Pieter Zeeman

Pieter Zeeman was born on 25 May 1865 in the Netherlands and trained as an experimental physicist at a time when the atom was still a black box. In 1896, he placed a sodium flame between the poles of a powerful electromagnet and watched its spectral lines split - the effect now bearing his name. Hendrik Lorentz supplied the theoretical scaffolding, proposing that oscillating charges inside atoms responded to the field, and in 1902 the two men shared the Nobel Prize in Physics. The Zeeman effect became a critical diagnostic tool, used to probe magnetic fields in everything from laboratory plasmas to distant stars. He continued his work in Amsterdam until his death on 9 October 1943, by which point his experiment had become a cornerstone of atomic and astrophysics.