A physicist.[ref]
https://actorenregister.nationaalarchief.nl/actor-persoon/kamerlingh-onnes-prof-h-te-leiden. Independent biographical identity and professional specialization
Helium liquefaction supplied a route to very low temperatures. The resistance-versus-temperature experiment for superconductivity and measurements of superconducting persistent current show how reaching those conditions opened new questions about electrical behavior.
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Heike Kamerlingh Onnes was a Dutch physicist known for his pioneering work in low-temperature physics. He was born on September 21, 1853, and passed away on February 21, 1926. Onnes is perhaps best known for his discovery of superconductivity in 1911, when he observed that the electrical resistance of mercury disappeared completely when it was cooled below a certain critical temperature (approximately 4.2 K, or -268.95 °C).