GHOSTS, OPTICAL. Many remarkable exhibitions have been introduced in recent years, based on certain simple laws of optics long known to scientific men. The mys terious phantom appearances have led to the designation of ghosts; but nothing sarily either ghostly or ghastly attaches to the exhibition. No new principle has been discovered; it is nothing more than an ingenious application of mechanism to render visible to a body of spectators certain phenomena of reflection and transmission, by varying the intensity of light passing upon or through large plates of glass, and by adjusting the position of the actors with reference to the,glass and to the spectators.
Mr. Direks, in a paper read before the British association at Leeds in 1858, and after wards embodied in a volume, said that his attention had long been directed to this matter. In 1838, he devised something which, under the name of a "transparent mirror," he thought likely to be productive of curious optical effects; but he abandoned the subject for nearly 20 years. In 1856, he happened accidentally to see a body so peculiarly placed as to appear to be transparent; and this led him to make a variety of experiments, to combine an object with its shadow or its reflection in such a way as to render their discrimination difficult. He supposed a theater or room, with spectators placed on an elevated and darkened series of seats; and he showed how they might see two illuminated figures on a stage, without knowing that one was a reality and the other a reflection. By following out the idea, he saw how an actor might get behind a plate of glass, and seem to communicate with the shadow or " double '' of a second actor—how, in other words a living or solid figure might be so associated with a mere phantom, that the two. could play a sort of a drama together, suddenly terminated, per haps by one of them fading away, and vanishing through the wall or furniture of the apartment.
Mr. Eircks constructed a small box or model to illustrate the principle; and as it really contains the germ of most of the large subsequent exhibitions, we will describe it. The accompanying diagram shows the vertical section. ABODE is an oblong box
inclosed on all sides, higher at one end than at the other; there are two doors at the sides of the box; H, I, J,*are three flapped or hinged openings at the top of the box, 'II, for the eye of the spectator, I to put,in the models or figures, and J to admit light; KK is a transparent vertical plate of glass, forMing a partition in the box; L, M are two compartments separated by this partition; N is an opaque screen, to shield a por tion of the compartment L from the eye of the spectator. Now, with small figures or models, very curious optical effects can be presented in this box. Place two figures, Y' and Z, in the two compartments, one in each. An eye at A will see the real figure Z, and the reflection Y' of the figure Y, but not Y itself; and both will appear to be in the same compartment. By opening, in various degrees, of flap J and the side doors F and G, or by closing any one of 'dig three, and opening the two others, the admission of light may be so regulated as greatly to modify the effects. In order that Y' may appear real, no solid body should be placed immediately before or behind it, or its transparency would at once be detected. If the apparatus were large enough for living performers, Z would not see Y', although he would see Y; but by a little rehearsal, Z and Y' might appear to act together. If, omitting Z, two figures exactly alike, or two similar globes or cubes, were placed at Y and Y', then Y' would appear to a spectator like a substance and a phantom combined; and, according to the mode of throwing the light more strongly on the one or the other, the substance might seem to dis solve away into the phantom, or the phantom into the substance, By supposing a small theater or large room to be used instead of a box, living performers instead of model figures, and ranges of seats instead of an eye hole, this apparatus would become a phantom exhibition for many spectators at once.