If you were born anywhere between 1920 and about 1950, you probably recall an odd-looking cabinet that once lured customers into shoe stores across the country.

The shoe-fitting fluoroscope used cutting-edge technology—the x-ray—to reveal the bones and soft tissue of the foot inside the shoe, ostensibly for a better fit. For three decades beginning in the mid-1920s, millions of children and adults in the United States, Europe and other parts of the world peered into the machines for an inside view of their usually wiggling toes.

In 1986, the National Museum of American History acquired a fluoroscope, one of perhaps only a handful extant, from a shoe store in northern Ohio. The mid-1930s vintage, walnut-cabinet machine was one of thousands produced by the Adrian X-Ray Company of Milwaukee, Wisconsin, a leading manufacturer of the devices.

From the start, the fluoroscope, invoking the authority of modern science and technology to sell more shoes, functioned more as sales gimmick than fitting aid. O. C. Hartridge, who founded the other major fluoroscope manufacturer, England’s Pedoscope Company, understood the power of this marketing ploy. The machines, he wrote in 1937, proved a "valuable ally of the retailer. By enabling him to demonstrate the correctness of his fitting, it permits him to impress customers with the reliability of his service; and in those rare instances where people insist on having shoes that are wrong, it puts the onus on them."

Children, in particular, loved the quirky machines. Fluoroscopes proved "as attractive and exciting to little customers as ‘free balloons and all-day suckers,’" wrote Jacalyn Duffin and Charles R. R. Hayter, in their journal article "Baring the Sole: The Rise and Fall of the Shoe-Fitting Fluoroscope." Paul Frame, a health physicist with Oak Ridge Associated Universities, in Oak Ridge, Tennessee, recalls his friends in Toronto, where he grew up, going into shoe stores just to stick their feet in the machines: "Seeing the greenish yellow image of your bones was great fun."

The device reached its peak of popularity in the early 1950s, with some 10,000 in use in shoe stores in the United States. Then, as concerns about the potentially damaging effects of radiation grew, the machines began to disappear. (Researchers have yet to determine whether the machine was responsible for any ill effects.) Smithsonian curator Ramunas Kondratas says the fluoroscope represents "the triumph of salesmanship over common sense and a lack of knowledge about the health consequences of certain technologies." In 1957, Pennsylvania became the first state to ban the machines. By the mid-1960s, they were history.

How do people react today when they encounter a fluoroscope? It’s mostly a matter of age. Jim Connor, a curator at the National Museum of Health and Medicine at Walter Reed Army Medical Center in Washington, D.C., where one is on display, says that "visitors over 50 have a flashback experience as they recognize the device. These things are real memory triggers."