Absolute X-Ray Wave-Lengths by Refraction in Quartz

The refractive index of quartz for Cu $K{\alpha }_1$ radiation was measured by means of the double crystal spectrometer. The quartz prism was placed between the two crystals of the spectrometer and the deviation measured. Measurements were made with the x-rays incident both internally and externally on the prism. Accuracy was such that the refractive index could be determined as $1-\mu =\delta =(8.553\mathrm{}\pm 0.005)\times {10}^{-6\mathrm{}}$. The absolute wave-length of the x-rays was calculated from the quantum theory of dispersion and was found to agree with wave-lengths as measured by ruled gratings. With the newer data on fundamental constants, positions of the critical absorption limits of Si and O and the resonating strengths of bound electrons the previous photographic results were recalculated and found to likewise substantiate the ruled grating value.