Brittin, W. E., Downs, B. W., & Downs, J. (1962). Lectures in theoretical physics: V4. lectures delivered at the Summer Institute for Theoretical Physics, University of Colorado, Boulder, 1961. Interscience.

Brittin, Wesley E., B. W. Downs, and Joanne Downs. Lectures in Theoretical Physics: V4. Lectures Delivered at the Summer Institute for Theoretical Physics, University of Colorado, Boulder, 1961. New York: Interscience, 1962.

Brittin, Wesley E., et al. Lectures in Theoretical Physics: V4. Lectures Delivered at the Summer Institute for Theoretical Physics, University of Colorado, Boulder, 1961. Interscience, 1962.