This delusion is very simple indeed, and is produced by placing a card-figure on a screen, and throwing shadows from this upon another screen, by means of several lights, held by assistants. Thus each light throws its own shadow, and if the candles are moved up and down, and about, the shadows will dance, jump over each other, and do all sorts of wonderful things. Robertson, and other public exhibitors, had quite complicated arrangements of this kind, but they all acted on the same principle. But all of those who exhibit to the public the freaks of light are not as honest as Mr. Robertson. You may have heard of Nostradamus, who also lived in Paris, but long before Robertson, and who pretended to be a magician. Among other things, he asserted that he could show people pictures of their future husbands or wives. Marie de Medicis, a celebrated princess of the time, came to him on this sensible errand, and he, being very anxious to please her, showed her, in a looking-glass, the reflected image of Henry of Navarre, sitting upon the throne of France. This, of course, astonished the princess very much, but it need not astonish us, if we carefully examine the picture of that conjuring scene.
The mirror into which the lady was to look, was in a room adjoining that in which Henry was sitting on the throne. It was placed at such an angle that her face would not be reflected in it, but an aperture in the wall allowed the figure of Henry to be reflected from a looking-glass, hung near the ceiling, down upon the "magic" mirror. So, of course, she saw his picture there, and believed entirely in the old humbug, Nostradamus.
But there are much simpler methods by which the vagaries of light may be made amusing, and among the best of these are what are called "Chinese shadows." These require a little ingenuity, but they are certainly simple enough. They consist of nothing but a card or paper, upon which the lights of the picture intended to be represented are cut out. When this is held between a candle and a wall, a startling shadow-image may be produced, which one would not imagine to have any connection with the card, unless he had studied the manner in which said card was cut. Here is a picture of a company amusing themselves with these cards. No one would suppose that the card which the young man is holding in his hand bore the least resemblance to a lion's head, but there is no mistaking the shadow on the wall.
The most wonderful public exhibitions of optical illusions have been those in which a real ghost or spectre apparently moves across the stage of a theatre. This has frequently been done in late years, both in this country and Europe. The audiences were perfectly amazed to see a spirit suddenly appear, walk about the stage, and act like a regular ghost, who did not seem to be in the least disturbed when an actor fired a pistol at him, or ran him through with a sword. The method of producing this illusion is well shown in the accompanying picture. A large plate of glass is placed in front of the stage so that the audience does not perceive it. The edges of it must be concealed by curtains, which are not shown in the picture. An actor, dressed as a ghost, walks in front of the stage below its level, where he is not seen by the audience, and a strong electric light being thrown upon him, his reflected image appears to the spectator as if it were walking about on the stage. When the light is put out of course the spirit instantly vanishes.