Apparitions at the spot where some crime was committed are usually thought-forms projected by the criminal, who, whether living or dead, but most especially when dead, is perpetually thinking over again and again the circumstances of his action; and since these thoughts are naturally specially vivid in his mind on the anniversary of the original crime, it is often only on that occasion that the artificial elementals he creates are strong enough to materialize themselves to ordinary sight--a fact which accounts for the periodicity of some manifestations of this class. Another point in reference to such phenomena is, that wherever any tremendous mental disturbance has taken place, wherever overwhelming terror, pain, sorrow, hatred, or indeed any kind of intense passion has been felt, an impression of so very marked a character has been made upon the astral light that a person with even the faintest glimmer of psychic faculty cannot but be deeply impressed by it, and it would need but a slight temporary increase of sensibility to enable him to visualize the entire scene--to see the event in all its detail apparently taking place before his eyes--and in such a case he would of course report that the place was haunted, and that he had seen a ghost. Indeed, people who are as yet unable to see psychically under any circumstances are frequently very unpleasantly impressed when visiting such places as we have mentioned; there are many, for example, who feel uncomfortable when passing the site of Tyburn Tree, or cannot stay in the Chamber of Horrors at Madame Tussaud's, though they may not be in the least aware that their discomfort is due to the dreadful impressions in the astral light which surround places and objects redolent of horror and crime, and to the presence of the loathsome astral entities which always swarm about such centres. [Sidenote: Family Ghosts.] The family ghost, whom we generally find in the stock stories of the supernatural as an appanage of the feudal castle, may be either a thought-form or an unusually vivid impression in the astral light, or again he may really be an earth-bound ancestor still haunting the scenes in which his thoughts and hopes centred during life. [Sidenote: Bell-ringing, stone-throwing, etc.] Another class of hauntings which take the form of bell-ringing, stone-throwing, or the breaking of crockery, has already been referred to, and is almost invariably the work of elemental forces, either set blindly in motion by the clumsy efforts of an ignorant person trying to attract the attention of his surviving friends, or intentionally employed by some childishly mischievous nature-spirit. [Sidenote: Fairies.]