Isophote shape and flattening are being used for studying a similarity between elliptical and lenticular galaxies.

The association of Hα flares with photospheric magnetic field patterns is reviewed on the basis of empirical evidence. The insertion of flares in the H∥ and H⊥ patterns is described. Present data on the evolution of magnetic structures in connection with flares suggest that flares result from special trends in this evolution leading to stressed and/or ‘misconnected’ fields. However no sudden changes with a flare-like time scale have been definitely observed in photospheric fields.

By action of the Executive Committee of IAU, the report for 1970 is restricted to half the length of the 1967 draft report; the bibliography and the abstracting of work already published are essentially eliminated. The report is no longer to serve primarily as a review of accomplishments between General Assemblies but rather as a report of work in progress. These changes were adopted by the Executive Committee in order to reduce the cost of publishing the reports.

Several commission members have voiced the opinion that the extensive bibliographies in past reports have been the most valuable contributions of the reports and they have objected to the elimination of the bibliography. Also, material from some observatories and from some national groups that have been submitted for inclusion in this draft report have contained only abstracts of work already published. The rules adopted by the Executive Committee do not permit the report to abstract published works except in evaluating general progress in solar astronomy. We express our regret to these commission members and to these institutions that we have not been able to include the abstracts and bibliography in the present report.

The reader is kindly asked to consider this report for some sort of greatly unbalanced equilibrium between the pressure exercised by the steadily increasing flow of papers discussing the vastly extending subject of solar activity, and the equally steady pressure exercised by the editor who insists on having this report twice as short as three years ago. Therefore, some selection of the subjects and papers had to be made, a fairly severe one, since only about one third of all published papers could have been mentioned in the references, and I am well aware that almost everyone who will read the report, could suggest some improvement of the selection scheme. Nevertheless, I believe that the report as it stands, can fulfill its basic purpose, i.e. to give to the readers a general picture on the progress, which has been achieved in the field of solar activity research since the Prague meeting and on some of the research activities which are in progress at the present time.

It is a great pleasure to acknowledge the enormous help I have received from the authors of the individual sections of the Draft Report, as well as from many other members of the Commission, who have very kindly provided me, or the co-authors, with useful information on the recent progress of their work. It is necessary to add that some highly valuable comments made by V. Bumba, J. T. Jefferies, C. Sawyer, E. v. P. Smith, B. Valníček and J. M. Wilcox, have also been included in other chapters than those prepared by themselves.

The slowly varying component of solar X-rays has been studied through records of the satellite Explorer-30 instrumented by the U.S. Naval Research Laboratory. Correlations with plage areas, and flux at radiofrequencies have been studied. High flux values in the 8–20 Å and, still more, the 1–8 Å bands are related to specific ARs, also characterized by great flare productivity, high intensities on 3 cm, and anomalous magnetic structure.

From the material gathered during the ‘Cooperative Study of Solar Active Regions’, we studied the flare locations in AR magnetic structure, and flare relations to changes in the magnetic fields and spot configurations. Besides a confirmation of previous results, we find that flares are often associated with two features of the spot configuration evolving in opposite senses, one growing, the other declining.

The ‘Cooperative Study of Solar Active Regions’ (or CSSAR) originated from a suggestion of E. R. Mustel at the IQSY General Assembly in Rome, 1963. Later on it was also endorsed by IAU Commission 10, and a special Working Group of this Commission, under chairmanship of the writer, had the duty to organize this project, an experiment in both solar physics and international cooperation.

The discovery of oscillatory motion in the solar photosphere and of the ‘super-granulation’ in the chromosphere has changed our ideas about the hydrodynamics of the solar atmosphere considerably. In this Joint Discussion we shall mainly consider the theoretical implications of this change. As the ultimate aim is an understanding of the hydrodynamics in all stellar atmospheres—not only in the Sun, some discussion of other stellar atmospheres will be included.