An accidental discovery
Röntgen was experimenting with a discharge tube covered in black paper when he noticed that a screen on the table was glowing. The rays passed through the paper and even through a hand. He called them X-rays because he did not know what they were.
Medicine
Within a year, X-rays were in use in hospitals. For the first time, doctors could see fractures without operating. Nobody knew about the dangers of radiation at the time, and many pioneers suffered burns.
Computers and X-rays
Computed tomography (CT), introduced in 1971, combines hundreds of images into a 3D picture. Today X-rays also check luggage at airports and welds in industry.