Sometimes we see leaves and grass sparkle with water-drops, early in the
morning, When the sun shines out and warms the air; what happens?

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.

[Illustration: "THINK 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.