The Crystallographic Community

Bernard Wheeler Robinson 1904-1997

J. Appl. Cryst. (1997). 30 1173

Bernard Wheeler Robinson died on July 7, 1997, aged 93. An obituary appeared in the London Times for August 6, dealing mainly with his extended contributions to amateur music making in Britain and his creation and support of Music Camp from 1927 onwards. Dr Robinson should also be remembered for his unique contribution to X-ray crystallography while at the Royal Institution in London in W. H. Bragg's group. This work was reported in two papers: Proc. R. Soc. London Ser. A (1933), 142, 422-447 and Proc. R. Soc. London Ser. A (1934), 147, 467-478. The intent of the first work was to establish the absolute structure factor of the 001 reflection of anthracene with Cu Kalpha and Mo Kalpha radiation from measurements on small single crystals. The result would provide a reference for crystallographic studies of other organic molecules. The measurements were made on a Bragg spectrometer with monochromated radiation and reasonable angular resolution. Eighteen crystals were individually measured by comparison with a calibrated direct beam. The crystals varied in weight from 44 to 480 micrograms, all being weighed on a special balance. Their physical dimensions were measured in detail so that corrections for absorption and extinction could be estimated by determination of the beam paths through the various levels of the crystal. The corrections for extinction involved the individual reflection profiles, which were quite varied. The corrected intensities appeared to be reasonably in accord with the weight of the crystal. This work constituted effectively the first intensity measurement project on small single crystals. It can truly be regarded as unique for, despite technical advances and great improvements in measurement procedures since the middle 1930s, there has not been a compable project that has in any wise imitated Robinson's intention of obtaining absolute structure-factor values. To read his paper in all its details in the context of his time and of the limited facilities for calculations is an incredible and slightly frightening experience, especially for us now pampered by almost unlimited computational capability.

In his second piece of work, he carried out measurements on a powdered specimen of anthracene. This yielded a result (34.3) that was slightly larger than the single-crystal value for Mo (32.8), and even more so than that for Cu (30.5). Despite the imperfections in respect of the corrections for extinction, so that the single-crystal project did not achieve its original intention, it was, nevertheless, a most valiant attempt, and Wheeler Robinson should be remembered for it.

A. McL. Mathieson