1. 1) Barkhausen, H. and K. Kurz: Phy. Zeit.. 91 (1920).
2. 2) Boltzman L.: Pogg. Ann., 151 (1874), 153 (1874), 155 (1875).
3. 3) Curie, J.: Ann. Chem. Phy., (6) 17 (1889).
4. 4) Deer, W. A. and L. R. Wager: Min. Mag., 5 (1938).
5. 5) Endo, K. and S. Kozu: Jour. Japanese Association of Mineralogists, Petrologists and Economic Geologists, 14 (1935).