Firstly, orbs. I am not convinced that orbs represent definite signs of Paranormal activity. I am convinced by experiments done by ASSAP and the Ghost Club that most sightings can be explained by dust, fireflys, lens flare caused be reflections etc. After all, when you go into a "haunted house", you are probably disturbing a lot of dust and muck, which are picked up by cameras. But why have orbs become so prominent recently? Is it due to pixelation faults caused by digital cameras?

This brings me to another topic: the use of digital cameras. Yes, they are handy and convenient, but the images are too easy to manipulate. Most models also suffer from a lack of resolution. For instance, you can enhance and blow up a photographic negative many times until the grain shows. You try doing that with a digital image, and the picture dissolves into coloured squares!

Perhaps cameras can pick up what the human eye sees, in the same way as infra red cameras and image intensifiers can see what the human eye cannot. For instance, if you point a TV remote control at an imagine intensifying scope and press a button, you can see a bright light - the infrared emission, which is invisible to the human eye. And, except for a few special cases, the human eye cannot see into the ultraviolet either.

I would love to see technical data describing the spectral response of film and digital cameras. One team, on the Ghosts-UK website, is attempting to prove that orbs are definitely paranormal by positioning four cameras in a square configuration, each camera pointing at one directly opposite. The theory is that if an orb appears in two cameras that are looking at each other, but not the others, then this would prove that orbs are 2 dimensional, and hence must be paranormal, as sparkles caused by water etc. would "apparently" cause 3 dimensional spherical orbs. (Incidentally, one of my absoulute pet hates is when ghost hunters - and even TV people who should know better! - describe image intensifying "night-sights" as infrared scopes. THEY ARE NOT!!!)

Back to orbs: whilst writing this, it occurred to me that there is a pre-digital age precedent: the glowing balls of light seen on American Civil War battle fields, and the like. Often these have been dismissed as igniting methane, but this doesn't account for prolonger, moving balls of light. Methane ignites - "poof" - and its gone!

Tony Cornell of the SPR (Society for Psychical Research) bemoaned the lack of ghost reports in 2002, blaming possible interference by mobile phone masts. But, maybe there are the same number of ghosts, but we are interpreting them differently. Put simply- maybe the typical apparition has mutated or evolved into orbs, thanks to increased levels of EM pollution? So, while I believe that most orbs are bunkum, there are a few that defy explanation so far.

Tantalising pieces of experimental evidence and observations have given us a few clues, but, to refer to the quote on the Society for Psychical Research homepage "a ghost is a mass of data waiting for a correct interpretation". It is fair to mention another quote (which I hope I will report reasonably accurately): "In the world of parapsychology, we not only await an Einstein, but an Aristotle". An excellent comment indeed on crude knowledge that we have into understanding the nature of ghosts.

For the sake of discussion, let us assume that you do believe in ghosts, either by faith, religious or otherwise, or by actually seeing one. You do not need convincing. Now, do ghosts occur "all in the mind" as many critics have cruelly suggested, or do they occur in the enviroment? Hopefully, in the discussion that follows, you will be intrigued as I am and will hopefully want to learn more of these elusive apparitions.

Those who ascribe ghosts as being a figment of the mind have one compelling piece of evidence on their side: the seeming lack of interplay between spirits and their environment: on the whole, they do not move things around although there are of course exceptions to this. One could easily create a theory that accounts for the movement of objects by psychokinetic abilities on the part of the observer or poltergeist phenomena, but this is hardly satisfactory since it attempts to explain one mystery by invoking another. Furthermore, ghosts rarely appear on film or videotape; again, there are exceptions to this. Even with infrared imaging equipment the chances of successfully recording a ghost on film or tape is remote.

Of interest are those cases where, of many people in a group, only a few see the apparition, the others excitedly asking "what do you see?" One may attempt to use 'mass hysteria' or 'mass hallucination' as one possible explanation but for it to be remarkably selective is intriguing to say the least. Also, sometimes video/film equipment does record something. I should also point out here that sometimes cameras have picked up images when even humans don't see anything at all - a physical impossibility surely?

The most widely touted theory regarding ghosts is known as "The Stone Tape" theory, after the excellent BBC TV drama production shown in 1972, and written by Nigel Kneale (the creator of "Quatermass" in the 1950s). In this dramatisation, a group of scientists realise that the image and sounds of the ghost is stored materially in the fabric of an old room and that people sensitive to the recording can play it back in their heads - a fascinating idea since it presupposes that everyone's reaction to the 'ghost' is different - "like eyesight or hayfever". The production is noteworthy for predicting the digital revolution many years early.

"The Stone Tape" theory relies on no 'external' ghost - everything is perceived in the mind, and nothing can be recorded or analysed on their equipment. Such a 'ghost' would follow a predetermined course of action- walking the same path as in life, although how the recording comes to be imprinted on stone is an interesting theoretical question!

This explanation does have many parallels with 'real' ghost stories; the apparition that walk through walls where doors used to be, climb up steps that no longer exist etc. The most spectacular cases of this are at The Treasurer's House in York (where a worker in the basement saw a legion of Roman soldiers, whose legs were cut off at the ankles - the current level of the ground), Westminster Abbey (where a priest is seen walking an inch or two above the ground, marking the settling of the ground since he 'died') and Bell Lane in Enfield, London (where a phantom stagecoach allegedly rushes along - 6 feet above the ground).

Another example of a possible pseudo-tape recording occurred in 1982, when the landlord at the Prince of Wales inn at Kenfig in Mid-Glamorgan (Wales) complained of the sound of organ music and voices. when he had retired for the night. John Marke, an electrical engineer and Allan Jenkins, an industrial chemist, connected electrodes to the wall of the pub after closing time one night. They fed 20,000 volts across the electrodes and locked tape recorders in the room for four hours. When the tapes were analysed, they had succeeded in taping voices (speaking in old Welsh), organ music and a clock ticking (although there was no clock in the room at the time). It was mentioned a few years back that the stones in the wall contain may contain similar substances to those found in modern tape. One unanswered question remains however; would the sounds have occurred in the room anyway even if the scientists hadn't pumped 20,000 volts into the wall?

The "Stone Tape" theory does not explain those instances where ghosts communicate with the observer (sometimes being able to understand a foreign language), but one could always explain this as due to telepathy, which, conveniently does not seem to be a quantifiable subject under current undertanding of physical laws! Also a mystery are those cases that seem to incorporate a 'sentient' ghost, and in this category one could include Poltergeists, which love to put on a good show for the obsevers, but only once recording media (video, tape recorders etc.) have been turned off or directed elsewhere.

One seemingly obligatory feature of paranormal manifestation seems to be a sudden drop in temperature, or a very localised zone of cold air - the so-called "cold spot". Again, this is sometimes real and is measureable on a thermometer, and other time it seems to be a perceived effect. One idea is that the ghost is somehow extracting energy from the air. Alternately, the "cold spot" may not be real and may simply be an artefact of the way the human body reacts to such things, such as shivering uncontrollably when in a state of shock, for instance. Incidentally, a story I vaguely recall from a few years back refers to the fact that one ghost would shift locations to another room if an ioniser was left activated in its original haunted location; more recently, a mention in a Ghost Club circular referred to a build-up of static electricity during a vigil. A friend once related how, during an otherwise uneventful vigil, a digital multimeter (used by, for example, car mechanics and electricians to measure electrical conductivity, voltage etc.) registered a massive surge just before a crash was heard to emanate from an empty room. Alas, I cannot recall which electrical property (voltage, current or resistance) showed the "spike". How all these enviromental effects affect, or are affected by ghosts is an open area for research.

I am also intrigued by the cases where animals can "sense" the presence of ghosts. Dogs often bark at the air, and cats purr as if stroked by invisible hands. One story from York related how a dog, in its attempt to pursue something, ran into a brick wall! It is known that some animals possess superior senses to humans (such as hearing and smell) - do they use these enhanced senses, or do they possess other abilities, enabling them to see ghosts?

Attempts to record ghosts on equipment have met with remarkable degrees of unsuccess (for want of a better word): they are camera-shy even when cornered! At a lodge in Dudley Castle, near Birmingham, the oppressive nature of the building totally vanished when each room had two people, a video camera and a tape recorder installed! Members of ASSAP tried a tactic a few years back at Dover Castle: they reasoned that since ghosts never appear where video cameras are, they would place machines in every room and station themselves in a 'nerve centre', playing Monopoly and waited for things to happen! A good plan, but it never worked.....

In a similar fashion, John Spencer once related a theory that stated that ghosts seem to have a prediliction towards appearances when the witness is least expecting it, and hardly ever during vigils. The theory goes that the logical, rational hemisphere of the human brain may be blocking the appearance of ghosts (it should also be noted that the "artistic vs. scientific" hemisphere theory of the brain seems to be controversial too!). With the permission of the National Trust, an attempt was made by a party at Dover Castle to switch off the logical, reasoning side of the brain by getting drunk (!) and engaging in a musical jamboree. This vigil was unsuccessful as far as seeing ghosts was concerned!

Perhaps the inclusion of equipment changes the nature of the environment; perturbs it in such a way as to prevent spontaneous cases occurring. A lot has been written about the effect that ghosts have on equipment. In Borley Church, a tape was ripped from the spools of an audio tape recorder. In the Enfield poltergeist case, three flashguns rapidly drained of power, tapes machines jammed, tapes were either wholly or partially wiped and a metal part inside one machine was bent. In Rosenheim in Bavaria, a poltergeist somehow created very localised voltage and current surges (which didn't trip the fuses) and even caused investigators to speculate about invisible forces causing direct pressure on the crystal in a microphone, springs inside a telephone and the pen of a instrument that recorded voltage fluctuations on a paper chart. But has anyone ever considered the effects that the introduction of equipment has on the appearance of ghosts? Maybe the electrical and magnetic fields reduce the probability of a presence. In the Australian Humpty-Doo case, the poltergeist would only put on a show once the TV cameras batteries had run out of power, and any witnesses had left the building. An interesting coincidence, or just malice on the part of the poltergeist?

At a Society for Psychical Research talk, council member Tony Cornell mentioned that his infrared-triggered monitoring system (called 'SPIDER', or Spontaneous Psychophsysical Incident Data Electronic Recorder) had been used for 10 years and had not produced one single, verifiably paranormal event on tape. This implies that humans need to be present for manifestations to occur.

A friend has pointed out the corroboration, noted by Michael Persinger, on the corroboration of the Earth's magnetosphere (magnetic field) during occurrences of spontaneous psychic events. This is rather akin to the cases of Spontaneous Human Combustion, which were noted (controversially) many years ago to follow the same trend. Some tantalising experimental evidence does exist that suggests that the stimulation of the brain by an external magnetic field can rekindle old, dormant memories, and 'create' new hallucinations ("Temporal Lobe Epilepsy"). This may explain the many cases of Alien Abduction prevalent througout the world. There might also be an element of chaos and 'non-reproducibility of results' involved here. If the reports are anything to go by, phantoms should appear all over the place. Clearly this is not the case. Perhaps they require certain environmental conditions to be (even approximately) met before they appear?

The Hutchinson Effect is a more recent attempt to mimic poltergeist activity using electrical and magnetic fields. The equipment, when activated, caused items to levitate and various items to move seemingly by themselves. Fires would spontaneously erupt, too. The effect of these fields on the human body is quite damaging, and there is talk of electricity being stored by the body, then released catastrophically. However, if the Hutchinson Effect is a good start to unravelling the mystery of the paranormal, it doesn't seek to explain how such strong electrical or magnetic fields can be generated in the environment. But, if magnetic fields are a partial answer to this conundrum, then a good, cheap piece of equipment that may be of use during vigils is the magnetic compass; any deviation from North caused by a field would be observable. You don't have to have a big equipment budget to perform science!

A recent Discovery Channel programme has suggested the possible link between high rates of spectral appearances and geological fault lines; the evidence was intriguing but faulty, since no control of non-fault areas was performed. The idea is that somehow the stresses in the Earth causes bursts of electro-magnetism, in much the same way as Earth Lights, and this affects eyewitness perceptions. An acquaintance has also suggested this link, but has suggested that the natural conductivity of the surrounding ground may also play a part in somehow causing phantoms some distance away from an earth tremor or fault line. If this phantom fault line connection is proven, then the mechanism will still be a mystery: is it simply due to the natural effect of electricity and magnetism on the brain, or some unknown force?

In the last year or so, a news article (that appeared in the national press and in the SPR journal) presented a discussion that low frequency standing waves, caused by (in this case) a faulty fan, disrupted vision (mainly peripheral vision) and caused a great feeling of discomfort and dread. The article says that this could account for apparitions seen in corridors, where a standing wave is created. This may account for some cases, and the scientific and analytical explanation is to be applauded for attempting to solve this mystery. Naturally, the media tried to conclude that this low frequency sonic wave was the cause of all ghost stories.

The last point I wish to refer to are those periodic phantoms - the ghosts that such re-enact some event on a regular, periodic basis (comparatively rare). For Royal phantoms (say) that appear on the anniversary of their execution in the Middle Ages is bizarre, since with the 10-day shift in dates, when Britain changed from the Julian to the Gregorian calendar, in the mid-18th century, not to mention the various leap days added to the years by now, such sighting should be days or even weeks away from their expected appearances, but they aren't! Nature itself does not operate on a weeks/months/years system - this a purely human invention for the convenience of keeping appointments etc. Surely this must mean some form of human (perhaps psychological) trigger for such periodic events to take place?

An interesting tale is regaled in the book "Ghostwatching - The Ghosthunter's Handbook": a family were regularly disturbed just before midnight by the sounds of footsteps on the stairs, even though there was no-one there. ASSAP were called, and various sensors were placed in locations around the flat; an infrared sensor was situated on the staircase. Nothing was seen or heard though. The next day, however, upon reviewing the output of the sensors, it seemed that, at about five minutes to eleven, the sensors on the stairs were activated and continued to relay data for several minutes. What is interesting in this case is that a few days before, there had been a change from British Summer Time to Greenwich Mean Time. As "Ghostwatching" notes: "The implication was that the sensor had triggered at close to midnight, but midnight British Summer Time. The ghost had 'ignored' the change-over to Greenwich Mean Time".

With regards to re-enactment, I am grateful to a friend, Chris Huff, for pointing out one interesting snippet. In a letter to me, he refers to two famous historical battles - Edge Hill, fought in 1642 and Flodden Field in 1513. Both are famous for their visual and audio 'playbacks': indeed, in the years after Edge Hill, King Charles was so concerned about the tales of fighting at Edge Hill that he sent along a team of investigators, who duly noted the phantom fighting! Edge Hill it seems no longer visualises (the last recorded case was in the mid-19th century), but Flodden is quite active. Sounds of a battle have often been heard and drivers using the A697 have reported soldiers crossing their path. "The difference", as Chris writes, "is that a power line runs very close to the battle field at Flodden, and this may have prolonged the haunting". Chris also points out the effect on a haunting caused by the renovation, rebuilding or remodelling of a building and that this can cause sporadic, spontaneous outbursts. Why this latter effect occurs is, like most of parapsychology, unknown.

It is clear from the meagre collection of experimental data that a great deal of work needs to be done to quantify and qualify the nature of ghosts. Hopefully, with the small but growing band of dedicated amateurs throughout the world some significant advances in our understanding will be achieved. But for those of you lucky enough to have seen a ghost, no amount of argument or debate is necessary for you - you are convinced that they do exist. Now let's try and understand them.