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Abstract

The note discusses the validity of the rotational invariance condition used in lattice dynamics. It is pointed out that rotations of non-central fields cannot be represented by displacements alone. Formulating the equations of lattice dynamics referred to Lagrangean co-ordinates imbedded in the crystal it is shown that the usual formulae do not strictly represent the physical requirement of rotational invariance. The result has considerable effect on several applications of the lattice theory.