374 SCIENTIFIC RECORD FOR 1883. 



t wet n each star of each almanac and the Jahrbuch. From this table 

 the elements by which the catalogue of each almanac can be reduced to 

 the system of the Jahrbuch are deduced. A subsequent table gives the 

 two reductions which must be added to each almanac E. A., and the 

 two reductions which must be added to each almanac Dec, in order to 

 reduce to the system of the Jahrbuch. 



The catalogue of each almanac, after the application of the system- 

 atic reductions from this table, is then compared with the Fundamental 

 Catalogue. For the Nautical Almanac the mean difference in declina- 

 tion is 0".395 ; in E. A. (from 134 stars), 8 .0332. Of the 168 stars com- 

 mon to both almanacs, there are 27 whose E. A. differs more than0 8 .0G7, 

 and 8 whose declinations differ by more than 1". These differences are, 

 in the main, errors of the Nautical Almanac, and are largely due to the 

 erroneous proper motions adopted in the Greenwich catalogues. 



For the Connaissance des Temps, the table shows large systematic 

 errors. After these have been eliminated, the comparison gives for 229 

 stars, common to the Connaissance des Temps and the Berliner Jahrbuch, 

 a mean difference of 0".373 in declination, and a mean difference of 

 8 .0282 (from 162 stars) in E. A. The errors here again are largely due 

 to erroneous proper motions. The correspondence of the reduced 

 positions of the American Ephemeris with those of the Jahrbuch varies 

 according as one or another basis of comparison is chosen. A complete 

 comparison can only be made for those stars for which ephemerides are 

 given, siuce the newer stars have their positions derived from several 

 sources, not comparable among themselves. 



The declinations of the American Ephemeris and those of the Jahrbuch 

 agree excellently for those stars which have been investigated by Boss. 

 The mean difference (162 stars) is 0".177. The other 111 stars do not 

 agree so well, there being 12 differences between 0".5 and 1". The stars 

 north of 64° depend upon Gould's E. A. ; and, of the 36 stars common 

 to both almanacs, 15 differ by more than s .lo. Of the remaining 126 

 stars whose ephemerides are given, 8 have differences as great as S .067. 

 The mean difference for 100 stars between +40° and —20° is 8 .0127. 

 For 111 stars without ephemerides, there are seven cases where the 

 difference is more than 9 .067. 



For the stars south of —32° the Nautical Almanac will give the best 

 positions, on account of its data being derived from the most recent 

 catalogues. 



A comparison of the system of the Jahrbuch 1861-'82 with the new 

 system, and a general table for the reduction of the data of any almanac 

 to the Berliner Jahrbuch system, concludes this very important paper. 

 It appears to be highly desirable, ill the interests of uniformity, that 

 that the admirable star list of the Berliner Jahrbuch be adopted as the 

 standard system, for all differential observations at least. The position 

 of every star to the 9th magnitude, inclusive, from the pole to — 23°, 

 will in a few years be determined on this system ; and, except for weighty 



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