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I. I. RABI 317 years was the major reference for microwave and electronic technology. Rabi also served as an influential consultant to J. Robert Oppenheimer, director of the Los Alamos nuclear research laboratory. Shortly before the end of the war, in his 1945 Richtmeyer Lecture, Rabi discussed the possible use of an atomic beam magnetic resonance apparatus as the control element of an accurate clock. The New York Times report on this lecture is the first published account of atomic clocks, which have now become so accurate that they are the basis of the international definition of the second. RETURN TO COLUMBIA Following the end of the war, Rabi, Ramsey, and Kusch returned to Columbia to reestablish the molecular beam laboratory. Nierenberg and Ramsey rebuilt an old apparatus and measured the radiofrequency spectra of a number of alkali halides. Rabi, with his students J. Nafe and E. Nelson, successfully applied the magnetic resonance method to atomic hydrogen and discovered that the hyperfine separation due to the interaction of the magnetic moment of the proton with the electron was slightly different from the theoretical expectation from the Dirac quantum theory; this result was the first indication that the magnetic moment of the electron was different from the expected Dirac value, an observation later confirmed at Columbia by Kusch's direct measurements of the electron magnetic moment. These observed anomalies were the principal stimuli to the development of relativistic quantum electrodynamics, the first successful quantum field theory. Another important molecular beam development was the adaptation by Rabi and his student H. Hughes of the resonance method to electric deflecting and oscillating fields. With subsequent improvements by Rabi, J. Trischka,
I. I. RABI 318 V. Hughes, and others,3 the electric resonance method has been used for many precise measurements of the spindependent internal interactions within molecules in specific rotational states. Most of Rabi's experiments were with molecular beams, but he also participated with W. Havens and J. Rainwater in a neutron-electron scattering experiment which provided the first experimental evidence for the neutron- electron interaction. Rabi's classroom lectures were often chaotic, but he was a stimulating teacher who made his students think. He was an inspiring supervisor of Ph.D. students whose research experiments were innovative and fundamental. Rabi and his wife Helen were personally very helpful to his students and associates, most of whom remained lifelong friends. Rabi gave his students freedom and independence while maintaining high standards for the research. The influence of Rabi has been extended by his students, such as Zacharias, Ramsey, Nierenberg, Schwinger, and Hughes, who in turn have had a number of excellent students; many of the scientists now active in physics can trace their scientific ancestry back to Rabi or his former students. Rabi not only contributed innovative new resonance techniques to the field of atomic physics but imparted to his students and associates high standards for both the quality and the interest of the research. His lifelong interest in scientific taste and standards is illustrated by his last publication, written just a few weeks before he died. In paying tribute to Wolfgang Pauli and Otto Stern, Rabi wrote: From Stern and Pauli I learned what physics should be. For me it was not a matter of more knowledge. I learned a lot of physics as a graduate student. Rather it was the development of taste and insight; it was the development of standards to guide research, a feeling for what was good and what is not
