Referee's report by William Thomson, Lord Kelvin, on a paper 'On the relation between the diurnal range of magnetic declination and horizontal force, as observed at the Royal Observatory, Greenwich, during the years 1841 to 1877, and the period of solar spot frequency' by William Ellis Recommended for publication in the 'Philosophical Transactions of the Royal Society'. The method is 'most faulty'. Suggests that the 'harmonic analysis should be applied', with the current paper acting as a provisional account of the features of the observations, until a fuller and more complete account has been completed. Calculating the harmonic analysis would probably have been quicker and simpler than the methods used in the current paper. Subject: Physics and Chemistry [Published in the Philosophical Transactions of the Royal Society, 1880] 6 January 1880