Lawrence Bragg
Sir William Lawrence Bragg was a British X-ray crystallographer who uniquely shared a Nobel Prize with his father William Henry Bragg – the 1915 Nobel Prize in Physics "for their services in the analysis of crystal structure by means of X-rays", an important step in the development of X-ray crystallography.
As of 2025, Bragg is the youngest ever Nobel laureate in physics, or in any science category, having received the award at the age of 25. Bragg was the director of the Cavendish Laboratory, Cambridge, when James D. Watson and Francis Crick reported the discovery of the structure of DNA in February 1953.
Education
William Lawrence Bragg was born on 31 March 1890 in Adelaide, South Australia, the son of William Henry Bragg, who was appointed Elder Professor of Mathematics and Physics at the University of Adelaide in 1885, and Gwendoline, daughter of Charles Todd, government astronomer of South Australia.In 1900, Bragg enrolled at Queen's School, North Adelaide, followed by five years at St Peter's College, Adelaide. He went to the University of Adelaide at the age of 16 to study mathematics, chemistry, and physics, graduating in 1908. The same year, his father accepted the Cavendish Chair of Physics at the University of Leeds and brought the family to England.
Bragg enrolled at the University of Cambridge as an undergraduate student of Trinity College, Cambridge in the autumn of 1909, receiving a major scholarship in mathematics, despite taking the exam while in bed with pneumonia. After initially excelling in mathematics, he transferred to the physics course in the later years of his studies, and graduated with first class honours in 1911. In 1914, Bragg was elected to Fellow of Trinity College.
Among Bragg's other interests was shell collecting; his personal collection amounted to specimens from some 500 species; all personally collected from South Australia. He discovered a new species of cuttlefish – Sepia braggi, named for him by Joseph Verco.
Career and research
X-rays and the Bragg equation
In 1912, as a first-year research student at Cambridge, W. L. Bragg, while strolling by the river, had the insight that crystals made from parallel sheets of atoms would not diffract X-ray beams that struck their surface at most angles because X-rays deflected by collisions with atoms would be out of phase, cancelling one another out. However, when the X-ray beam struck at an angle at which the distances it passed between atomic sheets in the crystal equalled the X-ray's wavelength then those deflected would be in phase and produce a spot on a nearby film. From this insight he wrote the simple Bragg equation that relates the wavelength of the X-ray and the distance between atomic sheets in a simple crystal to the angles at which an impinging X-ray beam would be reflected.His father built an apparatus in which a crystal could be rotated to precise angles while measuring the energy of reflections. This enabled father and son to measure the distances between the atomic sheets in a number of simple crystals. They calculated the spacing of the atoms from the weight of the crystal and the Avogadro constant, which enabled them to measure the wavelengths of the X-rays produced by different metallic targets in the X-ray tubes. W. H. Bragg reported their results at meetings and in a paper, giving credit to "his son" for the equation, but not as a co-author, which gave his son "some heartaches", which he never overcame.
Work on sound ranging
Bragg was commissioned early in World War I in the Royal Horse Artillery as a second lieutenant of the Leicestershire battery. In 1915 he was seconded to the Royal Engineers to develop a method to localise enemy artillery from the boom of their firing. On 2 September 1915 his brother was killed during the Gallipoli Campaign. Shortly afterwards, he and his father were awarded the Nobel Prize in Physics. He was 25 years old and remains the youngest science laureate. The problem with sound ranging was that the heavy guns boomed at too low a frequency to be detected by a microphone. After months of frustrating failure he and his group devised a hot wire air wave detector that solved the problem. In this work he was aided by Charles Galton Darwin, William Sansome Tucker, Harold Roper Robinson, Edward Andrade and Henry Harold Hemming. British sound ranging was very effective; there was a unit in every British Army and their system was adopted by the Americans when they entered the war. For his work during the war he was awarded the Military Cross and appointed Officer of the Order of the British Empire. He was also mentioned in dispatches on 16 June 1916, 4 January 1917 and 7 July 1919.Hot wire sound ranging was used in World War II during which he served as a civilian adviser.
Between the wars, from 1919 to 1937, he worked at the Victoria University of Manchester as Langworthy Professor of Physics. He became the director of the National Physical Laboratory in Teddington in 1937.
After World War II, Bragg returned to Cambridge, splitting the Cavendish Laboratory into research groups. He believed that "the ideal research unit is one of six to twelve scientists and a few assistants".
University of Manchester
When demobilised he returned to crystallography at Cambridge. They had agreed that father would study organic crystals, son would investigate inorganic compounds. In 1919 when Ernest Rutherford, a long-time family friend, moved to Cambridge, Lawrence Bragg replaced him as Langworthy Professor of Physics at the Victoria University of Manchester and was elected to membership of the Manchester Literary and Philosophical Society on 4.11.1919. He recruited an excellent faculty, including former sound rangers, but he believed that his knowledge of physics was weak and he had no classroom experience. The students, many veterans, were critical and rowdy. He was deeply shaken but with family support he pulled himself together and prevailed. He and R. W. James measured the absolute energy of reflected X-rays, which validated a formula derived by C. G. Darwin before the war. Now they could determine the number of electrons in the reflecting targets, and they were able to decipher the structures of more complicated crystals like silicates. It was still difficult: requiring repeated guessing and retrying. In the late 1920s they eased the analysis by using Fourier transforms on the data.In 1930, he became deeply disturbed while considering a job offer from Imperial College London. His family rallied around and he recovered his balance while they spent 1931 in Munich, where he did research.
National Physical Laboratory
He became director of the National Physical Laboratory in Teddington in 1937, bringing some co-workers along. However, administration and committees took much of his time away from the workbench.University of Cambridge
Rutherford died and the search committee named Lawrence Bragg as next in the line of the Cavendish Professors who direct the Cavendish Laboratory. The Laboratory had an eminent history in atomic physics and some members were wary of a crystallographer, which Bragg surmounted by even-handed administration. He worked on improving the interpretation of diffraction patterns. In the small crystallography group was a refugee research student without a mentor: Max Perutz. He showed Bragg X-ray diffraction data from haemoglobin, which suggested that the structure of giant biological molecules might be deciphered. Bragg appointed Perutz as his research assistant and within a few months obtained additional support with a grant from the Rockefeller Foundation. The work was suspended during the Second World War when Perutz was interned as an enemy alien and then worked in military research.During the war the Cavendish offered a shortened graduate course which emphasised the electronics needed for radar. Bragg worked on the structure of metals and consulted on sonar and sound ranging, for which the Tucker microphone was still used. Bragg was knighted and became Sir Lawrence in 1941. After his father died in 1942, Bragg served for six months as Scientific Liaison Officer to Canada. He also organised periodic conferences on X-ray analysis, which was widely used in military research.
After the war Bragg led in the formation of the International Union of Crystallography and was elected its first president. He reorganised the Cavendish into units to reflect his conviction that "the ideal research unit is one of six to twelve scientists and a few assistants, helped by one or more first-class instrument mechanics and a workshop in which the general run of apparatus can be constructed." Senior members of staff now had offices, telephones, and secretarial support. The scope of the department was enlarged with a new unit on radio astronomy. Bragg's own work focused on the structure of metals, using both X-rays and the electron microscope. In 1947 he persuaded the Medical Research Council to support what he described as the "gallant attempt" to determine protein structure as the Laboratory of Molecular Biology, initially consisting of Perutz, John Kendrew and two assistants. Bragg worked with them and by 1960 they had resolved the structure of myoglobin to the atomic level. After this Bragg was less involved; their analysis of haemoglobin was easier after they incorporated two mercury atoms as markers in each molecule. The first monumental triumph of the MRC was decoding the structure of DNA by James Watson and Francis Crick. Bragg announced the discovery at a Solvay conference on proteins in Belgium on 8 April 1953, though it went unreported by the press. He then gave a talk at Guy's Hospital Medical School in London on Thursday, 14 May 1953, which resulted in an article by Ritchie Calder in the News Chronicle of London on Friday, 15 May 1953, entitled "Why You Are You. Nearer Secret of Life". Bragg nominated Crick, Watson and Maurice Wilkins for the 1962 Nobel Prize in Physiology or Medicine; Wilkins' share recognised the contribution of X-ray crystallographers at King's College London. Among them was Rosalind Franklin, whose "photograph 51" showed that DNA was a double helix, not the triple helix that Linus Pauling had proposed. Franklin died before the prize was awarded.