1. Alurkar, S. K...Ind. Jour. Pure and Appl. Phys., 1965,3(2), 58.
2. Ananthakrishnan, S. and Ramanathan, K. R.Proc. Ind. Acad. Sci., 1966,55, 38.
3. Branscomb, L. M...Ann. Geophys., 1964,20, 88.
4. Hultqvist, B... ——Ibid., 1966,22, 235.
5. Reid, G. C...Rev. in Geophys., 1964,2, 311.