CHAPTER VII.
ON THE CONSTRUCTION AND USEOF THE SIMPLE KALEIDOSCOPE.
In order to construct the Kaleidoscope in its most simple form, we must procure two reflectors, about five, six, seven, or eight inches long. These reflectors may be either rectangular plates, or plates shaped like those represented inFig. 1, having their broadest endsA O,B O, from one to two inches wide, and their narrowest endsaE,bE, half an inch wide. If the reflectors are of glass, the newest plate glass should be used, as a great deal of light is lost by employing old plate glass, with scratches or imperfections upon its surface. The plate glass may be either quicksilvered or not, or its posterior surface may be ground, or covered with black wax, or black varnish, or anything else that removes its reflective power. This, however, is by no means absolutely necessary, for if the eye is properly placed, the reflexions from the posterior surface will scarcely affect the distinctness of the picture, unless in very intense lights. If it should be thought necessary to extinguish, as completely as possible, all extraneous light that may be thrown into the tube from the posterior surface of the glass plates, that surface should be coated with a varnish of the same refractive and dispersive power as the glass.
If the plates of glass have been skilfully cut with the diamond, so as to have their edges perfectly straight, and free from chips, two of the edges may be placed together, as inFig. 17 (p. 49), or one edge of one plate may be placed against the surface of the other plate, as shown in the section of Mr. Bates’s Kaleidoscope. But if the edges are rough and uneven, one of them may be made quite straight, and freed from all imperfections, by grinding it upon a flat surface, with very fine emery, or with the powder scraped from a hone. When the two plates are laid together, so as to form a perfect junction, they are then to be placed in a brass or any other tube, so as to form an angle of 45°, 36°, 30°, or any even aliquot part of a circle. In order to do this with perfect accuracy, direct the tube containing the reflectors to any line, such asm n,Fig. 2, placed very obliquely to one of the reflectorsA O, and open or shut the plates till the figure of a star is formed, composed of 8, 10, or 12 sectors, or with 4, 5, or 6 points, corresponding to angles of 45°, 36°, and 30°. When all the points of the star are equally perfect, and none of the lines which form the salient and re-entering angles disunited, the reflectors must be fixed in that position by small arches of brass or woodA B,a b,Fig. 21, filed down till they exactly fit the space between the open ends of the plates. The plates must then be kept in this position by pieces or wedges of cork or wood, or any other substance pushed between them and the tube. The greatest care, however, must be taken that these wedges press lightly upon the reflectors, for a very slight force is capable of bending and altering the figure even of very thick plates of glass.
When the reflectors are thus placed in the tube, as inFig. 21, their extremitiesaE,bE, next the eye, mustreach to the very end of the tube, as it is of the greatest importance that the eye get as near as possible to the reflectors. The other ends of the reflectorsA O,B O, must also extend to the other extremity of the tube, in order that they may be brought into contact with the objects which are to be applied to the instrument. In using transparent objects the cell or box which contains them may be screwed into the end of the tube, so as to reach the ends of the reflectors, if they happen to terminate within the tube; but an instrument thus constructed is incapable of being applied to opaque objects, or to transparent objects seen by reflected light.
Fig. 21.
Fig. 21.
If the plates are narrower at the eye-end, as inFig. 21, the angular pointEshould be a little on one side of the axis of the tube, in order that the aperture in the centre of the brass cap next the eye may be brought as near as possible toE. When the plates have the same breadth at both ends, the angular pointEwill be near the lower circumference of the tube, as it is atO; and in this case it is necessary to place the eye-hole out of the centre, so as to be a little above the angular pointE. This construction is less elegant than the preceding; but it has the advantage of giving more room for the introduction of a feather, or a piece of thin wood covered with leather, for the purpose of removing the dust which is constantly accumulating between the reflectors. In some instances the plates havebeen put together in such a manner that they may be taken out of the tube, for the purpose of being cleaned; but though this construction has its advantages, yet it requires some ingenuity to replace the reflectors with facility, and to fix them at the exact inclination which is required. One of the most convenient methods is to support the reflector in a groove cut out of a solid cylinder of dry wood of nearly the same diameter as the tube; and after a slip of wood, or any other substance, is placed along the open edges of the plates, to keep them at the proper angle given by the groove, the whole is slipped into the tube, where it remains firm and secure from all accident.
If the length of the reflectors is less than the shortest distance at which the eye is capable of seeing objects with perfect distinctness, it will be necessary to place at the eye-endEa convex lens, whose focal length is equal to, or an inch or two greater than, the length of the reflectors. By this means the observer will see with perfect distinctness the objects placed at the object end of the Kaleidoscope. This lens, however, must be removed when the instrument is to be used by persons who are short-sighted.
The proper application of the objects at the end of the reflectors is now the only step which is required to complete the simple Kaleidoscope. The method of forming, selecting, and mixing the objects, will be described in the next chapter. At present, we shall confine our attention to the various methods which may be employed in applying them to the end of the reflectors.
Fig. 22.
Fig. 22.
The first and most simple method consists in bringing the tube about half an inch beyond the ends of the reflectors. A circular piece ofthin plane glass of the same diameter as the tube, is then pushed into the tube, so as to touch the reflectors. The pieces of coloured glass being laid upon this piece of glass when the tube is held in a vertical position, another similar disc of plane glass, having its outer surface ground with fine emery, is next placed above the glass fragments, being prevented from pressing upon them, or approaching too near the first plane glass by a ring of copper or brass; and is kept in its place by burnishing down the end of the tube. The eye being placed at the other end of the instrument, the observer turns the whole round in his hand, and perceives an infinite variety of beautiful figures and patterns, in consequence of the succession of new fragments, which are brought opposite the aperture by their own gravity, and by the rotatory motion of the tube. In this rude state, however, the instrument is by no means susceptible of affording very pleasing exhibitions. A very disagreeable effect is produced by bringing the darkest sectors, or those formed by the greatest number of reflexions, to the upper part of the circular field, and though the variety of patterns will be very great, yet the instrument is limited to the same series of fragments, and cannot be applied to the numerous objects which are perpetually presenting themselves to our notice. These evils can be removed only by adopting the construction shown inFig. 22, in which the reflectors reach thevery end of the tube. Upon the end of the tubea b,c d,Fig. 22, is placed a ring of brass,m n, which moves easily upon the tubea b c d, and is kept in its place by a shoulder of brass on each side of it. A brass cell,M N, is then made to slip tightly upon the moveable ringm n, so that when the cell is turned round by means of the milled end atM N, the ringm nmay move freely upon the tube. The fragments of coloured glass, etc., are now placed in a small object-box, as it may be called, consisting of two glasses, the innermost of which,m n, is transparent, and the other ground on the outsideP, and kept at the distance of ⅛th or ⅒th of an inch by a brass rim: this brass rim generally consists of two pieces, which screw into one another, so that the object-plate can be opened by unscrewing it, and the fragments changed at pleasure. This object-box is placed at the bottom of the cellM N, as shown atO P, and the depth of the cell is such as to allow the sideOto touch the end of the reflectors, when the cell is slipped upon the ringm n. When this is done, the instrument is held in one hand with the angular pointE,Fig. 21, downwards, which is known by a mark on the upper side of the tube betweenaandb, and the cell is turned round with the other hand, so as to present different fragments of the included glass before the apertureA O B. The tube may be directed to the brightest part of the sky in the day-time, or in the evening to a candle, or an Argand Lamp, so as to transmit the light directly through the coloured fragments; but it will always be found to give richer and more brilliant effects if the tube is directed to the window-shutter, a little to one side of the light, or is held to one side of the candle—or, what is still better, between two candles or lamps placedas near each other as possible. In this way the picture created by the instrument is not composed of the harsh tints formed by transmitted light; but of the various reflected and softened colours which are thrown into the tube from the sides and angles of the glass fragments. When the pattern remains fixed in any position of the instrument, a variety of beautiful changes may be effected by making the end of the tube revolve round a candle or a bright gas flame, placed near the object-plate. The general pattern remains the same, but its colours vary both in their position and intensity, as the light falls upon different sides of the fragments of glass.
In the preceding method of applying the objects to the reflectors, the fragments of coloured glass are introduced before the aperture, and pass across it in concentric circles; and as the fragments always descend by their own gravity, the changes in the picture, though infinite in number, constantly take place in a similar manner. This defect may be remedied, and a great degree of variety exhibited in the motion of the fragments, by making the object-plates rectangular instead of circular, and moving them through a groove cut in the cell atM N, in the same manner as is done with the pictures or sliders for the magic lantern and solar microscope. By this means the different fragments that present themselves to the aperture may be made to pass across it in every possible direction, and very interesting effects may be produced by a combination of the rotatory and rectilineal motions of the object-plate. When the object or objects are fixed, and the tube with the reflectors moved round a centre, asdescribed inChapter II.,[3]we have the same succession of symmetrical pictures; but in this case every alternate sector is stationary, and the same number in motion, the moving figures always changing their form, and assuming that of the figures in the stationary sectors, which of course change, while the ends of the mirror pass over the fixed objects.
When the simple Kaleidoscope is applied to opaque objects, such as a seal, a watch-chain, the seconds hands of a watch, coins, pictures, gems, shells, flowers, leaves, and petals of plants, impressions from seals, etc., the object, instead of being held between the eye and the light, must be viewed in the same manner as we view objects through a microscope, being always placed as near the instrument as possible, and so as to allow the light to fall freely upon the object. The object-plates, and all transparent objects, may be viewed in this manner; but the most splendid exhibition of this kind is to view minute fragments of coloured glass, and objects with opaque colours, etc., placed in a flat box, the bottom of which is made of mirror-glass. The light reflected from the mirror-glass, and transmitted through the transparent fragments, is combined with the light reflected both from the transparent and opaque fragments, and forms an effect of the finest kind.
As dust is apt to collect in the angle formed by the reflectors, it may be removed when the reflectors are fixed, either by the end of a strong feather, or blown away with a pair of bellows. When the dust is lodged upon the face of the reflectors, it should be removed by a piece of soft leather.