This article was published in Australian Dictionary of Biography, Volume 7, (MUP), 1979
Sir William Henry Bragg (1862-1942), and BRAGG, Sir WILLIAM LAWRENCE (1890-1971), physicists, were father and son. William Henry was born on 2 July 1862 at Westward near Wigton, Cumberland, England, son of Robert John Bragg, merchant navy officer and farmer, and his wife Mary, née Wood. His mother died when he was 7 and, almost isolated from other children, he was raised by his uncle William Bragg at Market Harborough, Leicestershire. He won scholarships to the local grammar school and to King William's College, Isle of Man, where he became head of the school and won an exhibition to Trinity College, Cambridge. There he worked almost entirely at mathematics; later he regretted this early specialization. Lacking both spending money and easy sociability, he was saved from loneliness by his skill at games. In 1884 he graduated as third wrangler and a year later was awarded a first in part III of the tripos.
In 1886 Bragg arrived in Adelaide to take up the university post of '(Sir Thomas) Elder Professor of Pure and Applied Mathematics, who shall also give instruction in Physics'; it had been recently vacated by, (Sir) Horace Lamb. He was ignorant of physics, in which he was to become one of the most eminent men of his time. Although at first he had only two students, he did not proceed to engage in any research. He apprenticed himself to a firm of instrument-makers to make apparatus for his deficient teaching laboratory.
Meeting with a friendly reception, particulary from the family of (Sir) Charles Todd, Bragg enjoyed a wide popularity, and his personality blossomed. He played tennis and golf and helped to introduce lacrosse to South Australia. On 1 June 1889 he married Todd's daughter Gwendoline, a skilled water-colourist; Bragg took up painting and they exhibited together. They had two sons, one of whom was later killed at Gallipoli, and a daughter. Bragg was active in the affairs of the Public Library, Museum and Art Gallery of South Australia, the School of Mines and Industries and the Teachers' Guild.
At the university he encouraged student activities, particularly the formation of the union. He believed that the greatest work a colonial university could do was to act as 'the centre from which all education radiates' and help to bring all teachers in touch with the best thinking. Country teachers were welcomed to his lectures and not required to pay fees. His academic interest shifted to physics: he developed a flair for expounding the subject both in formal classes and in public lectures often enlivened with experimental demonstrations. Electromagnetism interested him; one day in 1895 he was experimenting with a Hertzian oscillator when he was visited by Ernest Rutherford who was on his way to Cambridge and had worked on radio transmission at Christchurch, New Zealand. It was the beginning of a valuable lifelong friendship.
Early next year Bragg learned of W. K. Röntgen's discovery of X-rays and, with his able assistant A. L. Rogers, set about producing the new radiation. On 13 June they obtained a photograph with their own Röntgen tube. One of the first beneficiaries was Bragg's 6-year-old son William Lawrence, whose broken elbow was photographed with the primitive equipment. But many years passed before Bragg began his serious studies of X-rays and other ionizing radiations.
In 1898 he spent a year's leave in England; he reported on technical education and the central importance of design in industry. On his return Bragg carried out experimental work on radio communication with Todd. Their transmissions from the State Observatory were successful over a distance of 600 yards (550 m) on 10 May 1899, and by 20 July, over five miles (8 km) from the Observatory to Henley Beach.
The turning-point in Bragg's career came in 1904 when he gave the presidential address to section A of the Australasian Association for the Advancement of Science at Dunedin, New Zealand, 'On some recent advances in the theory of the ionization of gases'. He discussed the penetration of matter by α and β particles, concluding that the massive α particles, unlike the β and γ rays, would move undeviated through a gas until all the energy was lost through ionization of the gas molecules, and consequently α particles of a given initial energy should have a definite range in the gas. This idea was followed up in a brilliant series of researches which within three years earned him a fellowship of the Royal Society of London. He was helped by a student Richard Kleeman, whom Bragg had invited to act as his assistant.
The first experiments showed clearly the well-defined ranges of α-particles and distinguished the four groups of α-particles emitted by radium, radon, RaA and RaC. They also showed the 'stopping power' of substances was approximately proportional to the square roots of the atomic weights. Bragg wrote long accounts of his work to Rutherford at McGill University, Canada. The work continued with studies of the ionization of gases by α particles, in which Bragg was helped considerably by J. P. V. Madsen. Bragg concluded that X-rays and γ rays were streams of neutral-pair particles rather than electromagnetic waves. This made him the centre of a controversy for several years. In January 1909, shortly before leaving to occupy the Cavendish chair of physics at the University of Leeds, Bragg delivered the presidential address to the A.A.A.S. meeting at Brisbane, in which he summarized his work of the past five years and commented on the significance of scientific research for the development of Australia.
In 1912 Max von Laue showed that X-rays could be diffracted by crystals and established their wave nature. During that summer Bragg and his son William Lawrence, who was then at Trinity College, Cambridge, discussed this development. While the father, with his experience of ionization measurements, went on to construct an X-ray spectrometer for the further study of the properties of X-rays, the son found a brilliant simplification of Laue's diffraction problem and formulated Bragg's Law, relating the location of maxima of the diffraction pattern to the wavelength of the radiation and the distance between the appropriate planes of atoms in the crystal. He also realized that analysis of X-ray diffraction patterns provided a means of locating the atoms in crystals. From Laue patterns W. L. Bragg derived the structures of ZnS and the alkali halides, and then, joining forces with his father who now had a superior experimental method, they together initiated the whole subject of X-ray crystallography, for which they received the Nobel prize for physics in 1915. W. L. Bragg was then 25.
The outbreak of war temporarily ended this work. W. H. Bragg became occupied with the problems of submarine detection and his son worked on sound-ranging for the artillery in France; both made notable contributions.
In 1915 W. H. Bragg was appointed to the Quain chair of physics at University College, London. Here, and on becoming Fullerian professor of chemistry and director of the Royal Institution of Great Britain in 1923, he built up vigorous schools of X-ray crystallography concerned principally with the study of organic molecules. At the institution he established a tradition of popularizing science in his Christmas lectures for young people, which were models of clarity and intellectual excitement.
W. H. Bragg maintained an active interest in X-ray crystallography until his death and made a monumental contribution to the subject, as well as serving the scientific world in other capacities. Many honours were bestowed upon him by learned institutions, including election in 1920 as an honorary fellow of Trinity College, Cambridge. He was appointed C.B.E. (1917) and K.B.E. (1920) and admitted to the Order of Merit (1931). He received the Rumford (1916) and Copley (1930) medals of the Royal Society of which he was president in 1935-40. Predeceased by his wife, he died in London on 12 March 1942 after a period in which heart trouble reduced his activity.
Sir William Bragg was a tall, rosy-cheeked man, whose large eyes were dark and kindly. His religious beliefs were strong, but not dogmatic, and are admirably expressed in his Riddell Memorial Lecture of 1941. He was always modest and ready to change his views, and his personal character shines through the records as that of a gentle and humane man.
William Lawrence Bragg was born in Adelaide on 31 March 1890 and educated at the Collegiate School of St Peter and the University of Adelaide (B.A., 1908). He graduated also at Trinity College, Cambridge, where he became a fellow and lecturer in natural science. Following the period of collaboration with his father and the war years, he was in 1919 appointed Langworthy professor of physics at Victoria University, Manchester, where he fostered a school of X-ray crystallography devoted mainly to the study of inorganic structures, notably silicates, metals and alloys. On 10 December 1921 at Cambridge he married Alice Grace Jenny Hopkinson who pursued a successful career in municipal affairs.
In 1937 Bragg became director of the National Physical Laboratory, Teddington, but a year later succeeded Rutherford as Cavendish professor of experimental physics at Cambridge. Here he joined in the attack upon the structures of the proteins, haemoglobin and myoglobin. In 1954 he was appointed to the positions earlier held by his father at the Royal Institution. At his retirement in 1966 he had seen the subject of X-ray crystallography, pioneered by his father and himself, grow from the elucidation of the structures of the simplest crystals to that of enormously complicated molecules containing thousands of atoms. He visited Australia in 1960 and spoke at the University of Adelaide of the latest triumphs of crystallography.
Sir Lawrence Bragg was widely honoured: he had been the youngest-ever Nobel laureate. His war service earned him the O.B.E. and M.C.; he was elected F.R.S. (1921), knighted (1941) and appointed C.H. (1967), and received the Hughes, Royal and Copley medals of the Royal Society. He died on 1 July 1971, survived by his wife, two sons and two daughters.
S. G. Tomlin, 'Bragg, Sir William Henry (1862–1942)', Australian Dictionary of Biography, National Centre of Biography, Australian National University, http://adb.anu.edu.au/biography/bragg-sir-william-henry-5336/text9021, published first in hardcopy 1979, accessed online 31 May 2015.
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This article was first published in hardcopy in Australian Dictionary of Biography, Volume 7, (MUP), 1979