Karl Ferdinand Braun was a German physicist who made improvements to Guglielmo Marconi's system of wireless telegraphy. He was born in 1850 at Fulda, and died in 1918. He and Marconi shared the 1909 Nobel Prize for Physics. Braun also discovered crystal rectifiers (used in early radios), and invented the oscilloscope in 1895. He was educated at Marburg and Berlin. He held academic posts at a number of German universities, ending his career as professor and from 1895 director of the Institute of Physics at Strasbourg. In an attempt to increase the radio transmitter range to more than 15 km, Braun devised a system in which the power from the transmitter was magnetically coupled (using electromagnetic induction) to the antenna circuit. He patented this invention in 1899, and the principle of magnetic coupling has since been applied to all similar transmission systems. Later Braun developed directional antennas. In 1874 Braun discovered that some mineral metal sulphides conduct electricity in one direction only. These were later used in the crystal radio receivers that preceded valve circuits. Braun's oscilloscope was an adaptation of the cathode-ray tube. A laboratory instrument to study high-frequency alternating currents, it was the forerunner of television and radar display tubes.