HAVE you ever seen the fairy vessels in the sky as they go sailing by? What are these ships, and how did they come there?
We know there is vapor in the air, though we cannot see it. Think from how many things the heat of the sun can draw vapor.
It draws it from the ocean, the lakes, the rivers, the little mud puddles, the ground, and the dishes of water standing around. The plants give moisture to the air. People and animals breathe out moisture. There are so many ways in which the air obtains moisture, that we could hardly name all of them.
When the air is warm, the vapor is carried off into higher parts of the air; but when cold air strikes it, it is turned into water-dust or clouds.
When the vapor is changed into water-dust high in the air, we call it clouds; but when it is changed close to the earth, we call it fog.