Page:The wonders of optics (1869).djvu/193

Rh distance of the screen, a very small picture is shown to them first, the illumination being reduced to a minimum by pulling the cords which act on the diaphragm. The little picture first seen by them will appear to be situated at an enormous distance; but as the lantern is brought almost imperceptibly nearer to the screen, the image appears to advance towards them in a very surprising

manner, at last appearing almost as if it were going to fall upon the spectators.

Robertson, an English optician who was settled in Paris some fifty years since, was one of the first to exhibit the phantasmagoria with success. In order to obtain the best results he used a room some sixty or eighty feet long, and twenty-four wide, which he hung entirely with black. Of this a strip twenty-five feet long