Spool of lead wire for superconductivity, 1913
From the Physics Laboratory of the University of Leiden, Inv V09968

Kamerlingh Onnes had two good reasons for researching electrical resistance at low temperatures. First, with the knowledge gained he could make electric thermometers for his low-temperature laboratory. But the second reason was more exciting. There were two rival theories. According to one, resistance became lower and lower and finally at -273°C equalled zero. The other theory predicted that at this temperature the electrons would freeze together, and the resistance would on the contrary become infinite. Such a situation, with two totally different predictions, was ideal for an experimenter like Kamerlingh Onnes, since the outcome of his experiments would decide which of the theories was correct. However, in 1911 both theories proved wrong. Even at a higher temperature the resistance suddenly dropped. Kamerlingh Onnes thought up a name for this: superconductivity. An explanation for the phenomenon did not come till forty-six years later.