Abstract
The polarization vectors of lattice vibrations in anisotropic crystals of cubic structure are considered from a quantitative point of view. A new anisotropy index A = c11/(c12 + 2c44) is shown to be more adequate as a measure of anisotropy than the conventional s = (c11c12)/2c44. The reason for anisotropy is discussed briefly, with special emphasis on simple metals. The approximation of assuming the lattice vibrations to be strictly longitudinal or transverse is discussed for several properties of metals, with sodium taken as an example.