Zeeman, Pieter (1865–1943)

Dutch physicist who discovered in 1896 that when light from certain elements, such as sodium or lithium (when heated), is passed through a spectroscope in the presence of a strong magnetic field, the spectrum splits into a number of distinct lines. He was awarded the Nobel Prize for Physics in 1902 for his discovery, known as the Zeeman effect, of the influence of magnetism on radiation phenomena. He shared the award with Hendrik Lorentz.

Zeeman was born in Zonnemaire, Zeeland, and studied under Lorentz at Leiden. He was professor at Amsterdam 1900–35, and from 1923 director of a new laboratory named the Zeeman Laboratory.

Lorentz proposed that light is caused by the vibration of electrons and suggested that imposing a magnetic field on light would result in a splitting of spectral lines by varying the wavelengths of the lines. Using a sodium flare between the poles of a powerful electromagnet and producing spectra with a large concave diffraction grating, Zeeman was able to detect a broadening of the spectral lines when the current was activated. In 1897 he refined the experiment and was successful in resolving the broadening of the narrow blue-green spectral line of cadmium produced in a vacuum discharge into a triplet of three component lines.

Zeeman's attention turned to the velocity of light in moving media and he was able to show that the results were in agreement with the theory of relativity.