1. Zener, C., Elasticity and Anelasticity of Metals (University of Chicago Press, Chicago, 1948).
2. Randall, M., Physics of Earth and Planetary Interiors (in the press).
3. Liu, H., Anderson, D. L., and Kanamori, H., Geophys. J. R. astr. Soc. (in the press).
4. Jeffreys, H., Nature, 215, 1365–1366 (1967).
5. Carpenter, E., and Davies, D., Nature, 212, 134 (1966).