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.