DOUBLE STARS. 279 



2787 double stars, several imperfectly observed objects being 

 carefully excluded. 



Sir John Herschel's unwearied diligence, during his four 

 years' residence in Feldhausen, at the Cape of Good Hope, 

 which, by contributing to an accurate topographical know- 

 ledge of the southern hemisphere, constitutes an epoch in 

 astronomy, 12 has been the means of enriching this number by 

 the addition of more than 2100 double stars (which, with 

 few exceptions, had never before been observed). All these 

 African observations were taken by a twenty-feet reflecting 

 telescope; they were reduced for the year 1830, and are in- 

 cluded in the six catalogues which contain 3346 double stars, 

 and were transmitted by Sir John Herschel to the Astronomical 

 Society for the 6th and 9th parts of their valuable Memoirs. 1 * 

 In these European catalogues are laid down the 380 double 

 stars which the above celebrated astronomer had observed in 

 1825, conjointly with Sir James South. 



We trace in this historical sketch the gradual advance 

 made by the science of astronomy towards a thorough know- 

 ledge of partial, and especially of binary systems. The num- 

 ber of double stars (those both optically and physically double) 

 may at present be estimated with some certainty at about 6000, 

 if we include in our calculation those observed by Bessel 

 with the excellent Fraunhofer heliometer, by Argelander 14 



whole 2641 + 146, . e. 2787 double stars have been ob- 

 served. (Madler, in Schum. Jahrb., 1839, s. 64.) 



12 Sir John Herschel, Astron. Observ. at the Cape of Good 

 Hope, pp. 165-303. 



3 Ibid., pp. 167 and 242. 



4 Argelander, in order carefully to investigate their proper 

 motion, examined a great number of fixed stars. See his 

 essay, entitled " DLX Stdlarum fixarum positiones media, 

 ineunte anno 1830, ex observ. Aboce habitis (Helsingforsiai, 

 1825)." Madler (Astr., s. 625) estimates the number of mul- 

 tiple stars in the northern hemisphere, discovered at Pulkowa 

 since 1837, at not less than 600. 



