Spiritualism can be blamed on young Margaret Fox’s toes. She could crack them audibly, and, in 1848, the fourteen-year-old teamed up with her younger sister Kate to fool their parents into believing the house echoed with the coded replies of departed souls. Kate asked questions and Margaret’s joints provided what became known as “spirit rapping.” Rumours spread. Within days curious visitors besieged the little house in Hydesville, New York. The girls became famous and spent the next several decades exhibiting their mediumistic powers to rapt audiences across the United States.

The public’s appetite for supernatural wonders soon collided with a grislier reality: the American Civil War and the Franco-Prussian War had produced a surfeit of departed souls, and the bereaved were eager to make contact. Over the years the spiritualist movement came to include diverse theories about supernatural forces (and eventually influenced figures as disparate as Yeats and Hitler), but all adherents to the movement shared the belief that the dead could communicate with the living.

A séance was the most common way to summon a spirit; a medium, usually female, acted as a go-between. Sitting in a dimly lit room, participants gripped each other’s hands and bore witness to odd sounds, or the medium speaking in an altered voice, or furniture lifting into the air. By 1870, spiritualism had 10 million adherents in the United States alone, and a seemingly scientific ally in photography.

After all, what could be more objective—what better proof of the existence of ghosts—than an image caught on a plate of glass through a mechanical lens? The Perfect Medium: Photography and the Occult, an exhibit shown at the Metropolitan Museum of Art in New York last fall and at the Maison européenne de la photographie in Paris, attests to the power of paranormal paparazzi. The show classified photos into three groups: nineteenth-century spirit photographs (disembodied ghost-like faces float above living loved ones sitting stiffly in chairs); striking, abstract Victorian-era photographs of the vital fluids said to animate all objects; and documentary-style photographs from the early twentieth century (mediums are caught mid-levitation or disgorging moistened gauze that masquerades as ectoplasm). Also included were thoughtographs—Polaroids from the nineteen-sixties and seventies in which the image in a medium’s mind is recorded directly onto the print.

Spiritualism’s heyday may have passed, but the photos still draw a crowd. On one of the first Saturdays after the Met show opened, the exhibit’s rooms were mobbed with the sort of audience you’d expect at a carnival: relaxed folk ready to be amused by images drifting up from some chemical bath of the past. The Perfect Medium was thoughtful and informative about individual photographers—it’s clear why the show’s lavish catalogue continues to enjoy brisk sales—but offered scant historical context. The eccentric photos may be fascinating and comical, but the backstory provides the better show.

What now appears like a primitive belief in ghosts was, in fact, a movement allied with progressive causes like women’s rights and with bona fide scientific discoveries. The innovations of the eighteen-hundreds persuaded people that anything was possible. Railways and steamboats changed the relationship between distance and time. New electrical applications revolutionized domestic life and industry. A British naturalist claimed that humans were related to apes. Indeed, the very boundaries of science were constantly being pushed.

Spiritualists may have emerged in reaction to the pure materialism of science, but some of the epoch’s most prominent scientists seriously entertained supernatural theories. For example, Sir William Crookes, who discovered the element thallium, conducted experiments with Florence Cook, a medium. The tests were designed to explore this pressing question: was Cook summoning the actual ghost of Katie King (daughter of seventeenth-century buccaneer Henry Morgan) or psychically projecting just an image of her? Empirical and ethereal pursuits alike were, as Henry James wrote in The Bostonians, “accepted and recognized wonders, natural in an age of new revelations.”

The Bostonians explores a connection that the Perfect Medium failed to hint at: in the eighteen-seventies, the “new revelation” of spiritualism was entwined with legitimate political causes like fighting for equal rights for women. Here was an alliance between two outsiders: a fringe belief in the paranormal that questioned mainstream Christian views and a radical belief that challenged the political status quo. As Barbara Goldsmith notes in Other Powers: The Age of Suffrage, Spiritualism and the Scandalous Victoria Woodhull, her 1998 biography of the famous women’s-rights activist and medium, trance-like states allowed firebrands to voice dissent “without personal responsibility for what they said.” The Perfect Medium fails to mention this most radical spiritualist connection. By the early twentieth century, when the scope of occult photography finally expanded (with action shots of female mediums replacing family-with-ghost portraiture), the feminist–spiritualist alliance had all but vanished.

Ironically, the spirit photographs taken in the early eighteen-seventies—when the politically progressive roots of spiritualism thrived—are the exhibit’s most staid and bourgeois. William H. Mumler shot the early spiritualist pictures during a relatively short but lucrative career as the world’s first official spirit photographer. Mumler worked as an engraver, teaching himself the photographic process on his days off. One day, an improperly cleaned plate left the trace image of a young girl on Mumler’s self-portrait. A visiting spiritualist friend proved an irresistible target. “Not at that time being inclined much to the spiritual belief myself,” Mumler wrote in his 1875 memoir, “and being of a jovial disposition, always ready for a joke, I concluded to have a little fun, as I thought, at his expense.”

The prank eventually backfired, but Mumler profited from it. Spiritualist newspapers in New York and Boston published the print as proof of the existence of ghosts. Interest in such images grew, and demand for this evidence of near-physical contact was so great that Mumler charged ten dollars per sitting at a time when most photographs sold for a few cents. His trademark pose involved a customer sitting in a chair while the deceased floated behind them, hands draped spectrally around their flesh-and-blood shoulders. Each portrait conforms exactly to the sort of prim composition you’d expect from a standard portrait studio (without the ghost, of course), suggesting just how respectable spiritualist beliefs were at the time.

By the nineteen-twenties, occult photography had grown less dreamy and more dynamic, shifting focus from wispy ghosts to blowsy mediums. In the new generation of spiritualist photographs, rather unkempt women grimaced and looked like they were whopping and excreting ectoplasm. Furniture flew around rooms. Humans levitated (clearly fast-exposure snaps of people leaping into the air). These photos are amusing but betray a meagreness of imagination, a narrow vision of the afterlife as simply another variation on life—one that was conveniently easy for the living to apprehend.

In contrast with those images, the photographs of Ada Emma Deane (she produced some 2,000 images in the nineteen-twenties) exude real emotion. Plain, weary-looking people (usually women or couples) face the camera, their folded hands seeming to reveal a certain vulnerability. Above the sitters’ heads hangs a small cloud containing the face of a departed person. The mourners’ torsos are often cropped, relegating the living subjects to the margin of the frame and pulling the hovering ghosts toward the centre. One can’t know whether these were deliberate composition choices, but Deane’s portraits certainly show people looking genuinely sad in situations that are undeniably preposterous. This tension animates her photographs, forcing you to look twice and consider their subjects as individuals who, like us all, are both ridiculous and hopeful.

Which leads us to the inevitable outcome of occult photography: accusations of fraud. Almost all of the photographers featured in the Perfect Medium show were accused of deception at one time or another. William Mumler was acquitted of fraud in 1869. Édouard Isidore Buguet, a prominent French spirit photographer, was arrested in 1875 on similar charges. Unlike Mumler, he did not deny them, and he was fined and sentenced to one year in prison. Upon his release, he became an enthusiastic meta-spirit-photographer, selling much the same images as before, but on the understanding that these were meant to amuse rather than persuade viewers. Even after Buguet admitted under oath to using photographic tricks, devoted spiritualists refused to accept his confession.

One of them was Sir Arthur Conan Doyle. The Sherlock Holmes creator had become a devoted spiritualist after he felt that his son, who died in the First World War, had contacted him during a séance. Conan Doyle took up the defence of various spirit photographers and mediums accused of dishonesty, among them Ada Emma Deane. In 1925, he founded the Psychic Press, a firm that published some forty books in support of the cause. But the Perfect Medium exhibit omits the juiciest chapter of Conan Doyle’s story: his friendship with Harry Houdini, who was as serious about debunking spiritualism as Conan Doyle was about defending it.

Conan Doyle seemed wilfully naive. When two of his favourite mind readers—married couple Julius and Ada Zancigs—confessed their deception to Houdini, Conan Doyle replied, “The only thing I can’t understand is why Z. should wish to hide [his telepathic gift] from you, and mislead you.” Several times Conan Doyle intimated that Houdini’s prodigious talent might be governed by supernatural forces—a compliment Houdini always politely denied. The two men exchanged wonderfully cordial letters for several years and met a number of times, gently rebuking each other but never explicitly disagreeing. The friendship soured when Houdini scoffed at a séance led by Conan Doyle’s wife, which culminated in a feud conducted in the letters’ pages of the New York Times.

By 1920, all US women had obtained the right to vote, and it seemed astonishing that spiritualism could ever have lent force to the serious cause of women’s suffrage. The press frequently mocked Conan Doyle’s spiritualist beliefs, cultivating a climate that forced true believers (including Canadian prime minister William Lyon Mackenzie King) to court the afterlife in secret. Today, spiritualist trappings enjoy a high cultural profile (witness the success of TV shows like Supernatural and Ghost Whisperer), but one that is far removed from the movement’s political and theological roots.

Past the bevy of liars, frauds, believers and jokers, the implicit lesson of the Perfect Medium is that even the most obviously fake images of ghosts ultimately collapse into reality. Maybe that’s why the images from the eighteen-hundreds remain the most poignant: the people in these nineteenth-century pictures, be they transparent or solid, have all passed away—and so, too, has the Victorian belief that technology might reveal a spiritual presence invisible to the naked eye, that our own ingenuity might yield optimistic answers to life’s fundamental questions. That’s a spell long since broken.