474 



NA TURE 



{Sept. 13, 1883 



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 hemisphere by 

 means of meridian circles ; but he proposed at the same time 

 that the positions of stars fainter than the ninth magnitude should 

 be determined by means of differential observations with equa- 

 torial instruments. After explaining certain plans and arrange- 

 ments relating particularly to his own observatory, he introduced 

 the following resolution : — 



" The Astronomische Gesdhchaft regards it as needful that all 

 the stars to the ninth magnitude occurring in the Durchmus- 

 terung should be ob-erved with meridian circles, and commissions 

 the Council to arrange for the execution of the work." 



This proposal occa ioned a li *ng and somewhat animated dis- 

 cussion, in which Argelander, Ilir-ch, Bruhns, Forster, Schonfeld, 

 and Struve took part. 



Argelander declared himself surprised at this proposal, which 

 called for the rapid realisation of a plan of organisation which 

 he had been considering for years wilh the greatest care, the 

 difficulties of which he had maturely considered, and the execu- 

 tion of which still demanded the most careful deliberation and 

 preparation. One of the necessary preliminary steps was a 

 plan which he had already prepared, published, and presented to 

 the Society in an informal way, which provided for contempo- 

 raneous and corresponding observations of the brighter stars. 

 As president of the Society he felt unequal to undertaking the 

 charge which 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 this 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 consideration of it and the pre- 

 paration for it to his zealous friends in the Council. 



Upon the motion of Struve, the Society, by a rising vote, ex- 

 pressed its confidence in the assurance of the president that he 

 would bring forward his plan at the proper time, as soon as the 

 means for its execuli n could be assured. 



At the meeting held at lionn in 1867 Argelander again 

 brought up the subject in a communication which appears to 

 have been an exhaustive discussion of the whole problem. This 

 paper is not printed in the Proceedings oj tlie Gtstllschaft, but at 

 its conclusion a committee was appointed to take definite action 

 with respect to the recommendations which it contained. The 

 committee reported at the same session, and their report, which 

 is published in the place of the paper presented by Aigelander, 

 is probably identical in substance with it. The plan proposed 

 and adopted was finally published in the form of a programme, 

 in which the details of the work are arranged with consider- 

 able minuteness. As this programme has been widely distri- 

 buted, it seems unnecessary to give anything more than a general 

 abstract of it. Since it differ- in a few minor points from the 

 first report of the committee at the Bonn meeting, the essential 

 features of this report will be given instead of an abstract of 

 the programme itself. 



They are as follows : — 



a. The limits in declination of the proposed series of observa- 

 tions are -2° and +80°. The first limit was chosen on account 

 of the lack of suitable fundamental stars south of the equator. 

 It is probable, also, ibat Argelander had a suspicion of the fact, 

 since proven, that the uncertainty with respect to the systematic 

 errors of southern stars is, of neces>ity, considerably greater than 

 for northern stars, and that on this account it would be better tc 

 defer this part of the work until further inve tigations in this 

 direction could be made. 



The limit + So° was chosen because the repetition of Carring- 

 ton's observations between 81° and 90 was considered super- 

 fluous, and Hamburg had already undertaken the extension of 

 Carrington's observations from 8i° to 8o°. 



i. Within these limits, all stars in the Durchmuslcrung to the 

 ninth magnitude, and, in addition, all stars which have been 

 more exactly observed by Lalande, by Bessel at Kbnigsberg, 

 and by Argelander at Bonn, are to be observed. 



c. The observations are to be differential. The clock errors 

 are not to be found from the fundamental stars usually chosen 

 for this purpose, and the equator point corrections are not to be 

 derived from observations at upper and lower culminations, but 

 these elements are to be derived from a series of 500 or 600 stars, 

 distributed as uniformly as possible over the northern heavens. 



The exact coordinates of these stars are to be determined at 

 Pulkowa, thus securing the unity necessary in order to connect 

 in one system the observations of different zones. 



d. Every star is to be observed twice. If the two observa- 

 tions differ by a quantity greater than ought to be expected, a 

 third observation will be necessary. 



e. In order to facilitate the work it will be desirable to use 

 only three or four transit threads and only one or two micro- 

 scopes. In order to facilitate the reductions to apparent place 

 the working-li-.t of stars should be comprised within narrow 

 limits. 



f. Before the commencement and after the close of each zone, 

 two or three fundamental stars are to be observed upon the same 

 threads and with the same microscopes as were used in the zone 

 observations. When the seeing is not good, and when for any 

 other cause it seems desirable, one or more fundamental stars 

 may be observed in the course of the zone. The number and 

 selection of the stars will depend upon the character of the in- 

 strument empl yed. If it remains steady for several hours and 

 has no strongly marked flexure or division errors, or if these 

 errors have been sharply determined, the fundamental stars may 

 be situated ten degrees or fifteen degrees away from the zone 

 limits. However, there must remain many things for which 

 no general rule can be given, and which must be left to the judg- 

 ment of the observer, aided by an accurate knowledge of his 

 instrument, 



g. With a Repsold or a Martin instrument one microscope 

 will be sufficient, if its po-ition with respect to the whole four 

 can be determined. It will be sufficient if the change in position 

 during the observations can be interpolated to 02s. 



h. Jt will be desirable to divide beforehand the zones into 

 such time intervals that the observations can be easily made. 



1. Zones exceeding one and a half or at the most two hours 

 are not advisable, first, because the zero points will be too far 

 apart, and, second, because a longer duration will involve too 

 much fatigue physically and mentally. 



At the conclusion of this report all the astronomers present 

 who were willing to take part in this work were requested to 

 communicate with the Council, stating the regions of the heavens 

 which they preferred to select for observation. 



At this meeting, Berlin, Bonn, Helsingfors, Leipzig, and 

 Mannheim signified their intention to share in the work. Leyden 

 also expressed its intention of taking part as soon as the work 

 already undertaken should be completed. 



When the stars to be observed had been selected from the 

 Durchmusteriing, it was found that the number would not vary 

 much from 100,000, requiring rather more than 200,000 obser- 

 vations. Preparations for the work of observation were imme- 

 diately commenced, and, by the time of the next report in 1869, 

 considerable progress had been made. 



In the report for this year the provisional places of a catalogue 

 of 539 fundamental stars were published. This catalogue is 

 composed of two parts. The list of Hauplsterne consists of 

 336 stars to the fourth magnitude, observed at Pulkowa by 

 Wagner with the large transit instrument, and by Gylden with 

 the Ertel vertical circle. The list of zu za t-sterne consists of 

 203 stars fainter than the fourth magnitude. As the details of 

 the work in the formation of the provisional places of the stars 

 of this list are not given in the report, it is not quite clear upon 

 what authority they rest. The work assigned to the Pulkowa 

 observatory by the Zone Commission was the exact determina- 

 tion of the places of the stars of this list. The* observations 

 were undertaken by Grornadski with the Repsold meridian circle. 

 In accordance with the plan adopted each star was observed 

 eight times — four times in each position of the instrument. The 

 observations were differential with respect to the Haupt-sterne. 



The results were published by Struve in 1876, and the places 

 there given were used in the first reduction of the Harvard 

 College observations for 1874-75, an & perhaps in some other 

 cases. 



About this time a change seems to have been made in the 

 original plan wilh respect to the formation of the final catalogue 

 of fundamental stars, of which I have been unable to find a 

 clear account. The original intention was to make the posi- 

 tions depend entirely upon the observations at Pulkowa. The 

 Zone Commission established by the Gesdhchaft, how ever, com- 

 mitted the formation of this catalogue to Auwers ; and it is to 

 him that we owe the most complete and the most perfect cata- 

 logue of fundamental stars yet published. The Pulkowa system 

 for 1865 was adopted as the basis ; but, in order to obtain greater 



