Zeeman, Pieter (1865-1943) Dutch physicist Born at Zonnemair in the Netherlands, Zeeman (zay-mahn) studied at Leiden University and received a doctorate in 1893. This was for his work on the Kerr effect, which concerns the effect of a magnetic field on light. In 1896 he discovered another magnetooptical effect, which now bears his name – he observed that the spectral lines of certain elements are split into three lines when the sample is in a strong magnetic field perpendicular to the light path; if the field is parallel to the light path the lines split into two. This work was done before the development of quantum mechanics, and the effect was explained at the time using classical theory by Hendrik Antoon LORENTZ, who assumed that the light was emitted by oscillating electrons.