1. Hoggett, P., Chorley, R. S., Stoddard, D. R., Nature (GB), 205, 844 (1965).
2. Nettleton, L. L., Geophysical Prospecting for Oil, p. 15 ( N. York: McGraw-Hill, 1940 ).
3. Glazebrook, R. T., Dictionary of Applied Physics, Vol 1, p. 583 ( London: Macmillan, 1922 ).
4. Polis, V. R., and Chai, A., Amer. J. Phys., 40, 676 (1972).
5. Thomas, B., and Wyers, J., Amer. J. Phys., 41, 139 (1973).