The principal molecular polarizabilities of some molecules of the 4, 4′-di-n-alkyloxy-azobenzenes and of the 4, 4′-di-n-alkyloxy-azoxy-benzenes are calculated of the high frequency dielectric constants ϵ1∞and ϵ2∞of the magnetically oriented nematic liquid crystals. The increases of the principal polarizabilities of such molecules in complete trans-forms by adding CH2groups to the alkyl chains are known from an estimation. By comparing these values to the differences between the principal polarizabilities of the investigated molecules it follows that the molecules in the liquid crystals are in a stretched form.