William Lawrence Bragg (left) and William Henry Bragg.
Courtesy Edgar Fahs Smith Memorial Collection, Department of Special Collections, University of Pennsylvania Library.
For progress in pharmaceuticals research to occur along the lines Paul Ehrlich had suggested, the structure of complex organic molecules had to be studied in greater depth. By studying the chemical reactions that a compound and its degradation products could enter into with other compounds of known structure, chemists were able to deduce the structures of many complex organic molecules—although it sometimes took years of experimentation and analysis of results. When X-ray crystallography was introduced in 1912, it became possible to determine molecular structure from the compound itself. In this method, structural information is obtained by mathematical analysis of the intensity of X-rays scattered (or diffracted) from parallel planes in a crystal, as recorded photographically or by an electronic detector. Until electronic computers were developed during World War II, these calculations were incredibly laborious. In 1915 a unique father-son team, William Henry Bragg (1862–1942) and his son, William Lawrence Bragg (1890–1971), won the Nobel Prize in physics for their seminal roles in X-ray crystallography.
William Henry's mother died when he was just seven years old, and he was sent to live with a bachelor uncle, whose place he regarded as home during his years away at school and at Cambridge University. At the university he studied mathematics, but his first academic appointment, to the University of Adelaide in Australia—in mathematics and physics—required that he learn much of physics on his own.
An early Bragg X-ray spectrometer.
From W.H. Bragg and W. L. Bragg, X-rays and Crystal Structure (London: G. Bell and Sons, 1915).
Not until 1903–1904, at the age of 41, did William Henry embark on studies of ionizing radiation—a rather late-in-life start on a topic that was to bring a Nobel Prize. On the basis of his early publications on radiation, he was named Cavendish professor at the University of Leeds in 1908. His eldest son, William Lawrence, who had begun his university studies in mathematics in Australia, transferred to Cambridge, where he changed his focus to physics.
In 1912 Max von Laue reported the diffraction of X-rays by a crystal (for which he received a Nobel Prize in physics in 1914). The elder Bragg and his son, who was by then a doctoral student with J. J. Thomson at Cambridge, began exploring this phenomenon immediately. They brought different interests and skills to the collaboration. William Henry's original interest was in what diffraction showed about the nature of X-rays, and he was a skilled experimenter and designer of instruments. William Lawrence was more concerned with what X-rays revealed about the crystalline state, and he possessed a powerful ability to conceptualize physical problems and express them mathematically. Simple inorganic crystals like sodium chloride were the subjects of the original studies in X-ray crystallography. Here the surprising result was that in the solid state these ionic compounds did not exist as paired positive and negative ions. Sodium chloride, for instance, did not exist as NaCl units; rather, Na and Cl alternated in a regular fashion in the crystal lattice.
In 1915, the same year William Henry received the Nobel Prize, he was appointed to University College, London. But the work on X-ray crystallography came to a halt during World War I, and both Braggs served as scientific advisers to the military—especially on the problem of submarine detection. After World War I, William Lawrence began his academic career, following in the footsteps of Ernest Rutherford—first at the University of Manchester and then at the Cavendish Laboratory in Cambridge. In 1923 William Henry became head of the Royal Institution, a position in which he served 20 years and to which his son succeeded in 1954. In their various positions the Braggs continued their work in X-ray crystallography and built up programs for doctoral and postdoctoral students. Under their leadership the field moved on to such fields of study as the structure of metals and organic compounds and later to those of biochemical and pharmaceutical importance.