The kaleidoscope

by David Brewster

CHAPTER XI.

ON THE CONSTRUCTION AND USE OF
POLYANGULAR KALEIDOSCOPES, IN WHICH
THE REFLECTORS CAN BE FIXED
AT ANY ANGLE.

In all the preceding instruments, the reflecting planes are fixed at an invariable angle, which is some even aliquot part of 360°; and therefore, though the forms or patterns which they create are literally infinite in number, yet they have all the same character, in so far as they are composed of as many pairs of direct and inverted images as half the number of times that the inclination of the reflectors is contained in 360°.

It is therefore of the greatest importance, in the application of the Kaleidoscope to the arts, to have it constructed in such a manner, that patterns composed of any number of pairs of direct and inverted images may be created and drawn. With this view, the instrument may be fitted up in various ways, with paper, cloth, and metallic joints, by means of which the angle can be varied at pleasure; but the most convenient methods are shown in the Figures from [Fig. 29 to 35], inclusive, which represent two different kinds of Polyangular Kaleidoscopes, as made by the late Mr. R. B. Bate, Optician, London, who had devoted much time and attention to the perfection of this species of Kaleidoscope.

Bate’s Polyangular Kaleidoscope with
Metallic Reflectors.

Fig. 29.

Fig. 30.

The three Figures, viz., [29], [30], and [31], represent the Polyangular Kaleidoscope with metallic reflectors, as made by Mr. Bate. [Fig. 29] shows the complete instrument, when mounted upon a stand; [Fig. 30] is a section of it in the direction of its length; [Fig. 31] is a transverse section of it through the line S T, [Fig. 30], and [Fig. 32] shows the lens of the eye-hole E. The tube of this instrument is composed of two cones, M M, N N, [Fig. 30], connected together by a middle piece or ring, R R, into which they are both screwed. These two cones enclose two highly polished metallic reflectors, A O, B O, [Fig. 31], only one of them, viz., B O E, being seen in [Fig. 30]. One of these reflectors, B O E, is fixed to the ring R R, by the intermediate piece K G L. The reflector is screwed to this piece by the adjustable screws K, L; and the piece K G L is again fixed to the ring R R, by two screws seen above and below G, in [Fig. 31]. Hence the tube, consisting of the cones M M, N N, and the ring R R, are immovably connected with the mirror B O E. The surface of the reflector B O E is adjusted by the screws at K and L, till it passes accurately through the axis of the cones and ring as seen in [Fig. 31]. The other reflector A O, is fixed to an outer ring r r, by means of an intermediate piece, similar to K G L, the arm F of which, corresponding to G, passes through an annular space or open arch, of more than 90°, cut out of the circumference of the inner ring R R. The arm F is fixed to the outer ring r r by two screws, seen above and below F; and the reflector A O is fixed to the bar corresponding to K L, [Fig. 30], by similar screws, for the purpose of adjusting it.

Fig. 31.

Fig. 32.

The lower edge O E of the reflector B O E extends about the 15th of an inch below the axis of the cones, as represented by the dotted line in [Fig. 30]; but the lower edge O E of the other reflector A O E, which is finely ground to an acute angle, forming a perfectly straight and smooth line, is placed exactly in the axis of the cones, so as just to touch a line in the reflector A O E, which coincides with the axis of the cone, and to form a junction with that line in every part of the two meeting planes. The very nice adjustments which are necessary to produce so exact a motion are effected by the screws corresponding to K and L.

If we now fix the outer ring r r into the ring of a stand S T, so as to be held fast, and turn the cones with the hand, we shall give motion to the reflector B O, so as to place it at any angle we please, from 0° to 90°; and during its motion through this arch, the junction of the two reflectors must remain perfect, if the touching lines are adjusted, as we have described them, to the axis of motion, which must also be the axis of the cones and rings. If, on the contrary, we take away the stand, and, holding the instrument in the hand by either of the cones M, N, turn the ring R R with the other, we shall give motion to its reflector A O, and produce a variation in the angle in the same manner as before. The same effect may be produced by an endless screw working in teeth, cut upon the circumference of the outer ring r r.

In order to enable the observer to set the reflectors at once to any even aliquot part of a circle, or so as to give any number of pairs of direct and inverted images, the most convenient of the even aliquot parts of the circle are engraven upon the ring r r; so that we have only to set the index to any of these parts, to the number 12, for example, and the reflectors will then be placed at an angle of 30° (12 × 30 = 360°), and will form a circular field with twelve luminous sectors, or a star with six points, and consequently a pattern composed of six pairs of direct and inverted images.

As the length of the plates is only about five inches, it is necessary, excepting for persons very short-sighted, to have a convex lens placed in front of the eye-hole E, as shown in [Figs. 30] and [32]. A brass ring containing a plane glass screws into the outer ring C D, when the instrument is not in use; and there is an object-box containing fragments of differently coloured glass. This object-box consists of two plates of glass, one ground and the other transparent, set in brass rims. The transparent one goes nearest the reflector, and the brass rim which contains it screws into the other, so as to enclose between them the coloured fragments, and regular figures of coloured and twisted glass. A loose ring surrounds this object-box; and when this ring is screwed into the circular rim C D, the object-box can be turned round so as to produce a variety of patterns, without any risk of its being detached from the outer cone.

In applying this instrument to opaque objects, such as engravings, coins, gems, or fragments of coloured glass laid upon a mirror, the aperture of the mirrors is laid directly over them, the large cone M M having been previously unscrewed, for the purpose of allowing the light to fall freely upon the objects. This property of the Kaleidoscope is of great importance, as in every other form of the instrument opaque objects must be held obliquely, and therefore at such a distance from the reflectors as must affect the symmetry of the pattern.

As the perfection of the figures depends on the reflectors being kept completely free of dust, particularly at their junction, where it naturally accumulates, the greatest facility is given by the preceding construction in keeping them clean. For this purpose, the large cone must be unscrewed; the reflectors having been previously closed, by turning the index to 60 on the ring. They are next to be opened to the utmost, and the dust may in general be removed by means of a fine point wrapped in clean and dry wash-leather. If any dust, however, still adheres, the small screw in the side of the ring opposite to the index should be removed, and the smaller cone, N N, also unscrewed. By easing the supporting screws of either of the reflectors, their touching sides will separate, so as to allow a piece of dry wash-leather to be drawn between them. When every particle of dust has been thus removed, the metals should be re-adjusted and closed before the cones are replaced; both of which should be screwed firmly into the ring R R.

As the axis of motion in the preceding construction is necessarily the axis of the cones and rings, the diameter of these cones and rings must everywhere be double the breadth of the reflectors. From this cause, the tube, and consequently the object-box, are wide, and the instrument is, to a certain degree, not very portable. This defect is completely avoided in another Polyangular Kaleidoscope constructed by Mr. Bate, upon entirely different principles, which we shall now proceed to describe.

Bate’s Polyangular Kaleidoscope
with Glass Reflectors.

Fig. 33.

Fig. 34.

Fig. 35.

Fig. 36.

A section of the whole of this instrument, in the direction of its length, is shown in [Fig. 33]. A section through M N or O P, near the eye-end, is shown in [Fig. 35], [Fig. 34] representing the mode of supporting the fixed reflector, and [Fig. 36] the mode of supporting the movable reflector. The tube of the Kaleidoscope, in [Fig. 33], is represented by b c d e f g h, and consists of two parts, b c g h, and c d e f g. The first of these parts unscrews from the second, and the second contains all the apparatus for holding and moving the reflectors. At the parts M N O P, of the tube, are inserted a short tube, a section of which is shown in [Fig. 34]. The object of these tubes is to support the fixed mirror A O, which rests with its lower end O upon the piece of brass t. It is kept from falling forwards by the tongue r, connected with the upper part s s, and from falling backward by the piece of cork Q, which may be removed at any time, for the purpose of taking out and cleaning the reflectors. This little tube is fixed to the outer tube by the screws s, s. The contrivance for supporting and moving the second reflector B O, is shown in [Fig. 36], in section; and a longitudinal view of it is given in [Fig. 33]. The mirror B O lies in an opening, cut into two pieces of brass, v B p, one of which is placed at M N, and the other at O P. These two pieces of brass are connected by a rod m n, [Fig. 33]; and in the middle of this rod there is inserted a screw k, which passes through the main tube c d e f g, into a broad milled ring w w, which revolves upon the tube. As the screw k, therefore, fastens the ring w w to the rod m n, the reflector B O will be supported in the tube by the ring w w. The lower part of the mirror B O, or rather of the brass piece v B p, rests at y, upon the piece of watch-spring x y z, fastened to the main tube at z. This spring presses the face of the reflector B O against the ground and straight edge of the other reflector A O, so as always to effect a perfect junction in every part of their length:—The apparatus for both reflectors is shown in [Fig. 35]. An arch of about 45° is cut out of the main tube, so as to permit the screw k to move along it; and hence, by turning the broad ring w w, the reflector B O may be brought nearly to touch the reflector A O, and to be separated from it by an arch of 45°, so as to form every possible angle from nearly 0° to 45°, which is a sufficient range for the Kaleidoscope. The main tube terminates in a small tube at E, upon which may be screwed, when it is required, a brass cap e f, containing a convex lens. A short tube, or cell, a a a a, for containing the object-boxes, slips upon the end of the tube, and should always be moved round from right to left, in order that the motion may not unscrew the portion of the tube b c g h, upon which it moves. When the instrument is used for opaque objects, the end piece, b c g h of the tube, screws off, so as to admit the light freely upon the objects.

The advantages which the Polyangular Kaleidoscopes possess over all others are—

1st, That patterns of any number of sectors, from the simplest to the most complicated, can be easily obtained.

2d, That the reflectors can be set, with the most perfect accuracy, to an even aliquot part of a circle.

3d, That the reflectors can be at any time completely cleaned and freed from all the dust that accumulates between them, and the instrument rendered as perfect as when it came from the hands of the maker.

In order to apply this Kaleidoscope to distant objects, or make it telescopic,[6] a piece of tube with a lens at the end of it is put upon the end piece, b c g h, and may be suited to different distances within a certain range.