We may think of the air around us as a vast ocean, through which waves conveying light and sound are constantly travelling. When a sound-wave strikes the ear, we hear; when a light-wave, moving like a water-wave, reaches the eye, we see. Light comes chiefly from the sun: it is beautiful to think, is it not?--of waves of light streaming always, day and night, from that wonderful sun so far away, and coming, wave after wave, to paint beautiful pictures on our eyes! For if you and I both look at the same lovely view, we have each a picture of it--the mountains, and sea, and green fields, and houses--all to ourselves; and so it would be if, not two people, but two hundred were looking. One thing about light of which we are quite sure is, that it travels very quickly. It makes its noiseless journey all round this great earth eight times in one second--in less time than it takes for my watch to give one tick; and it comes all the long, long way from the sun to the earth in less than ten minutes. I spoke just now of the light painting pictures upon our eyes. Did you know that if there were no light there would be no beautiful colours? Where the sun shines very brightly, in those parts of the world called the tropics, it is not only very hot, but travellers tell us that there the green of the leaves is darker than we are accustomed to see it, and the colours of the flowers and of the birds' feathers are more brilliant than in our own country, where the sunlight is never so strong. 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."