Pepper's Ghost: A Masterful Illusion with Staying Power / by Bharat Rao

Excerpt from Magical:

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“One of the most popular illusions ever conceived was first used in a stage production of the Charles Dickens story, The Haunted Man. This clever optical illusion, developed at the Polytechnic in London in the 1860s (now called the Royal Polytechnic Institution), was named “Pepper’s Ghost”. A three-dimensional, ghost like figure would appear on stage, with an ability to move and glide through solid objects. Unknown to the audience, there existed another room adjacent to the stage, and the actions taking place in it were then projected onto the stage using the right placement of a clean sheet of glass. In the case of Pepper’s ghost, this room happened to be below the stage, but it can also work with the room on the same level situated at the correct angle. This effect observed is similar to our experience when we see the contents of the room we are in reflected in the window glass, while at the same time seeing the scene outside the window itself. This is because glass can both reflect and transmit light under some conditions. The underlying technique is used to this day and can be seen at the Haunted Mansion exhibit as well as in an appearance of the Blue Fairy in Pinocchio's Daring Journey at Disneyland in Anaheim, California. When Pepper’s Ghost was at its prime at the Polytechnic, it was a sensation and attracted a steady stream of visitors.”