How did Kamerlingh Onnes achieve such low temperatures?
The pursuit of extremely low temperatures necessitated the development of sophisticated apparatus and meticulous techniques. My work centered on the cryogenic laboratory at Leiden, where we focused on the liquefaction of gases. This involved a cascade process, starting with the liquefaction of oxygen and nitrogen, which were then used to pre-cool and condense hydrogen. Finally, hydrogen was used to liquefy helium, the most challenging gas to liquefy due to its very low critical temperature. We employed advanced pumps and carefully constructed vacuum jackets to minimize heat ingress. The 'Onnes cycle,' a method of regenerative cooling, was crucial. It was through these painstaking engineering efforts, detailed in 'On the Cryogenic Laboratory at Leiden and the Production of Very Low Temperatures,' that we created the conditions for our discoveries.
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