It may seem that I am bestowing too much praise upon our own sun; but if you are surprised that I should seek to exalt this brilliant globe of ever-burning fire, I must ask you to recollect, that though the starry heavens are full of suns as vast and important as ours, and possibly affording brilliant colourless light to worlds full of inhabitants, there are others that give forth rays that are far from being white. Some are as green as emeralds, others are as blue as sapphires, while others give out a warm light like a ruby or topaz. The worlds which surround these can only receive light of a certain colour, or at any rate they are restricted to a few shades and hues. Imagine living in a world where everything was always _couleur de rose_, or in which the inhabitants were continually looking blue! A residence in either of them for a short time would undoubtedly cause us to appreciate the relative value of our own little sun, small as it is in comparison with some of the mighty orbs floating about in space. The fact that the light of the sun is the source of all the changing hues to be found on the surface of the earth season after season was first discovered by Newton, and his experiments are easily repeated with a very few and inexpensive appliances. A small round hole is made in the window-shutter of a room, facing the sun, and the pencil of light proceeding from it is allowed to fall upon the surface of a three-sided prism, held in a horizontal position, and placed at a distance of a few inches from the aperture (fig. 5, Frontispiece). The pencil of light does not pass through the prism as if it were a plate of glass with parallel sides, but in virtue of the laws of refraction, of which we have already spoken, it is turned out of its natural course, and is thrown upon the wall in the direction indicated in the figure. The pencil of light is not only turned aside, but it is also widened out into a band which is truly painted with all the colours of the rainbow, every tone and hue being of the most marvellous brilliancy. This long coloured stripe, which constitutes one of the most beautiful sights that the science of optics can afford us, is known to scientific men by the name of the solar spectrum.