Innes, Robert Thorburn Ayton

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Innes, Robert Thorburn Ayton

(b. Edinburgh, Scotland, 10 November 1861; d. Surbition, England, 13 March 1933)


Innes, the eldest of twelve children of John Innes and Elizabeth Ayton, left school at the age of twelve; although thereafter he was entirely self-taught, this was apparent only in his unprejudiced and often unconventional outlook. His proficiency as a mathematician, even in his earlier years, isa shown by his published contributions to celestial mechanics. Always preferring the direct approach, he tented to favor numerical methods such as Cowell’s (he would have been in his element in the computer age) and his arithmetical adroitness was legendary. Yet it is by his outstanding ability as a practical astronomer and observer that Innes is chiefly remembered. He was elected a follow of the Royal Astronomical Society at the age of seventeen, of the Royal Society of Edinburgh in 1904, and of several other learned Societies; his doctorate of science from the University of Leiden was conferred in 1923 honoris cause. Throughout his life he took a leading part in civic cultural activities, where his wide range of interests, his persuasive diplomacy, and his unfailing urbanity found a natural outlet.

Shortly after his marriage in 1884 to Anne Elizabeth Fennell, by whom he had three sons, Innes emigrated to Sydney. Australia, where he prospered as a wine merchant; his leisure was devoted, as before, to astronomy. His success in a search for new double stars led Sir David Gill to offer him the post of secretary at the Cape Observatory, South Africa, at a very modest salary. Here Innes somehow found time to continue his double-star observations, to compile a catalog of southern double stars, and to revise the Cape photographic Durchmusterung. In 1903 he was appointed director of the newly established Transvaal Observatory in Johannesburg. Although his official duties were meteorological, by 1907 he had acquired a nine-inch telescope; and in 1909, three years before the renamed Union Observatory became a purely astronomical institute, he persuaded the government to order a 26.5-inch refractor. Unfortunately. he had the use of it for only two years before his retirement in 1927.

Innes was the first to place double-star research in the southern hemisphere on a sound modern footing. He had unusually acute eyesight, discovering with small telescopes doubles that are difficult to observe with much larger instruments. Altogether Innes is credited with 1, 628 new doubles; in addition he made many thousands of measurements that drew attention to the excellence of the astronomical “seeing” on the high veld. His second general catalog of southern double stars appeared in 1927, and in 1926 his interest in practical computation led to his proposal of the orbital parameters now known as the Thiele-Innes constants.

But double-star astronomy was not enough for a man of Innes’ versatility; he also found time to do important work in such diverse fields as proper motions, variable stars, lunar occultations, and the Galilean satellites of Jupiter. He always insisted that the proper function of an observatory was first and foremost to observe, especially in the southern hemisphere; theoretical work could be left to the more numberous observatories in the north, which are often situated in less favorable climates. But his selfconfessed personal preference for theoretical work was not always to be denied, and he was probably the first to offer a definite proof of the variability of the earth’s rotation. Innes was a pioneer in the use of the blink microscope in astronomy—in the face, surprisingly, of some criticism. It was with this instrument that he made his celebrated discovery, as the result of a deliberate search, of Proxima Centauri, still the nearest known star to the solar system.


I. Original Works. Innes’ writings include “Reference Catalogue of Southern Double Stars.” in Annals of the Royal Observatory, Cape Town,2 , pt. 2 (1899); “Revision of the Cape photographic Durchmusterung,” ibid., 9 (1903); “Discovery of Variable Stars, etc., With Pulfrich’s Blink-Milkroskop, and Remarks Upon Its Use in Astronomy,” in Union Observatory Circular, no. 20 (1914)—see also nos. 28 (1915), and 35 (1916); “A Faint Star of Large Proper Motion,” ibid., no. 30 (1915), which concerns Proxima Centauri—see also no. 40 (1917); “Transits of Mercury, 1677—1924,” ibid., no. 65 (1925), on the variability of the earth’s rotation; “Orbital Elements of Binary Stars,” ibid., no. 68 (1926), written with W. H. van den Bos; and Southern Double Star Catalogue − 19° to − 90 (Johnnesburg, 1927), written with B. H. Dawson and W. H. van den Bos. Many other papers are in Transvaal (later Union) Observatory Circular, Monthly Notices of the Royal Astronomical Society, and Astronomische Nachrichten.

II. Secondary Literature. An obituary notice with curriculum vitae by W. de Sitter is in Monthly Notices of the Royal Astronomical Society, 94 (1934), 277. See also D. Brouwer, “Discussion of Observations of Jupiter’s Satellites Made at Johannesburg in the Years 1908-1926” in Annalen van de Sterrewacht te Leiden, 16 , pt. 1 (1928); and J. Hers, “R. T. A. Innes and the Variable Rotation of the Earth,” in Monthly Notes of the Astronomical Society of southern Africa, 30 (1971), 129.

W. S. Finsen