72 Biographical Memoirs He was an ardent admirer of Gandhi and of the philosophy of non-violent passive dissent, and was disgusted by violent sports such as boxing. He was a vegetarian from conviction; although he was a keen gardener he refused any space to vegetables and concentrated entirely on flowers. He was much too reserved and diffident to take an active part in politics.
74 Biographical Memoirs and he made friends with Henry Lipson and Arnold Beevers, at that time research students in Bragg’s laboratory. In 1944 he was invited by Dorothy Hodgkin to take part in the structure determination of penicillin; this work is discussed below.
Charles William Bunn 75 the originator of a skeletal molecular modelling kit, later perfected by Kendrew. Ids papers, like his books, are illustrated with particularly clear and well-chosen drawings. Although he had a good knowledge of mathematical techniques he found that, for himself, mathematical representations by themselves were lacking. He was a master of physical techniques which are somewhat neglected today, using them to very good effect in many diverse investigations. In his text book Chemical crystallography  he wrote ‘It must be emphasized that the combination of different lines of evidence is often of much greater value than any single method of approach. X-ray methods should never be used alone; the combination of evidence given by X-ray diffraction patterns with that given by optical properties, habit, cleavage, and so on may lead to valuable conclusions in circumstances where each of these lines of evidence taken by itself would leave unresolved ambiguities.’ In this text book the sections on the use of the polarizing microscope are especially good and his popular book on crystals  contains many photographs that vividly evoke his appreciation of the beautiful and colourful phenomena seen in the polarizing microscope.
Charles William Bunn 77 In another paper (26) published in 1949 he described studies done in 1932 on the effects of concentration gradients on crystal growth. Following up a suggestion by T.R. Scott, he devised an elegant method in which the crystals were grown between slightly inclined half-silvered glass plates; concentration differences were shown up by refractive index changes which distorted the interference fringes seen when the plates were viewed under the microscope in parallel monochromatic light. This method was later taken up by Berg (1938). Bunn found that supersaturation was greatest at the edges and least at the centres of crystal faces and he established that there is effectively no correlation of growth rate with the degree of supersaturation. He saw growth as being determined by concentration gradients and to a convergent diffusion momentum which is greatest at face centres. In unpublished notes written in the 1970s he writes that to assume that spiral growth originating at screw dislocations is the main or only mechanism in crystal growth ‘is going much too far’. Some recent work on crystal growth tends to support this view.
78 Biographical Memoirs An examination of a series of saturated organic molecules led Bunn to suggest (13) that in long-chain molecules a £staggered-bond configuration’ is favoured, that is, that the non-chain bonds of the carbon atom tend to be at the maximum distance from one another. This principle allowed him to predict chain configurations in other saturated polymers. He postulated further that the presence of double bonds in the chain led to a free rotation about adjacent single bonds. He showed that, as in other polymers, in natural rubber individual molecules wound through crystalline and amorphous regions; on stretching the sizes of the former increased at the expense of the latter. He was thus able to explain rubber-like elasticity in polymers with highly flexible molecules (10) such as raw rubber and polychloroprene (the basis of ‘neoprene’ synthetic rubbers) and the differences in physical properties of these materials from rigid ^-gutta-percha (12).