1. Uyeda, S., Yukutake, T., and Tanaoka, I., Bull. Earthq. Res. Inst., Tokyo Univ., 36, 251 (1958). Hôrai, K., ibid., 37, 571 (1959). Uyeda, S., and Hôrai, K., ibid., 38, 421 (1960).
2. Uyeda, S., and Hôrai, K., Bull. Earthq. Res. Inst., Tokyo Univ., 41, 85, 109 (1963). Hôrai, K., ibid., 41, 137, 149, 167 (1963).
3. Uyeda, S., Hôrai, K., Yasui, M., and Akamatsu, H., J. Geophys. Res., 67, 1186 (1962). Oceanograph. Mag., 13, 185 (1962); 14, 147 (1963).
4. Beck, A. E., J. Sci. Instrum., 34, 186 (1957).
5. Ratcliffe, E. H., Brit. J. App. Phys., 10, 22 (1958), and personal communication.