The implementation of whole-body scanners in airport security lines and news about the possibility of using smartphones to detect terahertz radiation have inevitably led to talk about x-ray vision. We often use this as shorthand for “the ability to see through things we shouldn’t be able to see through;” a Google search will give you thousands of hits in reference to whole-body scanners alone. But what do we know about history of the idea? When did it first appear on the scene? And in what ways has it been wielded over the years? Speculation about x-ray vision began almost immediately after Wilhelm Roentgen reported his discovery of the x-ray in the final days of 1895. On Feb. 1, 1896, the British Medical Journal proclaimed: “The application of the discovery to the photography of hidden structures is a feat sensational enough and likely to stimulate even the uneducated imagination.” And indeed, like so many new technologies before and since, it led people everywhere to wonder: how might this serve the more prurient interests? Word quickly spread that x-rays could see through clothing, sowing concern among the decent, decorous elements of late-Victorian society. A London firm advertised “X-ray proof underclothing — especially for the sensitive woman,” and is said to have made a killing with it. In the US, an assemblyman in New Jersey introduced a bill banning the use of x-rays in opera glasses. The discovery stimulated the imagination in other ways as well. When journalist H.J.W. Dam sat down with Roentgen for an interview — the only interview Roentgen granted in the wake of the discovery — the first question he asked was, “Is the invisible visible?” He was referring to the newfound ability to peer inside the living body, but he might just as well have been asking another question, one on the minds of many observers. The x-ray suggested new ways of seeing, new ways of perceiving. And this raised a deeper, perhaps more profound concern: “Is the unknowable knowable?” It didn’t take long for proto-science fiction writers to pick up on this theme. In 1896, only months after Roentgen reported the new ray, French writer and Protestant minister Charles Recolin published his story “Le Rayon X” (“The X-Ray”). The story tells of a Dr. Cornelius Schwanthaler, who, after his talents as a surgeon are called into question, injects one of his eyes with a serum, “an inoculable substance endowed with the astonishing power of making the eyes accessible to Roentgen rays — the famous rays then impassioning all Europe” (an English translation of the story is included in the 2012 collection The World Above the World, from Black Coat Press). Schwanthaler uses his x-ray vision to redeem himself in the operating room, but he has more than job security on his mind: “To see inside everything, to penetrate to the very center of matter, to scrutinize the framework that sustains the human membrane and perhaps discover, in those depths, the secret of the soul and the prime movement of thought was a double dream of medicine and philosophy.” He finds that he sees too much, though — that in gaining access to the heretofore unknown he is no longer capable of perceiving beauty; illusion and hope have been torn away. Ecclesiastes was right, he decides: “Whoever increases knowledge increases sorrow. God has retained the worst part for himself: the truth.” Next: Superman, and the perennial desire to see people without their clothes.