The equation N1/N = e-E/RT, where N1 is the number of excited atoms, N the total number of atoms, E the energy, R the gas constant, and T the absolute temperature, was applied by Dr. Loyarte and myself in the case of the absorption spectrum of tin vapour, with good agreement with experimental results (Phys. Zeit., 30, 68; 1929). In this case it is only necessary to consider the numerical values of spectral terms, because these are originated by the same electronic configuration.