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The subjects of resonance and stability are closely related to the problem of evolution of the solar system. It is a physically involving problem and the methods available to mathematics today seem unsatisfactory to produce pure non linear ways of attack. The linearization process in both subjects is clearly of doubtful significance, so that, even if very restrictive, numerical solutions are still the best and more valuable sources of informations. It is quite possible that we know now very little more of the entire problem that was known to Poincare, with the advantage that we can now compute much faster and with much more precision. We feel that the papers collected in this Symposium have contributed a step forward to the comprehension of Resonance, Periodic Orbits and Stability. In a field like this, it would be a surprise if one had gone a long way toward that comprehension, during the short time of two weeks. But we are sure that the joint efforts of all the scientists involved has produced and will produce a measurable acceleration in the process. If this is true it will be a great satisfaction to us that this has happened in Brasil. The Southern Hemisphere in America has now begun to participate actively in the Astro nomical Society and for this, we are grateful to everyone who has helped.
This volume contains the fifteenth tri-annual reports of the Presidents of the forty Commissions of the International Astronomical Union; it refers to the progress in our discipline during the three years 1970, 1971 and 1972. As compared to earlier volumes a gradual change in character is unmistakable. The ever increasing flow of publications, combined with the obvious necessity to keep the Reports at a reasonable size and price level has gradually forced the Commission Presidents to be more selective than before in drafting their Reports. I have certainly stimulated them into that direction - in order that Reports like these be valuable and lasting, it seems imperative that the individual contributions have the character of a critical overall review, where a fairly complete summary is given of the major develop ments and discoveries of the past three years, and in which the broad developments and new trends be clearly outlined, while at the same time essential problems for future research are identified. With respect to the latter item I have suggested the Commission Presidents to add to their reports a brief section on scientific priorities for future research in the field of their Commissions. In order to save space I have suggested to Commission Presidents that references to published papers are given on the basis of their number in the published issues of Astronomy and Astrophysics Abstracts. For instance, the indication (06. 078. 019) or (AAA 06. 078.
During the last twenty-five years or so, studies in Thomistic existentialism have repeatedly indicated that the notion of creation played a decisive role in St. Thomas Aquinas' view of existence as an existential act or actus es sendi. The importance for metaphysics of this view of existence as act war rants an investigation of the relation between creation and actus essendi; for St. Thomas is the only one, in the history of philosophy, to have con sidered existence as an act-of-being. This study will be limited to the early works of St. Thomas. By the time of the Summa Contra Gentiles, he had reached the key positions of his metaphysics. And the first fifty-three chap ters of the Summa Contra Gentiles were written in Paris before June, 1259; 1 the rest was completed in Italy before 1265. The project was therefore con ceived by St. Thomas during the first period of his career. How the notion of creation enabled him to transform the Aristotelian metaphysics of essence into a metaphysics of esse can be seen from three sections of the Summa Contra Gentiles. Although primarily a theological treatise, the Contra Gentiles never theless accomplishes a radical metaphysical transformation of Aristotelian ism by shifting the whole perspective from esse in actu per formam to actus essendi. Seen from the perspective of existential act as the absolute perfec tion, metaphysics is raised to a strictly transcendental plane of consideration.
The XIIlth General Assembly of the International Astronomical Union, held in Prague from 22 to 31 August, 1967, brought together more than 1800 active astron omers from 40 countries. The agenda of the Assembly ranged from administrative questions to highly intricate scientific problems. Thirty-eight Presidents of the IAU Commissions contributed by their reports to a detailed survey of Astronomy for the period 1964-67. These reports were published in the Transactions of the IAU, Volume XIIIA. Transactions volume XIIIB bring the results of the administrative meetings and of the meetings of Commissions held during the General Assembly. The present volume is devoted to the most important scientific results of the General Assembly as presented in the Invited Discourses, Joint Discussions, and at Special Meetings. It is an established policy of the Union to invite prominent astronomers to hold, during the General Assembly, formal discourses on topics of major importance due to recent significant developments. These Invited Discourses cover, as a rule, broad fields of astronomical interest and are meant to give basic information also to scien tists from other branches. Subjects which call for a more detailed technical approach are dealt with in the Joint Discussions or at Special Meetings. Here, invited speakers present authoritative surveys complemented by communications on current or envisaged projects. The proceedings of two other meetings, on Moon Probes and on Coordination of Solar Observations Made at Ground-based Observatories and with Space Vehicles, are of a sufficiently wide interest to warrant the inclusion into this volume.