The physics laboratory in Leiden became the "coldest place on earth" under the direction of Heike Kamerlingh Onnes (1853-1926). Helium was first liquefied there in 1908 and three years later mercury became the first metal to be cooled to the superconducting state. The old liquefactor (shown below in a photograph from 1919) can still be admired as you enter our building. The painting above (by Heike's nephew Harm) depicts a more abstract view of the apparatus.

Heike Kamerlingh Onnes (far right) shows his helium liquefactor to three theoretical physicists: Niels Bohr (visiting from Kopenhagen), Hendrik Lorentz, and Paul Ehrenfest (far left)