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 v B p, one of which an opening, cut into two pieces of brass, is placed at M N, and the other at o P. These two pieces of brass are connected by a rod mn, 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 FIG. 36. 20 ww, which revolves upon the tube. As the screw k, therefore, fastens the ring w w to the rod m n, the reflector BO will be supported in the tube by the ring w w. The lower part of the mirror B 0, 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 Bo 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 ef, 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 gh, upon which it moves. When the instrument is used for opaque objects, the end piece, bcgh 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,1 a piece of tube with a lens at the end of it is put upon the end piece, bcg h, and may be suited to different distances within a certain range. 1 See Chapter X. G CHAPTER XII. ON THE CONSTRUCTION AND USE OF ANNULAR AND IN the instruments already described, the pictures which they create, though they may be made of various outlines, have all a centre to which the reflected images are symmetrically related. The same instruments give an annular pattern, or a pattern returning into itself, and included between two concentric circles, by keeping the objects from the central part of the aperture; but as such a pattern can never have its greatest radius more than the breadth of the mirror, and as annular patterns of a very great radius, where the eye can see only a portion of them at a FIG. 37. B time, are often required, it becomes of importance to adapt the Kaleidoscope for this species of ornament. Let A C B D, Fig. 37, be two plane mirrors, and let their inclination be measured by the angle A OB; then, if the eye is placed between c and D, it will observe the reflected images of the objects which are placed before the aperture A C B D, arranged, in the annular segment M A B N, round o, as a centre. The effect is exactly the same as if the reflectors had been continued to o, with this difference only, that the annular segment can never be complete. This defect in the segment arises from two causes: When the centre o is near CD, the defect is occasioned by the want of a reflecting surface to complete the ring, and not from any want of light in the reflected images; but when the centre o is remote from C D, the defect arises from the want of light in the last reflexions, as well as from the want of a reflecting surface. The theory of the Annular Kaleidoscope is exactly the same as that of the common instrument; and therefore all the contrivances for producing symmetrical pictures, from near and distant objects, are applicable to this instrument. As the picture, however, never can return into itself, it is of no importance that the angle A O B be the aliquot part of a circle, the picture being equally complete at all angles. In order to have the most perfect symmetry with this Kaleidoscope, the eye should be placed at E, between the nearest ends of the reflectors, as it will there be nearer the plane of both reflectors than in any other position. If the two mirrors are brought nearer each other, so that their surfaces always pass through the point o, the deviation from perfect symmetry will diminish as the eye becomes more and more in the plane of both; and for the same reason the light of the field will be more brilliant. When the point o is infinitely distant, the two reflectors become parallel to each other, as in Fig. 38, and the series of reflected images extends in a straight line, forming beau In this position tiful rectilineal patterns for borders, &c. of the reflectors the eye should be placed in the centre at E, and the symmetry of the picture and the light of the field will increase as the distance of the reflectors diminishes, or as their length is increased. Two different kinds of instruments have been constructed on the preceding principles, the one by Mr. Dollond, and the other by Mr. John Ruthven, both of which possess very valuable properties. Mr. Dollond's Universal Kaleidoscope. The instrument constructed by Mr. Dollond is represented in Figs. 39, 40, and 41, in section, and is intended to unite the properties of a common Kaleidoscope, in which the reflectors are inclined at an angle of 30°, and also those of an Annular and a Parallel Kaleidoscope. Fig. 39 represents the reflectors, etc., when they act as a common Kaleidoscope; and Fig. 40 shows them when they form a parallel Kaleidoscope, an annular Kaleidoscope being formed when they have an intermediate position. The tube of the instrument is shown, in section, by TT; and to this tube is fixed, by the screws ss, a frame of metal, ab, to which the reflectors are fastened. The reflectors, which are made |