Interesting directions in crystals from the aspect of the voigt and Laval-Raman theory of the elastic properties of crystals

In an experiment carried out by Le Corre in ADP crystals Bull. Soc. Franc. Minér. Cryst.77 (1954), 1963] the validity of the Laval-Raman theory of the elastic properties of crystals was borne out by the experimental finding that different values of the phase velocity correspond to two suitably chosen elastic waves; in the case of the validity of Voigt's theory they would have to agree. The method described in this paper permits systematic examination of the possibility of performing in principle the same experiment for crystals of all classes of symmetry.