William Henry Bragg (2.06.1862-12.03.1942) was an English physicist and a Fellow of the Royal Society (1907), and its president in 1935—40. He was born in Wigton. He graduated from the University of Cambridge (1885). In 1885-1908 he was professor at the University of Adelaide (Australia), in 1909—15 at the University of Leeds and in 1915 —23 at the University of London. From 1923 he was professor and director of the Royal Institution (London). His research concerned the study of X-rays, the penetrating and ionising power of fast charged particles, X-ray structural analysis and X-ray spectroscopy. Using the diffraction of X-rays by crystals, he was the first, together with his son W. L. Bragg, to carry out (1912) a study of crystal structures, and he gave experimental proof of the periodicity of the atomic structure of crystals. Analysing the reflection of monochromatic X-ray radiation from various sections of plane-parallel configurations of atoms in the crystal lattice, they determined the wavelength of the radiation and the type of symmetry of the lattice (the lattice constants). He developed a method of X-ray analysis of crystal structures — the rotating-crystal method — for the study of X-ray spectra, and invented (1913) the X-ray spectrometer. The Braggs' experiments on the study of crystal structures began X-ray structural analysis and X-ray spectroscopy. For his great contribution to the study of the structure of crystals by means of X-rays W. H. Bragg (together with his son) was awarded the Nobel Prize in 1915. He studied the stopping power of various elements and established that alpha particles have a definite range; he investigated the specific ionisation produced by alpha particles in air at various distances from the source (the Bragg curve).
He was the author of several popular science books, some of them translated into Russian. A member of a number of academies. The B. Rumford (1916) and Copley (1930) Medals. In 1923-30 he was president of the International Union of Pure and Applied Physics.