Penguin Books Ltd, Harmondsworth, Middlesex
Penguin Books Inc., 3300 Clipper Mill Road, Baltimore 11, Md, U.S.A.
Penguin Books Pty Ltd, Ringwood, Victoria, Australia
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First published 1966
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Copyright © Penguin Books, 1966
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Made and printed in Great Britain by Richard Clay (The Chaucer Press) Ltd. Bungay Suffolk Set in Monotype Times
The cover design is adapted from a figure by L. S. Penrose
This book is sold subject to the condition that it shall not, by way of trade or otherwise, be lent, re-sold, hired out, or otherwise circulated without the publisher's prior consent in any form of binding or cover other than that in which it is published and without a similar condition including this condition being imposed on the subsequent purchaser