After a short introduction into the history of the building of the Physics Institute of the University of Breslau, the development under Otto Lummer is sketched: influenced by the newly founded Technische Hochschule, the building as well as the faculty, were enlarged. The collection of instruments for instruction and research was built up and the cooperation with industry and with guests from abroad strengthened. Young scientists were promoted, making Lummer's institute into one of the leading ones in optics at that time.