Sir William Henry Bragg (2 July 1862 – 12 March 1942) was a British X-ray crystallographer who uniquely shared a Nobel Prize with his son Lawrence 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.
William Henry Bragg was born on 2 July 1862 in Westward, Cumberland, England, the son of Robert John Bragg, a merchant marine officer and farmer, and Mary Wood, a clergyman's daughter. His mother died when he was age 7, and was raised by his uncle (also named William Bragg) in Market Harborough. He was educated at the Grammar School there, at King William's College on the Isle of Man, and—having won an exhibition—at Trinity College, Cambridge. He graduated in 1884 as third Wrangler, and in 1885 earned First Class Honours in the mathematical Tripos.
In 1885, Bragg was appointed Elder Professor of Mathematics and Physics at the University of Adelaide in Australia, and started work there in early 1886. Being a skilled mathematician, at that time he had limited knowledge of physics, most of which was in the form of applied mathematics he had learnt at Trinity College. Also at that time, there were only about a hundred students doing full courses at Adelaide, of whom less than a handful belonged to the science school, whose deficient teaching facilities he improved by apprenticing himself to a firm of instrument makers. He was an able and popular lecturer; he encouraged the formation of the student union, and the attendance, free of charge, of science teachers at his lectures.
Bragg's interest in physics developed, particularly in the field of electromagnetism. In 1895, he was visited by Ernest Rutherford, en route from New Zealand to Cambridge; this was the commencement of a lifelong friendship. He had a keen interest in the new discovery of X-rays by Wilhelm Röntgen. On 29 May 1896 at Adelaide, he demonstrated before a meeting of local doctors the application of "X-rays to reveal structures that were otherwise invisible". Samuel Barbour, senior chemist of F. H. Faulding & Co., an Adelaide pharmaceutical manufacturer, supplied the necessary apparatus in the form of a Crookes tube, a glass discharge tube. The tube had been obtained at Leeds, England, where Barbour visited the firm of Reynolds and Branson, a manufacturer of photographic and laboratory equipment. Barbour returned to Adelaide in April 1896. Barbour had conducted his own experiments shortly after return to Australia, but results were limited due to limited battery power. At the University, the tube was attached to an induction coil and a battery borrowed from Sir Charles Todd, Bragg's father-in-law. The induction coil was utilised to produce the electric spark necessary for Bragg and Barbour to "generate short bursts of X-rays". The audience was favorably impressed. He availed himself as a test subject, in the manner of Röntgen and allowed an X-ray photograph to be taken of his hand. The image of the fingers in his hand revealed "an old injury to one of his fingers sustained when using the turnip chopping machine on his father's farm in Cumbria".
As early as 1895, Bragg was working on wireless telegraphy, though public lectures and demonstrations focussed on his X-ray research which would later lead to his Nobel Prize. In a hurried visit by Rutherford, he was reported as working on a Hertzian oscillator. There were many common practical threads to the two technologies and he was ably assisted in the laboratory by Arthur Lionel Rogers who manufactured much of the equipment. On 21 September 1897 Bragg gave the first recorded public demonstration of the working of wireless telegraphy in Australia during a lecture meeting at the University of Adelaide as part of the Public Teachers' Union conference. Bragg departed Adelaide in December 1897, and spent all of 1898 on a 12-month leave of absence, touring Great Britain and Europe and during this time visited Marconi and inspected his wireless facilities. He returned to Adelaide in early March 1899, and already on 13 May 1899, Bragg and his father-in-law, Sir Charles Todd, were conducting preliminary tests of wireless telegraphy with a transmitter at the Observatory and a receiver on the South Road (about 200 metres). Experiments continued throughout the southern winter of 1899 and the range was progressively extended to Henley Beach. In September the work was extended to two way transmissions with the addition of a second induction coil loaned by Mr. James Oddie of Ballarat. It was desired to extend the experiments cross a sea path and Todd was interested in connecting Cape Spencer and Althorpe Island, but local costs were considered prohibitive while the charges for patented equipment from the Marconi Company were exorbitant. At the same time Bragg's interests were leaning towards X-rays and practical work in wireless in South Australia was largely dormant for the next decade.
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 in Dunedin, New Zealand, on "Some Recent Advances in the Theory of the Ionization of Gases". 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. This paper was also the origin of his first book Studies in Radioactivity (1912). Soon after the delivery of his 1904 address, some radium bromide was made available to Bragg for experimentation. In December 1904 his paper "On the Absorption of α Rays and on the Classification of the α Rays from Radium" appeared in the Philosophical Magazine, and in the same issue a paper "On the Ionization Curves of Radium", written in collaboration with his student Richard Kleeman, also appeared.
At the end of 1908, Bragg returned to England. During his 23 years in Australia "he had seen the number of students at the University of Adelaide almost quadruple, and had a full share in the development of its excellent science school." He had returned to England on the maiden voyage of the SS Waratah, a ship which vanished at sea on its second voyage the next year. He had been alarmed at the ship's tendency to list during his voyage, and had concluded that the ship's metacentre was just below her centre of gravity. In 1911, he testified his belief that the Waratah was unstable at the Inquiry into the ship's disappearance.
There is a bust of Bragg in North Terrace, Adelaide, South Australia.
From 1909 to 1915, Bragg was Cavendish Professor of Physics at the University of Leeds. He continued his work on X-rays with much success. He invented the X-ray spectrometer and with his son, Lawrence, then a research student at Cambridge, founded the new science of X-ray crystallography, the analysis of crystal structure using X-ray diffraction.
Both of his sons, Lawrence and Robert, were called into the army after the First World War broke out in 1914 . The following year, Bragg was appointed Quain Professor of Physics at University College London. He had to wait for almost a year to contribute to the war effort; in July 1915, he was appointed to the Board of Invention and Research set up by the Admiralty. In September, his younger son Robert died of wounds at Gallipoli. In November, he shared the Nobel Prize in Physics with Lawrence. The Navy was struggling to prevent sinkings by unseen, submerged U-boats. The scientists recommended that the best tactic was to listen for the submarines. The Navy had a hydrophone research establishment at Aberdour, Scotland, staffed with navy men. In November 1915, two young physicists were added to its staff. Bowing to outside pressure to use science, in July 1916, the Admiralty appointed Bragg as scientific director at Aberdour, assisted by three additional young physicists. They developed an improved directional hydrophone, which finally convinced the Admiralty of their usefulness. Late in 1916, Bragg with his small group moved to Harwich, where the staff was enlarged and they had access to a submarine for tests. In France, where scientists had been mobilized since the beginning of the war, the physicist Paul Langevin made a major stride with echolocation, generating intense sound pulses with quartz sheets oscillated at high frequency, which were then used as microphones to listen for echoes. Quartz was usable when vacuum tubes became available at the end of 1917 to amplify the faint signals. The British made sonar practicable by using mosaics of small quartz bits rather than slices from a large crystal. In January 1918, Bragg moved into the Admiralty as head of scientific research in the anti-submarine division. By war's end, British vessels were being equipped with sonar manned by trained listeners.