Contents Page Table 8 1. Figure of the Earth’s surface 104 2. Gravity at the surface; mass, mean density, moment of inertia 104 3. Pressure, density, acceleration of gravity and ellipticity of layers of equal density in the Earth 105 4. The Earth’s core 106 1. Benfield, Z. f. Geophys. 13, 157, 1937. 2. Birch, Bull. Seism. Soc. Amer. 29, 463, 1939. 3. Bullen, M. N. R. A. S. Geophys. Supp. 3, 395, 1936. 4. Bullen, Trans. Roy. Soc. New Zealand, 67, 122, 1937. 5. Bullen, idem, 69, 188, 1939. 6. Bullen, Bull. Seism. Soc. Amer. 30, 235, 1940. 7. Gutenberg and Richter, Beitr. z. Geophys. 54, 94, 1939. 8. Gutenberg and Richter, M. N. R. A. S. Geophys. Supp. 4, 363, 1938. 9. Jeffreys, M. N. R. A. S. Geophys. Supp. 4, 537, 548 and 594, 1939. 10. Lambert, The Internal Constitution of the Earth, Chap. 13, McGraw-Hill, New York, 1939. 11. Olczak, Acta Astron. 3, 81, 1938. 12. Williamson and Adams, J. Washington Acad. Sci. 13, 413, 1923. T able 8–1.—F igure of the E arth’s S urface (Ref. 10) Semi-axes of International Ellipsoid of Reference (1924): Equatorial, a = 6378.388 km. Polar, c = 6356.912 km. Radius of sphere of equal volume, α 0 = 6371 km. Ellipticity of surface, ( a – c )/ a = 1/297 = 0.00337. (For ellipticity of internal levels, see Table 8–3.) Quadrant of a meridian = 10,002.288 km. Quadrant of the equator = 10,019.148 km. Area of surface = 5.101 × 10 18 cm. 2 Volume = 1.083 2