Book Review: Electrical Machines: An Introduction to Principles and Characteristics, 2nd Ed.

Electromagnetismfor Engineers an Introductory Course. 3rd ed.: P. HAMMOND (Pergamon Press, 1986, 187 pp., U.S. $35 hardback, U.S. $10.75 paperback) Professor Hammond is acknowledged as one of the leading experts of electromagnetic theory and a reading of the third edition of this book will give pleasure to all interested in the fundamentals of electrical and electronic engineering. The introduction demonstrates a keen insight into the close association between the development of mathematical theory and applications in electronic and electrical equipment. He chooses to start with a description of the electric field a conventional approach but one creating a difficulty as it is not until the magnetic field has been sufficiently understood to define current that the unit of charge can be defined. The treatment throughout the book is deceptively well presented and many will wonder why such a simple subject should arouse terror in the minds of many students. This is a good example of the way in which the author's penetrating intellect helps the reader. Starting from first principles, the reader is taken to the formulation of Maxwell's equations and then on a little way towards aerials and waveguides. This is an entirely appropriate coverage for an introductory text. Many authors introduce reference frames and vector calculus into the theory but this is shrewdly avoided without loss of generality or rigour. Similarly, our old friends div, grad and curl are not allowed to trouble the reader. It is unlikely that any two teachers of this subject will completely agree on the material to be covered. I missed any reference to the method of images as applied to fields, to the treatment of coin and needle shaped cavities in dielectrics and magnetic materials and, thus, to the directions of B, H, E and D at boundaries and also spherical conductors in electric fields. The section on permanent magnets is welcomed, especially as it is often omitted from texts such as this, but surely there should be a mention of recoil loops in permanent magnets since these are important for permanent magnets incorporated in indicating instruments. I was a little disturbed to see inductance quoted as Ojl, even though a couple of pages later the analysis was extended to a multi-turn coil with the accepted definition of flux linkage per ampere. The internal inductance of a conductor also could usefully have been mentioned, especially as there is a most acceptable explanation of skin effect and the diffusion equation. A price of $10.75 is quoted for a book by a British author when printed and published in Britain what are we coming to? If this represents £7 for the softback edition, the publishers are obviously aware of the pressure on student grants and the value is quite exceptional. Even the hardback edition at $35 compares favourably in price with the softback versions of certain alternatives. Finally, the reader will welcome the list of alternative texts offered in the appendix, particularly the mention of the similar volume by Charles Oatley. I feel Oatley contains rather more material but is more difficult to read. Percy Hammond selects a narrower body of material but makes it quite delightfully easy to understand. I can recommend this book with genuine enthusiasm. C. B. COOPER, Professor ofElectrical Engineering, UMIST