Readers of my essays know that I think the skeptics' case against the paranormal is often badly flawed, and that the evidence for psychic powers is much greater than most people suppose. Nonetheless, not all the evidence is equally strong. Some investigations - even some that were noteworthy in their day and continue to attract respectful attention - are less than impressive when viewed with a critical eye. What follows is a case in point.
But first, a brief detour from the world of spirits into the realm of the dinosaurs.
In 1922 Sir Arthur Conan Doyle played a trick on an audience of magicians. As told by Orville Goldner and George E. Turner, "A movie projector was brought in, a screen erected and the lights extinguished. In a brief speech, Doyle said that he would answer no questions about the film he was about to present ... [which] was then screened without titles or comment. The audience was astonished. The [New York] 'Times' reported that 'dinosaurs of one tribe appeared on the screen and rubbed jowls in an affectionate manner. Then entered the tyrannosaurs or dinosaurs of the killing type which preyed on the browsing members of their family. The tyrannosaurs fought among themselves, interlocked their great jaws and wrestled ...'" After more effusive descriptions, the newspaper ended its report by declaring that the monsters on screen "were extraordinarily lifelike. If fakes, they were masterpieces." (The Making of King Kong, 1975; pp. 46-47)
The footage, of course, was fake. It was a reel of stop-motion animation created by special effects pioneer Willis O'Brien for the screen version of Doyle's adventure novel The Lost World. What is remarkable about this story is that no one watching The Lost World today could possibly be fooled by its illusions. The dinosaurs were indeed "masterpieces" of their time, but by modern standards, they are obvious miniatures occupying even more obvious miniature sets, and their movements are jerky and unconvincing. In the era of JurassicPark, I doubt that even a small child would be fooled by O'Brien's jittery latex-rubber creations. In 1922 the footage could fool an audience of magicians, who prided themselves on their ability to detect trickery.
Photo: A family of triceratops, observed by human explorers in the bottom left corner, from The Lost World (1925)
What does this musty old anecdote tell us? Only that people living in the early years of the last century had not yet developed the visual sophistication we take for granted today. The art of trick photography and of related visual illusions was new and unfamiliar. To them, seeing was believing. While they were no less intelligent or well-educated than we are, they were in some respects easier to fool. This fact has important implications when we look at early investigations into mediumship, especially so-called "physical mediumship," which involved the manifestation of physical entities, usually phantoms, in the darkness of the séance room.
One of the more notable researchers in this area was the Frenchman Charles Richet. No mere crank, Richet was a celebrated physiologist honored with a Nobel Prize. His investigations in parapsychology were a sidelight to his main work, but one that he took most seriously. Nor was he blindly credulous. He drew sharp distinctions between the "psychic" entertainers of his day, such as the Davenport brothers (who produced apparitional effects on stage) and legitimate mediums who could be tested under controlled conditions. He conceded that nearly all the physical phenomena of mediumship - spirit raps, table tilting and levitation, and the materialization of phantoms - could be simulated through trickery, but felt that adequate precautions would eliminate the possibility of fraud.
He certainly believed that his own precautions were adequate. Indeed, Richet said that fear of being tricked was "my chief, and even only anxiety throughout my experiments," and he exposed one fake medium, Anna Roth, who claimed to be able to materialize flowers out of thin air. Richet found that she had hidden them on her person.
Despite his initial skepticism, Richet came to believe in most forms of physical phenomena. He felt that a properly attuned "sensitive" could emanate an enigmatic substance called ectoplasm - Richet, in fact, coined this term - and that the ectoplasm could shape itself into a variety of physical forms, including hands, faces, and even whole figures that walked and talked. His most memorable experiments in this regard involved Marthe Beraud, who in later years was known by the pseudonym "Eva C."
Marthe had been engaged to the son of General and Madame Noel, and although the young man died on the battlefield before the marriage, Marthe went to live with the Noels anyway. It was at the Noels' home in Algiers that Richet performed a series of experiments with Marthe, producing what he considered to be spectacular and irrefutable results. These sessions, though given little if any weight by most parapsychologists today, are still cited as solid evidence by some proponents of the paranormal.
Nevertheless, there are reasons to suspect that Richet's experimental conditions were not nearly as stringent as they should have been. Consider his own description of the procedures, as presented in his 1923 memoir, Thirty Years of Psychical Research.
The sessions, he writes, "were held in a small, isolated building over a stable. The window was blocked up and remained shut at all times. The only door was locked at the beginning of every séance. It is the only room in the building, and before every séance everything was minutely inspected by [Richet's associate] Delanne and myself. Two curtains were stretched across one corner of the room... so as to make a kind of dark cabinet ..." As was almost invariably the case in physical mediumship, the enclosed space, or cabinet, was said to be necessary so that the medium could concentrate her psychic powers.
Richet, Delanne, General and Madame Noel, and a woman known in the reports as "Mademoiselle X" were all present for the séances. In addition, Marthe's two younger sisters, Marie and Paule, were in attendance. At times, there was another participant, an African woman named Aischa, apparently a member of the household staff. When Aischa was there, she actually sat in the curtained-off cabinet with Marthe. What purpose she served, and why she was allowed inside the cabinet, are questions Richet does not raise or answer. He does claim, "The part played by Aischa seems absolutely nil. Mme. Noel made a point of her being present, but our best results occurred in Aischa's absence." He also says, reflecting the casual racism of his era, "It is useless to incriminate Aischa, an unintelligent creature sitting passively beside Marthe ..."
A couple of concerns might occur to us at this point. First, why did Madame Noel want Aischa to attend the séances? Possibly she was worried that Marthe might suffer harm while in her entranced condition, and ordered the servant to stay close to her so as to offer protection or sound an alarm. But there is a less charitable explanation - that Aischa acted as Marthe's confederate.
Second, how closely were Marthe's two younger sisters observed during the séances? Richet states that they "sat far from the curtain," i.e., the cabinet. Even if they were initially seated far away, could they not have come closer once the lights went out? How certain is it that one or both of the sisters did not smuggle props into the room? Were they searched? Was Aischa searched?
The answer to each of the two last questions appears to be no. In fact, astonishingly enough, even Marthe herself was not searched. Richet comments, "Marthe was not undressed, but in that very hot climate she wore only a thin dress, and as I made magnetic passes over her to awake her from trance, I could be sure, by passing my hand all over her body, then she had nothing on but this thin garment."
Surely this is inadequate. By "magnetic passes," Richet means hypnotic gestures (hypnotism being originally associated with "animal magnetism"). These passes would not have touched the body, and of course no actual magnet was used. Moreover, Richet carried out this procedure only when waking Marthe from her trance - after the phenomena had been observed. There was nothing to prevent her from hiding items in her dress, carrying them into the cabinet, deploying them in the séance, and then secreting them somewhere else or giving them to Aischa before being "awakened."
Richet states that the room was lit by a photographer's red lamp. "Everything that took place in the room could be seen perfectly well, and I am absolutely certain that no stranger could enter during the séances. As Marthe was not tied, nor her hands held, the conditions of control were less severe than in [a previous] case; they were, however, strict enough to allow of a definite opinion."
Again, this hardly sounds adequate. There were no restraints on the medium. She was free to carry out any sort of trickery. While reddish lamplight was preferable to the total darkness that often prevailed in séances, it probably still did not permit clear viewing.
Even so, Richet feels confident enough to state, "It is therefore established that there was no instrumentation and no theatrical accessories that the medium could use, and that no stranger could enter the room."
If one can judge by his own description, his confidence is badly misplaced. Instrumentation or theatrical accessories could have been smuggled in by Marthe under her dress, or by either of her sisters, or by Aischa. For that matter, since the stable was on the property where Marthe lived, there was probably nothing to prevent her or an accomplice from entering it prior to the séance and stashing items in a secret location - under a loose floorboard, for instance. There is also no way to ascertain whether or not an accomplice might have hidden on the premises before the search was conducted. Someone hiding under the floor or behind a sliding panel in the wall or ceiling would not be found.
Richet then describes one of the more noteworthy appearances of the phantom customarily summoned by Marthe - the spirit, it was said, of an Indian prince named Bien Boa. Although the scientist was skeptical of the claim that Bien Boa was actually who he claimed to be - believing instead that the apparition was an ectoplasmic production of Marthe's subconscious mind - he nevertheless had no doubt as to the phantom's corporeal reality. How could he, when Bien Boa had taken form right before his eyes?
"....after a long wait," Richet writes, "I saw close to me, in front of the curtain which had not been moved, a white vapour, hardly sixteen inches distant. It was like a white veil or handkerchief on the floor; it rose up still more, enlarged, and grew into a human form, a short bearded man dressed in a turban and white mantle, who moved, limping slightly, from right to left before the curtain. On coming close to General Noel, he sank down abruptly to the floor with a clicking noise like a falling skeleton, flattening out in front of the curtain. Three or four minutes later ... he reappeared rising in a straight line from the floor, born from the floor, so to say, and falling back on it with the same clicking noise.
"The only un-metapsychic explanation possible ["metapsychic" was Richet's term for "paranormal"] seemed to be a trap-door opening and shutting: but there was no trap door, as I verified the next morning and as attested by the architect."
When I read this, my first thought was that Richet had looked in the wrong direction. Rather than inspecting the floor for a trap-door, he should have inspected the ceiling. I thought that the bearded phantom could have been a life-size marionette, operated on strings from above. In this scenario, an accomplice of the medium would have lowered the figure from the ceiling.
This hypothesis, however, is probably wrong. A more plausible explanation is suggested by Richet's description of a photo taken of Bien Boa: "A thick, black, artificial-looking beard covers the mouth and chin ... Bien Boa would seem to be a bust only floating in space in front of Marthe, whose bodice can be seen.Low down, between the curtain and Marthe's black skirt, there seem to be two small whitish rod-like supports to the phantom form."
Presumably the beard was "artificial-looking" because it was, in fact, artificial, and Bien Boa "seem[ed] to be a bust" because he was a bust. But what is really interesting are the "two small whitish rod-like supports to the phantom form" - the kind of supports that are still used in puppetry today, to manipulate so-called "rod puppets" from behind or below.
Photo: Bien Boa hovering in front of the curtain, with his "artificial-looking beard" and legless body. Note that the curtain is partly open, allowing manipulation of the figure from behind
A rod puppet would make an altogether more satisfactory phantom than a marionette. No overhead wires or hidden accomplice was needed. Marthe, operating behind the curtain, manipulated the figure herself. The puppet, lying flat, was pushed out from underneath the curtain, its appearance concealed by smoke effects ("a white vapour"). Marthe then pulled the figure upright ("it rose up still more, enlarged, and grew into a human form"), and made it walk ("limping slightly" - i.e, moving jerkily). After a few steps (which Richet describes elsewhere as "halting"), the puppet was simply made to collapse to the floor, "with a clicking noise like a falling skeleton" - the "clicking noise" of its hollow or lightweight components. The act was then repeated ("he reappeared rising in a straight line from the floor ... and falling back on it with the same clicking noise").
"The phantom of Bien Boa," Richet writes, "appeared five or six times under satisfactory conditions in the sense that he could not be Marthe masquerading in a helmet and sheet. Marthe would have had not only to bring, but also to conceal afterwords, the helmet, the sheet, and the burnous [in modern spelling, "burnoose" - a hooded cloak]. Also Marthe and the phantom were seen at the same time. To pretend that Bien Boa was a doll is more absurd still; he walked and moved, his eyes could be seen looking round, and when he tried to speak his lips moved."
But rod puppets can move and walk around, and the impression of eyes moving and following the viewer can be created even in a painting. It is interesting that Bien Boa merely "tried to speak" - apparently he could actually speak only through Marthe herself, whose voice at such times was described as "halting and wooden and guttural."
Richet himself points out, though without attaching much importance to the fact, that in one photo of Marthe and Bien Boa together, Marthe's left sleeve "appears empty, though the vacuity is not complete." Could the sleeve have been empty because Marthe's arm was actually engaged in holding up the puppet figure at her side?
It might be objected that only a child could be tricked by a puppet, a thing of stiff rods supporting a sheet and a mask. No adult, and certainly not a sophisticated scientist alert to any sign of chicanery, could be taken in by such a device.
But remember O'Brien's dinosaurs, and the magicians who fell for them.
Although a rod puppet could explain some of Bien Boa's appearances, there were other times when a living person must have masqueraded as the phantom. On one such occasion, Richet asked the phantom to blow into a flask of water, which Bien Boa did, producing visible bubbles. A possible explanation was provided by a coachman in General Noel's employ, a man named Areski, who claimed that he had "played the ghost." This assertion was made only after Areski had been fired for theft, and it may be that he was simply seeking revenge on his former boss. Aleski's claim is made somewhat less probable by the fact that he said he had disappeared via a trap door, but as we have seen, no trap door was discovered.
In any case, it was not necessary for the coachman to act as an accessory. There were others who might have been in a position to impersonate the phantom - Aischa for example, or one of the two younger sisters, or Marthe herself.
Sometime after Marthe completed her experiments with Richet, the story circulated that she had confessed to producing her effects by trickery. Whether or not she actually did confess remains unknown. The story was attributed to an anonymous source and could never be checked, and Marthe evidently did not endorse it.
Indeed, she went on to work with other researchers. In these later sessions, far more extensive precautions against trickery were said to have been taken. Marthe was stripped and searched before each séance, a search that included the examination of her hair, nose, mouth, armpits, knees, and even her rectum and vagina. On some occasions she was said to have been given an emetic, forcing her to void her stomach and esophagus, thereby removing any suspicion that she had swallowed some muslin to be later regurgitated as ectoplasm. In addition, detectives were employed to follow Marthe and investigate her background and associates; they found no evidence of fraud.
This all sounds convincing enough, except that if Marthe had secreted her materials in the séance room prior to the session, then no amount of bodily searching would avail the investigators, and if she was acting alone, then the detectives' trail would inevitably be cold. In any case, photographs produced in these later investigations are no more believable than those taken of Bien Boa.
Richet himself seemed to acknowledge this. When writing of some "faces" that seemed to extrude from Marthe's body, he admitted, "... these faces (and many others) are not in relief. They are like drawings; and, more strange still, something like folds in the paper of a drawing are visible; as if a drawing had been folded three or four times and unfolded to be photographed, so that the materializations are in these cases flat, or materialized drawings. These folds in flat images gave immense suspicion of fraud. But that presumes extreme stupidity in [Marthe], since she knew that the photographs would be taken."
Perhaps it merely presumed extreme boldness in Marthe, who by that point had found that she could get away with almost anything.
Photo: Ectoplasmic "face" produced by "Eva C." (Marthe Beraud)
Great latitude was given to the medium when photographs were taken. Richet complains that photography interrupted a session, necessitating "intermissions of observation while the curtain is drawn," because "continuous observation is not permitted by the medium when waiting for the photograph." Marthe herself would signal the photographer when it was time to take the shot. Obviously this setup gave her both the time and the privacy necessary to arrange her materials for the camera.
During these later researches, accounts of her manifestations became ever more elaborate. Marthe was said to emit ectoplasm from her mouth, navel, breast, and armpits. The damp, enigmatic material, which "resembles moist and sticky muslin," proved elusive. Richet says that when one researcher tried to seize a strand of ectoplasm, he "could grasp nothing, for it disappeared at once." In other instances, some ectoplasm was recovered and subjected to microscopic examination, revealing "vestiges of epithelium, bacterial forms, and a notable amount of fat. In certain cases it looked like vegetable tissue; in others like a filament of cotton surrounded by a granular substance whose nature could not be determined."
One seemingly paranormal phenomenon eagerly cataloged by Marthe's later investigators was the production of pariffin gloves - molds of human hands produced in paraffin wax, ostensibly during the séance. It was asserted that these molds, which endured long after the séance was over, constituted proof that a hand had materialized in the liquid wax and then dematerialized after the wax had set. How else, it was asked, could such molds have been made? If a living hand had been inserted in the wax, it would have broken the mold when it was removed. In fact, when artisans made such molds of living hands, they had to separate the mold into two pieces to release the hand, then reattach the halves. Richet wrote, "We defy the skilful modellers to obtain such moulds without using the plan of two segments separated by thread and afterwards reunited."
It took many years for "skilful modellers" to take up this challenge - but in 1997 a pair of Italian investigators, Massimo Polidoro and Luigi Garlaschelli, decided to give it a try. They found that it was possible to make an excellent paraffin glove of a living hand and to extract the hand, slowly and carefully, without cracking the mold. The extreme maneuverability of the hand allows it to work its way free of the mold in the same way that one might free one's hand from a very tight glove. Even when the mold in question was extremely fragile, made with only a thin shell of wax, it was still possible to extricate the hand and leave the mold undamaged. Whether this technique was actually used during the séance, or was employed in advance, with the completed molds hidden in the room and produced when needed, may never be known. It is worth pointing out that the report on producing paraffin gloves was published in the Journal of the Society for Psychical Research, as just one of many skeptical assessments of paranormal phenomena to appear in that publication. ("Spirit Moulds: A Practical Experiment"; Vol. 62, No. 848; July 1997 p. 58-62).
Some have maintained that Marthe would not have subjected herself to years of tedious testing merely to pull off a hoax. Brian Ingliss writes, "There was no money in it for the investigators and little enough for the medium; certainly far less than she could have earned displaying her powers on the halls. And there was no kudos; such research attracted only mockery, if it were noticed at all." (Natural and Supernatural, 1992; p. 435)
But human motivation is a tricky thing. There are other rewards besides money and fame. Doctors are familiar with the condition known as Munchausen syndrome, in which a patient makes himself ill - sometimes seriously so - in order to garner the attention of the medical staff. Members of religious cults may surrender all their worldly goods and personal freedom, abandoning even their families, for no obvious gain. Recently there have been news reports of people who opt to have healthy limbs amputated because of an irrational aversion to their own bodies.
Plainly, it is not enough to say that Marthe and her investigators had no reason to cheat or to delude themselves. People's reasons are not always reasonable.
In making these points, I don't mean to say that all the evidence of physical mediumship is equally suspect. Table tilting and the levitation of tables, other objects, and even persons are phenomena that have been widely reported and reproduced. So-called "spirit raps," a catchall term for a variety of sounds and vibrations, have been known since antiquity. There are even cases of spirit manifestations that may be strong enough to count as evidential – as in some sittings of the famed 19th century medium D.D. Home. By no means am I dismissing the great mass of evidence for these assorted phenomena, many of which I believe to be genuine.
But for Marthe Beraud, what evidence is there? In the end, all we have are paraffin gloves that could have been faked, photos of apparitions and ectoplasmic extrusions that are less than convincing, a record of Richet's inadequate precautions against cheating, and the reports of witnesses who may or may not have been reliable.
On the other hand, in Marthe's favor, we have the insistence on the part of later investigators that thorough precautions were taken and that the phenomena continued and became even more impressive. Certainly if we take the researchers at their word, then no amount of trickery can explain what they saw.
Here, for example, are Richet's contemporaneous notes on a session with Marthe:
"In the quite small room which I search thoroughly ... Mme. de S., whom I will call A., is alone with Marthe and myself. We both sit close to Marthe, so close that I can touch her hands without getting up. The light is an electric lamp covered with red stuff, and gives light enough to show all the white in Marthe's garments and the white ribbons in her hair. After about half an hour, I open the curtains and see a faint luminosity on the floor, so feeble that I doubt its reality. By degrees this light increases; it is like a small, luminous handkerchief lying on the floor. Marthe's whole body is motionless. The luminous spot grows; its outlines are milky, undefined and cloudy, less defined and softer than would be those of a woven stuff. It approaches the chair, increases in size, and takes a serpentine form which tends to rise towards the left arm of A.'s chair. Its outlines become sharper; it is like a mass of half-empty fabric. Then follows an extraordinary sight: a point detaches itself from the mass, mounts up, bends and directs itself to Marthe's breast, her hands being held the whole time. The point continues to advance in a terrifying way like an animal pointing its beak; and as it advances, on the rigid stalk there appears a thin gauzy structure like a bat's wing, so thin and transparent that Marthe's garments can be seen through it. The stem is easily distinguishable from the membrane round it. Marthe is motionless and speaks at intervals.
"I can approach and look very closely, only an inch away. I see what looks like a swollen substance, moving as if alive, and changing its form. For five or six minutes I examine it attentively. I see extensions like the horns of a snail, which start up to right and left; these horns are like transparent gelatin, they project from and sink back into the more defined central mass."
And in a later session:
"Fairly good light. The curtain remains closed for about an hour. I open it; a white spot on the floor grows rapidly, and two horns protrude from the mass X, from which other horns appear, very mobile, pointing in every direction. The mass, then much larger, disaggregates into particles, taking on the semblance of a hand ... a greyish hand with ill-defined outlines.
"This hand moves, looking like the hand of a mummy emerging from some stuff; it raises and lowers itself like a hand. Marthe's hands are firmly held by me and are quite motionless. The fingers of the ectoplasm, thin and spindly, seem to end in cloudy masses. I can examine them very closely. I touch one of these spindles; it feels like a cold liquid. I can press it and it feels like the bone of a finger covered with skin. The hand rests on my knee and I feel the slight friction of a body of little resistance. The hand then rises of itself, swaying on a long stem that connects it with the floor; it falls back on to the floor with a slight noise; it remains there and I think I see the two bones of the forearm as though wrapped in cloudy muslin.
"The hand then rises, bends, and moves towards me. The wrist is lowered and the fingers pendant; they move and there seems a torsional movement of this strange fore-arm. I still think I see the carpal bones in the muslin-like cloud.
"The hand rests on my knee again. I feel its weight (very light), it makes little movements at my request that I can feel quite well. Then Marthe says to me, `That is the muscles beginning to form,' and I see, or I think I see, something dark in the space between the two bones. The hand rises and moves very close to me, having no connection with the ground but a slight white trail. It then falls to the ground with a slight noise, rises from it and suddenly disappears at the moment that Marthe gets up."
The key to the whole question is in a few words of the preceding paragraph: "I see, or I think I see."
If Richet really did see these things, then his confidence in Marthe's genuineness must have been justified. But did he only think he saw them? In the dim light (described only as "fairly good"), in the excitement of the moment, perhaps urged on by Marthe's own suggestions ("That is the muscles beginning to form"), did he see what was really there or what he wanted to see?
It may never be possible to know. But we do know that when an audience of magicians watched Willis O'Brien's animated dinosaurs, they saw something that no modern viewer would perceive.
If there are fewer spirit materializations in the modern world, perhaps it is because we now see with clearer eyes.
Postscript: After posting this essay, I became aware of some comments by psychical researcher Montague Keen which bear directly on the topic. These comments are found in Keen's essay "The Scole Investigation: A Study in Critical Analysis of Paranormal Physical Phenomena," which can be read in its entirety at www.survivalafterdeath.org/articles/keen/scole.htm. (Incidentally, I highly recommend www.survivalafterdeath.org as a source of articles and book excerpts on the issue of life after death.)
Keen criticizes "the assumption that, because the purported [spirit] communicators do not behave as we would expect, do not give us the winning lottery number, the resolution of Fermat's last theorem or the date on which the next seismic heave strikes the San Andreas Fault, they must be figments of the medium's brain ...
"The assumption underlying this criticism has very widespread implications. Among the most frequently reproduced photographs designed to illustrate the obviously fraudulent nature of so-called ectoplasmic images of the past are those of somewhat grotesque and crude paper masks. They featured in Baron von Schrenck Notzing's celebrated series of tests on a medium known to history as Eva C. [Marthe Beraud]. But a study of the elaborate precautions taken by the medical investigator and his two qualified colleagues shows that, if Eva had contrived to smuggle in the mask during the séance of August 7th 1912 (to take one example), she would have had to have packed and concealed about her body a plastic mask of natural size, a head shape of paper or textile fabric, and a quantity of a substance, the size of a hand, which would leave traces on her dress. In spite of all the precautions, including prior examination of her bare body, hair, mouth and ears, and being sewn into a séance costume which was found after the sitting to have remained unopened, the medium would have had to pack this equipment in or on her body, open it up, use it before the cameras, fold it all up again and conceal around her bare body so that it would remain undetected despite a subsequent body search. Such precautions, which extended to hand-holding and the unexpected shining of torches and taking of flashlight plates, have had not the slightest effect on those who consider it obvious that no genuine spirit would want, even if able, to project an image with such manifest signs of crude human fabrication."
This is a fair point, well worth considering. Nearly a century after the Beraud investigations, the debate goes on.
Postscript: Indeed it does. I continue the debate in "Of Dinosaurs and Phantoms: The Sequel," posted here.
Orville Goldner and George E. Turner, The Making of King Kong, 1975
Charles Richet, Thirty Years of Psychical Research, 1923; Ch. 3, "Ectoplasms (Materializations)" can be read online at freewebs.com/afterlife/richetecto.htm; the entire book can be downloaded as a Zip file at myweb.wvnet.edu/~gsa00121/books/richet30.zip.
Massimo Polidoro and Luigi Garlaschelli, "Spirit Moulds: A Practical Experiment," Journal of the Society for Psychical Research, Vol. 62, No. 848; July 1997 pp. 58-62; www.luigigarlaschelli.it/Altrepubblicazioni/moulds.htm
Brian Ingliss, Natural and Supernatural, revised edition, 1992
Montague Keen, "The Scole Investigation: A Study in Critical Analysis of Paranormal Physical Phenomena," www.survivalafterdeath.org/articles/keen/scole.htm