Main article: List of works by Erich Mendelsohn  Work hall of the Herrmann hat factory, Luckenwalde (1919-1920) Einsteinturm (solar observatory on the Telegraphenberg ) in Potsdam , 1917 or 1920-1921 (building), 1921-1924 (technical equipment). The building, its expressionistic form giving the impression of concrete as a building material, was mostly built