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The self-diffusion coefficient D of 99.95% purity gold has been measured in the temperature range 704°C to 1048°C using the sectioning method. D was found to vary with temperature according to the equation

D=(0.091±0.001) exp [-(41 700±300)/RT] cm² sec^-1.

A detailed comparison of this result is made with those of earlier workers.

The ideal phase transition in superconductors is analysed in such a way as to examine the connection between the two types of second-order phase change which are mathematically possible, viz. those associated with a finite length of transition line, and those confined to a singular point on a transition line which is elsewhere of first order. It is concluded (i) that the latter category of second-order transition appears only as a somewhat trivial case of the former, (ii) that it is very doubtful whether points of second-order equilibrium really exist in isolation. The discussion also shows how the superconducting phenomenon provides a good example of the existence of first-order transitions possessing volume discontinuities which are exceedingly small, but non-zero; this circumstance allows an Ehrenfest-type second-order phase change to be regarded as the limiting case of a first-order transition.

An approximate distribution is deduced for the directions of the `lines of maxima' on a random surface. The theoretical distribution is found to be in good agreement with some experimental results obtained previously by Briggs and Page.

The magnetic susceptibilities of the rare-earth metals lanthanum, cerium, praseodymium, neodymium and samarium have been measured over the temperature range 1.5°K to 300°K. Low temperature anomalies correlating with recent specific heat measurements have been found in cerium, neodymium and samarium at temperatures of 12.5°K, 7.5°K and 14.8°K respectively, and it is believed that these metals become anti-ferromagnetic below these temperatures. At higher temperatures the susceptibilities of cerium and praseodymium obey the Curie-Weiss law, with effective atomic moments of 2.51 and 3 56 Bohr magnetons respectively. Neodymium obeys a law of the form χ = C/(T − θ) + K, where the Curie constant C indicates an effective atomic moment of 3.3 Bohr magnetons (μ_B). These moments are in fair agreement with the values expected for the trivalent ions of the elements, assuming Russell-Saunders coupling of the orbital and spin moments of the 4f electrons.

It is shown that the Fowler-Darwin definitions of the temperature and chemical potential can be extended in a natural way to cover non-equilibrium but steady assemblies. The concept of equilibrium is replaced by the more general one of `compatibility', and it becomes possible to show that the proposed statistical definitions of quantities like temperature reduce to suitable averages over the assembly of the locally measured quantities. The usual restrictions to small departures from equilibrium are unnecessary. A simple problem (flow of gas in a tube) is discussed from the new point of view.

The theory of transport phenomena in semiconductors is extended to include the effects of `phonon drag' on electrons and `electron drag' on phonons. A simple phenomenological theory is developed first, and it is shown that this gives a good semi-quantitative account of the effects under investigation Commencing with the Boltzmann equation for electrons and phonons, the electrical conductivity, the thermal conductivity and the thermoelectric coefficients are calculated exactly, under certain simplifying assumptions. Where possible, the theoretical results are compared with experimental data and it is shown that general, though not exact, agreement prevails.

Thin films of oxides, hydroxides or metals have been shown to increase the stress at which plastic deformation starts by an amount which cannot be explained by the strength of the films themselves. Most experiments have been on creep, showing the effect of oxides and hydroxides. This paper records an investigation into the effect of thin films of gold on the stress-strain curves of cadmium crystals.

The crystals were grown in an Andrade-Roscoe furnace and extended in a rigid frame machine with a Polanyi beam and photographic recording. The gold films were deposited by sputtering.

It was found that thin gold films increased the stress at which plastic deformation started by about 6 g wt mm^-2. The increase was independent of film thickness for films of 1500-24000 Å. The nature of the effect of the film upon the stress-strain curves depended upon the orientation of the crystals.