The magnetization curves of a supraconducting sphere and ring

Abstract

The discovery by Meissner and Ochsenfeld that zero permeability seems to be as essential a feature of the supraconducting state as infinite conductivity, has shown the inadequacy of the assumption that the magnetic properties can be completely predicted by application of ordinary electrodynamics to the limiting case of high conductivity, and has therefore revived interest in a direct experimental study. During the last two years a number of such investigations has been published based essentially on measurements of the disturbance of a uniform magnetic field by the presence of the supraconductor, and revealing important new features. An alternative method is that of Faraday, in which the magnetic moment of a specimen is deduced directly from the force acting on it in an inhomogeneous field, and the present paper deals particularly with the magnetic properties of a supraconducting pure lead sphere, investigated by this method. Some experiments with a sphere of impure lead and with an anchor ring of pure lead, are also described here, mainly, however, from the point of view of clearing up various features of the magnetization curve of the pure sphere.