1. L. I. Mandel'shtam and N. D. Papaleksi, eds., Recent Studies of Radio Wave Propagation along the Earth's Surface [in Russian], Gostekhizdat, p. 7, 1945.
2. N. D. Papaleksi, Collection: Transactions of the Expedition to observe the Total Eclipse of the Sun [in Russian], 19 June, 1936, Vol. 1, izd. AN SSSR, p. 115, 1937.
3. J. C. Seddon, J. Geophys. Res.,58, no. 3, 323, 1953.
4. K. I. Gringauz, DAN SSSR,120, no. 6, 1234, 1958.
5. J. C. Seddon and J. E. Jackson, Ann. Geophys.,14, 1, 1958.