The physicist Karl Ferdinand Braun was an important contributor to the fields of television , radio, and electronics . For his work he shared the 1909 Nobel Prize for Physics with Guglielmo Marconi. Braun was born in Fulda, Germany, and later attended the Universities of Marburg and Berlin. After receiving his doctorate in 1872, he held several academic positions at the Technical University of Karlsruhe, the University of Tübingen, and the University of Strasbourg. He began his first important experimental work in 1874. That year, while studying mineral metal sulfide, he noted that certain crystals transmitted electricity in one direction more easily than in the other. These crystals, called rectifiers, were useful in converting alternating current (which travels in two directions) into direct current (which travels in one). The first use of crystal rectifier s was in crystal-set radios. These rectifiers were replaced eventually by triodes and other valve circuits, but...