i8o 



NATURE 



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une 21, i 



been likewise engaged in the study of the new instrument 

 they have devised for the measurement of the stellar 

 photographs, and in the preparation of tables of instru- 

 mental corrections, and of corrections for the effect of 

 refraction ; whilst M. Thiele has been inquiring into the 

 degree of accuracy of which the measures are capable, 

 with most encouraging results, and Admiral Mouchez 

 considers that the precision thus attainable "will permit 

 the carrying out under good conditions of the Catalogue 

 of all the stars down to the nth magnitude as decided 

 by the Congress." It should be noted, however, that 

 this interpretation of the resolution of the Congress 

 has been challenged, and it has been urged that the 

 Catalogue to be formed was to contain simply as many 

 suitably placed stars as would be necessary as reference 

 points for the great photographic chart, and that stars 

 down to the nth magnitude might be used for this 

 purpose. 



As to the publications of the Observatory, the first 

 volume of the Catalogue, ch.-6h. of R.A., is shortly to be 

 followed by the second, 6h.-i2h., the first sheets of which 

 were already in the printers' hands. The volume of 

 Observations for 1882 was published last August, that for 

 1883 was passing through the press, whilst the reduction 

 of apparent to mean places was completely finished for 

 1884. The nineteenth volume of the Memoirs was in course 

 of publication, and would contain, besides the works 

 mentioned in the Report for 1886, a memoir on the theory 

 of the figure of the planets, by M. Callandreau, and 

 another on an allied subject, by M. Hamy. Amongst the 

 works published by the individual members of the 

 Observatory, the most important have been M. Lcewy's 

 new method for the determination of the constant of 

 aberration, and a work by M. Wolf, on the pendulum. M. 

 Leveau is still engaged in his work upon Vesta, and M. 

 Bossert is preparing for the determination of a definitive 

 orbit of the Pons-Brooks comet. Under the head of 

 " Mate'riel " the progress of the new equatorial coude of 

 2 feet aperture and 60 feet focal length is referred to. Its 

 completion is expected during the present year, but the 

 building for it has not yet been begun. 



The chief exception to the record of progress which 

 Admiral Mouchez's Report supplies is found in the short 

 paragraph which records the closing of the astronomical 

 school, on financial grounds. The necessity for this step 

 is to be most deeply regretted. 



THE PHOTOGRAPHIC CHART OF THE 

 HE A VENS. 



\X7E lately reprinted from the Observatory (N AT\jRE,May 

 * * 10, p. 38) an article by the editors of that periodical 

 on Dr. Gill's proposal that two million stars should be 

 catalogued. The following is the reply of the editors, 

 printed in the June number of the Observatory, to letters 

 addressed to them on the subject by Admiral Mouchez 

 and Mr. E. B. Knobel :— 



We print above letters from Admiral Mouchez and 

 from Mr. Knobel, concerning the remarks we made last 

 month on Dr. Gill's proposition to catalogue 2,000,000 

 stars. There is a somewhat personal implication in both 

 letters, to which we must at once reply before proceeding 

 to treat of the real question at issue — a suggestion that 

 we have been so emphatic in our disapproval of the 

 scheme as to be discourteous to its supporters. We may 

 perhaps venture to doubt whether either writer has done 

 us the honour to read our remarks carefully enough. 

 Admiral Mouchez " nous trouve bien severe pour un 

 projet aussi bien etudie' et venant d'un savant aussi habile 

 et competent que le Directeur de l'Observatoire du Cap." 

 We have not said a single word in disparagement of the 

 skill and care with which Dr. Gill's paper has been 

 written ; we have vehemently objected to the question 



being raised at all ; and that we have objected so vehe- 

 mently may be taken as a full recognition of Dr. Gill's 

 prominent position, which makes it a matter of necessity 

 to bring all our forces to bear against a scheme which ho 

 chooses to advance. Mr. Knobel is perhaps more unjust 

 to us. We have not in an unqualified manner character- 

 ized a catalogue of 2.000,000 stars as " an utter waste of 

 time, labour, and money " ; but we did use even stronger 

 language about cataloguing stars " for the purpose only of 

 getting their places written down," in order to call 

 attention to the reductio ad absurdum of cataloguing 

 towards which we very much fear there is some apparent 

 tendency. And, finally, if we have been so emphatic as 

 to be accused of exaggeration, let us again point out that 

 a scheme, which we contend has not been assented to or 

 even considered by the members of the Astrophotographic 

 Conference, has been quietly launched, and is now so far 

 under way that it is referred to by the President in the 

 opening sentence of his letter as a matter already accepted 

 by the " Comite" permanent," and as only remaining to be 

 discussed in detail. Surely it is time for those who have 

 the welfare of the scheme really sanctioned by the 

 Conference to raise their voices loudly in protest! 



So much in explanation of the tone we have adopted in 

 speaking of this proposal, and we now return to the 

 letters. The main point of both is that this scheme of a 

 catalogue of 2,000,000 stars has not been originated by 

 Dr. Gill, but was really considered and approved by the 

 Conference. As we have stated above, we hold the 

 opposite opinion, — that although two resolutions of the 

 Conference do mention a catalogue, this term cannot be 

 supposed to sanction a catalogue of 2,000,000 stars with- 

 out further specification. The Conference met to discuss 

 the advisability of making a chart. With the invitations 

 sent out to the various astronomers to attend this Confer- 

 ence there was sent a " programme provisoire " (which, it 

 is to be very much regretted, was not that considered by 

 the Congress). This first "programme provisoire" was 

 dropped, and at the first seance of the Congress another 

 was produced. In the first, in article 19 a catalogue of 

 reference stars was mentioned, and properly so, but in the 

 second there was no mention of any such catalogue. 

 Mention was made in section 4 of a means of publishing 

 the chart and the form of publication, but up to this 

 time there was absolutely no question before the Confer- 

 ence of publication of a catalogue either of 2,000,000 

 or any other number of stars. There was no doubt a 

 feeling amongst some astronomers present that a catalogue 

 would be as useful, in their judgment, as the chart ; and 

 they took the opportunity of putting forward their views 

 when the question of a second series of plates was brought 

 forward. The taking of this second series of plates was 

 proposed to meet an anticipated difficulty in photographing 

 parts of the heavens where the stars differed greatly in 

 magnitude. It was decided (Resolution 17) that a second 

 series of plates should be taken, in order to insure the 

 greatest precision in the micrometrical measurement of 

 the stars of reference, and to render possible the con- 

 struction of a catalogue. Here we have the first mention 

 of a catalogue in the resolutions noted. A reference to 

 the minutes of the Congress will show that this resolution 

 was a compromise, for there had already been before the 

 Congress a direct proposition (that of M. Tacchini) for a 

 catalogue, which, however, was not voted upon. The 

 resolution was in fact an endeavour to settle a question 

 that was before the Congress, viz. whether the plates 

 should be so taken as to be capable of accurate measure- 

 ment ; and this is decided by the specification that they 

 shall render possible the construction of a catalogue. 

 The next two resolutions speak of the second series of 

 plates as destines a la construction du catalogue, but no- 

 where is any direct resolution to be found as to the 

 construction of a catalogue of all the stars. 



If these resolutions need interpretation by the light of 



