Since their first detection 15 years ago, radio recombination lines from several elements have been observed in a wide variety of objects including HII regions, planetary nebulae, molecular clouds, the diffuse interstellar medium, and recently, other galaxies. The observations span almost the entire range from 0.1 to 100 GHz, and employ both single djsh and aperture synthesis techniques. The theory of radio recombination lines has also advanced strongly, to the point where it is perhaps one of the best-understood in astro physics. In a parallel development, it has become possible over the last decade to study these same highly-excited atoms in the laboratory; this work provides further confirmation of the theoretical framework. However there has been continuing controversy over the astrophysical interpre tation of radio recombination line observations, especially regarding the role of stimulated emission. A workshop was held in Ottawa on 24-25 August, 1979, bringing together many of the active scientists to review the field and discuss these questions of interpretation. A broad concensus has emerged: the subtleties of the line-formation process are understood, and the conditions under which reliable in formation can easily be extracted from the line measurements are known. It thus appears likely that the emphasis will shift increasingly from the study of the line phenomenon itself to further application in other areas of astrophysics, ranging from physical processes in plasmas (temperatures, densities, ionization structure), to the large-scale properties of our galaxy (abundances, kinematics, structure), and studies of extragalactic systems."

This publication, in two volumes, includes most of the scientific papers presented at the first meeting of the International Society for the Study of the Origin of Life (ISSOL), held on June 25-28, 1973 in Barcelona, Spain. The first volume contains the invited articles and the second volume the contributed papers, which also appear in the 1974 and 1975 issues, respectively, of the new journal Origins of Life, published by D. Reidel. A relatively large number of meetings on the subject of the origin of life have been held in different places since 1957. In terms of its organization, scope, and number and nationality of participants, the Conference celebrated last year in Barcelona closely followed the three international conferences held earlier in Moscow, U.S.S.R., 1957, Wakulla Springs, U.S.A., 1963, and Pont-a-Mousson, France, 1970. For this reason the first ISSOL meeting was also named the Ath International Conference on the Origin of Life.

If you want to understand the invisible, look careful at the visible. The Talmud A 'bird's eye' or rather a distant spacecraft's view of the solar system reveals an assembly of planets, terrestrial, giant and Pluto. The orbital motions are in the same sense, counter clockwise, as seen from the north of the general flattened space within which the planetary motions are confined. This state of affairs is corevolving and, more or less, coplanar. The rotations are in the same sense as the revolutions, with the strikiiig exception of Uranus whose sense of rotation is perpendicular to its plane of revolution. As time goes by, most of the planets remain fairly close to a general plane and at no time stray unduly far from it; they remain confined within a rather narrow box or disk with a large 'equatorial' extent. The most distant planet, Pluto, requires a diameter of some 80 astronomical units for the disk. One astronomical unit is the distance of the Earth to the Sun, to be more precise the length of half the major axis of the Earth's slightly elliptical orbit around the Sun, and amounts to nearly 149600000 km.

This volume is the documentation of the second Course on 'Neutron Stars, Active Galactic Nuclei and Jets', held at Erice in September 1988. This second Course was devoted to our knowledge about neutron-star sources. The poster spoke of: pulsars, accreting X-ray sources and jet englnes, perhaps also UHE pulsars, X ra~' bursters and black-hole candidat.es. Neutron stars have even been proposed as the primary cosmic-ray boosters. Most of theil' properties are stil1 controversial, such as their birth mechanism (neutrino versus magnetic piston), internal structure (neutrons, quarks, strange particles), magnetic, thermal and spin histories, wind generation (hydrogen versus pair plasma, radiation versus centrifugal pressure), magnetospheric structure and accretion modes (along field lines versus quasi-Keplerian). The listed controversies have largely survived through the Course and entered into the proceedings. Several lecturers speak of 'magnetic-field decay' in neutron stars, of the 'recycling' of old pulsars, and of 'accretion-induced collapse' of white dwarfs as though such processes were textbook knowledge. Terms and abbreviations like RPSR (=recycled pulsar), spinup line, AIC, and ADC (=accretion disk corona) help to foster the assumptions. It is not clear to me at this time whether any of these notions has an application to reality.

It is hard to appreciate but nevertheless true that Michael John Seaton, known internationally for the enthusiasm and skill with which he pursues his research in atomic physics and astrophysics, will be sixty years old on the 16th of January 1983. To mark this occasion some of his colleagues and former students have prepared this volume. It contains articles that de scribe some of the topics that have attracted his attention since he first started his research work at University College London so many years ago. Seaton's association with University College London has now stretched over a period of some 37 years, first as an undergraduate student, then as a research student, and then, successively, as Assistant Lecturer, Lecturer, Reader, and Professor. Seaton arrived at University College London in 1946 to become an undergraduate in the Physics Department, having just left the Royal Air Force in which he had served as a navigator in the Pathfinder Force of Bomber Command. There are a number of stories of how his skill with instruments and the precision of his calcula tions, later to be so evident in his research, saved his crew from enemy action, and on one occasion, on a flight through the Alps, from a collision with Mount Blanc that at the time was shrouded in clouds."

Stellar mass loss is an essential part of the cycling of material from the interstellar medium into stars and back, and must be understood if we are to model processes on galactic to cosmological scales. The study of stellar winds and the effects of stellar mass loss has reached a particularly exciting stage where observational capabilities are increasingly able to provide interesting constraints on models and theories. Recent resu1ts from theoretical and observational work for both hot and cool stars with substantial winds have led to the suggestion that a combination of pulsation with other mechanisms makes for particularly efficient mass loss from stars. This provided the original motivation for the organization of this workshop. The conference was organized along relatively conventional lines according to the types of objects being scrutinized. However the true unity of the proceedings comes from the interplay of the mechanisms involved. For example, for the cool, luminous Mira variables, pulsation leads to shock waves that extend the atmosphere, enhancing dust formation; radiation pressure on dust drives the wind, cooling the atmosphere and in some cases suppressing the shocks. Similarly for the Be stars, both pulsation (in this case, non-radial) and radiation pressure (due to UV resonance lines) are expected to be important, and this expectation is at least qualitatively borne out by the observations.

Over the last decade we have witnessed a rapid change in our understanding of the late stages of stellar evolution. A major stimulus to this has been the synthesis of observational data from different wavebands of the electromagnetic spectrum. The advent of infrared astronomy has led to the discovery of many luminous. late-type stars obscured by their circumstellar dust envelope. Sources discovered in the IRC and AFGL infrared sky surveys were followed up by radio observa tions, leading to the widespread use of the OH and CO molecules as probes of the circumstellar envelopes. Advances in the technique of aperture synthesis have made possible observations with unprecedent resolving power, both in spectral-line and continuum. The success of the recent IRAS sky survey, with the detection of over 250,000 sources, brings the promise of even more exciting years ahead. This area of astronomical research is also blessed with the close collaboration between theorists and observers. New ideas are constantly being quantitatively tested by new data. Theoretical predictions are eagerly used as guides for further observations. This conference was initiated with the following objective: bring together workers in optical, infrared, radio and theoretical astronomy and let them confront each other. Based on the post-conference res ponses we received, many of the participants have indeed found this Workshop a stimulating experience. The Workshop on the Late Stages of Stellar Evolution was held from 2-5 June 1986 in Calgary, Canada."

My interest in the history of the Struve family is long-standing but lay dormant until 1972, when I found myself organizing a symposium of the International Astronomical Union in memory of the second Otto Struve. To satisfy my own curiosity, I investigated the precise relationships of the famous astronomers in the family and published an account of them, based mainly on secondary sources. The exercise made me a ware that there was no biography in English of the first and probably still the greatest astronomer in the clan - Friedrich Georg Wilhelm Struve. Wilhelm's son, the first Otto, wrote an account (in German) of his father's life, intended primarily for family and close friends and --though printed-- not generally available. Through the kindness of a family member I have a copy from which I have been able to work. The Soviet historian of science, Z. K. Sokolovskaya, wrote a biography in Russian, in 1964, to mark the centenary of Wilhelm's death. This had a limited edition, and my efforts to obtain a copy failed. Neither work has, in its entirety, been translated into English, although Michael Meo of Oakland, California, and Kevin Krisciunas of Hilo, Hawaii, have kindly made available to me their unpublished translations of some sections of the latter. In the of a complete copy, however, when I decided to attempt an English absence language biography, I thought it best to do so independently of Sokolovskaya's."

Scientists in the late twentieth century are not the first to view galaxy formation as a phenomenon worthy of explanation in terms of the known laws of physics. Already in 1754 Kant regarded the problem as essentially solved. In his Univerlal Natural Hutory and Theory 0/ the H eaven$ he wrote; "If in the immesurable space in which all the suns of the Milky Way have formed themselves, we assume a point around which, through some cause or other, the first formation of nature out of chaoo began, there the largest mass and a body of extraordinary attraction will have arisen which has thereby become capable of compelling all the systems in the process of being formed within an enormous sphere around it, to fall towards itself as their centre, and to build up a system around it on the great scale . . . . Observation puts this conjecture almost beyond doubt. " More than 200 years later, a similar note of confidence was voiced by Zel'dovicb at an IAU symposium held in Tallin in 1911; "Extrapolating . . . to the next symposium somewhere in the early eighties one can be pretty sure that the question of the formation of galaxies and clusters will be solved in the next few years. " Perhaps few astronomers today would share Kant's near certainty or feel that Zel'dovich's prophecy has been fulfilled, Many, however, will sympathize with the optimistic olltlook of these two statements.

Although there are, in addition to the classic but somewhat dated books'l-, some excellent recent books on ionospheric physics and aeronomy'l-..., their scope is quite different from that of the present monograph. This monograph concentrates on the fundamental physical and chemical processes in an idealized planetary ionosphere as a general abstraction, with actual planetary ionospheres representing special cases. Such an approach appears most appropriate for a concise in troduction to the field, at a time when increasing experimental in formation on the ionospheres of other planets can be anticipated. The main purpose of this monograph, in line with that of the whole series, is to appraise where we stand, what we know and what we still need to know. It is mainly addressed to graduate students and researchers who are in the process of getting acquainted with the field. Within the scope of this monograph it would be impossible to do justice to all relevant publications. Hence, references are somewhat selective and largely limited to the more recent original papers and to authoritative reviews, the latter generally providing also detailed references regarding the historical development of the particular topic. Cgs (gaussian) units are generally used in this book, except where practical units are more appropriate. This book has evolved from a graduate course of the same title which I gave at the Catholic University of America, Washington, D. C."

IAU Symposium Number 52 on Interstellar Dust and Related Topics was held at Albany, N.Y., on the campus of the State University of New York at Albany from May 29 to June 2, 1972. The members of the Organizing Committee were: Dr A. D. Code, University of Wisconsin, Madison, Wis., U.S.A. Dr B. D. Donn, Goddard Space Flight Center, Greenbelt, Md., U.S.A. Dr A. Elvius, Stockholm Observatory, Saltsjobaden, Sweden. Dr T. Gehrels, Lunar and Planetary Laboratory, University of Arizona, Tucson, Ariz., U.S.A. Dr J. M. Greenberg (Chairman), State University of New York at Albany, Albany, N.Y., U.S.A. Dr H. C. van de Hulst, Sterrewacht, Leiden, Holland. Dr S. B. Pikel'ner, Sternberg Astronomical Institute, Moscow, U.S.S.R. Dr E. E. Sal peter, Cornell University, Ithaca, N.Y., U.S.A. Dr B. E. Turner, National Radio Astronomy Observatory, Charlottesville, Va., U.S.A. The suggestion was first made in 1971 that a symposium on interstellar grains would be timely. The response to the first preliminary announcement, which was sent out on November 29, 1971, was well beyond our expectations. The meeting was locally sponsored by the State University and by Dudley Observatory. The National Aeronautics and Space Administration and the National Science Foundation con tributed along with the JAU. There were 158 participants of whom 49 were from 15 countries outside the United States. A total of 92 papers were presented.

Much has been said and written about the abilities of modern instrumentation to help solve problems of combustion in engines. In the main, however, the design and fabr ication of combustion chambers continues to be based on extrapolation of exper ience gained from use and rig tests, with little input from advanced techniques such as those based on optical diagnotics. At the same time, it has become increasingly difficult to design better combustion chambers without knowledge of the relevant flow processes. Thus, the future must involve improved understanding which, in turn, will require detailed measurements of velocity, temperature and concentration. The need to narrow the gap between current industrial practice and the acquisition and implementation of improved techniques motivated the organization of the Advanced Study Institute upon which this volume is based. This Institute on Instrumentation for Combustion and Flow in Engines was arranged to display the needs of industry and the possibilities made available by modern instrumentation and, at the same time, to make clear the relative advantages of optical and probe techniques. Held at Vimeiro during the period from 13 to 26 September, 1987, the Institute was attended by 120 participants and 16 invited lecturers.

The near Infra-Red emission of the Interstellar Medium is a very puzzling subject. In the brightest regions, where spectroscopic observa tions are possible from the ground, several bands (3.3 - 3.4 - 6.2 - 7.7 - 8.6 - 11.3 ~m) have been observed since 1973. The absence of satisfying explanation was so obvious that they were called "Unidenti fied IR Emission Bands". The puzzle still increased when were known the first results of the general IR sky survey made by the satellite IRAS. On a large scale, the near IR emission of the Interstellar medium was expected to be very small but it was observed to be about one third of the total IR emission for our own galaxy ..* The situation has moved in 1984 when it was suggested that a class of stable organic molecules, the Polycyclic Aromatic Hydrocarbons (PAH's) could be at the origin of this near IR emission. Initially based on the required refractory character of particules that should be heated to high temperature without subliming, this hypothesis leads to a sugges tive spectroscopic similarity with the observed astronomical bands. This hypothesis is attractive and it has many implications, for ins tance, the PAHs would be the most abundant organic molecules in the universe. However, many points have to be clarified and the different consequences of this suggestion should be explored.

Text no 1 Radio Recombination Lines (RRLs), discovered in the USSR in 1964, have become a powerful research tool for astronomers. Available throughout the radio spectrum, these lines carry information regarding the density, temperature, turbulence and velocity of thermal plasmas. Their very existance shows the presence of thermal gas. They also can carry information regarding magnetic fields if Zeeman splitting were to be detected. Containing the proceedings of an IAU Colloquium celebrating the 25th anniversary of their detection, this volume tells us what has happened since. It contains the story of the detection of RRLs and reviews of many areas of physics of the interstellargas from which stars form, HII regions excited by newly formed stars, planetary nebulae involving dying stars, and the structure of our Milky Way and other galaxies reflecting the large-scale morphology of the star formation process. In addition there is an article describing modern laboratory studies of Rydberg atoms to probe the basic physics of atomic structure, and articles describing the theory of collisions and radiation upon Rydberg atoms leading to observate effects to be used as diagnostic tools in astromony. This book focuses on the 25 years of astronomical research with radio recombination lines (RRLs) since their discovery in 1965. It covers a wide range of topics: papers dealing with research into Rydberg atoms both in the laboratory and in the interstellar medium of our galaxy and others; papers on the interaction of radiation and atomic systems, as well as with the effects of inadiabatic collisions between these atoms and both ions and electrons. It deals with astronomical observations of atoms with `diameters' ranging from 0.08 to 50 mum a size factor of 625. It deals with RRLs in absorption, in emission and as true masers. And it deals with plasmas with temperatures ranging from 10 to greater than 104 kelvins, and with an even greater range of volume densities. Much new work is reported, including low frequency RRLs discovered in 1980 and the maser RRLs from the star MWC349, discovered in 1989. The advent of aperture synthesis telescopes and large single-element telescopes have made possible RRL studies with high angular resolution. The sum total of the work reported here will make the volume a platform from which to search new horizons in RRL research.

SOHO, the Solar and Heliospheric Observatory, is a project of international cooperation between ESA and NASA to study the Sun, from its deep core to the outer corona, and the solar wind. To achieve its scientific goals it carries a complement of twelve sophisticated, state-of-the-art instruments. Three helioseismology instruments are expected to provide unique data for the study of the structure and dynamics of the solar interior, from the very deep core to the outermost layers of the convection zone. A set of five complementary remote sensing instruments, consisting of EUV and UV imagers, spectrographs and coronagraphs, will give us our first comprehensive view of the outer solar atmosphere and corona, leading to a better understanding of the enigmatic coronal heating and solar wind acceleration processes. Finally, three experiments will complement the remote sensing observations by making in-situ measurements of the composition and energy of the solar wind and charged energetic particles. This volume contains detailed descriptions of all the twelve instruments on board SOHO. Also included are an overview paper and a description of the SOHO ground system, science operations and data products. The aim of these papers is to make the broader scientific community, and in particular potential guest investigators, aware of the scientific objectives and capabilities of the SOHO payload and to provide a reference document for the various instruments.

The words of this preface were written when the book was ready to go to the press; and are limited to only a few points which are best made in this place. As is intimated by the sub-title, the whole volume was written with appli cations in mind to double-star astronomy. The latter is, however, not the only branch of our science which could benefit from its contents. The same is true of certain aspects of the dynamics of stellar systems or galaxies (the stellar popula tions of which are also characterized by the fact that the mean-free-path of their constituent stars are long in comparison with the dimensions of the respective systems); the central condensations of which are high enough to approximate the gravitational action of a "mass-point." This fact did not, to be sure, escape the attention of previous investigators (in the case of globular clusters, in particular, the Roche model was introduced in their studies under the guise of polytropic models characterized by the index n = 5); though no particular attention will be paid to these in this book. But possible applications of the Roche model are not limited to problems arising in stellar astrophysics. With Coulomb forces replacing gravitation, the equilibrium model finds a close analogy in the field of electrostatics-as was pointed out already at the beginning of this century by (then young) J. H. Jeans (cf."

As it was said by one of the participants to this workshop" In our attempts to understand the spectral evolution of galaxies, we are fortunate indeed to have the ability to look back in time and observe galaxies as they were billions of years ago. Perhaos in no other discipline is it possible to gain such a direct view to hJstory. The galaxies we seek to study are remote, their light faint, and thus only recently has it become technicaJlv feasible to sample the spectra of normal luminosity galaxies at lookback times of five billion years or more" .... or, perhaps. even to see galaxies in the process of their formation. or shortly afterwards. This fourth workshop organized by the "Advanced School ot Astronomy was indeed centered on the "Spectral Evolution of Galaxies." on reviewing and discussing the relevant astrophysical processes and on assessing our current ability to model and understand the evolution of stellar populations. Following an opening session dealing with some outstanding questions of galaxy evolution. Session I addressed the specific problems of galaxy and star formation processes. topics of uncertainty and controversy to which IRAS observations may give novel perspectives. The properties of stellar populations in the local group of galaxies formed the basis of Session II. Session III dealt with the fundaments of the theory of spectral and photometrical evolution of stellar populations. and with recent developments in the theory of stellar structure. a necessary step to model and understand galactic evolution.

In light of the barrage of popular books on physics and cosmology, one may question the need for another. Here, two books especially come to mind: Steven Weinberg's The First Three Minutes, written 12 years ago, and the recent best-seller ABriefHistory of Time by Stephen Hawking. The two books are complementary. Weinberg-Nobel prize winner/physicist-wrote from the standpoint of an elementary particle physicist with emphasis on the contents of the universe, whereas Hawking wrote more as a general relativist with emphasis on gravity and the geometry of the universe. Neither one, however, presented the complete story. Weinberg did not 13 venture back beyond the time when temperature was higher than 10 K and 32 perhaps as high as 10 K. He gave no explanation for the origin of particles and the singularity or source of the overwhelming radiation energy in our uni verse of one billion photons for each proton. Hawking presents a uni verse that has no boundaries, was not created, and will not be destroyed. The object of this book is to describe my new theory on the creation of our uni verse in a multi-universe cosmos. The new cosmological model eliminates the troublesome singularity-big bang theory and explains for the first time the origin of matter and the overwhelming electromagnetic radiation contained in the universe. My new theory also predicted the existence ofhigh-energy gamma rays, which were recendy detected in powerful bursts.

I. COSIIIC GAMMA RAYS AIm COSIIIC DUnmos L. Scarsi GAMMA RAY ASTRONOMY -- AN OVERVIEW OF THE GALACTIC DIFFUSE EMISSION: THE ORIGIN AND CONFINEMENT OF COSMIC RAyS ************ 1 P. L. Biermann PHOTON AND NEUTRINO-EMISSION FROM SHOCKWAVES IN ACTIVE GALACTIC NUCLE I ************************************************* 21 T. Stanev PRODUCTION OF ENERGETIC GAMMA-RAYS AND NEUTRINOS AT BINARY SySTEMS *********************************************** 3 9 F. W. Stecker COSMIC GAMMA-RAYS AND COSMIC-RAY NEUTRINOS FROM GALACTIC AND SOLAR DARK MATTER ANNIHILATION ****************************** 49 E. P. Liang GAMMA RAYS FROM CYGNUS X-I: NEW DIAGNOSTICS FOR A BLACK HOLE ******** 73 F. W. Stecker GAMMA-RAY ASTRONOMY AND THE HOLISTIC GALAXY ************************* 85 A. W. Wolfendale THE NEUTRINO SIGNAL FROM SNI987A *********************************** 12I A. E. Chudakov, Ya. S. Elensky and S. P. Mikheyev ON THE SPECTRUM OF NEUTRINOS FROM SNI987A ************************** 13I L. V. Volkova A COMMENT ON v Iv RATIO IN ATMOSPHERIC NEUTRINO FLUXES ************ 139 e 1I L. V. Volkova FLUXES OF MUONS AND NEUTRINOS GENERATED BY PRIMARY RADIATION IN THE MOON ****************************************** 141 viii P. I. Krastev and S. T. Petcov THREE-NEUTRINO OSCILLATIONS IN THE EARTH: RESONANCE AMPLIFICATION AND T-VIOLATION EFFECTS ************************** 145 A. E. Chudakov VHE AND UHE GAMMA RAY ASTRONOMY: HISTORY AND PROBLEMS ************** 163 G. B. Yodh ULTRA HIGH ENERGY ASTRONOMY **************************************** 183 A. E. Chudakov, G. Navarra and V. A. Tizengauzen ON THE 100 TeV UHE GAMMA-RAY DATA FROM CYGNUS X-3 AND HERCULES X-1 IN 1986 *************************************** 211 G. B.

This book on reference systems is the first comprehensive review of the problem of celestial and terrestrial reference systems and frames. Over 20 years, the importance of this problem emerged slowly as the accuracy of new observational techniques improved. The topic has already been approached in several symposia such as Stresa (1967), Morioka (1971), Perth (1973), Columbus (1975, 1978 and 1985), Kiev (1977) and San Fernando (1978). Two IAU colloquia held in Turin (1974) and in Warsaw (1980) were exclusively devoted to discuss reference systems. During this time, the problem of terrestrial and celestial reference systems has been discussed also in many astronomical and geodetic symposia, but always among other topics. Thus, a review devoted solely to the definition and practical realization of such systems was needed. It is hoped that this book, containing modern comprehensive reviews of important facets of this problem will contribute not only to a better and wider understanding of the mathematics and the physics that are behind the concepts and the realizations, but also to future development in a field that can only expand with the rapidly increasing accuracy of geodetic and astronomical observations. We are pleased to thank all the authors of the book who have enthusiastically agreed to contribute to the book in their field of competence and have gracefully accepted guidance from the editors in the definition of the subject and of the interfaces with other chapters. We thank Prof. Y.

Robert J. Rutten Sterrekundig Instituut Utrecht, The Netherlands Why this workshop? Why this workshop? Or rather, since the real question that arose about a year ago was not whether there should be another OAC workshop, but only what it should be about: why a workshop on granulation? To answer this question I will play an unfair trick on you. I will simply present the scientific justification which I included last autumn in a grant application to NATO's Scientific Affairs Division. It lists the reasons why I thought a workshop on this particular topic and at this particular moment ought to be worthwhile. There must be something in its reasoning, because NATO has indeed agreed to co-sponsor this workshop, and because all of you have decided to spend time and effort on your contributions and to journey to this beautiful island in order to participate. But since the proof is in the pudding, I am eager to see whether indeed this workshop will be as outstanding as I have promised; in the meantime, you are entitled to know what we got you here for. The justification went as follows: "The subject 'granulation' has recently become a hot topic, at the center of much new research, observational as well as interpretational and theoretical, and both in solar physics and in stellar physics.

A new approach to the teaching of quantum physics. The first seven chapters present nonrelativistic quantum mechanics and its interpretation, as well as perturbations and scattering theory. While including Dirac's and Feynman's formalisms, the chapter on symmetry also treats gauge transformations. The quantum theory of angular momentum includes the isospin of leptons and quarks and uses as a new tool the graphical spin algebra. The second part of the book is devoted to quantum fields: Boson fields including Higgs fields, Dirac's theory of Fermion fields, quantum electrodynamic and quantum chromodynamics. The whole is rounded off by a brief review guaranteed to raise the students' interests in quantum cosmology.
Readers will also find many detailed worked examples and numerous problems designed to test their own understanding.

In the development of Fundamental Physics on one side, and of Astronomy/Cosmology on the other side, periods of parallell, relatively independent progress seem to alternate with others of intense interaction and mutual influence. To this latter case belong the very beginnings of Modern Physics, with Galileo and Newton. There is now a widespread feeling that another of such flourishing periods may have started some ten years ago, with the advent of Unified Theories and the introduction of Inflationary Cosmologies. The interaction between the two disciplines has become tighter ever since, spurring studies of e. g. astronomical and particle Dark Matter candidates, Superstrings and Cosmic Strings, phase transitions in the Early Universe, etc. etc. Then the recent birth of Neutrino Astronomy has added further flavor to this splendid conjunction. It was indeed with the clear perception of this trend that six years ago CERN and ESO decided to jointly organize a series of symposia focusing on the interactions between Astronomy, Cosmology, and Fundamental Physics, to be held about every two years. The aim of these meetings is to bring together astronomers, cosmologists, and particle physicists to exchange information, to discuss scientific issues of common interest, and to take note of the latest devolopments in each discipline that are relevant to the other. The First ESO-CERN Symposium was held at CERN (Geneva) on November 21-25, 1983. Then for its Second edition the ESO-CERN Symposium moved to Garching bei Miinchen, where ESO headquarters are located, and took place on March 17-21, 1986.

Recent years have seen increasing evidence that the main epoch of galaxy formation in the universe may be directly accessible to observation. An gular fluctuations in the background relict radiation have been detected by various ground-based instruments as well as by the COBE satellite, and suggest that the epoch of galaxy formation was not so very early. Combined optical and radio studies have found galaxies at redshifts above 2. 0, systems that at least superficially show the characteristics expected of large galaxies seen only shortly after their formation. And absorption lines in the spectra of quasars seem to be telling us that most cold gas at early to intermediate cosmological epochs was in clouds having roughly galaxy sized masses. What kinds of new observations will best help us study this high redshift universe in future? What new instruments will be needed? These are questions that loom large in the minds of the Dutch astronom ical community as we celebrate 25 years of operation of the Westerbork Synthesis Radio Telescope. Celebration of this Silver Jubilee has included a birthday party (on 23 June, 1995), a commemorative volume looking at both the history and the future of the facility ("The Westerbork Observa tory, Continuing Adventure in Radio Astronomy," Kluwer 1996), and an international workshop, held in the village of Hoogeveen on 28-30 August, 1995.