Science of Pepper’s Ghost illusion

Imagine settling into a plush seat and allowing your eyes to adjust to a darkened theatre as you wait patiently for the performers to arrive. Now imagine that during the performance a ghostly apparition appears on stage and interacts with the other actors – talking, moving, holding objects or even fighting, before slowly dissolving into thin air. Now imagine this isn’t a modern, multimillion-dollar Las Vegas production. In fact, it isn’t even 2018 – this phantasmagoria is taking place in 1863! For a brief period, this incredible ghost illusion was all the rage in Victorian theatre, and modern versions are still wowing audiences today.

The basic principle of what is now referred to as ‘Pepper’s Ghost’ can be traced to the mid-16th century and was explained by the Neapolitan scholar and scientist Giambattista della Porta. His book Magia Naturalis (‘Natural Magic’) describes using a pane of glass to reflect an object positioned behind an observer in such a way that it appears to be in front of the viewer. Undoubtedly, you have had the experience of looking through a window at night and seeing something in the room behind you – a lamp, perhaps – appear as though it was outside. This is the same optical effect described by della Porta, and used to great effect 200 years later.

In the late 1850s an engineer named Henry Dircks delivered an address and paper to the British Association for the Advancement of Science, describing a theatre with a concealed compartment under the audience seating area. This would hold an actor, illuminated by strong chemical lighting. Oxyhydrogen-driven ‘lime light’ would reflect off the actor, onto a large pane of glass set between the audience and the main stage. The audience would view the stage and the principal actors normally, and the glass would provide just enough of a mirror-like surface for the hidden actor to appear as a ghost. Although Dircks’ theatre was never constructed, a working model was successfully exhibited.

Enter John Henry Pepper, a chemist and honorary professor of the Royal Polytechnic in London. Pepper not only popularised Dircks’ invention but also made improvements to the set-up of the stage and the concealed compartments. Most notably, he suggested angling the glass at about 45 degrees towards the audience and having the actors lie against a similarly angled board in the orchestra pit.

In a matter of months Pepper’s name eclipsed Dircks’, and ‘Pepper’s Ghost’ was how the illusion was known on the streets of Victorian London.

Eventually Pepper’s Ghost faded from popularity on the mainstream stage. It did, however, find a new home on the carnival circuit. A sideshow staple for years was the ‘Girl to Gorilla’ transformation: spectators would gather in a darkened tent and watch as a young girl slowly changed into a gorilla. The ape would invariably burst out of his cage and chase the attendees, ensuring an exciting finish. The transformation was accomplished by slowly adjusting the lighting: dimmer on the girl and brighter on the gorilla until the change was complete.

In the late 1960s Walt Disney and his crew of ‘imagineers’ created the famous ‘Haunted Mansion’ at Disneyland, complete with a ballroom full of dancing ghosts. The ‘actors’ portraying the ghosts are animatronic and concealed underneath the rail track used to convey visitors through the mansion. The mansion is one of the most visited attractions at Disney parks, largely due to the magic of Pepper’s Ghost. Today the principle is used in teleprompters and the ‘heads-up’ displays in fighter jets, some cars and various museum exhibits.

In 2008 the National Sports Museum in Melbourne installed a lifesized projection of cricketer Shane Warne using the principle behind Pepper’s Ghost.

In 2012 at the Coachella music festival in California, the illusion allowed deceased rapper Tupac Shakur to sing two songs with hip-hop stars Dr Dre and Snoop Dogg. A similar set-up was used to show Michael Jackson on stage at the 2014 Billboard music awards ceremony.

When modern audiences see Pepper’s Ghost for the first time, the explanation for what they are witnessing is invariably ‘holograms’. The word is constantly mentioned in stories about the Tupac and Michael Jackson events. Rarely is the true effect acknowledged. Holograms do exist, but they use lasers to create and to view the finished effect. Additionally, they weren’t conceived until the late 1940s, nearly 90 years after Pepper’s Ghost made its mark on the stage.