Geomagnetism and aeronomy

BookReviews LINEARSYSTEMS,by Ralph J. Schwarz and Bernard Friedland. 521 pages, diagrams, 6X9 in. New York, McGraw-Hill Book Company, 1965. Price, $12.50. Most topics of current interest in the theory of linear engineering dynamical systems are treated in this carefully written and well produced book. The analysis of lumped dynamical systemz is consistently carried out in terms of state variables and using vectormatrix notation; both continuous-time and discrete-time systems are considered. Fourier, Laplace and Z-transform methods are clearly explained; random signals are well covered; there is a comprehensive treatment of stability and a useful fmal chapter on distributed systems. The emphasis throughout the book is on analytical methods, and topics of great value to the designer, such as the root locus method, are given a disappointingly brief treatment. In several places the authors’enthusiasm for analysis has led them to make assertionswhich read strangely to anyone engaged in engineering work with reasonable access to computing facilities. For example, one reads on page 400 that an attempt to calculate the zeros of a polynomial of degree greater than three is “not feasible.” A rather similar disregard of practical techniques leads to the statement on page 427 that “ . . . the Nyquist diagram. . . is usually obtained by direct calculation,” whereas a great deal of its value lies in the fact that it is one of the few stability criteria related to practically obtainable measurements. There is no discussion of the synthesis techniques which now form a large and important body of knowledge in linear systems theory. In general, this book should he of great value to students and teachers who require a treatment of the standard topics of linear dynamical theory with equal emphasis on differential equation and transform approaches. It is well printed, with many clearly drawn diagrams, and has an excellent index.

.WD AERONOMY, edited by A. H. Waynick. Antarctic Research Series, Vol. 4. 236 pages, diagrams, illustrations, 7f X lOi in. Washington, D. C., The American Geophysical Union, 1965. Price, $10.00.

GEOMAGNETISM

This book consists of nine papers on extensive studies of the ionosphere, geomagnetic disturbances, atmospheric noise, and others, based on data collected internationally during the IGY/C. The ionosphere is the subject of the first four papers. The next three papers are concerned with geomagnetic disturbances (by using the K and Q indices) and also with geomagnetic micropulsations. The last two papers are on atmospherics and on electrical properties of blowing snow. It is particularly interesting to see that the gross feature of the ionosphere over the entire Antarctic region is extensively studied, and a comparison is made with the behavior of the ionosphere over the Arctic region. A largescale motion of the F2 ionization associated with geomagnetic storms is also revealed. The reviewer feels, however, that it would be more useful for the readers if this volume could have presented the whole scope of the Antarctic researchers conducted in this country (rather than the contributions from only two groups), so az to establish a milestone of the Antarctic researches in Geomagnetism and Aeronomy and also to serve ss a reference book for future Antarctic research programs in this field. Obviously, duplication of some of the material iz unavoidable. Nevertheless, many of the papers in the volume could have been shortened a little to accommodate other papers on the geomagnetic survey, the aurora, cosmic rays, and the airglow, or even to include a list of papers related to this great enterprise. SYUN-ICHI Ax~sozu A. G. J. MACFARLANE Department of Physics and Astronomy University of London University of Iowa Iowa City, Iowa

Queen Mary College London, England

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