“it was common delusion”

Modern Spiritualism, which held that the spirits of former humans could communicate with the living, originated in Hydesville, New York, in 1848,

Belief: The Power of Suggestion.

Allan Kardec is the pen name of the French teacher and educator Hippolyte Léon Denizard Rivail (Lyon, 1804 – Paris, 1869). He is known today as the systematizer of Spiritism for which he laid the foundation with the five books of the Spiritist Codification.
He was already in his early 50s when he became interested in the wildly popular phenomenon of spirit-tapping. At the time, strange phenomena attributed to the action of spirits were reported in many different places, most notably in the U.S. and France, attracting the attention of high society. The first such phenomena were at best frivolous and entertaining, featuring objects that moved or "tapped" under what was said to be spirit control. In some cases, this was alleged to be a type of communication: the supposed spirits answered questions by controlling the movements of objects so as to pick out letters to form words, or simply indicate "yes" or "no."

Of course the tappings, or the rappings were proved to be staged and Quimby's manuscript explains other phenomena.

Rochester Rappings

The Fox sisters were three sisters from New York who played an important role in the creation of Spiritualism. The three sisters were Leah Fox (1814–1890), Margaret Fox (also called Maggie) (1833–1893) and Kate Fox (1837–1892). The two younger sisters used "rappings" to convince their much older sister and others that they were communicating with spirits. Their older sister then took charge of them and managed their careers for some time. They all enjoyed success as mediums for many years.

Healing #5: The trouble is in the mind

All effects produced on the human frame are the result of a chemical change of the fluids with or without our knowledge, and all the varieties and changes are accompanied by a peculiar state of mind. If the mind should be directed to any particular organ, that organ might become deranged or it might not. In either case the trouble is in the mind, for the body is only the house for the mind to dwell in, and we put a value upon it according to its worth. Therefore if your mind has been deceived by some invisible enemy into a belief, you have put it into the form of a disease, with or without your knowledge. By my theory or truth I come in contact with your enemy and restore you to health and happiness. This I do partly mentally and partly by talking till I correct the wrong impressions and establish the truth, and the truth is the cure. I use no medicines of any kind and make no applications. I am no spiritualist after the manner of the Rochester rappings[1] and I am not dictated to by any living man but am guided by the dictations of my own conscience as a lawyer is in pleading a case governed by the evidence. A sick man is like a criminal cast into prison for disobeying some law that man has set up. I plead his case, and if I get the verdict, the criminal is set at liberty. If I fail, I lose the case. His own judgment is his judge, his feelings are his evidence. If my explanation is satisfactory to the judge, you will give me the verdict. This ends the trial, and the patient is released. P. P. Quimby's Writings - December 1859