Leiden University at the university. The learning and reputation of Jacobus Gronovius, Herman Boerhaave, Tiberius Hemsterhuis and David Ruhnken, among others, enabled Leiden to maintain its reputation for excellence down to the end of the 18th century. At the end of the nineteenth century, Leiden University again became one of Europe's leading universities. At the world’s first university low-temperature laboratory, professor Heike Kamerlingh Onnes achieved temperatures of only one degree above absolute zero of −273 degrees Celsius. In 1908 he was also the first to succeed in liquifying helium and can be credited with the discovery of the superconductivity in metals. The
Frans Michel Penning Derksen in 1921 and they had four children named Lourens, Hendricus, Paul, and Nellie. In 1924, Penning was hired as an experimental physicist at the Dutch section of the Phillips research department located in the Strijp district of Eindhoven. Gilles Holst, former assistant to Heike Kamerlingh Onnes, and head of the Philips Natuurkundig Laboratorium (NatLab), tasked Penning with continuing research on gas discharge phenomena to develop new lamps. Penning investigated breakdown energy potentials of low pressure inert gas discharges. In 1926, Penning observed that electrons under direct voltage current in low-pressure mercury discharges reach high velocities due to high-frequency oscillations