The incomplete polarization of $\ensuremath{\lambda}2537\mathrm{A}$ of mercury in resonance radiation is due to the peculiar behavior of the outer two hyperfine structure lines. The three remaining hyperfine structure lines behave in accordance with the predictions of the theory of the anomalous Zeeman effect for a
11S0-
23P1 line. Von Keussler's observation of complete polarization in 7900 gausses is explained, in part at least, by the observed shift of the -25.6 hyperfine structure line, and complete polarization is obtained with a field only 2000 gausses using a resonance radiation source.