existing. You will be able to do it at once—but if you try to cut it across the crystals you cannot; by hammering, you may bruise and break it up—but you can only divide it into these beautiful little rhomboids.
Now I want you to understand a little more how this is—and for this purpose I am going to use the electric light again. You see, we cannot look into the middle of a body like this piece of glass. We perceive the outside form, and the inside form, and we look through it; but we cannot well find out how these forms become so, and I want you, therefore, to take a lesson in the way in which we use a ray of light for the purpose of seeing what is in the interior of bodies. Light is a thing which is, so to say, attracted by every substance that gravitates (and we do not know anything that does not). All matter affects light more or less by what we may consider as a kind of attraction, and I have arranged (fig. 18) a very simple experiment upon the floor of the room for the purpose of illustrating this. I have put into that basin a few things which those who are in the body of the theatre will not be able to see, and I am going to make use of this
