Here the pattern—imaginative and rhetorical—governing his work is in bold relief once again. He has been reading the literature and seeing ample evidence here and there (but never in one place!), allowing him to move from mere empirical published data, distributions of temperatures and other meteorological elements, to an organizing hypothesis and even to confirming evidence. He had done this with the cloud layers, and again in the seasonal variation of the altitude of the tropopause (the upper inversion), each time extracting a law-like conclusion from some set of them.
“One finds,” he wrote, “for this supposition [of a boundary layer at 70 kilometers] … a completely unexpected confirmation when one calculates the composition of the atmosphere in different altitudes.” If one examines the matter from this angle, he continued, “one comes to the astonishing conclusion that at precisely the altitude of the supposed layer boundary, the composition of the atmosphere changes with extraordinary rapidity, so much so that one is justified to characterize the area below the boundary as the Nitrogen Atmosphere and the layer above it as the Hydrogen Atmosphere.”85
Wegener was here arguing that the optical data had been confirmed by chemical data, and for him this was the more exciting point, since the latter notion (of the chemical differentiation of the atmosphere at altitude) was so widely accepted. What Wegener was doing here was not providing new data but once again integrating uncorrelated ideas into a unified picture capable of producing an explanation that others might and ought to have seen but had not.
When this article went to press in 1910, Wegener added the following footnote to his title: “Humphreys [William J. Humphreys (1862–1949), U.S. atmospheric physicist] had already carried out an investigation in 1909, Distribution of Gases in the Atmosphere in the Bulletin of the Mountain Weather Observatory II, which came into my hands only when this article was already in press, with the same calculations of the volume percentages of gases for the different altitudes and even employing the same graphical presentation used here, without however, drawing any broader conclusions from it.”86 For Wegener, priority and originality lay not in the realm of data but in the ability “to draw broader conclusions from it.” One mentions this because much of Wegener’s work ended up with divided priority, usually because he himself reported the parallel publication.
The data in question on the changing chemical composition of the atmosphere with altitude had been in the literature since 1903. Julius Hann had published an article in Meteorologische Zeitschrift in 1903, when the investigations of Teisserenc de Bort and others were making it starkly clear that the “Weather Zone” of the atmosphere, where turbulent mixing took place, was the limit of vertical circulation, and that cyclonic and anticyclonic systems were trapped between the surface of Earth and the tropopause a scant 10 kilometers above it.
Hann had immediately seen both thermodynamic and chemical conclusions to be drawn from the existence of the upper inversion, conclusions drawn directly from Dalton’s law of partial pressures, whereby each gas in a mixture of gases behaves independently of the others, based on its temperature. If one knows the mean temperature at a given altitude, one can calculate the partial pressure of any gas at that altitude. Hann had estimated the mean temperature of the atmosphere at 0, 10, 20, 50, and 100 kilometers and calculated the percentage (by volume) of nitrogen, oxygen, argon, hydrogen, and helium, for each of these altitudes. This produced the astonishing conclusion that while the percentage of nitrogen in the atmosphere is virtually the same at 50 kilometers as at the surface, at 100 kilometers it had fallen to 0.1 percent, while hydrogen, composing only 0.01 percent of the atmosphere at Earth’s surface, at 100 kilometers is 99.4 percent of the atmosphere.
Wegener (and apparently W. J. Humphreys in the United States at the same time) had interpolated temperature data for 10-kilometer intervals from the surface to 200 kilometers and produced both tabular and graphical data showing the very rapid decrease in the percentage of nitrogen with altitude from 79.7 percent at 50 kilometers to 57.9 percent at 60 kilometers, 24.3 percent at 70 kilometers, and 6.6 percent at 80 kilometers.
Once the turbulent mixing of gases at the surface was no longer a factor, the atmosphere would necessarily, Wegener reasoned, begin to layer out based on specific gravity, producing a very rapid decrease in the presence of nitrogen and in the disappearance of oxygen in all but trace amounts above 60 kilometers. In order to introduce his diagram, Wegener gave the following introduction:
In the graphical presentation one can see with great clarity the marked boundary between the nitrogen and hydrogen atmospheres. The cause of this extraordinarily sharp separation is the gross difference in a specific gravity of N and H. It is clear that the transition must continue longer the smaller this difference is. On the other hand, the gases would have a tendency to separate from one another and form layers in direct proportion to the difference of their specific gravities. What is of interest in this connection is that the sudden change in composition occurs just at the altitude at which we, on entirely separate grounds, have hypothesized a boundary surface.87
Alfred Wegener’s reasoning on chemical grounds for a sharp boundary in the atmosphere at 70 kilometers was bold, original, fascinating, and almost entirely incorrect. There is an important change in the atmosphere in this region between 60 and 100 kilometers, as Hann had shown. But current conceptions (those of the early twenty-first century) argue for turbulent mixing and therefore constant composition of the atmosphere up to about 100 kilometers, with that surface taken as actually the outer boundary of the atmosphere, with about 99.5 percent of the atmosphere’s mass below that level (figures that Wegener and Hann also knew).88
The point, however, is not whether Wegener was correct, but whether his arguments were well founded at the time he made them, which they were. There is a significant boundary in the atmosphere near where he put it, now known as the “mesopause.” The atmosphere above 100 kilometers is mostly hydrogen. The analysis of the spectrum of the aurora does shed light on the composition of the atmosphere, just as Wegener said it would. The aurora does indeed extend from altitudes of about 500 kilometers down to the surface of Earth, though there are frequency maxima near 200 kilometers and 60 kilometers, with the former showing similarities to hydrogen spectra and the latter to nitrogen spectra. All this is in Wegener’s paper.89 Further, the absence of oxygen between 150 and 100 kilometers, where most shooting stars appear, does mean, as Wegener claimed it did, that they are not burning but vaporizing, and that their spectra as they glow do allow analysis of the composition of the atmosphere at the altitude observed.
It is a slight irony that where Wegener was most certain that he was right he was most certainly wrong, and where he showed caution and tentativeness in his conclusions he was more nearly correct. One hastens to add that our current conclusions concerning the character of the upper atmosphere belong to the era of rocketry and investigation of the “ionosphere,” 1945–1960.
Near the end of the paper, Wegener ventured some highly interesting if guarded speculations concerning the outermost layers of the atmosphere. The idea of a hydrogen atmosphere with a sharp limit, he wrote, offers an interesting analogy to the Sun, where (in the chromosphere) a strongly delimited hydrogen sphere could be detected. “Perhaps one could in the future push this analogy a little further and above the Hydrogen atmosphere find another atmosphere made of a still lighter gas corresponding to the Coronium of the Solar Corona within which the highest polar lights play and which, just as Coronium, gives a green spectral line at 532 Å units producing the known line in the northern lights at 557 Å units.”90
Wegener’s picture of the layering of the atmosphere based on chemical composition. The horizontal axis is the percentage of a given atmospheric component; the vertical axis is altitude. Sauerstoff = oxygen, Stickstoff = nitrogen, Wasserstoff = hydrogen, Wolken-zone = cloud zone, Porlarlicht = aurora, Grenze der Dämmerung = twilight limit, and Leuchtenede Nachtwolken = noctilucent clouds. From Alfred Wegener, “
Zur Schichtung der Atmosphäre,” Beiträge zur Physik der freien Atmosphäre 3 (1910): 33.
Wegener did not, out of the blue, hypothesize the presence in Earth’s atmosphere of something very like an element “Coronium.” Julius Scheiner, the lone stellar astronomer at Berlin during Wegener’s time there, had in his book on the spectra of stars (1898) suggested that such a rare, light gas might be found in the upper reaches of Earth’s atmosphere. The spectrum of the aurora (Polarlicht) was intensively investigated in the first decade of the twentieth century, and Wegener was well read in this work.
Moreover, suggestion of new and rare elements was a common subject of speculation then as now. Helium had been discovered as an element in the analysis of the solar spectrum during the eclipse of 1868, and in 1869 a new spectral line near 530 Å had been suggested as the signature of an extremely light gas: coronium. This element was still under consideration as late as the 1930s. Dmitri Mendeleev, using the same logic that led to his discovery of germanium, had, in 1904, proposed an extremely light element of atomic weight 0.4 and suggested that this element was identical with the “Coronium” detected in the Sun’s atmosphere.
Wegener’s interest in these auroral spectra, on which he depended for his most important conclusions about the composition of the atmosphere, had several sources. First, auroras were a favorite subject of his old Berlin professor, Förster, and in Wegener’s November 1908 article for the Mathematisch-Naturwissenschaftliche Blätter, the house organ of the Berlin astronomy department, he had written a semipopular article about the auroral phenomena in Greenland and how they cried out for explanation. Like the composition of stars, the character of the aurora had moved from “things we shall never know” to “things we know well” through the development of spectroscopy.91
Second, Wegener’s Greenland work, including the time spent at Pustervig, had shown him that auroras, contrary to what he had read, do indeed descend nearly to the surface of Earth. This had bearing on studies of atmospheric electricity and magnetism, then being vigorously pursued everywhere and indeed locally by his professor at Marburg, Richarz. Finally, the interest marks him as a “cosmic physicist” since he was willing and even anxious to explore the analogy between the atmospheres of Earth and the Sun and had always in mind that Earth was a planetary body in orbit about a star and in constant interaction with the rest of the universe: elementally, gravitationally, magnetically, and electrically.
The picture of Earth’s atmosphere as a series of well-defined concentric shells marked by sharp surfaces of discontinuity, each with different physical properties, and (above 70 kilometers) different chemical properties as well, emerges here as the kernel for Wegener’s dream—as yet more a dream than a plan—to produce a comprehensive physics of the atmosphere. It is important to remember once again that Wegener was not part of the group (Bjerknes, Margules, and others) working on the dynamics and hydrodynamics of the “Weather Zone,” the troposphere, and therefore investigating that branch of study now called dynamical meteorology. Wegener’s atmospheric physics was what we now call physical meteorology, the thermodynamic, optical, and acoustic properties of the atmosphere at every altitude. For Wegener, the atmosphere was not the thin shell of ambient, breathable air, but all the regions above Earth that had any thermal, optical, or acoustic signature. Given the height of the aurora, this meant the envelope extending to 500 kilometers above Earth.
Wegener sent this paper off to Aßmann with considerable satisfaction and then turned to an analysis of his lot. He was back in Marburg, he had no students, and he had no money. He was actually reduced to begging. On 15 February 1910, he wrote to the Danmark Committee, asking them to please count the full month as having been work on the expedition results even though he had only worked half a month. He made a good show of work, pushing Lüdeling forward and asking for forbearance from the committee, assuring them that he was as anxious as they were to see the work finished.92
He had to find some way to make a living. With the Danmark work winding down and no students, he had no source of income. With his father, Richard Wegener, retired—and a man of modest means who was not much of a money manager—there was no hope or expectation that his father could be much help. Had he been chosen to join the Filchner expedition to Antarctica, he might have expected a new salary stream to begin with the late fall of 1910, when the expedition was scheduled to go to Spitzbergen for training, an income that would have continued for several years. Filchner, as we have noted, had amassed a great deal of money, and the members of the expedition were to be very generously paid. But as Wegener wrote to Peter Freuchen in March of 1910, this was looking more and more doubtful, to the point where Wegener no longer expected to be chosen, an outcome to which he was now more or less reconciled. He would now have to turn his attention to teaching and preparing a comprehensive course of lectures on physics of the atmosphere.93 His exploring work would be confined to his study in Marburg, and the closest he would get to the Arctic for the foreseeable future was the polar bear rug at his feet.
8
The Atmospheric Physicist (2)
MARBURG, 1910
A theory is the more impressive the greater the simplicity of its premises, the more varied the kinds of things that it relates, and the more extended the area of its applicability. Therefore classical thermodynamics has made a deep impression upon me. It is the only physical theory of universal content which I am convinced, within the area of the applicability of its basic concepts, will never be overthrown.
ALBERT EINSTEIN, Autobiographical Notes (1946)
Wegener’s decision to offer a course of lectures in the summer semester of 1910 at Marburg entitled “Physics of the Atmosphere” was an obvious choice under the circumstances. He had, after all, been brought to Marburg as a physicist; his expertise, though it did extend into astronomy, was in the physics of the atmosphere. On the way back from South America, he had conceived a plan (while working to extend his studies of atmospheric discontinuities) to begin the writing of a complete physics of the atmosphere. The transformation of meteorology into a physics of the atmosphere was spoken of everywhere, and a number of Wegener’s closest contemporaries were at work on it. Richard Aßmann’s strong desire to have a theoretician to replace Berson as Observator (and that is what Berson was, an observer), as well as his desire that Wegener should fill that role, had already, as we have noted, pushed Wegener further in the direction of theory.
Albert Einstein’s remark about the impregnability of classical thermodynamics, which serves as the epigraph at the head of this chapter, was made in 1949. Einstein had many times said that the best a theory might hope for was that it should become a limiting case of a theory of still higher generality. His characterization of classical thermodynamics seems to indicate that this theory, and this theory alone, would never suffer such a fate “within the area of applicability of its basic concepts.” Since these basic concepts include the law of conservation of energy and the second law of thermodynamics (which says that in an isolated physical system, differences in temperature, pressure, and density tend to even out), it is clear that Einstein was being characteristically droll. The area of applicability of these basic concepts is the universe as a whole. In fact, the third law of thermodynamics expresses the consequences of applying the first and second laws to the entire universe.
Within physics, the unifying power and impregnability of thermodynamics give it a special status that is not often noted in treatments directed at the lay public. Popular works on physics are almost invariably concerned with gravitation, electromagnetism, relativity, and quantum mechanics, and almost never with thermodynamics. The search for a unified theory of physics, whether this is found (as is the case in the early twenty-first century) in string theory or in loop quantum gravity, means the unification of gravitational, electromagnetic, and nuclear forces. In a larger sense, however, the unification of physics is already achieved in thermodynamics, which is universal. Thermodynamics covers everything from t
he very small to the very large, applies over any time interval, works with both living and dead matter, and applies to the quantum mechanical, relativistic, and classical realms.
It was obvious to Wegener that he should begin a general physics of the atmosphere with a study of the thermodynamics of the atmosphere. We may recall that in his early studies in Berlin he had taken Max Planck’s course in thermodynamics, in which Planck avoided reference to microphysical entities and instead developed the first and second laws of thermodynamics out of consideration of bulk properties of the world: temperature, pressure, and volume; he had even given special attention to the atmosphere. The latter reflects the very close attention given to such problems in Berlin by Hermann von Helmholtz (1821–1894) and Heinrich Hertz (1857–1894). In the 1860s Helmholtz, simultaneously with Julius von Hann (1839–1921) in Austria, was concerned with the problem of temperature changes in moist air as it rose and descended adiabatically.1 In 1884 Heinrich Hertz (then still at Berlin) had introduced a graphical method for determining adiabatic changes in the state of moist air, and this was further developed in 1886 and thereafter by Bezold in his “First Report on the Thermodynamics of the Atmosphere” and subsequent publications.2
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