Referee's report by Thomas Smith, on a paper 'On crystal and slit systems for X-ray monochromatization and spectroscopy' by G I Harper Sectional Committee: Physics Recommended for publication in the 'Proceedings of the Royal Society of London'. Some parts of the paper are superfluous, whereas others require further addition. The mathematics requires modification in places. [Published in the 'Proceedings of the Royal Society of London'] Endorsed on verso as received 20 October 1934. [October 1934]