Both the absorption and emission spectra were photographed simultaneously on the same plate, using a special float-operated mechanism to turn the crystal very slowly so as to obtain the faint lines between ${\beta }_2$ and ${\beta }_5$. The absorption wave-lengths were found to be: L${\mathrm{A}}_1$, 1.2122A; L${\mathrm{A}}_2$, 1.0716A; L${\mathrm{A}}_3$, 1.0217A; KA,.17802A. Table I gives the emission wave-lengths of 28 L emission lines including the four new lines ${\beta }_{15}$ (1.2432), ${\beta }_{16}$ (1.2166), ${\gamma }_{12}$ (1.0748) and n (1.0699), and of the $\mathrm{K}{\beta }_3$ line (.18525) which is the line found by DeBroglie. Comparison with the Bohr theory. The agreement of the emission frequencies computed from the energy levels with the measured wave-lengths is better than 1/10 per cent, except for ${\beta }_{15}$ and ${\beta }_{16}$. The lines ${\beta }_{10}$, ${\beta }_9$, ${\gamma }_{12}$, and ${\gamma }_{11}$, however, correspond to transitions between energy levels which are not predicted by the selection principle, and lines ${\beta }_8$ and n are not in agreement with the accepted energy levels. While Ln may be due to an impurity, ${\beta }_8$ is probably a tungsten line.

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