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 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 dew