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,
Leiden if there's a Sunday involved) and includes parades, a hutspot feast, historical reenactments, a funfair and other events. The city has recently started to host the Leiden International Film Festival, the fastest growing festival of its type in the Netherlands. Leiden has important functions as a shopping and trade centre for communities around the city. The University of Leiden is famous for its many discoveries including Snells law (by Willebrord Snellius), the famous Leyden jar, a capacitor made from a glass jar, invented in Leiden by Pieter van Musschenbroek in 1746. Another development was in cryogenics: Heike Kamerlingh Onnes (1913