1. Veiel, U.: Ann. Physik 24 (1935) 697.
2. Kido, K.: Sci. Rept. Tohoku Univ. 21 (1932) 149.
3. Kido, K.: Rept. Yokohama Tech. Coll. Jpn. 2 (1934) 223.
4. Pascal, P.: Compt. Rend. 218 (1944) 175.
5. Prasad, M., Dharmatti, S.S., Biradar, N.S.: Curr. Sci. India 17 (1948) 324.