ENDLESS GALLERY. 311 



can be turned round, shaking up the beads, &c., as it revolves, 

 so that they assume new positions with respect to one another. 

 Every different position gives rise to an 8-fold (or a 6-fold) 

 figure of extremely pleasing character when the bits of glass, 

 &c., are brightly coloured and happen by chance to form an 

 appropriate grouping, the figure being perceived on looking into 

 the tube through the eyepiece b, at the end opposite to the cap. 

 The best results are obtained when the tube is pointed slantingly 

 downwards towards a candle flame, or a flat mirror laid on a 

 table before a window, so that the bits of glass can be readily 

 moved by rotating the cap, whilst a brightly illuminated field of 

 view is observed. 



Another form of the instrument contains three flat vertical mirrors 

 inclined to one another at angles of 60, so that the section of the 

 three mirrors in position would be an equilateral triangle ; a much 

 brighter definition is thus obtained, as three reflecting surfaces are 

 employed instead of two, and consequently more light rays 

 actually meet the eye. In this case a 6-rayed figure results. 



In another form of kaleidoscope, two mirrors are provided with 

 an adjusting arrangement, so that the angle between them can be 

 altered at will. Pieces of card with devices on them, or other 

 objects, such as flowers, &c., are then placed between the mirrors 

 and viewed by looking slightly downwards into the angle of the 

 mirrors, when a 6-fold, 8-fold, 9-fold, 10-fold, 12-fold, &c., multi- 

 plication of the object will be visible star-fashion, according as the 

 angle is 60, 45, 40, 36, 30, &c. Arrangements on this principle 

 are sometimes used for designing geometrically arranged patterns 

 for wall papers, floor cloths, &c. 



Expt. 345. The Endless Gallery. When two mirrors are 

 arranged exactly parallel to one another an observer situated 

 between the two will see an apparently endless succession of 

 images, formed by repeated reflections from the two mirrors alter- 

 nately. If two large pierglasses or full length toilet mirrors be 

 arranged perfectly vertical and parallel with one another, an 

 observer standing between them with a lighted candle or lamp in 

 his hand, held nearly level with his eye, will see an apparently 

 interminable line of candles, extending far away into the distance 

 until they become almost too faint to be visible. Any consider- 

 able degree of want of parallelism of the mirrors will greatly 

 shorten the line of images formed. In Expt. 343, when a candle 

 is looked at obliquely in a mirror consisting of a moderately thick 

 plate of glass silvered behind, it will often happen that not only 

 are two images seen (one by reflection from the front surface of 

 the glass and the other from the silvered back surface), but in 



