A soap bubble really makes one able to believe in worlds where fairies live. Like our world of land and water it is round. It floats in space. Although it is hollow, it is packed and crammed with beautiful mysteries. But mysteries and miracles and magic are usually just the working of natural laws that we do not understand.

In the first place, the soap bubble is only a tiny, hot-air balloon with a skin of soapy water around it. The hot air is forced from your lungs when you blow. Hot air is expanded, so it takes less of it to fill a given space. Therefore it is lighter than cold air. In this little balloon the air inside is so much lighter and hotter than the air outside that it is able to hold up the water-film that forms the skin. Another thing that helps it float is this. If all the water was in one big drop, or even in several smaller drops, it would fall like rain. But the water is stretched and spread out very thin over a great deal of air. So it floats, just as a thin hollow iron ship floats on water, or a kite flies in the air.

Now water alone cannot be stretched in that way. Soap has a much greater power of cohesion, or sticking-togetherness. Soap with glycerine, or a kind of mucilage in it, is still more cohesive than ordinary soap. See how easy it is to make lather, or a great many foam bubbles in soapy water. The soap bubble is round for the same reason that the earth is round. All the little particles of water cling together on all sides with the same force. The air pressure outside is the same on every part, and every part is being pulled toward its own center. It isn't easy to believe that the smooth water-film is made up of tiny separate molecules. But see the rainbow colors it reflects. A diamond cut in faces, catches white light rays and breaks them tip in the same way. So the soap bubble would not be able to break up light rays, if it did not have millions and billions of little flat faces.

If you watch a soap bubble closely you will see it sag and gather a drop on the underside. No sooner is it in the air than the earth tries to pull it down. Because of this pull the water on the upper parts slides down the slopes. That makes it heavier below. The heaviness drags it out of its perfect sphere shape. All this time the air inside is growing cooler and is shrinking. The water-film shrinks to fit the air inside, and is pressed in by the outside air. When both are the same weight and temperature, the water skin makes the bubble heavier than the air it floats in, so it falls, just as an apple does. When the bubble touches the ground all the little molecules of water fall together, downward, and make one drop.

You cannot believe the glittering little fairy world is all in the soapy splash on the table, can you?