Cloud chamber photographs of the cosmic radiation

BOOK REVIEWS CLOUD CHAMBER PHOTOGRAeHS OF THE COSMIC RADIATIOn', by G. D. Rochester and J. G. Wilson. 128 pages, illustrations, 21 X 28 cm. London, Pergamon Press Ltd.; New York, Academic Press Inc., 1952. Price: L3.10s; $10.80. To those who have had limited experience in interpreting cosmic ray cloud chamber photographs, and to those who are starting out on such fields of investigation, this book will serve in a most valuable capacity. In his Foreword to the book, Professor P. M. S. Blackett, referring to cloud chamber photographs, writes: "An important step in any investigation using these methods is the interpretation of a photograph, often of a complex photograph, and this involved the ability to recogniz~ quickly many different types of sub-atomic events. To acquire skill in interpretation, a preliminary study must be made of many examples of photographs of the different kinds of known events. Only when all known types of event can be recognized will the higherto unknown be detected." All who read the book will join with Professor Blackett in recognizing that, in facilitating the acquirement of the essential skills for cloud chamber work, namely that of interpretation and that of recognition and attainment of high technical quality, the authors have succeeded brilliantly. The book is divided into six sections. Section 1, "Technical Features of Operation," contains some fourteen pages devoted to the illustration of various types of cloud chamber photographs, with emphasis on technical features and such phenomena--distortion at the edge of the piston, turbulent distortion, effects of contamination, etc.--as play important roles in effective cloud chamber operation. The descriptions of the apparatus associated with the photographs are quite detailed and provide a mine of information, particularly for the novice in this realm of experimentation. Section 2 comprises about 28 pages and is devoted to electron and cascade showers. The interpretation of the photographs is carried out in considerable detail, both as regards the nature of the events and the magnitudes associated with them. Incidentally, this section contains a reproduction of Anderson's classic experiment, from which he inferred the existence of the positive electron. Section 3 is devoted to slow u-mesons and the decay of such mesons. Some 15 pages of examples are given, with detailed illustrations, and include some very beautiful photographs showing the death of mesons, both with and without the accompaniment of decay electrons. Again the photographs contain detailed descriptions and quantitative estimates of magnitudes such, for example, as the energies associated with decay electrons. Section 4 devotes some 32 pages to nuclear disintegration and interaction of secondary particles. Among other things of interest, it contains many photographs taken with large numbers of lead plates in the cloud chamber. In addition to phenomena of nuclear disintegration and allied phenomena, there are pictures of penetrating showers. Section 5, comprising some 20 pages, is devoted to V-particles and is rich in qualitative and quantitation associated phenomena. Section 6 comprises a very beautiful picture of a heavy cosmic ray particle passing through four slabs, one comprising 6 mm. of carbon and the others 6 ram. of lead each. The book is presented in excellent form and the clarity of the pictures is exceptional. The authors have also enhanced the interest of the publication by including photographs of historical interest. Finally, it is worthwhile calling attention to an aspect of such a group of pictures which, while presumably always implicit in the mind, is apt not to be recognized in its full force. This aspect is recognized in Professor Blackett's Foreword in the following sentence: "If one asks why some of these complicated events happen, one may be led into the subtle intricacies and uncertainties of modern fundamental theoretical physics, but if the experimenter contents himself with asking how they happen, then these pictures, and the attached commentaries, are an ideal guide to the world of energetic elementary particles." W . F . G . SWANS 76