Editor’s note: Norman Ramsey, a giant of 20th-century physics and a scientific statesman, died on 4 November 2011 (see Physics Today, February 2012, page 64). In March 2012 a memorial symposium was held at Harvard University to celebrate his life and legacy. The articles on pages 25 and 27 grew out of that symposium and address one of Ramsey’s signature accomplishments, which he discusses here in an article that originally appeared in Physics Today 33 years ago.

In 1949 I was looking for a way to measure nuclear magnetic moments by the molecular-beam resonance method, but to do it more accurately than was possible with the arrangement developed by I. I. Rabi and his colleagues at Columbia University. The method I found1,2 was that of separated oscillatory fields, in which the single oscillating magnetic field in the center of a Rabi device is replaced by...

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