1. Hájíček P.: Czech. J. Phys.B 17 (1967), 969.
2. Toupin R. A.: J. Rational Mech. Anal.5 (1956), 849.
3. Hájíček P.: Czech. J. Phys.B 17 (1967), 613.
4. Thurston R. N.: Wave Propagation in Liquids and Solids. In Physical Acoustics, ed. by W. P. Mason, Vol. I, Part A, Chap. 1, § 2, Sect. 5. Academic Press, New York-London 1964.