Why does vapor rise into the air?

Why does smoke go up? Because it is lighter than air. As vapor is lighter than air; what do you think ought to happen to it?

LESSON XV.

HOW VAPOR IS CHANGED TO WATER,

Heat, as you have learned, changes water into vapor. You must also know that cold turns vapor back into water again.

[Ill.u.s.tration: "THINK OF THE KETTLE WITH THE BOILING WATER."]

Now let us think of the kettle with the boiling water. You will notice a little s.p.a.ce; quite close to the spout, where nothing can be seen. Is there no vapor there?

Yes, there is vapor there, but it cannot be seen; it is invisible. A little way from the spout we see something white, like smoke. This is only the vapor that has been chilled by the cool air and changed back again into water. The water is in the form of very fine particles, and may be called water-dust.

Hold a cold plate over boiling water. Observe how the water-dust gathers into drops that roll down the plate.

You have seen the inside of windows in cold weather covered with moisture. Where does it come from? Why did it form there? Why does it sometimes run down on the cold pane?

The vapor in our breath turns into water on frosty mornings. Explain this.

Carry a pitcher of ice-water into a room, and notice what takes place. A thin mist at once gathers on the outside of the pitcher. What takes place among the little drops of mist? What becomes of these larger drops?

Where does the water which collects on the outside of the pitcher come from? Does it come through the pitcher from the inside? Would the same thing have taken place if some other cold object had been used instead of a cold pitcher?

_Write_ out what you have learned about vapor.

LESSON XVI.

DEW, CLOUDS, AND RAIN.

The sun is all the time heating the water on the land and in the sea, and changing it into vapor, which rises in the air. We cannot see the vapor; but it is in the air around us.

If the vapor in the air is suddenly cooled, a strange thing happens.

Some of it quickly changes back into water. You have often seen, in the early morning, little drops of water hanging like pearls upon the blades of gra.s.s.

Now, where do these drops come from? They come from the air. The vapor in the air floats against the cold gra.s.s and leaves, and is cooled and changed into tiny drops of water. We call this _dew_.

Of what use is dew?

If the night is quite cold, the dew will freeze. It is then called frost. You have seen the frosty window pane with the beautiful pictures upon it.

Make a picture of the window as you remember it, covered with the pretty things made by the frost.

[Ill.u.s.tration: "WHEN VAPOR RISES HIGH IN THE COOL AIR."]

When vapor rises high in the cool air it is turned into very small drops of water or minute crystals of ice, and we can see it floating about in the air. It is then called a _cloud_. Almost any clear day you may see clouds form and then seem to melt away.

You have seen on a blue sky, light, fleecy feather-clouds. They are very high up, and it is very cold where they are. You have also noticed the clouds at sunset with their beautiful colors. As the sun sank lower and lower, how did they change, in shape and color?

When clouds are low down, near the earth, we call them _fogs_ or _mist_.

If clouds are cooled, the little particles of water gather into large drops and fall as _rain_. If the drops should freeze in falling, we would call them _hail_.

What shape are the raindrops? Of what use is the rain?

[Ill.u.s.tration: "HAVE YOU EVER SEEN SNOWFLAKES THROUGH A MICROSCOPE?"]

Sometimes, when it is very cold, the moisture in the air freezes before it forms into drops, and falls in the beautiful flakes we call _snow_.

Have you ever seen snowflakes through a microscope?

Snow keeps the roots of plants warm. Many plants would die in winter if it were not for the snow. What other uses has snow?

Observe the clouds; fog, rain, snow, dew, frost, and tell what you have noticed.

_Write_ what you have _seen_ or _noticed_ about vapor, clouds, rain, etc.

LESSON XVII.

THE FAIRY ARTIST.

Oh, there is a little artist Who paints in the cold night hours Pictures for little children Of wondrous trees and flowers!

Pictures of snow-white mountains Touching the snow-white sky; Pictures of distant oceans Where pretty ships sail by.

Pictures of rushing rivers By fairy bridges spanned; Bits of beautiful landscape Copied from elfin land.

The moon is the lamp he paints by; His canvas the window pane; His brush is a frozen snowflake; Jack Frost the artist's name.

LESSON XVIII.

HOW RIVERS ARE MADE.

Have you ever seen a brook or creek? A river? Is there a brook or river near here? Who can tell where it begins? where the water conies from that fills it? where it goes? Let us try to understand this.

As vapor rises into high, cool air, or is carried with the air in winds up the sides of mountains, it turns into water again, and comes falling down as rain.