Alfred Wegener
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What the table purports to show is indicated by the numbers clustered near the 1,500-meter mark. Wegener was convinced that he had discovered in Greenland evidence of a stable layer in the atmosphere at about 1,500 meters—a surface of discontinuity, whether or not clouds were present. It might be a little higher or lower, it might not always be present, but it was, he was certain, a persistent structural phenomenon. The evidence for this conclusion is indeed there, but it is extremely slight, and it bears careful scrutiny.
Of the four sets of figures in the table, the most reliable were the measurements of humidity and wind rotation: the increments and decrements of humidity are large—often several percentage points—and the wind rotation is easily read by the compass direction of the kite or balloon cable relative to its direction at the time of release. The wind speed data are somewhat suspect, because almost all of them are estimated. Wegener was claiming that he could detect, from cable tension, angle of flight, and the general behavior of the kite, variations in wind speed of the order of 0.5 meters per second (about 1 mile per hour).29 This may be the case, but even with highly developed craft skills, which he possessed, these are very fine discriminations. Then again, in the age of sail that Wegener inhabited, ship’s officers and crews were capable of such discriminations of wind speed by similar methods, such as feeling the tension of the rigging and looking at the bellying of the sails; the claim is not outlandish.
Wegener’s principal result from two years of work in Greenland. The shift in three meteorological elements (temperature, wind speed, and relative humidity) away from the trend of the values lower than 1,000 meters and those above 1,500 meters indicated to him the possibility of a new layer in the atmosphere. From left to right, the columns are as follows: Altitude Interval, Decrease in Temperature, Wind Speed, Wind Direction, and Relative Humidity. From Alfred Wegener, “Über eine neue fundamentale Schichtgrenze der Erdatmosphäre,” Beiträge zur Physik der freien Atmosphäre 3 (1910).
The temperature data, though they appear almost fanciful on first inspection, are probably real. Wegener’s bimetallic thermometers were capable of this accuracy. While normal ground-station thermographs with bimetallic thermometers are generally accurate only to about 0.5°C (1°F), calibrations of the kind Wegener carried out meticulously before and after each flight would have allowed ten times that accuracy. This would mean that he could discriminate with confidence an interval of 0.05°C.
Here is the result Wegener thought he had obtained: between 1,000 and 1,500 meters, the decrease in temperature with altitude suddenly slowed and even reversed slightly. At the same altitude, the wind speed, which had been dropping, increased again. The wind’s rotation, which had been decreasing, increased again, and the relative humidity, which had been increasing, dropped sharply, almost 5 percent. Wegener took these four trends as independent lines of evidence for his proposed surface of discontinuity in the atmosphere.
Before Wegener could make this crucial plunge into his data, however, he had to turn again to preparing the full ensemble of measurements to meet his expedition obligations. With his completed manuscript of the Greenland aerology data in hand, Wegener traveled to Denmark in late November 1908.30 The manuscript was much too valuable to consign to the post; it was his ticket to freedom from the expedition contract. Wegener interpreted the act of delivering this manuscript as proof he had completed his contractual obligation to work “full-time” on the scientific results of the expedition. This was in spite of the fact that he had only been at it for six weeks, and that everything else he had done in Greenland remained to be worked up. This new attitude grew out of a conversation with his friend and expedition comrade Johan Koch.
In talking to Koch after his correspondence with Prof. Warming in October, he had discovered that the Danmark Committee had let Koch “off the hook” on publication, asking only that he immediately complete the results of the “Great Sledge Journey” which would document the territorial claim to that section of Greenland. All of the other material—the geodetic triangulation, the detailed maps, the maps of the regions south and west of Cape Bismarck, and the repeated determinations of latitude and longitude at Danmarkshavn (in all of which Wegener had a hand)—would be published outside the volumes devoted to the Danmark Expedition. Wegener was annoyed by this imbalance in publication demands on himself as opposed to Koch, perhaps inflicted by his own dutiful naïveté, and resolved not to be bound any more severely than his closest expedition colleague.31
A New Atmospheric Layer
When he returned to Berlin, he closed himself off from everyone and everything and set to work. Meteorology has often been a passion of solitary men, but perhaps never more so than in Wegener’s case. He might as well have been at Pustervig still, or on the Moon, for all the contact he had with the rest of the world in these months. He calculated and reflected. He wrote. He smoked. From time to time he saw his parents. For the rest, he had no friends; he sought no amusements, and he rarely went out except to consult the library at the University of Berlin, to drink coffee, or to buy tobacco.
In one sense, the search for a context was quite simple. He had made a series of observations that indicated a discontinuity in the atmosphere at an elevation of about 1,500 meters. The simplest possible context for such a set of observations would be the record of other observations that exhibited the same layering. This is the first move in a theoretical exercise: it is the expansion of the data at hand, as well as the demonstration that one’s own empirical results are not anomalous or idiosyncratic. To find such confirmation, Wegener turned to the most obvious and nearest materials, beginning with the widely known results of Aßmann and Berson’s Berlin balloon observations from the 1890s. From these he moved on to an extensive set of observations made by Süring at Potsdam from 1904 to 1906, and then to Süring’s collection of the results from seven different meteorological stations around the world, published in 1907.32
The numbers (from Süring) that Wegener used to verify the existence of a fundamental discontinuity at 1,500 meters did not initially look very promising. Süring had been measuring cloud altitudes and trying to find the modal altitude for the different cloud forms. These indeed had particular altitudes: stratus most often at 0.6 kilometers (0.4 miles), fracto-cumulus at 1.6 kilometers (1.0 miles), stratocumulus and/or nimbus at 1.7 kilometers (1.1 miles), cumulus at 2.1 kilometers (1.3 miles), altocumulus and altostratus at 3.0 kilometers (1.9 miles), and so on up to cirrus at 9.0 kilometers (5.6 miles). Süring’s averaging of the results of the seven other stations around the world gave varying but comparable values: stratus at 0.5 kilometers (0.3 miles), cumulus at 2.0 kilometers (1.2 miles), but then altostratus and altocumulus at 4.3 kilometers (2.7 miles)—a rather large departure from Süring’s own observations. Note that, to this point, the numbers cannot have been much help to Wegener—a characteristic altitude of 1,500 meters is nowhere in sight. However, Süring, to reduce the discrepancy between his own cloud altitudes and those of the other stations, had made a separate calculation: without regard for the type of cloud, he had calculated the altitudes at which clouds of any kind were most frequently found. These altitudes were 1.6, 4.4, 6.8, 8.8, and 10 kilometers (1.0, 2.7, 4.2, 5.5, and 6.2 miles, respectively).
The latter numbers, the frequency maxima for the appearance of certain types of clouds, gave Wegener an altitude sufficiently close to his surface, which, after all, was itself an average of a number of values spread across the interval of several hundred meters (a mean for 1,000–1,500 meters, and a mean for 1,500–2,000 meters). He recognized that 1,500 meters could only be defended as a mean level—that his discontinuity was mobile—and he took this as his first task.
The type case for atmospheric discontinuity was, of course, the “upper inversion,” the tropopause. Via its ubiquity and its strength, it had created a benchmark idea of what a structural discontinuity in the atmosphere should look like. Wegener’s argumentative starting point was, therefore, that the tropopause was not the typical case
but the limiting case of atmospheric discontinuities.
Underneath this “great laminar boundary,” Wegener argued, from the surface of Earth up to the limit in the region near 10 kilometers, “the atmosphere is populated by a whole family of surfaces of discontinuity, which appear as stable layers, and which reveal themselves either as cloud surfaces, or in the absence of condensation, as stepwise jumps in the value of the various meteorological elements.”33 Unlike the tropopause, however, these layer boundaries were incompetent—easily broken through by adiabatically ascending parcels of air. As a result, the atmospheric phenomena in this lower region lost their simplicity, their consistency, and their completeness. They grew weaker and more rare with increasing altitude, and in consequence, “the law governing these layers is, in many instances, often completely concealed.”34
This framing of the phenomena allowed Wegener to use the statistical method he championed: “It is, in fact, a fruitless undertaking to try to fixedly locate these lower surfaces of discontinuity by investigating any single case. On the contrary, it is obvious that any law-like distribution of these layers will only be revealed in the mean alteration of the meteorological elements with [increasing] altitude.”35 This characterization of the situation, with these layers becoming less visible with altitude, allowed him to argue for the importance of “his” 1,500-meter layer.
He immediately pushed forward, in a companion paper running parallel to the first, to build this idea into the practice of meteorology by establishing it as part of an observational paradigm. The means of this advance was a novel correction factor in extrapolating the adiabatic cooling of the atmosphere, from an altitude where the values had been observed (say, 1,000 meters) to an altitude where the values were unknown (say, 1,500 meters). The so-called Zustandskurve (state curve) of the atmosphere was the basis of a standard graphical aid in meteorology and aerology, a nomogram containing two curves representing the fall in temperature (with increasing altitude) of a given volume of air. One of these curves represented the fall of temperature in dry air, and the other in saturated air. Such a diagram, in which these curves were printed on graph paper with intersecting isotherms and isobars, allowed simultaneous calculation of a variety of meteorological elements.
In a paper entitled “Über die Ableitung von Mittelwerten aus Drachenaufsteigen ungleicher Höhe” (Averaging the mean values for kite ascents to unequal altitudes) Wegener argued that in extrapolating from a known value to an unknown value, rather than using the dry adiabatic curve or the wet adiabatic curve, there was a third curve, intermediate between them, which represented not one or another ideal state of the atmosphere but the actual structure of the atmosphere. Rather than use the theoretical extrapolation for the full atmospheric column based on a uniform change in the meteorological elements with altitude, one used the observed mean difference, over many observations, between the elements at 1,000 meters and the elements at 1,500 meters. He showed that the mean value of the change between 1,000 and 1,500 meters, when applied to the 1,000-meter value, always gave more accurate values for the meteorological elements at 1,500 meters than theoretical extrapolation alone.36
This does not sound like much, but it makes an important point: purely theoretical calculations taken by themselves are misleading and need to be empirically modified. Wegener is here arguing that the empirical Zustandskurve of the atmosphere contains a knick point at 1,500 meters, which ought to be graphically represented every bit as much as the upper inversion—the discontinuity between the troposphere and the stratosphere. His point was not the importance of any given layer, but rather that the future advance of the science of meteorology lay in turning an idealized, generalized, homogeneous, theoretical atmosphere into a real, specific, layered, empirical atmosphere—via aerological discovery.
Aßmann’s enthusiasm for Wegener’s correction factor (Wegener had described it to him in 1908 at the Hamburg meeting) was very much the driving force for writing this paper immediately. In late January, Wegener wrote to the committee of the Danmark Expedition asking for permission to publish it, because “in this article a problem is discussed for which I have worked out a new calculation method which Herr Geheimrat Aßmann will recommend for general adoption at the international meeting, on April 1 in Monaco, of directors of aerological institutes.”37 This, of course, was great news for Wegener, because it was a validation not only of the existence of his layer but of Wegener’s more general, semiempirical and statistical method of determining discontinuities within the atmospheric structure.
Marburg
With one year of postdoctoral work at Lindenberg and two years of field experience in Greenland, Wegener was working well within the conceptual frames he had inherited from Wilhelm von Bezold and Richard Aßmann. On the theoretical side this meant the extension of atmospheric thermodynamics through the study of boundary layers and discontinuities. On the empirical side it meant kite and balloon aerology and manned balloon ascents using standard instrumentation in standard ways.
Wegener’s appointment as a technical assistant at the Aerological Observatory at Lindenberg expired on 1 January 1909, along with the leave of absence granted in April 1906. The Danmark Expedition committee was still paying him a stipend, though this also would expire in a few months, leaving him without employment or funds. He had some savings from his expedition salary, but much of that sum had been eaten up beforehand in equipping himself for the expedition, and the remaining savings would not last long.
There was, he had concluded, no real future for him at Lindenberg as a technical assistant. Berson was apparently solidly in place as the Observator, and whatever Aßmann’s original plans for staffing the institution, the turnover of technical assistants was very rapid, with most of the helpers staying only a year or two. This mirrors the turnover of support staff at Lindenberg at all but the very highest levels, and by the time Wegener returned from Greenland there was no longer any expectation that he would remain in his position, nor was their much intellectual continuity or promise of community.
The obvious alternative, and in fact the only alternative, was a university position as a Privatdozent (instructor). At some point in January 1909, Wegener decided in favor of pursuing this option at the University of Marburg. Marburg was a city with a population of approximately 20,000 located in Prussia, in the state of Hesse-Nassau, about 100 kilometers (60 miles) north of Frankfurt, on the main line of the Prussian State Railway. The university was a Protestant shrine of sorts, the first Protestant university in Germany, and in 1905 had about 1,500 students. Contemporary photographs, as well as the early twentieth-century paintings by the Marburg artist Karl Bantzer (1857–1941), show a completely rural landscape surrounding the Oberstadt (the hill containing the old town, the palace, the Lutheran church, and the university), with some of the nearby agricultural open land already returning to forest. In Wegener’s time there were mature and extensive forest tracts around Marburg, in spite of the region’s relatively dense population.
At the time of Wegener’s decision to move to Marburg, in 1909, the professor of physics and director of the university’s Physics Institute was Franz Richarz (1860–1920), well known for his work on the interaction of light and electricity. Richarz had made persuasive speculations about atomic charges and had edited textbooks on both theoretical physics and Earth’s magnetism. Richarz had also been a close colleague of Paul Drude (1863–1906) and, at about the time of Wegener’s application, had become interested in using manned balloons to map variations in Earth’s magnetic field, with a fledgling program of this kind under way around Marburg.
This was a good fit for Wegener. Richarz was known to be sympathetic to the claims of meteorology to be recognized as a science. Moreover, many of the doctoral students in physics at Marburg were training to be high school teachers (Oberleher), and this meant that the department was also sympathetic to the claims of cosmic physics (at this time a standard high school subject but not one in which professorial positions were availabl
e at the university level). This was also a plus for Wegener. Finally, the physics department’s close connections with both Berlin and Göttingen also implied a strong sympathy for geographical exploration and expedition science.
The application process for the Marburg position created an entire new stratum of work and correspondence for Wegener, to be completed immediately, on top of the consuming activity of his original scientific work and his continuing work on the Greenland data, including the minute and laborious correction of proofs from the Greenland aerology manuscript submitted to the Danmark Committee the previous November.
Wegener’s chief recommenders for the Marburg job were his old professor from Berlin, Wilhelm Förster, and his recent supervisor at Lindenberg, Richard Aßmann. Förster sent a positive but entirely perfunctory recommendation to Richarz on 8 February 1909 endorsing Wegener’s Habilitation at Marburg, describing his dissertation as “solid” and “valuable,” and expressing the likelihood that “his work as an investigator and teacher will be competent.”38 Aßmann, on the other hand, sent a superlative recommendation. “Dr. Wegener,” he wrote, “is in every respect an excellent man and it is extraordinarily regrettable for my observatory to have lost him. Solidly trained, and endowed with sharp understanding and a rich scientific imagination, he is industrious, energetic, and persistent, the prototype of the most strenuous, most ambitious sort of young scholar, who, unless I’m much mistaken, will produce very significant work.”39 Aßmann went on to praise Wegener’s personal qualities: “Moreover he is on the personal side, a pure type, a high-minded and likable man, the sort of person who would be desirable in any academic setting.”40