Zeeman entered Leyden University in 1885 and became mainly a pupil of Kamerlingh Onnes (mechanics) and Lorentz (experimental physics): the latter was later to share the Nobel Prize with him. An early reward came in 1890 when he was appointed assistant to Lorentz, enabling him to participate in an extensive research programme which included the study of the Kerr effect - an important foundation for his future great work. He obtained his doctor's degree in 1893, after which he left for F. Kohlrausch's institute at Strasbourg, where for one semester he carried out work under E. Cohn. He returned to Leyden in 1894 and became "privaat-docent" (extra-mural lecturer) from 1895 to 1897.