Superconductivity was discovered in 1911 by Heike Kamerlingh Onnes in Leiden. That discovery can be traced to the steady advance in laboratory techniques for obtaining ever lower temperatures that began when Louis Cailletet in France and Raoul Pictet in Switzerland succeeded in liquefying trace amounts of the “permanent gases,” nitrogen, air and hydrogen. These gases were so named because previous attempts to liquefy them, by Michael Faraday among others, had been unsuccessful.