William Barlow was an English amateur geologist specialising in crystallography. He is regarded for his research and examination of the forms of crystalline structures, deducting that there were only 230 forms of symmetrical crystal arrangements, known as space groups. He is also noted for his service as the president of the English Mineralogical Society from 1915 to 1918, and Fellow of the Royal Society.
Background
William Barlow was born on August 8, 1845, in Islington, London. He was the second son of Frederick Barlow, a speculative builder and building surveyor of Kensington. 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.
Education
Barlow, a privately educated genius, was perhaps one of the last great amateurs in science.
Career
It was only when Barlow was in his early thirties, however, after he attained the leisure afforded by an inheritance from his father, that he began to study and work in crystallography.
His first paper (1883) in some respects marked no great departure from earlier theories - some dating from the time of Kepler - in which a crystal was regarded as resembling an orderly stack of cannonballs. Barlow was probably unaware of these earlier theories, for by his time a considerable body of chemical theory emphasized the association of atoms into the molecular groupings of compounds. Nearly all of the two-element crystals that Barlow knew, principally the alkali halides, formed cubic crystals, whatever their chemical composition. As he stated in his introductory sentence of “Probable Nature of the Internal Symmetry of Crystals”, this “. . . led him to believe that in the atom-groupings which modern chemistry reveals to us the several atoms occupy distinct portions of space and do not lose their individuality.” Thus, by treating the atoms as individual spheres, Barlow was able to stack them in five arrangements that he considered to be the only “very symmetrical” ones; these correspond to structures known today as body-centered cubic, simple cubic, face-centered cubic (cubic closest-packed), body- centered hexagonal (hexagonal closest-packed), and one kind of double hexagonal (but not closest-packed).
In his first paper, Barlow also recognized that body-centered cubic and simple cubic structures admit packing of spheres of two kinds (but of equal size), and are therefore suited to be structures of the alkali halides. Not until his definitive paper on structure, read before the Royal Society of Dublin in 1897, did Barlow explicitly display the variations possible in making the two kinds of spheres of two corresponding sizes. This was a correct guess for the structure of alkali halides, and through Barlow’s collaboration with W. J. Pope, later professor of chemistry at Manchester, this structure was suggested by Pope to W. L. Bragg, who in 1913 confirmed it with the first structure determination by X-ray diffraction.
His career spanned a critical stage in the development of crystallography. His self-educated guesses were sometimes off the mark, but often clear and to the point, and always provocative.
Views
Barlow`s original view of the nature of crystalline matter united the mathematical system of symmetry, for which he wrote his own final chapter in the 1890’s, with an anticipation of the new determinations of atomic structure that were to follow after 1910, and also with certain speculations on the relation of symmetry to structure that have not yet been fully elucidated. Barlow’s theories of the properties of crystals were based on the close packing of atoms.
Membership
Barlow was elected to the Royal Society in 1908 and was president of the Mineralogical Society in 1915-1918.
Personality
Quotes from others about the person
In Barlow`s obituary of Barlow, Pope says:
"Although X-ray analysis has increased our knowledge of crystal structure in an astounding way and has proved a most useful tool, it has not led to a mechanical theory of crystal structure; it reveals the atomic arrangement but offers no reason why the component atoms seem to be closely packed in some crystalline structures and often loosely in others. The required mechanical theory of crystal structure may be found in some kind of generalisation of Barlow’s conception of equilibrium conditions."