1. E. H. Barton &W. Williams, The electrician, v. 29, p. 432 (1892).
2. G. E. Allen, Phil. Mag., (s. 6) v. 7, p. 45–61 (1904).
3. H. Takagi, Sci. Rep., Tohoku Univ., v. 2, p. 15–24 (1913).
4. R. Chevallier &J. Pierre, Ann. de Phys., (s. 10) v. 18, p. 385–477 (1932).
5. T. Nagata, Bull. Earth. Res. Inst., v. 19, p. 579–596 (1941).