When light is incident upon the most perfectly polished metals, a very considerable quantity of it is absorbed, and even when the reflexion is made at the greatest obliquities, there is a very manifest difference in the intensity of the direct and the reflected pencil. In the total reflexion of light from the second surfaces of transparent bodies, the loss of light is very inconsiderable, and the reflexion is made with a degree of brilliancy far surpassing that of the most resplendent metals. [Illustration: FIG. 49.] In constructing a Kaleidoscope upon this principle, we must procure a piece of glass entirely free from veins, and cut it into the form shown in Fig. 49.[7] The two surfaces =B O E=, =A O E=, must be inclined at an angle which is the even aliquot part of a circle. They must be ground perfectly flat and highly polished, and the junction =O E= must be made as fine as possible. The upper surface =A B E= should be rough-ground, and the side =A B O=, and the side at =E=, should be parallel and well polished. If the glass is colourless and good, the eye, when placed at =E=, will see the very same appearance as in the simple Kaleidoscope; and objects placed at =A B O= will be arranged into the same beautiful figures. The only defects attending this form of the Kaleidoscope, are the loss of light occasioned by its passing through a mass of solid glass, not perfectly transparent, and the difficulty of obtaining a perfect junction of the two reflecting planes. The first of these evils is, however, counterbalanced by the great intensity of the light which suffers total reflexion; and the second does not exist when the Kaleidoscope is intended to give rectilineal or annular patterns. [7] When this chapter was written (1818), it was very difficult to procure glass sufficiently homogeneous for this purpose: but it can now be procured from the Glass Works of Messrs. Chance & Co., at Smethwick, near Birmingham.