The same kind of lateral illumination may be obtained from polyhedral cones or hemispheres of solid glass. If =A B C D=, Fig. 25, is the section of a polyhedral cone of flint or plate glass, a portion _m n o p_ is cut out of its base =A B=, to form an object-box for the reception of the pieces of coloured glass, or other objects. The sides _m n_, _m o_, _o p_, being highly polished, rays of light, either parallel, as emanating from the sun, or diverging from artificial sources of light, will be refracted and fall obliquely upon the faces of the object-box, and illuminate its contents with the irregular prismatic spectra which are formed by refraction. The apex =D C E= may, in some cases, be cut off, and the polygonal section =D E= blackened in order to prevent the introduction of direct light, and act as the stop =S S= in the preceding figure. [Illustration: FIG. 25.] A similar effect will be obtained from a polyhedral solid, of a hemispherical form, as shown in Fig. 26, where =A C=, =C D=, =D E=, =B F=, =F G=, =G E=, are polished facets, by which parallel or diverging rays immediately before it, or incident in any lateral direction, may be refracted so as to illuminate by the prismatic rays the objects in the box _m n o p_. The front =D E C= may have an apex, as in Fig. 25, or may be made spherical to act as a condensing lens, the surface of which may be blackened when necessary, for the purpose of excluding the direct light. These illuminators may be attached in various ways to the tube containing the reflectors, so to have a rotatory motion in front of them. [Illustration: FIG. 26.] When the light is strong, a circular disk of fine grained white paper may be advantageously placed upon the outer face _m o_ of the object-box. CHAPTER X. ON THE CONSTRUCTION AND USE OF THE TELESCOPIC KALEIDOSCOPE, FOR VIEWING OBJECTS AT A DISTANCE. We have already seen, in explaining the principles of the Kaleidoscope, that a symmetrical picture cannot be formed from objects placed at any distance from the instrument. If we take the simple Kaleidoscope, and holding an object-box in contact with the reflectors, gradually withdraw it to a distance, the picture, which is at first perfect in every part, will, at the distance of one-tenth of an inch, begin to be distorted at the centre, from the disunion of the reflected images; the distortion will gradually extend itself to the circumference, and at the distance of eighteen inches, or less, from the reflectors, all the symmetry and beauty of the pattern will disappear. An inexperienced eye may still admire the circular arrangement of the imperfect and dissimilar images; but no person acquainted with the instrument could endure the defects of the picture, even when the slightest distortion only is visible at the centre.