For Wegener it was a pleasure to meet and befriend Exner, but there was much else for him here. For the first time he met the young Swedish meteorologist Tor Bergeron (1891–1977). Bergeron, a protégé of Bjerknes, had spent the winter of 1917/1918 reading Wegener’s Thermodynamics of the Atmosphere and was completely engrossed in it because it was the only source he could find to feed his own fascination with the physics of clouds.16 Wegener also met Johan Sandström (1874–1947), whose work on the thermodynamics of layered ocean water provided Wegener much to think about in terms of his own work on the atmosphere.17
Wegener found in Bergen that he was known, understood, and admired. He also found that while controversy swirled around him, he need not always take sides. The Norwegians and the Swedes were undisputed leaders in the study of ocean circulation and layering, and Bjerknes had long aimed to match that leadership in the realm of meteorology. Both dynamic meteorology and dynamic oceanography were fertile grounds for controversy. The controversy between Exner and Bjerknes was both long-standing and bitter, but there was no need for Wegener to take any role in it, because he was, by his own admission (and everyone else’s admission), not a dynamic meteorologist. He enjoyed the same immunity in Hamburg, where he could easily refrain from taking sides in the bitter and protracted dispute between Carl Brennecke, his colleague in Hamburg, and Alfred Merz (1880–1925), Brennecke’s Berlin counterpart, in the determination of cause and character of the deep-water circulation in the Atlantic.18 These disputes involve theoretical positions so close together that it might seem (in retrospect) that they involved the “pathology of small differences.” This would be a mistake: while a controversy is alive, even the smallest details seem important, and only years or decades after the fact, when the question is decided, do these differences become small. In any case, Wegener, in Bergen, was the friend of all and the enemy of none.
Wegener was deeply affected by the sense of goodwill and scientific community he found in Bergen. He had a chance here to “see himself” outside of Germany for the first time in seven years. That he should feel close to the Scandinavians was no surprise, given his work with Koch in Greenland; he was known and respected as a “man of the North,” both in meteorology and in exploration. But there was another and more striking change: he was meeting younger men who had been affected by his writing, as well as older men who accepted him as a colleague both because of the quality of his scientific work and because of his position at the observatory in Hamburg. He was not someone who required the approval of others; now, others wanted approval from him.
Wegener and Exner traveled back from Norway to Germany together, and Wegener urged Exner to stay on for a few days at Großborstel. During his stay, Exner gave a colloquium at the observatory, and the response was so positive that Wegener decided to establish a regular geophysical colloquium at Hamburg. He had, both at Mülhausen and at Sofia during the war, organized colloquia that brought stimulation to his young subordinates and local colleagues. Though the geologists at Hamburg had made it clear that they had no interest in Wegener’s work, there were physicists and geophysicists at the university (including his helpful colleague, the young seismologist Ernst Tams). He had the education and careers of his own assistants and colleagues at the observatory to think about, and even some students from the university. Karl Frisch (1892–1953) had come to Hamburg from Dorpat to study with Wegener. He was Wegener’s first PhD student since Walther Brand—before the war in Marburg—and Frisch was working on atmospheric layering; Wegener eventually assigned him a thesis topic to study the structure of inversion zones in an atmosphere without turbulence, a difficult problem and a good beginning for Frisch’s successful career.19
Hamburg was a major seaport and a major rail terminus, as well as an easy destination for scientists from both neutral countries and the Central Powers in the First World War (Holland, Denmark, Norway, Sweden, Finland, Austria, Hungary, and Serbia). Alfred, Kurt, and Köppen began regularly to attach invitations to their correspondence, and these quickly bore fruit. Willem van Bemmelen (1868–1941), a great early investigator of geomagnetism, had been the head of the Dutch scientific station in Batavia (Jakarta), and when he returned to Holland in 1920, Kurt got him to come to Hamburg. Köppen got his old friend and colleague Svante Arrhenius (1859–1927) to come and speak; they were both enthusiasts for a single universal language.20 Alfred’s old Greenland companions and supporters in displacement theory, Lundager and Koch, came, as did Sandström and Bergeron.
Vilhelm Bjerknes came several times, and he sent his sons one after another for a semester at Hamburg, during which time they lived at the Köppen-Wegener household. Almost all the invited guests stayed for several days in Großborstel, and Else remembered spirited conversations lasting far into the night: it was reminiscent of the intellectual excitement that characterized this household in the years before the war.21
Wegener was excited enough by what had happened in Bergen to shift his attention (temporarily) from climate and from the work on continental displacements back to meteorology. He had published a brief article in January 1920 in Meteorologische Zeitschrift (written in the fall of 1919) extending his theory of cold cloud precipitation to the formation of cirrus clouds. He had also written a very interesting short piece on considering the atmosphere as a colloid structure when supercooled droplets were interacting, referencing there the idea of Brownian motion. It would take us too far afield to consider this argument in detail, but it shows that Wegener’s physical imagination, even with this deep involvement in geography and climate, was still vital and productive.22 While he did not begin a new research program in meteorology on returning to the observatory in August, he did decide to shift his teaching at the university, for at least one term, from climatology to “Weather and Weather Bureaus,” probably an introduction to the new forecast network that Bjerknes envisioned, using protocols that (Bjerknes hoped) would be adopted by the League of Nations.23
For the book on displacements, the summer of 1920 was a time for reading proof, thanking friends and collaborators, and waiting for the finished book to appear. Wegener wrote to Cloos in June, thanking him for his help in locating geological references to the first edition, and again in July, requesting an opinion about the work of Leopold Kober (1883–1970); apparently Wegener was now reading prospective manuscripts for Vieweg on geological topics. He wrote to Cloos again on 1 October 1920 to tell him that the book had come out, expressing his hope that in its new form it would be more widely read and make an impression sooner rather than later. He also added, touchingly, “Thanks for your expert advice about what I can do to speed up the process of the adoption of my ideas, so that I may live to see the result.”24
Sometime in the period between the sending off of final proofs in July and the appearance of the second edition of Die Entstehung der Kontinente und Ozeane in October, Wegener was able to help Köppen work his way through the final draft of the first of the two articles for Petermanns. Köppen had constructed his argument to show that the pathway led from paleontology to geophysics and not the other way around. It is important for us to consider this article in more detail, because both Köppen and Wegener declare that they wrote it together, and it expresses both their views; it is therefore a part of Wegener’s scientific development, even if it appears under someone else’s name.
As we noted above, Köppen had begun the paper with the history of attempts to explain past climates, aiming to show how both the displacement of the poles and the relative displacement of the continents were required to match the history of two data sets. The first was a shift through time of latitude zones based on the fossil record for given locales. The second was Theodor Arldt’s compilation of fossil data concerning the connection, or lack of it, between different regions of Earth in different periods.
The core of the article was a discussion to accompany “Maps of the Earth for the Carboniferous and the Quaternary.”25 In introducing the maps, Köppen requested the following of his rea
ders: “In the following journey through the history of the earth, pursuing the question of the changes in the position of the poles and the continents, I would ask you if possible to have a globe ready to hand and not simply make good with a world map; a small globe of about 10 centimeters diameter is sufficient to the task and very convenient. Only,” he continued, “by the use of this means is one safe from the sort of glaring errors to which, for instance, Diener (for example) fell prey in an attack on Wegener’s first edition whereby he believed that with a South Pole in Natal [South Africa] the corresponding North Pole would be between Florida and Bermuda.”26
The maps, five in all, appear in the published version in a foldout at the end of the issue. These were the maps Wegener had not had time to complete before sending his manuscript to the press. They marked a significant step in his visualization of continental displacements and included new map projections and new conventions of representation. Wegener used two different kinds of equal-area maps. In his figures 4, 6, and 7, showing the movements of the pole, he used the “oblique orthographic Lambert azimuthal equal-area projection.” Translated into ordinary English, this is a Lambert equal-area map with true directions away from the center, drawn to show Earth as a sphere and not a flat surface (thus “orthographic), and with the pole not at the top of the map but inclined slightly toward the viewer (thus “oblique”). He had used this projection in his second edition in the map showing the clustering of the various portions of Gondwanaland.
Wegener and Köppen’s calculated paths (for both hemispheres) for the displacement of Earth’s pole of rotation from the Carboniferous to the present, on a Lambert oblique equal-area projection. The continents are in their present position, and the latitudes and longitudes are calculated from the current position of Africa. From W[ladimir] Köppen, “Polwanderung, Verschiebungen der Kontinente und Klimageschichte,” Petermanns Mitteilungen 67 (1921).
These maps show Earth as a sphere, with lines of latitude and longitude curving as they would on a globe held in the hand. The position of these lines, the Gradnetz (graticule), shows Africa in its current latitude and longitude. This was a convention Wegener would maintain ever afterward: arbitrarily holding Africa in its current latitude and longitude, and measuring all continental motions relative to the current position of Africa. In his scheme of (absolute) continental motions, Africa had probably moved the least, sliding a bit northward in the Carboniferous, but remaining largely fixed, or oscillating slightly north and south. There were good reasons to do this, but it would be a source of considerable confusion, as many readers then and now have imagined that he thought that Africa had never moved, and never would, and this is not the case. It is also worth noting that Kreichgauer used a similar oblique orthographic projection to show the path of the pole, on the title page of his Die Äquatorfrage (1902).27 The more one looks, the more Wegener and Köppen seem to owe to Kreichgauer.
Wegener’s figures 1 and 2 use a different projection, this time borrowed directly from Kreichgauer’s use of the same in his work. This is the Mollweide equal-area projection of a sphere on an ellipse, obtained by stretching out the equatorial diameter to be twice as long as the polar diameter. The linear distances are true only on the major axis (the equator), and shapes become more distorted the farther away they are from the center of the map. It was a favorite of geographers and paleogeographers because it showed the whole Earth on one elliptical map. Astronomers liked this map because it allowed them to show the entire celestial sphere, and meteorologists liked it because it is ideal for drawing isobars and isotherms for the whole planet in a single view.28
Wegener and Koppen’s map, on a Mollweide projection of the whole Earth on an ellipse, showing the position of the continental blocks and the parallels of latitude in the Permo-Carboniferous. Outlines of the present continents are shown with dotted lines, and the paleoequator of the early Carboniferous is shown as a dot-dashed line. The graticule is that of contemporary Africa. From Köppen, “Polwanderung.”
On these maps, Wegener displayed two data sets simultaneously: the difference between the continental positions in the Permo-Carboniferous (his fig. 1) and those in the Quaternary (his fig. 2), and the displacement of the equator through time. Seeing Earth represented thus takes a little getting used to, but one can see very quickly that it allows one to superimpose, as curving lines, the positions of the equator in previous periods and how they pass through different parts of the continents than they do today. Once again, he represented Africa in its current latitude and longitude on the Gradnetz in both maps, while arranging the other continents relative to Africa and to one another depending on the time in the geological past. Thus, in the Permo-Carboniferous map (his fig. 1) South America is snugged up against Africa in its current position, and in the Quaternary map (his fig. 2) it has moved far to the west of a “stationary” Africa.
Wegener derived the maps of the displacement of the equator and the maps showing the path taken by the migrating poles of Earth under the influence of the shifting continents from paleontological data about plants and animals at different latitudes at different times. Köppen had contrasted this strategy very strongly with the attempts by Wegener’s predecessors, Simroth and Kreichgauer. Simroth had a fixed idea that the poles had swung back and forth like a pendulum, and Köppen criticized him for trying to shoehorn empirical data into this fixation, in the context of a nearly impenetrable book in which he had “ridden the idea to death.”29 Kreichgauer, on the other hand, had been comfortably readable in his presentation and flexible in his attachment to the idea of a shifting crust over the interior of Earth. His problems had been a lack of sufficient data for continents outside of Eurasia and a mistaken picture of the physics of Earth.
Wegener and Koppen’s map, on a Mollweide projection of the whole Earth on an ellipse, showing the position of the continental blocks and the parallels of latitude in the Quaternary. The stippled area covering northern Europe, Greenland, and northern North America is the Quaternary glaciation. The graticule is that of contemporary Africa. A parenthetical at the bottom says, “Epicontinental seas are not represented.” From Köppen, “Polwanderung.”
This approach by Köppen, linking the work to predecessors, positioned Wegener not as a brilliant theorist but as someone in possession of enough adequate data to see the deficiencies of previous schemes and to inductively, not deductively, determine that the continents must move, and the poles must move as well, if we are to make sense of the empirical data at our disposal. That is how Köppen’s argument ran and how it concluded in a commentary on these maps, drawn by Wegener and reproduced by Petermanns with a craftsmanship and clarity that invoke admiration even today.
The second edition of Die Entstehung der Kontinente und Ozeane appeared in October 1920, to Wegener’s intense pleasure and excitement, and in November there was another major event: he turned forty. It caused him to reflect. When he had first thought of the idea of continental displacements, he had just turned thirty and was an unmarried instructor in physics and astronomy at Marburg who had liked the pose of the “brilliant theorist,” someone who drops in on an existing dilemma and provides a breakthrough idea. Köppen and Aßmann had encouraged him in this view of himself and thought that his ideas would lead to breakthroughs in meteorology, especially in the area of atmospheric layering. Now he was a forty-year-old government scientist with a wife and three daughters, as well as a veteran of the Great War and two expeditions to Greenland.
He could look over his work in meteorology with some satisfaction, but little that he had done had led to major breakthroughs in that scientific world. His work on atmospheric layering and atmospheric thermodynamics had certainly made an impression; his postulation of geocoronium and his notion of an atmosphere vertically segregated in terms of the abundance of elements were still very much in play. Yet the conference in Bergen in August 1920 made it clearer than ever that the next big steps in meteorology would be in dynamics, and that Bjerknes would lead the way. In t
his area Wegener could be a commentator and a resource, but not a principal player. Exner’s bitterness at having lost out to Bjerknes was not something Wegener felt himself, but he had to think about the direction his own career was going. He had no research program under way in meteorology, and other than his work on tornadoes and waterspouts—deliberately written in a way that suppressed his penchant for theorizing ahead of the data—his only original contributions to atmospheric physics in nearly a decade had been his papers on atmospheric optics and his speculations on concentric, intermittent zones of audibility.
His theory of continental displacements was, in 1920, by far the most prominent and interesting science associated with his name. Thermodynamics of the Atmosphere had received good and bad reviews, but no one had taken time to write book-length defenses of or attacks on his work in meteorology. In that world, even his most vociferous opponent, Felix Exner, was now on his way to being a close colleague and a personal friend. It was much different with his theory of continental displacements, which had generated a major controversy, and in which supporters and opponents (most of whom he had never met) had devoted considerable time and intellectual resource to defending or opposing his ideas.
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