It has become a tradition in the Union to publish the Invited Discourses and the Proceedings of the Joint Discussions held at a Gene ral Assembly in a separate volume entitled HIGHLIGHTS OF ASTRONOMY. This is the fourth volume of its kind and it contains some of the scientific highlights of the Grenoble General Assembly. In order to reduce its size it was decided to publish its content in two separate parts. The part (I) contains the full texts of the In vited Discourses given by Prof. J.-C. Pecker and by Dr. C. Sagan, and an abstract of Dr. P. Morrison's paper, thus complying with his wish to forego publication of the full text of his Discourse. Furthermore it collects the proceedings of three Joint Discussions and one Joint Meeting all of which are related essentially to observations from space, to external galaxies and to cosmology. Part (TI) contains the proceedings of the four Joint Discussions and one Joint Meeting related essentially to stars and the structure of our Galaxy. Clearly Volume 4 (parts I and TI) of the Highlights reflects only a part of the scientific activities which took place at the Grenoble General Assembly. Many more important papers and discussions were held during Commission meetings and joint meetings. They may be found in the Commissions' reports published in the Transactions Vol. XVI B, 1977."

The General Assemblies of the International Astronomical Union are landmarks in the life of the world-wide astronomical community, as they review, at triennial intervals, the progress made in this scientific field, promulgate the most spect acular astronomical achievements, formulate scientific programmes for the years to come and, last but not least, deal with the administration and finances of the IAU. The Reports on Astronomy 1976, published as Transactions XVIA (in 3 volumes) before the XVlth General Assembly, are a synopsis of the work done in astronomy from 1973 to 1975. The volume "Highlights of Astronomy, as presented at the XVlth General As sembly of the IAU in Grenoble, 1976" includes some selected scientific topics, and will appear in the first half of 1977. Apart from the Invited Discourses and the Proceedings of the seven Joint Discussions, the Highlights volume No.4 con tairsthe proceedings of two Joint Commissions Meetings."

The Symposium on "The Mechanics of Sound Generation in FLows" th st was held in Gottingen, Germany, 28 - 31 August 1979, at the joint initiative of the International Union of Theoretical and Applied Mechanics (IUTAM), the International Commission on Acoustics (ICA) and the American Institute of Aeronautics and Astronautics (AIAA). From the whole field of flow-acoustics the Symposium concen trated on prob lems of sound generation, while sound propagation and the creation of flows by sound were left in the ba- ground. 82 delegates from 12 countries attended the Symposium. 38 papers were given 5 of which were invited general lectures. Emphasis was placed on discussion, a plenary discussion closing the sym- sium. A s care had been taken to invite as many active workers in the field as possible with their most recent results the Symposium provided a momentary overview of the current state of the ra pidly developing field of flow-acoustics. Participants appreciated the meeting as a possibility to inform themselves, to discuss their own results and to obtain incentives for future efforts."

It has become a tradition in the Union to publish the Invited Discourses and the Proceedings of the Joint Discussions held at a Gene ral Assembly in a separate volume entitled HIGHLIGHTS OF ASTRONOMY. This is the fourth volume of its kind and it contains some of the scientific highlights of the Grenoble General Assembly. In order to reduce its size it was decided to publish its content in two separate parts. The part (I) contains the full texts of the In vited Discourses given by Prof. J.-C. Pecker and by Dr. C. Sagan, and an abstract of Dr. P. Morrison's paper, thus complying with his wish to forego publication of the full text of his Discourse. Furthermore it collects the proceedings of three Joint Discussions and one Joint Meeting all of which are related essentially to observations from space, to external galaxies and to cosmology. Part (TI) contains the proceedings of the four Joint Discussions and one Joint Meeting related essentially to stars and the structure of our Galaxy. Clearly Volume 4 (parts I and TI) of the Highlights reflects only a part of the scientific activities which took place at the Grenoble General Assembly. Many more important papers and discussions were held during Commission meetings and joint meetings. They may be found in the Commissions' reports published in the Transactions Vol. XVI B, 1977."

It has become a tradition in the Union to publish the Invited Discourses and the Proceedings of the Joint Discussions held at a Gene ral Assembly in a separate volume entitled HIGHLIGHTS OF ASTRONOMY. This is the fourth volume of its kind and it contains some of the scientific highlights of the Grenoble General Assembly. In order to reduce its size it was decided to publish its content in two separate parts. The part (I) contains the full texts of the In vited Discourses given by Prof. J.-C. Pecker and by Dr. C. Sagan, and an abstract of Dr. P. Morrison's paper, thus complying with his wish to forego publication of the full text of his Discourse. Furthermore it collects the proceedings of three Joint Discussions and one Joint Meeting all of which are related essentially to observations from space, to external galaxies and to cosmology. Part (n) contains the proceedings of the four Joint Discussions and one Joint Meeting related essentially to stars and the structure of our Galaxy. Clearly Volume 4 (parts I and TI) of the Highlights reflects only a part of the scientific activities which took place at the Grenoble General Assembly. Many more important papers and discussions were held during Commission meetings and joint meetings. They may be found in the Commissions' reports published in the Transactions Vol. XVI B, 1977."