October 23, 1905-September 10, 1983

BY ROBERT HOFSTADTER

FELIX BLOCH was a historic figure in the development of physics in the twentieth century. He was one among the great innovators who first showed that quantum mechanics was a valid instrument for understanding many physical phenomena for which there had been no previous explanation. Among many contributions were his pioneering efforts in the quantum theory of metals and solids, which resulted in what are called ''Bloch Waves" or "Bloch States" and, later, "Bloch Walls," which separate magnetic domains in ferromagnetic materials. His name is associated with the famous Bethe-Bloch formula, which describes the stopping of charged particles in matter. The theory of "Spin Waves" was also developed by Bloch. His early work on the magnetic scattering of neutrons led to his famous experiment with Alvarez that determined the magnetic moment of the neutron. In carrying out this resonance experiment, Bloch realized that magnetic moments of nuclei in general could be measured by resonance methods. This idea led to the discovery of nuclear magnetic resonance, which Bloch originally called nuclear induction. For this and the simultaneous and independent work of E. Purcell, Bloch and Purcell shared the Nobel prize in physics in 1952.

The aim of the physicist is to carry out and interpret