Very beautiful objects may be made by cementing a plate of sulphate of lime (_selenite_), 0.01818 of an inch thick, to a plate of glass, and cutting out, upon a turning-lathe, grooves or bands of such different depths, as to give different colours by polarized light. Beautiful patterns may be thus executed in bands or lines of different colours; but for the purposes of the Kaleidoscope, it will be sufficient to have curves or portions of curves of such different forms and curvatures, as will produce agreeable figures by their combination. These curves and irregular forms of any kind, may be scratched or excavated in the plate of selenite by the point of a sharp knife, and afterwards polished, or even deepened, by the action of water, which has the property of slowly dissolving the selenite. In order to observe the effects produced by polarized light, it is not necessary to have the polarizing and analysing apparatus attached to the Kaleidoscope. The polarizer, in the form of a plate of black glass, or a bundle of plates of common window-glass, may be laid on the table so as to reflect the light into the Kaleidoscope at an angle of 56°, and the analyser may be held in one hand, and the Kaleidoscope in the other. In this case, however, it would be better to have the Kaleidoscope fixed, in order that the observer may have the use of his left hand, to turn the object-box, which contains the doubly-refracting crystal. Without the use of polarized light, very fine forms, and these splendidly coloured, may be obtained by means of the coloured rings exhibited in the _Iriscope_.[10] When two such systems of rings are formed by breathing through a tube upon black glass, over which soap has been rubbed and subsequently wiped off, by a piece of chamois leather, they form a double system, similar to the biaxial system in mica and topaz, with curves of various shapes, which exhibit beautiful combinations in the Kaleidoscope. [10] _Treatise on Optics_, p. 120. CHAPTER XVII. ON THE CONSTRUCTION OF STEREOSCOPIC KALEIDOSCOPES. If we apply the Kaleidoscope to any statue or architectural ornament, or any other solid object represented, photographically, on a transparent binocular slide, the figures will be combined into a flat symmetrical pattern, as shown in a future chapter. But if, in the lenticular stereoscope, we place a Kaleidoscope between each of the two semi-lenses and the statue, or other object in the binocular slide, we shall then see the statue or other object in full relief in the symmetrical figure. This, in a rude form, is the Stereoscopic Kaleidoscope.