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We have measured the dependence upon target-foil temperature of the linear polarization fraction (M / I) of the 2s1S-3p1P, 5016-Å transition in He I for ion energies between 60 and 180 keV. The thin carbon exciter foils were heated externally by Nichrome resistance elements. The measurements of Hight et al. are duplicated; the energy and current dependencies of M / I are the same, assuming correspondence between beam heating and external heating. We also observe that γ, the number of secondary electrons produced per incident ion, decreases with increasing foil temperature. These two effects, in conjunction, offer a plausible explanation for the variation of polarization with beam-current density. The temperature of the foil is shown to depend on beam current to the one-fourth power, indicating that radiation is the primary energy-loss mechanism.