ASTRONOMY. 



107 



is thus put ou his guard, and kuows that he should use the places of 

 certain stars with circumspection. Herr Auwers thinks jihat 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 publishing the results of iuvestigations 

 he has made as to the mean errors of the diiierent catalogues employed 

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

 iSG.j; Greenwich, 18G1 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 : 



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

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

 plernentary 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 aud 0".14 in E. A. and Decl., 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 — 10c> and + 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".15 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 occultations have been observ^ed, zones of stars used for scale or 

 screw values, or stars that have been used for geodetic purposes. Among 

 the observatories ready for this work are, the Cai»e of Good Hope, 

 Neuchatel, Bruxelles, Coiute, Taschkent, and Cordoba. 



