The stage illusion known as “Pepper’s ghost,” as seen by the audience, wood engraving, Amédée Guillemin, The Forces of Nature, 1872 (Linda Hall Library)

The stage illusion known as “Pepper’s ghost,” as seen by the audience, wood engraving, Amédée Guillemin, The Forces of Nature, 1872 (Linda Hall Library)

John Henry Pepper

JUNE 17, 2024

John Henry Pepper, an English chemist and popular science lecturer and author, was born June 17, 1821. Pepper was one of the early demonstrators at...

Scientist of the Day - John Henry Pepper


John Henry Pepper, an English chemist and popular science lecturer and author, was born June 17, 1821. Pepper was one of the early demonstrators at the Royal Polytechnic Institution in London, which had been founded in 1838 by aviation pioneer George Cayley, as a place where the public might be educated about science. There were permanent exhibits, as well as regular lectures by such as Pepper, who joined the staff in 1848. Within ten years, Pepper had become director, and sometime before 1862, he published his first book, The Playbook of Metals: including Personal Narratives of Visits to Coal, Lead, Copper, and Tin Mines; with a Large Number of Interesting Experiments relating to Alchemy and the Chemistry of Fifty Metallic Elements; we have an 1862 edition in the library, and it does not appear to be the first. This is a delightful book, filled with wood engravings about anything related to metallic objects, from mines to manufactures. We must write a post on it someday. But not today. Today, we are going to talk about something quite different – an invention that Pepper did not make, but which he appropriated and to which his name is now firmly attached.

The invention is an illusion for the stage, called "Pepper's ghost." An individual in an under-stage room in a theater is strongly illuminated by an arc lamp. The image is projected upward to the stage, where there is a large sheet of glass slightly inclined toward the audience. The viewers look right through the glass and see the image of the hidden figure as if he or she is right on stage. If he or she is dressed as a ghost, they will appear ghostly, as in our first image, and can seem to interact with a real human actor. It is an extremely effective illusion, and was apparently quite popular in the 1860s and 1870s. Our first image, showing just the illusion, was taken from the 1872 edition of The Forces of Nature, by Amédée Guillemin, which was first published as Les phénomènes de la physique in 1868. It was while writing a post on Guillemin three years ago that I first learned about Pepper's ghost. Our fourth image also comes from Guillemin’s book, and shows how the trick works. In this view, the pane of glass, shown edgewise, is represented by a gray slanted line. Our last image of the illusion, which cleverly manages to show what the audience sees, and how the trick works, in one picture, comes from an 1865 issue of the French newspaper, Le Monde Illustré (fifth image).

It turns out that the illusion was first invented by another Englishman, Henry Dircks, who built several models and showed them to theater owners. But his version, if scaled up and applied to existing theaters, would require extensive reconstruction, and owners were not interested. It did not help that Dircks’s model did not produce a very realistic illusion.

Pepper, sometime around 1862, acquired one of Dircks’s models, and he figured out how to modify it (primarily by using an existing orchestra pit as the room for the hidden actor) so that it could be implemented by theaters with little further expense. He himself first demonstrated the illusion at the Royal Polytechnic in late 1862 or early 1863, and it was an immediate sensation, which helped him sell theaters on the idea. Pepper and Dircks entered into an agreement, whereby Pepper would receive the profits, but Dircks would get credit for the initial invention, and they would share the patent. Pepper was careful to include Dircks’s name in his professional and legal papers, but when it came to the public, he used his name alone, and then blamed the press for omitting any mention of Dircks. Dircks protested, and I think even sued, but it did no good. For the public, it was Pepper's ghost. And it still is.

Pepper's ghost is one of the best examples of a law of eponymy called Stigler's Law. Stephen Stigler was a professor of statistics at the University of Chicago, now presumably retired, who observed that no scientific discovery or invention is named after the person who really made it. This is Stigler's Law. Thus the Fermi paradox was actually first formulated by the Russian Konstantin Tsiolkovsky, long before Enrico Fermi, and Dyson spheres were invented by Olaf Stapleton, as Freeman Dyson freely admitted. Stigler even pointed out that his own law of eponymy was first set down by sociologist Robert Merton, making Stigler’s Law itself an example of Stigler’s Law.

The funny thing about pseudo-eponymous names (if we may coin the term) like Pepper’s ghost, is that no matter how much anyone protests, and whatever the merits of their claim, it never, ever, makes any difference. Historians have been complaining about the naming of Olbers’s paradox – discovered by many people long before Heinrich Olbers – for a century now, and it is still Olbers’s paradox, and probably will be forever. Poor Dircks wrote a book in his own defense in 1863, called Optical Illusions: The Ghost!, offering his own name for the phenomenon, the "Dircksan Phantasmagoria,” but of course it had no effect. We do not have this work in our library (although we have several books by Dircks). I hope we acquire a copy someday, so we can build a “Stigler’s Law” collection.  

To return to John Henry Pepper, he lived a full life and died at the age of 78 on Mar. 25, 1900, not quite making it into the new century. He was buried in West Norwood Cemetery, one of London’s “Magnificent Seven” cemeteries. Five years ago, his grave marker was stolen (or perhaps it was an illusion, and someone turned it off). Anyway, it has now been replaced, or turned back on, according to a newsletter of the Friends of West Norwood Cemetery.

William B. Ashworth, Jr., Consultant for the History of Science, Linda Hall Library and Associate Professor emeritus, Department of History, University of Missouri-Kansas City. Comments or corrections are welcome; please direct to