In 1895 the German physicist Wilhelm Roentgen discovered X-rays whilst experimenting with beams of electrons inside a vacuum tube.

When he applied an electric voltage to the tube, he noticed a very sensitive light detection screen in the room started glowing.

Roentgen theorised that this faint shimmering was caused by a new type of invisible radiation coming off the tube. He named the rays ‘X’ for unknown. In a series of subsequent experiments Roentgen discovered X-rays could pass through materials such as cardboard and human tissue, but not through denser substances such as metal and bone, which absorb the rays.

In 1901, Roentgen became the first recipient of the Nobel Prize for Physics for his discovery. Despite his fame, Roentgen refused to patent the discovery, stating that it belonged to the world. 

Source: Al Jazeera