on neze Double and Multiple Stars. 91 



read before the Astronomical Society of London on the 11th 

 January 1828. As it is so intimately connected with the pre- 

 ceding paper by Professor Struve, we have thought it right to 

 place beside it the following abstract from the Annals of Philo- 

 sophy, till we shall be enabled to publish a more copious ana- 

 lysis of it. 



" This paper, as its title imports, is a continuation of the 

 two papers previously communicated by the author on the 

 same subject. The field of discovery in this department of 

 astronomy, though narrowed by the great work recently pub- 

 lished by Professor Struve, the author considers as not yet 

 exhausted ; since, on an average of the part of the heavens 

 swept by him not above one in four of double stars, suffici- 

 ently remarkable to attract attention in sweeping, have been 

 catalogued by the eminent astronomer last named ; not to 

 mention the vast number of interesting close double stars,, be- 

 low the ninth magnitude, which a minuter examination than the 

 nature of his sweeps permits would no doubt produce. The 

 double stars of this catalogue, he observes, are considerably 

 more select than those of his two former ones ; those whose dis- 

 tance exceeds 32 7/ being (except in particular cases) excluded, 

 and the limit of distance being narrowed according to the faint- 

 ness of the component stars. 



" The author prefaces his catalogue with a comparison of 

 the magnitudes habitually assigned to the stars by himself and 

 Professor Struve ; from which it appears that on the average 

 his magnitudes have a denomination about one unit lower than 

 those of that astronomer ; — a star (for example) which M. 

 Struve would call of the ninth magnitude, being, in Mr Hers- 

 chefs nomenclature, of the tenth. The limit of vision in the 

 Dorpat telescope, he presumes to lie about his average four- 

 teenth magnitude, though such a determination must neces- 

 sarily be liable to some latitude. This conclusion he deduces 

 from a series of instances, in which small companions have been 

 seen by him attached to large stars, within the limits of Pro- 

 fessor Struve's fourth class, which have escaped the notice of 

 the latter. 



" The author then states the principle on which he estimates 

 magnitudes below the sixth, which is that of continual bisection 



