Bragg, William Henry (1862–1942)

English physicist. He shared with his son Lawrence Bragg the Nobel Prize for Physics in 1915 for their research work on X-rays and crystals.

Crystallography had not previously been concerned with the internal arrangement of atoms but only with the shape and number of crystal surfaces. The Braggs' work gave a method of determining the positions of atoms in the lattices making up the crystals, and for accurate determination of X-ray wavelengths. This led to an understanding of the ways in which atoms combine with each other and revolutionized mineralogy and later molecular biology, in which X-ray diffraction was crucial to the elucidation of the structure of DNA.

Bragg was born in Westward, Cumberland. He obtained a first-class degree in mathematics from Cambridge in 1885 and was immediately appointed professor of mathematics and physics at the University of Adelaide, South Australia. In 1909 he returned to the UK as professor at Leeds; from 1915 he was professor at University College, London.

Bragg became convinced that X-rays behave as an electromagnetic wave motion. He constructed the first X-ray spectrometer in 1913. He and his son used it to determine the structures of various crystals on the basis that X-rays passing through the crystals are diffracted by the regular array of atoms within the crystal. He was knighted in 1920.