then I +think you will agree with me that this is not the least wonderful +part of the plant. + +Remember that the seed is the one important thing and then notice +how the flower protects it. First, look at the outside green +covering, which we call the calyx. See how closely it fits in +the bud, so that no insects can creep in to gnaw the flower, nor +any harm come to it from cold or blight. Then, when the calyx +opens, notice that the yellow leaves which form the crown or +corolla, are each alternate with one of the calyx leaves, so that +anything which got past the first covering would be stopped by +the second. Lastly, when the delicate corolla has opened out, +look at those curious yellow bags just at the top of the tube +(b,2, Fig. 43). What is their use? + +But I fancy I see two or three little questioning faces which +seem to say, "I see no yellow bags at the top of the tube." Well, +I cannot tell whether you can or not in the specimen you have in +your hand; for one of the most curious things about primrose +flowers is, that some of them have these yellow bags at the top of +the tube and some of them hidden down right in the middle. But +this I can tell you:those of you who have got no yellow bags at +the top will have a round knob there (I a, Fig. 43), and will find +the yellow bags (b) buried in the tube. Those, on the other hand, +who have the yellow bags (2 b, Fig. 43) at the top will find the +knob (a) half-way down the tube. + +Now for the use of these yellow bags, which are called the +anthers of the stamens, the stalk on which they grow being +called the filament or thread. If you can manage to split them +open you will find that they have a yellow powder in them, +called pollen, the same as the powder which sticks to your nose +when you put it into a lily; and if you look with a magnifying +glass at the little green knob in the centre of the flower, you +will probably see some of this yellow dust sticking on it (A, +Fig. 43). We will leave it there for a time, and examine the +body called the pistil, to which the knob belongs. Pull off the +yellow corolla (which will come off quite easily), and turn back +the green leaves. You will then see that the knob stands on the +top of a column, and at the bottom of this column there is a +round ball (s v), which is a vessel for holding the seeds. In +this diagram (A, Fig. 43) I have drawn the whole of this curious +ball and column as if cut in half, so that we may see what is in +it. In the middle of the ball, in a cluster, there are a number of +round transparent little bodies, looking something like round +green orange-cells full of juice. They are really cells full of +protoplasm, with one little dark spot in each of them, which +by-and-by is to make our little plantlet that we found in the +seed. + +"These, then, are seeds," you will say. Not yet; they are only +ovules, or little bodies which may become seeds. If they were +left as they are they would all wither and die. But those little +grains of pollen, which we saw sticking to the knob at the top, +are coming down to help them. As soon as these yellow grains +touch the sticky knob or stigma, as it is called, they throw out +tubes, which grow down the column until they reach the ovules. In +each one of these they find a tiny hole, and into this they +creep, and then they pour into the ovule all the protoplasm from +the pollen-grain which is sticking above, and this enables it to +grow into a real seed, with a tiny plantlet inside. + +This is how the plant forms its seed to bring up new little ones +next year, while the leaves and the roots are at work preparing +the necessary food. Think sometimes when you walk in the woods, +how hard at work the little plants and big trees are, all around +you. You breathe in the nice fresh oxygen they have been +throwing out, and little think that it is they who are making +the country so fresh and pleasant, and that while they look as if +they were doing nothing but enjoying the bright sunshine, they +are really fulfilling their part in the world by the help of +this sunshine; earning their food from the ground working it up; +turning their leaves where they can best get light (and in this it +is chiefly the violet sun-waves that help them), growing, even at +night, by making new cells out of the food they have taken in the +day; storing up for the winter; putting out their flowers and +making their seeds, and all the while smiling so pleasantly in +quiet nooks and sunny dells that it makes us glad to see them. + +But why should the primroses have such golden crowns? plain green +ones would protect the seed quite as well. Ah! now we come to a +secret well worth knowing. Look at the two primrose flowers, 1 +and 2, Fig. 43, p. 163, and tell me how you think the dust gets +on to the top of the sticky knob or stigma. No. 2 seems easy +enough to explain, for it looks as if the pollen could fall down +easily from the stamens on to the knob, but it cannot fall up, +as it would have to do in No. 1. Now the curious truth is, as Mr. +Darwin has shown, that neither of these flowers can get the dust +easily for themselves, but of the two No. 1 has the least +difficulty. + +Look at a withered primrose, and see how it holds its head down, +and after a little while the yellow crown falls off. It is just +about as it is falling that the anthers or bags of stamens burst +open, and then, in No. 1 (Fig. 44), they are dragged over the +knob and some of the grains stick there. But in the other form +of primrose, No. 2, when the flower falls off, the stamens do +not come near the knob, so it has no chance of getting any +pollen; and while the primrose is upright the tube is so narrow +that the dust does not easily fall. But, as I have said, neither +kind gets it very easily, nor is it good for them if they do. The +seeds are much stronger and better if the dust or pollen of one +flower is carried away and left on the knob or stigma of another +flower; and the only way this can be done is by insects flying +from one flower to another and carrying the dust on their legs and +bodies. + +If you suck the end of the tube of the primrose flower you will +find it tastes sweet, because a drop of honey has been lying +there. When the insects go in to get this honey, they brush +themselves against the yellow dust-bags, and some of the dust +sticks to them, and then when they go to the next flower they +rub it off on to its sticky knob. + +Look at No. 1 and No. 2 (Fig. 43) and you will see at once that +if an insect goes into No. 1 and the pollen sticks to him, when +he goes into No. 2 just that part of his body on which the +pollen is will touch the knob; and so the flowers become what we +call "crossed," that is, the pollen-dust of the one feeds the +ovule of the other. And just the same thing will happen if he +flies from No. 2 to No. 1. There the dust will be just in the +position to touch the knob which sticks out of the flower. + +Therefore, we can see clearly that it is good for the primrose +that bees and other insects should come to it, and anything it +can do to entice them will be useful. Now, do you not think that +when an insect once knew that the pale-yellow crown showed where +honey was to be found, he would soon spy these crowns out as he +flew along? or if they were behind a hedge, and he could not see +them, would not the sweet scent tell him where to come and look +for them? And so we see that the pretty sweet-scented corolla is +not only delightful for us to look at and to smell, but it is +really very useful in helping the primrose to make strong +healthy seeds out of which the young plants are to grow next +year. + +And now let us see what we have learnt. We began with a tiny +seed, though we did not then know how this seed had been made. +We saw the plantlet buried in it, and learnt how it fed at first +on prepared food, but soon began to make living matter for +itself out of gases taken from the water through the cells to +its stomach - the leaves! And how marvellously the sun-waves +entering there formed the little green granules, and then helped +them to make food and living protoplasm! At this point we might +have gone further, and studied how the fibres and all the +different vessels of the plant are formed, and a wondrous history +it would have been. But it was too long for one hour's lecture, +and you must read it for yourselves in books on botany. We had to +pass on to the flower, and learn the use of the covering leaves, +the gaily coloured crown attracting the insects, the dust-bags +holding the pollen, the little ovules each with the germ of a new +plantlet, lying hidden in the seed- vessel, waiting for the +pollen-grains to grow down to them. Lastly, when the pollen crept +in at the tiny opening we learnt that the ovule had now all it +wanted to grow into a perfect seed. + +And so we came back to a primrose seed, the point from which we +started; and we have a history of our primrose from its birth to +the day when its leaves and flowers wither away and it dies down +for the winter. + +But what fairies are they which have been at work here? First, +the busy little fairy Life in the active protoplasm; and +secondly, the sun-waves. We have seen that it was by the help of +the sunbeams that the green granules were made, and the water, +carbonic acid, and nitrogen worked up into the living plant. And +in doing this work the sun-waves were caught and their strength +used up, so that they could no longer quiver back into space. But +are they gone for ever? So long as the leaves or the stem or the +root of the plant remain they are gone, but when those are +destroyed we can get them back again. Take a handful of dry +withered plants and light them with a match, then as the leaves +burn and are turned back again to carbonic acid, nitrogen, and +water, our sunbeams come back again in the flame and heat. + +And the life of the plant? What is it, and why is this protoplasm +always active and busy? I cannot tell you. Study as we may, the +life of the tiny plant is as much a mystery as your life and +mine. It came, like all things, from the bosom of the Great +Father, but we cannot tell how it came nor what it is. We can +see the active grains moving under the microscope, but we cannot +see the power that moves them. We only know it is a power given +to the plant, as to you and to me, to enable it to live its +life, and to do its useful work in the world. + + + + +Week 22 + +LECTURE VIII + +THE HISTORY OF A PIECE OF COAL + +I have here a piece of coal (Fig. 45), which, though it has been +cut with some care so as to have a smooth face, is really in no +other way different from any ordinary lump which you can pick for +yourself out of the coal-scuttle. Our work to-day is to relate +the history of this black lump; to learn what it is, what it has +been, and what it will be. + +It looks uninteresting enough at first sight, and yet if we +examine it closely we shall find some questions to ask even about +its appearance. Look at the smooth face of this specimen and see +if you can explain those fine lines which run across so close +together as to look like the edges of the leaves of a book. Try +to break a piece of coal, and you will find that it will split +much more easily along those lines than across the other way of +the lump; and if you wish to light a fire quickly you should +always put this lined face downwards so that the heat can force +its way up through these cracks and gradually split up the block. +Then again if you break the coal carefully along one of these +lines you will find a fine film of charcoal lying in the crack, +and you will begin to suspect that this black coal must have been +built up in very thin layers, with a kind of black dust between +them. + +The next thing you will call to mind is that this coal burns and +gives flame and heat, and that this means that in some way +sunbeams are imprisoned in it; lastly, this will lead you to +think of plants, and how they work up the strength of the +sunbeams into their leaves, and hide black carbon in even the +purest and whitest substance they contain. + +Is coal made of burnt plants, then? Not burnt ones, for if so it +would not burn again; but you may have read how the makers of +charcoal take wood and bake it without letting it burn, and then +it turns black and will afterwards make a very good fire; and so +you will see that it is probable that our piece of coal is made +of plants which have been baked and altered, but which have still +much sunbeam strength bottled up in them, which can be set free +as they burn. + +If you will take an imaginary journey with me to a coal-pit near +Newcastle, which I visited many years ago, you will see that we +have very good evidence that coal is made of plants, for in all +coal-mines we find remains of them at every step we take. + +Let us imagine that we have put on old clothes which will not +spoil, and have stepped into the iron basket (see Fig. 46) called +by the miners a cage, and are being let down the shaft to the +gallery where the miners are at work. Most of them will probably +be in the gallery b, because a great deal of the coal in a has +been already taken out. But we will stop in a because there we +can see a great deal of the roof and the floor. When we land on +the floor of the gallery we shall find ourselves in a kind of +tunnel with railway lines laid along it and trucks laden with +coal coming towards the cage to be drawn up, while empty ones are +running back to be loaded where the miners are at work. Taking +lamps in our hands and keeping out of the way of the trucks, we +will first throw the light on the roof, which is made of shale or +hardened clay. We shall not have gone many yards before we see +impressions of plants in the shale, like those in this specimen +(Fig. 47), which was taken out of a coal-mine at Neath in +Glamorganshire, a few days ago, and sent up for this lecture. +You will recognize at once the marks of ferns (a), for they look +like those you gather in the hedges of an ordinary country lane, +and that long striped branch (b) does not look unlike a reed, and +indeed it is something of this kind, as we shall see by-and-by. +You will find plenty of these impressions of plants as you go +along the gallery and look up at the roof, and with them there +will be others with spotted stems, or with stems having a curious +diamond pattern upon them, and many ferns of various kinds. + +Next look down at your feet and examine the floor. You will not +have to search long before you will almost certainly find a piece +of stone like that represented in Fig. 48, which has also come +from Neath Colliery. This fossil, which is the cast of a piece +of a plant, puzzled those who found it for a very long time. At +last, however, Mr. Binney found the specimen growing to the +bottom of the trunk of one of the fossil trees with spotted +stems, called Sigillaria; and so proved that this curious pitted +stone is a piece of fossil root, or rather underground stem, like +that which we found in the primrose, and that the little pits or +dents in it are scars where the rootlets once were given off. + +Whole masses of these root-stems, with ribbon-like roots lying +scattered near them, are found buried in the layer of clay called +the underclay which makes the floor of the coal, and they prove +to us that this underclay must have been once the ground in which +the roots of the coal-plants grew. You will feel still more sure +of this when you find that there is not only one straight gallery +of coal, but that galleries branch out right and left, and that +everywhere you find the coal lying like a sandwich between the +floor and the roof, showing that quite a large piece of country +must be covered by these remains of plants all rooted in the +underclay. + +But how about the coal itself? It seems likely, when we find +roots below and leaves and stems above, that the middle is made +of plants, but can we prove it? We shall see presently that it +has been so crushed and altered by being buried deep in the +ground that the traces of leaves have almost been destroyed, +though people who are used to examining with the microscope, can +see the crushed remains of plants in thin slices of coal. + +But fortunately for us, perfect pieces of plants have been +preserved even in the coal-bed itself. Do you remember our +learning in Lecture IV, that water with lime in it petrifies +things, that is, leaves carbonate of lime to fill up grain by +grain the fibres of an animal or plant as the living matter +decays, and so keeps an exact representation of the object? + +Now, it so happens that in a coal-bed at South Ouram, near +Halifax, as well as in some other places, carbonate of lime +trickled in before the plants were turned into coal, and made +some round nodules in the plant-bed, which look like cannon- +balls. Afterwards, when all the rest of the bed was turned into +coal, these round balls remained crystallized, and by cutting +thin transparent slices across the nodule we can distinctly see +the leaves and stems and curious little round bodies which make +up the coal. Several such sections may be seen at the British +Museum, and when we compare these fragments of plants with those +which we find above and below the coal-bed, we find that they +agree, thus proving that coal is made of plants, and of those +plants whose roots grew in the clay floor, while their heads +reached up far above where the roof now is. + +The next question is, what kind of plants were these? Have we +anything like them living in the world now? You might perhaps +think that it would be impossible to decide this question from +mere petrified pieces of plants. But many men have spent their +whole lives in deciphering all the fragments that could be found, +and though the section given in Fig. 49 may look to you quite +incomprehensible, yet a botanist can reed it as we read a book. +For example, at S and L, where stems are cut across, he can learn +exactly how they were build up inside, and compare them with the +stems of living plants, while the fruits cc and the little round +spores lying near them, tell him their history as well as if he +had gathered them from the tree. In this way we have learnt to +know very fairly what the plants of the coal were like, and you +will be surprised when I tell you that the huge trees of the +coal-forests, of which we sometimes find trunks in the coal-mines +from ten to fifty feet long, are only represented on the earth +now by small insignificant plants, scarcely ever more than two +feet, and often not many inches high. + +Have you ever seen the little club moss or Lycopodium which grows +all over England, but chiefly in the north, on heaths and +mountains? At the end of each of its branches it bears a cone +made of scaly leaves; and fixed to the inside of each of these +leaves is a case called a sporangium, full of little spores or +moss-seeds, as we may call them, though they are not exactly like +true seeds. In one of these club-mosses called Selaginella, the +cases near the bottom of the cone contain large spores, while +those near the top contain a powdery dust. These spores are full +of resin, and they are collected on the Continent for making +artificial lightning in the theatres, because they flare when +lighted. + +Now this little Selaginella is of all living plants the one most +like some of the gigantic trees of the coal-forests. If you look +at this picture of a coal-forest (Fig. 51), you will find it +difficult perhaps to believe that those great trees, with diamond +markings all up the trunk, hanging over from the right to the +left of the picture, and covering all the top with their boughs, +could be in any way relations of the little Selaginella; yet we +find branches of them in the beds above the coal, bearing cones +larger but just like Selaginella cones; and what is most curious, +the spores in these cones are of exactly the same kind and not +any larger than those of the club-mosses. + +These trees are called by botanists Lepidodendrons, or scaly +trees; there are numbers of them in all coal-mines, and one trunk +has been found 49 feet long. Their branches were divided in a +curious forked manner and bore cones at the ends. The spores +which fell from these cones are found flattened in the coal, and +they may be seen scattered about in the coal-ball. + + + +Week 23 + +Another famous tree which grew in the coal-forests was the one +whose roots we found in the floor or underclay of the coal. It +has been called Sigillaria, because it has marks like seals +(sigillum, a seal) all up the trunk, due to the scars left by the +leaves when they fell from the tree. You will see the +Sigillarias on the left-hand side of the coal-forest picture, +having those curious tufts of leaves springing out of them at the +top. Their stems make up a great deal of the coal, and the bark +of their trunks is often found in the clays above, squeezed flat +in lengths of 30, 60, or 70 feet. Sometimes, instead of being +flat the bark is still in the shape of a trunk, and the interior +is filled with sane; and then the trunk is very heavy, and if the +miners do not prop the roof up well it falls down and kills those +beneath it. Stigmaria is the root of the Sigillaria, and is +found in the clays below the coal. Botanists are not yet quite +certain about the seed-cases of this tree, but Mr. Carruthers +believes that they grew inside the base of the leaves, as they do +in the quillwort, a small plant which grows at the bottom of our +mountain lakes. + +But what is that curious reed-like stem we found in the piece of +shale (see Fig. 47)? That stem is very important, for it +belonged to a plant called a Calamite, which, as we shall see +presently, helped to sift the earth away from the coal and keep +it pure. This plant was a near relation of the "horsetail," or +Equisetum, which grows in our marshes; only, just as in the case +of the other trees, it was enormously larger, being often 20 feet +high, whereas the little Equisetum, Fig. 52, is seldom more than +a foot, and never more than 4 feet high in England, though in +tropical South America they are much higher. Still, if you have +ever gathered "horsetails," you will see at once that those trees +in the foreground of the picture (Fig. 51), with leaves arranged +in stars round the branches, are only larger copies of the little +marsh-plants; and the seed-vessels of the two plants are almost +exactly the same. + +These great trees, the Lepidodendrons, the Sigillarias, and the +Calamites, together with large tree-ferns, are the chief plants +that we know of in the coal-forests. It seems very strange at +first that they should have been so large when their descendants +are now so small, but if you look at our chief plants and trees +now, you will find that nearly all of them bear flowers, and this +is a great advantage to them, because it tempts the insects to +bring them the pollen-dust, as we saw in the last lecture. + +Now the Lipidodendrons and their companions had no true flowers, +but only these seed-cases which we have mentioned; but as there +were no flowering plants in their time, and they had the ground +all to themselves, they grew fine and large. By-and-by, however, +when the flowering plants came in, these began to crowd out the +old giants of the coal-forests, so that they dwindled and +dwindled from century to century till their great-great- +grandchildren, thousands of generations after, only lift up their +tiny heads in marshes and on heaths, and tell us that they were +big once upon a time. + +And indeed they must have been magnificent in those olden days, +when they grew thick and tall in the lonely marshes where plants +and trees were the chief inhabitants. We find no traces in the +clay-beds of the coal to lead us to suppose that men lived in +those days, nor lions, nor tigers, nor even birds to fly among +the trees; but these grand forests were almost silent, except +when a huge animal something like a gigantic newt or frog went +croaking through the marsh, or a kind of grasshopper chirruped on +the land. But these forms of life were few and far between, +compared to the huge trees and tangled masses of ferns and reeds +which covered the whole ground, or were reflected in the bosom of +the large pools and lakes round about which they grew. + +And now, if you have some idea of the plants and trees of the +coal, it is time to ask how these plants became buried in the +earth and made pure coal, instead of decaying away and leaving +behind only a mixture of earth and leaves? + +To answer this question, I must ask you to take another journey +with me across the Atlantic to the shores of America, and to land +at Norfolk in Virginia, because there we can see a state of +things something like the marshes of the coal-forests. All round +about Norfolk the land is low, flat, and marshy, and to the south +of the town, stretching far away into North Carolina, is a large, +desolate swamp, no less than forty miles long and twenty-five +broad. The whole place is one enormous quagmire, overgrown with +water-plants and trees. The soil is as black as ink from the +old, dead leaves, grasses, roots, and stems which lie in it; and +so soft, that everything would sink into it, if it were not for +the matted roots of the mosses, ferns, and other plants which +bind it together. You may dig down for ten or fifteen feet, and +find nothing but peat made of the remains of plants which have +lived and died there in succession for ages and ages, while the +black trunks of the fallen trees lie here and there, gradually +being covered up by the dead plants. + +The whole place is so still, gloomy, and desolate, that it goes +by the name of the "Great Dismal Swamp," and you see we have here +what might well be the beginning of a bed of coal; for we know +that peat when dried becomes firm and makes an excellent fire, +and that if it were pressed till it was hard and solid it would +not be unlike coal. If, then, we can explain how this peaty bed +has been kept pure from earth, we shall be able to understand how +a coal-bed may have been formed, even though the plants and trees +which grow in this swamp are different from those which grew in +the coal-forests. + +The explanation is not difficult; streams flow constantly, or +rather ooze into the Great Dismal Swamp from the land that lies +to the west, but instead of bringing mud in with them as rivers +bring to the sea, they bring only clear, pure water, because, as +they filter for miles through the dense jungle of reeds, ferns, +and shrubs which grow round the marsh, all the earth is sifted +out and left behind. In this way the spongy mass of dead plants +remains free from earthy grains, while the water and the shade of +the thick forest of trees prevent the leaves, stems, etc., from +being decomposed by the air and sun. And so year after year as +the plants die they leave their remains for other plants to take +root in, and the peaty mass grows thicker and thicker, while tall +cedar trees and evergreens live and die in these vast, swampy +forests, and being in loose ground are easily blown down by the +wind, and leave their trunks to be covered up by the growing moss +and weeds. + +Now we know that there were plenty of ferns and of large +Calamites growing thickly together in the coal-forests, for we +find their remains everywhere in the clay, so we can easily +picture to ourselves how the dense jungle formed by these plants +would fringe the coal-swamp, as the present plants do the Great +Dismal Swamp, and would keep out all earthy matter, so that year +after year the plants would die and form a thick bed of peat, +afterwards to become coal. + + + +Week 24 + +The next thing we have to account for is the bed of shale or +hardened clay covering over the coal. Now we know that from time +to time land has gone slowly up and down on our globe so as in +some places to carry the dry ground under the sea, and in others +to raise the sea-bed above the water. Let us suppose, then, that +the great Dismal Swamp was gradually to sink down so that the sea +washed over it and killed the reeds and shrubs. Then the streams +from the west would not be sifted any longer but would bring down +mud, and leave it, as in the delta of the Nile or Mississippi, to +make a layer over the dead plants. You will easily understand +that this mud would have many pieces of dead trees and plants in +it, which were stifled and died as it covered them over; and thus +the remains would be preserved like those which we find now in +the roof of the coal-galleries. + +But still there are the thick sandstones in the coal-mine to be +explained. How did they come there? To explain them, we must +suppose that the ground went on sinking till the sea covered the +whole place where once the swamp had been, and then sea-sand +would be thrown down over the clay and gradually pressed down by +the weight of new sand above, till it formed solid sandstone and +our coal-bed became buried deeper and deeper in the earth. + +At last, after long ages, when the thick mass of sandstones above +the bed b (Fig. 46) had been laid down, the sinking must have +stopped and the land have risen a little, so that the sea was +driven back; and then the rivers would bring down earth again and +make another clay-bed. Then a new forest would spring up, the +ferns, Calamites, Lepidodendrons, and Sigillarias would gradually +form another jungle, and many hundred of feet above the buried +coal-bed b, a second bed of peat and vegetable matter would begin +to accumulate to form the coal-bed a. + +Such is the history of how the coal which we now dig out of the +depths of the earth once grew as beautiful plants on the surface. +We cannot tell exactly all the ground over which these forests +grew in England, because some of the coal they made has been +carried away since by rivers and cut down by the waves of the +sea, but we can say that wherever there is coal now, there they +must have been then. + +Try and picture to yourselves that on the east coast of +Northumberland and Durham, where all is now black with coal- +dust, and grimy with the smoke of furnaces; and where the noise +of hammers and steam-engines, and of carts and trucks hurrying to +and fro, makes the country re-echo with the sound of labour; +there ages ago in the silent swamp shaded with monster trees, one +thin layer of plants after another was formed, year after year, +to become the coal we now value so much. In Lancashire, busy +Lancashire, the same thing was happening, and even in the middle +of Yorkshire and Derbyshire the sea must have come up and washed +a silent shore where a vast forest spread out over at least 700 +or 800 square miles. In Stafford-shire, too, which is now almost +the middle of England, another small coal-field tells the same +story, while in South Wales the deep coal-mines and number of +coal-seams remind us how for centuries and centuries forests must +have flourished and have disappeared over and over again under +the sand of the sea. + +But what is it that has changed these beds of dead plants into +hard, stony coal? In the first place you must remember they have +been pressed down under an enormous weight of rocks above them. +We can learn something about this even from our common lead +pencils. At one time the graphite or pure carbon, of which the +blacklead (as we wrongly call it) of our pencils is made, was dug +solid out of the earth. but so much has now been used that they +are obliged to collect the graphite dust, and press it under a +heavy weight, and this makes such solid pieces that they can cut +them into leads for ordinary cedar pencils. + +Now the pressure which we can exert by machinery is absolutely +nothing compared to the weight of all those hundreds of feet of +solid rock which lie over the coal-beds, and which has pressed +them down for thousands and perhaps millions of years; and +besides this, we know that parts of the inside of the earth are +very hot, and many of the rocks in which coal is found are +altered by heat. So we can picture to ourselves that the coal +was not only squeezed into a solid mass, but often much of the +oil and gas which were in the leaves of the plants was driven out +by heat, and the whole baked, as it were, into one substance. +The difference between coal which flames and coal which burns +only with a red heat, is chiefly that one has been baked and +crushed more than the other. Coal which flames has still got in +it the tar and the gas and the oils which the plant stored up in +its leaves, and these when they escape again give back the +sunbeams in a bright flame. The hard stone coal, on the contrary, +has lost a great part of these oils, and only carbon remains, +which seizes hold of the oxygen of the air and burns without +flame. Coke is pure carbon, which we make artificially by driving +out the oils and gases from coal, and the gas we burn is part of +what is driven out. + +We can easily make coal-gas here in this room. I have brought a +tobacco-pipe, the bowl of which is filled with a little powdered +coal, and the broad end cemented up with Stourbridge clay. When +we place this bowl over a spirit-lamp and make it very hot, the +gas is driven out at the narrow end of the pipe and lights easily +(see Fig. 53). This is the way all our gas is made, only that +furnaces are used to bake the coal in, and the gas is passed into +large reservoirs till it is wanted for use. + +You will find it difficult at first to understand how coal can be +so full of oil and tar and gases, until you have tried to think +over how much of all these there is in plants, and especially in +seeds - think of the oils of almonds, of lavender, of cloves, and +of caraways; and the oils of turpentine which we get from the +pines, and out of which tar is made. When you remember these and +many more, and also how the seeds of the club-moss now are +largely charged with oil, you will easily imagine that the large +masses of coal-plants which have been pressed together and broken +and crushed, would give out a great deal of oil which, when made +very hot, rises up as gas. You may often yourself see tar oozing +out of the lumps of coal in a fire, and making little black +bubbles which burst and burn. It is from this tar that James +Young first made the paraffin oil we burn in our lamps, and the +spirit benzoline comes from the same source. + +From benzoline, again, we get a liquid called aniline, from which +are made so many of our beautiful dyes - mauve, magenta, and +violet; and what is still more curious, the bitter almonds, pear- +drops, and many other sweets which children like to well, are +actually flavoured by essences which come out of coal-tar. Thus +from coal we get not only nearly all our heat and our light, but +beautiful colours and pleasant flavours. We spoke just now of +the plants of the coal as being without beautiful flowers, and +yet we see that long, long after their death they give us lovely +colours and tints as beautiful as any in flower-world now. + +Think, then, how much we owe to these plants which lived and died +so long ago! If they had been able to reason, perhaps they might +have said that they did not seem of much use in the world. They +had no pretty flowers, and there was no one to admire their +beautiful green foliage except a few croaking reptiles, and +little crickets and grasshoppers; and they lived and died all on +one spot, generation after generation, without seeming to do much +good to anything or anybody. Then they were covered up and put +out of sight, and down in the dark earth they were pressed all +out of shape and lost their beauty and became only black, hard +coal. There they lay for centuries and centuries, and thousands +and thousands of years, and still no one seemed to want them. + +At last, one day, long, long after man had been living on the +earth, and had been burning wood for fires, and so gradually +using up the trees in the forests, it was discovered that this +black stone would burn, and from that time coal has been becoming +every day more and more useful. Without it not only should we +have been without warmth in our houses, or light in our streets +when the stock of forest-wood was used up; but we could never +have melted large quantities of iron-stone and extracted the +iron. We have proof of this in Sussex. The whole country is +full of iron-stone, and the railings of St. Paul's churchyard are +made of Sussex iron. Iron-foundries were at work there as long +as there was wood enough to supply them, but gradually the works +fell into disuse, and the last furnace was put out in the year +1809. So now, because there is no coal in Sussex, the iron lies +idle, while in the North, where the iron-stone is near the coal- +mines, hundreds of tons are melted out every day. + +Again, without coal we could have had no engines of any kind, and +consequently no large manufactories of cotton goods, linen goods, +or cutlery. In fact, almost everything we use could only have +been made with difficulty and in small quantities; and even if we +could have made them it would have been impossible to have sent +them so quickly all over the world without coal, for we could +have had no railways or steamships, but must have carried all +goods along canals, and by slow sailing vessels. We ourselves +must have taken days to perform journeys now made in a few hours, +and months to reach our colonies. + +In consequence of this we should have remained a very poor +people. Without manufactories and industries we should have had +to live chiefly by tilling the ground, and everyone being obliged +to toil for daily bread, there would have been much less time or +opportunity for anyone to study science, or literature, or +history, or to provide themselves with comforts and refinements +of life. + +All this then, those plants and trees of the far-off ages, which +seemed to lead such useless lives, have done and are doing for +us. There are many people in the world who complain that life is +dull, that they do not see the use of it, and that there seems no +work specially for them to do. I would advise such people, +whether they are grown up or little children, to read the story +of the plants which form the coal. These saw no results during +their own short existences, they only lived and enjoyed the +bright sunshine, and did their work, and were content. And now +thousands, probably millions, of years after they lived and died, +England owes her greatness, and we much of our happiness and +comfort, to the sunbeams which those plants wove into their +lives. + +They burst forth again in our fires, in our brilliant lights, and +in our engines, and do the greater part of our work; teaching us + + "That nothing walks with aimless feet + That not one life shall be destroyed, + Or cast as rubbish to the void, + When God hath made the pile complete." + +In Memoriam + + + +Week 25 + +Lecture IX +Bees in the Hive + +I am going to ask you to visit with me to-day one of the most +wonderful cities with no human beings in it, and yet it is +densely populated, for such a city may contain from twenty +thousand to sixty thousand inhabitants. In it you will find +streets, but no pavements, for the inhabitants walk along the +walls of the houses; while in the houses you will see no windows, +for each house just fits its owner, and the door is the only +opening in it. Though made without hands these houses are most +evenly and regularly built in tiers one above the other; and here +and there a few royal palaces, larger and more spacious than the +rest, catch the eye conspicuously as they stand out at the corners +of the streets. + +Some of the ordinary houses are used to live in, while others +serve as storehouses where food is laid up in the summer to feed +the inhabitants during the winter, when they are not allowed to +go outside the walls. Not that the gates are ever shut: that is +not necessary, for in this wonderful city each citizen follows +the laws; going out when it is time to go out, coming home at +proper hours, and staying at home when it is his or her duty. +And in the winter, when it is very cold outside, the inhabitants, +having no fires, keep themselves warm within the city by +clustering together, and never venturing out of doors. + +One single queen reigns over the whole of this numerous +population, and you might perhaps fancy that, having so many +subjects to work for her and wait upon her, she would do nothing +but amuse herself. On the contrary, she too obeys the laws laid +down for her guidance, and never, except on one or two state +occasions, goes out of the city, but works as hard as the rest in +performing her own royal duties. + +From sunrise to sunset, whenever the weather is fine, all is +life, activity, and bustle in this busy city. Though the gates +are so narrow that two inhabitants can only just pass each other +on their way through them, yet thousands go in and out every hour +of the day; some bringing in materials to build new houses, others +food and provisions to store up for the winter; and while all +appears confusion and disorder among this rapidly moving throng, +yet in reality each has her own work to do, and perfect order +reigns over the whole. + +Even if you did not already know from the title of the lecture +what city this is that I am describing, you would no doubt guess +that it is a beehive. For where in the whole world, except +indeed upon an anthill, can we find so busy, so industrious, or +so orderly a community as among the bees? More than a hundred +years ago, a blind naturalist, Francois Huber, set himself to +study the habits of these wonderful insects and with the help of +his wife and an intelligent manservant managed to learn most of +their secrets. Before his time all naturalists had failed in +watching bees, because if they put them in hives with glass +windows, the bees, not liking the light, closed up the windows +with cement before they began to work. But Huber invented a hive +which he could open and close at will, putting a glass hive +inside it, and by this means he was able to surprise the bees at +their work. Thanks to his studies, and to those of other +naturalists who have followed in his steps, we now know almost +as much about the home of bees as we do about our own; and if we +follow out to-day the building of a bee-city and the life of its +inhabitants, I think you will acknowledge that they are a +wonderful community, and that it is a great compliment to anyone +to say that he or she is "as busy as a bee." + +In order to begin at the beginning of the story, let us suppose +that we go into a country garden one fine morning in May when +the sun is shining brightly overhead, and that we see hanging +from the bough of an old apple-tree a black object which looks +very much like a large plum-pudding. On approaching it, however, +we see that it is a large cluster or swarm of bees clinging to +each other by their legs; each bee with its two fore-legs +clinging to the two hinder legs of the one above it. In this way +as many as 20,000 bees may be clinging together, and yet they +hang so freely that a bee, even from quite the centre of the +swarm, can disengage herself from her neighbours and pass +through to the outside of the cluster whenever she wishes. + +If these bees were left to themselves, they would find a home +after a time in a hollow tree, or under the roof of a house, or +in some other cavity, and begin to build their honeycomb there. +But as we do not wish to lose their honey we will bring a hive, +and, holding it under the swarm, shake the bough gently so that +the bees fall into it, and cling to the sides as we turn it over +on a piece of clean linen, on the stand where the hive is to be. + +And now let us suppose that we are able to watch what is going on +in the hive. Before five minutes are over the industrious little +insects have begun to disperse and to make arrangements in their +new home. A number (perhaps about two thousand) of large, +lumbering bees of a darker colour than the rest, will it is true, +wander aimlessly about the hive, and wait for the others to feed +them and house them; but these are the drones, or male bees (3, +Fig. 54), who never do any work except during one or two days in +their whole lives. But the smaller working bees (1, Fig. 54) begin +to be busy at once. Some fly off in search of honey. Others walk +carefully all round the inside of the hive to see if there are any +cracks in it; and if there are, they go off to the horse-chestnut +trees, poplars, hollyhocks, or other plants which have sticky +buds, and gather a kind of gum called "propolis," with which they +cement the cracks and make them air-tight. Others again, cluster +round one bee (2, Fig. 54) blacker than the rest and having a +longer body and shorter wings; for this is the queen-bee, the +mother of the hive, and she must be watched and tended. + +But the largest number begin to hang in a cluster from the roof +just as they did from the bough of the apple tree. What are they +doing there? Watch for a little while and you will soon see one +bee come out from among its companions and settle on +the top of the inside of the hive, turning herself round and +round, so as to push the other bees back, and to make a space in +which she can work. Then she will begin to pick at the under +part of her body with her fore-legs, and will bring a scale of +wax from a curious sort of pocket under her abdomen. Holding +this wax in her claws, she will bite it with her hard, pointed +upper jaws, which move to and fro sideways like a pair of +pincers, then, moistening it with her tongue into a kind of +paste, she will draw it out like a ribbon and plaster it on the +top of the hive. + +After that she will take another piece; for she has eight of +these little wax-pockets, and she will go on till they are all +exhausted. Then she will fly away out of the hive, leaving a +small lump on the hive ceiling or on the bar stretched across +it; then her place will be taken by another bee who will go +through the same manoeuvres. This bee will be followed by +another, and another, till a large wall of wax has been built, +hanging from the bar of the hive as in Fig. 55, only that it +will not yet have cells fashioned in it. + +Meanwhile the bees which have been gathering honey out of doors +begin to come back laden. But they cannot store their honey, for +there are no cells made yet to put it in; neither can +they build combs with the rest, for they have no wax in their +wax-pockets. So they just go and hang quietly on to the other +bees, and there they remain for twenty-four hours, during which +time they digest the honey they have gathered, and part of it +forms wax and oozes out from the scales under their body. Then +they are prepared to join the others at work and plaster wax on +to the hive. + + + + +Week 26 + +And now, as soon as a rough lump of wax is ready, another set of +bees come to do their work. These are called the nursing bees, +because they prepare the cells and feed the young ones. One of +these bees, standing on the roof of the hive, begins to force +her head into the wax, biting with her jaws and moving her head +to and fro. Soon she has made the beginning of a round hollow, +and then she passes on to make another, while a second bee takes +her place and enlarges the first one. As many as twenty bees +will be employed in this way, one after another, upon each hole +before it is large enough for the base of a cell. + +Meanwhile another set of nursing bees have been working just in +the same way on the other side of the wax, and so a series of +hollows are made back to back all over the comb. Then the bees +form the walls of the cells and soon a number of six-sided +tubes, about half an inch deep, stand all along each side of the +comb ready to receive honey or bee-eggs. + +You can see the shape of these cells in c,d, Fig. 56, and notice +how closely they fit into each other. Even the ends are so +shaped that, as they lie back to back, the bottom of one cell +(B, Fig. 56) fits into the space between the ends of +three cells meeting it from the opposite side (A, Fig. 56), +while they fit into the spaces around it. Upon this plan the +clever little bees fill every atom of space, use the least +possible quantity of wax, and make the cells lie so closely +together that the whole comb is kept warm when the young bees +are in it. + +There are some kinds of bees who do not live in hives, but each +one builds a home of its own. These bees - such as the +upholsterer bee, which digs a hole in the earth and lines it +with flowers and leaves, and the mason bee, which builds in +walls - do not make six-sided cells, but round ones, for room is +no object to them. But nature has gradually taught the little +hive-bee to build its cells more and more closely, till they fit +perfectly within each other. If you make a number of round holes +close together in a soft substance, and then squeeze the +substance evenly from all sides, the rounds will gradually take +a six-sided form, showing that this is the closest shape into +which they can be compressed. Although the bee does not know +this, yet as gnaws away every bit of wax that can be +spared she brings the holes into this shape. + +As soon as one comb is finished, the bees begin another by the +side of it, leaving a narrow lane between, just broad enough for +two bees to pass back to back as they crawl along, and so the +work goes on till the hive is full of combs. + +As soon, however, as a length of about five or six inches of the +first comb has been made into cells, the bees which are bringing +home honey no longer hang to make it into wax, but begin to +store it in the cells. We all know where the bees go to fetch +their honey, and how, when a bee settles on a flower, she +thrusts into it her small tongue-like proboscis, which is really +a lengthened under-lip, and sucks out the drop of honey. This she +swallows, passing it down her throat into a honey-bag or first +stomach, which lies between her throat and her real stomach, and +when she gets back to the hive she can empty this bag and pass +honey back through her mouth again into the honey-cells. + +But if you watch bees carefully, especially in the spring-time, +you will find that they carry off something else besides honey. +Early in the morning, when the dew is on the ground, or later in +the day, in moist shady places, you may see a bee rubbing itself +against a flower, or biting those bags of yellow dust or pollen +which we mentioned in Lecture VII. When she has covered herself +with pollen, she will brush it off with her feet, and, bringing +it to her mouth, she will moisten and roll it into a little ball, +and then pass it back from the first pair of legs to the second +and so to the third or hinder pair. Here she will pack it into a +little hairy groove called a "basket" in the joint of one of the +hind legs, where you may see it, looking like a swelled joint, as +she hovers among the flowers. She often fills both hind legs in +this way, and when she arrives back at the hive the nursing bees +take the lumps form her, and eat it themselves, or mix it with +honey to feed the young bees; or, when they have any to spare, +store it away in old honey-cells to be used by-and-by. This is the +dark, bitter stuff called "bee- bread" which you often find in a +honeycomb, especially in a comb which has been filled late in the +summer. + +When the bee has been relieved of the bee-bread she goes off to +one of the clean cells in the new comb, and, standing on the +edge, throws up the honey from the honey-bag into the cell. One +cell will hold the contents of many honey-bags, and so the busy +little workers have to work all day filling cell after cell, in +which the honey lies uncovered, being too thick and sticky to +flow out, and is used for daily food - unless there is any to +spare, and then they close up the cells with wax to keep for the +winter. + +Meanwhile, a day or two after the bees have settled in the hive, +the queen-bee begins to get very restless. She goes outside the +hive and hovers about a little while, and then comes in again, +and though generally the bees all look very closely after her to +keep her indoors, yet now they let her do as she likes. Again +she goes out, and again back, and then, at last, she soars up +into the air and flies away. But she is not allowed to go alone. +All the drones of the hive rise up after her, forming +a guard of honour to follow her wherever she goes. + +In about half-an-hour she comes back again, and then the working +bees all gather round her, knowing that now she will remain +quietly in the hive and spend all her time in laying eggs; for +it is the queen-bee who lays all the eggs in the hive. This she +begins to do about two days after her flight. There are now many +cells ready besides those filled with honey; and, escorted by +several bees, the queen-bee goes to one of these, and, putting +her head into it remains there a second as if she were examining +whether it would make a good home for the young bee. Then, +coming out, she turns round and lays a small, oval, bluish-white +egg in the cell. After this she takes no more notice of it, but +goes on to the next cell and the next, doing the same thing, and +laying eggs in all the empty cells equally on both sides of the +comb. She goes on so quickly that she sometimes lays as many as +200 eggs in one day. + +Then the work of the nursing bees begins. In two or three days +each egg has become a tiny maggot or larva, and the nursing bees +put into its cell a mixture of pollen and honey which they have +prepared in their own mouths, thus making a kind of sweet bath +in which the larva lies. In five or six days the larva grows so +fat upon this that it nearly fills the cell, and then the bees +seal up the mouth of the cell with a thin cover of wax, made of +little rings and with a tiny hole in the centre. + +As soon as the larva is covered in, it begins to give out from +its under-lip a whitish, silken film, made of two threads of silk +glued together, and with this it spins a covering or cocoon all +round itself, and so it remains for about ten days more. At last, +just twenty-one days after the egg was laid, the young bee is +quite perfect, lying in the cell as in Fig. 57, and she begins to +eat her way through the cocoon and through the waxen lid, and +scrambles out of her cell. Then the nurses come again to her, +stroke her wings and feed her for twenty-four hours, and after +that she is quite ready to begin work, and flies out to gather +honey and pollen like the rest of the workers. + +By this time the number of working bees in the hive is becoming +very great, and the storing of honey and pollen-dust goes on +very quickly. Even the empty cells which the young bees have +left are cleaned out by the nurses and filled with honey; and +this honey is darker than that stored in clean cells, and which +we always call "virgin honey" because it is so pure and clear. + +At last, after six weeks, the queen leaves off laying worker- +eggs, and begins to lay, in some rather larger cells, eggs from +which drones, or male bees, will grow up in about twenty days. +Meanwhile the worker-bees have been building on the edge of the +cones some very curious cells (q, Fig. 57) which look like +thimbles hanging with the open side upwards, and about every three +days the queen stops in laying drone-eggs and goes to put an egg +in one of these cells. Notice that she waits three days between +each of these peculiar layings, because we shall see presently +that there is a good reason for her doing so. + +The nursing bees take great care of these eggs, and instead of +putting ordinary food into the cell, they fill it with a sweet, +pungent jelly, for this larva is to become a princess and a +future queen bee. Curiously enough, it seems to be the peculiar +food and the size of the cell which makes the larva grow into a +mother-bee which can lay eggs, for if a hive has the misfortune +to lose its queen, they take one of the ordinary worker-larvae +and put it into a royal cell and feed it with jelly, and it +becomes a queen-bee. As soon as the princess is shut in like the +others, she begins to spin her cocoon, but she does not quite +close it as the other bees do, but leaves a hole at the top. + + + +Week 27 + +At the end of sixteen days after the first royal egg was laid, +the eldest princess begins to try to eat her way out of her +cell, and about this time the old queen becomes very uneasy, and +wanders about distractedly. The reason of this is that there can +never be two queen-bees in one hive, and the queen knows that +her daughter will soon be coming out of her cradle and will try +to turn her off her throne. So, not wishing to have to fight for +her kingdom, she makes up her mind to seek a new home and take a +number of her subjects with her. If you watch the hive about this +time you will notice many of the bees clustering together after +they have brought in their honey, and hanging patiently, in order +to have plenty of wax ready to use when they start, while the +queen keeps a sharp look-out for a bright, sunny day, on which +they can swarm: for bees will never swarm on a wet or doubtful day +if they can possibly help it, and we can easily understand why, +when we consider how the rain would clog their wings and spoil the +wax under their bodies. + +Meanwhile the young princess grows very impatient, and tries to +get out of her cell, but the worker-bees drive her back, for +they know there would be a terrible fight if the two queens met. +So they close up the hole she has made with fresh wax after +having put in some food for her to live upon till she is +released. + +At last a suitable day arrives, and about ten or eleven o'clock +in the morning the old queen leaves the hive, taking with her +about 2000 drones and from 12,000 to 20,000 worker-bees, which +fly a little way clustering round her till she alights on the +bough of some tree, and then they form a compact swarm ready for +a new hive or to find a home of their own. + +Leaving them to go their way, we will now return to the old hive. +Here the liberated princess is reigning in all her glory; the +worker-bees crowd round her, watch over her, and feed her as +though they could not do enough to show her honour. But still +she is not happy. She is restless, and runs about as if looking +for an enemy, and she tries to get at the remaining royal cells +where the other young princesses are still shut in. But the +workers will not let her touch them, and at last she stands still +and begins to beat the air with her wings and to tremble all over, +moving more and more quickly, till she makes quite a loud, piping +noise. + +Hark! What is that note answering her? It is a low, hoarse sound, +and it comes from the cell of the next eldest princess. Now we +see why the young queen has been so restless. She knows her +sister will soon come out, and the louder and stronger the sound +becomes within the cell, the sooner she knows the fight will +have to begin. And so she makes up her mind to follow her +mother's example and to lead off a second swarm. But she cannot +always stop to choose a fine day, for her sister is growing very +strong and may come out of her cell before she is off. And so +the second, or after swarm, gets ready and goes away. And this +explains why princesses' eggs are laid a few days apart, for if +they were laid all on the same day, there would be no time for +one princess to go off with a swarm before the other came out of +her cell. Sometimes, when the workers are not watchful enough, +two queens do meet, and then they fight till one is killed; or +sometimes they both go off with the same swarm without finding +each other out. But this only delays the fight till they get +into the new hive; sooner or later one must be killed. + +And now a third queen begins to reign in the old hive, and she +is just as restless as the preceding ones, for there are still +more princesses to be born. But this time, if no new swarm wants +to start, the workers do not try to protect the royal cells. The +young queen darts at the first she sees, gnaws a hole with her +jaws, and, thrusting in her sting through the hole in the cocoon, +kills the young bee while it is still a prisoner. She then goes to +the next, and the next, and never rests till all the young +princesses are destroyed. Then she is contented, for she knows no +other queen will come to dethrone her. After a few days she takes +her flight in the air with the drones, and comes home to settle +down in the hive for the winter. + +Then a very curious scene takes place. The drones are no more +use, for the queen will not fly out again, and these idle bees +will never do any work in the hive. So the worker-bees begin to +kill them, falling upon them, and stinging them to death, and as +the drones have no stings they cannot defend themselves, and in +a few days there is not a drone, nor even a drone-egg, left in +the hive. This massacre seems very sad to us, since the poor +drones have never done any harm beyond being hopelessly idle. +But it is less sad when we know that they could not live many +weeks, even if they were not attacked, and, with winter coming, +the bees cannot afford to feed useless mouths, so a quick death +is probably happier for them than starvation. + +And now all the remaining inhabitants of the hive settle down to +feeding the young bees and laying in the winter's store. It is +at this time, after they have been toiling and saving, that we +come and take their honey; and from a well-stocked hive we may +even take 30 lbs. without starving the industrious little +inhabitants. But then we must often feed them in return and give +them sweet syrup in the late autumn and the next early spring when +they cannot find any flowers. + +Although the hive has now become comparatively quiet and the work +goes on without excitement, yet every single bee is employed in +some way, either out of doors or about the hive. Besides the +honey collectors and the nurses, a certain number of bees are +told off to ventilate the hive. You will easily understand that +where so many insects are packed closely together the heat will +become very great, and the air impure and unwholesome. And the +bees have no windows that they can open to let in fresh air, so +they are obliged to fan it in from the one opening of the hive. +The way in which they do this is very interesting. Some of the +bees stand close to the entrance, with their faces towards it, +and opening their wings, so as to make them into fans, they wave +them to and fro, producing a current of air. Behind these bees, +and all over the floor of the hive, there stand others, this time +with their backs towards the entrance, and fan in the same +manner, and in this way air is sent into all the passages. + +Another set of bees clean out the cells after the young bees are +born, and make them fit to receive honey, while others guard the +entrance of the hive to keep away the destructive wax-moth, +which tries to lay its eggs in the comb so that its young ones +may feed on the honey. All industrious people have to guard +their property against thieves and vagabonds, and the bees have +many intruders, such as wasps and snails and slugs, which creep +in whenever they get a chance. If they succeed in escaping the +sentinel bees, then a fight takes place within the hive, and the +invader is stung to death. + +Sometimes, however, after they have killed the enemy, the bees +cannot get rid of his body, for a snail or slug is too heavy to +be easily moved, and yet it would make the hive very unhealthy +to allow it to remain. In this dilemma the ingenious little bees +fetch the gummy "propolis" from the plant-buds and cement the +intruder all over, thus embalming his body and preventing it +from decaying. + +And so the life of this wonderful city goes on. Building, +harvesting, storing, nursing, ventilating and cleaning from morn +till night, the little worker-bee lives for about eight months, +and in that time has done quite her share of work in the world. +Only the young bees, born late in the season, live on till the +next year to work in the spring. The queen-bee lives longer, +probably about two years, and then she too dies, after having had +a family of many thousands of children. + +We have already pointed out that in our fairy-land of nature all +things work together so as to bring order out of apparent +confusion. But though we should naturally expect winds and +currents, rivers and clouds, and even plants to follow fixed +laws, we should scarcely have looked for such regularity in the +life of the active, independent busy bee. Yet we see that she, +too, has her own appointed work to do, and does it regularly and +in an orderly manner. In this lecture we have been speaking +entirely of the bee within the hive, and noticing how +marvellously her instincts guide her in her daily life. But +within the last few years we have learnt that she performs a most +curious and wonderful work in the world outside her home and that +we owe to her not only the sweet honey to eat, but even in a great +degree the beauty and gay colours of the flowers which she visits +when collecting it. This work will form the subject of our next +lecture, and while we love the little bee for her constant +industry, patience, and order within the hive, we shall, I think, +marvel at the wonderful law of nature which guides her in her +unconscious mission of love among the flowers which grow around +it. + + + +Week 28 + +Lecture X +BEES AND FLOWERS + +Whatever thoughts each one of you may have brought to the +lecture to-day, I want you to throw them all aside and fancy +yourself to be in a pretty country garden on a hot summer's +morning. Perhaps you have been walking, or reading, or playing, +but it is getting too hot now to do anything; and so you have +chosen the shadiest nook under the old walnut-tree, close to the +flower-bed on the lawn, and would almost like to go to sleep if +it were not too early in the day. + +As you lie there thinking of nothing in particular, except how +pleasant it is to be idle now and then, you notice a gentle +buzzing close to you, and you see that on the flower-bed close +by, several bees are working busily among the flowers. They do +not seem to mind the heat, nor to wish to rest; and they fly so +lightly and look so happy over their work that it does not tire +you to look at them. + +That great humble-bee takes it leisurely enough as she goes +lumbering along, poking her head into the larkspurs, and +remaining so long in each you might almost think she had fallen +asleep. The brown hive-bee on the other hand, moves busily and +quickly among the stocks, sweet peas, and mignonette. She is +evidently out on active duty, and means to get all she can from +each flower, so as to carry a good load back to the hive. In +some blossoms she does not stay a moment, but draws her head back +directly she has popped it in, as if to say "No honey there." +But over the full blossoms she lingers a little, and then +scrambles out again with her drop of honey, and goes off to seek +more in the next flower. + +Let us watch her a little more closely. There are plenty of +different plants growing in the flower-bed, but, curiously +enough, she does not go first to one kind and then to another; +but keeps to one, perhaps the mignonette, the whole time till she +flies away. Rouse yourself up to follow her, and you will see +she takes her way back to the hive. She may perhaps stop to +visit a stray plant of mignonette on her way, but no other flower +will tempt her till she has taken her load home. + +Then when she comes back again she may perhaps go to another kind +of flower, such as the sweet peas, for instance, and keep to them +during the next journey, but it is more likely that she will be +true to her old friend the mignonette for the whole day. + +We all know why she makes so many journeys between the garden and +the hive, and that she is collecting drops of honey from each +flower, and carrying it to be stored up in the honeycomb for +winter's food. How she stores it, and how she also gathers +pollen-dust for her bee-bread, we saw in the last lecture; to-day +we will follow her in her work among the flowers, and see, while +they are so useful to her, what she is doing for them in return. + +We have already learnt from the life of a primrose that plants +can make better and stronger seeds when they can get pollen-dust +from another plant, than when they are obliged to use that which +grows in the same flower; but I am sure you will be very much +surprised to hear that the more we study flowers the more we find +that their colours, their scent, and their curious shapes are all +so many baits and traps set by nature to entice insects to come +to the flowers, and carry this pollen-dust from one to the other. + +So far as we know, it is entirely for this purpose that the +plants form honey in different parts of the flower, sometimes in +little bags or glands, as in the petals of the buttercup flower, +sometimes in clear drops, as in the tube of the honeysuckle. +This food they prepare for the insects, and then they have all +sorts of contrivances to entice them to come and fetch it. + +You will remember that the plants of the coal had no bright or +conspicuous flowers. Now we can understand why this was, for +there were no flying insects at that time to carry the pollen- +dust from flower to flower, and therefore there was no need of +coloured flowers to attract them. But little by little, as +flies, butterflies, moths and bees began to live in the world, +flowers too began to appear, and plants hung out these gay- +coloured signs, as much as to say, "Come to me, and I will give +you honey if you will bring me pollen-dust in exchange, so that +my seeds may grow healthy and strong." + +We cannot stop to inquire to-day how this all gradually came +about, and how the flowers gradually put on gay colours and +curious shapes to tempt the insects to visit them; but we will +learn something about the way they attract them now, and how you +may see it for yourselves if you keep your eyes open. + +For example, if you watch the different kinds of grasses, sedges +and rushes, which have such tiny flowers that you can scarcely +see them, you will find that no insects visit them. Neither will +you ever find bees buzzing round oak-trees, nut-trees, willows, +elms or birches. But on the pretty and sweet-smelling apple- +blossoms, or the strongly scented lime-trees, you will find bees, +wasps, and plenty of other insects. + +The reason of this is that grasses, sedges, rushes, nut-trees, +willow, and the others we have mentioned, have all of them a +great deal of pollen-dust, and as the wind blows them to and fro, +it wafts the dust from one flower to another, and so these plants +do not want the insects, and it is not worth their while to give +out honey, or to have gaudy or sweet-scented flowers to attract +them. + +But wherever you see bright or conspicuous flowers you may be +quite sure that the plants want the bees or some other winged +insect to come and carry their pollen for them. Snowdrops +hanging their white heads among their green leaves, crocuses with +their violet and yellow flowers, the gaudy poppy, the large- +flowered hollyhock or the sunflower, the flaunting dandelion, the +pretty pink willow-herb, the clustered blossoms of the mustard +and turnip flowers, the bright blue forget-me-not and the +delicate little yellow trefoil, all these are visited by insects, +which easily catch sight of them as they pass by and hasten to +sip their honey. + +Sir John Lubbock has shown that bees are not only attracted by +bright colours, but that they even know one colour from another. +He put some honey on slips of glass with coloured papers under +them, and when he had accustomed the bees to find the honey +always on the blue glass, he washed this glass clean, and put the +honey on the red glass instead. Now if the bees had followed +only the smell of the honey, they would have flown to the red +glass, but they did not. They went first to the blue glass, +expecting to find the honey on the usual colour, and it was only +when they were disappointed that they went off to the red. + +Is it not beautiful to think that the bright pleasant colours we +love so much in flowers, are not only ornamental, but that they +are useful and doing their part in keeping up healthy life in our +world? + +Neither must we forget what sweet scents can do. Have you never +noticed the delicious smell which comes from beds of mignonette, +thyme, rosemary, mint, or sweet alyssum, from the small hidden +bunches of laurustinus blossom, or from the tiny flowers of the +privet? These plants have found another way of attracting the +insects; they have no need of bright colours, for their scent is +quite as true and certain a guide. You will be surprised if you +once begin to count them up, how many white and dull or dark- +looking flowers are sweet-scented, while gaudy flowers, such as +tulip, foxglove and hollyhock, have little or no scent. And +then, just as in the world we find some people who have +everything to attract others to them, beauty and gentleness, +cleverness, kindliness, and loving sympathy, so we find some +flowers, like the beautiful lily, the lovely rose, and the +delicate hyacinth, which have colour and scent and graceful +shapes all combined. + +But we are not yet nearly at an end of the contrivances of +flowers to secure the visits of insects. Have you not observed +that different flowers open and close at different times? The +daisy receives its name day's eye, because it opens at sunrise +and closes at sunset, while the evening primrose (Aenothera +biennis) and the night campion (Silene noctiflora) spread out +their flowers just as the daisy is going to bed. + +What do you think is the reason of this? If you go near a bed of +evening primroses just when the sun is setting, you will soon be +able to guess, for they will then give out such a sweet scent +that you will not doubt for a moment that they are calling the +evening moths to come and visit them. The daisy opens by day, +because it is visited by day insects, but those particular moths +which can carry the pollen-dust of the evening primrose, fly only +by night, and if this flower opened by day other insects might +steal its honey, while they would not be the right size or shape +to touch its pollen-bags and carry the dust. + +It is the same if you pass by a honeysuckle in the evening; you +will be surprised how much stronger its scent is than in the day- +time. This is because the sphinx hawk-moth is the favourite +visitor of that flower, and comes at nightfall, guided by the +strong scent, to suck out the honey with its long proboscis, and +carry the pollen-dust. + +Again, some flowers close whenever rain is coming. The pimpernel +(Anagallis arvensis) is one of these, hence its name of the +"Shepherd's Weather-glass." This little flower closes, no doubt, +to prevent its pollen-dust being washed away, for it has no +honey; while other flowers do it to protect the drop of honey at +the bottom of their corolla. Look at the daisies for example +when a storm is coming on; as the sky grows dark and heavy, you +will see them shrink up and close till the sun shines again. +They do this because in each of the little yellow florets in the +centre of the flower there is a drop of honey which would be +quite spoiled if it were washed by the rain. + +And now you will see why cup-shaped flowers so often droop their +heads - think of the harebell, the snowdrop, the lily-of-the- +valley, the campanula, and a host of others; how pretty they look +with their bells hanging so modestly from the slender stalk! +They are bending down to protect the honey-glands within them, +for if the cup became full of rain or dew the honey would be +useless, and the insects would cease to visit them. + + + +Week 29 + +But it is not only necessary that the flowers should keep their +honey for the insects, they also have to take care and keep it +for the right kind of insect. Ants are in many cases great +enemies to them, for they like honey as much as bees and +butterflies do, yet you will easily see that they are so small +that if they creep into a flower they pass the anthers without +rubbing against them, and so take the honey without doing any +good to the plant. Therefore we find numberless contrivances for +keeping the ants and other creeping insects away. Look for +example at the hairy stalk of the primrose flower; those little +hairs are like a forest to a tiny ant, and they protect the +flower from his visits. The Spanish catchfly (Silene otites), on +the other hand, has a smooth, but very gummy stem, and on this +the insects stick, if they try to climb. Slugs and snails too +will often attack and bite flowers, unless they are kept away by +thorns and bristles, such as we find on the teazel and the +burdock. And so we are gradually learning that everything which +a plant does has its meaning, if we can only find it out, and +that even very insignificant hair has its own proper use, and +when we are once aware of this a flower-garden may become quite a +new world to us if we open our eyes to all that is going on in +it. + + But as we cannot wander among many plants to-day, let us take a +few which the bees visit, and see how they contrive not to give +up their honey without getting help in return. We will start +with the blue wood-geranium, because from it we first began to +learn the use of insects to flowers. + +More than a hundred years ago a young German botanist, Christian +Conrad Sprengel, noticed some soft hairs growing in the centre of +this flower, just round the stamens, and he was so sure that +every part of a plant is useful, that he set himself to find out +what these hairs meant. He soon discovered that they protected +some small honey-bags at the base of the stamens, and kept the +rain from washing the honey away, just as our eyebrows prevent +the perspiration on our faces from running into our eyes. This +led him to notice that plants take great care to keep their honey +for insects, and by degrees he proved that they did this in order +to tempt the insects to visit them and carry off their pollen. + +The first thing to notice in this little geranium flower is that +the purple lines which ornament it all point directly to the +place where the honey lies at the bottom of the stamens, and +actually serve to lead the bee to the honey; and this is true of +the veins and marking of nearly all flowers except of those which +open by night, and in these they would be useless, for the +insects would not see them. + +When the geranium first opens, all its ten stamens are lying flat +on the corolla or coloured crown, as in the left-hand flower in +Fig. 58, and then the bee cannot get at the honey. But in a +short time five stamens begin to raise themselves and cling round +the stigma or knob at the top of the seed-vessel, as in the +middle flower. Now you would think they would leave their dust +there. But no! the stigma is closed up so tight that the dust +cannot get on to the sticky part. Now, however, the bee can get +at the honey-glands on the outside of the raised stamens; and as +he sucks it, his back touches the anthers or dust-bags, and he +carries off the pollen. Then, as soon as all their dust is gone, +these five stamens fall down, and the other five spring up. +Still, however, the stigma remains closed, and the pollen of +these stamens, too, may be carried away to another flower. At +last these five also fall down, and then, and not till then, the +stigma opens and lays out its five sticky points, as you may see +in the right-hand flower, Fig. 58. + +But its own pollen is all gone, how then will it get any? It +will get it from some bee who has just taken it from another and +younger flower; and thus you see the blossom is prevented from +using its own pollen, and made to use that of another blossom, so +that its seeds may grow healthy and strong. + +The garden nasturtium, into whose blossom we saw the humble-bee +poling his head, takes still more care of its pollen-dust. It +hides its honey down at the end of its long spur, and only sends +out one stamen at a time instead of five like the geranium; and +then, when all the stamens have had their turn, the sticky knob +comes out last for pollen from another flower. + +All this you may see for yourselves if you find geraniums* in the +hedges, and nasturtiums in you garden. But even if you have not +these, you may learn the history of another flower quite as +curious, and which you can find in any field or lane even near +London. The common dead-nettle (Fig. 59) takes a great deal of +trouble in order that the bee may carry off its pollen. When you +have found one of these plants, take a flower from the ring all +round the stalk and tear it gently open, so that you can see down +its throat. There, just at the very bottom, you will find a +thick fringe of hairs, and you will guess at once that these are +to protect a drop of honey below. Little insects which would +creep into the flower and rob it of its honey without touching +the anthers of the stamens cannot get past these hairs, and so +the drop is kept till the bee comes to fetch it. (*The scarlet +and other bright geraniums of our flower-gardens are not true +geraniums, but pelargoniums. You may, however, watch all these +peculiarities in them if you cannot procure the true wild +geranium.) + +Now look for the stamens; there are four of them, two long and +two short, and they are quite hidden under the hood which forms +the top of the flower. How will the bee touch them? If you were +to watch one, you would find that when the bee alights on the +broad lip and thrusts her head down the tube, she first of all +knows her back against the little forked tip. This is the sticky +stigma, and she leaves there any dust she has brought from +another flower; then, as she must push far in to reach the honey, +before she comes out again has carried away the yellow powder on +her back, ready to give it to the next flower. + +Do you remember how we noticed at the beginning of the lecture +that a bee always likes to visit the same kind of plant in one +journey? You see now that this is very useful to the flowers. +If the bee went from a dead-nettle to a geranium, the dust would +be lost, for it would be of no use to any other plant but a dead- +nettle. But since the bee likes to get the same kind of honey +each journey, she goes to the same kind of flowers, and places +the pollen-dust just where it is wanted. + +There is another flower, called the Salvia, which belongs to the +same family as our dead-nettle, and I think you will agree with +me that its way of dusting the bee's back is most clever. The +Salvia (Fig. 60) is shaped just like the dead-nettle, with a hood +and a broad lip, but instead of four stamens it has only two, the +other two being shrivelled up. The two that are left have a very +strange shape, for the stalk or filament of the stamen is very +short, while the anther, which is in most flowers two little bags +stuck together, has here grown out into a long thread, with a +little dust-bag at one end only. In 1, Fig. 60, you only see +one of these stems, because the flower is cut in half, but in the +whole flower, one stands on each side just within the lip. Now, +when the bee puts her head into the tube to reach the honey, she +passes right between these two swinging anthers, and knocking +against the end pushes it before her and so brings the dust-bag +plump down on her back, scattering the dust there! you can +easily try this by thrusting a pencil into any Salvia flower, and +you will see the anther fall. + +You will notice that all this time the be does not touch the +sticky stigma which hangs high above her, but after the anthers +are empty and shrivelled the stalk of the stigma grows longer, +and it falls lower down. By-and-by another bee, having pollen on +her back, comes to look for honey, and as she goes into No. 3, +she rubs against the stigma and leaves upon it the dust from +another flower. + +Tell me, has not the Salvia, while remaining so much the same +shape as the dead-nettle, devised a wonderful contrivance to make +use of the visits of the bee? + +The common sweet violet (Viola odorata) or the dog violet (Viola +canina), which you can gather in any meadow, give up their +pollen-dust in quite a different way from the Salvia, and yet it +is equally ingenious. Everyone has noticed what an irregular +shape this flower has, and that one of its purple petals has a +curious spur sticking out behind. In the tip of this spur and in +the spur of the stamen lying in it the violet hides its honey, +and to reach it the bee must press past the curious ring of +orange-tipped bodies in the middle of the flower. These bodies +are the anthers, Fig. 61, which fit tightly round the stigma, so +that when the pollen-dust, which is very dry, comes out of the +bags, it remains shut in by the tips as if in a box. Two of +these stamens have spurs which lie in the coloured spur of the +flower, and have honey at the end of them. Now, when the bee +shakes the end of the stigma, it parts the ring of anthers, and +the fine dust falls through upon the insect. + +Let us see for a moment how wonderfully this flower is arranged +to bring about the carrying of the pollen, as Sprengel pointed +out years ago. In the first place, it hangs on a thin stalk, and +bends its head down so that the rain cannot come near the honey +in the spur, and also so that the pollen-dust falls forward into +the front of the little box made by the closed anthers. Then the +pollen is quite dry, instead of being sticky as in most plants. +This is in order that it may fall easily through the cracks. +Then the style or stalk of the stigma is very thin and its tip +very broad, so that it quivers easily when the bee touches it, +and so shakes the anthers apart, while the anthers themselves +fold over to make the box, and yet not so tightly but that the +dust can fall through when they are shaken. Lastly, if you look +at the veins of the flower, you will find that they all point +towards the spur where the honey is to be found, so that when the +sweet smell of the flower has brought the bee, she cannot fail to +go in at the right place. + +Two more flowers still I want us to examine together, and then I +hope you will care to look at every flower you meet, to try and +see what insects visit it, and how its pollen-dust is carried. +These two flowers are the common Bird's-foot trefoil (Lotus +corniculatus), and the Early Orchis (Orchis mascula), which you +may find in almost any moist meadow in the spring and early +summer. + +The Bird's-foot trefoil, Fig. 62, you will find almost anywhere +all through the summer, and you will know it from other flowers +very like it by its leaf, which is not a true trefoil, for behind +the three usual leaflets of the clover and the shamrock leaf, it +has two small leaflets near the stalk. The flower, you will +notice, is shaped very like the flower of a pea, and indeed it +belongs to the same family, called the Papilionaceae or butterfly +family, because the flowers look something like an insect flying. + +In all these flowers the top petal stands up like a flag to catch +the eye of the insect, and for this reason botanists call it the +"standard". Below it are two side-petals called the "wings," and +if you pick these off you will find that the remaining two petals +are joined together at the tip in a shape like the keel of a +boat. For this reason they are called the "keel". Notice as we +pass that these two last petals have in them a curious little +hollow or depression, and if you look inside the "wings" you will +notice a little knob that fits into this hollow, and so locks the +two together. We shall see by-and-by that this is important. + + + +Week 30 + +Next let us look at the half-flower when it is cut open, and see +what there is inside. There are ten stamens in all, enclosed +with the stigma in the keel; nine are joined together and one is +by itself. The anthers of five of these stamens burst open while +the flower is still a bud, but the other stamens go on growing, +and push the pollen-dust, which is very moist and sticky, right +up into the tip of the keel. Here you see it lies right round +the stigma, but as we saw before in the geranium, the stigma is +not ripe and sticky yet, and so it does not use the pollen +grains. + +Now suppose that a bee comes to the flower. The honey she has to +fetch lies inside the tube, and the one stamen being loose she is +able to get her proboscis in. but if she is to be of any use to +the flower she must uncover the pollen-dust. See how cunningly +the flower has contrived this. In order to put her head into the +tube the bee must stand upon the wings, and her weight bends them +down. but they are locked to the keel by the knob fitting in the +hole, and so the keel is pushed down too, and the sticky pollen- +dust is uncovered and comes right against the stomach of the bee +and sticks there! As soon as she has done feeding and flies +away, up go the wings and the keel with them, covering up any +pollen that remains ready for next time. Then when the bee goes +to another flower, as she touches the stigma as well as the +pollen, she leaves some of the foreign dust upon it, and the +flower uses that rather than its own, because it is better for +its seeds. If however no bee happens to come to one of these +flowers, after a time the stigma becomes sticky and it uses its +own pollen: and this is perhaps one reason why the bird's-foot +trefoil is so very common, because it can do its own work if the +bee does not help it. + +Now we come lastly to the Orchis flower. Mr. Darwin has written +a whole book on the many curious and wonderful ways in which +orchids tempt bees and other insects to fertilize them. We can +only take the simplest, but I think you will say that even this +blossom is more like a conjuror's box than you would have +supposed it possible that a flower could be. + +Let us examine it closely. It has sic deep-red covering leaves, +Fig. 62, three belonging to the calyx or outer cup, and three +belonging to the corolla or crown of the flower; but all six are +coloured alike, except that the large on in front, called the +"lip", has spots and lines upon it which will suggest to you at +once that they point to the honey. + +But where are the anthers, and where is the stigma? Look just +under the arch made by those three bending flower-leaves, and +there you will see two small slits, and in these some little +club-shaped bodies, which you can pick out with the point of a +needle. One of these enlarged is shown. It is composed of +sticky grains of pollen held together by fine threads on the top +of a thin stalk; and at the bottom of the stalk there is a little +round body. This is all that you will find to represent the +stamens of the flower. When these masses of pollen, or pollinia +as they are called, are within the flower, the knob at the bottom +is covered by a little lid, shutting them in like the lid of a +box, and just below this lid you will see two yellowish lumps, +which are very sticky. These are the top of the stigma, and they +are just above the seed-vessel, which you can see in the lowest +flower in the picture. + +Now let us see how this flower gives up its pollen. When a bee +comes to look for honey in the orchis, she alights on the lip, +and guided by the lines makes straight for the opening just in +front of the stigmas. Putting her head into this opening she +pushes down into the spur, where by biting the inside skin she +gets some juicy sap. Notice that she has to bite, which takes +time. + +You will see at once that she must touch the stigmas in going in, +and so give them any pollen she has on her head. but she also +touches the little lid and it flies instantly open, bringing the +glands at the end of the pollen-masses against her head. These +glands are moist and sticky, and while she is gnawing the inside +of the spur they dry a little and cling to her head and she +brings them out with her. Darwin once caught a bee with as many +as sixteen of these pollen-masses clinging to her head. + +But if the bee went into the next flower with these pollinia +sticking upright, she would simply put them into the same slits +in the next flower, she would not touch them against the stigma. +Nature, however, has provided against this. As the bee flies +along, the glands sticking to its head dry more and more, and as +they dry they curl up and drag the pollen-masses down, so that +instead of standing upright, as in 1, Fig. 63, they point +forwards, as in 2. + +And now, when the bee goes into the next flower, she will thrust +them right against the sticky stigmas, and as they cling there +the fine threads which hold the grains together break away, and +the flower is fertilized. + +If you will gather some of these orchids during your next spring +walk in the woods, and will put a pencil down the tube to +represent the head of the bee you may see the little box open, +and the two pollen-masses cling to the pencil. Then if you draw +it out you may see them gradually bend forwards, and by thrusting +your pencil into the next flower you may see the grains of pollen +bread away, and you will have followed out the work of a bee. + + Do not such wonderful contrivances as these make us long to know +and understand all the hidden work that is going on around us +among the flowers, the insects, and all forms of life? I have +been able to tell you but very little, but I can promise you that +the more you examine, the more you will find marvellous histories +such as these in simple field-flowers. + +Long as we have known how useful honey was to the bee, and how it +could only get it from flowers, yet it was not till quite lately +that we have learned to follow out Sprengel's suggestion, and to +trace the use which the bee is to the flower. But now that we +have once had our eyes opened, every flower teaches us something +new, and we find that each plant adapts itself in a most +wonderful way to the insects which visit it, both so as to +provide them with honey, and at the same time to make them +unconsciously do it good service. + +And so we learn that even among insects and flowers, those who do +most for others, receive most in return. The bee and the flower +do not either of them reason about the matter, they only go on +living their little lives as nature guides them, helping and +improving each other. Think for a moment how it would be, if a +plant used up all its sap for its own life, and did not give up +any to make the drop of honey in its flower. The bees would soon +find out that these particular flowers were not worth visiting, +and the flower would not get its pollen-dust carried, and would +have to do its own work and grow weakly and small. Or suppose on +the other hand that the bee bit a hole in the bottom of the +flower, and so got at the honey, as indeed they sometimes do; +then she would not carry the pollen-dust, and so would not keep +up the healthy strong flowers which make her daily food. + +But this, as you see, is not the rule. On the contrary, the +flower feeds the bee, and the bee quite unconsciously helps the +flower to make its healthy seed. Nay more; when you are able to +read all that has been written on this subject, you will find +that we have good reason to think that the flowerless plants of +the Coal Period have gradually put on the beautiful colours, +sweet scent, and graceful shapes of our present flowers, in +consequence of the necessity of attracting insects, and thus we +owe our lovely flowers to the mutual kindliness of plants and +insects. + +And is there nothing beyond this? Surely there is. Flowers and +insects, as we have seen, act without thought or knowledge of +what they are doing; but the law of mutual help which guides them +is the same which bids you and me be kind and good to all those +around us, if we would lead useful and happy lives. And when we +see that the Great Power which rules over our universe makes each +work for the good of all, even in such humble things as bees and +flowers; and that beauty and loveliness come out of the struggle +and striving of all living things; then, if our own life be +sometimes difficult, and the struggle hard to bear, we learn from +the flowers that the best way to meet our troubles is to lay up +our little drop of honey for others, sure that when they come to +sip it they will, even if unconsciously, give us new vigour and +courage in return. + + And now we have arrived at the end of those subjects which we +selected out of the Fairy-land of Science. You must not for a +moment imagine, however, that we have in any way exhausted our +fairy domain; on the contrary, we have scarcely explored even the +outskirts of it. The "History of a Grain of Salt," "A +Butterfly's Life," or "The Labours of an Ant," would introduce us +to fairies and wonders quite as interesting as those of which we +have spoken in these Lectures. While "A Flash of Lightning," "An +Explosion in a Coal-mine," or "The Eruption of a Volcano," would +bring us into the presence of terrible giants known and dreaded +from time immemorial. + +But at least we have passed through the gates, and have learnt +that there is a world of wonder which we may visit if we will; +and that it lies quite close to us, hidden in every dewdrop and +gust of wind, in every brook and valley, in every little plant or +animal. We have only to stretch out our hand and touch them with +the wand of inquiry, and they will answer us and reveal the fairy +forces which guide and govern them; and thus pleasant and happy +thoughts may be conjured up at any time, wherever we find +ourselves, by simply calling upon nature's fairies and asking +them to speak to us. Is it not strange, then, that people should +pass them by so often without a thought, and be content to grow +up ignorant of all the wonderful powers ever active in the world +around them? + +Neither is it pleasure alone which we gain by a study of nature. +We cannot examine even a tiny sunbeam, and picture the minute +waves of which it is composed, travelling incessantly from the +sun, without being filled with wonder and awe at the marvellous +activity and power displayed in the infinitely small as well as +in the infinitely great things of the universe. We cannot become +familiar with the facts of gravitation, cohesion, or +crystallization, without realizing that the laws of nature are +fixed, orderly, and constant, and will repay us with failure or +success according as we act ignorantly or wisely; and thus we +shall begin to be afraid of leading careless, useless, and idle +lives. We cannot watch the working of the fairy "life" in the +primrose or the bee, without learning that living beings as well +as inanimate things are governed by these same laws of nature; +nor can we contemplate the mutual adaptation of bees and flowers +without acknowledging that it teaches the truth that those +succeed best in life who, whether consciously or unconsciously, +do their best for others. + +And so our wanderings in the Fairy-land of Science will not be +wasted, for we shall learn how to guide our own lives, while we +cannot fail to see that the forces of nature, whether they are +apparently mechanical, as in gravitation or heat; or intelligent, +as in living beings, are one and all the voice of the Great +Creator, and speak to us of His Nature and His Will. + + + + + + + + + +End of Project Gutenberg's The Fairy-Land of Science , by Arabella B. 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