He studied physics at the Universities of
Heidelberg and
Berlin, earning his doctorate in 1894 under
August Kundt with a thesis on the dispersion of
ultraviolet radiation. Afterwards, he served as an assistant to
Eilhard Wiedemann at
Erlangen, obtaining his habilitation in 1896. Two years later, he became an assistant to
Eduard Riecke at the
University of Göttingen, then relocated to
Frankfurt am Main as director of the physics laboratory. In 1901 he returned to Göttingen as an associate professor and director of the department of
applied electricity. In 1907 he was appointed as a full professor at the University of Göttingen. With Eduard Riecke, he was editor of the physics journal
Physikalische Zeitschrift. He discovered the "singing arc" phenomenon and reported it in 1898. Specifically, he found that the dominant frequency in the buzzing sound made by an
electric arc light can be controlled by the voltage across the arc light, so that by varying the voltage, the arc can be made to "sing". His research led to a light telephone, with searchlight modulated by a microphone as the transmitter, and a
photosensitive selenium cell as the receiver. == Selected writings ==