L’œuvre entreprise il y a cinquante ans par l’ancien Comité Permanent de la Carte du Ciel n’a pas été intégralement accomplie. Si certaines de ses parties peuvent être considérées comme terminées, d’autres ont été perdues de vue ou abandonnées.

La tâche de la Commission de la Carte du Ciel doit être maintenant d’examiner, à la lueur de cinquante années de progrès scientifiques, et en tenant compte du travail déjà fait, quelles sont celles des anciennes recommandations du Comité Permanent dont il y a lieu de poursuivre l’exécution.

Since the Paris meeting of the Union 3050 parallax plates have been secured and in the same interval 5604 plates have been measured and 182 parallaxes have been determined.

The committee of the Carte du Ciel in 1910 adopted the following convention : That for Ao stars between magnitudes 5·5 and 6·5 the mean photographic magnitude should equal the mean Harvard visual magnitude. As a corollary, the colour index of Ao stars would then be zero.

The zero point of the photographic magnitudes of the International Polar Sequence was fixed as nearly as possible in accordance with this definition; but it was by no means certain that the magnitudes thus adopted for the few stars of the Sequence represented the zero point defined by all the Ao stars specified.

The discovery of southern double stars carried out at Bloemfontein by Dr R. A. Rossiter and his collaborators with the 27-inch Lamont refractor has recently been brought to a close. The total number of new pairs found in this way and published now amounts to 5252. It is a great satisfaction to know that Dr Rossiter has been enabled to complete his work by micrometrical measures of these objects. Only in this way can full value be given to our knowledge of these new pairs.

The Commission again subscribes to a number of the good resolutions it has made in the past, for example, to follow the almost universal practice of counting the observed times, either in decimals of a day or in hours and minutes, from Greenwich mean noon, even though one is convinced that the rest of the world should adopt U.T.; and to prepare a chart, identifying the variable and the comparison stars, to form a part of the discovery announcement of a variable which cannot be easily identified through a Durchmusterung number and which is bright enough to invite further observation.

During the past three years observational and theoretical work has been uncommonly extensive and fruitful in two of the fields within the interests of Commission 28—namely, the distribution of external galaxies and the analysis of diffuse nebulosity, the latter including interstellar absorbing material. Important work is also under way at a number of observatories in the interpretation of planetary nebulae. Studies of clusters, however, have been limited to a few active workers, and progress has not been rapid in the analysis of individual galaxies.

Two-thirds of the members of the Commission have replied to the request of the chairman for an expression of their opinion. Most of them are in general well satisfied with the existing system of classification and nomenclature. Lindblad reports on successful work upon the determination of absolute magnitudes of faint stars, in many ways. Adams writes: “I might suggest that attention be called in the report to the fact that the ultra-violet spectra, even of stars like β Orionis, show large numbers of lines. As you probably remember, the spectrum of Sirius resembles, at first sight, the solar spectrum. If all observatories had the facilities for getting spectra in the far ultra-violet, this region would probably furnish the best criteria for spectral type.” Merrill suggests: “The nomenclature which, upon the basis of atomic transition, assigns the adjective ‘nebular’ to lines which may not occur in nebulae, and ‘ auroral ‘ to lines which may not occur in the aurora, is surely not an ideal one.

During the past three years the measurement of stellar radial velocities has formed an important part of the spectroscopic programme of most observatories possessing large telescopes. As observations are carried to fainter and fainter stars and the number of observable objects increases rapidly, a natural development has been the selection of special groups and types of stars, the radial velocities of which will aid in the solution of certain specific problems. Illustrations are the studies of the O, B and A type stars made at the Dominion Astrophysical, the Lick, and the Simeis Observatories, of the members of the galactic clusters at the Lick Observatory, and of the fainter Cepheid variables and early-type stars with strong interstellar lines at the Mount Wilson Observatory.

Durant la période de 1933 à 1936 le Bulletin Horaire a donné les heures définitives des signaux horaires d’après la moyenne de 15 observatoires. A partir du Ier janvier 1937 on introduit trois observatoires en plus (Kharkov, Manille et Tokyo), qui communiquent régulièrement leurs résultats au B.I.H.

Au Bureau International de l’Heure certains perfectionnements sont actuelle ment en voie de réalisation. Il s’agit d’une horloge à diapason d’une part, et, de l’autre, d’un ensemble nouveau pour l’émission des signaux horaires. M. Lambert va donner une communication sur ce sujet.

The following lines give a summary of the work concerning Kapteyn’s Plan of Selected Areas up to December 1937.

The following report, which has been drawn up partly on the basis of the reports of the members of the Commission, touches briefly and without any attempt at completeness a few points of the recent developments in certain important fields falling within the domain of the Commission.

The Commission has found no opportunity of acting collectively in the last triennial period. Progress in the theoretical study of the constitution of the stars must be mainly a matter of individual effort; and it would be impracticable and undesirable to seek uniformity of views and methods.

A brief reference may here be made to some of the problems now especially engaging attention. In this connection I would call attention to a valuable Report on “Die Theorie des Sterninnern und die Entwicklung der Sterne” (Ergebnisse der exakten Naturwissenschaften, Bd. XVI, 1937) by a member of the Commission, B. Strömgren, which deals especially with progress in the last ten years, and shows very clearly the present state of the subject.

At the first meeting of the newly formed Commission on Spectrophotometry, at Paris in 1935, a thorough discussion, aided by several reports, took place on the principles of this branch of astrophysics. So it will be sufficient now to treat only such special points of theory and practice as have won interest by researches of the last few years.