In November 1934 the President circulated a letter to the members of the Commission as follows:

Since the 1932 meeting the following projects have been completed, or are nearing completion:

1. (1) The publication of many lists of trigonometric parallaxes.

2. (2) The determination of the spectroscopic parallaxes of 4179 stars at Mt Wilson Observatory by Adams, Joy and Humason.

3. (3) A discussion of systematic errors of trigonometric parallaxes by van Maanen and a re-discussion in the Astrophysical Journal of the same material by Mitchell and by Sterne.

4. (4) The compilation of a second Yale Catalogue to include parallaxes completed before the end of 1934.

5. (5) Substantial progress on the proper motions of 32,000 stars by Boss and his associates at the Dudley Observatory.

6. (6) The publication at the Radcliffe Observatory of the proper motions of 32,000 stars from photographs on 115 Selected Areas.

7. (7) The completion of the dynamical parallaxes of 2000 stars.

8. (8) The completion of the proper motions of 18,000 stars derived from parallax plates at the Leander McCormick Observatory.

9. (9) The publication at the Yale Observatory of the proper motions of 40,000 stars with a probable error less than 0”.010 determined from photographs by re-observing in zones the Astronomische Gesellschaft stars.

10. (10) The determination of the proper motions of 50,000 stars in the Southern Hemisphere by Luyten from Harvard photographs.

The following summarizes the activities of various members of the Commission in matters pertaining to stellar photometry during the interval 1932-35:

La partie photométrique des trois derniers volumes du Catalogue Astrographique (zone de Catane entre +46° et +55°) est soigneusement dressée sur le système de Miss Leavitt (Harv. Annals, 81). L’erreur moyenne des grandeurs, d’après la réduction de 100 plaques (zones +51° à + 54°, entre 6h et I2h), n’est que de ± om.o8. Nos réductions photométriques ont été effectuées par la formule

D = a-bg+cg2-dg3,

où D dénote le diamètre de l’image photographique et G=8m+g dénote la grandeur de l’étoile.

As double stars too close for photography must be discovered, before they can be observed, it is only natural to start a report about the progress made in double star astronomy during the last 3 years by mentioning the work done by Dr R. A. Rossiter with the Lamont 27-inch refractor at Bloemfontein. The first results have been published in a Ust numbering 2234 new pairs. Approximate positions are given, but as yet no measures are reported. These pairs are distributed as follows between different Umits of distance. For comparison the corresponding numbers for the 1900 discoveries, previously made by Dr W. H. van den Bos, are added.

It is well-nigh impossible to give, in a short report, an adequate idea of the enormous activity in Variable-Star Astronomy during the past three years. Without attempting to be complete I shall give a summary of the most important recent occurrences in this field of research.

Statistical data for eclipsing binaries were given by Gaposchkin (Veröff. Berlin-Bab. 9, Heft 5), for long-period variable stars by Ludendorff (Sitz.-ber. Ak. d. Wiss. Berlin, 1932), Thomas (Veröff. Berlin-Bab. 9, Heft 4) and Sterne and L. Campbell (Harvard Annals).

Some valuable catalogues have been issued: a Finding List for Observers of Eclipsing Variables by Dugan (Princeton Contr. No. 15), a Catalogue of Eclipsing Variables, together with a Program of Investigations, by Martinoff (Engelhardt Obs. Bull. No. 2), a Catalogue and Ephemeris of Short-period Cepheids by Zessewitsch (Len. Un. A. 0. Bull. No. 3).

1. Since the field covered by Commission No. 28 extends over the problems of three very different types of objects—external galaxies, galactic nebulae, and star clusters—it has been proposed occasionally that the Commission might well be subdivided, or possibly eventually split into three separate Commissions. As Trumpler points out, these three fields “have often been grouped together...more on a historical basis than on an actual similarity of the researches... which are more and more drifting apart.” But some members of the Commission have noted that a distinct difference also separates globular clusters and galactic clusters; and that planetary nebulae and dark absorbing clouds involve at times widely different types of investigations. The chairman of the Commission has made a canvass of the opinions of the members and finds that a large majority believe that no division or subdivision is advisable at this time. It is suggested that the organization or reorganization of a Commission should be left to the Union as a whole or to the Executive Committee.

There has been a marked change in the past few years in the incidence of interest in stellar spectra. The great initial task of classification has attained its first objective—though the Henry Draper Extension, and other investigations are still progressing. Perhaps a million stars are still accessible to classification with existing instruments; but more and more time is being spent upon individual spectra, and upon theoretical investigations. In these fields progress has been very rapid, and only some of the more important results may be mentioned here.

The three years that have elapsed since the Harvard meeting of the Union have witnessed steady progress in the determination of radial velocities. While the three large Pacific Coast Observatories have naturally been able to make the greatest additions to radial velocity work, the Yerkes Observatory, the Simeiz Observatory and the Observatory of the University of Michigan have also made valuable contributions. It is a pleasure to report that there will soon be three major accessions to the list of observatories capable of determining radial velocities. The David Dunlap Observatory of the University of Toronto with its 74-inch telescope, which should be in operation soon after the meeting, will have radial velocities as a prominent feature of its programme. The McDonald Observatory of the University of Texas with an 80-inch telescope now under construction should be ready to commence operations in 1936 and will undertake an extensive radial velocity programme. The Radcliffe Observatory at Oxford has now been granted permission by the Courts to remove to Pretoria, South Africa, and will establish there a 74-inch reflecting telescope, which will also be largely employed in the determination of the urgently needed radial velocities of the southern stars fainter than 5.5 visual magnitude. The Commission may, I believe, congratulate itself that substantial assistance in the preliminary steps leading to this permission of removal was provided by our action at the last meeting in presenting a resolution to the Union, duly passed by the General Assembly, pointing out the urgent need for additional radial velocities in the southern sky, and strongly supporting the project of the Radcliffe Observatory to establish a large telescope at Pretoria.

Depuis la dernière réunion, notre commission s’est transformée en une commission internationale mixte dépendant à la fois de l’Union astronomique et de l’Union géodésique et géophysique internationales.

On se rappelle que l’Assemblée générale, réunie à Leiden, a émis le vœu que le Président de l’U.A.I. s’entretienne avec le Président de l’Union de Géodésie et de Géophysique et le prie d’examiner s’il serait possible que celle-ci apporte quelque contribution aux dépenses du Bureau international de l’Heure. Comme suite à ce vœu, l’Assemblée générale de cette dernière Union, réunie à Lisboa en 1933, a adopté la résolution suivante:

“L’Union géodésique et géophysique internationale décide qu’une subvention régulière annuelle sera allouée par elle au Bureau international de l’Heure, dans les limites de ses crédits et des besoins du Bureau.

The Plan of Selected Areas was suggested by the late Prof. J. C Kapteyn in 1906. The aim of the plan is to bring together, as far as possible, all the elements which seem most necessary for a successful attack on the problem of the structure of the sidereal world. The first, second and third reports on the progress of the plan were published by the Kapteyn Laboratory in 1909, 1910 and 1923 respectively, the fourth report appeared in Bulletin of the Astronomical Institutes of the Netherlands, No. 211, 1930. Many observatories and astronomers have co-operated on the plan and for the northern hemisphere most of the work has been finished or is now in progress.

In the wide field of research covered by the Commission considerable progress has been made in recent years, and it is only possible here to touch briefly on the results of a few lines of investigation, without any attempt to completeness.

Stellar luminosities. On the basis of the new list of Mount Wilson spectroscopic parallaxes and a compilation of the long series of modern trigonometric parallaxes A. van Maanen finds 617 objects within a distance of 20 parsecs from the sun. It is very doubtful, however, if we know all the stars even in the region of 5 parsecs radius. Almost all the known stars within 20 parsecs belong to the main sequence, the faintest star being of absolute magnitude +16.6. The most interesting deviations from the main sequence are the three “white dwarfs”, Сотр. of Sirius, Comp. o2 Eridani, and van Maanen’s F type star. G. P. Kuiper lists 3 additional white dwarfs at larger distances which were estimated to be of types Bo, B7 and A2. For the first two stars, A.C. 70°8247 and Wolf 1346, a revision of the spectral types by Adams and Humason gives A2 and A5, respectively, although the spectra differ considerably from normal ones. The A2 star in Kuiper’s list is the one discovered by Oosterhoff in the region of the cluster h, X Persei; its spectral characteristics have been examined by Öhman and by Humason. The absence of the high-numbered members of the Bahner series and of the continuous absorption at the Balmer limit seems to be an important criterion of such stars. A white dwarf of quite peculiar spectrum (type probably about B8) is the companion of o Ceti discovered spectro-graphically by Joy in 1922. There appear several additional deviations towards faint magnitudes from the main sequence which may be classed more or less safely among the white dwarfs. A few such cases have been discussed at Lund by J. Tuominen.

Much progress has been made since the last meeting of the Union in the measurement and reduction of photographic plates and in the reduction of micrometric observations obtained near the opposition of Eros, 1930-31. The reduction of photographs and measures which are dependent upon positions of secondary comparison stars have had necessarily to be postponed until the positions of these ‘stars are available. In this report, the present position of the investigations is summarized.

1. Reference Stars, (a) Primary. The positions of these stars, based on meridian observations at several observatories, were published by A. Kopff, H. Nowacki and F. Gondolatsch in Ast. Nach. 241, Nos. 5781-2 and 244, Nos. 5852-3. The reduction of series of path plates, taken for the purpose of providing positions of secondary reference stars, and of series of Eros plates obtained with telescopes of astrographic focal length have shown that the positions of some of these stars are considerably in error. As is to be expected in view of their smaller average weight, the largest discordances are in the positions of some of the southern stars.

The Commission has found no opportunity for acting collectively during the last three years. The study of the constitution of the stars has been advanced by individual contributions, which it would be impracticable and undesirable to guide officially.

Whilst much useful work has been done, it would be difficult to point to any outstanding development in the study of the interior of the stars during this period. But there is a prospect of great advances in the near future. From 1932 onwards experimental physicists in all countries have been largely occupied with the phenomena of transmutation of the elements, and it is clearly possible to determine in the laboratory most of the quantitative data as to the rate of the subatomic processes (especially those due to the encounters of protons and electrons with nuclei) and the consequent liberation of energy, for which astronomers have long been waiting.

The present report is the first for which this newly-formed Commission has been responsible. In view of this fact, and in view of the still exploratory nature of many investigations in spectrophotometry, as well as the need for the highest measure of individuality in the attack of the not simple problems involved, it would be premature to propose, simple though it might be to do so, any far reaching plans for co-operative schemes of investigation. These undoubtedly will play a part in the later work of the Commission, but what appears to be needed now is a closer definition of the aims of spectrophotometry, and at least a reference to the many branches of the subject where investigation is needed. The present report attempts to deal with these topics in three successive sections, concerned in turn with the unique property of spectrophotometric measures, the fields of application of spectrophotometry, and recent developments in a still incomplete and difficult technique.

The President submitted to the Meeting, with some diffidence, the preliminary set of notations covering the whole field of astronomy, which he had prepared, and which had been printed in the Draft Report. It was, he said, a compromise between different systems of notations. He pointed to some misprints in the Draft Report and invited discussion.

Prof. Stroobant expressed his pleasure that the President had retained a number of the notations which he had presented at the Rome Meeting. While rendering homage to the completeness of the new scheme, he said that it had been submitted at too short a notice to allow a thorough discussion. He therefore proposed, at all events, to postpone a final decision.

Prof. Eddington and Prof. Russell agreed to this view, but emphasized the necessity of the new scheme being printed. They suggested some slight changes in a few of the proposed notations.

A meeting with Commission 8 (Dr Jackson in the chair) was held to discuss two questions:

1. (a) Which stars are to be used in future as fundamental stars?

2. (b) What positions are to be used for these stars?

The two systems available are the General Catalogue of Boss, with about 32,000 stars, and the FK3 of the Astronomisches Rechen-Institut, containing, with a supplement to be completed, 1535 stars.

At its meeting the Commission adopted the cipher code for astronomical telegrams, proposed by the President, with two minor alterations, and agreed that the new code was to be used from 1935 Nov. 1. The corrected cipher code is given below in this volume (p. 391).

The Commission also asked for an annual grant of 1200 Swiss francs to the Bureau of Astronomical Telegrams until the next meeting of the Union.

(A joint discussion with Commission 20 is reported by the latter Commission. p. 309.)

M. Stroobant estime que les questions soulevées à ce sujet par MM. Dittrich, Brasch et Pogo sont du ressort de la Commission 2; cette Commission devant les difficultés matérielles que présentait pareille entreprise sous les auspices de l’U.A.I. a cessé son activité au Congrès de Rome (1922).

M. Lundmark estime que la question est importante, qu’il convient que l’U.A.I. s’y intéresse et que la Commission s’en occupe.

M. Collinder considère, d’expérience personnelle, que parfois, tout au moins en ce qui concerne certains ouvrages anciens importants au point de vue historique, une publication partielle serait suffisante.