The polarization of a number of He and Hg spectral lines, excited by a beam of electrons, has been measured as a function of the electron energy. The transitions studied are: for helium 41D → 21P, 51D → 21P, 43S → 23P, 33D → 23P 43D → 23P, for mercury 61D2 → 61P1, 63D2 → 61P1, 73S1 → 63P1, and 71D1 → 61P1.\ud The electron energy was varied from the threshold energy to a few eV above it. The results indicate that in most cases the polarization measured near the threshold is much lower than the theoretically predicted threshold polarization. For some transitions a detailed structure near threshold is observed in the polarization function. The observed behaviour of the polarization near threshold is discussed and a qualitative interpretation is presented
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