Eric Chassefiere - Physics of the Terrestrial Environment, Subtle Matter and Height of the Atmosphere

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Series Editor

Denis-Dider Rousseau

Eric Chassefière

First published 2021 in Great Britain and the United States by ISTE Ltd and John Wiley & Sons, Inc.

Apart from any fair dealing for the purposes of research or private study, or criticism or review, as permitted under the Copyright, Designs and Patents Act 1988, this publication may only be reproduced, stored or transmitted, in any form or by any means, with the prior permission in writing of the publishers, or in the case of reprographic reproduction in accordance with the terms and licenses issued by the CLA. Enquiries concerning reproduction outside these terms should be sent to the publishers at the undermentioned address:

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© ISTE Ltd 2021

The rights of Eric Chassefière to be identified as the author of this work have been asserted by him in accordance with the Copyright, Designs and Patents Act 1988.

Library of Congress Control Number: 2021940067

British Library Cataloguing-in-Publication Data

A CIP record for this book is available from the British Library

ISBN 978-1-78630-717-0

This book presents the methods developed in the 17th and 18th centuries for estimating the height of the atmosphere, methods essentially based on the observation of the light refracted and reflected by the atmosphere, and of certain meteors. As a result, these methods gave rise to a number of contradictions and advances. This question of determining the height of the atmosphere is inseparable from how the atmosphere is represented, with the atmosphere passing from the status of an idealized and purely mathematical object up to the middle of the 17th century, to that of a complex, eminently variable physical object, whose nature was the subject of a multitude of hypotheses, and which 18th-century scientists tried to reconcile within a coherent overall vision. The quest to determine how high the atmosphere reached, which the different phenomena studied did not all place at the same height, proved a powerful motivator of new research and debate during this time, as well as for the necessary syntheses that resulted. Rather than addressing, one by one, the different methods used to estimate the height of the atmosphere, in this book, we adopt a transverse approach by examining the various matters of a more subtle nature introduced by the scientists of the time to explain the phenomena from which they derived this height – the milestones in the construction of the representation of the atmosphere as a physical object. These subtle matters, most of which are part of the legacy of René Descartes, offer a broad field of investigation, which allows us to set the stage for the evolution of the scientific thinking of the time in relation to the understanding of atmospheric phenomena. There is a strong overall coherence between the hypotheses formulated at that time, far beyond the question of the validity of these hypotheses with respect to today’s knowledge, showing to what extent their abundance and the confrontation of points of view allow knowledge to mature, until the conceptual leap that overturned old ideas and allowed for an objective advance took place. These processes occurred over a considerable period of time, on the scale of over a century. It is this work of progressive maturation – the product of a permanent tension between the legacy of old ideas and the new ideas resulting from ever more numerous, rich and precise observations – which we present in this book.

Chapter 1provides an analysis of the meaning of words used in the 18th century to characterize air, atmosphere, ether and, more generally, subtle matters. Understanding the literature of the time on the atmosphere and subtle fluids requires a good understanding of the exact meaning of the terms used, which often differs from the meaning given to them today. For example, the term vapor , which we apply today to a gas, was used at that time to refer to a component of small particles emanating from the Earth or water, the union of which can eventually lead to the formation of clouds or mists. The term air takes on different meanings depending on whether it is, for example, coarse air or elementary air. There are similarly varying definitions of ether, which surrounds and, according to some, penetrates the atmosphere, in the latter case providing it with such characteristics as, for example, its elasticity. The proliferation of scientific ideas in the 18th century is accompanied by a multiplicity of meanings given to different words, which is necessary to keep in mind to fully understand the nature of the mechanisms that are analyzed. Chapter 1, which is not intended to be an exhaustive study, provides illuminating observations on the basis of the analysis of a number of articles on different words concerning the atmosphere in several dictionaries: the Dictionnaire Universel de Furetière , whose first edition dates back to 1690; the Encyclopédie by Diderot and d’Alembert, published from 1751; and, as a comparison between the terms used by the French and English scientific communities, the Lexicon Technicum , whose first edition dates back to 1704. There are many parallels between the words used in France and across the channel in England, with dictionary articles from either country frequently quoting authors from the other country, but there are also differences, which are due to the scientific conceptions underlying the use of the words, which in the case of the French articles are infused with Cartesian doctrine. The use of the three dictionaries also makes it possible to note certain progressions that took place in the definition of scientific words between the dawn and the middle of the Enlightenment, in a period of rapid development of scientific thought.