In the 1890s, when technologies like telephones and automobiles and lightbulbs were still strange and wonderful and new, inventors promised another remarkable device would soon be ubiquitous: the mind-reading machine.
Inspired by the phonoautograph—a new device that showed what sound waves looked like on paper—the scientist Julius Emmner invented a machine that he said could record thoughts. It was simple, really. If invisible sound vibrated in a ways that could be measured, Emmner figured, why wouldn't unseen thoughts do the same?
"Sound is addressed to the ear," he told The Times of Washington, D.C., in August 1895, "yet it may be made visible, a proof of which fact is found in the phono-autograph, in which the vibrations of sound are made distinctly visible." Reporters took him at his word. From that same article: "Mr. Emmner is carefully guarding his secret, but he speaks so enthusiastically of his success that he must have obtained the most satisfactory results so far from his investigations."
Reports of thought-reading machines were common in those days. "Secrets will cease to be hidden in the day when the perfected psychometer comes into general use," the Seattle Star declared in a 1908 article about Columbia University professor Frederick Peterson's lie-detector-esque "mind-reading machine."
Peterson's device was made out of a mirror, a lamp, a horizontal glass scale, and a galvanometer—a tool to measure electric current. It was designed to shine light on a person whose hands would be resting on copper-plate electrodes. That person would be instructed to say any words that came to mind, and if the beam of light shining on him moved more than 6 to 8 centimeters in response, Peterson interpreted it as a "complex" emotion.
Okaaay. So it doesn't exactly sound like the "instrument of precision" the Star claimed it to be, but coverage of Peterson's apparatus clearly highlights the era's cultural obsession with mind-reading as the next big thing in technology. By 1910, a British psychologist claimed that thoughts vibrated enough to be discernible to those "constantly attuned" to the phenomenon. Others in academia focused on the visible form a thought might take—what colors could thoughts be? And what would those different colors mean? In 1938, The New York Times called the idea of a thought-reading machine "delightfully plausible."
Decades of neuroscience research later, most of these mind-reading designs sound absurd. But you can't blame people for wanting to believe. The best real-life technology begins with marvelous, outlandish ideas. Consider the technological advances that adults of the late 1800s had just lived through: Humans could now be captured on camera (1838), there were devices that could snatch sound from the air and record it (1860), people in different houses could have real-time voice conversations by talking into machines (1876), and electric lights had just been installed in the White House (1891)!