146 Double Stars. 



probably so, and sixty-six suspected. In 1849, Madler, bis 

 successor at Dorpat, considered tbat 650 pairs throughout tbe 

 beavens were certainly of binary cbaracter ; and tbe subsequent 

 period, if, in some instances, it may bave tbrown doubt upon 

 hasty inferences, bas on tbe wbole added materially to tbe 

 number. The chief increase, however, bas not been due to tbe 

 discovery of fresb objects, for tbe superiority of tbe Dorpat 

 telescope, wbicb bas 9*43 incbes of aperture, and tbe unwearied 

 zeal of Struve, wbo carefully examined witb it in two years 

 about 120,000 stars, left comparatively bttle to be done in tbe 

 nortbern hemisphere; it is tbe interval of time, wbicb by 

 enabling tbe slower movements to be recognized and measured, 

 bas developed a new cbaracter of connexion in many pans pre- 

 viously known. » 



Tbe amateur wbo is impressed witb tbe extreme sublimity 

 and beauty of tbese distant exhibitions of tbe Creator's glory, will 

 not be satisfied witb a cursory glance, but will bke to see, and 

 see carefully, all tbat bis instrument can sbow bim. It will be, 

 therefore, well to specify tbe following as tbe points of interest 

 in double stars. 



1. Magnitude. — It is to be regretted tbat on tbis bead tbere 

 is mucb tbat is very arbitrary and uncertain ; tbe magnitudes 

 of stars as given by different autborities varying sometimes to a 

 surprising degree. Sir J. Herscbel, Argelander, and others, 

 bave indeed done mucb in tbe very difficult inquiries of stellar 

 photometry, but tbe results are either not fully satisfactory, or 

 have met with a very limited appbcation. In the present series 

 of papers the data of Admiral Smyth's most accurate and valu- 

 able Bedford Catalogue will be adopted as the standard, in this 

 as well as all other respects, with occasional additions from 

 other quarters. 



2. Distance. — This is one of the most important elements of 

 observation, and gives more especially its cbaracter to tbe aspect 

 of a pair of stars. It is always measured from centre to centre, 

 and expressed in seconds and decimals of arc (on space) . We 

 often find tbe decimals carried to three places in these measures, 

 but it is of course not to be supposed tbat instruments exist 

 capable of marking, or eyes of discriminating, such subdivi- 

 sions ; they merely express a mean deduced from many obser- 

 vations. In Smyth's measures such refinements are not 

 employed. The Dorpat Catalogue terminates at 32" as its 

 exterior limit, but from a calculation of chances it appears that 

 there is a possibility of mutual relation even as far as 15'; that 

 is to say, between stars, double, even to the naked eye. 



•3. Position of the components with respect to each other. — 

 Tbis deserves the more attention, as being one of tbe elements 

 wbicb would vary on tbe supposition of orbital motion, and by 



