An external electric field, meeting it and passing through it, affects the negative as much as the positive quanta of the atom, and pushes the former to one side, and the latter in the other direction.

Die elektrischen Quanten. Career
Stark worked in various positions at the Physics Institute of his alma mater until 1900 when he became an unsalaried lecturer at the University of Göttingen. (Sonderabdruck aus 'Annalen der Physik' 4.