PORTION OF THE COSMOS. MULTIPLE STARS. 205 



John Herschel himself notices the very uncertain assign- 

 ments of the periods of a Geminorum (334 years instead of 

 according to Madler, 520), ( 338 ); of 7 Virginias (70,8 year? 

 instead of 169); and of y Leonis (1424 of Struve's great 

 catalogue), a superb pair of stars, golden yellow and reddish- 

 green (1200 years). 



After William Herschel, the foundations of this impor- 

 tant branch of astronomy were laid in a more thorough and 

 special manner by Struve (Senior), 1813 1842, and Sir 

 John Herschel, ]819 1838, with admirable activity and 

 by the aid of highly improved instruments (more particu- 

 larly in micrometric apparatus). Struve published his first 

 Dorpat Table of double stars (796 in number) in 1820. 

 This was followed in 1824 by a second, containing 3112 

 double stars down to the 9th magnitude at distances apart 

 less than 32 /x , only about one-sixth of which had been pre- 

 viously seen. Tor the execution of this work, 120000 fixed 

 stars had been examined in the great Fraunhofer refractor. 

 Struve' s third Table was published in 1837, and forms the 

 important work entitled, " Stellarum Compositarum Men- 

 surse imcrometricse." ( 339 ) It contains, (several insecurely 

 observed objects being carefully excluded,) 2787 multiple 

 stars. 



During Sir John Herschel's four years' residence at Feld- 

 hausen, at the Cape of Good Hope, a residence which 

 constitutes an epoch in respect to the more exact topogra- 

 phical knowledge of the southern heavens, his perseverance 

 enriched the department of astronomy which we are now 

 considering by upwards of 2100 double stars, which, with 

 a few exceptions, had never been observed before. ( 34C ) All 

 these African observations were made with a twenty-feet 



