French scientist, known for his important contributions to the study of electrodynamics. Ampere, the son of a Lyon city official, was born in Polémieux-au-Mont-d'Or, near Lyon. The ampere, the unit of electric current, is named after him. His electrodynamic theory and his views on the relationship of electricity and magnetism were published in his Recueil d'observations électrodynamiques (Collection of Observations on Electrodynamics, 1822) and in his Théorie des phénomcnes électrodynamiques (Theory of Electrodynamic Phenomena, 1826). Ampcre invented the astatic needle, which made possible the modern astatic galvanometer (see Electric Meters). He was the first to show that two parallel conductors carrying currents traveling in the same direction attract each other and, if traveling in opposite directions, repel each other.
Ohm, Georg Simon (1787-1854), German physicist, best known for his research on electrical currents. He was born in Erlangen and educated at the University of Erlangen. From 1833 to 1849 he was director of the Polytechnic Institute of Nürnberg, and from 1852 until his death he was professor of experimental physics at the University of Munich. His formulation of the relationship between current, electromotive force, and resistance, known as Ohm's law, is the basic law of current flow. The unit of electrical resistance was named the ohm in his honor. See Electric Circuit.
Kirchhoff, Gustav Robert (1824-87), German physicist, born in Königsberg (now Kaliningrad, Russia), and educated at the University of Königsberg. He was professor of physics at the universities of Breslau, Heidelberg, and Berlin. With the German chemist Robert Wilhelm Bunsen, Kirchhoff developed the modern spectroscope for chemical analysis. In 1860 the two scientists discovered the elements cesium and rubidium by means of spectrum analysis. Kirchhoff conducted important investigations of radiation heat transfer and also postulated two rules, now known as Kirchhoff's laws of networks, concerning the distribution of current in electric circuits.

Marconi, Guglielmo, Marchese (1874-1937),

Italian electrical engineer and Nobel laureate, known as the inventor of the first practical radio-signaling system. He was born in Bologna and educated at the University of Bologna. As early as 1890 he became interested in wireless telegraphy, and by 1895 he had developed an apparatus with which he succeeded in sending signals to a point a few kilometers away by means of a directional antenna. After patenting his system in Great Britain, he formed (1897) Marconi's Wireless Telegraph Company, Ltd., in London. In 1899 he established communication across the English Channel between England and France, and in 1901 he communicated signals across the Atlantic Ocean between Poldhu, in Cornwall, England, and St. John's, in Newfoundland. His system was soon adopted by the British and Italian navies, and by 1907 had been so much improved that transatlantic wireless telegraph service was established for public use. Marconi was awarded honors by many countries and received, jointly with the German physicist Karl Ferdinand Braun, the 1909 Nobel Prize in physics for his work in wireless telegraphy. During World War I he was in charge of the Italian wireless service and developed shortwave transmission as a means of secret communication. In the remaining years of his life he experimented with shortwaves and microwaves.

Maxwell, James Clerk (1831-1879),

British physicist, best known for his work on the connection between light and electromagnetic waves (traveling waves of energy). Maxwell discovered that light consists of electromagnetic waves (see Electromagnetic Radiation) and established the kinetic theory of gases. The kinetic theory of gases explains the relationship between the movement of molecules in a gas and the gas's temperature and other properties. He also showed that the rings of the planet Saturn are made up of many small particles and demonstrated the principles governing color vision. Maxwell was born in Edinburgh, Scotland. He was educated at Edinburgh Academy from 1841 to 1847, when he entered the University of Edinburgh. He then went on to study at the University of Cambridge in 1850, graduating with a bachelor's degree in mathematics in 1854. He became a professor of natural philosophy at Marischal College in Aberdeen in 1856. Then in 1860 he moved to London to become a professor of natural philosophy and astronomy at King's College. On the death of his father in 1865, Maxwell returned to his family home in Scotland and devoted himself to research. In 1871 he moved to Cambridge, where he became the first professor of experimental physics and set up the Cavendish Laboratory, which opened in 1874. Maxwell continued in this position until 1879, when illness forced him to resign.
Hertz, Gustav (1887-1975),
German physicist and Nobel laureate, born in Hamburg, and educated at the universities of Göttingen, Munich, and Berlin. In conjunction with the American physicist James Franck, Hertz studied the effect of the impact of electrons on atoms. As a result of these experiments, which were the first demonstration of the quantum theory of the German physicist Max Planck, Hertz and Franck were awarded the 1925 Nobel Prize in physics. Hertz served as professor of experimental physics at the University of Halle from 1925 to 1927 and at the Berlin Technische Hochschule from 1928 to 1935, when he became director of the Siemens Research Laboratory in Berlin. In 1945 he went to the USSR to continue his work in atomic research; he was awarded the Stalin Prize in 1951.
Faraday, Michael (1791-1867),
British physicist and chemist, best known for his discoveries of electromagnetic induction and of the laws of electrolysis.
Faraday was born on September 22, 1791, in Newington, Surrey, England. He was the son of a blacksmith and received little formal education. While apprenticed to a bookbinder in London, he read books on scientific subjects and experimented with electricity. In 1812 he attended a series of lectures given by the British chemist Sir Humphry Davy and forwarded the notes he took at these lectures to Davy, together with a request for employment. Davy employed Faraday as an assistant in his chemical laboratory at the Royal Institution and in 1813 took Faraday with him on an extended tour of Europe. Faraday was elected to the Royal Society in 1824 and the following year was appointed director of the laboratory of the Royal Institution. In 1833 he succeeded Davy as professor of chemistry at the institution. Two years later he was given a pension of 300 pounds per year for life. Faraday was the recipient of many scientific honors, including the Royal and Rumford medals of the Royal Society; he was also offered the presidency of the society but declined the honor. He died on August 25, 1867, near Hampton Court, Surrey.

Braun, Karl Ferdinand (1850-1918),

German physicist, inventor, and Nobel Prize winner. Braun is best known for his invention of the first oscilloscope (an electronic instrument that displays changes in the voltage of an electric circuit) made out of a cathode-ray tube (CRT), but he also contributed much to the study of electricity and telegraphy, or wireless communication (see Radio), through groundbreaking research and inventions. He shared the 1909 Nobel Prize in physics with Italian electrical engineer and inventor Guglielmo Marconi for their work on wireless communication.
Born in Fulda, Braun studied at the University of Marburg and received his doctorate from the University of Berlin in 1872, after a dissertation on the vibrations of elastic rods and strings. He began his career as a research assistant at the University of Würzburg, and later held positions at universities in Leipzig, Marburg an der Lahn, Karlsruhe, and Tübingen, where he founded the Physics Institute. From 1880 to 1883 Braun was at Strasbourg, France, and he returned there in 1895 to become professor of physics and director of the Strasbourg Physics Institute.
In 1874 Braun published some of the results of his research on mineral-metal sulfides. He found that these crystals conducted electric currents in only one direction. At the time, the information was important in electrical studies and in measuring electrical conductivity, but Braun's discovery found practical application in the early 20th century when it was employed in crystal radio receivers. The crystal rectifier allowed current to flow in only one direction and improved radio transmission.
Braun also created the first oscilloscope, then called a Braun tube, in 1897. The Braun tube was a valuable laboratory instrument, and modified versions are used in electronic testing and research today. The principle of the Braun tube, moving an electron beam by means of alternating voltage, is the principle on which all television tubes operate.
While Braun also made many contributions to pure science, he won honors for his fundamental modification of Marconi's wireless transmitting system. Braun tried to overcome the difficulty in increasing the range of a transmitter beyond 15 km (9 mi). He believed he could expand this range by increasing the power of the transmitter.
Studying the Marconi transmitter, which used a sparking apparatus to produce periodic waves that travel through the air, he learned that attempts to increase the power output by increasing the length of the spark gap eventually reached a limit at which the spark caused a decrease in output. Braun solved this dilemma by producing a sparkles antenna circuit. He magnetically coupled the power from the transmitter to the antenna circuit using a transformer effect instead of having the antenna directly in the power circuit.
Braun's circuit has been applied to all similar transmission, including radio, radar, and television. A patent was granted on this circuit in 1899. Braun also invented a transmitter that channeled the transmission of electric waves in one direction.
Braun gained notoriety outside the laboratory as well when he was called to the United States in 1914 to testify in litigation involving radio broadcasting. He was still in the country in 1917 when the United States entered World War I, and he was not allowed to return to Germany. He died in a Brooklyn, New York, hospital in 1918.