Magnetic transition curves of supraconductors

The experiments of Meissner and Ochsenfeld and others* have suggested that in a pure supraconducting body which has not the shape of a ring the magnetic induction B is always equal to zero, independently of the previous treatment and of the external magnetic field, provided the latter does not exceed the “threshold value”. Gorter and Casimir have given a thermodynamic treatment of the behaviour of a long-shaped supraconductor in a longitudinal magnetic field. This treatment is based on the assumption that the supraconductor is in thermal euilibrium, even if B = O in the interior in the presence of an external magnetic field, and that the perturbation of the supraconductivity on passing the threshold is a reversible process. These assumptions were made extremely plausible, if not certain, by the experiments mentioned above.