Harper, G. I.; Salaman, E. (1 April 1930), "Measurements on the Ranges of Formula-Particles", Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences, 127 (804): 175–185, doi:10.1098/rspa.1930.0049
Harper, G. I.; Smith, T. (1935), "On Crystal and Slit Systems for X-Ray Monochromatization and Spectroscopy", Proceedings of the Royal Society of London. Series A, Mathematical and Physical Sciences, 151 (872): 118–141, Bibcode:1935RSPSA.151..118H, doi:10.1098/rspa.1935.0137
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Harper, G. I.; Smith, T. (1935), "On Crystal and Slit Systems for X-Ray Monochromatization and Spectroscopy", Proceedings of the Royal Society of London. Series A, Mathematical and Physical Sciences, 151 (872): 118–141, Bibcode:1935RSPSA.151..118H, doi:10.1098/rspa.1935.0137