Liquid helium of liquid water. Helium was first liquefied on July 10, 1908, by the Dutch physicist Heike Kamerlingh Onnes at the University of Leiden in the Netherlands. At that time, helium-3 was unknown because the mass spectrometer had not yet been invented. In more recent decades, liquid helium has been used as a cryogenic refrigerant, and liquid helium is produced commercially for use in superconducting magnets such as those used in magnetic resonance imaging (MRI), nuclear magnetic resonance (NMR), Magnetoencephalography (MEG), and experiments in physics, such as low temperature Mössbauer spectroscopy. The temperature required to produce liquid helium is low because
Johannes Kuenen experiments with x-rays with the physiologist Edward Waymouth Reid. In 1907 he was appointed professor of physics at Leiden University. Heike Kamerlingh Onnes and Kuenen led the Kamerlingh Onnes physics Laboratory. On the basis of his scientific work he was elected in 1911 as a member of the Royal Netherlands Academy of Arts and Sciences (KNAW), and became a member of the Hollandsche Maatschappij der Wetenschappen in 1915. He discovered retrograde condensation and published his findings in 1892 in the Ph.D. thesis with the title "Metingen betreffende het oppervlak van Van der Waals voor mengsels van koolzuur en chloormethyl". (Measurements