AbstractShortly after its discovery the electron was recognized as the carrier of electricity in metals. The difficulties encountered in treating the conduction electrons as a classical ideal gas was removed upon the advent of quantum mechanics and led to a satisfactory explanation of normal metallic conductivity. Although superconductivity was discovered more than fifty years ago, however, the first phenomenological theory did not come until the middle thirties and it took another twenty years before the first microscopic theory was presented. It was based upon the assumption that the conduction electrons formed a degenerate Bose gas but was soon replaced through the recognition that the pairing of electrons in a Fermi gas furnished a more realistic and quantitative explanation of superconductivity. The striking manifestation of superconductivity as a quantum phenomenon on macroscopic scale was demonstrated in the early sixties through the discovery of flux‐quantization in a closed superconductive ring and led shortly afterwards to the interesting related effects which arise from the introduction of a dividing barrie