Search

The dynamical system of the planets and satellites shows many regularities that appear to have arisen during the evolution of the system. The study of some of the subsystems suggests that tidal friction has played an important role in bringing them into states in which the direct gravitational perturbations have become sufficiently strong to maintain the regular relationships between the orbits. In other cases it appears to be necessary to invoke the action of collision processes in order to find a satisfactory explanation of the observed regularities. Many of the subsystems are compatible with Ovenden's principle of least interaction action, but it is by no means clear that this principle can be satisfactorily applied to the planetary system as a whole. 1. INTRODUCTORY REMARKS Saturn was the outermost planet known to Copernicus, but today we realize that there are three major planets beyond - Uranus and Neptune are slightly smaller, but otherwise probably similar in physical constitution to Jupiter and Saturn, while Pluto is an enigmatic object, probably only half the size of the Earth. Copernicus was also unaware of the existence of the satellite system of Jupiter; its discovery by Galileo in I6Io was made possible by the invention of the telescope and its existence was then used as circumstantial evidence in favour of the Copernican theory. Since then the number of known natural satellites, apart from our own Moon, has increased from 4 to 31. In addition, there are large numbers of minor planets, or asteroids, that move mainly in the region between the orbits of Mars and Jupiter. The orbits of about 1700 of these are known sufficiently well to justify their being given individual names and observed from time to time to update the orbital data. Many of these satellites and asteroids are so small and faint that we know very little about their physical properties, but the study of their orbits provides us with many interesting problems, as well as clues about their origins. It is our intention in this review paper to draw attention to some of the interesting features of this complex dynamical system and to discuss some of the hypotheses that have been put forward to account for the origin and evolution of the system that we now observe. This paper is based on material intended for oral presentation to a non-specialist audience; it is therefore completely free of mathematics, and uses only a very limited amount of specialist terminology, even t This paper is based on the lecture given by G. A. Wilkins at the Copernicus Quincentenary Symposium on Planetary Science held on 25 January 1973, but it differs from it in several respects. In particular, most of the diagrams and tables that were shown for illustrative purposes have been omitted, while some additional historical and technical details have been included.

This lecture, delivered on 8th November 1962 to the Club der Luftfahrt in Bonn, is an account of blind landing prepared with the aim of interesting a non-specialist audience in this and other British developments.

Published in 1931 to complement Seward's magisterial four-volume textbook Fossil Plants, this book is a digest of his earlier detailed study, written for a non-specialist audience as an introduction to the field of palaeobotany. Seward begins by describing the basics of geology and palaeobotany in order to explain how the interpretation of fossilised plant remains found in rocks can shed light on the natural world of prehistoric times. He then covers geological periods in chronological sequence, from the Pre-Cambrian to the Quaternary. Throughout, he emphasises the fragmentary nature of the evidence and the difficulties in extrapolating from the surviving fossil record, but he also explains the great discoveries made in the field and how they came about. The accompanying drawings give an impression of the likely combinations of plants found in each period, allowing the reader to visualise the different landscapes evoked in Seward's engaging prose.

A discussion of the modern French-Canadian novel for a non-specialist audience should probably begin with a word of caution concerning "modern." Although the term is relative, of course, one could argue with conviction that, for example, the modern American novel begins as early as Huck Finn and the early Henry James, that is, with the last quarter of the nineteenth century. But the first French-Canadian novel of any importance that could conceivably be called "modern" is Louis H6mon's Maria Chapdelaine, published in 1914; and even here the only "modern" element is the publication date; in both subject matter and approach it is very much a novel of the past century. It is interesting to note that Father Paul Gay, C.S.SP., in his attempt to classify the twentiethcentury French-Canadian novel, lists only one book Maria Chapdelaine published before 1923,1 and only two before 1930; the vast majority are post1945.

By I. R. Williams and M. W. Williams London: George Newnes Ltd. 1962. Pp. vii + 280. Price 42s. This book was written to provide background information on nuclear physics for those concerned with practical applications such as the uses of radioisotopes and reactors. The approach is basically non-mathematical, as befits a wide non-specialist audience.