The change from the zero to the first approximations is accompanied by the change of the sign ofK 1,K 2 1 being of the same order asK 1 1 . It implies that the neglection of further members of the expansion in (2) may not be quite right. Therefore it might be better to take into consideration also the effect of the further members in (5), but in such a case equation (7) would contain so many unknown parametersK i j , that another way how to solve it would be necessary. In our case, (7) is an equation of a tangent to the curveK 1 0 =f(1−x 2) at const.H, which has enabled us to determine the dependencesK 1 1 (T, H) andK 2 1 (T, H). Generally, there are other methods of studying the parametersK i j (based on the analysis of torque curves for example) which are more suitable in similar cases, but these methods usually allow necessary measurements only in the fields considerably less than those used in [5].