This book first appeared in 1925. The basic principles of relativity have not changed since then, but both the theory and its applications have been much extended, and some revision has been necessary for the second and subsequent editions. For the second and third editions I carried out these revisions with Bertrand Russell's approval. The revisions for this fourth edition are entirely my responsibility. I have again altered a number of passages to agree with present knowledge or opinion, and I have attempted to eliminate the possessive case, as applied to laws or theories, where it seemed to me no longer appropriate | Ask a dozen people to name a genius and the odds are that Einstein will spring to their lips. Ask them the meaning of relativity and few of them will be able to tell you what it is. The ABC of Relativity is Bertrand Russell s most brilliant work of scientific popularisation. With marvellous lucidity he steers the reader who has no knowledge of maths or physics through the subtleties of Einstein s thinking in easily assimilable steps he explains the theories of special and general relativity and describes their practical application among much else to discoveries about gravitation and the invention of the hydrogen bomb . Einstein wrote Russell revolutionised our conception of the physical world but the innumerable popular accounts of his theory generally cease to be intelligible at the point where they begin to say something important. The basic principles of relativity have not changed since Russell first published his lucid guide for the general reader. This new edition takes account of the extension of our knowledge about the theory and its applications. BERTRAND RUSSELL ABC OF RELATIVITY Fourth Revised Edition Edited by Felix Pirani LONDON Preface to the Fourth Edition This book first appeared in 1925. The basic principles of relativity have not changed since then but both the theory and its applications have been much extended and some revision has been necessary for the second and subsequent editions. For the second and third editions I carried out these revisions with Bertrand Russell s approval. The revisions for this fourth edition are entirely my responsibility. I have again altered a number of passages to agree with present knowledge or opinion and I have attempted to eliminate the possessive case as applied to laws or theories where it seemed to me no longer appropriate. I have also done my best to renounce the convention that the masculine includes the feminine. Sixty years ago this may have been acceptable or at least tolerated now it is no longer so .
