ABSTRACT
July 10, 1908, is a largely forgotten landmark in the history of science. It was on that day at the University of Leiden in Holland that Heike Kamerlingh Onnes and his assistants became the first people to liquefy helium (He). In so doing, they paved the way for the study of matter very close to the absolute zero of temperature. Superconductivity, which Kamerlingh Onnes found a few years later, is the most unexpected and exciting of the many discoveries that have taken place as a result of the production of temperatures close to the absolute zero. To appreciate fully the triumph achieved by Kamerlingh Onnes in liquefying helium gas, it is necessary to view his work within its historical context as the end of the long quest to achieve lower and lower temperatures using gas liquefaction. Helium was the last of the gaseous elements to be liquefied. Low temperatures and gas liquefaction are closely interconnected. Even lower temperatures resulted from trying to liquefy more and more gases and the work of Kamerlingh Onnes concluded a history of gas liquefaction which extended for well over 100 years starting from the end of the eighteenth century.
