232 



SCIENCE 



[Vol. II., No. 29. 



struments, and by different observers. He says, 

 " With all tbese precautions, we do not find, by com- 

 paring the present observations with those of Bradley 

 made eighty years ago under the same roof, and com- 

 puted by the same table of ref inactions, that we can 

 obtain by interpolation any intermediate catalogue 

 which shall agree with the observations within the 

 probable limits of error." 



We owe to the investigations of Auwers {Astron. 

 nachr., nos. 1532-15.S6), the first definite system of 

 declinations which is measurably absolute in its 

 character. Tet the deviations of this system from 

 that derived by the same author, but from much 

 additional data in publication xiv. of the geseilschaft, 

 is no less than 1.2". The present difference outstand- 

 ing between thePulkova and the Greenwich systems 

 at 10° south declination is 1.7". 



Within the past five years, the labors of Auwers, 

 of Safford, of Boss, and of Nevvcomb, have resulted 

 in the establishment of a mean system of declinations 

 from which accidental errors may be considered to 

 be eliminated in the case of a large number of stars; 

 but the diffeient systems still differ systematically 

 inter se by quantities which are considerably greater 

 than the probable error of any single position. 



When the discussion of the question of a uniform 

 determination of all the stars in the northern heavens 

 to the ninth magnitude was taken up by the geseil- 

 schaft at its session in Leipzig in 1S65, Argelander, 

 who was then president of the society, appears to 

 have been the only astronomer who had a clear ap- 

 prehension of the diiBculties of the problem, lie 

 alone had detected the class of errors whose existence 

 subsequent investigations have definitely established. 

 He alone had found a well-considered plan by which 

 these errors might be eliminated, as far as possible, 

 from future observations. 



Argelander, however, always claimed for Bessel 

 the first definite proposal of the proposition under 

 cotisideration (see Astron. nachr., i. 257). It was in 

 pursuance of this plan that the zones between — 15° 

 and + 15° in declination were observed. These 

 zones were to form the ground-work of the Berlin 

 charts; and Argelander, in the execution of the 

 Bonn Durohmusterung, simply carried out the second 

 part of Bessel's recommendation. 



With the exception of the observations of Cooper 

 at Makree observatory, and the charts of Chacornac, 

 these two great works — the second being a con- 

 tinuation of the first, under a better and more feasible 

 plan — are the only ones in existence which give us 

 any knowledge of the general structure of the stellar 

 system. 



The observations of stars to the ninth magnitude, 

 found in the catalogues of Bessel, Lalande, and 

 Piazzi, form the ground-work of these charts. The 

 co-ordinates in right ascension and declination of the 

 stars found in these authorities were first reduced to 

 the epoch 1800; the resulting right ascension being 

 given to seconds of tinie, and the declination to 

 tenths of minutes of arc. With these places as points 

 of reference, all other stars were filled in, down to 

 the ninth magnitude, by observations with equatorial 



instruments. The work was divided into zones of 

 one hour each. Bremiker undertook five zones; 

 Argelander and Schmidt, two; Wolfers, three; and 

 Harding, two. The remaining zones were under- 

 taken by different astronomers in widely separated 

 localities. 



The work seems to have been performed with 

 somewhat unequal thoroughness, some zones con- 

 taining nearly all the stars to the ninth m.agnitude, 

 while in others a large number of stars having this 

 limit in magnitude are wanting. 



The Durclnnusterung undertaken by Argelander 

 at Bonn was a far more serious and well-considered 

 undertaking. This unequalled work consists in the 

 approximate determination of the co-ordinates of 

 324,198 stars situated between — 2° and -f-00° decli- 

 nation. It includes stars to the 9.5 magnitude, the 

 co-ordinates being given to tenths of minutes of 

 time, and the declinations to tenths of minutes of 

 arc. 



The first definite proposal of this work undertaken 

 by the geseilschaft, however, appears to have been 

 made by Brnhns. In the course of a report upon the 

 operations of the Leipzig observatory, he stated, that, 

 in his view, the time had come for undertaking a 

 uniform system of determinations of the places of 

 stars to the ninth magnitude in the northern hemi- 

 sphere by means of meridian circles; but he pro- 

 posed, at the same time, that the positions of stars 

 fainter than the ninth magnitude should be deter- 

 mined by means of differential observations with 

 equatorial instruments. After explaining certain 

 plans and arrangements relating particularly to his 

 own observatory, he introduced the following resolu- 

 tion: — 



" The Astronomische geseilschaft regards it as need- 

 ful that all the stars to the ninth magnitude, occurring 

 in the Durchmusterung, should be observed with 

 meridian circles, and commissions the council to 

 arrange for the execution of the work." 



This proposal occasioned a long and somewhat 

 animated discussion, in which Argelander, Hirsch, 

 Bruhns, Forster, Schonfeld, and Struve took part. 



Argelander declared himself surprised at this pro- 

 posal, which called for the rapid realization of a plan 

 of organization which he had been considering for 

 years with the greatest care, the difficulties of which 

 he had maturely considered, and the execution of 

 which still demanded the most careful deliberation 

 and preparation. One of the necessary preliminary 

 steps was a plan which he had already prepared, pub- 

 lished and presented to the society in an informal 

 way, which provided for contemporaneous and cor- 

 responding observations of the brighter stars. As 

 president of the society, he felt unequal to undertak- 

 ing the charge whiph the acceptance of the resolution 

 proposed would involve; as this procedure seemed to 

 him premature without previous preparation. He 

 would admit, however, that every call to action of 

 tliis kind tended to stimulate enthusiasm, and should 

 therefore be encouraged; but he felt obliged to ask 

 the society not to require from him the immediate 

 execution of the plan, but to intrust the serious con- 



