Regarding the calculation of the secondary scattering of the solar radiation from the clear sky, a modification of the theoretical formula of A. Hamm. ad and S. Chapman (Phil.. Mag.1939)was done considering the effect of polarization cansed by primary scattering. A quantitative treatment became possible by the new formula in the vicinity of the zenith, that is, in the range from 0° to 45° of the zenith angle.