What is a ghost?
In spite of the great age of ghostly legend, the range of behavior of ghosts is relatively limited. They soar over graveyards, roam through ruined castles and deserted houses, turn over tables, and other furniture, and produce knocking noises, moans, groans, wails, and "eldritch shrieks." Rarely they are represented as wreaking physical violence upon human beings. More significant than these perfunctory activities attributed to them in legend is their function as mediators or counselors. Because ghosts are supposed to have access to superhuman power and wisdom, the curious and inquisitive of all ages have sought to conjure them, usually through the aid of a "medium," a person peculiarly fitted to communicate with the spirit world. The medium's power consists of an extreme psychic sensitivity, and this faculty is common to the shamans, witch doctors, and medicine men of primitive society, the sibyls of classical antiquity, the seers and necromancers of the Middle Ages, and the mediums and clairvoyants of modern occultism.
In America, in 1850, the curious demonstrations of the Fox sisters awakened new interest in the subject of ghosts and apparitions, though in their demonstrations the ghostly manifestation consisted only of mysterious knockings. As the vogue for consulting spirits grew, the movement took on a religious character, and in 1863 a Spiritualist church was founded. The London Society for Psychical Research, founded in 1882, devoted itself to scientific investigation of ghostly phenomena produced during spiritualistic seances.