Superconductivity is the phenomenon of certain materials exhibiting zero electrical resistance and the expulsion of magnetic fields below a characteristic temperature. The history of superconductivity began with Dutch physicist Heike Kamerlingh Onnes's discovery of superconductivity in mercury in 1911. Since then, many other superconducting materials have been discovered and the theory of superconductivity has been developed. These subjects remain active areas of study in the field of condensed matter physics. The study of superconductivity has a fascinating history, with several breakthroughs having dramatically accelerated publication and patenting activity in this field, as shown in the figure on the right and described in details below. Noteworthy, the number of non-patent publications about superconductors is much larger than the number of patent families, which is characteristic of a commercially unsuccessful technology. Exploring ultra-cold phenomena (to 1908) James Dewar initiated research into electrical resistance at low temperatures. Dewar and John Ambrose Fleming predicted that at absolute zero, pure metals would become perfect electromagnetic conductors (though, later, Dewar altered his opinion on the disappearance of resistance, believing that there would always be some resistance). Walther Hermann Nernst developed the third law of thermodynamics and stated that absolute zero was unattainable. Carl von Linde and William Hampson, both commercial researchers, nearly at the same time filed for patents on the Joule–Thomson effect for the liquefaction of gases. Linde's patent was the climax of 20 years of systematic investigation of established facts, using a regenerative counterflow method. Hampson's designs was also of a regenerative method. The combined process became known as the Hampson–Linde liquefaction process. Onnes purchased a Linde machine for his research. On March 21, 1900, Nikola Tesla was granted a patent for the means for increasing the intensity of electrical oscillations by lowering the temperature, which was caused by lowered resistance. Within this patent it describes the increased intensity and duration of electric oscillations of a low temperature resonating circuit. It is believed that Tesla had intended that Linde's machine would be used to attain the cooling agents. A milestone was achieved on July 10, 1908 when Heike Kamerlingh Onnes at Leiden University in the Netherlands produced, for the first time, liquified helium, which has a boiling point of 4.2 kelvins at atmospheric pressure. Sudden and fundamental disappearance Heike Kamerlingh Onnes and Jacob Clay reinvestigated Dewar's earlier experiments on the reduction of resistance at low temperatures. Onnes began the investigations with platinum and gold,