343. =The Kaleidoscope.=--I have already noticed the multiplication of the images of objects by using two or more mirrors. In the kaleidoscope, by a particular arrangement of mirrors, the images are multiplied, and by changes in the position of the objects the relative positions of the images are infinitely varied. Fig. 229 will serve to explain the operation of the instrument. Let A B and B C be two plane mirrors placed at right angles to each other, and _a_ an object before them. Let I be the position of the eye looking at the mirrors. The rays _a f_ and _a g_ will be reflected to I as represented, and the eye will see two images, which appear to be at _b_ and E. But the ray _a_ K will be reflected to _c_, and then to I, so that a third image will be seen at _d_. Here is but a single second reflection, or reflection of an image; but by placing the mirrors at an angle of 60°, 45°, and 30° the images may be increased to six, eight, and ten, having a circular arrangement. In the kaleidoscope two mirrors are placed in a tube at an angle of 30°, and variously-colored pieces of glass in the farther end of the instrument, changing their relative position with every movement of it, give an endless variety of images symmetrically arranged. [Illustration: Fig. 230.] [Illustration: Fig. 231.] 344. =Curved Mirrors.=--These may be concave or convex. The action of a concave mirror upon light may be illustrated by Fig. 230. If parallel rays, as represented, strike upon the mirror they will, in their reflection, be made to _converge_, or come together, at the focus, _a_. But suppose the light comes from this focus, the rays of course _diverging_, or going away from each other; then the rays, as reflected, will be parallel. If the light or object be nearer to the mirror than the focus, and the rays of course be more diverging, then the effect of the mirror will be to lessen the divergence when the rays are reflected. You see that the tendency is to make the rays converge. And hence concave reflectors are much used when it is desired to throw a great amount of light in one direction. The effect of the concave mirror upon the apparent size and position of objects placed before it varies with the relation of their position to the focus. The action of a convex mirror upon light is the opposite of that of the concave. Its tendency is to make the rays diverge. Thus (Fig, 231), if parallel rays strike upon a convex mirror they diverge, as if they came from a focus behind the mirror, as _b_, as indicated by the dotted lines. [Illustration: Fig. 232.] [Illustration: Fig. 233.]