The present volume is one of a series on physics and mathematics, for the upper forms at school and the first year at the university. The books have been written by a team of experienced teachers at the Royal Military College of Science, and the series therefore forms an integrated course of study. In preparing their manuscripts the writers have been mainly guided by the examination syllabuses of London University, the Joint Board of Oxford and Cambridge and the Joint Matriculation Board, but they have also taken a broad view of their tasks and have endeavoured to produce works which aim to give a student that solid foundation without which it is impossible to proceed to higher studies. The books are suitable either for class teaching or self study; there are many illustrative examples and large collections of problems for solution taken, in the main, from recent examination papers. It is a truism too often forgotten in teaching that knowledge is acquired by a student only when his interest is aroused and maintained. The student must not only be shown how a class of problems in mathematics is solved but, within limits, why a particular method works and in physics, why a technique is especially well adapted for some particular measurement. Throughout the series special emphasis has been laid on illustrations which may be expected to appeal to the experience of the student in matters of daily life, so that his studies are related to what he sees, feels and knows of the world around him. Treated in this way, science ceases to be an arid abstraction and becomes vivid and real to the inquiring mind. The books have therefore been written, not only to ensure the passing of examinations, but as a preparation for the exciting world which lies ahead of the reader. They incorporate many of the suggestions which have been made in recent years by other teachers and, it is hoped, will bring some new points of view into the classroom and the study. Last, but by no means least, they have been written by a team working together, so that the exchange of ideas has been constant and vigorous. It is to be hoped that the result is a series which is adequate for all examinations at this level and yet broad enough to satisfy the intellectual needs of teachers and students alike.