The kaleidoscope

by David Brewster

The crystals which are to give the colours and forms produced by polarized light and its subsequent analysis, may be either uniaxal crystals, such as calcareous spar, or quartz, or beryl, or biaxal crystals, such as selenite, topaz, mica, arragonite, nitre, etc.[9] These crystals must be placed at the end of the reflectors, and when they transmit polarized light, their brilliant colours and forms will vary by turning the cell which contains them, or by giving a motion of rotation to the analyser. Thin films, or laminæ of selenite of different thicknesses, and generally of such a thickness as gives the bright rings of the second order of colours in Newton’s scale, may be placed in a narrow cell or object-box, and may have their outlines of various curvatures, so as to combine both form and colour in the Kaleidoscopic figure. Different forms may also be obtained by using pieces of colourless glass of different shapes, or pieces of thin wire bent into a variety of curves. If the outlines of the pattern are to be obtained from pieces of glass or wire, the films of selenite might be cemented to one of the glass plates of the object-box, so as to have their axes lying in different directions.

The coloured figures produced by glass quickly cooled, might also be advantageously employed, and, likewise, the remarkable forms of circular crystals and crystalline groups, when they are sufficiently large to be seen by the naked eye.

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.

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.

In order to construct the instrument independently of the stereoscope, we have only to combine two equal Kaleidoscopes, with their reflecting mirrors equally inclined to each other, and place at the eye-end of them two semi-lenses or quarter lenses, at the distance of two and a half inches, and having their focal lengths equal to the length of the stereoscope. If the two right and left eye photographs, to which we apply them, are opaque, upon paper or silver plate, an opening must be left above the object end of the reflectors, of sufficient size to allow light to be thrown upon the photographs. When the figures are transparent, this aperture must be closed.