Harry Houdini and his exposure of the fraud spiritualist, spirit photography, spirit slate writing, ectoplasm, clairvoyance, and other quakery and cons perpetrated on the gullible, by the likes of the Boston Medium Margery, the Davenport Brothers, Annie Eva Fay, the Fox Sisters, Daniel Dunglas Home, Eusapia Pallandino, and other con artists of their ilk.
The whole country got excited by Houdini's campaign against faking spiritualists. He careened through the country, offering money for spirit contacts he couldn't duplicate by admitted magical chicanery. It was a heyday not only for Houdini but for the spirit-callers and there was an equally famous protagonist who thought the spirits could indeed be contacted, Sir Arthur Conan Doyle. A photo at the front records a meeting between Houdini and Doyle and Houdini gives Doyle his own chapter. There's an earlier chapter on Daniel Dunglas Home, the English engineer of spectacular paranormal effects. Houdini raises hell with spiritualists who were giving their (usually paying) clients a vision of heavens to come, and shares the methods used to practice "fake" and sensational spiritualism.
Houdini was nothing if not unrelenting. As a taste of things to come, he ends his introduction with the words: "Up to the present time everything that I have investigated has been the result of deluded brains."