gems, corundum, color.4, pleochroism, birefringence, optical absorption

I propose to discuss some consequences of the general equations governing electromagnetic disturbances in a medium that is imperfectly insulating; in particular, to show that these equations satisfy the necessary and sufficient condition for the medium to be birefringent and only birefringent. I will apply the results obtained to the absorption of light in weakly absorbing crystals, showing by numerical examples that all common crystals are sufficiently weakly absorbing for these results to be valid. 2. In a partially conductive medium, anisotropic from the double point of view of dielectric properties and conductive properties, but isotropic from the magnetic point of view, the components X, Y, Z of the electric field, and L, M, N of the magnetic field, are governed by the two following systems of equations (?): 12. From this example, one can see how the equations of electromagnetic theory provide a simple and easy interpretation of the fundamental laws of crystalline absorption: they make it possible to deduce from general principles—without any new hypothesis introduced for the sake of the argument—the truly essential laws of the phenomenon, and, for those of these laws that are only approximate, to determine their degree of accuracy.