Fluorescence of the visible triplet lines of mercury (4047, 4358, 5461) was obtained by exciting a mixture of mercury vapor and a small amount of nitrogen by radiation from a quartz mercury arc. The fluorescence was observed at right angles to the exciting light beam and the polarization of each line, isolated by suitable filters, was measured by the method of crossed Wollaston prisms. Measurements in zero magnetic field (polarized excitation) gave 88.2 percent for 4047, -65.5 for 4358, and 14.55 for 5461, compared to theoretical values (broad line excitation) of 84.7, -67.0, and 8.7 percent, respectively. Measurements were then made of the polarization as a function of a magnetic field applied in the observation direction and the mean life of the $7{}_{}{}^3{}_{}{}^{}S_1^{}{}_{}{}^{}$ state calculated from the data. The mean life of this state as measured by 4047 and 4358 was 0.8±0.1×${10}^{-8\mathrm{}}$ sec. at about 3.0 mm nitrogen pressure. The mean life as measured by the line 5461 was about 0.6±0.1×${10}^{-8\mathrm{}}$ sec. The collision cross section for the $7{}_{}{}^3{}_{}{}^{}S_1^{}{}_{}{}^{}$ state against nitrogen was measured by measuring the polarization of 4358 at a field of 3 gauss and varying nitrogen pressures, giving the result ${{\sigma }_q}^2=1.3\mathrm{}\times {10}^{-16\mathrm{}}$ ${\mathrm{cm}}^2$.

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