The dependence of source function S in a grey atmosphere on the optical depth τ (the full line). In the parts of atmosphere with a higher gravity g, layers with a given temperature are shifted to lower optical depths (the dashed line). This corresponds to increase of the radiative flux in large optical depths (the dotted line), which gives, however, a temperature incompatible at low depths with the homogeneity on equipotential. The actual value of emergent flux H for different shifts of S in g is shown in Fig. A.2.