Here we will show how the use of a geometrical approach leads to a reduction of the number of the viscosity coefficients of the nematic liquid crystals. Usually they are described by five free parameters; we will show that a geometrical approach can reduce this number to three. This result will follow from the modified version of the Hess-Baalss approach. As a consequence of the application of the Onsager relation, these three viscosity terms become related by the effective eccentricity of the nematic grain, leading to a connection between the Miesowicz's coefficients.