S.r Dariel Brewster subsequently found mean, to obtain multiplied images of such objects as flowers, trees, and even persona or things motson. For this purpoee he caused the two mirrors to be fixed in a tube as before, but this tube was contained In another from which, bke the eye tube of a telescope, it could be drawn at pleasure towards this eye : at the opposite end of the exterior tube was fixed a glass lens of convenient focal length, by which there were formed images of distant objects at the place of the sector • c B. These images thus became objects which being multiplied by successive reflections from the mirrors, produced In the field of view symmetrical patterns of great beauty.
Some kaleidoscopes have been executed in such a manner that the two mirrors may be placed at any required angle with one another, by which wan, the images in the visible field of view may be varied at pleasure. The Instrument In capable also of being constructed so that the multiplied image may be projected on a screen, and thus made visible at one time to many spectator*. In order to obtain this end, the rays of light from a powerful lamp are, by mean, of a lens, made to fall upon the object In A CD at the farther extremities of the two mirrors; and at the eye-end of the instrument is placed a lens of such focal length that the rays in each of the emergent pencils may eon eerge at the screen : there will Grua be formed on the latter a magnified image of the whole pattern. The tube containing the glass plates is frequently mounted on a stand having a ball-and-socket joint, on which It may be turned in any convenient direction ; and the instrument being thus supported, the figures in its field may be easily sketched by a skilful artist, who by means of such an apparatus may be assisted in designing beautiful patterns.
Sir David Brewster's account of his Invention is contained in his 'Treatise on the Kaleidoscope,' Edinburgh, 1819, of which a new edition has just been published (1860). Dr. Rogct has shown (' Annals of Philosophy; vol. xi.) that the propertiea of the instrument may be greatly extended by employing, not only two, but three, and even four plane mirrors, united together at their edges so as to form a hollow prian, or a frustum of a pyramid, the reflecting surfaces being towards the Interior. Of these, which are called l'olycentrot kaleidoscopes, the instruments constructed with three plane mirrors appear to produce the most plowing effects ; the mirront may be disposesd so that a section perpendicular to the taxi. shall be an equilateral triangle, a right-angled isosceles triangle, or a right-angled triangle having its two acute angles equal to 30' and 60'. The first disposition of the mirrors affords regular combinations of Images in three different directional which eras each ether at angle. of 60' and 120'; and to instrument, of this kind Dr. Beget gave the 11All10 of 7'riascope. With the second dimposition the field Is divided into square compartments having the by-wherries, of the triangle for their sides : this is called a Tetra rept. The third disposition exhibits • field of view divided into 1,setagonal compartments ; and hence the instrument is designated a Ilessueepe.
ICA 1.1iN DsE. (Kates pan.)