William Henry Bragg, English physicist, c 1910s.
© Science Museum / Science & Society Picture Library
Signed photograph of Sir William Henry Bragg (1862-1942) who founded X-ray crystallography, the determination by x-ray diffraction methods of the molecular structure of crystals. He was the father of William Lawrence Bragg (1890-1971), also a physicist, and they worked together, jointly winning the Nobel prize for physics in 1915. Bragg became director of the Royal Institution in 1923 as did his son after him.