As a fan of both mystery and ghost stories, I loved last week's special Halloween episode of Castle, in which mystery writer Rick Castle and detective Kate Beckett (a.k.a. "Caskett") must solve the murder of one Jack Sinclaire, star of a (fictional) TV reality series called Ghost Wranglers. Sinclaire is filming an episode in a supposedly haunted house when the lights flicker out, there is a sudden cold breeze, and the cameras record his look of horror before it cuts out and the monitor shows nothing but static.

Sinclaire's assistant rushes inside to find the ghost wrangler lying on the floor with his throat slashed clean to the bone. Sinclaire had been locked in the house for the night; his people had searched the premises to make sure he was alone. There are no footprints other than the victim's, and the blood spatter pattern is fairly uniform -- meaning, there was no object or body standing within spatter range when the victim's throat was cut. The film footage shows a camera tripod in the corner starting to move forward on its own accord, as if pulled by an invisible force.

Spooooky! It's just the kind of macabre puzzle that fires up Castle's novelist imagination, and he pursues the ghoulish history behind the house with gusto, undaunted by Beckett's baleful skepticism. Turns out there have been eight murders in that old house, the last in the 1990s, when a husband allegedly murdered his wife and then disappeared. And for all those murders, people claimed the killings were the work of a demon. Castle is thrilled at the prospect of a killer ghost -- um, "Apparition American." Beckett, the hard-nosed cop? Not so much:

Beckett's right that there's usually a perfectly rational explanation. Yet, like Castle, we're suckers for a gripping ghost story. Witness the popularity of TV shows like Medium, Jennifer Love Hewitt's Ghost Whisperer, the new series American Horror Story, or cable TV's documentary-style Ghost Hunters. (Jen-Luc Piquant fails to see what's so compelling about a couple of guys with cheap video equipment who are afraid of the dark, and thinks it's high time they grew a pair. Give her Scooby-Doo any day.)

Modern day ghost stories persist, such as this May 14, 2007, story in Infoworld about "the ghost who sabotaged the mainframe." Hearken to the sad tale of Ernie, who, back in 1971, was head of data processing for an unnamed nonprofit in New York City. Ernie had recently retired, having spent years setting up the department and writing all the programs for the mainframe. A week after retiring, he was killed in a car crash. And soon after, strange things started happening around the office. Nobody took much notice, until the door to the computer room began opening and closing on its own.

Even weirder, instead of the usual cold blast of air that met the workers when they opened the door, there was a warm gentle breeze. Then, the new director of data processing tried to replace the old mainframe computer. The Ghost of Ernie was having none of it. The new system was beset with problems -- until the new director took a stand and got forceful, demanding that Ernie leave things alone. This worked, and once the new system was up and running, the old mainframe was sold as scrap. The Ghost of Ernie was sensed no more.

The author of that article, Jill Terry, admits she used to be such a skeptic, before she found herself arguing with a perceived ghost, and realized that "lunacy is relative." She's not alone: a 2005 Gallup poll found that more than a third of Americans believe that houses can be haunted, with 32% professing to believe in ghosts. Terry's story has some classic tropes of the genre: the warm gentle breeze (or, alternatively, an inexplicable chill), the prickling of the skin, the strange occurrences, and odd sounds. All that's missing is a visual: Ernie, apparently, was a shy sort of specter.

Tools of the Trade

The notion of ghosts has been around for millennia, even making an appearance in the Babylonian epic Gilgamesh. It's all part of man's strong desire for some sort of "life" after physical death, because it's so difficult for us to imagine the prospect of simply "not being."

In honor of Halloween, io9 pays tribute to early "ghost hunters," and the bizarre gadgetry used by same. Back in the day (pre-Victorian era, pre-Ghostbusters proton packs), all you needed was a dousing rod to help you find any unmarked graves where restless spirits lurked.

Candles were believed to turn blue in the presence of a spirit, and any self-respecting ghost hunter would be sure to have a mirror on hand -- legend held that you could see ghosts in them, even when you couldn't with the naked eye, and some folks insisted that ghosts could be trapped in mirrors. This belief persisted well into the Victorian age, except by then they had glass devices known as "tesseracts," 3D "representations" of magical "four-dimensional" shapes that the makers claimed could hold beings from the spirit dimension.

Oh, and salt was a staple outside of the kitchen, since it could ward off evil spirits. Sometimes spooked villagers resorted to cruder means, I guess in hopes of grossing out the incorporeal spirits so much, they'd take their haunting elsewhere:

Witches bowls were common spirit-fighting implements. People made a crude ceramic bowl and filled it with the hair, teeth, spit, and blood, (and often urine), of everyone in the house. They then hid it above the door or buried it under the floorboards near the front entrance.

By the Victorian era, investigators had access to cameras, trying to snap a photo of those elusive spirits. As io9 points out, however, those early cameras weren't exactly of the point-and-click variety. They required long exposure times, and developing the prints left ample opportunity for spots, shadows, and seemingly ghostly mists to creep into the finished product.

"If a ghost photographer had an assistant walk through the background of a slow exposure, there was a spectral form. If they put some radium on a screen behind a person's head, and then lowered the lights just before taking the picture, there was a strange light."

Heck, the lazier sorts would just hand-draw ghostly figures right onto the print.

Cameras are still a mainstay of the modern ghost hunter's equipment: digital cameras, ones that use actual film (assuming one can still purchase film), video cameras, high-tech cameras hooked up to motion sensors. Oh, and audio recorders and a temperature gauge to catch those sudden chills. It's also popular to have more "scientific" devices on hand, like an ion meter, or a Geiger counter in case the ghosts are radioactive, although it could also help ferret out casually stored uranium or something.

The fully tricked out ghost hunter always has an electromagnetic field detector too. In fact, I was surprised to discover that you can purchase something called an "ovilus," a type of EMF detector that supposedly measures the EMF fluctuations in a given room and translates those into displayed words. That's taking things like sonification a bit too far.

For all the public fascination,, no respectable scientist ever took this stuff seriously -- at least not in public -- until the late 19th century. That's when a renowned Harvard professor of psychiatry, William James, joined with a small group of other illustrious scientists to found the American Society for Psychical Research -- the US counterpart to the British Society for Psychical Research.

Together, they sought solid, scientific proof of supposedly "inexplicable" phenomena: ESP, mediums (slate writing, table rapping, etc.), and ghostly visitations, including "crisis apparitions": in which a loved one appears to a person at night, and said person finds out soon after that the loved one has died.

Not-So-Happy Mediums

James and his cohorts formed the basis for Deborah Blum's wonderful book, Ghost Hunters: William James and the Search for Scientific Proof of Life After Death. It's a meticulously researched, engagingly written, and fascinating book, which champions the courage of James and Co. in defying the scientific establishment by undertaking such a pursuit, without turning a blind eye to their failures and tortured humanity. True, the vast majority of the cases the SPR studied turned out to be fraudulent, sometimes ingeniously so. But a tiny fraction -- 5% -- defied all attempts at scientific explanation available at that time.

Physicist Michael Faraday was one of the outspoken skeptics, publishing a letter to The Times of London in 1853 explaining the "secret" behind table tilting, based on his own carefully designed experiment. "The experiment showed that table tilters were often unaware of their own actions," Blum writes. "As Faraday explained, the board was responding to unconscious muscular twitches, 'mere mechanical pressure exerted inadvertently by the turner.'"

On the other side of the fence was Faraday's fellow physicist William Crookes, who was an SPR member, off and on, although Blum reports that the objectivity of his research suffered on account of his susceptibility to the more attractive female mediums he studied. Still, the man was hardly a scientific crackpot, even if he wasn't in a par with Faraday's gigantic stature. Crookes and other SPR members investigated some of the most famous "mediums" of that era.

1. The Fox Sisters. In 1848, two young teenaged sisters, Kate and Margaret Fox, caused a sensation in Hydesvillee, New York, when their family moved into a new house. Soon after moving in, the family was spooked by constant "rappings", among other mysterious phenomena, and Kate and Margaret claimed to have made contact with a spirit they called "Mr. Splitfoot."

The spirit revealed he had once been a peddler named Charles Rosma, murdered five years before, and buried in the house's cellar. The spirit blamed a former occupant of the house, a man named Bell, for the murder, who was shunned by the community despite the lack of evidence. It wasn't until 1904 (56 years after the fact) that the remains of a man were found in the cellar, after a false wall crumbled.

But there was such a hunger for spiritualism, the Fox sisters found themselves instant celebrities, performing seances for the likes of William Cullen Bryant and James Fenimore Cooper, among other luminaries. There were skeptics, too, of course, most notably a patent examiner named Charles Grafton Page, who (rightly) pointed out that the rappings seemed to originate from other the Fox sisters' rather voluminous skirts -- and they refused to be examined for modesty reasons. (Crookes, it must be said, was completely taken in when he examined the sisters in 1871 and 1884. Clearly paranormal research was not his strong suit.)

Eventually the sisters' trickery caught up with them, in part due to a worsening drinking problem. Desperate for money, in 1888, Margaret Fox publicly denounced her former spiritualist career at the New York Academy of Music, demonstrating before a packed house how she could could easily produce raps on cue just by cracking her toe joints. As Margaret later recalled:

"Finding that we could make raps with our feet - first with one foot and then with both - we practiced until we could do this easily when the room was dark. Like most perplexing things when made clear, it is astonishing how easily it is done. The rapping are simply the result of a perfect control of the muscles of the leg below the knee, which govern the tendons of the foot and allow action of the toe and ankle bones that is not commonly known. Such perfect control is only possible when the child is taken at an early age and carefully and continually taught to practice the muscles, which grow stiffer in later years."

2. Eusapia Palladino. An Italian woman named Eusapia Palladino became known in Europe for her mystical powers: she could levitate herself (allegedly), cause the dead to materialize, and communicate with the dead through a spirit guide, among other supernatural "gifts." And she pulled the wool over the eyes of some very prominent intellectuals, including Pierre Curie.

Palladino traveled to Paris in 1905 for a series of seances, and drew the attention not just of Pierre and Marie Curie -- who wondered whether this kind of spiritualism might hold the secret to an unknown energy that could explain the newly discovered phenomenon of radioactivity -- but also future Nobel prize winner Charles Richet, Crookes, Louis Georges Gouay, and Paul Langevin. Pierre described their first seance in a letter to Gouay:

It was very interesting, and really the phenomena that we saw appeared inexplicable as trickery—tables raised from all four legs, movement of objects from a distance, hands that pinch or caress you, luminous apparitions. All in a [setting] prepared by us with a small number of spectators all known to us and without a possible accomplice. The only trick possible is that which could result from an extraordinary facility of the medium as a magician. But how do you explain the phenomena when one is holding her hands and feet and when the light is sufficient so that one can see everything that happens?

Marie Curie was less impressed than her husband by the medium's perceived "powers." Strangely, nobody seemed to attach any significance to the fact that Palladino had once been married to a traveling conjuror.

The SPR conducted one investigation of her in 1908, and again, more thoroughly, in 1910, this time with another conjuror in tow, William S. Marriott. To him, Palladino's tricks were obvious, and he denounced her as a fraud. "When one knows how a feat can be accomplished and what to look for, only the most skillful performer can maintain the illusion in the face of such informed scrutiny," Marriott observed at the time.

For instance, Palladino always made sure the lighting and "controls" were of her choosing and arranged according to her specifications. While a controller's foot was supposed to be in contact with hers at all times, in reality, she rested her feet on top of the controllers' feet, and made sure her shoes were unbuttoned so she could easily slip out a foot undetected to generate some kind of "phenomenon"-- like causing the table to rock or "levitate," or rapping on it with a freed hand or foot. Once she was even caught using her fist wrapped in a handkerchief to mimic a materialized spirit (albeit in dim light -- every medium's friend).

3. Helen Duncan. In the early 20th century, a Scottish medium named Helen Duncan was all the rage because she could (supposedly) excrete "ectoplasm" during seances. This seemed to convince a lot of people at first, although photographs and eyewitness accounts indicate that the stuff Duncan regurgitated was really cheesecloth she'd swallowed and coughed back up. Duncan had been prone to making dire prophecies since childhood, and started offering seances in 1926. By then she was a mother (six kids!) and working part-time in a bleach factory, so she was probably looking for a good distraction.

Duncan seems to have been sloppier in her chosen tricks than other, earlier compatriots, or maybe by then folks had rediscovered a healthy skepticism. She was investigated in 1931 by the London Spiritualist Alliance, although she refused to be x-rayed to check for swallowed cheesecloth (the investigator wasn't buying the "ectoplasm" argument). Three years later, during a seance, one of the clients grabbed a "materalized" spirit which turned out to be all too corporeal. She was arrested and fined 10 pounds for her trickery.

But Duncan really ran into trouble during World War II, when she announced during a November 1941 seance that the HMS Barham had been sunk. This hadn't yet been announced to the public, so the authorities suddenly took a keen interest in her pronouncements, curious as to her source of information. She'd moved from just being a charlatan to possibly jeopardizing national security.

Two Navy lieutenants attended a 1944 seance and arrested a supposed apparition shrouded in white -- which turned out to be Duncan herself. She fell afoul this time of section 4 of the Witchcraft Act 1735, accused of "fraudulent spiritual activity" (as opposed to actually being a witch, which would have carried a death sentence, one presumes). She was found guilty and sentenced to nine months in prison. While she promised to abstain from conducting seances upon her release, old habits died hard. By 1956, she'd been arrested again, and died shortly thereafter.

How could some of the best scientific minds in the Victorian era have been taken in? As James himself observed, "Your belief will help create the fact." The various SPR members -- both US and British -- passed on to the Other Side without ever definitively proving any real psychic powers, the existence of ghosts, or the existence of an afterlife. But it's hard not to feel a wee bit nostalgic for an era when some of the Western world's best scientific minds were brought to bear on the problem. Because that 5% of unexplained events remains just that: unexplained.

Skeptics Supreme

There are still a handful of skeptics seeking more than the usual debunking and unmasking of fraud. They seek a valid scientific explanation for such apparitions, other than the obvious: people can hallucinate or mistake reflections, shadows and strange noises for ghostly activity.

Richard Wiseman of the University of Hertfordshire is one of them. Wiseman is well-known to the skeptic community; I met him at TAM 9 From Outer Space this past summer, where he gave one of the wittiest talks of the entire conference.

His new book, Paranormality, is all about the psychology of the paranormal. It also has the dubious distinction of not being accepted for publication in the US, where acquisitions editors apparently decided that American gullibility about ghosts and paranormal activity meant that a book debunking that sort of thing would never sell. (You can, however, buy it from an online UK store or download a Kindle version, if you're keen. C'mon, you know you want to read about J.T. the Psychic Terrier!)

Over the last 15 years or so, Wiseman has collected anecdotes and measured a wide range of physical conditions at purported "haunted" sites -- light, humidity, sound, and magnetic fields -- and has reported some interesting findings. For instance, some haunted locations have magnetic fields that are stronger than normal. It's possible that the stronger fields affect the brain in some way. It's already known that electrical stimulation of the angular gyrus will make you feel as if someone is behind you, mimicking your movements.

Then there's temperature: people routinely report cold spots or sudden drops of temperature in specific areas, which they believe indicate a ghostly presence. More often than not, it's a draft coming from somewhere in the house, or the result of lower humidity. One of the sites Wiseman studied, Mary King's Close, showed lower humidity in those areas purported to be haunted.

The Close is a series of allegedly haunted streets and houses in Edinburgh. Wiseman's study of the area was carried out in 2005, part of an Einstein Year program sponsored by the National Endowment for Science, Technology, and the Arts. About 70% of the 200 members of the public who participated reported experiencing unusual phenomena, mostly mild (suddenly feeling cold, eg), although some felt they were being watched or touched, felt their clothes being tugged, or heard unexplained footsteps. The results indicate that these experiences are "real" in the sense that people actually feel those sensations.

That doesn't mean they're attributable to ghosts. Per Wiseman: "Although some people may view the results as evidence for ghosts, our findings suggest that participants' expectations, combined with subtle differences in the appearance and physical characteristics of the locations, may affect how anxious people feel when they enter the spaces, and this may create unusual sensations."

Although Wiseman holds that much ghostly phenomena is due simply to human beings' suggestibility, another culprit might be infrasound: low-frequency sound waves below the range of human hearing, that can nevertheless have tangible effects: feelings of nervousness, for example, or hyperventilation, or even a sense of another presence in the room. There's even speculation that these sound waves vibrate at the resonant frequency of the human eyeball, causing visual hallucinations.

Vic Tandy, a British engineer, was a strong proponent of the infrasonic theory, and even pegged the specific guilty frequency -- 18.9 Hz -- before his untimely death in 2005. Officially, he was affiliated with the school of international studies and law at Coventry University, but he was also the unofficial "chief ghost buster."

Tandy wrote two papers for the journal of the Society of Psychical Research: one citing infrasound as the cause of a "haunting" in a laboratory in Warwick, and another citing infrasound as the source of a "ghost" in the cellar at Coventry Cathedral. Lots of otherwise sane people felt uneasy descending into the cellar, sensing some kind of presence, and occasionally -- as in the case of a visiting journalist -- seeing the face of a woman peering over their shoulder.

Tandy himself worked at the Warwick Laboratory, and could personally attest that the effects of infrasound feel very real indeed. He was working late one night, and suddenly felt the hairs rise on the back of his neck. At the same time, he caught a glimpse of a gray apparition out of the corner of his eye, that disappeared when he turned to face it. The culprit? A newly installed extractor fan.

"When we finally switched it off, it was as if a huge weight was lifted," he told the Guardian in July 2000, and he suspected there may also be a connection between infrasound and "sick-building syndrome." Perhaps Ernie the Ghost's spooky effects were due to something like infrasonic vibrations from that old mainframe -- because when Terry and her colleagues got rid of it, the "ghostly presence" disappeared. Alas, Tandy died before he could complete his investigation into why some people are affected by infrasound and others, apparently, aren't.

As for the solution to the Castle murder-by-ghost, I won't spoil things for you. Suffice to say that the series adheres more to the pragmatic philosophy of Scooby Doo than The Ghost Whisperer. And just for the record? Beckett ain't afraid of no ghosts!