Sir William Lawrence Bragg

Sir William Lawrence Bragg was an Australian-born British physicist and Nobel Prize winner. Bragg shared the 1915 Nobel Prize in physics with his father, British physicist Sir William Henry Bragg, for their work in establishing X-ray crystallography, the study of crystal structures with X rays. Born in Adelaide, Australia, William Lawrence Bragg studied at Saint Peter’s College in Adelaide and at the University of Adelaide, graduating in 1908.

He enrolled at Trinity College, Cambridge, England, in 1909 to continue studying mathematics, but switched to physics at the suggestion of his father. Lawrence Bragg began research under the direction of British physicist Sir Joseph John Thomson in 1912. Bragg served in the British army during World War I, developing techniques to locate the enemy by the sound of their artillery fire. After the war, he held positions at Trinity College and then the University of Manchester.

In 1937 Lawrence Bragg moved to the National Physical Laboratory as director, but soon accepted an invitation to Cambridge as the Cavendish Professor of Experimental Physics. He stayed at Cambridge until 1953, when he moved to the Royal Institution, London, as director of the Davy-Faraday Research Laboratory, a position once held by his father. He stayed at the Royal Institution until his retirement in 1966. The work that brought the Braggs fame was based on the phenomenon of X-ray diffraction in crystals, discovered in 1912 by Max Theodor Felix von Laue.

Although the wave nature of X rays and the order of magnitude of their wavelength had been established, there were no methods developed to interpret the photographic interference pictures that two of von Laue’s colleagues had produced by directing X rays through crystals. Lawrence Bragg and his father had begun discussing von Laue’s findings in 1912, and worked together to treat them mathematically and simplify their interpretation. Lawrence Bragg discovered that certain planes in a crystal reflect X rays, in accordance with the normal law of reflection.

The distance between parallel planes of atoms determines the angle at which reflection can take place for a certain wavelength of the X rays. This relation, known as Bragg’s law, permitted physicists to measure the wavelengths of the X rays. For crystals of simple structure, like salt, physicists could calculate the distances between the planes of atoms from previous data and use the results to find the wavelength of the X rays. These discoveries served as the foundation for further research. The Braggs decided to build upon initial findings by using X rays to study the structure of solids, especially crystals.

With his father, Lawrence Bragg went on to determine the structure of increasingly complex compounds such as silicates, a family of crystalline minerals composed partly of silicon. In his position at the Royal Institution, Bragg built upon his early work by sponsoring and conducting crystallographic research. He also devoted his energy and talents to popularizing and teaching science and its history. Bragg was knighted in 1941. He retired in 1966, but maintained an active interest in both crystallography and scientific popularization.


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