albert+einstein

n. einsteinium (kemi-radioaktivt metalliskt grundämne uppkallat efter Albert Einstein)

SUBJECT AREA: Electricity, Electronics and information technology, Telecommunications

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At the age of 17 Hertz entered the Gelehrtenschule of the Johaneums in Hamburg, but he left the following year to obtain practical experience for a year with a firm of engineers in Frankfurt am Main. He then spent six months at the Dresden Technical High School, followed by year of military service in Berlin. At this point he decided to switch from engineering to physics, and after a year in Munich he studied physics under Helmholtz at the University of Berlin, gaining his PhD with high honours in 1880. From 1883 to 1885 he was a privat-dozent at Kiel, during which time he studied the electromagnetic theory of James Clerk Maxwell. In 1885 he succeeded to the Chair in Physics at Karlsruhe Technical High School. There, in 1887, he constructed a rudimentary transmitter consisting of two 30 cm (12 in.) rods with metal balls separated by a 7.5 mm (0.3 in.) gap at the inner ends and metallic plates at the outer ends, the whole assembly being mounted at the focus of a large parabolic metal mirror and the two rods being connected to an induction coil. At the other side of his laboratory he placed a 70 cm (27½ in.) diameter wire loop with a similar air gap at the focus of a second metal mirror. When the induction coil was made to create a spark across the transmitter air gap, he found that a spark also occurred at the "receiver". By a series of experiments he was not only able to show that the invisible waves travelled in straight lines and were reflected by the parabolic mirrors, but also that the vibrations could be refracted like visible light and had a similar wavelength. By this first transmission and reception of radio waves he thus confirmed the theoretical predictions made by Maxwell some twenty years earlier. It was probably in his experiments with this apparatus in 1887 that Hertz also observed that the voltage at which a spark was able to jump a gap was significantly reduced by the presence of ultraviolet light. This so-called photoelectric effect was subsequently placed on a theoretical basis by Albert Einstein in 1905. In 1889 he became Professor of Physics at the University of Bonn, where he continued to investigate the nature of electric discharges in gases at low pressure until his death after a long and painful illness. In recognition of his measurement of radio and other waves, the international unit of frequency of an oscillatory wave, the cycle per second, is now universally known as the Hertz.

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See also: Heaviside, Oliver

SUBJECT AREA: Weapons and armour

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The son of an engineer, Szilard, after service in the Austro-Hungarian army during the First World War, studied electrical engineering at the University of Berlin. Obtaining his doctorate there in 1922, he joined the faculty and concentrated his studies on thermodynamics. He later began to develop an interest in nuclear physics, and in 1933, shortly after Hitler came to power, Szilard emigrated to Britain because of his Jewish heritage.

In 1934 he conceived the idea of a nuclear chain reaction through the breakdown of beryllium into helium and took out a British patent on it, but later realized that this process would not work. In 1937 he moved to the USA and continued his research at the University of Columbia, and the following year Hahn and Meitner discovered nuclear fission with uranium; this gave Szilard the breakthrough he needed. In 1939 he realized that a nuclear chain reaction could be produced through nuclear fission and that a weapon with many times the destructive power of the conventional high-explosive bomb could be produced. Only too aware of the progress being made by German nuclear scientists, he believed that it was essential that the USA should create an atomic bomb before Hitler. Consequently he drafted a letter to President Roosevelt that summer and, with two fellow Hungarian émigrés, persuaded Albert Einstein to sign it. The result was the setting up of the Uranium Committee.

It was not, however, until December 1941 that active steps began to be taken to produce such a weapon and it was a further nine months before the project was properly co-ordinated under the umbrella of the Manhattan Project. In the meantime, Szilard moved to join Enrico Fermi at the University of Chicago and it was here, at the end of 1942, in a squash court under the football stadium, that they successfully developed the world's first self-sustaining nuclear reactor. Szilard, who became an American citizen in 1943, continued to work on the Manhattan Project. In 1945, however, when the Western Allies began to believe that only the atomic bomb could bring the war against Japan to an end, Szilard and a number of other Manhattan Project scientists objected that it would be immoral to use it against populated targets.

Although he would continue to campaign against nuclear warfare for the rest of his life, Szilard now abandoned nuclear research. In 1946 he became Professor of Biophysics at the University of Chicago and devoted himself to experimental work on bacterial mutations and biochemical mechanisms, as well as theoretical research on ageing and memory.

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