Superconducting magnet issues "shaken" out of them, until they are eventually able to operate reliably at their full planned current without experiencing quenches. Although the idea of making electromagnets with superconducting wire was proposed by Heike Kamerlingh Onnes shortly after he discovered superconductivity in 1911, a practical superconducting electromagnet had to await the discovery of superconducting materials that could support large critical supercurrent densities in high magnetic fields. The first successful superconducting magnet was built by G.B. Yntema in 1955 using niobium wire and achieved a field of 0.7 T at 4.2 K. Then, in 1961, J.E. Kunzler, E. Buehler, F.S.L. Hsu,
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