Mill served on many committees connected with meteorology and allied subjects, including the International Council for the study of the sea (1901-8), and the
Board of Trade committee on the water power of the British Isles (1918). In 1901, he became director of the British Rainfall Organization, and editor of
British Rainfall and ''Symons's Meteorological Magazine''. When the British Rainfall Organization was converted into a trust in 1910, he became chairman of trustees, a position from which he retired in 1919. From 1906 to 1919 he was rainfall expert to the
Metropolitan Water Board. In November 1891 he was elected a Fellow of the
Royal Geographical Society. He held the post of secretary to the Royal Geographical Society during the Society's involvement with the leading British
Antarctic expeditions of the late 19th and early 20th centuries. He was a friend and confidant to
Scott,
Shackleton, and especially to
William Speirs Bruce, who led the
Scottish National Antarctic Expedition, 1902–04. He initiated Bruce's move from medicine to polar research by recommending him to the
Dundee Whaling Expedition to the Antarctic, 1892–93, and to other
Arctic expeditions. In 1923 he produced the first full-length biography of Shackleton. Mill received the
honorary degree Doctor of laws (LL.D.) from the
University of St Andrews in 1900. He received the
Victoria Medal of the
Royal Geographical Society (1915), the Symons Medal of the
Royal Meteorological Society (1918), and the
Cullum Geographical Medal (1929) of the
American Geographical Society. In 1885, he was elected fellow of the
Royal Society of Edinburgh, and in 1936, he was elected member of the
Academy of Sciences Leopoldina. ==Recognition==