More about Pepper’s Ghost

Trick used to make a ghost appear on stage next to an actor. A sheet of glass is hung across the front of the stage so that the image of an actor standing in the orchestra pit appears to float on stage. First shown at the Royal Polytechnic Institution in London by J.H.Pepper on Christmas Eve, 1862. Following many subsequent events, Charles Dickens used it during readings of The Haunted Man. Several plays were written specially to use the effect around 1863, but the long-term future of the effect was limited by the fact that the ghost couldn’t speak. Pepper’s Ghost is now used to great effect in smaller scale applications like the Haunted Mansion in Disney theme parks.

A modern equivalent is the ‘holographic’ illusion created using the Eyeliner system by Musion (below). 
A semi-reflective foil is used instead of a sheet of glass, but it must be carefully positioned, and tightly stretched, and the audience must be within a relatively narrow field of view (or they see the edges of the screen).