Karl Braun. Portrait of Karl Ferdinand Braun (1850-1918), German physicist and inventor. In 1874 Braun noticed that some semiconductors would only allow electrical currents to flow one way. He later used this property to invent crystal diodes (electrical valves). Braun adapted the cathode ray tube so that the beam of electrons within it could be deflected by a changing voltage. With this he invented the oscilloscope and it was an early step in the development of television. He also helped to improve Marconi's wireless system and in 1909 they shared the Nobel prize for physics. In 1917 he was detained whilst on a trip to America and died in captivity.