Dutch physicist Pieter Zeeman was born #OTD in 1865.
In 1896, while studying the effect of magnetic fields on the light emitted by a sodium flame, Zeeman observed that the spectral lines of the light split into multiple components in the presence of a magnetic field- the Zeeman effect.
In 1902, Pieter Zeeman was awarded the Nobel Prize in Physics, shared with Hendrik Lorentz, for the discovery of the Zeeman effect and its theoretical explanation.