Using the general radiation from a tungsten target, dispersed by reflection from a crystal, the total mass absorption in fourteen elements of atomic number 6 to 83 (C, Mg, Al, S, Fe, Ni, Zn, Ag, Sn, W, Pt, Au, Pb and Bi) was determined for various wave-lengths from.10 A to.51 A by the ordinary ionization measurements. The $\mathrm{K}\alpha$ and $\mathrm{K}\beta$ radiation from a Mo target was used to give values for wave-lengths.63 A and.71 A. Very good agreement was found with the results of Richtmyer and Duane wherever these are comparable. For the elements from C(6) to W(74) the results are represented within a few per cent by the formula $\frac{\mu }{\rho }=\frac{\tau }{\rho }+\frac{\sigma }{\rho }=C{\lambda }^2{}_{}{}^{92}{}_{}{}^{}N_{}^{2.92}{}_{}{}^{}+\frac{\sigma }{\rho }$, where $C=7.82\mathrm{}{\mathrm{}\left(10\right)\mathrm{}}^{-3\mathrm{}}$ for the K absorption and 1.00${\mathrm{}\left(10\right)\mathrm{}}^{-3\mathrm{}}$ for the L absorption and the scattering coefficient $\frac{\sigma }{\rho }$ is assumed to increase with $N$ from.144 for Al to.50 for W at.12 A, and also with the wave-length. The jump in the value of the fluorescent absorption coefficient $\frac{\tau }{\rho }$ from L to K absorption is the ratio of $C_K \mathrm{to} C_L$ or 7.8. The atomic absorption ${\tau }_a=2.18\mathrm{}{\mathrm{}\left(10\right)\mathrm{}}^{-26\mathrm{}}{\lambda }^{2.92}{N}^4$ (Bragg-Owens law). For the heavier elements Pt, Au, Pb and Bi the values of $C_K$ get progressively lower to 4.7 ${\mathrm{}\left(10\right)\mathrm{}}^{-3\mathrm{}}$ and those of $C_L$ increasingly higher to 1.12 ${\mathrm{}\left(10\right)\mathrm{}}^{-3\mathrm{}}$, the ratio or jump decreasing to 4.1 for Bi.

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