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A plot of the superconducting threshold temperatures as a function of the Debye characteristic temperatures of the known superconducting elements discloses .a number of interesting relationships. These relationships, in conjunction with previously known empirical rules, are used to discuss the occurrence of superconduction among other elements. It is concluded that Sc, Y, and Sm are not likely to be found superconducting, but that Ce, Pr, Nd, and Ac (should its atomic volume prove to be of the order of 22 cm 3 /mole) are expected to be superconducting. Data on Pa is very sketchy. The best that can be inferred is that Pa should be superconducting with a threshold temperature in excess of 2 °K.

A superconducing torus was subjected to a magnetic field normal to the plane of the torus and the field distribution across the plane of the superconducting torus was determined experimentally. The magnetic field near the axis of the torus was found to have the same direction as the applied field, but near the inner surface of the torus the field reversed direction in such a manner that the total flux enclosed by the torus was zero. It is concluded that the magnetic field distribution about a superconducting torus in weak magnetic fields can be adequately described by classical electrodynamics and the assumption of perfect diamagnetism.

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