A crystal is made up of molecules, that is to say, little parts of itself. You can't see a molecule; you just have to think it. Each different thing in the world—as salt and sugar, boys and bumble-bees, little girls and butterflies—is made up of its own kind of molecules or little parts of itself. In order to grasp the idea of certain scientific facts, the men of science thought of the molecules themselves as being made of little bits of themselves, which the scientists called "atoms." Now they find that it is necessary—in order to work out still further their ideas of how things are made and done and changed, in this wonderful mystery we call the world—to imagine these atoms as made up of what they call "electrons." You mustn't think, however, that this is all mere fancy. We can, of course, think of anything as made up of small particles or parts of itself which we can call "molecules," and that these molecules are made of still smaller parts which we can call "atoms." But there is reason to believe that while each different kind of thing is made of its own kind of molecules and their atoms, all the atoms are made of the same thing—electrons or little bits of electricity. For reasons which need not be gone into here, it is known that electrons actually exist. These electrons are so much smaller than an atom that there is as much room for them to move around in an atom as there is for the planets to move around the sun.
And they do move—travelling round and round. There are, even in so small a thing as a grain of sand, untold numbers of these circling worlds; systems like the sun with its planets and other vast star systems of the sky.
And that, it is thought, may be one of the secrets of the continual change of things; clay rock changing to granite, granite to soil, soil to fruit, fruit to children, and so on—everything on the move and the electrons doing the moving—carrying the changes, so to speak—these wonderful little myriad messenger boys of the universe!
HIDE AND SEEK IN THE LIBRARY
Don't imagine, for all I've talked so long about them, that I've told you everything there is to know about the crystal fairies. For example, did you know that if it wasn't for the crystal people we wouldn't have any ice? (Ice.)
You will also find that if it wasn't for ice—ice and the Greeks—we wouldn't have the word "crystal" at all. (Crystal.)
One of the most striking things in the whole conduct of these clever crystal folks you will find in reading about ice. If it wasn't for a peculiar—a very peculiar—habit the ice crystals have, all the waters of the world that ever freeze at all, would freeze solid to the bottom and never would thaw out!
I'll tell you this much about it:
While everything else in the world—including boys and girls—contracts when it gets cold, ice expands, and so becomes lighter than water, and so floats.
And yet the ice crystals know how to contract as well as expand, and that's why ice sometimes builds stone walls, as we will see when we come to study "The Stones of the Field" in July.