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Superconducting systems partitioned by barriers which are thin enough to allow supercurrents to pass through them are discussed. The implications for such systems of superconducting long-range order are considered, and a phenomenological theory developed and applied to a number of topics: penetration of a magnetic field into a barrier, interference of supercurrents in the presence of a magnetic field, the cut-off frequency associated with the propagation of electromagnetic waves along a barrier, a.c. supercurrents, and structure in the d.c. current-voltage characteristics of a barrier resulting from an applied microwave field or the a.c. supercurrent. The phenomenological theory is justified by the use of microscopic theory, and a new approach, based on the Gor'kov method, is described. The results of this approach, which is of more general validity than the tunnelling Hamiltonian method, are shown to be expressible in terms of Feynman diagrams. Attention is drawn to the analogy between supercurr...

The events leading to the discovery of tunnelling supercurrents are discussed. The devopment of the theory for d.c. and for a.c. supercurrents is discussed. 24 references.

Two functions of state ξ and η are derived, such that any equation of state for the critical region consistent with the scaling hypothesis can be expressed in the form η = (ξ). The representation has the useful property that the function has no unphysical singularities (such as the branch points associated with the critical isotherm or elsewhere in the usual representations of scaling-law equations of state).