At the end of the 19th century, while studying the effects of passing an electrical current through gases at low pressure, German physicist Wilhelm Röntgen accidentally discovered X-rays—highly energetic electromagnetic radiation capable of penetrating most solid objects. His discovery transformed medicine almost overnight. Within a year, the first radiology department opened in a Glasgow hospital, and the department head produced the first pictures of a kidney stone and a penny lodged in a child’s throat. Shortly after, an American physiologist used X-rays to trace food making its way through the digestive system. The public also embraced the new technology—even carnival barkers touted the wondrous rays that allowed viewing of one’s own skeleton.
Although Röntgen’s lab records were burned at his request when he died, many people have speculated about the sequence of events leading to his discovery. In November 1895, according to one popular account, Röntgen was experimenting with an electron-discharge tube, which he had covered with black cardboard to block the distracting glow caused by electrons striking the tube’s glass walls. To his surprise, he noticed out of the corner of his eye that a fluorescent screen more than a meter away was also glowing. Röntgen dubbed these mysterious rays capable of passing through glass “X” (for unknown) and subsequently tried to block them with a variety of materials—aluminum, copper, even the walls of his lab—to no avail.
When Röntgen held a piece of lead in front of the electron-discharge tube, it blocked the rays, but he was shocked to see his own flesh glowing around his bones on the fluorescent screen behind his hand. He then placed photographic film between his hand and the screen and captured the world’s first X-ray image. Six weeks later, at the close of 1895, he published his observations and mailed his colleagues a photograph of the bones of his wife’s hand, showing her wedding ring on her fourth finger.
More than 100 years after Röntgen’s first X-ray experiments, Gerrit Kemerink, a medical physicist at the Maastricht University Medical Center in the Netherlands, discovered an X-ray machine from the 1890s very similar to Röntgen’s original and used it to X-ray a hand specimen from his hospital. He found that to acquire the image, the hand received a radiation dose 1,500 times greater than today’s dosage—which explains why many people who were X-rayed or who worked with the original machines suffered from radiation burns and loss of hair. There was also a marked difference in the exposure time required: it took Kemerink 90 minutes to image the hand using the 19th century machine, compared to 20 milliseconds using modern X-ray machines. "How you could keep still, I don't know!" Kemerink says.