ASTRONOMY. 



107 



is thus put on his guard, and knows that he should use the places of 

 certain stars with circumspection. Herr Auwers thinks that it would 

 be premature to attempt any correction of the catalogue-places before 

 the completion of the general revision, which has been undertaken by 

 the observers of the zones and by the Pulkowa astronomers. He, how- 

 ever, takes this opportunity of ijublishing the results of investigations 

 he has made as to the mean errors of the different catalogues emploj'ed 

 in the formation of the Fundamental Catalogue, viz, Pulkowa, 1845 and 

 18G5; Green.wich, 1861 and 1872; Cambridge (U.S.), 1872; Leipzig, 

 1868 ; and Leiden, 1868, for the principal-stars ; and in addition to these, 

 Pulkowa, 1871, for the supplementary stars. 



The following are, in the mean (for declination — 10° to + 90°), the 

 mean errors, referred to the unit of weight, for the principal stars : 



R. A, (£ cos 5). 

 Decl. (£) 



And for the supplementary stars 



L. 1868. 



0".58 



R. A. (e cos (5) 

 •Decl. (e) 



P. 1845. 



0^043 



P. 1871. 



0^057 

 0".72 



G. 1861. 



G. 1872. 



Os.053 

 0".64 



0^034 

 0".52 



C. 1872. 



0^035 

 0".89 



Lp. 1868. 



0".72 



L. 1868. 



Wo have then, finally, for mean error of the right ascensions 0^.033 

 (for supplementary stars 0^042), and for the declinations 0".59 (for sup- 

 plementary stars 0".67). The somewhat considerable difference in the 

 results for principal and for supplementary stars arises from the cir- 

 cumstance that Herr Auwers gave relatively too much weight to Pul- 

 kowa 1871, at least for the right ascensions. For the catalogue-places, 

 the mean errors are 0^009 and 0".14 in E. A. and Deck, respectively, for 

 the principal stars, and 0^026 and 0".19 for the supplementary stars; 

 where the mean error in E. A. refers to the total number of stars be- 

 tween — 10<^ and -f 50'^. At the present time, in Herr Auwers' opinion, 

 the probable error of the star-places is not greater than 0^02 in E. A. 

 (for moderate declinations), and 0'M5 in Decl. (Observatory, 9 : 202, 

 May, 1886.) 



In response to a suggestion by Dr. Gill, a number of astronomers 

 have expressed their willingness to co-operate in the systematic observa- 

 tion of stars which have been used in comet comparisons, faint stars 

 whose occultatious have been observed, zones of stars used for scale or 

 screw values, or stars that have been used for geodetic i^urposes. Among 

 the observatories ready for this work are, the Cape of Good Hope, 

 Keuchatel, Bruxelles, Cointe, Taschkeut, and Cordoba. 



