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.

If the objects in the binocular slides represent either basreliefs or alto-relievos, or statues, or vases, or portions of any solid bodies, such as animals, plants, or flowers, which can be combined into symmetrical patterns, they will appear in their true relief in the Stereoscopic Kaleidoscope. In this way the artist may avail himself of the instrument in designing circular Gothic windows, the circular decorations of ceilings, and rectilineal or curvilineal belts, that are to be cut out of metals, marble, freestone, or wood, or formed of plaster of Paris, or metals susceptible of fusion.1

If we combine two Telescopic Kaleidoscopes, in the manner already described, so that the centres of their object-lenses are distant two and a half inches, and receive the right and left eye pictures of real objects upon disks of ground glass, with the ground side touching the ends of the reflectors, these objects, though themselves in true relief, will be reduced to plane pictures on the ground glass, and again brought into stereoscopic relief, and combined into symmetrical patterns by the instrument. The effect thus produced is different from what we should see were the ground glass removed, and the image of the object formed in the air at the end of the reflectors, for the same reason that the picture of an object in the stereoscope is different from what it appears if viewed directly by the eyes.

1 See my Treatise on the Stereoscope, Chap. xi. p. 86.

CHAPTER XVIII.

ON THE CONSTRUCTION OF MICROSCOPIC KALEIDOSCOPES.

THE name of Microscopic Kaleidoscope may be given to the instrument, under two forms, namely, when it is made to produce symmetrical patterns from microscopic objects, or when it is made so short that a lens of a high power is necessary at one end of the reflectors, to see distinctly, and magnify the objects at the other end. In both these forms I have often constructed them so small as one inch and one inch and a half in length. As the Kaleidoscope, in this minute state, has been applied both in this country and abroad, as a female ornament, we shall proceed to point out the best method of constructing it.

Since the aberration from symmetry increases, as the length of the reflectors is diminished, and since the light of the field diminishes from the same cause, it becomes extremely difficult to obtain correct figures, and uniformity of light in small instruments. In order to overcome these difficulties, as far as possible, the reflectors should be metallic, and may be either made of polished steel or polished speculum metal. The inclination at which they are fixed should not be less than 36° or 45°; and the eye-hole, which should not exceed 1-15th of an inch in diameter,

must be placed as near as possible to the angular point. Since the aberration from symmetry increases with the distance of the object from the reflectors, and is much augmented in small instruments, the greatest care must be taken to have the objects at the least possible distance from the reflectors. To accomplish this, the objects themselves should be as thin and slender as they can be made; the colours should be brilliant and not gloomy; and they should be separated from the reflectors by a thin film of the most transparent mica, which is superior to glass of equal thickness, even if it could be got, from its extreme toughness and elasticity. The mica, indeed, is easily scratched, but if this should take place to any extent, it can easily be replaced by a new film. It would even be of consequence to bend the mica into a slight concavity, so as to permit the objects to lie rather within than without the extremity of the reflectors. In order to see the pattern with perfect distinctness, a lens must be placed at the end of the instrument; the focal length of this lens, however, must not be exactly equal to the distance of the objects from the eye, but as much greater as possible, so that the eye, by a little exertion, may be able to obtain distinct vision. The reason of this will be understood, by considering that the images of the objects, seen by reflexions, are thrown to a greater distance, as it were, from the eye, and could not therefore be seen distinctly by using a lens adjusted exactly to the nearest part of the picture. Consequently, the focal length of the lens must be a mean between the distances of different parts of the picture, that is, a little greater than that which is suited to the sector seen by direct vision.

I

When small Kaleidoscopes are made with four or with three mirrors, the preceding directions are equally applicable, the greatest care being taken that the reflectors taper nearly to a point at the eye-end, so as not to leave an aperture greater than 1-15th of an inch in diameter. When they are made of solid glass, the focal length of the lens must be determined from the principles contained in the last chapter.

The preceding instruments may be fitted up with a drawtube and lens, and when it is required to introduce drawings of pictures and statues, small microscopic photographs may be employed.