  There is a substantial article on this topic in the 1984 The Encyclopedia of Ghosts by Daniel Cohen. It runs to around five pages of text, which I could, I guess, e-mail to anyone who sent me an e-mail. There is also a substantial article in the Guiley Encyclopedia of Ghosts and Spirits which I might be able to get by the weekend. Or, if anyone were interested, it might be possible to get those articles, and maybe more, from WP:RX. Anyway, if anyone wants at least the first article, drop me an e-mail. Alternately, if anyone wants me to contact RX, or chooses to contact them themselves, it would probably be a good idea to let others know the documents are available.   