Astronomer (astrophysics of stars, spectroscopy, interstellar studies, origin of universe) and administrator. On the staff of Yerkes Observatory (1921-1932), director (1932-1947); on the astrophysics faculty at the University of Chicago (1932-1950); director, McDonald Observatory (1932-1950); editor, Astrophysics Journal (1932-1947); on the astrophysics faculty, department chair, and director, Leuschner Observatory, University of California, Berkeley (1950-1959); and director, National Radio Astronomy Observatory from 1959.