There was much time in December for Wegener to work on the thermodynamics. He had completed the manuscript on the chemical differentiation of the atmosphere, especially the upper atmosphere, and including his hypothetical geocoronium, and sent it to Emil Wiechert at Göttingen, who was then editing Physikalische Zeitschrift. He had also sent a version of the same paper to Meteorologische Zeitschrift and was prepared to publish shorter versions in various other periodicals in order to publicize his find. But for now, the idea in its several forms was off his desk.
The only course he was teaching that term was a practicum on astronomical position finding on expeditions, something that he had done many times and could perform by rote without new work. The weather at that time of year was not conducive to ballooning, and he had a momentary respite from the lecture circuit. Under these advantageous and unusual circumstances he threw himself into the composition and revision of the remaining portions of the book. On the solstice he wrote to Köppen, “I have put a lot of time in on the design of the physical part of the work which I hope was not in vain, but it is such that the size of the book has now grown in consequence, and there are many chapters which you would hardly recognize any longer … while I’m in Berlin I plan to finish it and send the manuscript to the publisher.”58
With his manuscript nearly complete and only a few references to chase down, he was ready for a vacation. He was to travel to Berlin to spend Christmas with his parents. Before he could leave, however, there was something he still had to do. He had a present for the Köppen family and took great pains to pack it with care. Köppen’s daughter Else remembers that a few days before Christmas 1910 a very large crate arrived with the legend “Stop!! Don’t be curious! Don’t open till Christmas Eve.” The crate had come from Marburg and within it was a lot of excelsior surrounding a carton, and inside the carton, packed in cotton, was a still smaller box of the kind used for photographic slides. It was sealed all around with tape that bore the legend “open only by lamplight!” Else said she could not bear the suspense and immediately pulled off the tape and opened the box. At the bottom of the box there was a scrap of paper that said, “I told you that you shouldn’t be so curious!” She said that she and her brother laughed until they cried. She was almost sorry that she had done it, but the next day another package arrived addressed to her and the rest of the family, containing the German translation of Achton Friis’s book about the Danmark Expedition, in which, as we have already seen, Wegener figured prominently. Else was overjoyed: “I buried myself in the adventure in Greenland and for a long time saw and heard nothing else.”59
Wegener’s Thermodynamics of the Atmosphere
By the time he had sent his package to Hamburg, the book manuscript had reached the final form, and this is therefore an apposite point for a discussion of its structure and contents, as well as its intellectual implications for both Wegener and meteorology.
As an entryway to discussion of Wegener’s thermodynamics of the atmosphere, let us consider first where, in that period of time, such a textbook might have fit into the state of the science. To put this question in context, let us consider a remark made by the dynamic meteorologist Edward Lorenz (1917–2008) when asked in 1995 to provide an essay on the “evolution of dynamic meteorology” for the seventy-fifth anniversary of the American Meteorological Society: “What constitutes the state of an evolving scientific discipline—dynamic meteorology or something else—at a particular moment in history? Does it encompass the ideas taking shape in the minds of the most forward-looking scientists? Does it include only those ideas that have found their way into the refereed literature? Is it the knowledge that is regularly imparted in the classroom in institutions of higher learning, available to all who have the opportunity to enroll? Is it limited to the material appearing in textbooks, available to a still greater audience?”60
Each scientific culture has its own answer to this question, but our concern here will be with Germany in the early twentieth century. In bound-book publication in the sciences in Germany at that time there was a quadripartite hierarchy of certainty, and at the top were the Handbücher, the reference volumes, containing material deemed certain, such as physical constants and well-established calculation techniques. Slightly less solid, but still generally dependable throughout, were the Lehrbücher, or textbooks, a designation given to freestanding introductions to a subject, whether this be a scientific theory or instructions in technical practice for beginning students. Closer to the research front and farther from absolute certainty were Vorlesungen, or “lectures,” associated with the lectures given in a specific course of study, delivered by a specific professor, and deemed to be the course guide for students enrolled in his course in that subject in that year. Finally, there was just ein Buch, a monograph, with no specific rank with regard to certainty.
Wegener’s thermodynamics of the atmosphere was a hybrid product that fell between these genres. It had some of the characteristics of a textbook but also read like a series of lectures. It contained well-confirmed results suitable to a textbook for introductory students, as well as frontline results in the form of lectures incorporating summaries of recent monograph literature. The book also contained previously unpublished and therefore, from the standpoint of scientific culture, unverified material. Wegener was quite aware of this hybrid character and the extent to which the book was a resumé of themes he had absorbed in graduate school and during his time at Lindenberg, melded with his experiences in Greenland and his published papers in aerology since his return from Greenland. His specification of his desired audience (in the foreword) included active meteorologists whom he hoped to inspire, physicists who might learn about an exciting new field of investigation, aeronauts who might benefit from the work on clouds, and even the “educated lay public,” with the latter group able to find, he hoped, “certainly not a popular but rather an easily comprehensible presentation of the most recent branches of meteorology.”61 Neither the book’s hybrid character nor its various and probably immiscible audiences can convey the freshness and idiosyncratic character of this book, in so many ways the external realization of his own scientific imagination and the perpetually ingenuous enthusiasm that drove it.
Wegener’s chosen standpoint was always that of cosmic physics. This book obviously was not a complete cosmic physics of Earth, which, on the model of Svante Arrhenius’s Lehrbuch der kosmischen Physik, would have covered the physics of everything from the stars down to the core of the solid Earth and would have weighed in at 2 kilograms (4 pounds), with 1,000 pages of text.62 Nevertheless, Wegener, the astronomer and cosmic physicist, started on page 1 characterizing Earth’s atmosphere as only a single example of a planetary atmosphere within the solar system. Of the eight planets then known, seven had atmospheres, and Earth belonged to a family that included Venus and Mars, but not the gas giants Jupiter and Saturn, nor Uranus or Neptune. Yet even before he can get around to characterizing Earth’s atmosphere and its composition, Wegener is already discussing coronium and geocoronium as the most likely gases to be found in interplanetary space. Then attention turns to Venus, Earth, and Mars, which make a nice trio with regard to cloud cover and albedo: Venus entirely cloud covered, Earth about half cloud covered, and Mars with no cloud cover, but all with detectable atmospheres. Here again, by pages 3 and 4 we are involved with work he was currently doing with Stuchtey on measuring Earth’s albedo. On pages 6 and 7, we see Wegener’s theory of the chemical differentiation of the atmosphere featured in his initial presentation of atmospheric structure: “The researches of the author and others partition the atmosphere in three main sections: a nitrogen sphere from Earth’s surface to about 70 km, a hydrogen sphere between 70 and about 200 km, and the still hypothetical sphere of an unknown extraordinarily light gas for which the name ‘Geo-coronium’ has been proposed between 200 and more than 500 km altitude.”63
Just as one begins to feel that this is not a textbook on the thermodynamics of the atmosphere but a resum�
� of the opinions of Alfred Wegener, the text veers away sharply from simple declarative statements and begins a twenty-page explanation of the physical reasoning behind the conclusions given in the first six or seven pages.64 With great clarity, and with reference to the way the data were collected, how the data have been interpreted, and how we know anything at all about the upper atmosphere, he moved through what we can discern from the aurora, what we can discover from meteors and their trails, what we find out about the twilight limit, what the zodiacal light tells us, what we learned from noctilucent cloud studies after the volcanic eruption at Krakatoa, and finally what we learn from aerology. The chapter ends with an analysis of the gaseous composition of the atmosphere and the way measurements were carried out to determine the fractional volumes of the different gases.
Wegener’s cross section of the atmosphere, treating his conjectural geocoronium layer and his hypothesis of the chemical differentiation of the atmosphere as established facts. From Alfred Wegener, Thermodynamik der Atmosphäre (Leipzig: J. A. Barth, 1911).
When Wegener wrote to Köppen saying that he had put a lot of energy into the physical part of the book and that this had made it grow larger, he was speaking of this complete revision of the manuscript away from a didactic summary of received results, along with the mathematical formulas for obtaining them, and toward a reasoned and inviting conversation about how it is that physicists interpret evidence in order to characterize things that they cannot see and touch directly. This procedure—giving a result, explaining how the result was obtained, by whom, when, how, and with what degree of certainty—is a view of science from the ground level, a human view, not that of the “eye of God.”
This treatment becomes quite striking when he moves on from this introductory chapter to the thermodynamics of gases. In two successive chapters he winnows his focus to the actual world. Beginning with the chapter on the general thermodynamics of ideal gases and the laws by which they are understood, he moves on to the general thermodynamics of real gases: how they flow, how we map them with isobars and isotherms, how we obtain temperatures and pressures, and how condensation takes place. There is room here for his theory of ionic condensation, for condensation nuclei, for all the work of Lehmann on snow crystals, accompanied by beautiful microphotographs. To this he added a clear physical consideration of supercooling and the phase diagram for water including its triple point. In every case there is direct reference to the literature from which he has taken it and an evaluation of the degree of certainty of the results.65
The evaluation of evidence becomes even more detailed as he moves from the general thermodynamics of gases, ideal or real, to the special thermodynamics of adiabatic processes. It is only at this point in the text, nearly one-third of the way through, that we begin to encounter thermodynamic reasoning: the concepts of latent and specific heat and the mechanical equivalent of heat, the principle of the conservation of energy, and a discussion of energy and entropy. The mathematics are sparse, nothing more than is absolutely required to understand the relations, with an absolute minimum of subscripts and superscripts. There are a few differentials, but not an integral sign in the full 331 pages. He covers all the essential topics, again referring to the original literature back to the middle of the previous century: convective equilibrium in the atmosphere, potential temperature, mechanisms for the achievement of equilibrium in a water vapor atmosphere, and adiabatic changes in air with condensation. Each of these topics is treated qualitatively wherever possible, with easy-to-read tabular data and very simple diagrams. This section concludes with a very extensive discussion of the mean partition of temperature in the vertical (with a discussion of föhn winds), a fifty-page discussion of all the different kinds of inversions and the implications of inversions for the vertical structure of the atmosphere and its discontinuities, and finally a consideration of the contrast between the turbulent phenomena of the troposphere and the undisturbed laminar flow of the stratosphere.66
The diagrams that accompany the text are not what we would see in a modern textbook, in which sophisticated graphics would be used to draw a picture of the atmosphere, perhaps with contrasting colors or different textures and sidebars, among other things. What we generally have are graphic presentations of real data: temperature data from real balloon flights, collated data of mean cloud heights in different geographical latitudes, and the oscillation of relative humidity at different altitudes over Berlin and its correlation with different classes of clouds from stratus at the bottom to cirrostratus 8 kilometers (5 miles) higher. The overall message here is that this is not a picture of the world itself; rather, it is a picture of what we think the world is based on the measurements we take with the instruments at our disposal, and known to a certain degree of accuracy but no more.
The final third of the book, section 5, is the longest and uses all the information previously developed about atmospheric structure, the behavior of gases, and the special thermodynamics of adiabatic processes, in order to elaborate a detailed picture, in three successive chapters, of the physics of clouds. First, a general morphology of clouds is given, and then the physical reasoning behind Wegener’s theory of precipitation, with respect to both the special structure of water clouds and finally the special structure of ice clouds. This part of the book he illustrated with very good photographs of cloud forms of every kind, supplementing them with simple line drawings that schematize the contents of photographs.67 It is in this last section of the book that Wegener goes deeply into his own theory of precipitation, the formation of raindrops, the speed of their fall, a reconsideration of ionic condensation, and the role of supercooling in forming large ice crystals, as a result of differential vapor pressure over supercooled water droplets and ice nuclei. Even here there is a long and sophisticated discussion of alternative hypotheses for droplet formation. The book ends with jarring abruptness after a consideration of optical phenomena in ice clouds: one senses that the pressure to get the manuscript to the press did not even leave time for a conclusion, as there is none.68
As striking as what is in the book is what is not in the book. It is the only book one is ever likely to see that has the word “thermodynamics” in the title but does not have any pictures of the Carnot cycle or Otto engine cycle, or of isothermal exchanges, or of pistons moving back and forth in rigid cylinders, or discussions of reversible and irreversible processes. The book is not about the atmosphere as a heat engine; it is about the atmosphere as an atmosphere, on planet Earth, without any reference to human contrivances, other than the instruments used to discover the physical values on which the behavioral relations of pressure, temperature, and volume are based. It is not the atmosphere explained thermodynamically with reference to human concerns and machines (though the information on clouds is very much directed to balloonists); it is the atmosphere explained thermodynamically with reference to what the atmosphere does, as it has been observed doing by real human beings, looking at real gases, at real elevations, employing real instruments, and employing still other instruments to arrive at sound inferences about things happening at elevations that humans have not yet reached. The only theoretical entities here are inferred molecular processes of otherwise unobservable entities, and these are (throughout the book) restricted entirely to phenomena of condensation. Even these theoretical discussions are premised on and referenced to experimental literature.
The tentative and idiosyncratic character of Thermodynamik der Atmosphäre notwithstanding, the meteorology it contained and the structure and the arrangement of its topics were the result of a close collaboration with Köppen and could therefore be expected to be reliable and useful. Wegener’s book was certainly the most abundantly illustrated treatise on cloud forms which had yet appeared in a textbook of any kind, and it contained much durable, novel physics. The book, unaltered, would remain continuously in print for the next seventeen years and would give Wegener a permanent place in the history of meteorology. It was his first full-length book, an
d its completion gave him an immense sense of relaxation, satisfaction, and release. The release, however, was conditional: it released him only to deliver him back to the rapidly accumulating backlog of work on his very long (and growing) list of commitments.
9
At a Crossroads
MARBURG, 1911
Dans les champs de l’observation, le hasard ne favorise que les esprits préparés. (In matters of observation, chance favors only the prepared mind.)
LOUIS PASTEUR, Lecture, University of Lille, 7 December 1854
When Galvani’s laboratory attendant saw the leg muscles of the sensitized frog quiver, he had discovered a fact; Galvani himself had not noticed it at all; but when this great scientist was told of the fact, there flashed through his brain a brilliantly intellectual thought, something altogether different from the gaping astonishment of the attendant or the unknown current passed along the frog’s leg; to him with his scientific training was revealed the vision of extensive connections with all kinds of known and still unknown facts and this spurred him on to endless experiments and variously adapted theories.
H. S. CHAMBERLAIN, Foundations of the Nineteenth Century (1899)
A Christmas Gift
Alfred Wegener Page 40
