Distinguished for his work in many branches of solid-earth geophysics, particularly seismology, but also gravity, geomagnetism, tectonophysics and marine geophysics. As Director of the Bernard Price Institute and subsequently as first Head of the Geosciences Division of the University of Texas at Dallas, he built up and actively participated in a wide range of investigations into these and related fields. His personal researches have centered around the application of body-wave travel-time studies to determine the structure of the earth's crust and mantle. These studies, carried out both on land and sea, represent a major contribution to knowledge of the earth's interior. He was one of the first to study the detailed structure of the low-velocity zone in the upper mantle, to interpret the unusual seismic properties of this region in terms of partial melting, and to appreciate the key significance of the low-velocity zone in tectonic processes. He was a pioneer in the study of convection processes in the earth's mantle, now believed to be the ultimate cause of continental drift. Professor Hales is one of the world's leading solid-earth geophysicists. Originally trained as a mathematician, he combines this background with great physical insight and considerable skill in instrumentation and electronics. He has been responsible for the organization and successful execution of many complex, large-scale geophysical experiments which have provided important new data on the upper mantle.