It is by spectra-analysis that not only the stars, but the things of which the earth is made today are studied. The telescope, the spectroscope and the camera are united in wonderful ways, to give us true stories and pictures and explanations of the stars. Astronomers can tell us by these, what a star is made of, whether it is coming toward or going from us, how rapidly it is moving and many other things.
Isn't it wonderful that we can catch a light ray from a star millions of miles away in a little glass prism, split it up into a band of seven colors, photograph that band and keep it for a record, and find out from these records that all the suns and stars are made of the same things as the dear home earth we live upon? (See Spectrum, Spectroscopy.)
A WORLD OF WONDERS IN A SOAP BUBBLE
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
