Then, though the sunlight gives their lovely colours to the anemones and seaweeds, as it shines into their homes in the shallow places near shore, if you could go far down into the ocean depths, where the light can hardly reach, you would find the colours of any creatures, or plants, or shells that might be there soft and pure, but not brilliant.
But how does the light make the colours? It seems only white, or perhaps gold-coloured, in itself.
This is what I should like to explain to you, for it is a very beautiful lesson, and not difficult to learn.
When I asked the children if they could tell me what we mean when we say that a thing reflects the light, Chrissie said he had often seen the red sunset reflected by the windows opposite, but he could not quite tell how to explain it.
We may read in books this explanation: "The reflection of light is the turning back of its rays by the surface upon which they fall." And while we read this we must remember that the surface or outside of everything has some peculiarity about it, which affects the light as it falls upon it.
The light of the sun is made up of seven colours, though God has so perfectly blended them that we see only white light; but all these colours may be traced in the seven-coloured arch, which is a token to men of His mercy, and a sign that while the earth remains "seed-time and harvest, cold and heat, summer and winter, day and night, shall not cease."
The smallest portion of light which we can speak of is called a ray of light. You have seen, when what you call a beam of light comes in at a hole, before the shutters have been opened, how the little specks of dust glance up and down in it, as if they were at an endless game of puss-in-the-corner. But have you ever seen beautiful colours, like those of the rainbow, dance about the room—now on the ceiling, now on the floor?
You can best see this lovely little rainbow by darkening the room, and letting just one ray of light stream in through a small hole. Then take a bit of glass, cut so that it has at least three sides—a "drop" of cut glass from the lustre on the mantelpiece will do—and hold it up between you and the light. This little piece of glass, which is called a prism, because it has been sawn or cut, will do a wonderful thing, as you turn it about in the sunbeam. The ray of light, as it passes through the three-cornered bit of glass, will be turned out of its straight path, and this causes it to be split up into many colours, so that you will have a tiny rainbow, which can be seen beautifully if you allow it to fall upon a sheet of white paper; and the colours are always arranged in the same way. Look! in the centre of your rainbow there are green and yellow; then comes red, then blue, then violet. You can easily see these five colours; and two more are counted; indigo, or dark blue, and orange. The only difficulty about saying how many colours you can see is this. If you begin with the violet, and count till you come to the red, you will find that the soft hues are so blended, or run into each other, that it is not easy to see where one ends and the other begins.
I want you to make this little rainbow, not only because the colours which it paints upon the ceiling are so pure and beautiful, and it is so curious to see the bright band of red and blue and green dancing from place to place as you turn your bit of glass, but because you can see in this way how a ray of light spreads itself out when it passes through this glass with three sides. The colours are separated from each other because no two waves of light are of quite the same length; some move slowly and others fast, and the faster a wave travels the more it is turned aside out of the straight road.
This is a difficult subject, but I think you will understand that if all rays were alike, the whole beam would be bent; but as some are more easily bent than others, as they pass through the prism they are spread out.