The author describes in this book various aspects of hypnosis. His idea was that any contact with "spirits" was contact with the medium's or the subject's own subconscious. Anything else could be explained by telepathy, which he defined as contact between two or more subconsciouses.

Thomson Jay Hudson (1834–1903), was a chief examiner of the US Patent Office and a psychical researcher, known for his three laws of psychic phenomena, which were first published in the book The Law of Psychic Phenomena in 1893.