I found this in a review of another book: Plato’s Ghost: Spiritualism in the American Renaissance, by Cathy Gutierrez.
“I argue that esoteric teachings of Platonic and Neoplatonic thinking, brought to America through groups like the Freemasons and perpetuated by a new interest in what we would now call world religions, made for a new kind of ethics,” she said. “Knowledge and progress rather than us-versus-them were the hallmarks of progressive religion.”
The book’s title is a reference to Plato’s influence on the movement, but it also evokes one of Spiritualism’s more lurid chapters: spirit photography.
William Mumler accidentally made the first ghost photograph while using a wet-plate process to make a self-portrait. A ghostly figure appeared behind his image. Gutierrez said he showed it to a Spiritualist friend to tease him, but after the photograph was splashed across Spiritualist publications, Mumler recognized an opportunity.
He claimed to become a convert and opened a studio specializing in “spirit sittings,” charging as much as $10 dollars for a 50-cent photograph. He was eventually prosecuted for fraud but it was never clear to some experts who examined his techniques how he did it — despite apparitions of living persons occasionally appearing in his photographs and court testimony showing 10 different ways to fake the images with wet-plate photography.
“Mumler was acquitted on all counts and compared to Galileo, fighting an uphill battle for science in the face of treachery,” Gutierrez said.