Wilhelm Ludwig Franz Hallwachs (9.07.1859—20.06.1922) was a German experimental physicist. He was born in Darmstadt. He studied at the universities of Strasbourg and Berlin. In 1883 he received the degree of doctor at Strasbourg. In 1884 — 93 he worked at the universities of Strasbourg, Würzburg and Leipzig. From 1893 he was professor at the Higher Technical School in Dresden (rector in 1921 — 22). His research concerned the study of the photoelectric effect, optics and electromagnetism. He rediscovered the photoelectric effect, showing that a metal plate becomes positively charged when it is irradiated with short-wavelength ultraviolet radiation (1888). He detected the phenomenon of photoelectric fatigue. He designed a number of electrical measuring instruments (a quadrant electrometer, a colour refractometer and others)