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 Bosscha Kamerlingh Onnes was his assistant from 1878 to 1882, after which Kamerlingh Onnes became professor at Leiden University. In 1885 Boscha needed to resign as director because of poor health. His "Verspreide Geschriften" (Diverse Writings) were published in three volumes (Leyden, 1902). In 1855 he married Paulina Emilia Kerkhoven in the town of Voorst. They had four daughters and two sons. The Bosscha Observatory on Java has been named after his son Karel Albert Rudolf Bosscha (1865–1928), who contributed much to the technical development of Indonesia. Johannes Bosscha Johannes Bosscha Jr. (18 November 1831 – 15 April 1911) was a