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James Clerk Maxwell's (1831-1879) contributions to twentieth-century science and technology - in particular, the displacement current and the electromagnetic theory of light - are among the most spectacular innovations in the history of physics, but the technical complexities and thematic subtleties of his work have been difficult to unravel. In considering the historical development of Maxwell's work, Dr Siegel's close analysis of the original texts - with careful attention to the equations as well as to the words - reveals that mechanical modeling played a crucial role in Maxwell's initial conceptualizations of the displacement current and the electromagnetic character of light. Beyond this, Siegel locates Maxwell's work in the full sweep of nineteenth-century electromagnetic theory - from Oersted, Ampere, and Faraday, through Hertz and Lorentz - and in the context of the methodological traditions and perspectives of early physics research at the Universities of Edinburgh and Cambridge.
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Innovation in Maxwell's electromagnetic theory
Innovation in Maxwell's electromagnetic theory Molecular vortices, displacement current, and light
DANIEL M. SIEGEL University of Wisconsin
7Ai' right of the University of Cambridge to print and sell all manner of book s was granted by Henry VIII ,n 1534. The Uni versity has printed and published continuously since 1584.
CAMBRIDGE UNIVERSITY PRESS Cambridge New York Port Chester Melbourne Sydney
PUBLISHED BY THE PRESS SYNDICATE OF THE UNIVERSITY OF CAMBRIDGE The Pitt Building, Trumpington Street, Cambridge, United Kingdom CAMBRIDGE UNIVERSITY PRESS The Edinburgh Building, Cambridge CB2 2RU, UK 40 West 20th Street, New York NY 10011-4211, USA 477 Williamstown Road, Port Melbourne, VIC 3207, Australia Ruiz de Alarcon 13, 28014 Madrid, Spain Dock House, The Waterfront, Cape Town 8001, South Africa http ://www. Cambridge. org © Cambridge University Press 1991 This book is in copyright. Subject to statutory exception and to the provisions of relevant collective licensing agreements, no reproduction of any part may take place without the written permission of Cambridge University Press. First published 1991 First paperback edition 2002 A catalogue record for this book is available from the British Library Library of Congress Cataloguing-in-Publication Data Siegel, Daniel M. Innovation in Maxwell's electromagnetic theory : molecular vortices, displacement current, and light / Daniel M. Siegel. p. cm. ISBN 0 521 35365 3 hardback 1. Electromagnetic theory. 2. Physics - History. I. Title. QC670.S48 1991 530.1'41-dc20 90-42511 CIP ISBN 0 521 35365 3 hardback ISBN 0 521 53329 5 paperback
For the women in my life Rebecca Shulamith Ruth Rebecca, Deborah, Sarah
CONTENTS
Preface
page ix
Introduction 1 The background to Maxwell's electromagnetic theory 2 Mechanical image and reality in Maxwell's electromagnetic theory 3 The elaboration of the molecular-vortex model 4 The introduction of the displacement current 5 The origin of the electromagnetic theory of light 6 Beyond molecular vortices Conclusion Appendix 1. Draft of "On Physical Lines of Force," a fragment Appendix 2. Drafts of "A Dynamical Theory of the Electromagnetic Field"
1 5
180
Appendix 3. Vortex rotations in a curl-free region
182
Notes
185
Index
221
29 56 85 120 144 168 174
PREFACE
The historian of science cannot be unmindful of the fact that, for better or for worse, science, as practiced now and in the past, furnishes one of our central models of rational thought and judgment. Some would use history to demonstrate the worthiness of science as a model for rationality; others would use history to demonstrate the limitations of science in this respect. A