Today, people study auras and look to New Age priests. Decades ago, they held séances and consulted mediums. Then (as now), believers longed to prove the skeptics wrong and catch a ghost on film. For “The Perfect Medium: Photography and the Occult,” at the Metropolitan Museum, curators have collected about 120 astonishing photographs of paranormal phenomena. They focus on the period from around 1860 to World War II, a time when the Spiritualist movement attracted much attention and people argued passionately about whether the dead can communicate with the living. In the 1860s, for example, William H. Mumler created a new kind of family portrait, photographing Mary Todd Lincoln with the benevolent spirit of her assassinated husband. In addition to chasing spirits, fairies, and the like, photographers also documented séances and tried, quasi-scientifically, to depict the energy, force fields, and fluids that were believed to emanate from thoughts: Some eminent figures even placed their brilliant foreheads directly on sensitized plates to capture the sublime buzz. This exhibition could be better than a trip to Santa Fe.