THE PERSPECTIVE GLASS.
At one end of a box, twenty inches long and twelve high and wide, place a concave mirror, of which the focus should be about fifteen inches from the reflecting surface. Blacken the other end inside, and cut an eyehole in it.
Darken the mirror by covering the top in from it to a little less than half way along the box, where a blackened frame should be set, with a sufficient opening to let the mirror reflect any object just under the eyehole at the other end, where a grooved cleat permits picture-slides to be inserted. Cover the other part of the box with ground glass or other transparent media, to keep the inside from being seen.
Fig. 126.
If you must use artificial light, let an aperture be practised in the mirror end, so that the source of the illumination cannot be perceived.
Simple as is this contrivance, the figure drawn on a plane surface will be given a natural perspective as wonderful as entertaining.