Bragg, Sir William Henry
- Talal Debs
Sir William Henry Bragg (1862–1942)
Bragg, Sir William Henry (1862–1942), physicist, was born at Westward, near Wigton in Cumberland, on 2 July 1862, the eldest of the three sons of Robert John Bragg (1830–1885), a merchant navy officer who became a farmer at Stoneraise Place, Westward. His mother, Mary (1833–1869), the daughter of Robert Wood, perpetual curate of Westward, died when he was seven years old. After her death he lived with his uncle William Bragg for six years in Market Harborough, Leicestershire, where he attended the grammar school. He went on to King William's College, Isle of Man, in 1875, and in 1881 entered Trinity College, Cambridge, as a scholar studying mathematics. Third wrangler in part I of the tripos in 1884, Bragg graduated with first-class honours in 1885.
Teaching in Australia, 1886–1909
Bragg accepted the Elder professorship at the University of Adelaide in 1886. While his responsibilities included lecturing on applied mathematics, he was primarily teaching physics, much of which he had not covered in his mathematical training at Cambridge. Bragg was forced to teach himself a great deal of this material. Soon after his arrival he met Gwendoline (1869–1929) whose father Charles Todd FRS, postmaster-general and government astronomer of South Australia, had been instrumental in bringing Bragg to Adelaide; they married in 1889. They had three children, (William) Lawrence Bragg (1890–1971), Robert (b. 1892), and Gwendoline Mary (b. 1907). The expenditure of Bragg's energies on teaching, lectures, and demonstrations, combined with the priority he gave to family life, meant that he published only three research papers in the eighteen years from his arrival until 1904, two in Australian journals. It was in this year that his research career might be said to have begun.
As president of section A (covering astronomy, mathematics, and physics) of the Australian Association for the Advancement of Science, Bragg presented 'On some recent advances into the theory of the ionization of gases' at their January 1904 meeting in Dunedin, New Zealand. Bragg discussed recent international developments in physics, which he decided to follow up with a series of experiments on the absorption of alpha particles. Through the years of instruction and demonstration Bragg had acquired considerable experimental skill, and was probably the first in Australia to set up an X-ray tube following their discovery in 1895. These skills became crucial as he embarked on his research career, and his work was received with interest abroad. Bragg's early results on alpha particles were seen as a confirmation of some predictions of Ernest Rutherford, the rising expert on radiation, who in the same year published a textbook, Radio-Activity, the first in its field. Bragg's research and publications catapulted him into the forefront of physicists attempting to explain the various newly discovered forms of radiation. He was elected FRS in 1907, and in 1908 was invited to take up the Cavendish professorship in physics at the University of Leeds.
Research on radiation
Bragg arrived in 1909, and during his first three years at Leeds continued his research on radiation including alpha particles, beta rays, gamma rays, and X-rays. He continued to develop and make use of ionization chamber techniques and favoured a corpuscular model of some of these phenomena. In particular, he became an early champion of the particle-like nature of X-rays through one such corpuscular theory, the neutral pair hypothesis. This was the proposal that X-rays were corpuscles each made up of a pair of positive and negative particles, accounting for a combination of high penetration and weak ionization characteristics. By 1912 he became aware of the need for a theory which had both particle and wave aspects. While he was partially vindicated by the wave–particle duality of electromagnetic radiation supported by quantum mechanics, Bragg's specific mechanisms were only briefly supportable by his experimental evidence. In 1912 Bragg brought much of his work during this period together in his Studies in Radioactivity. The relationships formed and techniques developed during this time were very significant in the next phase of his research, which was to come in response to new experimental results coming out of Germany.
Discovery of X-ray crystallography, 1912–1915
In the summer of 1912 the results of some experiments done at Arnold Sommerfeld's institute at the University of Munich began to be received with great interest both within Germany and abroad. Bragg had briefly corresponded with Sommerfeld the year before and, as one of the top British physicists in the field, he was one of the first in the country to get news of these results. Max von Laue, with the assistance of W. Friedrich and P. Knipping, had produced a number of photographic plates displaying symmetrical patterns of spots. The spots had been created by the multiple deflection of a single beam of X-rays after passing through a crystal of zinc-blende, and these results led to the conclusion that X-rays could interfere in crystals and that consequently they should be considered as electromagnetic waves. This result was of crucial importance to a wide group of scientists working at the time, most notably those interested in the physics of radiation and those interested in the structure of matter, the crystallographers.
Bragg, working with his son William Lawrence, was among the first in Britain to begin to tackle the problem of explaining Laue's photographic plates. Laue's own explanation, that the crystal's symmetrical arrangement of atoms acted as a sort of diffraction grating, was soon questioned by Bragg and others, including Röntgen himself. Laue's formulae correctly predicted some of the spots' positions on the photographic plates, but the result seemed to be independent of the wavelength of the radiation. This was a major problem as wavelength was one of the crucial parameters for a wave explanation of the phenomenon. In addition, Bragg was faced with pressure from the crystallographers to take into account the parameters imposed by their discipline; among these were the Miller indices, which described the internal geometry of crystalline substances. Bragg was even publicly challenged to take crystallographic details into account by A. E. H. Tutton in the pages of Nature.
Acting in part on his son's suggestion, Bragg attempted to defend his corpuscular view of X-rays by proposing that Laue's spots were caused by X-ray corpuscles passing through gaps in the crystal structure. This explanation was soon superseded by his son's masterful synthesis of crystal structure concepts and wave mechanics. In this solution the spots were considered to be due to reflections from classes of reflecting planes within the crystal structure, each denoted by a set of Miller indices. This approach accounted for all of the spots and was dependent on wavelength and internal crystal symmetry. Bragg and his son immediately followed up with a very fruitful collaboration in which they began to explore crystal properties and structures. The techniques and tools they developed, the ionization spectrometer for example, drew heavily on Bragg's past work and expertise. These techniques became the basis of an entire field of scientific research, that of X-ray crystallography, which was to develop along many different lines in subsequent years, notably resulting in the discovery of the DNA double helix four decades later.
The year 1915 saw many changes in Bragg's life including the closure of the early period of collaboration with his son on X-ray diffraction. This was marked by the joint publication of X-Rays and Crystal Structure, which came to be the first basic text for the field of X-ray crystallography. This same year both Braggs, father and son, shared the Nobel prize in physics for their work over the previous three years. In addition there were changes in Bragg's academic life as he left Leeds for London to become the Quain professor of physics at University College. In terms of X-ray crystallographic work Bragg temporarily lost momentum owing to war research; he became a member of the Admiralty board of invention and research resulting in a period of time at the Naval Experiment Station at Hawkcraig and at Harwich working on submarine detection. War research, the completion of the work with his son Lawrence, and perhaps the loss of his younger son Robert in the Dardanelles that same year, all meant that X-ray crystallographic research did not become a full-time endeavour again until after the war.
Royal Institution, 1923–1942
Bragg was recognized for his war research by being made CBE (1917) and KBE (1920). His research environment changed again when he succeeded Sir James Dewar in the joint post of Fullerian professor of chemistry at the Davy–Faraday Research Laboratory and director of the Royal Institution in 1923. Bragg brought his students across from University College and established a very important centre of early X-ray crystal structure physics in the Davy–Faraday Laboratory. Among distinguished scientists who trained and worked there were Kathleen Lonsdale and J. D. Bernal. The area of research was limited to the structure of organic substances by unwritten agreement with his son, who worked on inorganic structures. His role at the Royal Institution provided a platform for Bragg's interest in communicating with a non-scientific audience. He was renowned for his skills of presentation and demonstration, notably through the regular Christmas lectures for young people. These were characterized by elegant means of explaining technical concepts, and several of them were published as books, including The World of Sound (1920) and The Nature of Things (1925). His wife died in 1929, only a few years after they had moved into the director's residence at the Royal Institution.
Although he had been awarded the Royal Society's Rumford medal in 1916, and been made an honorary fellow of Trinity College, Cambridge, in 1920, it was only after becoming director of the Royal Institution that Bragg began to be seen as one of the great statesmen of science in his day. In 1928 he presided over the Glasgow meeting of the British Association. He received the Royal Society's Copley medal in 1930 and served as president of the Physical Society from that year until 1932. In 1931 he was honoured with the Order of Merit, and served as president of the Royal Society from 1935 to 1940. He was often called upon to present scientific issues to a non-scientific audience; his 1941 Riddell memorial lecture at Durham University, 'Science and faith', provides a retrospective insight into his scientific career. He saw science as a collection of observations of nature, and the role of the researcher to arrange and extend the scope of these observations. Significantly, he observed that experimental physics often involved steps of faith in the pursuit of these objectives. It was this role to which he was committed until his death, at the director's residence in the Royal Institution, 21 Albemarle Street, London, on 12 March 1942. He was cremated on 19 March after a funeral in London, and a plaque was placed in Chiddingfold church, Surrey.
- E. N. da C. Andrade, Obits. FRS, 4 (1942–4), 277–300
- P. Forman, ‘Bragg, William Henry’, DSB
- Lord Rayleigh [J. W. Strutt], Proceedings of the Physical Society, 54 (1942)
- L. Hoddeson, E. Braun, J. Teichman, and S. Weart, eds., Out of the crystal maze: chapters from the history of solid-state physics (1992)
- R. H. Stuewer, ‘William H. Bragg's corpuscular theory of X-rays and ɣ rays’, British Journal for the History of Science, 5 (1970–71), 258–81
- W. L. Bragg, ‘The diffraction of short electromagnetic waves by a crystal’, Proceedings of the Cambridge Philosophical Society, 17 (1912–14), 43–57
- W. H. Bragg, ‘On the properties and natures of various electric radiations’, London, Edinburgh, and Dublin Philosophical Magazine, 6th ser., 14 (1907), 429–49
- A. E. H. Tutton, ‘The crystal space-lattice revealed by Rontgen rays’, Nature, 90 (1912–13), 306–9, esp. 307
- W. H. Bragg, ‘Science and faith’, Riddel memorial lecture, U. Durham, 7 March 1941
- L. Badash, ‘Rutherford, Ernest’, DSB
- G. M. Carol, William Henry Bragg: man and scientist (1978)
- private information (2004)
- d. cert.
- Bodl. Oxf., corresp. relating to Society for Protection of Science and Learning
- Royal Institution of Great Britain, London, corresp. and papers
- RS, letters to Royal Society
- U. Leeds, Brotherton L., notebook
- CAC Cam., corresp. with A. V. Hill
- CUL, corresp. with Lord Rutherford
- Ransom HRC, letters to Sir Owen Richardson
- Trinity Cam., corresp. with Sir Joseph John Thomson
- BFINA, current affairs footage
- W. Stoneman, photographs, 1920–38, NPG
- E. Kennington, pencil drawing, 1927, Trinity Cam.
- W. Nicholson, oils, 1932, Royal Institution of Great Britain, London
- R. Schwabe, pencil drawing, 1932, NPG [see illus.]
- C. E. S. Phillips, oils, 1939, Royal Institution of Great Britain, London
- H. Knight, oils, RS
- T. Purvis, pen-and-ink drawing, Royal Institution of Great Britain, London
- W. Rothenstein, drawing, Carlisle; [in possession of city of Carlisle
Wealth at Death
£27,039 5s. 0d.: probate, 5 May 1942, CGPLA Eng. & Wales
- Bragg, Sir William (Henry), (2 July 1862–12 March 1942), President of the Royal Society, 1935–40; Hon. Fellow, Trinity College, Cambridge; Director of the Royal Institution of Great Britain; Fullerian Professor of Chemistry, Royal Institution, and Director of Davy-Faraday Research Laboratory, since 1923; Member of Advisory Council for Scientific and Industrial Research since 1937 in Who Was Who