Eduard Ketteler (18.04.1836- 8.12.1900) was a German physicist. He was born in Bocholt (now in Belgium). He graduated from the University of Heidelberg. From 1872 he was professor at the University of Bonn and from 1899 at the Münster Academy.
His research concerned mainly optics, in particular the study of the dispersion of gases, the anomalous dispersion of light, the propagation of light in absorbing media, circular and elliptical polarisation, and the aberration of stars. Independently of H. Helmholtz he developed (1876) a theory of the anomalous dispersion of light (the Helmholtz–Ketteler theory). He constructed a theory of the “elastic light ether”.