1. W. Band:Mathematical physics. Princeton 1959, p. 76: the anisotropy factor in elasticity.
2. D. Bohm:Quantum theory Englewood Cliffs (1. Auflage 1951) 1960, pp. 351–353.
3. L. Brillouin:Wave propagation in pcriodic structures. New York (1. Auflage 1946) 1953, pp. 157–167: frequency distribution for waves in an actual crystal.
4. L. Brillouin:Les tenseurs en mécanique et en élasticité. Paris 1949, pp. 324–326: hypothèses simplificatrices pour un solide isotrope.
5. G. Cocconi, E. Salpeter:A search for anisotropy of inertia. Nuclear physics 10 (1958), pp. 646–651.