Simply by chance, the physicist Wilhelm Conrad Röntgen discovered light in a test setup, where, according to previous physical knowledge, there should have been none. The special thing about this light is its ability to penetrate matter.
This gave him the idea to photograph the inside of people. In contrast to soft tissue, the hard tissue absorbs the radiation especially well and leaves behind white shadows in the x-ray image. This makes it especially easy to diagnose broken bones. A medical revolution!
(Information taken from “German Stars – 50 innovations,” produced by the Federal Foreign Office, the Press and Information Office of the Federal Government, Invest in Germany, and the Goethe Institut.)