Here reviewed are the recent progress and the present status of the organic superconductors. Aspects on synthesis, physical properties, electronic structure and mechanism of superconductivity are covered as for these several years. First we follow the development in the synthesis leading to the organic superconductor with Tc=13K. Basic molecules constituting organic superconductors have been extensively explored with the result that all successful ones are derivatives or an isolobal analogue of TTF. The investigation of the electronic structure by means of magneto-transport experiments has been fruitful. It has been established that the tight-binding band based on the highest occupied molecular orbital in the Hueckel approximation provides appropriate descriptions for the organic superconductors. The controversy over the nature of superconductivity in organics, i.e., s-type or d-type, is still hot. Concerning the mechanism of superconductivity the theory on the basis of the mediation by the intramolecular vibrations has recently received hopeful supports from isotope-effect experiments replacing the constituting atoms by their isotopes and from a point-contact tunneling experiment.
Control of cryogenic systems require flow-measurements and liquid level-measurements of cryogenic fluid. Further, stress-strain measurements are indispensable for mechanical strength testing of various materials of which cryogenic equipments compose. In this paper, measurement's principle and the way to use at low temperature are described in detail. Also, for new type measurement-systems, the prospects of cryogenic use are noted together.