Various other astronomers have devoted themselves to the observation of double stars, among them _Ercole Dembowski_ (1815-1881), of Milan; _Karl Hermann Struve_ (born 1854), son of Otto Struve; _William Doberck_ (born 1845); _William J. Hussey_ (born 1864), now director of the Detroit Observatory; Camille Flammarion; N. C. Dunér; G. V. Schiaparelli; _Thomas Jefferson Jackson See_ (born 1866). But the greatest living _discoverer_ is _Sherburne Wesley Burnham_ (born 1838), now employed at the Yerkes Observatory, in Wisconsin. Born in 1838 at Thetford, Vermont, he commenced his career as a shorthand reporter, studying astronomy in his leisure hours. With a small 6-inch refractor, mounted in a home-made observatory, Burnham commenced in 1871 his discoveries of double stars, which soon attracted the attention of noted astronomers, who permitted him to use larger telescopes, with which he continued his researches. His first official appointment was in 1888, when he became chief assistant at the Lick Observatory, which position he resigned in 1892. Some years later he became astronomer in the Yerkes Observatory. Altogether he has discovered 1308 double stars, with telescopes ranging from a 6-inch refractor to the gigantic 40-inch of the Yerkes Observatory. The computation of double-star orbits has been undertaken by various astronomers, among them Mädler, Klinkerfues, Dunér, Flammarion, Seeliger, See, Gore, Burnham, _Robert Grant Aitken_ (born 1864) of the Lick Observatory, and _Giovanni Celoria_ (born 1842), who was, from 1866 to 1900, assistant in the Brera Observatory of Milan, and since 1900 director of that institution. On June 9, 1890, Gore presented to the Royal Irish Academy a catalogue of computed binaries containing reference to fifty-nine stars. In 1844 Bessel discovered a remarkable irregularity in the proper motion of Sirius. He ascribed this to the gravitational influence of some obscure body, probably a large satellite. In 1857 Peters calculated an orbit for the supposed satellite with a period of 50 years. In 1861 an orbit was computed by _Truman Henry Safford_ (1836-1901), which indicated the position of the satellite. Close to this position it was accidentally discovered by _Alvan Clark_ (1832-1897), the famous American optician. The period of the star seems to be about 50 years. In 1844 Bessel noticed irregularities in the proper motion of Procyon, and put forward the idea of a disturbing satellite, as in the case of Sirius. This was confirmed by Mädler, and in 1874 an orbit was computed by Auwers, who found a period of 40 years. In 1896 the satellite was found by Schaeberle with the 36-inch refractor of the Lick Observatory. A period of 40 years was found by See, in agreement with the hypothetical orbit.