What is superconductivity according to Kamerlingh Onnes?
Superconductivity, as we first observed it, is the complete and utter disappearance of electrical resistance in certain materials when they are cooled to sufficiently low temperatures. In my experiments with mercury, as documented in 'The Resistance of Pure Mercury at Helium Temperatures,' we found that at around 4.2 Kelvin, the electrical current flowed without any impediment whatsoever. This was not merely a reduction in resistance; it was its complete cessation. The material, in this state, behaves in ways that challenge classical understanding of electrical flow, and it is a testament to the power of venturing into the realm of extreme cold. The lowest temperature is not a limit but a frontier, and superconductivity is one of its most striking revelations.
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