ROBERTS, ISAAC

(b. Groes, near Denbigh, North Wales, 27 January 1829; d. Crowborough, Sussex, England, 17 July 1904) astronomy.

The son of a farmer, Roberts was brought up in Liverpool and after an elementary education was apprenticed in 1844 to a local firm of builders and lime burners. He became manager of the firm but in 1859 set up in Liverpool, independently, the firm of Roberts and Robinson, which secured many important contracts in the city.

Gradually scientific interests occupied more and more of Roberts’ attention. In 1870 he became a fellow of the Geological Society; and in 1878 he purchased a seven-inch refractor, made by Cooke, for visual astronomy. In 1883, however, he began to experiment with stellar photography and eventually obtained a twenty-inch reflector, with a 100-inch focal length, from Howard Grubb of Dublin. (The photographs were taken in the focus of the mirror.) In January 1886 Roberts announced to the Royal Astronomical Society that during the previous year he had taken 200 photographs of stars that might be measured for position and also long-exposure photographs of the Orion and Andromeda nebulae and of the Pleiades cluster. Later in 1886 he exhibited a three-hour exposure of the Pleiades that revealed the astonishing and unsuspected nebulosity that surrounds these stars. In 1887 he attended the Conference of Astronomers in Paris; this conference planned an international photographic chart of the sky, and thereafter Roberts concentrated his own efforts on objects of special interest.

In 1888 Roberts retired from business to devote himself to his scientific work; and in 1890 he settled in Crowborough, in the south of England, where the skies offered better viewing than near Liverpool. At Crowborough he supervised the work of his assistant, W. S. Franks, in the photography of stars, star clusters, and nebulae. The dramatic photographs that resulted were for many years exhibited regularly at the Royal Astronomical Society. In 1893 Roberts published a volume containing photographs and descriptions of his observatory, his telescope, and fifty-one celestial objects. Although his photographs of nebulae lacked the definition that Keeler attained at the Lick Observatory at the close of the century, they offered an objective record to replace the subjective sketches on which earlier generations had been forced to rely in their efforts to establish the structure of the nebulae. Indeed, “the detection of changes in the structure of nebulae,” which would establish such nebulae as small-scale objects and not as island universes of stars, was the first use Roberts foresaw for his book. But the photographs were often misinterpreted. William Huggins (Scientific Papers [London, 1909], 173) considered the Andromeda nebula “a planetary system at a somewhat advanced stage of evolution.” Roberts, in a second volume published six years later, expressed his belief that this nebula had rotated. The photographs, in short, were more significant for the possibilities of nebular photography that they demonstrated than for the inferences drawn from them.

Roberts was twice married but had no children. The honors that his astronomical photography earned included the 1895 Gold Medal of the Royal Astronomical Society.

BIBLIOGRAPHY

I. Original Works. Roberts published his photographs in Photographs of Stars, Starclusters and Nebulae, 2 vols. (London, 1893–1899); and Mrs. Isaac Roberts (née Dorothea Klumpke), his widow, published a further portfolio, Isaac Roberts’ Atlas of 52 Regions, A Guide to Herschel’s Fields (Paris, 1929). His articles appeared principally in Monthly Notices of the Royal Astronomical Society, Astrophysical Journal, Astronomische Nachrichten, and Proceedings of the Liverpool Geological Society; lists of these are given in Poggendorff, IV, 1259; and V, 1057; and in a posthumous article edited by Mrs. Isaac Roberts, “The Nebula H. V. 20 Ceti,” in Monthly Notices of the Royal Astronomical Society, 65 (1915), 191–200.

II. Secondary Literature. Useful, short biographies are in Monthly Notices of the Royal Astronomical Society, 65 (1905), 345–347; Observatory, 27 (1904), 300–303; and Dictionary of National Biography, 1901–1911, 209–211. See also Gérard de Vaucouleurs, Astronomical Photography (London, 1961).

Michael A. Hoskin