William Barlow (1845–1934): Speculative builder, man of leisure and inspired crystallographer

In the history of physical science in the twentieth century, it is rare for anyone to conduct experiments or conclude hypotheses whilst an amateur, and rise to become an established name in science, later a Fellow of the Royal Society. One who did achieve this was William Barlow, a Londoner, born in 1845 into a family where his father was a speculative builder and building surveyor. This occupation enabled William to take a private education, but he preferred to accompany his father in the building trade, constructing new homes in the rapidly expanding areas of north London. When his father died in 1875, William and his elder brother inherited a fortune and William, from then on, was not required to work for a living. With this freedom he was able to indulge in his passion of crystallography, in which he had a remarkable ability to spatially visualize atomic structures in three dimensions. Using this ability, he initially looked at the possible structures of well-known compounds and was eventually able to deduce that for all compounds there are just 230 different kinds of symmetry arrangements which form the basis for crystal structures. These arrangements of symmetry elements are known as space groups. Though he was beaten to publication by a Russian and a German, Barlowʹs explanation, when it was published, showed a novel way of arriving at the same conclusion. It was this kind of novel approach which was Barlowʹs trademark. In 1908, he was elected to be a Fellow of the Royal Society and, in 1915, became President of the Mineralogical Society of Great Britain, a post he held for three years. Barlow also postulated on some structural models, which were later shown to be essentially correct when X-ray diffraction analysis, developed by Sir W. Bragg at Cambridge, enabled the internal structure to be studied. Barlow died in 1934 at his home in Stanmore.