The consistent method of solving the coupled slowing down equations developed in the previous paper was extended to a study of the second spacial moment of neutron slowing down in a hydrogenous mixture. The duonucleic sys:em constituted by a mixture of hydrogen and non-hydrogen nuclei was treated analytically by application of the G.G.A. and Fermi approximations to the latter nucleus.Applying the G.G.A. approximation, an interference effect of scattering due to the respective nuclei appeared in the quantities concerning the first and the last flight of neutrons, and it is shown that, when the mass of the non-hydrogen nucleus becomes infinitely large, our general expression coincides with the result obtained by Volkin.Numerical calculations were performed to compare the different methods proposed in the past.