1. Lehmann, I. Un. Geodyn. Geophys., Int., Ass. seis., Ser. A, Trav. Sci. 14, 87–115 (1936).
2. Jeffreys, H. & Bullen, K. E. Seismological Tables (British Association for the Advancement of Science, London, 1940).
3. Gutenberg, B. & Richter, C. F. Mon. Not. R. astr Soc., Geophys. Suppl. 4, 363–372 (1938).
4. Bullen, K. E. The Earth's Density (Chapman and Hall, London, 1975).
5. Birch, F. Am. J. Sci. 238, 192–211 (1940).