折射度指示体的若干问题

ASPECTS OF THE REFRACTIVITY INDICATRIX

The indicatrix of Gladstone-Dale refractivity is the one whose radius in a cer-tain direction equals n - 1 in this direction. It can be replaced by an ellipsoid whose principal axes are n - 1 The refractivity indicatrix is always smaller than the n ?l ellipsoid,but the difference is negligible. The radial difference can be cal-culated by an equation from which we can estimate that the maximum difference is usually below 0.0008. For most minerals the difference of 2V between the re-fractivity indicatrix and the n -1 ellipsoid is smaller than 2?but it may be quite large when a mineral has a strong birefringence and a small refractive index, and the 2V approaches 90? Gladstone - Dale equation can be regarded as an approxi-mation of Lorentz-Lorenz equation. Other equations including Lichtenecker equa-tion, Drude equation and Allen equation can also be substituted for by Gladstone-Dale equation. As a result of these approximations,if other refractivity indicatri-xes are to be defined, based on different equations, they will be in effect the same as the Gladstone-Dale refractivity indicatrix.