Which Dutch physicist later rediscovered the theorem found in Bohr's 1911 thesis?

The Dutch physicist who later rediscovered the theorem found in Bohr’s 1911 thesis was Hendrika Johanna van Leeuwen. She independently derived the result during doctoral research at Leiden University, several years after Bohr had reached it.

The Bohr–Van Leeuwen theorem shows that classical statistical physics cannot account for magnetism in thermal equilibrium: when classical mechanics and statistics are applied, the net magnetic moment vanishes. Magnetism therefore requires quantum-mechanical explanations, a conclusion that became central to modern physics.

Bohr’s result appeared in his 1911 doctoral thesis on the electron theory of metals, but it attracted little attention at the time. Van Leeuwen’s 1919 thesis brought the result back into view, and her independent derivation eventually led to the shared name. The answer is sometimes shortened to “Van Leeuwen,” but her full name is Hendrika Johanna van Leeuwen.