This illustration dates to before 1876. It shows the apparatus used for a ghost illusion, often referred to as "Pepper's Ghost." The real actors are seen through a large plate of colorless and transparent glass, and from the front surface of this glass rays are reflected that apparently proceed from a phantom taking part in a scene among real actors. Parallel to the glass is a silvered mirror placed out of spectators' sight and receiving the rays from a person, also out of sight of spectators, in which the rays are reflected from the silvered mirror to the plate-glass, and hence reflected so as to reach the spectators and give them the impression of a figure standing on the stage, is sufficiently indicated by the lines drawn in the diagram. Later a second mirror was introduced that allowed the ghost to appear upright - as seen here.