Robert Bunsen, who was born in 1811 in Gttingen, Germany. Bunsen studied at the University of Gttingen, where he later became a professor. Chemistry students mostly know Bunsen thanks to the burner he invented, but he also made several important scientific discoveries. Working with the physicist Gustav Kirchhoff, Bunsen pioneered the use of emission spectroscopy in chemical analysis. With that technique, Bunsen and Kirchhoff discovered the elements cesium and rubidium. Bunsen evidently valued physics. He once said, "A chemist who is not a physicist is nothing at all."

On this day in 1911 Heike Kamerlingh Onnes dipped a wire made of solid mercury into liquid helium and lowered the temperature. At 4.2 K, the wire's electrical resistance suddenly vanished. Onnes wrote in his lab book: "Mercury has passed into a new state, which on account of its extraordinary electrical properties may be called the superconductive state." He had discovered superconductivity!