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Pieter Zeeman, a Dutch physicist known for his discovery of the Zeeman effect, passed away on October 9, 1943. The Zeeman effect is the splitting of spectral lines in the presence of a magnetic field. Zeeman's discovery earned him the Nobel Prize in Physics in 1902, shared with Hendrik Lorentz. He made significant contributions to the understanding of the interaction between light and matter and the nature of magnetism.