Page:The wonders of optics (1869).djvu/215

Rh image of the objects to be looked at. This mirror sends the image downwards to another placed diagonally at, a third being placed at , and a fourth at. The

horizontal ray, meeting the mirror at, is consequently bent downwards to , then travels horizontally to , when it is reflected upwards to , in which it is seen by the eye. Of course a simple tube without any lenses at all would serve the same purpose, but the fact of its being a telescope serves to distract the attention of the too curious observer.

Another illusion of the same kind is often practised at fancy fairs and bazaars, when a spectator looking into what he supposes to be an ordinary looking-glass, sees his companions instead of himself. The way in which this is effected is very simple. A looking-glass is placed diagonally across a square box, the apertures in the sides being so arranged that the spectator does not perceive that he is looking into a glass that is placed at an angle. Of course the exhibitor endeavours to