Braun, Karl Ferdinand

SUBJECT AREA: Electricity, Electronics and information technology, Telecommunications

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b. 6 June 1850 Fulda, Hesse, Germany

d. 20 April 1918 New York City, New York, USA

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German physicist who shared with Marconi the 1909 Nobel Prize for Physics for developments in wireless telegraphy; inventor of the cathode ray oscilloscope.

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After obtaining degrees from the universities of Marburg and Berlin (PhD) and spending a short time as Headmaster of the Thomas School in Berlin, Braun successively held professorships in theoretical physics at the universities of Marburg (1876), Strasbourg (1880) and Karlsruhe (1883) before becoming Professor of Experimental Physics at Tübingen in 1885 and Director and Professor of Physics at Strasbourg in 1895.

During this time he devised experimental apparatus to determine the dielectric constant of rock salt and developed the Braun high-tension electrometer. He also discovered that certain mineral sulphide crystals would only conduct electricity in one direction, a rectification effect that made it possible to detect and demodulate radio signals in a more reliable manner than was possible with the coherer. Primarily, however, he was concerned with improving Marconi's radio transmitter to increase its broadcasting range. By using a transmitter circuit comprising a capacitor and a spark-gap, coupled to an aerial without a spark-gap, he was able to obtain much greater oscillatory currents in the latter, and by tuning the transmitter so that the oscillations occupied only a narrow frequency band he reduced the interference with other transmitters. Other achievements include the development of a directional aerial and the first practical wavemeter, and the measurement in Strasbourg of the strength of radio waves received from the Eiffel Tower transmitter in Paris. For all this work he subsequently shared with Marconi the 1909 Nobel Prize for Physics.

Around 1895 he carried out experiments using a torsion balance in order to measure the universal gravitational constant, g, but the work for which he is probably best known is the addition of deflecting plates and a fluorescent screen to the Crooke's tube in 1897 in order to study the characteristics of high-frequency currents. The oscilloscope, as it was called, was not only the basis of a now widely used and highly versatile test instrument but was the forerunner of the cathode ray tube, or CRT, used for the display of radar and television images.

At the beginning of the First World War, while in New York to testify in a patent suit, he was trapped by the entry of the USA into the war and remained in Brooklyn with his son until his death.

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Principal Honours and Distinctions

Nobel Prize for Physics (jointly with Marconi) 1909.

Bibliography

1874, "Assymetrical conduction of certain metal sulphides", Pogg. Annal. 153:556 (provides an account of the discovery of the crystal rectifier).

1897, "On a method for the demonstration and study of currents varying with time", Wiedemann's Annalen 60:552 (his description of the cathode ray oscilloscope as a measuring tool).

Further Reading

K.Schlesinger \& E.G.Ramberg, 1962, "Beamdeflection and photo-devices", Proceedings of the Institute of Radio Engineers 50, 991.

KF