Note on the solutions of the model of coupled oscillators in crystalline optical activity for the direction perpendicular to the optic axis

In the past, Chandrasekhar's method of two coupled oscillators was successfully used for the interpretation of crystalline optical activity. The optical activity dispersion relations were obtained in the direction of the optic axis and also in the direction perpendicular to the optic axis. However, Chandrasekhar's approach to the solution method is based on a mistake in his calculations. This mistake does not influence the character of the dispersion relations in the direction of the optic axis, which was proved by the solution of the model of coupled oscillators using the Condon relations. Similar conclusions have not been introduced for the direction perpendicular to the optic axis. For that reason, the model of coupled oscillators, using the Condon relations, is presented also for the direction perpendicular to the optic axis. The considered model of coupled oscillators is more complicated and therefore corresponds to the structure of real crystals more closely. It can be proved that, in spite of Chandrasekhar's mistake in the calculations, his conclusions hold. The character of the dispersion relations in the directions parallel and perpendicular to the optic axis is the same and differs only by a constant multiplicative factor. However, Chandrasekhar's factor differs from the derived form of this factor, which is presented in this paper. It is also presented for the example of an atomic crystal of tellurium that the form of Chandrasekhar's factor is incorrect. The mistakes in Chandrasekhar's derivations are also discussed.