382 SCIENTIFIC RECORD FOR 1883. 



DOUBLE STARS. 



Sydney double star results.*— An important contribution to our knowl- 

 edge of the southern heavens has been made by Mr. Russell's publication, 

 in a very compact little volume, of the measures of double stars made- 

 at the Sydney Observatory from 1871 to 1881. The catalogue comprises 

 remeasures of about 746 of HerschePs stars and measures of 350 new 

 doubles, the whole representing some 15,000 measures of angle and dis- 

 tance. Of the new pairs, nine are separated by less than one second of 

 arc, and sixty-six by less than five seconds. The search for new pairs 

 has, however, been merely incidental to Mr. Russell's main object, the 

 examination of Sir John Herschel's Cape list between 34° south and the 

 Pole, a work the more important and valuable that no measures of any 

 large numbers of these stars have been published since the appearance 

 of that catalogue. Mr. Russell, however, remarks that though only an 

 evening now and then was devoted to the search for new objects, the 

 number recorded might easily have been doubled had he adopted the 

 same limit of distance as Sir John Herschel. Only a few of the new 

 stars have been repeatedly measured ; but of these several show signs 

 of motion. 



Mr. Russell gives lists of objects in which his results differ from Sir 

 John Herschel's. Thus in 46 eases he failed to find doubles where Her- 

 schel has recorded them, owing, probably, in many cases, to errors in 

 the Cape Catalogue, and in seventeen other instances finds easy doub- 

 les in fields which Herschel examined without seeing any. Of these, 

 one of the most striking is h 4900, a group of five stars which Herschel' 

 described with great particularity, and which now shows a sixth within 

 the pentagon formed by the others, and as bright as three of the ex- 

 terior stars. Of stars which show real or supposed change since Her- 

 schel's observations, p or 6 Eridani seems, from the later measures, not 

 to be a binary, as these observations plot into a straight line as if the 

 preceding star had a separate proper motion. The doubles y and n 

 Lupi both seem to show motion ; for whilst Herschel found y easily 

 separated and n excessively difficult, Mr. Russell has always failed to 

 divide the former, whilst the latter is now an easy object. 



The observations up to 1874 were made with a fine 7|-inch refractor 

 by Merz, the powers ordinarily used being 159 and 330. Since then an 

 ll^inch refractor of 12£ feet focus by Schroder has been used, with 

 powers from 100 to 1500, 800 being employed for all difficult objects. 



Mr. Russell indicates the date of the observations in an unusual man- 

 ner, three columns being given with the " day of the month," " month 

 of the year," and " year in the nineteenth century," a decidedly less 



* Results of double star measures, made at the Sydney Observatory, New South 

 Wales, 1871 to 1881, under the direction of H. C. Russell, B. A., F. R. A. S., Govern- 

 ment Astronomer for New South Wales. 



