DR. ARTHUR MATTHEW WELD DOWNING, whose death was announced in NATURE of December 13, was born in Ireland on April 13, 1850, being the youngest son of the late Mr. A. M. Downing. He graduated at Trinity College, Dublin, where he gained the gold medal of his year in mathematics. He went soon afterwards to the Royal Observatory, Greenwich, where he was an assistant for twenty years. He was elected a fellow of the Royal Astronomical Society in 1875, and of the Royal Society in 1896. He was secretary of the former society from 1889 to 1892, and afterwards vice-president. He contributed seventy-five papers to it between 1877 and 1910, which show the keen interest that he took in the improvement of the fundamental constants of astronomy. He revised Taylor's Madras Catalogue and made systematic comparisons of the Star Catalogues of Greenwich, the Cape, Washington, Cordoba, Melbourne, Hong-Kong, etc., with the object of deriving their systematic errors. He discussed the measures of the planetary diameters, and investigated the errors of the tabular orbits of Juno and Flora.