Physicist, born on 7 June 1877 at Widnes, Lancs. Educated at the Liverpool Mechanics' Institution and University College, Liverpool, he obtained a first class BSc in Maths and Physics in 1899 and won a scholarship to work under J.J. Thompson at the Cavendish Laboratory, Cambridge. In 1902 at Thompson's suggestion, he began studying some of the properties and effects of X-rays and was awarded a research BA in 1903. In 1909 he was appointed Wheatstone Professor of Physics at King's College, London and was elected fellow of the Royal Society in 1912. In 1913 he became Professor of Natural Philosophy at Edinburgh, where he helped to establish the honours school of Physics. In 1917 his work on X-ray scattering was recognised by the award of the Nobel Prize for Physics and the Hughes Medal of the Royal Society. A lunar crater was named Barkla in his honour. In 1918 he turned down an opportunity to return to Cambridge.
He regarded scientific investigation as a part of the quest for God, the Creator. In later life he was prepared to take mental jumps by which others in the field thought he risked going off track. An example of this is his statement that It is to the apparent violations of known laws, and not to further confirmation under very precise and specialised conditions that we must look for an advance in knowledge. This idea was not well received at the time, but new experiences and new insights do cause established ideas to be revised.
In Edinburgh he and his family were members at Nicolson Square, where he served as society steward, poor steward and trustee 1921-1944, and exercised his musical interests and talents: he had a rich bass voice. His son Michael, a surgeon in the RAF, was killed in North Africa in 1943. He himself died in Edinburgh on 23 October 1944.