1. M. G. Lamé, Leçons sur la Théorie Mathématique de l’Élasticité des Corps Solides (Gauthier-Villars, Paris, 1886), second edition, p. 170.
2. These modes were employed recently by H. Ekstein and T. Schiffman, J. Appl. Phys. 27, 405 (1956), as trial functions in obtaining approximate solutions for other modes in isotropic parallelepipeds.
3. W. P. Mason, Piezoelectric Crystals and Their Applications to Ultrasonics (D. Van Nostrand Company, Inc., New York, 1950), pp. 44–46.
4. R. A. Sykes, “Modes of motion in quartz crystals” in Quartz Crystals for Electrical Circuits, edited by R. A. Heising (D. Van Nostrand Company, Inc., New York, 1946), Chap. VI, p. 247.
5. Reference 2, p. 84.