Natural X-Ray Line Widths: Correction for Finite Resolving Power

The resolving power of the x-ray double spectrometer has been increased by a factor of 2 to 4 by employing etched quartz crystals. The shapes of the $K\alpha$ lines of Mo, Cu and Ti have been observed in anti-parallel positions and the correction for the finite resolving power of the crystals is shown to be practically negligible. Data on the Au $L\alpha$ line is also considered.