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 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