J. D. Bernal

The Bakerian Lecture, 1962. The Structure of Liquids

A satisfactory picture of the structure of liquids has lagged far behind that of other states of matter. Ever since the time of Euler in the eighteenth century or, in a more precise form, since that of Maxwell in the nineteenth, we have had a convincing qualitative and quantitative picture of the chaos that is represented by the movements of the ideal gas molecules. The notion of a crystal or a solid in general as an arrangement of molecules ‘ in rank and file’, as Newton put it, is, in fact, older than Newton yet its quantitative statement was made possible only through the work of Born and others in our own century. But it is admitted even by those who work most in the field that the study of the structure of liquids or any exposition of their properties in atomic terms is still largely to be sought. This is not for want of trying. A vast number of researches have been devoted to attempts to analyze the structure of liquids, either directly by the diffraction methods which have proved so successful in crystalline solids, or, indirectly, through the construction of models and their thermodynamic testing. But we still lack either an adequate picture of the arrangement of molecules in a liquid or the necessary quantitative theory to explain their thermal and other properties.

An optical machine for measuring sphere coordinates in random packings

A simple optical machine for measuring and automatically recording quickly and accurately the coordinates of steel spheres in any array is described. Results over very large (similar 8000) assemblies of ¼ in spheres show an improved accuracy of measurement over previous instruments, the standard deviation of the error curve being reduced by over a factor of 2, or 5 when the increased capacity of the machine is taken into account. The machine may be used for a variety of systems, including multicomponent mixtures.

X-Rays and the Cyclol Hypothesis

THE purpose of the vector map described by Fankuchen and Riley1 to which Dr. Wrinch has taken exception in her recent letter2 was merely to show that the cyclol C2 skeleton does not contribute anything to the specific character of the observed X-ray reflections from crystalline insulin. No one imagines that insulin contains only (CCN) groups, but these are the only atoms of which the positions have been definitely stated by Dr. Wrinch, and therefore the only ones amenable to exact computation. Dr. Wrinch is, of course, at liberty to place other concentrations of density wherever she likes, but she cannot logically claim in this case that the structure arrived at in this way offers any confirmation of the cyclol hypothesis. Moreover, as has been shown already3, Dr. Wrinchs construction of the vector map from such concentrations4 has been incorrectly carried out, and therefore cannot confirm her proposed model of the insulin structure. Finally, the shape and size of the cyclol molecule do not offer a particularly convincing fit into the cell of insulin. Any spherical molecule of approximately the right molecular weight would fit the cell equally well. The only positive agreement is in the presence of a trigonal axis of symmetry, which can scarcely be claimed to justify the acceptance of such an elaborate construction.