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" (unnamed) 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 an
Officer of the Order of the British Empire (OBE). 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 commemorating Bragg's work at the
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. 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 (MRC) 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 (which only goes to living people) was awarded.
Royal Institution In 1953 the Braggs moved into the elegant flat for the Resident Professor in the
Royal Institution in London, the position his father had occupied when he died. In 1934 and 1961 Lawrence had delivered the
Royal Institution Christmas Lecture and since 1938 he had been Professor of Natural Philosophy in the Institution, delivering an annual lecture. His father's successors had weakened the Institution, so Bragg had to rebuild it. He bolstered finances by enlisting corporate sponsors, the traditional Friday Evening Discourses were followed by a dinner party for the speaker and carefully selected possible patrons, more than 120 of them each year. "Two of these Discourses in 1965 gave him particular pleasure. On 7 May, Lady Bragg, who had been a member of the Royal Commission on Marriage and Divorce (1951–55) and was Chairman of the
National Marriage Guidance Council, lectured on 'Changing patterns in marriage and divorce'; and on 15 November, Bragg listened with evident pride to the Discourse on 'Oscillations and noise in jet engines' given by his engineer-son
Stephen, who was then Chief Scientist at Rolls-Royce Ltd and later became Vice-Chancellor of
Brunel University." He also introduced a programme of highly regarded Schools' Lectures, enlivened by the elaborate demonstrations that were a hallmark of the Institution. He gave three of these lectures on "electricity". He continued research in the Institution by recruiting a small group to work in the Davy-Faraday Laboratory in the basement and in the adjoining house, supported by grants he obtained. A visitor to the laboratory succeeded in inserting heavy metals into the enzyme
lysozyme; the structure of its crystal was solved in 1965 at the Royal Institution by
David Chilton Phillips and his coworkers, with the computations on the 9,040 reflections performed on the digital computer at the University of London, which greatly facilitated the work. Two of the illustrations of the positioning of amino acids in the chain were drawn by Bragg. Unlike myoglobin, in which nearly 80 per cent of the amino-acid residues are in the
alpha-helix conformation, in lysozyme the alpha-helix content is only about 40 per cent of the amino-acid residues found in four main stretches. Other stretches are of the
310 helix, a conformation that they had proposed earlier. In this conformation, every third peptide is hydrogen-bonded back to the first peptide, thus forming a ring containing ten atoms. They had the complete structure of an enzyme in time for Bragg's 75th birthday. He became Professor Emeritus in 1966. X-ray analysis of protein structure flourished in subsequent years, determining the structures of scores of proteins in laboratories around the world. Twenty eight Nobel Prizes have been awarded for work using X-ray analysis. The disadvantage of the method is that it must be done on crystals, which precludes seeing changes in shape when enzymes bind substrates and the like. This problem was solved by the development of another line Bragg had initiated, using modified electron microscopes to image single frozen molecules:
cryo-electron microscopy. In his long association with the
Royal Institution he was: • Professor of Natural Philosophy, 1938–1953 •
Fullerian Professor of Chemistry, 1954–1966 • Superintendent of the House, 1954–1966 • Director of the Davy-Faraday Research Laboratory, 1954–1966 •
Director of the Royal Institution, 1965–1966 • Emeritus Professor, 1966–1971 == Personal life ==