Dictionary of National Biography, 1885-1900/Dunlop, James (1795-1848)
DUNLOP, JAMES (1795–1848), astronomer, was born in Ayrshire in 1795. He accompanied Sir Thomas Makdougall Brisbane [q. v.] to New South Wales in 1821 as assistant in the observatory founded by him at Paramatta, of which, after Rümker's departure on 16 June 1823, Dunlop remained in sole charge. The greater part of the observations for the ‘Brisbane Catalogue’ of 7385 southern stars, brought to a close on 2 March 1826, were thus made by him. He detected Encke's comet on 2 June 1822, at its first calculated return, and observed the bright comet of 1825 from 21 July to 8 Nov., inferring axial rotation from striking changes in the figure of its tail. An occultation by the same body of the third magnitude star η Eridani was carefully watched by him on 3 Oct. (Edinb. Journ. of Science, vi. 84).
After the return of his principal to Europe late in 1825 Dunlop resolved, at some sacrifice of his private interests, to remain in the colony for the purpose of exploring its little-known skies. A nine-foot reflector of his own construction served him for sweeping from the pole to latitude 30°; and his micrometrical measures of double stars were executed with a 46-inch equatorial, which he had provided with two micrometers—a parallel-line, and a double-image on Amici's principle. His own house at Paramatta was his observatory. The chief results were embodied in ‘A Catalogue of Nebulæ and Clusters of Stars in the Southern Hemisphere, observed at Paramatta in New South Wales,’ presented to the Royal Society by Sir John Herschel, and read on 20 Dec. 1827 (Phil. Trans. cxviii. 113). The collection included 629 objects, nearly all previously unknown, and was accompanied by drawings of the more remarkable among them. Its merit was acknowledged by the bestowal of the Astronomical Society's gold medal, in presenting which, on 8 Feb. 1828, Sir John Herschel spoke in high terms of Dunlop's qualities as an observer (Monthly Notices, i. 60). Unfortunately this favourable opinion was not altogether confirmed by subsequent experience. No more than 211 of Dunlop's nebulæ were disclosed by Herschel's far more powerful telescopes at the Cape, and he was driven to conclude that in a great number of cases ‘a want of sufficient light or defining power in the instrument used by Mr. Dunlop has been the cause of his setting down objects as nebulæ where none really exist’ (Observations at the Cape, p. 4). Nor did the ‘Brisbane Catalogue’ afford him the well-determined star places he expected from it. The polar distances proved indeed satisfactory; but the right ascensions were affected by comparatively large instrumental errors imperfectly investigated. Moonlit and other nights unfavourable to the discovery of nebulæ were devoted by Dunlop at Paramatta to the observation of double stars, of which 254 were catalogued, and 29 micrometrically measured by him. In the form of a letter to Brisbane these results were imparted to the Astronomical Society on 9 May 1828, and were published in their ‘Transactions’ with the title ‘Approximate Places of Double Stars in the Southern Hemisphere’ (Mem. R. A. Soc. iii. 257). Some have not since been re-identified, no doubt owing to faultiness in their assigned positions.
Dunlop returned to Europe in April 1827 and took charge of Sir Thomas Brisbane's observatory at Makerstoun in Roxburghshire, where he observed Encke's comet 26 Oct. to 25 Dec. 1828 (ib. iv. 186), and determined the ‘difference of the right ascensions of the moon and stars in her parallel,’ with a four-foot transit instrument in 1829–30 (ib. v. 349). In 1827, 1828, and 1829 he made an extensive series of magnetic observations in various parts of Scotland, and arranged the ascertained particulars in ‘An Account of Observations made in Scotland on the Distribution of the Magnetic Intensity,’ communicated to the Royal Society of Edinburgh on 19 April 1830 by Brisbane, who had borne the entire expense of the undertaking (Edinb. Phil. Trans. xii. 1). A chart of the isodynamical magnetic lines throughout Scotland was appended.
On Rümker's resignation in 1829, Dunlop was by the government of New South Wales appointed director of the Paramatta Observatory, and repaired to his post in 1831. He there discovered two small comets on 30 Sept. 1833 and 19 March 1834 respectively (Monthly Notices, iii. 100); determined the relative brightness of about four hundred southern stars with a double image eye-piece (ib. ii. 190); and his observations of the ‘Moon and Moon-culminating Stars, Eclipses of Jupiter's Satellites, and Occultations of Fixed Stars by the Moon’ during 1838 were laid by Brisbane before the Royal Astronomical Society (ib. v. 8). These were the last signs of activity from the Paramatta Observatory. Dunlop resigned in 1842, and the instruments were removed to Sydney five years later. He died at Bora Bora, Brisbane Water, on 22 Sept. 1848, aged 53. He had been since 1828 a fellow of the Royal Astronomical Society, and he was a corresponding member of the Paris Academy of Sciences.[Sydney Morning Herald, 27 Sept. 1848; Comptes Rendus, xxxii. 261; Observatory, iii. 614; H. C. Russell on the Sydney Observatory; Roy. Soc.'s Cat. of Sci. Papers.]