Magicians have a long history of exposing the fraudulent methods of mediumship. Early debunkers included Chung Ling Soo, Henry Evans and Julien Proskauer.[59] Later magicians to reveal fraud were Joseph Dunninger, Harry Houdini and Joseph Rinn. Rose Mackenberg, a private investigator who worked with Houdini during the 1920s, was among the most prominent debunkers of psychic fraud during the mid-20th century.[60]
Mina Crandon claimed to materialize a "spirit hand", but when examined by biologists the hand was discovered to be made from a piece of carved animal liver.[143] The German apport medium Heinrich Melzer was discovered to be a fraud in 1926. In a séance psychical researchers found that Melzer had small stones attached to the back of his ears by flesh coloured tape.[144] Psychical researchers who investigated the mediumship of Maria Silbert revealed that she used her feet and toes to move objects in the séance room.[145]
In 1880 the American stage mentalist Washington Irving Bishop published a book revealing how mediums would use secret codes as the trick for their clairvoyant readings.[84] The Seybert Commission was a group of faculty at the University of Pennsylvania who in 1884–1887 exposed fraudulent mediums such as Pierre L. O. A. Keeler and Henry Slade.[85] The Fox sisters confessed to fraud in 1888. Margaret Fox revealed that she and her sister had produced the "spirit" rappings by cracking their toe joints.[86]
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