Abstract
The hydrostatic pressure dependence of the silicon (222) X‐ray reflection power is calculated by means of a molecular‐theoretic model of the bond charge. The experiment, published by Yoder‐Short is explained by the variation of the s‐like portion of a/s + sp3> ‐ like model valence orbital. Furthermore, the uniaxial stress dependence of the “forbidden” reflections are calculated. Such experiments indicate the p‐like amount of the model valence orbitals in a direct manner.