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A mischievous and sometimes malevolent spirit or energy that is characterized by noises, moving objects and general physical disturbances. "Poltergeist" comes from the German words poltern, "to knock" and geist, "spirit."

Reports of poltergeist disturbances date back to ancient Roman times, appear in the medieval records of Germany, China and Wales, and continue to be reported from countries around the world. Poltergeists have been studied extensively by psychical researchers and parapsychologists since the 1890s. Various theories have been advanced to explain them.

In earlier times, reports of poltergeist disturbances cite primarily rock and dirt throwing, flying objects, loud noises, strange lights and other apparitions, terrible smells, raps, physical and sexual assaults, and shrieks. Modern disturbances include these plus high-tech antics such as lightbulbs spinning in their sockets and telephones repeatedly dialing certain numbers. Physical assaults--biting, spitting, pinching, punching and sexual molestations--continue to be reported in a small percentage of cases.

Poltergeist activity usually starts and stops suddenly. It may last from a few hours to years but rarely lasts longer than a few months. Activity rarely takes place when no one is at home and usually occurs when a particular individual, or agent, is present. In the late 1970s, English researchers Alan Gauld and A.D. Cornell made a computer analysis of 500 poltergeist cases collected from around the world since 1800.

They found 63 general characteristics, such as 24% of poltergeist incidents lasted longer than a year; 58% were most active at night; 48% include rapping sounds; 64% involved the movement of small objects--by far the most common phenomenon; 36% involved the movement of large pieces of furniture; and 12% were characterized by the opening and shutting of doors and windows. In those cases where there was an apparent agent, a person who was the focus of the activity, it was most often female and under the age of 20 years old; 16% of the cases indicated active communication between poltergeist and agent.

Up to about the 19th century, poltergeist activities were routinely blamed on the Devil, demons, witches and the ghosts of the dead. Beginning in the 19th century, poltergeist activities were associated with the physical mediums of spiritualism, who allowed themselves to become temporarily possessed by the spirits of the dead. In more modern times, poltergeists are widely believed to be an involuntary or unconscious thought processes that produce the disturbance. Nandor Fodor was among the first to pursue this theory in his investigations in the 1930s; his conclusions were controversial.

Nandor Fodor

Of the 500 cases since the 1800 analyzed by Gauld and Cornell, only 7% were blamed on witchcraft, and 2%, on demons. Demonic cases resemble possession and are characterized by a seemingly intelligent and malevolent being. Gauld and Cornell noted that in such cases, the supposedly intelligent being does not announce itself as a supposedly intelligent being does not announce itself as a demon, nor is there any clear evidence to prove a demonic presence. Such cases seem to be a matter of interpretation on the part of the victims, who, believing they are haunted by demons, call in clergy for exorcisms, which reinforce their belief. Beliefs about demon and witchcraft caused poltergeists are more common in European U.S. cultures; exorcisms are the typical cures. 9% of the Gauld--Cornell cases were attributed to the spirits of the dead. The most common manifestation was a code of raps and scratches, which were common in mediumistic communications with the dead during the peak of spiritualism.

Perhaps the first scientist credited with taking poltergeists seriously is Robert Boyle, a 17th-century British physicist and chemist. Boyle met a Protestant minister, Francis Perrault, while on a visit to Geneva. Perrault told him about strange, inexplicable noises and movements of objects that occurred at his home in France. Perrault published his story about "the devil in Mascon" at Boyle's suggestion, and it may be the first detailed account of a poltergeist.

Robert Boyle

An early investigator was Sir William Barrett, a 19th-century physicist and one of the founders of the Society for Psychical Research (SPR), London. Barrett personally witnessed poltergeist activity during visits to a home in Ireland where a widower and his five children lived. The center of activity appeared to be focused on the 20-year-old daughter, but Barrett found that the poltergeist respond to his mental requests for knocks. In four successive trials, Barrett silently asked the entity to knock a certain number of times, and each time it correctly complied.

A contemporary of Barrett, English psychical researcher Frederic W.H. Myers, theorized that some poltergeist cases were genuine and noticed that poltergeist phenomena seldom coincided with the phenomena of hauntings.

In the 1920s and 1930s, it was widely believed among researchers that sexual conflicts, especially during puberty, were the cause of poltergeists. While sexual tension may be a cause or factor in some cases, it cannot explain them all. In the 1940s and 1950s, researchers theorized that poltergeists were the projections of repressed emotions, such as hostility and anger.

The modern approach to poltergeists was stimulated by the 1947 Cottage City Poltergeist. The case, which inspired William Peter Blatty's best-selling novel and move The Exorcist, came to the attention of J.B. Rhine at Duke University's Parapsychology Laboratory. Rhine was interested because he realized that many poltergeist phenomena could be conceptualized as large scale PK, which he had begun to explore with dice tests in his laboratory. When a few years later word came of the Seaford Poltergeist, Rhine sent J.G. Pratt and William G. Roll to investigate. Roll went on to investigate several other cases, described in his 1972 book The Poltergeist.</