ONNES,KAMERLINGH AND THE DISCOVERY OF SUPERCONDUCTIVITY

Many papers begin with the statement that Kamerlingh Onnes discovered superconductivity in 1911; one wonders what urged him to do the experi ment that led to this discovery. Superconductivity was definitely not foreseen at that moment, and for many years the theory could not even predict it. Hence what drove Kamerlingh Onnes to measure the electrica l resistivity at a temperature range where one could not expect to fin d anything radically new? What were the prevailing theories; at that t ime? This is discussed after a general description of the man, his lab oratory and the state of physics in the preceding years. Conclusion: A lhough the driving factor in the low temperature resistance work was m ost likely the need for a reliable and reproducible thermometer, the s peculations about what would happen in these regions were based on Kel vin's theory, at least in the initial phase of the work. This theory p redicted exactly the opposite of what was found eventually.