OF THE KETTLE WITH THE BOILING WATER."]

Now let us think of the kettle with the boiling water. You will notice a
little space; 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 grass.

Now, where do these drops come from? They come from the air. The vapor
in the air floats against the cold grass 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.

[Illustration: "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