Page:The wonders of optics (1869).djvu/224



every one in his younger days has possessed and broken that pretty instrument known as the kaleidoscope. His researches into its construction no doubt taught him that it consisted of a cylindrical tube in tin or cardboard, with a moveable cap at one end and a small hole at the other. In the interior of the tube were found three long glasses, blackened on the back, placed at an angle, and kept in position by pieces of cork. The moveable cap was provided with two circular pieces of glass, one ground and the other transparent, between which were placed a number of pieces of coloured glass. On holding the instrument up to the light and looking through the eye-hole, a beautifully coloured star was seen whose form and hue changed by simply shaking the tube.

The kaleidoscope was invented by Sir David Brewster, and is exceedingly simple in principle. We all know that if a luminous object, such as a taper, is placed before a mirror, it gives forth rays of light in all directions. Amongst these luminous rays, those that fall on the surface of the mirror are, of course, reflected in such a manner that the angle of reflection is equal to the angle of incidence. If another mirror be placed at right angles to the first, and an object be put in the angle, the image of it will be multiplied four times. If the angle be diminished to 60°, six reflections will be seen,