BRAGG, SIR WILLIAM HENRY (1862-1942), physicist,

son of Robert John Bragg, a sea captain who had become a farmer, and his wife Mary Wood, daughter of a clergyman, was born at Stoneraise Place, Wigton, Cumberland, on 2 July 1862. He was educated at King William's College, Isle of Man and, winning a scholarship, Trinity College, Cambridge. He graduated in 1884 as third wrangler in the mathematical tripos. In 1885 he was appointed Elder professor of mathematics and physics at the university of Adelaide and began his duties there early in 1886. He then had little knowledge of physics, but there were only about a hundred students doing full courses at Adelaide of whom scarcely more than a handful belonged to the science school. Bragg was thus enabled to develop his knowledge of the subject in his early years, but it was not until he was past 40 that he began to do research work of importance. At the meeting of the Australasian Association for the Advancement of Science, held at Dunedin in 1904, Bragg, as president of his section, delivered an address on "Some Recent Advances in the Theory of the Ionization of Gases". This paper was the origin of his first book Studies in Radioactivity, published in 1912. Shortly after the delivery of his 1904 address some radium bromide was placed at the disposal of Bragg with which he was able to experiment. In December 1904 a paper by him "On the Absorption of a Rays and on the Classification of the a Rays from Radium" appeared in the Philosophical Magazine, and in the same number a paper "On the Ionization Curves of Radium", written in collaboration with R. Kleeman, also appeared. At the end of 1908 Bragg resigned his professorship at Adelaide to become Cavendish professor at Leeds university. During his 23 years in Australia he had seen the number of students at Adelaide university nearly quadrupled, and had had a full share in the development of its excellent science school.

At Leeds Bragg continued his work on X-rays with much success. He invented the X-ray spectrometer and with his son, W. L. Bragg, founded the new science of X-ray analysis of crystal structure. In 1915 father and son were jointly awarded the Nobel prize. Their volume, X-Rays and Crystal Structure, published in this year, had reached a fifth edition 10 years later. Bragg was appointed Quain professor of physics at University College, London, in 1915 but did not take up his duties there until after the war. He did much work for the government at this time, largely connected with submarine detection, at Aberdour on Forth and at Harwich, and returned to London in 1918 as consultant to the admiralty. While Quain professor at London he continued his work on crystal analysis and in 1923 was appointed director of the Royal institution, Fullerian professor of chemistry, Royal Institution, and director of the Davy-Faraday laboratory. This institution was practically rebuilt in 1929-3O and under Bragg's directorship many valuable papers were issued from the laboratory. He had been elected a fellow of the Royal Society in 1907, was elected a vice-president in 1920, and from 1935 to 1940 was president. He died at London on 12 March 1942. He married in 1889 Gwendoline, daughter of Sir Charles Todd (q.v.), who died in 1929. He was survived by a daughter and a son, Sir William Lawrence Bragg, who was born at Adelaide in 1890, educated at St Peter's College, Adelaide, and Adelaide and Cambridge universities, and became one of the most distinguished scientists of his time. In 1938 he was appointed Cavendish professor of experimental physics at Cambridge.

Bragg was essentially modest and was long in realizing his powers. In later years his value was fully recognized and honours crowded upon him. He was given honorary degrees by many great universities and was awarded the Rumford medal of the Royal Society in 1916 and the Copley medal in 1930. He was created C.B.E. in 1917, K.B,E. in 1920, and in 1931 was given the Order of Merit. In addition to the books already mentioned Bragg wrote The World of Sound (1920), Concerning the Nature of Things (1925), Old Trades and New Knowledge (1926), An Introduction to Crystal Analysis (1928) and The Universe of Light (1933). The first three are reprints of lectures delivered before a "juvenile auditory" at the Royal institution, admirable examples of how a great man can simplify his matter so that it may be intelligible to a young audience. The last book is an extension of a similar course of lectures. Papers by Bragg will also be found in the Philosophical Magazine, in the Transactions of the Royal Society, and elsewhere. Some of his addresses were published separately as pamphlets. He also wrote with his son The Crystalline State, 1933. He was a strong exponent of the value of scientific research, was a member of the advisory council for scientific and industrial research from 1937, and here, as in the realm of pure science, his work was of the greatest value.