CHAPTER XI.
ON THE CONSTRUCTION AND USE OFPOLYANGULAR KALEIDOSCOPES, IN WHICHTHE REFLECTORS CAN BE FIXEDAT 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 fromFig. 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.
Fig. 29.Fig. 30.
Fig. 29.
Fig. 30.
The three Figures, viz.,29,30, and31, represent the Polyangular Kaleidoscope with metallic reflectors, as made by Mr. Bate.Fig. 29shows the complete instrument, when mounted upon a stand;Fig. 30is a section of it in the direction of its length;Fig. 31is a transverse section of it through the lineS T,Fig. 30, andFig. 32shows the lens of the eye-holeE. 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 inFig. 30. One of these reflectors,B O E, is fixed to the ringR R, by the intermediate pieceK G L. The reflector is screwed to this piece by the adjustable screwsK,L; and the pieceK G Lis again fixed to the ringR R, by two screws seen above and belowG, inFig. 31. Hence the tube, consisting of the conesM M,N N, and the ringR R, are immovably connected with the mirrorB O E. The surface of the reflectorB O Eis adjusted by the screws atKandL, till it passes accurately throughthe axis of the cones and ring as seen inFig. 31. The other reflectorA O, is fixed to an outer ringr r, by means of an intermediate piece, similar toK G L, the armFof which, corresponding toG, passes through an annular space or open arch, of more than 90°, cut out of the circumference of the inner ringR R. The armFis fixed to the outer ringr rby two screws, seen above and belowF; and the reflectorA Ois fixed to the bar corresponding toK L,Fig. 30, by similar screws, for the purpose of adjusting it.
Fig. 31.Fig. 32.
Fig. 31.
Fig. 31.
Fig. 32.
Fig. 32.
The lower edgeO Eof the reflectorB O Eextends about the 15th of an inch below the axis of the cones, as represented by the dotted line inFig. 30; but the lower edgeO Eof the other reflectorA 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 reflectorA O E, which coincides with the axis of the cone, and to form ajunction 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 toKandL.
If we now fix the outer ringr rinto the ring of a standS T, so as to be held fast, and turn the cones with the hand, we shall give motion to the reflectorB 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 conesM,N, turn the ringR Rwith the other, we shall give motion to its reflectorA 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 ringr 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 ringr 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 withtwelveluminous sectors, or a star withsixpoints, and consequently a pattern composed ofsixpairs 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-holeE, as shown inFigs. 30and32. A brass ring containing a plane glass screws into the outer ringC 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 rimC 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 coneM Mhaving 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 theutmost, 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 ringR 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.
Fig. 33.
Fig. 33.
Fig. 34.Fig. 35.Fig. 36.
Fig. 34.
Fig. 34.
Fig. 35.
Fig. 35.
Fig. 36.
Fig. 36.
A section of the whole of this instrument, in the direction of its length, is shown inFig. 33. A section throughM NorO P, near the eye-end, is shown inFig. 35,Fig. 34representing the mode of supporting the fixed reflector, andFig. 36the mode of supporting the movable reflector. The tube of the Kaleidoscope, inFig. 33, is represented byb c d e f g h, and consists of two parts,b c g h, andc d e f g. The first of these parts unscrewsfrom the second, and the second contains all the apparatus for holding and moving the reflectors. At the partsM N O P, of the tube, are inserted a short tube, a section of which is shown inFig. 34. The object of these tubes is to support the fixed mirrorA O, which rests with its lower endOupon the piece of brasst. It is kept from falling forwards by the tonguer, connected with the upper parts s, and from falling backward by the piece ofcorkQ, 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 screwss,s. The contrivance for supporting and moving the second reflectorB O, is shown inFig. 36, in section; and a longitudinal view of it is given inFig. 33. The mirrorB Olies in an opening, cut into two pieces of brass,vBp, one of which is placed atM N, and the other atO P. These two pieces of brass are connected by a rodm n,Fig. 33; and in the middle of this rod there is inserted a screwk, which passes through the main tubec d e f g, into a broad milled ringw w, which revolves upon the tube. As the screwk, therefore, fastens the ringw wto the rodm n, the reflectorB Owill be supported in the tube by the ringw w. The lower part of the mirrorB O, or rather of the brass piecevBp, rests aty, upon the piece of watch-springx y z, fastened to the main tube atz. This spring presses the face of the reflectorB Oagainst the ground and straight edge of the other reflectorA O, so as always to effect a perfect junction in every part of their length:—The apparatus for both reflectors is shown inFig. 35. An arch of about 45° is cut out of the main tube, so as to permit the screwkto move along it; and hence, by turning the broad ringw w, the reflectorB Omay be brought nearly to touch the reflectorA 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 atE, upon which may be screwed, when it is required, a brass cape 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 tubeb c g h, upon which it moves. When the instrument is used for opaque objects, the end piece,b c g hof 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.
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.