A History of Light and Colour Measurement Science in the Shadows A History of Light and Colour Measurement Science in the Shadows Sean F Johnston University of Glasgow, Crichton Campus, UK Institute of Physics Publishing Bristol and Philadelphia c IOP Publishing Ltd 2001 All rights reserved. No part of this publication may be reproduced, stored in a retrieval system or transmitted in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, without the prior permission of the publisher. Multiple copying is permitted in accordance with the terms of licences issued by the Copyright Licensing Agency under the terms of its agreement with the Committee of Vice-Chancellors and Principals. British Library Cataloguing-in-Publication Data A catalogue record for this book is available from the British Library. ISBN 0 7503 0754 4 Library of Congress Cataloging-in-Publication Data are available Commissioning Editor: James Revill Production Editor: Simon Laurenson Production Control: Sarah Plenty Cover Design: Fr´ed´erique Swist Marketing Executive: Laura Serratrice Published by Institute of Physics Publishing, wholly owned by The Institute of Physics, London Institute of Physics Publishing, Dirac House, Temple Back, Bristol BS1 6BE, UK US Office: Institute of Physics Publishing, The Public Ledger Building, Suite 1035, 150 South Independence Mall West, Philadelphia, PA 19106, USA Typeset in the UK by Text 2 Text, Torquay, Devon Printed in the UK by MPG Books Ltd, Bodmin, Cornwall CONTENTS PREFACE ix 1 INTRODUCTION: MAKING LIGHT COUNT 1 1.1 Organization of chapters 4 1.2 Terms 9 Notes 10 2 LIGHT AS A LAW-ABIDING QUANTITY 12 2.1 Beginnings 12 2.2 A lawless frontier 18 2.2.1 Photography: juggling variables 20 2.2.2 Astronomy: isolated forays 21 2.3 Techniques of visual photometry 22 2.3.1 Qualitative methods 22 2.3.2 Comparative methods 22 2.3.3 Physical methods 24 2.4 Studies of radiant heat 24 2.5 Describing colour 26 Notes 28 3 SEEING THINGS 33 3.1 Recurring themes 34 3.2 Altered perceptions 36 3.2.1 Astrophysics and the scientific measurement of light 37 3.2.2 Spectroscopy 41 3.2.3 Shifting standards: gas and electrotechnical photometry 42 3.2.4 Utilitarian connections 43 3.3 The 19th-century photometer 49 3.4 Prejudice and temptation: the problems in judging intensity 53 3.5 Quantifying light: n-rays versus blackbody radiation 58 Notes 64 4 CAREERS IN THE SHADOWS 72 4.1 Amateurs and independent research 72 4.2 The illuminating engineers 75 4.3 Optical societies 86 A History of Light and Colour Measurement Notes 88 5 LABORATORIES AND LEGISLATION 94 5.1 Utilitarian pressures 94 5.2 The Physikalisch-Technische Reichsanstalt 96 5.3 The National Physical Laboratory 99 5.4 The National Bureau of Standards 102 5.5 Colour at the national laboratories 104 5.6 Tracing careers 107 5.7 Weighing up the national laboratories 109 5.8 Industrial laboratories 111 5.9 Wartime photometry 114 5.10 Consolidation of practitioners 116 Notes 117 6 TECHNOLOGY IN TRANSITION 125 6.1 A fashion for physical photometry 125 6.1.1 Objectivity 126 6.1.2 Precision 128 6.1.3 Speed 129 6.1.4 Automation 129 6.2 The refinement of vision 130 6.3 Shifts of confidence 133 6.4 Physical photometry for astronomers 135 6.4.1 An awkward hybrid: photographic recording and visual analysis 135 6.4.2 A halfway house: photographic recording and photoelectric analysis 137 6.4.3 A ‘more troublesome’ method: direct photoelectric photometry 139 6.5 The rise of photoelectric photometry 142 6.6 Recalcitrant problems 148 6.6.1 Talbot’s law 148 6.6.2 Linearity 148 6.6.3 The spectre of heterochromatic photometry 150 Notes 151 7 DISPUTING LIGHT AND COLOUR 159 7.1 The Commission Internationale de Photom´etrie 161 7.2 The Commission Internationale de l’Eclairage´ 162 7.3 Legislative connections 167 7.4 Constructing colorimetry 168 7.4.1 Colour at the CIE 168 7.4.2 Disciplinary divisions 176 7.4.3 Differentiating the issues 177 7.5 Voting on colour 179 vi Contents 7.5.1 Configuring compromise 180 7.5.2 An uncertain closure 181 Notes 184 8 MARKETING PHOTOMETRY 191 8.1 Birth of an industry 192 8.2 Technological influences 194 8.3 Linking communities 197 8.3.1 Extension of commercial expertise 200 8.3.2 New practitioners 201 8.4 Making modernity 203 8.5 Backlash to commercialization 204 8.6 New instruments and new measurements 206 8.7 Photometry for the millions 208 8.8 A better image through advertising 210 Notes 213 9 MILITARIZING RADIOMETRY 220 9.1 The mystique of the invisible 220 9.2 Military connections 221 9.2.1 British research 222 9.2.2 American developments during the Second World War 222 9.2.3 German experiences 224 9.2.4 Post-war perspectives 225 9.2.5 New research: beyond the n-ray 227 9.2.6 New technology 227 9.3 New centres 229 9.4 New communities 230 9.5 New units, new standards 231 9.6 Commercialization of confidential expertise 232 9.6.1 New public knowledge 232 9.7 A new balance: radiometry as the ‘senior’ specialism 233 Notes 233 10 AN ‘UNDISCIPLINED SCIENCE’ 237 10.1 Evolution of practice and technique 237 10.2 The social foundations of light 240 10.3 A peripheral science? 243 10.3.1 On being at the edge 243 10.3.2 Technique, technology or applied science? 245 10.3.3 Attributes of peripheral science 247 10.4 Epilogue: declining fortunes 248 Notes 250 BIBLIOGRAPHY 255 Abbreviations 255 Periodicals 255 vii A History of Light and Colour Measurement Organizations 257 Other 258 Sources 258 Notes 261 Bibliography 261 INDEX 272 viii PREFACE This book is about how light was made to count. It explores a seemingly simple question: How was the brightness of light—casually judged by everyone but seldom considered a part of science before the 20th century—transformed into a measurable and trustworthy quantity? Why did the description of colour become meaningful to artists, dyers, industrialists and a handful of scientists? Seeking answers requires the exploration of territory in the history, sociology and philosophy of science. Light was made to count as a quantifiable entity at the same timeasitcametocount for something in human terms. Measuring the intensity of light was fraught with difficulties closely bound up with human physiology, contentious technologies and scientific sub-cultures. Explorations often begin with meanderings, tentative forays and more prolonged expeditions. This one ranges over a period of 250 years, and pursues social interactions at every scale. As the title hints, the subject was long on the periphery of recognized science. The illustrations in the book reinforce the reality of social marginalization, too: depictions of light-measurers are rare. Certainly their shrouded and blackened apparatus made photography awkward; but the reliance on human observers to make scientific measurements came to be an embarrassment to practitioners. The practitioners remain shadowy, too, because of the low status of their occupation, commercial reticence and—somewhat later—military secrecy. The measurement of brightness came to be invested with several purposes. It gained sporadic attention through the 18th century. Adopted alternately by astronomers and for the utilitarian needs of the gas lighting industry from the second half of the 19th century, it was appropriated by the nascent electric lighting industry to ‘prove’ the superiority of their technology. By the turn of the century the illuminating engineering movement was becoming an organized, if eclectic, community promoting research into the measurement of light intensity. The early 20th century development of the subject was moulded by organization and institutionalization. During its first two decades, new national and industrial laboratories in Britain, America and Germany were crucial in stabilizing practices and raising confidence in them. Through the inter-war period, committees and international commissions sought to standardize light and colour measurement and to promote research. Such government- and industry-supported ix A History of Light and Colour Measurement delegations, rather than academic institutions, were primarily responsible for the construction of the subject. Along with this social organization came a new cognitive framework: practitioners increasingly came to interpret the three topics of photometry (visible light measurement), colorimetry (the measurement of colour) and radiometry (the measurement of invisible radiations) as aspects of a broader study. This recategorization brought shifts of authority: shifts of the dominant social group determining the direction of the subject’s evolution, and a shift of confidence away from the central element of detection, the eye. From the 1920s, the highly refined visual methods of observation were hurriedly replaced by physical means of light measurement, a process initially a matter of scientific fashion rather than demonstrated superiority. These non-human instruments embodied the new locus of light and colour, and the data they produced stabilized the definitions further. The rise of automated, mechanized measurement of light and colour introduced new communities to the subject. New photoelectric techniques for measuring light intensity engendered new commercial instruments, a trend that accelerated in the 1930s when photometry was taken up with mixed success for a wide range of industrial problems. Seeds sown in those years—namely commercialization and industrial application, the transition from visual to physical methods and the search for fundamental limitations in light measurement—gave the subject the form it was to retain over the next half- century. Nevertheless, changing usage mutated the subject. Light proved to be a valuable quantity for military purposes during and after the Second World War.