The How and Why Library/Wonders/Section II
II. Water[edit]
The other thing this round world is made of is water. In going around the earth you crossed oceans, lakes and rivers. You saw ice or frozen water. You saw water broken up into rain drops, frozen into hailstones or snow. But there was a great deal of water everywhere that you did not see at all, or if you saw it you didn't know it was water.
The story of water is just as interesting and wonderful as the story of land. Where shall we begin to find out about it? Let us begin with one day when you were a small boy playing out of doors. Mama called you.
"Run in, Johnny, it's going to rain!"
"Why is it going to rain?" you asked. Bright little boys and girls are big question marks, running around on two stout legs. They want to know the "why" of everything. Nearly all of their "whys" are very sensible, too, and ought to be answered.
See that dark cloud rolling up the sky. That cloud is as wet as a soaked sponge. The wind is blowing it up. The wind is colder than the air was a few moments ago. Now the little drops come pattering down. They are as round as shot from whirling so far down from the sky. The sun is out again. The rain has stopped. The dark cloud is gone. Where did it go? It fell to the earth in rain drops. But how did the rain cloud get up in the sky? What is a cloud?
You can make a very small cloud if it is a cold day. Go to the door and breathe into the frosty air. You can see your breath, can't you? Not all of it, just the water in your breath. The water is broken up into very fine mist, or vapor. Vapor is a kind of water dust. The air soaks up vapor as a sponge soaks up water. There is a beautiful little vapor cloud coming from the teakettle. The air soaks that up too. A wash boiler full of boiling clothes makes a big cloud that fills the kitchen. If you open a window or door it will all go out and be soaked up by the air.
If a cloud of vapor is made in a house and cannot get out, let as see what happens. The vapor from boiling water is very warm. The glass window is colder. The vapor gathers on the glass in a mist of tiny drops. The little drops roil together into big drops.
These get so heavy that they roll down the glass. They roll down the walls, too, and drop from the ceiling. If vapor is not turned out of doors it makes a room damp. That is just what happens when it rains. The vapor in the air goes up into the sky. When it finds a cold layer of air it rolls into large drops and falls.
Vapor is always going up. Most of it goes up from the ocean, the lakes and rivers. Three fourths of our big world is covered with water, you know. The sun warms the top layer of water and turns it into vapor. Every leaf and blade of grass on the land has water in it. The sun steals this water, too. Sometimes it takes so much and gives so little back again that the grass turns brown, and the leaves wilt. Every animal and plant drinks water and breathes it out again from the lungs, or gives it to the air through little holes in the skin called pores. You know how you perspire on a hot day? Little beads of water ooze out, all over you. You can find your pores with a mag-ni-fy-ing glass. You can find pores in green leaves, too.
Plants and animals perspire more on a hot day than on a cold one. The land and water give off more vapor in the summer than in the winter. Wring a handkerchief out of hot water, hang it in the sun and see how quickly it dries. Set a shallow pan of water in the sun and see how soon the water disappears. The air is always thirsty. It drinks like a greedy fish.
But then, it is not stingy. It gives back every bit of water it gets. But it does not always give it back where it got it. Sometimes it rises in vapor from the ocean, goes up in the sky to a layer of cold air, and falls back into the ocean almost as quick as you can say Jack Robinson. But it's a very good thing for little boys and girls and trees and bees, that all the vapor doesn't do that. The ocean doesn't need the water rightaway, and the land does. A great deal of vapor goes on long journeys. It uses the wind for horses. Haven't you seen fleecy clouds floating across the sky? They were riding on the wind. The winds find it no trouble at all to carry these vapor clouds along with them. The vapor clouds travel until they strike a cold layer of air. Then they roll into rain drops and fall.
As oceans are the great vapor tanks, so mountains are the chief rain makers. The tops of mountains are very cold, and they are so high up in the air that the vapor clouds bump right into them and turn to rain. In the winter the air is so cold that the rain, in falling, freezes into snow. Wide river valleys, islands and sea coasts, get a great deal of rain and snow, too, if the winds blow over them from the ocean. If the wind blows away from the land, so that it gets no rain, that land becomes a desert.
Just as the ocean is a great tank for making vapor, so the mountains and woods and cold countries are big storage houses for snow; much of the summer rain is lost. It runs off at once into streams, or is soon taken up again by the sun, in vapor. But snow lies for months, in cold, high, or shaded places. In the spring it melts slowly and soaks into the fields. It takes snow a long time to get into rivers. It gives plants and seeds water just when they need it, to help them grow. A farmer can get along in a dry summer, if there has been a wet winter.
In the story about land you saw what a big part water plays in this world of ours. Every drop of rain that falls takes up just as much dust as it can carry on its tiny round back, and hurries away with it. It washes the dust and smoke and bad smells out of the air, and leaves it pure and clean. It washes the dust from all plants and makes them bright. It would give you a merry shower bath if you stood in it. It washes the houses and the streets. You can see muddy water running down the gutters. How clean everything is, even the pebbles in the road, after a bright, hard rain. Mother Earth has had her face washed, and she looks as if she liked it!
Sometimes vapor clouds cannot get above the earth. You know the steam from the boiling clothes could not get out of the kitchen until you opened a window at the top. If the air lies very heavy above it and does not open a place for vapor to go up, it lies on the earth. Such low clouds are called fogs. You remember the kitchen walls dripped with vapor, making the room damp? Thick fogs make people and plants almost as wet as rain. Fogs are oftenest seen over the ocean, lakes, river valleys and swamp land. Sometimes they cover miles of sea, and shut in ships with milky white curtains of vapor. Then the ships must blow fog horns to keep other ships from running into them. The morning sun pulls a fog up into the sky, or a brisk wind scatters it through the air.
There is always some vapor in the air near the earth, even if there isn't enough for you to see it. If a pitcher of cold water stands in a room a little while, beads of vapor form on the outside, just as they did on the cold window pane. Sometimes the earth is cold enough to collect vapor beads from the air. When a cool night follows a hot day, the earth becomes colder than the air above it. So the warm vapor collects on cold plants, and spangles them with dewdrops. If the night is very cold when dew forms, the little dew-drops are frozen on the plants. Then we have Jack Frost.
Jack Frost is busy with you, too. He takes the vapor of your breath and per-spi-ra-tion, as you lie warm in bed, and makes pictures with it on the cold window pane. Such pretty pictures! They are all mosses and ferns and grass spears, and spangles to trim fairy queen's dresses.
Cold is a wonderful artist with water. It makes snow crystals and hailstone pearls. Snow is made by rain drops falling through air that is at the freezing point. The drops burst, when they freeze. Now, when things burst they make noises. You know how it is when fire crackers ex-plode? And pop-corn? If you were away up in the clouds, when it was snowing, and you had the ears of a fairy, no doubt you could hear the tiny rain drops explode into snow.
The Indians called pop-corn the corn that flowers. So snow is rain that blossoms. The next time you see a quiet snow storm, when the snow falls in large soft flakes, ask your mother for a piece of black velvet or cloth. Put it out of doors to get cold, but keep it dry. Then catch some snow flakes on it and study them through your pocket microscope. Most of them will look like little broken feathers. But if you are patient, you will be sure to find some that are perfect, six-pointed stars. The points will be veined and fringed like the petals of a flower. All snow flakes should be six sided or pointed crystals. Most of them are torn by the wind, or get their points knocked off by falling against other flakes.
Hailstones are made in quite a different way from snow flakes. Snow falls only in the winter, but hail storms come in summer, on hot days. Weather men think that when rain drops are formed in clouds, and are all ready to fall, they are suddenly pulled up much higher, into freezing air. The rain drops freeze but do not burst. Then they fall through other rain clouds, and more water freezes on the balls of ice. They are tossed up and down until they become so heavy that they drop like bullets. They drop so fast that they pass through the warm air near the earth without melting. Sometimes they are as big as pigeon's eggs. Find a very big one, some day, and ask papa to cut it across quickly, with his strong knife. You will find that the hailstone was made in layer rings like a lily bulb. The oyster makes the beautiful pearl in the same way. Around a hard center it puts layers of the pearl with which it lines its shell house. The hailstone pearl is just as beautiful as the shell pearl, but it melts so fast it is hard to study it.But you can study larger pieces of ice. On very cold mornings you sometimes find a glass of water frozen. The water did not fill the glass, and was level. But the ice is pushed to the top, and into a little mound in the middle. When water freezes into ice it takes more room. Big people say it expands. In reading about land you learned that rocks are split by water freezing and expanding in the cracks. If water freezes in water pipes in a house, the pipes burst. Then a plumber has to come to mend them. Running water does not freeze as easily as still water. So, on cold nights, it would be a good thing to leave a faucet a little open, to keep the water flowing through the pipes.
Ice is lighter than water, that is, it fills more space for its weight, so it floats on water. It forms on top of water first, and freezes downward. You never can tell just how thick it is from the top. Before you try to slide or skate on a pond or river, you should take a hot poker and melt a hole through the ice to see how thick it is. And when ice is ready to break up, it gets "rotten" or spongy, first. You must always obey a "danger" sign that grown people put up on ice.
It is fine to see ice break up in a river. But keep off the bridges. The big blocks of ice crash against timbers and stone piers, and sometimes destroy the bridges. Sometimes, in fogs, icebergs crash into ships and sink them. When you crossed the ocean you may have seen icebergs as big as hills, floating in the sea. If you did you wondered how they were made.
Do you remember the ice rivers, or glaciers, in the high valleys of the Alps mountains? Away up north, where the Esquimos live, all the rivers are frozen. They melt a little in the summer, but more snow falls every year than is melted. The new snow presses on the old below, and squeezes it into ice, or very hard water rock, just as sea water presses sand into stone. This ice is pushed down the river beds by the weight above. The ice rivers reach the sea just as all other rivers do. In the summer the ice that is near the sea melts, or it becomes "rotten" and breaks off in large chunks. Those chunks are icebergs. They float into warmer water and melt.
It may have been a hundred years since the icebergs you saw were fleecy vapor clouds, riding on the wind-horses, in the blue sky. But there they were at last, in their old home in the ocean. Soon the berg will melt. Then the sun will turn it into vapor again, to begin another journey. (See Water, Ocean, Sea, Glacier, Waterpower, etc.)