While experimenting with electricity, Wilhelm Röntgen discovers the X-ray.

Wilhelm Conrad Röntgen, sometimes transliterated as Roentgen, was a German physicist who produced and detected electromagnetic radiation in a wavelength range known as X-rays. As a result of this discovery, he became the first recipient of the Nobel Prize in Physics in 1901.

An X-ray (also known in many languages as Röntgen radiation) is a form of high-energy electromagnetic radiation with a wavelength shorter than those of ultraviolet rays and longer than those of gamma rays. Roughly, X-rays have a wavelength ranging from 10 nanometers to 10 picometers, corresponding to frequencies in the range of 30 petahertz to 30 exahertz (3×10¹⁶ Hz to 3×10¹⁹ Hz) and photon energies in the range of 100 eV to 100 keV, respectively.