About a new type of inter-ionic forces

In the solid atomic theory, inter-ionic forces are explained by considering ions as formed by a nucleus surrounded by electronic layers with spherical symmetry, at least for normal ions (non para-magnetic). With such a model and for a highly symmetrical crystal, it is impossible to make evidence of a deviation in Cauchy relationships if the deformation of ions under the effect of the crystalline field is not taken into account. The author reports that this deformation exists, even if the crystal symmetry is high and can be estimated. Reprint of a paper published in 'Journal de Physique et le Radium', t. 13, Apr 1952, p. 243.