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 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