together give us white. We may also combine red and violet light, and get purple light. THE COLOR-TOP. This picture represents a common iron top, that may be found at the toy-shops. If you cannot find one exactly like it, there are others having a straight handle at the top, instead of the curved handle. Just under the flat part of the disk are two or three round pieces of drawing-paper, and under these is a thick disk of pasteboard. Each of these has a hole in the centre, so that it can be slipped over the leg of the top. In some tops, however, it may be easier to put these disks above on the handle. Such a top as this may be made to spin in a dinner-plate on the table by winding a string round the leg, and then pulling it away with the right hand, while the top is held upright by the left hand. Get some thick drawing-paper, and cut out three disks, each 4 inches (10 centimetres) in diameter, and make a hole in the centre of each, so that it will slip over the leg of the top. Cut each disk open from the circumference to the centre with a pair of scissors. Paint one with the red vermilion, one with the emerald-green, and the other with the violet that we used in the last experiment, and then, while these are drying, make a disk of thick pasteboard, and cut a hole in the middle, so that it will slip tightly over the leg of the top. When these are ready, take the red and green disks and hold them side by side with the cut places opposite, and slip one into the other, and then turn them round, so that the green covers the red. Then put them both on the leg of the top, and put the pasteboard disk under them, to hold them in place. Now, if you hold the top upright in a plate and make it spin, you will see a beautiful ring of green color round the spinning top. When it stops, take off the pasteboard, and revolve the colored disks one on the other, so that half of the red and half of the green can be seen. Now spin them on the top, and instantly you have a ring of yellow. Move the disks again, so as to display onequarter of the green and three-quarters of the red, and when the top spins you get a deep-orange ring. Move them again, and let the green hide nearly all the red, and the top shows a greenish-yellow ring. In this manner you may mix the red and green in greater or less proportions, and the ring of color on the top will exhibit new shades of yellow with every change. In the same way, combine the green disk and the violet, and the spinning top will show a new shade of blue with every proportion in which the green and violet are mixed. Put on the red and violet disks, and let each show more or less, and shades of purple will be shown. Put on all three disks-the red, green, and violet-and arrange them so that one-third of each is shown, and the ring will be gray. Change the proportions, and you will see each time new shades of gray or white. This is a very simple toy, but it serves to show how these three colors may be combined to produce every color in the solar spectrum. The color will vary very greatly, and new and beautiful shades of yellow, blue, purple, and gray, will be found at every trial. Red, green, and violet, may be tinted with other colors in the most charming manner, and hours can be filled with amusement and instruction by experimenting with this color-top and its ever-changing colored rings. To exhibit the colored rings on this top before a number of people, make a disk of stiff cardboard about 5 inches (12.7 centimetres) in diameter, and cut out three holes at equal distances from each other near the edge. Over these holes place pieces of red, green, and violet, or ultramarine-blue glass, one color on each hole, and fasten them down with little bands of paper at the edges, and secured with mucilage. Place this disk on the color-top, and hold it upside down just above the large lens in the water-lantern. Have the lantern prepared to give projections on the screen (see section on water-lens), and then you will see three spots of colored light on the screen, and, by making the top spin round on the handle by means of the string, the three spots of color will whirl round in a ring, and, if the top moves fast enough, we shall see a ring of white or gray. Cover the violet glass so as to shut out all the light, and then make the top spin, and the two spots of red and green will appear on the screen in the form of a yellow ring. In this manner all the effects exhibited by the color-top may be projected on a large scale on the screen, and make a most interesting and beautiful exhibition that will be sure to please all who see it. DIRECT RECOMPOSITION OF THE COLORS OF THE SPECTRUM. Let the spectrum fall on a mirror, and throw its reflection upon a distant part of the room. Procure a slip of looking-glass half an inch wide and about three inches long, and place this on the mirror in any color of the spectrum. By tilting the slip of lookingglass, any color can be thrown on to any other color of the spectrum, and thus an endless variety of colors can be formed by compounding their elementary component colors. EXPERIMENTS IN REFLECTED COLORS. Fig. 29 represents a flat block of wood having a short stick set up at one corner. On this stick is fastened, by means of a lump of wax, a strip of clear window-glass about 1 inch (25 millimetres) wide, |