440 



NA TURE 



[June io, 1909 



to a variation of only o^oi" in the apparent diameter, an 

 unmeasurable quantity. 



Camera Objectives for Spectrographs. — No. 4, vol. 

 -xxi.-i., of the Aslrophysical Journal contains an interesting 

 practical paper, by Mr. Plaskett, of the Dominion Observa- 

 tory, Ottawa, describing- a large number of tests he has 

 carried out whilst endeavouring to find the most universally 

 useful form of objective for spectrographic work. 



A number of tests were made by Hartmann's e.xtra-focal 

 image method adapted to spectrographic work, and the 

 results are given in detail and illustrated by diagrams. 

 For a dispersion of three prisms with a camera of fairly 

 Jong focus, it was found that, of the objectives tested, 

 ihe Zeiss " Chromat " and the Brashear Light Crown 

 were the best. The former gives a flatter field and 

 slightly better definition, but for the latter there is the 

 advantage that the plate has to be inclined only 8° instead 

 .of 16°, and the absorption is less. For short-focus work 

 the Zeiss Tessar and the Ross Special Homocentric gave 

 jjood definition and flat fields. 



T//£ AS7\K0GRAPHIC CONFERENCE AT 

 PARIS. 

 'T'HE permanent committee of the Astrographic Congress 

 •*- of 1887, as our readers are aware, recently held its 

 -fifth meeting at Paris. Invitations were by no means con- 

 fined, however, to members of that committee, and they 

 were largely accepted by other astronomers. The follow- 

 ing were present, representing observatories cooperating 

 i n the work : — 



Algiers : Gonnessiat ; Belgium : Lecointe ; Bordeaux : 

 Picard and Kromm ; Cape of Good Hope : Hough ; 

 ■Catania: Ricco ; Greenwich: Cowell ; Helsingfors : 

 Conner; Oxford: Turner; Paris: Baillaud ; Perth {W. 

 Australia): Cooke; Potsdam: Scheiner ; Rome: Lias; San 

 Fernando : Azcarate ; Tacubaya : Valle, Gallo ; Toidouse : 

 •Cosserat, Montagerand ; Sydney and Cordoba were not 

 represented, owing to the recent deaths of their respective 

 'directors. 



The following astronomers and others were also 

 .present : — 



America: Hale, Lcuschner, Perrine, Ritchey ; Austria: 

 Palisa ; Belgium : Dclvosal ; Denmark : Strbmgren ; 

 France : Andoyer, Andr^, Angot, Bayet, Benoit, Prince 

 Roland Bonaparte, Bouquet de la Grye, Bourget, de la 

 Baume Pluvinel, Carpcntier, Darboux, Deslandres, 

 Fontana, Fournier, Gaillot, Gautier, P., Hanusse, Hatt, 

 Lagarde, Lallemand, Lippmann, Lumi^re, Verschaffel ; 

 Paris Observatory : Baillaud, J., Bigourdan, Bouquet de la 

 ■Grye, Hamy, Leveau, Puiseux, Renan ; Germany: Hart- 

 wig, Kuslner, Zurhellen ; Gi-eaJ Britain: Dyson, Franklin- 

 Adams, Sir David Gill, Hinks, Knobel, Major MacMahon ; 

 Holland: Bakhuyzen, Kapteyn ; Italy: Boccardi ; Russia: 

 "Backlund. 



The conference assembled at the observatory at 10 a.m. 

 on Monday, April ig. For nearly an hour the members 

 were occupied in mutual greetings, introductions, and 

 general conversation. The chair was then taken by M. 

 Charles Bayet, Conseiller d'Etat, Directeur de I'Ense'igne- 

 ment supi^rieure au Ministfere de ITnstruction publique 

 et des Beaux Arts, who delivered an address, bidding the 

 members welcome in the most cordial terms, and express- 

 ing on the part of his Government and of the Republic 

 their interest in and sympathy with the great work to 

 promote which so many astronomers had now assembled 

 from all parts of the world. M. Baillaud, director of the 

 Paris Observatory, then delivered an admirable address. 

 "He thanked the assembly for the honour done him by 

 electing him unanimously as their president so soon after 

 his appointment as director of the Paris Observatory. 

 He briefly traced the history of the undertaking known 

 as the " Carte du Ciel," which had its origin in 1887. 

 He referred in touching terms to Admiral Mouchez, to 

 whom the " Carte du Ciel " owed in a great degree its 

 successful origin ; to Tisserand, whose classic labours so 

 adorned the science that he loved ; and to Loewy, who had 

 done so much, not only to develop the Paris Observatory, 

 'but to extend the scope and usefulness of the work of the 

 " Carte du Ciel." He described the great share which 



NO. 2067, VOL. 80] 



Loewy had taken in collecting, discussing, and printing 

 the observations of Eros in 1900, which, in the hands of 

 Mr. Hinks, had led to a very accurate determination of 

 the solar parallax. He showed that by undertaking these 

 observations, not only had thus a most important result 

 been arrived at, but by the refined discussion of the 

 observations of Eros some important systematic errors in 

 photographic observation had been detected, and the 

 sources of these errors found. We had, in fact, by this 

 extension of our field of work, not only arrived at important 

 new results, but greatly improved the results of our 

 previous labours. 



But much yet remained. We had now, for example, to 

 study the problems of perfecting the systematic correc- 

 tions applicable to the preliminary determinations of 

 magnitude Snd position of all the catalogue stars, so that 

 when the work of the different zones had been completed 

 Ihe final catalogue should present a harmonious whole. 

 It was also necessary that we should make preparation 

 for the regular observation of Eros in future, and begin 

 to consider what should be done in order to take the 

 fullest advantage of the extraordinarily favourable opposi- 

 tion of that planet in 1931. Everything that we did to 

 improve the work of the catalogue would go towards per- 

 fecting the determination of the places of the comparison 

 stars to be observed with Eros from now until 1931, and 

 the necessary striving after systematic accuracy which 

 must result from such researches must react in the way of 

 improving the fundamenta of sidereal astronomy. 



Such, at least, are the writer's recollections (without 

 notes) of this admirable and inspiriting address, after the 

 delivery of which M. Baillaud, in a few graceful words, 

 proposed the election of Sir David Gill as " President 

 d'Honneur," a proposal which was carried by acclamation. 



The bureau of the general assembly was then consti- 

 tuted as follows : — vice-presidents, Bakhuyzen, Backlund, 

 Kapteyn ; secretaries, Donner, Puiseux, Scheiner, Turner. 



A suggested programme for the work of the meeting had 

 been prepared by Sir David Gill, and was circulated by 

 the president, M. Baillaud, in January last. This pro- 

 gramme was accepted by the meeting, and, in accord- 

 ance with it, the president formally presented two volumes, 

 one marked A, containing advance proofs of the printed 

 reports of the progress of the work of the chart and cata- 

 logue at the different cooperating observatories, and 

 another, also in proof, marked B, containing papers and 

 discussions of very great interest, such, for example, as 

 Hinks's report on his great discussion of the Eros observa- 

 tions, Campbell's report on Perrine's discussion of the 

 Eros observations made at the Lick Observatory, Hough's 

 paper on a proposed method for the raccordcment of 

 astrographic plates, E. C. Pickering's report on a standard 

 scale of photographic magnitudes, and other papers on 

 kindred subjects by J. Baillaud, Pourteau, Cohn, and 

 Millozevich. 



Then, in accordance with the programme, the confer- 

 ence was divided into five commissions, viz. : — 



(A) To report on the state of the work and the steps 

 (0 be tal<en to perfect or accelerate the work. 



(B) To report on the method to be adopted for the con- 

 version of measured diameters of star-discs (or magni- 

 tudes, as estimated at the different observatories) into an 

 exact and uniform system of magnitudes. 



(C) To report on the existence and probable origin of 

 systematic errors in the measured coordinates of star-discs 

 on certain plates, on the best methods for avoiding such 

 errors in the future, and of putting in evidence and 

 eliminating their effects in the plates already measured. 



(D) The Catalogue Committee. — To examine the origin 

 of the star-positions employed in the preliminary reduction 

 of the plates of each zone, to study the 'best means of 

 coordinating the star-places of the different zones, and to 

 determine the systematic corrections necessary to reduce 

 the whole to a uniform and absolute system. 



(E) The Eros Committee.— (i) To "report on the steps 

 to be taken for the preparation of a preliminary ephemeris 

 of Eros at its opposition in 1931 of sufificient precision to 

 permit the earlv selection of comparison stars. (2) To 

 propose means for the regular observation of the planet 

 from the present time onwards in order to perfect the 

 ephemeris which will be finally employed for the definitive 



