You see water in the air in another shape besides fog. You see it in the clouds. A cloud is really fog, but it is high up in the air, while what we commonly call fog is near the ground.
Mists.
Sometimes rain comes from the clouds, and sometimes they give out no rain. Why is this? When the clouds do not rain, the water in them keeps in the state of fog. The particles are all in small companies; but when the rain comes from the clouds, it is because the cold air makes the particles gather into larger companies, so as to form drops. Then they fall. A mist is different from rain in this way—the companies of particles are not as large as in rain. On the other hand, they are larger than they are in fogs or in clouds.
How the rain is made to come from clouds.
You remember what I have told you about the gathering of water upon the tumblers in warm weather. It is the coldness of the tumbler that does this. It gathers, or condenses, as we commonly say, the water in the air into companies or drops on the tumbler, just as cold air coming upon a cloud condenses the water into drops that fall to the earth in rain.
How swiftly these collections of water, the clouds, are sometimes carried along by the wind! It seems as if they were chasing each other across the sky.
Shapes of clouds.
How different are the shapes of the clouds! Sometimes they lie along, stretched out like long straight stripes; and sometimes they are in heaps, piled up one above another. Then, again, they are spread like feathers. It seems strange that fog high up in the air should collect into such different forms, when near the ground it always appears very much the same.
Their beauty.
At morning and evening the clouds are often very beautiful. How do you think that the rich bright colors are made? They are made by the sun shining upon the little companies of water-particles of which the clouds are made. I will tell you more about this when I come to speak of Light.