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THE WONDERS OF OPTICS.
of a rack and pinion. There is also a movable diaphragm, which is worked with a couple of cords, by pulling which the aperture is made larger or smaller at will. By moving the lantern backwards and forwards, working
Fig. 52.—The Phantasmagoria.
the rack and pinion and the diaphragm at the same time, the view seen by the spectator seems to advance and recede. The pictures are painted on glass with transparent colours, the glasses being generally about five inches in diameter. To render the illusion perfect it is necessary that the spectator should be placed in a partially dark room, being separated from the operator by the screen already mentioned. Everything being ready, the spectators having but little notion of the
