1. A. V. Smirnov, ZhTF, 21, 12, 1486, 1951.
2. DuBois and Rubens, Wied. Ann., 49p, 593, 1893.
3. E. Braun, Verh. d. Phys. Ges., 6p, 77, 1964.
4. D. V. Chepur and N. G. Tsvelykh, ZhTF, 25, 3, 1955.
5. L. V. Koval'skii and V. K. Polyanskii, UFZh, 10, 1, 95, 1965.