Illustration representative of the book: the Challenger expedition (route, vol. 1), physical measurements (samples, vol. 2) and the compressibility of liquids (globes, vol.3)
First published 2019 in Great Britain and the United States by ISTE Ltd and John Wiley & Sons, Inc.
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Cover image © John Steven Dews (b.1949), H.M.S. Challenger in Royal Sound, Kerguelen Island, in the Southern Ocean (oil on canvas).
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The rights of Frédéric Aitken and Jean-Numa Foulc to be identified as the authors of this work have been asserted by them in accordance with the Copyright, Designs and Patents Act 1988.
Library of Congress Control Number: 2019943766
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ISBN 978-1-78630-376-9
It is a beautiful adventure that Frédéric Aitken and Jean-Numa Foulc have undertaken, using physical data from the Challenger expedition, the first major oceanographic expedition, sponsored by the British Admiralty in the 1870s. Indeed, this data, temperature and pressure readings at various depths and at multiple points of the world, was relatively little used at the time despite the visionary intuition of one of the initiators of the expedition, Professor Carpenter, that this data would allow for the reconstruction of ocean circulation. The authors attribute this relative lack of interest to the fact that most scientists on the expedition were naturalists, and that from the point of view of biology, the total benefits were already huge, with, for example, the discovery of life at a great depth.
Exploiting data is not the least interesting of the physicist’s tasks. To deal with the problem, we simplify the situation and try not to delete anything essential. The terms of the equations are evaluated, keeping only the most important, and then two situations may arise. Let us say that the discrepancy with the data is clear: we are generally convinced that it has been oversimplified, but where? We are tempted in bad faith to defend our idea, even if it means becoming the Devil’s advocate and destroying what we have built. We go back to the overlooked terms one by one, and, with some luck, this may lead to a new effect. We make do with what we know; the battle is tough, and this is its appeal.
Let us say that the similarity is acceptable. This is when a good physicist is suspicious: is it not a coincidence that two important effects are not offset by any chance? It would be necessary to make a prediction, and to repeat the experiment in different conditions, but it is not always possible. Another boat was not sent out with 200 people around the world for three years! The rigor with which experiments have been conducted, and the confidence that can be placed in the measures, are essential. The experimenters have had to multiply the situations blindly, without knowing which ones would be used as a test, with the sole aim of doing their best every time, by describing their protocol for future use.
The development of the measurement protocol is part of the experiment’s design, as was instrument construction. At that time, a physicist worth his salt would never have used an instrument that he did not know how to build. How can one measure a temperature in a place that one cannot reach oneself (2,000 m below the surface of the sea, for example)? We can record the maximum and minimum temperatures reached during the descent (I found, with much emotion, the description of the maximum and minimum thermometer used by my grandfather in his garden). But what to do for intermediate temperatures? How to make sure that the line does not break in bad weather under the boat’s blows? How to decide the real depth despite currents, and the fact that the line continues to run under its own weight once the sensor is at the bottom? The design phase of the experiment can be exciting: I knew a physicist who was ready to sabotage a barely built experience (under the pretext, of course, of improving it) to be able to move more quickly to the design of the following experiment.
Despite all the attention given to the design, sometimes an error is suspected in the measurements. This is the case here. Having reached unexpected depths (they discovered the Mariana Trench), the Challenger scientists wondered if their measurements had not been distorted by contraction of the glass envelopes. After their return, they assigned Peter Tait, a physicist from Edinburgh, the task of assessing these errors. One thing leading to another, he raised questions about the compressibility of seawater, and other liquids, and so about their equation-of-state, connecting pressure, temperature and density (and even salinity). The result of his studies left a lasting mark on the physics of liquids. Estimating errors, a task hated and despised by the typical physics student, yielded new knowledge.
From the same period as the van der Waals equation, Tait’s efforts were part of the first trials to represent the equation-of-state of dense, liquid and solid bodies by continuous functions. The goal was twofold: metrological, to interpolate between experimental results, and to provide experimenters and engineers with the most accurate characterization of the thermodynamic and physical properties of the fluids they use. But also more fundamental, in the wish to have a better understanding of the underlying physical mechanisms: formation of molecular aggregates, local crystalline order, shape of interaction potentials, etc. These two interests, pragmatism and rigor, are often in conflict, as is clear from the authors’ account, who apply the ideas from that time to fluids that were not of concern then, such as the fluid phases of the two stable isotopes of helium.
Many aspects of this scientific adventure are thus universal, and it is touching to see how the value codes of the scientific approach have been transmitted over decades, or almost centuries. But our step back in time gives us an advantage: the ability to judge the ideas from that period in light of the extraordinary sum of knowledge that has been accumulated since. However, a direct comparison would be unfair and clumsy. It is much more interesting to put us in the mindset of the players of that era, to share their doubts, their hesitations and even their mistakes. This is an aspect that is too often absent from our education. For the sake of efficiency, we do not mention brilliant ideas that have led to a stalemate. Yet these ideas may contribute elsewhere. There may be some hesitation in mentioning great names such as Clausius, Joule and van der Waals, who fill us not only with humility in the face of the mastery that allowed them to find the right path, but also with confidence when faced with our own doubts. The variety of players and points of view that have marked this period show how much science is a collective adventure.
It is all of this that I found in this book by Frédéric Aitken and Jean-Numa Foulc, and even more: the human adventure that was this trip of three years around the world, the incidents, drama and joys, what it revealed about the personality of each participant, their lives which, for some, are also described, the moving relay that is transmitted when a change of assignment, or worse, death, interrupts a task. There is also the welcome reserved for the expedition, sometimes idyllic (ah! the difficulty of leaving Tahiti), sometimes colder, the importance of the band and personal talent of the participants, not to mention the providence that the Challenger represented for the Robinsons, abandoned on an island by a boat that was unable to come back for them. After reading the story based on the logbook, how can we not mention Jules Verne’s novels? It is the same period, that of a thirst for knowledge about our environment, accessible to all of us, acquired by real yet so human adventurers, so close to us. The credit goes to the authors for having dedicated so much time, energy and enthusiasm to this humanist and complete book, with the spirit of this laboratory where I had the pleasure to come for discussions during my years at Grenoble.
Bernard CASTAING
Member of the French Academy of Sciences
In May 1876, the oceanographic expedition of the H.M.S. Challenger reached England after having sailed the seas of the world for more than three years. The main objectives of this expedition were to study animal life in depth, examine the ocean floor to improve knowledge of undersea reliefs, and observe the physical properties of the deep sea in order to establish the link between ocean temperatures and currents. The naturalist William Carpenter, one of the investigators of the Challenger expedition, suggested this previous point. However, although work on animal life was widely promoted after the expedition, the same was not true of the physical observations accumulated throughout the expedition because the theoretical knowledge of ocean dynamics was almost non-existent back then.
Another person played a decisive role after the return of the Challenger. It was the physicist Peter Tait, who was asked by the scientific leader of the expedition to solve a tricky question about evaluating the temperature measurement error caused by the high pressure to which the thermometers were subjected. On this occasion, Peter Tait used a new high-pressure cell that allowed him to accurately determine the correction to be made to the temperatures collected by the Challenger. Later, he embarked on more fundamental research on the compressibility of liquids and solids that led him, nine years later, to formulate his famous equation-of-state. Analysis of the properties of the compressibility of liquids is the second challenge of this book.
From Deep Sea to Laboratory has three volumes. The first volume relates the H.M.S. Challenger expedition and addresses the issue of deep-sea measurement. The second and third volumes offer a more scientific presentation that develops the two points raised earlier: the correlation between the distribution of temperature and ocean currents (Volume 2) and the properties of compressibility of seawater and, more generally, that of liquids (Volume 3).
Chapter 1 begins with a history of liquid compressibility measurement techniques and provides some details on the piezometers used during the Challenger’s expedition. This naturally leads us to present Tait’s work, starting from 1879, on the measurement of the compressibility of fresh water, seawater, mercury and glass, and we discuss his famous equation-of-state parameterized by two quantities.
Chapter 2 examines the physical evolutions and interpretations of the two parameters of Tait’s equation by using comparison and analogy techniques to discuss the best-known equations-of-state of the time, especially van der Waals’, to get a picture of the “structure” of compressed liquid media.
Chapter 3 proposes an in-depth study of the Tait-Tammann-Gibson equation (related to the isothermal mixed elastic modulus) and leads us to propose new equations-of-state that describe in particular the liquid phase of fresh water, seawater and helium-3 and 4. We show that these new relationships have a precision comparable to that of current reference equations. Different “anomalies” of these environments are then highlighted and discussed. Finally, we emphasize the difficulties encountered with various other approaches, other than Tait, Tammann and Gibson’s, in reproducing the compressibility properties of liquids in a simple way.
Chapter 4 focuses on the equation-of-state called the “modified Tait equation”, which is Tait’s ideas on the isothermal secant elastic modulus applied to the adiabatic tangent elastic modulus. It is an equation that is particularly well-suited for describing shock wave phenomena because it is a complete equation-of-state. After an in-depth theoretical study of the thermodynamic functions that can be deduced from the equation of the adiabatic tangent module, new equations-of-state are proposed to describe in particular the liquid and supercritical states of fresh water and helium-3 and 4. We also show here that these new relationships have a precision similar to that of reference equations. “Anomalies” on the adiabatic compressibility of these media are then identified and discussed.
Volume 1 presents the context, organization and conduct of the expedition of the H.M.S. Challenger. The detailed account of the cruise is embellished with numerous illustrations (maps, photographs, etc.) that are rarely presented together. The key role of the officers and scientists involved in this cruise is highlighted, and a brief biography of each of them is presented. In the first volume, we also discuss the problem of deep-sea sounding, which at the time was a delicate and not always well-controlled operation. A theoretical approach to the immersion velocity of a lead is given and compared to the experiment. We end with a presentation of some results of bathymetric surveys and physical observations made by the Challenger’s scientists. Bathymetric surveys are used to represent typical and known seabed reliefs (e.g. the Mariana Trench, South-Atlantic ridges, etc.), and physical observations appear in the form of temperatures, salinities and densities depending on the depth.
In Volume 2, we examine the measurement and distribution of temperature within the ocean and its relationship with the ocean circulation. We begin by describing the evolution of temperature measurement techniques in the 19th Century, by recalling the impact of pressure (at great depths) on measurements. After pointing out that the ocean is composed of different strata, we develop a simplified model of the thermocline in interaction with other ocean layers. This proposed model is limited to thermal aspects (water temperature variation between the equator and the poles) and mechanical aspects (effect of the Earth’s rotation and wind action on surface layers) to establish a link between the cartography of major ocean currents and the distribution of ocean temperatures. The Challenger’s observations and physical data collected in the Atlantic, Pacific and Indian Oceans are analyzed for the first time and compared with more recent works. We end with a general presentation of the mechanisms leading to the global mixing of ocean waters, called the thermohaline circulation.
The book describes a “journey over and through water” with a cross-examination of human history, the history of science and technology, terrestrial and undersea geography, ocean dynamics and thermics, and the sciences dealing with the physical properties of liquids. Curious readers, attracted by travel, science and history, will discover the background and conduct of a great scientific expedition in Volume 1. Students, engineers, researchers and teachers of physics, fluid mechanics and oceanography will also find subjects to deepen their knowledge in Volumes 2 and 3.
We would like to warmly thank Bernard Castaing, a former professor at the Joseph Fourier University of Grenoble (France) and at the École Normale Supérieure of Lyon, France, for carefully reading the manuscript and for his pertinent remarks. We express our gratitude to Ferdinand Volino and André Denat, Senior Researchers at the CNRS, and Jacques Bossy, CNRS researcher, who kindly shared their observations and advice during the preparation of the manuscript and read the final manuscript. We warmly thank Armelle Michetti, head of the library of physics laboratories of the CNRS campus in Grenoble, for her contribution to the search for often old and restricted documents that enabled us to illustrate and support the historical and scientific parts of the book.
We also thank the people who gave us special support: Michel Aitken, Philippe Vincent, Yonghua Huang, Glenn M. Stein and J. Steven Dews.
Finally, we would like to thank the organizations and their staff who have graciously allowed us to use some of their iconographic holdings, and in particular the Natural History Museum in London, the National Portrait Gallery in London, the United Kingdom Hydrographic Office in London, the University of Vienna (Austria), the scientific museum of the Lycée Louis-le-Grand in Paris and Orange/DGCI Company.
Bibliographical references on specific points appear in footnotes and those of a more general nature are collated in the references section at the end of each volume. The footnote reference numbers always correspond to footnotes of that chapter.
Frédéric AITKEN
Jean-Numa FOULC June 2019
