COMPARISON OF CATALOGUES OF STARS. 391 



The catalogue of Boss gives the exact coordinate in declination only, the right 

 ascension being given only to tenths of seconds of time. The observations of Bessel, 

 1821, of Struve, 1824, and of Argelander, 1829, combined with modern observations, 

 form the basis of this admirable system of declinations. The author has given an 

 elaborate discussion of the systematic corrections of each catalogue employed when 

 referred to this normal system, and from these corrected positions the present cata- 

 logue was constructed. The departure from the usual practice of assuming Bradley's 

 observations for 1755 as absolute, in the determination of proper motions, will not 

 meet with universal approval ; but there are many reasons which may be given in 

 its favor. It may be safely assumed that the normal system constructed by Pro- 

 fessor Boss fairly represents the observations of Bessel, Struve, and Argelander. 

 When, therefore, we find that the proper motions derived from this normal system 

 differ systematicallv from those derived from the Auwers-Bradley positions, we may 

 conclude that there is an inherent discordance between the two systems. Without 

 attempting to decide which is correct, it is well worth while to be able to establish 

 the fact of the discordance, since it bears a close relation to the questions of pre- 

 cession, of proper motion, and of the motion of the solar system in space. 



With reference to the formation of this normal system the author says: — 



'• It will be shown that the interval of time between the group of early determinations by Bessel 

 (1821), Struve (1824), and Argelander (1829), and the later ones at Leiden. Melbourne, Greenwich, and 

 Washington observatories (not to mention intermediate catalogues), is quite sufficient for an inde- 

 pendent judgment as to the approximate accuracy and consequent weight of Bradley's results, and that 

 a reliable system of corrections to the various catalogues may be founded on a discussion qf recent 

 catalogues alone, taking as the earliest that of Bessel for the mean epoch 1821." 



Struve's constants of precession were used throughout in the formation of this 

 catalogue. 



The catalogue of Newcomb was constructed mainly " for the purpose of obtaining 

 standard positions of reference stars for use in the lunar and planetary theories, espe- 

 cially in the reduction of the older occultations." The right ascensions are referred 

 to the author's fundamental system of equatorial stars published in the appendix to the 

 Washington Observations for 1870. The right ascensions of the polar stars are taken 

 without change from Dr. Gould's discussion in 1861. The declinations are referred to 

 the system of Boss. Struve's constants of precession were emplo}-ed in the reductions. 



The Harvard College Observations for 1871-2. published in Vol. X. of the Annals 

 of the Observatory, extend from April 26, 1871. to May 22. 1872. They depend 

 upon the places of the first or the provisional catalogue of 539 stars published in 



