Robert Thorburn Ayton Innes, astronomer, was the eldest of the twelve children of John Innes and his wife Elizabeth Ayton. He attended school in Dublin, Ireland, until the age of twelve and thereafter educated himself, developing outstanding proficiency in mathematics and arithmetic. He was interested in the mathematical aspects of astronomy and published three papers on the subject in the Monthly Notices of the Royal Astronomical Society: "Note on an error in Le Verrier's Tables du Soleil" (1889), "Secular perturbations of the Earth's orbit by Mars" (1892), and "Secular perturbations of the Earth's orbit by Venus" (1893). This work led to his election as a Fellow of the Royal Astronomical Society. In 1884 he married Anne E. Fennell and eventually they had three sons.
After working in London as a clerk for some time Innes emigrated to Sydney, Australia, in 1890. There he became a partner in a wine business which traded as Innes and Co. In 1894 he was loaned a 160 mm refractor by the Australian astronomer W.F. Gale and started his great life work in astronomy, the study of double stars in the southern hemisphere. In 1895 he published "A list of probably new double stars" in the Monthly Notices of the Royal Astronomical Society, based on his discovery of 26 pairs. Switching to a reflecting telescope he soon discovered more, the observations showing that he had an extraordinary visual acuity. Encouraged by these discoveries he decided to find a position in an astronomical observatory, with access to better equipment. Among others he contacted Dr David Gill* of the Royal Observatory, Cape of Good Hope, who informed him that the only available post at the Cape was clerical - a combination of secretary, librarian and book-keeper. Innes accepted the offer and assumed duty at the beginning of 1897.
In his spare time he continued his search for new double stars and measured those already found with a view to establishing the orbital characteristics of those that were binaries. Two years after his arrival he had discovered over 200 new doubles. In 1899 his "Reference catalogue of southern double stars", listing 2140 pairs, was published in the Annals of the observatory. He also looked for variable stars, measured the proper motions of many southern stars, and undertook the huge task of revising the Cape Photographic Durchmusterung, an important star catalogue.
In April 1903 Innes moved to Johannesburg to become, on Gill's recommendation, the first director of the Transvaal Meteorological Department and to establish the Government Meteorological Observatory (later the Transvaal Observatory). He applied himself with zeal to organising a meteorological service and during the next seven years contributed substantially to meteorological literature. By June 1904 he had organised more than 200 voluntary observers, mainly of rainfall, cloudiness, wind direction and speed, throughout the Transvaal Colony. In a paper on "The barometer in South Africa", read before the South African Association for the Advancement of Science in 1906, and another on "Meteorology in the Transvaal", published in the Journal of the Scottish Meteorological Society in 1909, he discussed the preparation of the first isobaric maps in South Africa and their use for forecasting, and correctly associated the periodic rain and north-west gales of the south-western Cape in winter with the passage of depressions from west to east. He also arranged that a forecast for the next 24 hours was displayed at every telegraph office in the Transvaal from 1 July 1906. His meteorological interests ranged widely, as reflected in papers dealing with the meteorological services of the Transvaal and the Union, different methods of measuring rainfall, the rainfall over South Africa, the reduction of temperatures to sea level, the distribution of temperature over northern South Africa, snow in Johannesburg, hail insurance, and effective protection from lightning.
Though his work during these years was mainly meteorological, Innes clearly intended to introduce astronomy at the Transvaal Observtory as soon as practicable. In 1905 he read three astronomy papers at the joint meeting of the British and South Arican Associations for the Advancement of Science. That same year the Russian astronomer Dr Oskar Backlund* visited him and as a result the observatory was authorised to participate in an international programme of observations to determine variations in latitude, using a Bamberg transit telescope loaned by the Russian government. In 1907 Innes acquired a 230 mm refractor and began a classic series of observations of the eclipses, transits and occultations of Jupiter's four largest satelites. Between 1909 and 1918 he published six papers dealing with perturbations of Jupiter's satelites and other aspects of perturbation theory in the Transactions of the Royal Society of South Africa. A micrometer was added to the telescope in 1911, enabling him to continue his measurements of double stars. Meanwhile in 1909 the acquisition of a 650 mm refractor was approved, but it was installed only in 1925 as a result of various delays, including World War I (1914-1918). In 1909 the observatory acquired the telescope and associated equipment that had been used by John Franklin-Adams* to photograph the southern skies.
After the formation of the Union of South Africa the observatory was renamed the Union Observatory in 1912 and from then on its work was purely astronomical. Innes thus became the first Union Astronomer, a post he retained to his retirement at the end of 1927. He was a very versatile astronomer, delivering many papers on a variety of topics at the annual meetings of the South African Association for the advancement of science. These dealt with "The earth and comet tails" (1909) - Halley's comet was on its way; Le Verrier's theory of the motion of Jupiter and Saturn (1910); determination of the places of the planets (1910); the mean distances of the planets (1911); the minor planets (1912); star positions and galactic coordinates (1913); cosmological hypotheses (1913); and the masses of visual binaries (1915). During his last two years in office he, W.S. Finsen* and W.H. van den Bos* undertook a systematic search for double stars south of 19 degrees southern declination, while Innes also published his General catalogue of southern double stars. He is credited with having discovered more than 1600 double stars during his career. In 1924 he published the results of his many accurate measurements of the positions of the moon, Mercury, and Jupiter's satelites, becoming the first astronomer to demonstrate quantitatively the variability of the earth's rotation. Furthermore, in 1915, after a systematic search, he discovered the star Proxima Centauri, faint companion of Alpha Centauri, which turned out to be the nearest star to the solar system. He read a paper on its parallax at the annual meeting of the South African Association for the Advancement of Science in 1917.
Innes pointed out the suitability of South Africa for astronomical work and played an important role in the establishment of European and American observatories here. Through his friendship with Willem de Sitter* he established close links with Leiden Observatory in the Netherlands and regularly received visiting astronomers from there. One of the visitors, W.H van den Bos, later became Union Astronomer.
In addition to his work in astronomy and meteorology, Innes was interested in a variety of scientific subjects and presented papers, usually before the South African Association for the Advancement of Science, on topics such as "Numerical summation of the reciprocals of the natural numbers" (1907), "Weights and measures for South Africa" (1909), "A logical notation for mathematics" (1910), daylight saving (1916), and metrication and the decimalisation of coinage (1916) In December 1905 he was appointed chairman of a commission to report on legislation pertaining to weights and measures for South Africa; its report recommended the legalisation, but not the compulsary use, of the metric system.
Though he never attended a university, the quality of his work was such that an honorary doctorate was conferred upon him by the University of Leiden in 1924. In addition to his Fellowship of the Royal Astronomical Society he was also elected a Fellow of the Royal Meteorological Society and the Royal Society of Edinburgh. He was the first president of the Johannesburg Astronomical Association in 1918; and when it amalgamated with the corresponding association in the Cape he became a foundation member of the resulting Astronomical Society of South Africa, served as president in 1923-1924, and in 1930/1 was still director of its computing section. He was also a member of the National Committee in Astronmy, established in 1929. In 1902 he became a foundation member of the South African Association for the Advancement of Science, served on its council for many years (as general secretary from 1909-1912), was president for 1915, and received the society's South Africa Medal (gold) in 1918. In 1905 he also joined the British Association for the Advancement of Science. He was a member of the South African Philosophical Society from 1903, and in 1908 was elected a Fellow of its successor, the Royal Society of South Africa. In 1920-1921 he served on the council of the South African Geographical Society.
Innes was full of enthusiasm. Sometimes he appeared conservative, for example when expressing doubt about deductions based on interferometer observations, but at other times he fielded daring hypotheses, such as ascribing the ice ages to the visitations of comets. He had many interests outside the natural sciences too. For example, he was an excellent chess player, competing in South African championship tournaments, and was active in the affairs of the Johannesburg Public Library from his arrival in the city until his death. He also presented papers on topics such as simplified spelling (1916), vocational training (1916), the eradication of venereal disease (1918), and the reconstitution of the Union Senate (1918). As an animal lover he was an active member of the SPCA and campaigned for a ban on animal-drawn vehicles in Johannesburg. In several respects he was unconventional. For example, despite an apparently stable relationship with his wife and sons he had affairs with other women, with one of whom he had a daughter who became part of the Innes family. All considered he was an impressive person who had a considerable influence on the scientific thinking of his time. He died during a visit to England.