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
Heike Kamerlingh Onnes a conductor would come to a complete halt or, in other words, metal resistivity would become infinitely large at absolute zero. Others, including Kamerlingh Onnes, felt that a conductor's electrical resistance would steadily decrease and drop to nil. Augustus Matthiessen said that when the temperature decreases, the metal conductivity usually improves or in other words, the electrical resistivity usually decreases with a decrease of temperature. On 8 April 1911, Kamerlingh Onnes found that at 4.2 K the resistance in a solid mercury wire immersed in liquid helium suddenly vanished. He immediately realized the significance of the discovery (as became clear