Localized excitations in solids : proceedings of the first International Conference on Localized Excitations in Solids, held at the University of Calfornia at Irvine, September 18-22, 1967 - International Conference on Localized Excitations in Solids; Wallis, R. F. (Richard Fisher); International Union of Pure and Applied Physics; University of California, Irvine (Plenum Press, 1968)