Pieter Zeeman

Today is the birthday of Pieter Zeeman, born in Zonnemaire, Netherlands, in 1865. He studied at Leiden University with Kamerlingh Onnes (who discovered superconductivity) and Hendrik Lorentz. In 1896 Zeeman performed a pivotal experiment to explore the effect of light passing through a magnetic field. He found that the spectral lines for sodium in a flame broadened, or more specifically split into distinct components, due to the magnetism. The “Zeeman effect” confirmed the theory of Lorentz, who had proposed that moving electrons, which are influenced by magnetic fields, produce light. (The theory would get tweaked soon after due to the introduction of quantum mechanics.) Zeeman correctly proposed that his technique would allow astronomers to study magnetic fields on the Sun and other stars. Zeeman also studied how light moves through materials such as water and experimentally confirmed Einstein’s equivalence principle. Zeeman and Lorentz shared the 1902 Nobel Prize in Physics.

Date in History: 25 May 1865