Used with
permission of Maiken Naylor, University at Buffalo, Buffalo, NY, USA,
http://ublib.buffalo.edu/libraries/units/sel/exhibits/stamps
Pieter Zeeman (1865-1943) and Hendrik Antoon Lorentz (1853-1928) shared the 1902 Nobel prize in physics for the investigation and explanation of the Zeeman effect: when a spectral source is placed in a magnetic field, the emission lines are found to be first broadened and then split into components as the magnetic field strength increases, and the emitted light is polarized. Lorentz' theoretical work on the electromagnetic theory of light assumed that charged particles called electrons carry currents or transport electric charge, and their vibrations are the cause of electromagnetic waves. The effect of a magnetic field on the light emitted and spectroscopically analyzed conformed to Lorentz' theory, confirming the electromagnetic wave nature of light.