For all that he is remembered for his groundbreaking work in optical illusions, Johann Karl Friedrich Zollner is also ironically remembered for his inabiilty to see the truth behind someone else's deception.
Along with his work in astrophysics (which included the first proof of the Doppler effect in astronomy), Zollner established himself in the fledgeling field of visual perception by demonstrating the effect of visual perspective. His now-classic Zollner illusion is still taught to introductory psychology students more than a century after his death.
By 1875 however, his scientific interests had turned in a new direction. Spiritualism was already in vogue with many prominent scientists such as William Crookes and Alfred Russel Wallace lending scientific credibility to what was happening in seances across Europe and North America. When Zollner visited Crookes in England, it was his intention to develop a formal scientific theory to explain spiritualist phenomena.
After witnessing seances in England and Germany, Zollner came to the conclusion that what he was seeing could be explained with a radical reconception of physics including the concept of a four-dimensional space. One of the things that spurred his interest, unfortunately, was his fascination with the American medium Henry Slade.
Though Slade had recently fled England after he was caught faking his seances, that hardly put an end to his career. Following a sensational trial that generated publicity across the entire United Kingdom, Slade and his manager had fled to France. When the publicity from his exposure made France too hot for him, Slade took his spiritualism act to Germany (this was a pre-Internet age when simply skipping across border was often enough to escape bad publicity). Although Slade's seances were enough to convince Zollner that he was genuine, other German intellectuals were not so convinced.
One of these skeptics was physiologist Wilhelm Wundt, who today is remembered as one of the founders of modern psychology. After founding one of the first formal laboratories for the study of human psychology at the University of Leipzig in 1875, Wundt's research into perception, abnormal psychology, and belief had already earned him enormous respect. One of the reasons he had accepted the professorship at the University of Leipzig was to be able to work with Zollner who, along with his own prominent research into perception, was an enthusiastic support of Wundt's research.
But that all changed in 1877 when Wundt, who had attended many of Henry Slade's seances with Zollner, failed to be convinced that the medium was not faking. The fact that the "messages" Slade was receiving from the spirit world were all in poor German (Slade never mastered the language) was a sticking point for Wundt though Zollner was quick to explain this away. Wundt expressed his doubts in a formal paper, "Spiritualism as a Scientific Question" which still represents a classic in skeptical thought since it represented a formal critique of the spiritualist movement.
In his paper, Wundt pointed out that Slade had complete control of the room and was in a good position to cheat since his hands were out of sight of the other people at the seance. Since Slade's particularl specialty was "spirit writing" using a special slate on which the spirits supposedly wrote messages, the fact that Slade had total freedom to write the messages himself failed to impress Wundt. Given that the messages were often in poor German (when they made sense at all) even though they were supposedly coming from the ghosts of people who were fluent in German, Wundt concluded that Slade was a likely fraud.
Wundt also pointed out that scientists were just as capable of being fooled as anyone else since they had no direct experience with the kind of magic tricks that Slade was likely using. He even suggested that professional magicians were better qualified to detect fraud and that he personally lacked the ability to spot what Slade was doing (he suggested that the seance effects were being produced by "jugglery").
Unfortunately, Wundt' article personally offended Johann Zollner. Not only had he staked his entire professional reputation on Slade being genuine, but he had carried out a series of experiments with Slade that he would later release in a book titled Transcendental Physics. Among the different experiments Zollner ran with Slade, he had the medium link two separate, unlinked wooden rings, turn left-handed snail shells into right-handed ones, and untie a knot whose ends were secured to a table. In his book, Zollner argued that Slade achieved these effects by moving into the fourth dimension.
Regarding Wundt's article as a personal betrayal, he causticly accused his former friend of being a "suckling child" who deserved to be jailed for five years for lying and for plagiarizing his "materialistic" colleagues. Since it seemed fairly obvious that Zollner had become mentally unbalanced by this time, Wilhelm Wundt did not reply to Zollner's rebuttal and the two of them never reconciled.
Zollner's colleagues were not impressed by the experiments described in his book though it was still a best-seller. The English translation ran to three editions in five years despite scathing criticism from numerous skeptics. In an 1881 issue of the Atlantic monthly, one reviewer stated that he "Opens this work of Zöllner with great interest, in the expectation of something substantial and more edifying than the dreary accounts of table-tippings, and the insane conversations of great men who, entering into a Nirvana, have apparently forgotten all they learned in this world, and have nothing better to do than to move chamber furniture. Unfortunately, this hope is not realized."
By the time of Zollner's death in 1882, his reputation was largely in tatters and his dream of proving the four-dimensional nature of the paranormal largely died with him. Once Germany became too hot for him, Henry Slade moved on to Russia to try to recapture his fame in the Czar's court. Even there, he was caught cheating despite making numerous converts. He eventually returned to the United States and sank into obscurity by the time of his death in 1892.
As for Wilhelm Wundt, he reprinted his Spiritualist article a few years later and added an introduction suggesting that belief in the paranormal served a useful function "like beer and tobacco". He rightly concluded that it was a form of superstition that would recur from time to time in "epidemics" which "like pain and illness, disappear from earth only with humanity." Though better remembered as an experimental psychologist than as a debunker, his warning about the nature of gullibility seems as relevant as ever. Certainly modern skeptics will find his treatment by Zollner all too familiar.
It's hard being a skeptic.