Pieter Zeeman (May 25, 1865-October 9, 1943) was a Dutch physicist. In 1885, he entered Leiden University to study physics under the guidance of Lorentz and Agnes, and served as Lorentz's teaching assistant. Influenced by Lorentz, Zeeman was very familiar with his electromagnetic theory and had superb experimental techniques. In 1892, Zeeman received the Gold Medal for carefully measuring the Kerr effect. Received his doctorate in 1893. Later, he entered the University of Amsterdam in the Netherlands. In 1896, Zeeman discovered the splitting of atomic spectra in a magnetic field, which was named the Zeeman effect. Lorentz then explained this phenomenon theoretically. They were awarded the 1902 Nobel Prize in Physics.