June io, 1909] 



NA TURE 



441 



reduction of the observations in 1931, that is to say, for 

 the direct determination of the solar parallax and mass 

 of the moon, as also for the ultimate determination of 

 the mass of the earth by means of the perturbations which 

 it produces in the motion of Eros. 



The bureauK of these committees were then constituted 

 as follows ; — 



A B C , D E 



President Turner Kapieyn Bakhuyzen Kustner Backlund 



Vice-l'res. Donner Fuistux Andre Hough Uysun 



Secretary Aniloyer Bourgct Hamy Luc. Ficart Lagaide 



,, — Azcarte Valle kicco Hmks 



A list was then submitted suggesting the names of 

 members who should serve on the different committees, 

 although any member of the conference was at liberty to 

 attend and vote on any of the committees he pleased. 

 .As there was sufficient, accommodation at the observatory 

 a separate room was assigned to each committee. The 

 conference then adjourned for the day, and many of the 

 members attended the meeting of the .\cademy of Sciences 

 at the Institute in the afternoon. 



The committees sat from 10 to 12.30 in the morning, 

 and from 3 to 5 in the afternoon, on Tuesday, Wednes- 

 dav, and Thursday, .April 20, 21, and 22, and by the 

 latter date had completed their labours. 



On Friday morning, .April 23, the resolutions of the 

 various commissions were successively submitted to the 

 general conference, and, as a rule, were adopted without 

 change. The resolutions as finally adopted are as 

 follows : — 



Vrom Commission A. 



The committee expresses the desirability that the 

 measures of the catalogue plates made at Sydney and 

 Melbourne should be published as soon as possible, and 

 that a copy of this resolution be sent to the Governments 

 concerned. 



It is desirable that the zone (dec. —17° to 23°) not yet 

 commenced should, for the catalogue, be divided between 

 the observatory of Santiago, the new observatory of 

 Hyderabad (Deccan), and, if necessary, the observatory of 

 the University of La Plata. M. Baillaud is charged to 

 arrange with the directors of these observatories for the 

 partition of the work. 



It is desirable that the Cordoba zone (dec. —24° to 

 — 30°) should be divided for the catalogue between the 

 observatories of Cordoba and the Cape of Good Hope. 

 M. Baillaud will arrange with Mr. Perrine, the new 

 director of the Cordoba Observatory, for this subdivision 

 of the work. 



The permanent committee directs attention to the interest 

 which attaches to a repetition of the catalogue plates even 

 after so short an interval as ten years. The high precision 

 of the measures will already furnish indications of proper 

 motion. It invites observatories, which are in a position 

 to do so, to repeat the catalogue plates, taking care that 

 the repeated plates be made at the same hour-angle and 

 at the same season of the year as in the earlier series. 



From Commission B. 



The participating observatories are recommended to 

 make direct photographic comparisons between the star- 

 images of the polar area and twenty-four regions of the 

 particular zone undertaken at each observatory. 



In this comparison two exposures of each area shall be 

 made, one of si.x minutes and one of twenty minutes, the 

 two regions being taken at equal zenith-distance and in 

 conditions as similar as possible. 



Those observatories where the construction of the tele-' 

 scope mounting prevents access to the polar region may 

 utilise the Pritchard-Kapteyn areas for the above-described 

 comparison. For the plates in the neighbourhood of the 

 pole it is recommended to select twenty-four areas, selected 

 in the manner that appears most convenient to the 

 astronomers engaged on the work. 



It is to be understood that there is no obiection to the 

 making of the above-mentioned comparisons of different 

 exposures on two different series of plates, nor to making 

 additional series with dilTerent exposures. 



NO. 2067, VOL. 80] 



The committee recommends a second series of twenty-four, 

 plates connecting in pairs the twenty-four type-regions of 

 the same zone.' In this series there should also be two 

 exposures, viz. of six minutes and twenty minutes re- 

 spectively, for each of the two regions compared ; but, as 

 before, there is no objection to the making of the above- 

 mentioned comparisons of different exposures on two- 

 different series of plates, nor to making additional series 

 with diliferent exposures. 



The committee recommends that the astronomers whose 

 zones include the declinations ±0°, ±15°, ±30^, ±45°, 

 + 60°, and ±75° should select Kapteyn's selected areas 

 for their type-regions, or at least regions including these 

 selected areas. 



The committee is of opinion that several observatories 

 should also undertake the photography of the Kapteyn- 

 Pritchard areas, connecting each of them, on the same 

 plate, with the pole, some with the North and others with, 

 the South Pole, and taking care to make both exposures 

 under conditions (as to Z.D., &c.) as similar as possible. 



The raccordement of the other regions of any zone 

 with the corresponding type-regions of that zone may be 

 made in a variety of ways. The committee thinks that 

 the choice of the method of raccordement should be 

 left to the participating observatories. 



The committee, believing it to be premature to fix ir>. 

 an absolute manner the origin and interval of the scale 

 of photographic magnitudes, entrusts the solution of the 

 problem to a commission constituted as follows : — Back- 

 lund, B. Baillaud, Gill, G. Hale, Kapteyn, E. C. Pickering, 

 Scheiner, Turner. 



The members of this commission are recommended to^ 

 select a photographic scale that is independent of the 

 visual scale. Stars of the ninth magnitude of the visual 

 scale should be taken as the point of departure for the 

 photographic scale. Until the commission has completed' 

 its labours observers should continue to publish the magni- 

 tudes of stars on the same basis as that previously adopted" 

 by them, on the understanding that each participating- 

 observatory shall describe, with all desirable precision, the- 

 methods which have been adopted to determine the pub- 

 lished magnitudes. In this way the corrections necessary 

 to pass from the scales respectively adopted by the different 

 observatories to the absolute scale which will result from 

 the labours of the commission can be made with the mini- 

 mum of uncertainty. .At the present moment the scale 

 most to be recommended is that which is defined by " the- 

 North Polar sequence of forty-seven stars " due to Prof. 

 E. C. Pickering. 



Observers may with advantage give to the three images 

 of the same star on the chart plates such a linear interval' 

 that the three images of a star of the eleventh magnitude- 

 shall appear neatly separated. 



Observers may diminish the duration of the exposure 

 of each of the three images (on a chart plate) — from thirty 

 to twenty minutes, for example — if it is recognised that 

 the diminished exposure is sufficient to show the images 

 of stars of the fourteenth magnitude on .Argelander's 

 scale, prolonged. 



The attention of participating astronomers is directed' 

 to the advantages which might arise if the three exposures 

 on the chart plates were made on different nights, with 

 a moderate interval, of not more than several weeks in 

 all. It appears preferable, indeed, to complete the plate- 

 exposure on two nights only, with one exposure on the 

 first night and the other two exposures on the second 

 night. The advantages which would result from this plan 

 of working would, on the one hand, be to facilitate the 

 search for vari.able stars, and on the other the eventual' 

 discovery of a trans-Neptunian planet. 



From Commission C. 



.At least twice a year the equatorial adjustment of the 

 photographic telescopes should be tested. 



Special attention must be given to the centring of the 

 object-glass, and to the rendering of the surface of the 



' It wa5 understood that in this way the rejion of R.A. oh. should be 

 taken at sh. hour anele W., and on the same p'at» th» region of R.A. 6h. at 

 3h. hour nna1<- E. ii c. at approximately the same Z.D.), then R.A. jh.onlhe 

 same plate with R.A. jh. and >o on. 



