A century ago Heike Kamerlinah Onnes set a new standard for physics research laboratories. But careless notebook entries have confused the story of his greatest discovery.

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One hundred years ago, Heike Kamerlingh Onnes first liquefied helium in a cryogenic laboratory whose excellence and scale were unparalleled. Creating, staffing, and running the Leiden laboratory required more than just scientific skill.

A lbert Einstein liked coming to Leiden, the Dutch city particularly known for its venerable university. Vienna-born theoretical physicist Paul Ehrenfest, professor at Leiden University since 1912, was one of his closest friends. 1 Last July Rowdy Boeyink, a history-of-science student, stumbled across a long-lost, handwritten Einstein manuscript in the Ehrenfest Library of Leiden University's Lorentz Institute for Theoretical Physics. The manuscript was part two of a paper entitled "Quantum Theory of Monatomic Ideal Gases," which Einstein presented at a 1925 meeting of the Prussian Academy of Sciences. 2 That paper has a special significance. It contained Einstein's last great discovery-Bose-Einstein condensation, as the effect came to be called. Unearthed amid the celebrations of the Word Year of Physics, the centenary of Einstein's 1905 annus mirabilis, the 16 handwritten pages attracted international media attention. 3 That same month, Boeyink also found among Ehrenfest's papers typescripts of two more Einstein papers-one from 1914, the other from 1920. Both manuscripts contain interesting differences from the version that eventually appeared in print (see box 1 on page 59). Last October I came across reprints of 22 articles by Einstein from the period 1902-15 in the archive of the Huygens Laboratory, home to experimental physics at the university. In some cases, including the famous 1905 article on the special theory of relativity, the reprints feature handwritten "improvements" by Einstein himself (see box 2 on page 60).

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