Abstract
RECENTLY Bäcklin (Inaug-Diss. Uppsala Universitets Årsskrift, 1928) and Bearden (Proc. U.S. Nat. Ac. Sci., 15, 528; 1929) have made precision measurements on X-ray diffraction by plane gratings. Both investigators deduce from these experiments values for the wave-length which are slightly higher than those calculated from crystal reflection measurements. As the latter values depend on Avogadro's number, they conclude that the accepted value of this constant is slightly in error. Part of the discrepancy, however, may be due to another cause; Bearden and probably Bäcklin do not seem to have taken account of the fact that the usual diffraction formula needs a correction (Porter, Phil. Mag., 5, 106; 1928) when applied to X-rays under the usual experimental conditions. In the case of Bearden's results, I find that for the first order spectrum this correction amounts to about half the difference in question. As the exact data of Bäcklin are not now at my disposal, I cannot judge how far the same remarkapplies to these.
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PRINS, J. X-Ray Diffraction by Plane Gratings. Nature 124, 370 (1929). https://doi.org/10.1038/124370a0
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DOI: https://doi.org/10.1038/124370a0
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