I have tried in this book to introduce the basic concepts of electromagnetic field theory at a level suitable for students entering degree or higher diploma courses in electronics or subjects allied to it. Examples and applications have been drawn from areas such as instrumentation rather than machinery, as this was felt to be more apt for the majority of such readers. Some students may have been following courses with a strong bias towards prac­ tical electronics and perhaps not advanced their understanding of the physics of electric and magnetic fields greatly since '0' level or its equivalent. The book there­ fore does not assume that 'A' level physics has been studied. Students of BTEC courses or 'A' level subjects such as technology might also find the material useful. At the other extreme, students who have achieved well on an 'A' level course will, it is hoped, find stimulating material in the applications discussed and in the marginal notes, which suggest further reading or comment on the deeper implica­ tions of the work.