442 



NA TURE 



[June io, 1909 



film normal (u llie axis of the object-glass. To examine 

 the quality of the object-glass or its distortion Hart- 

 mann's perforated screen method is recommended, its 

 efficacy having been already proved. 



In order to determine the effects of optical distortion 

 depending on the position-angle and distance, special plates 

 of the Pleiades should be taken. These plates should also 

 serve to show whether the formula and methods previously 

 employed in the reduction are sufficiently accurate and 

 complete. The committee is of opinion that the optical 

 errors should be studied on the plates already measured 

 by the methods referred to by Prof. Turner in Annex A 

 (reports of the participating observatories).' 



It is also desirable that observations should be made to 

 determine the relative flexure of the photographic and 

 visual telescopes. 



Fro}H Commission D, 



The permanent conimiltee, convinced of the importance 

 of the (meridian) determination of the positions of the 

 etoiles de repere as contemporaneously as possible with the 

 exposures of the plates, expresses its high satisfaction that 

 these stars have been so observed, or are about to be 

 observed in the near future. 



With reference to these observations which have as 

 yet to be made, the committee addresses its thanks to 

 MM. Verschaffel, Backlund, Struvc, and Boccardi, who 

 have so kindly undertaken this outstanding work, and 

 rests assured that these observations will be made by them 

 with all desirable precision and promptitude. 



The committee is of opinion that, in the future, meridian 

 observations of faint stars, excepting for special researches, 

 should be limited to the stars which have been selected 

 as itoiles de repere for the catalogue plates. In this way 

 the positions of the great majority of the stars (to the 

 eleventh magnitude) can be determined with the greatest 

 facility and precision. 



Meridian observations may be divided into three classes, 

 viz. fundamental stars ; intermediate stars ; Hoilcs de 

 repere. 



Fundamental Stars. — These should be so chosen that 

 there shall be one star in each area of twenty-five square 

 degrees, so that their distribution in the skv may be as 

 uniform as possible. The observatories willing to unite 

 in the formation of a new fundamental system should 

 agree to select a common list of stars, and to observe all 

 stars of that list which culminate at suitable altitudes 

 above their respective horizons. 



The observatories which at first sight appear to be 

 available for this cooperation are :— in the northern hemi- 

 sphere, Algiers, Greenwich, Leyden, Lick, Kiel, Paris, 

 Pulkova, Odessa, Washington ;' in the southern hemi- 

 sphere, Cape of Good Hope, Sydney. This resolution does 

 not exclude the cooperation of other observatories for 

 fundamental work, provided that they have time and 

 instruments of the necessary type. 



Intermediate Stars.— .\ second series, called intermediate 

 stars, and preferably of the eighth to ninth magnitude, 

 shall be established. These stars will be selected for the 

 purpose of determining the positions of the etoiles de 

 repere with respect to the fundamental stars with the least 

 systematic error possible, with the view of the elimina- 

 tion of personal equation depending on magnitude both in 

 right ascension and declination. The Bonn Catalogue of 

 Stars for 1900. dec. 0° to 51°, offers an example of 

 methods by which such a catalogue can be constructed. 

 It IS known that a similar catalogue is about to be made 

 between dec. 51° and qo° at the Observatory of Kasnn. 



It IS desirable that analogous observations should be 

 made in the northern hemisphere, and, if it is possible, 

 that two similar scries or more should be made in the 

 southern hemisphere. The stars which should be chosen 

 for these additional series may be loss numerous than 

 those above indicated, but thev ought to be taken ex- 

 clusively from the adopted lists of dtoiles de repere and 

 selected so that there shall be from four to six stars per 

 hour in each zone of two degrees in breadth. 

 ,1-LJk !. K^'Kl "■■''" •*''"'<^ '•''" =1 ""re comnlete system, viz. that 

 commu'ee. '' ^^'^ ®- ^- "<"■«'■ ('^""" "), has been overlooked by the 



NO. 2067, VOL. 80] 



So far as the determination of the positions of the 

 intermediate stars is concerned, the observatories which 

 have good recent meridian observations of the etoiles de 

 repere need not of necessity re-observe them. It will only 

 be necessary to determine the mean corrections of the 

 positions of the etoiles de repere of each plate by com- 

 paring the formerly adopted positions of these stars with 

 the definitive positions of the intermediate stars ; but for 

 all meridian observations of the etoiles de repere made 

 subsequent to the publication of the definitive positions 

 of the intermediate stars it will be desirable to employ 

 these positions as a basis for the reduction of the observa- 

 tions. ' 



The commission charged with this work by the per- 

 manent committee will consist of the directors of the 

 observatories engaged in cooperation, together with 

 Messrs. Auvvcrs, Gill, Kustner, and Newcomb. 



The following supplementary resolution was added in 

 general committee : — 



The committee' is of opinion that, in consideration of 

 the small number of observatories fitted for fundamental 

 work of high precision in the southern hemisphere, it is 

 very desirable, in the interests of science, that a meridian 

 instrument provided with all modern improvements should 

 be installed in Australia. The establishment of a new 

 observatory near Sydney offers a very fortunate opportunity 

 for the fulfilment of this great astronomical desideratum. 

 .\ copy of this resolution to be transmitted to the Govern- 

 ment of New South Wales through the usual diplomatic 

 channels. 



From Co 



ission E. 



Mr. Striimgren is charged to compute : — (i) an approxi- 

 mate ephemeris of Eros for 193 1; (2) precise ephemerides 

 for the successive oppositions until 1931; (3) an ephemeris 

 of high precision for 1931. 



The committee expresses the desire that the ephemerides 

 of Eros, relative to successive oppositions, be inserted in 

 the chief official ephemerides — Nautical Almanac, Con- 

 naissancc du Temps, S:c. 



The committee is of opinion that an international 

 arrangement should be arrived at for the computation, as 

 soon as possible, of the heliocentric positions of the chief 

 perturbating planets — Venus, Earth, Mars, Jupiter, and 

 Saturn — so that Mr. Stromgren may furnish in the course 

 of a few years an ephemeris of Eros for 193 1 which will 

 be sufficiently accurate to permit the selection of the com- 

 parison stars. 



The committee recommends the regular observation of 

 the planet Eros from the present epoch onwards. These 

 observations should be made, not only at opposition, but 

 as long before and after each opposition as possible. 



For the oppositions previous to 193 1, observatories are 

 requested to publish their results as early as possible. 

 Especially in the case of photographic observations, the 

 rectilinear coordinates of the planet and of the comparison 

 stars should be given. So far as possible, these should 

 refer to the etoiles de repere of the photographic catalogue 

 for the region ; the provisionally derived right ascension 

 and declination of the planet should also be given. 



As the etoiles de repere have already been selected for 

 the whole sky, one can easily ascertain (for example, by 

 correspondence) the stars to be measured with Eros. 



Front the Meeting of the General Conimiltee. 



The committee appoints a commission, viz. Messrs. 

 Knobel, Lippmann, Perrine, and Turner, to examine the 

 question of the production of star-images on a photographic 

 plate both from the optical and photographfc point of view, 

 and to study the means of obtaining star-images more 

 susceptible of exact measurement than those at present 

 found on our existing plates. 



This commission has power to add to its number. 



The meeting concluded with a vote of thanks to M. 

 Baillaud for the perfection of the arrangements made for 

 the business of the meeting, for the ability and tact with 

 which he had filled the post of president, and for the 

 hospitality and kindness he had shown to all. 



The following table, extracted from the printed reports; 



