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,
Heike Kamerlingh Onnes and Gustav Kirchhoff at the University of Heidelberg from 1871 to 1873. Again at Groningen, he obtained his masters in 1878 and a doctorate in 1879. His thesis was "Nieuwe bewijzen voor de aswenteling der aarde" ("tr". New proofs of the rotation of the earth). From 1878 to 1882 he was assistant to Johannes Bosscha, the director of the Delft Polytechnic, for whom he substituted as lecturer in 1881 and 1882. He was married to Maria Adriana Wilhelmina Elisabeth Bijleveld (m. 1887) and had one child, named Albert. His brother Menso Kamerlingh Onnes (1860–1925) was a fairly well known painter