99 years ago today, on February 21, 1926 (January 9, 1926 in the lunar calendar), Dutch physicist and discoverer of superconductivity, Kamelin Onnes passed away. Kamelin Onnes (1853 - 1926) Kamerlingh-Onnes, a Dutch physicist at Heike. Born in Groningen on September 21, 1853, and died on February 21, 1926. Received a doctorate from the University of Groningen in 1879. In 1882, he served as professor of experimental physics at Leiden University and established the world-famous cryogenic research center-Leiden Laboratory (later renamed the Camelin Onnes Laboratory in his memory). He taught at the school until his retirement in 1923. Kamelin Onnes's research in the field of cryogenic physics began with his work on liquefied gases (air) in 1877. Hydrogen was successfully liquefied in 1906, and helium, then considered a permanent gas, was further liquefied in 1908. Since then, he turned his research to measuring the change in metal resistance with temperature. In 1911, he discovered that the resistance of mercury completely disappeared at low temperatures of 4.22 to 4.27 K, and then discovered that some other metals also had these characteristics. He called this phenomenon superconductivity. This opened up a new field of cryogenic physics. Later, he discovered the critical current and critical magnetic field of superconductors. For his outstanding contribution to low-temperature physics, Kamelin Onnes won the 1913 Nobel Prize in Physics.