416 



KALEIDOSCOPE. 



tcopc. 



the axis of motion, which must also be the axis of the 

 cones and rings. It', 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 II with the 

 other, we shall give motion to its reflector AO, and 

 produce a variation in the angle in the same manner as 

 before. 



In order to enable the observer to set the reflectors at 

 ence to an even aliquot part of a circle, or so as to give 

 pairs of direct and inverted images, the most conveni- 

 ent of the even aliquot parts of the circle are engraven 

 upon the ring R ; so that we have only to set the in- 

 dex I to any of these parts, to No. 20 for example, and 

 thi' reflecton will then be set at an angle of 18, and 

 will form a circular field with twrnty luminous sectors, 

 or a star with Irn points, and consequently a pattern 

 composed often pair of direct and inverted images. 



As the length of the plates is onjy about 5 inches, it 

 is necessary for some eyes to have a convex lens placed 

 at E. A brass ring containing a plane glass screws in- 

 to the outer ring CD, arid there is an object plate ac- 

 companying the instrument, and containing fragments 

 of differently coloured glass. This object plate consists 

 of two plates of glass, one ground and the other trans- 

 parent, set in braes rims. The transparent one goes 

 nearest the reflectors, and the brass rim which contains 

 it screws into the other, so as to contain between them 

 the coloured fragments. A loose ring surrounds this ob- 

 ject plate ; and when this ring is screwed into the cir- 

 cular rim CD, the object plate can be turned round so 

 as to produce a variety of patterns, without any risk 

 of its being detached from the outer cone. 



Some of the preceding instruments have been fitted 

 up also with plates of glass ground perfectly flat and 

 highly polished, which reflect a great deal of light, and 

 are less liable to be injured by the operation of remo- 

 ving the dust, or by other causes. Flint glass, from its 

 high reflective power, is preferable to any other. The 

 polyangular kaleidoscope, as made by Mr. Bate with 

 glass plates, is constructed on different principles from 

 the one now described. The reflectors are placed in a 

 cylindrical tube, and the motion of the moveable re- 

 flector is produced by a contrivance extremely simple 

 and ingenious. A full account of this instrument will 

 be found in Dr Brewster's Treatise on the Kaleidoscope. 

 The kaleidoscope appears in its most perfect form 

 when the preceding instrument is constructed with an 

 outer tube containing one or more lenses, for the pur- 

 pose of creating patterns from distant objects. One of 

 the lenses intended for objects at a greater distance than 

 10 or 12 feet, should have its focal length nearly equal 

 to the greatest distance between the lens and the end 

 of the reflector, in order that these objects, if small, 

 may be introduced into the aperture as large as possi- 

 ble. The other lens, intended for objects at a less distance 

 than 10 or 12 feet, or for distant objects of a very great 

 size, should have a focal length a little greater than one 

 half the focal length of the other lens. By combining 

 these lenses, the effect of a more convex lens will be 

 obtained, which may often be useful, when we wish to 

 see objects held very near the instrument. 



SECT. VIII. On the applicat! n of 'he Kaleidoscope for 

 Projecting Die Pictures which it creates upon a tvall. 



The pictures created by the Kaleidoscope are visible 

 nly to one person at a time ; but it is by no means diffi- 

 cult to fit it up for the express purpose of exhibiting 

 ft at the same time to a number of spectators. The ne- 



*cope 



cessary limitation of the aperture at the eye end of the 

 instrument, is however very hortile to this species of ex- 

 hibition, and renders it necessary that the^jbjects should 

 be as transparent as possible, and very strongly illumi- 

 nated. 



The apparatus requisite for this purpose is shewn in $ 9 

 Fig. 9, where FG is the kaleidoscope, having its re* 

 flectors inclined at an angle of 22*, 2,5 [%*, 30', 36', 45", 

 60 or 90 ; for if the angle is made smaller, the last 

 reflections will not be easily seen. The objects out of 

 which the picture is created are placed in the object 

 plate DE, and are illuminated by means of a lens AD, 

 which concentrates upon them the direct light from the 

 lamp or candle C, and also the light reflected from the 

 concave mirror M. At the eye end of the kaleidoscope 

 is placed a lens L close to the end of the reflectors. 

 This lens should haye a focal length about an inch 

 less than the length FG of the reflectors, in order 

 that the image of the pattern created at F, may 

 be thrown upon the wall W, at a convenient distance 

 from L. 



When the instrument is thus fitted up, an enlarged 

 image of the pattern will be seen upon the wall W, 

 and this image will undergo every possible transfor- 

 mation, and exhibit to the spectator every variety of 

 tint and form by the motion of the object, either through 

 a groove or round the axis of the instrument. The 

 same effect may be produced by the light of the sun; 

 but in this case the mirror MN is unnecessary. 



One of the polyangular kaleidoscopes, as made by 

 Mr. Bate, has been fitted up in this manner, for exhibi- 

 tion at the lectures on natural philosophy delivered at 

 Guy's Hospital, by that eminent chemist, William 

 Allen, Esq. F. R. S. The light is derived from an oxy- 

 gen lamp, which produces the most intense illumina- 

 tion. 



SECT. IX. On Annular and Meet ilineal Kaleidoscopes. 



As it is often of considerable importance in the orna- 

 mental arts to have patterns for circular' and rectili- 

 neal borders, the kaleidoscope may be fitted up to ac- 

 complish these objects. If the two reflectors AC, BD 

 are placed in the manner shewn in Fig. 10. so that p,- g JQ 

 AO is the centre to which they converge, any objects 

 placed at the end of the reflectors will give an annular 

 pattern, forming part of a circle whose radius is AO. 

 As the point of convergence O recedes from CD, the 

 circle of which it is a portion increases in magnitude ; 

 and when O is infinitely distant, the reflectors have a 

 parallel position, as shewn in Fig. II, when the pat- 

 tern which they form becomes exactly rectilineal. A 

 portion of the pattern is seen of sufficient length to en- 

 able the artist to form the most correct opinion of its 

 effect. A very ingenious instrument 'has been con- 

 structed for this purpose by Messrs. P. and G. Dollond, 

 of which a complete drawing and description will be 

 found in Dr. Brewster's Treatise on the Kaleidoscope. 

 Two metallic mirrors are placed at an angle of 30, so 

 as to form a kaleidoscope for giving circular patterns 

 in the usual way ; and, by a particular contrivance, 

 these same mirrors may be thrown into the positions 

 shewn in Figs. 10, 11, so as to give rectilineal patterns, 

 and annular patterns of any radius. 



SECT. X. On Poll/central Kaleidoscopet. 



Hitherto we have considered the effects produced by 

 the use of two reflecting planes ; but it must be obvi- 



