Köppen was, in March 1921, reading final proof for the second article for Petermanns, and although he and Wegener could not make any major changes, they found that they could add a few paragraphs at the very end, without running over the page limit. Köppen had already written a list of eleven major points in the theory, a summary and conclusion to both papers. To this he and Wegener added a short section entitled “Remaining Questions to Be Clarified.”76
These questions are of some interest because they show just how far Wegener’s theory had moved in a decade from its original inspiration in the outline of the Atlantic continents. The Atlantic was now the most problematic part of the entire picture, and one of the most pressing work points was how the opening of the Atlantic had affected the relocation of Earth’s axis. Where did the North Pole move, and what was the effect on the total obliquity? The latter quantity, the obliquity, is the inclination of Earth’s axis with respect to the plane of the orbit.77 The effect of the opening of the Atlantic on the position of Earth’s axis was especially important, because of the movement of the Atlantic continents (mostly) toward the west while everything else moved toward the equator; the Westwanderung needed a special explanation.
The important question of the Atlantic continents led directly to a more general question. If it happens, as Wegener supposed, that the continents are thickening and elevating through time, what effect does this have on their movement? Does their velocity increase because of an increasing separation of the center of buoyancy from the center of gravity, or do they slow down because their greater bulk makes it harder for them to move through the Sima? Perhaps it could be that the Americas had torn off from Eurasia because the compression of North Asia, moving toward the equator, made that part of the continent thicker and made it harder for it to move through the Sima; thus, did the thinner western section tear off and drift away?
How could the paleontology of the Southern Hemisphere be integrated with what happens in the Tertiary and Quaternary movements of the pole? Wegener and Köppen had interpreted the paleontological data for the Northern Hemisphere to indicate that the North Pole was oscillating back and forth, with swings of 10°–20° in the past 20,000–30,000 years. This they inferred from the rapid movement of climate zones in the Northern Hemisphere. What about the Southern Hemisphere? Were such short-term rapid swings characteristic of any earlier geological period, and were they related in some way to other known astronomical periods of Earth’s axis?
Not all of these are questions that they intended to answer themselves, though they would certainly try, and on the physical side this would mostly be work for Wegener. They knew that in any case they needed to build on the momentum of the Berlin symposium. The twentieth meeting of the Deutscher Geographentag was to be held in Leipzig at the end of May, and Wegener would go and give a shorter version of his Berlin address. Köppen was preparing a shortened version of his two articles for Petermanns for the Geologische Rundschau. It was not likely that a contribution from Wegener would be welcome there, but Köppen had a huge reputation, and in any case Hans Cloos had joined the editorial board in 1921 and was most likely the conduit for this article.78
They decided on the following plan of action. Wegener would reorganize and rewrite the material of the second edition following the division of his presentation at Berlin, dividing the evidence discipline by discipline. This had the advantage that members of the component disciplinary communities they were trying to reach could find, in one place, the results and remaining issues to be resolved to which these disciplines could uniquely contribute.
Wegener would pursue this work in the two days per week he was spending at the aerological station at Großborstel. Though there was no observational work there other than the releasing of pilot balloons, his employment contract still specified his right to work there two days a week, and he could split his time between his work on displacements and work on the theodolite that he and Kuhlbrodt were trying to modify. In the summer of 1921 they took a prototype of their new instrument on a cruise on the research ship Poseidon, in the North Sea, and learned enough to settle on a design they could fabricate at Hamburg in winter 1921/1922.79
Wegener and Köppen together would continue their work several evenings a week on pole positions and paleoclimate. Moreover, Köppen had made a decision to update and expand his own textbook of climatology, incorporating his thinking of the past few years into the first major revision of his scheme in more than two decades. His longtime publisher, Goschen, had been merged in 1919 with the publishing house of Walter de Gruyter in an era of tight money, scarce paper, and skyrocketing printing costs. Köppen’s 1918 revision of his classic scheme had a short press run and had sold out quickly. De Gruyter had more resources and was willing to consider a new and much larger edition; the new book would be three times the size of the previous one.80
We know very little about Wegener’s activities from September 1921 through March 1922, other than that during those months he was hard at work researching and writing the third edition of his book on the origin of continents and oceans, doing his job at the observatory, and teaching at the university. Else’s memoir of her life in Hamburg gives few details of their life during this year. She has vivid individual anecdotes for the “Hamburg years,” but these are notably disjointed and out of sequence when compared with her recollections of earlier and later periods in her life with Wegener. It was a difficult time for them and became progressively more difficult the longer they were in Hamburg, with the shortages of food, fuel, and clothing, the skyrocketing inflation and consequent lack of money, Wegener’s endemic fatigue from driving himself too hard, and three small children to care for.
We can derive some information about the process of composing the third edition of his book on continents and oceans by looking at the notebook he began in November 1920. Almost none of the material in this notebook can be matched verbatim with what appeared in the published version of the third edition; these are notes and extracts from a variety of sources on a variety of topics. In the first dozen or so pages of this notebook there is a good deal of geology and geophysics, but as Wegener moved along, geology and geophysics gave way rapidly to the collection of citations to paleontology, and these in turn gave way to geological distribution of glacial, desert, and coal deposits. As these notes accumulated, they became longer and longer and tended to become divided by topic, and by the end they were barely short of page drafts for a projected manuscript.81
These notes fit with another story. Wegener later wrote that in the process of researching the book it became clear that the material on paleoclimatology was beginning to outweigh the rest of the evidence for displacements. He had wanted to make sure that he devoted nearly equal space to each of the lines of evidence involved in advancing the displacement theory: geophysical, geological, paleontological and biological, paleoclimatic, and geodetic. These were categories he had used in 1912, and they represented distinct groups of scientists publishing in different journals.82 He wanted to treat their work as equally important and equally worthy of discussion.
Additional evidence for his deeper focus on climatology comes from his teaching. Wegener was nominated for an extraordinary professorship at Hamburg in March 1921, shortly after his Berlin triumph, and this was confirmed in July. This had happened very fast and was very promising: it bode well for his ability to someday become a full professor at Hamburg or elsewhere.83 The course he elected to teach in the fall of 1921 and spring of 1922 was his course on climatology first offered from April to July 1920. For the Easter term, April–July 1922, he taught his course on weather and weather service but also added a course entitled “Climates of the Past.”84
The Third Edition of Die Entstehung, 1921–1922
Each of Wegener’s versions of his theory had a character sharply different from the one that preceded it. The first version, that of 1912, preserved faithfully the way in which the idea occurred to him and the way he filled out his original intuition. It
was dense and heavily geophysical: deeply concerned with gravity data, isostasy, solid mechanics, and strength of materials. In this version even geological topics such as mountain building and volcanoes were considered to be part of geophysics. The geological arguments were secondary and brief, and geology, paleontology, the theory of ice ages, pole displacements, and the difference of the Atlantic and the Pacific sides of Earth were all shoved together as “arguments from geology.”
The first book-length version, in 1915, pursued and expanded the initial conceit of a “Copernican rewriting” of Eduard Sueß’s Das Antlitz der Erde. Wegener expanded the treatment of geophysics (though that was already most of the paper of 1912) in a redundant and repetitive way, taking up more than sixty of the ninety-four pages of this brief book; he compressed the geological and paleontological evidence down to about twenty-five pages.
The second edition of the book, in 1920, was driven by Wegener’s desire to respond to his critics. Responding in detail to criticisms of the first edition tied the book very closely to its predecessor, now expanded with more geophysical data, some novel cartography, and considerable speculation. Wegener wrote an analytical table of contents and a much clearer introduction. Still, one had to enter his theory through thirty-five very dense pages of Geophysikalische Erläuterungen (geophysical elucidations) of the continents, the continental shelves, and the floors of the deep oceans. Here fact, interpretation, and speculation were all mixed together.
The actual narrative history of the displacement of the continents was much improved in the second edition, but it was also extraordinarily dense, with new factual material once again side by side with speculation. The novel material on displacements of the pole, which followed immediately, was partly a defense of the theory and partly an attempt to show the utility of the theory in the study of past climate.
When Albrecht Penck had said that the second edition had not solved the problems of the first, he was talking about not just missing explanations (the mechanism) but the difficulties in the book’s structure, which made it so hard to read and understand. Wegener had said that the book was a “sketch,” but he also insisted that the book should be studied, not just read, and with a globe and a series of maps and reference books, and even monographic literature ready to hand. He had gone so far as to suggest that his readers might well obtain some tracing paper to make cutouts of the continents and perform his experiments on a globe. It was less a sketch than an epitome, and it embodied objectives in direct competition with one another.
In writing his preface to the third edition, Wegener made it clear how well he understood all this: “The third edition is again completely revised and differs almost as much from the second edition as this did from the first. The reason for this lies not solely in the fact that in the intervening two years an extensive literature has appeared that directly or indirectly concerns the displacement theory, but also and especially that the entire substance of the book has been cast in a new, and I hope, more convincing form, in which the essentials are better separated from the embellishments [Beiwerk].”85
The third edition is vastly better than any of the versions that preceded it: better structured, clearer, and easier to read. Its tone is cautious, diffident, and accommodating—to the critics of displacement theory, to the proponents of other views, and to the reasonable doubts of the general reader. It is conciliatory with regard to the problems and prospects of the land bridge theory and the theory of continental permanence, and it makes evident how much work still needs to be done to fill out the bare details of the displacement theory.
Wegener divided the book into three parts. The first is titled “The Essential Content of the Displacement Theory.” His intention for simplicity and directness is evident from the very first sentence, as is his decision to mobilize and re-create his own original inspiration. Here is how the book begins:
Anyone who has looked at opposite coasts of the South Atlantic must be aware of the similar shapes of the coastlines of Brazil and Africa.… Experiment with a compass on a globe shows that their dimensions agree precisely.
This striking phenomenon was the starting point of a new conception of the nature of the Earth’s crust and the movements that take place in it, which is called the Theory of Continental Displacements, or, for short, Displacement Theory, since its most striking component is the assumption of the great horizontal drifting movements that the continental blocks have undergone in the course of geologic time, and which presumably continue even today.86
Wegener then laid out the entire theory in all its aspects in two and a half pages of text and illustrated it with two pages of maps. He wrote in a relaxed and colloquial style, and the only specialist terms are names of different periods of Earth history:
According to this idea, for example, millions of years ago the South American continental surface lay right next to the African continental surface, so that they formed a single large block that, beginning in the Cretaceous period, split into two parts that afterward, like ice floes in water, moved ever farther from one another.… Similarly, North America was located close to Europe.… In the same way it is assumed that Antarctica, Australia, and India lay adjoining South Africa, and with the latter and South America formed, until the beginning of the Jurassic a single large … continental area, which … split and disintegrated into its individual blocks that drifted away from one another in all directions.… The three maps of the Earth reproduced in Figures 1 and 2 show these developments during the Upper Carboniferous, Eocene and Lower Quaternary periods.87
The maps that Wegener refers to in this passage appear on pages 4 and 5 and are, after the Mercator map of the world, some of the most reproduced maps in the history of cartography and are likely known to every schoolchild. Beginning in 1922, they were copied and repeated in nearly every publication for, against, or describing the theory of continental displacements. The maps are not the whole theory, but they are the basic outlines of the theory. Wegener drew them using the new convention he adopted in 1921, with lines of latitude and longitude reflecting the present position of Africa. He also drew in, as stippled areas, shallow “epicontinental” seas, representing areas of continental crust inundated at one time or another by shallow water. These were not deep oceans; they were water-covered continental areas. There were no mountains, as they would be too small to see on this scale, but he did put in the world’s great rivers and sketched the present-day outlines of the continents “only for identification.”88
The maps have some wonderful features. First of all, they are on facing pages and have identical polar diameters. The maps on the left-hand page are elliptical maps using the Hammer projection, similar to the Mollweide but inflecting the parallels of latitude slightly to decrease distortion away from the center of the map. On the right-hand facing page are the “pictures of the globe” of the Lambert oblique projection, with both hemispheres (for each period) presented side by side. The Hammer projection allows one to see the entire ensemble of continents at a glance clustered near the center of the map with minimal distortion. The Lambert projection emphasizes the extent to which, in Wegener’s theory, there has always been, since the first emergence of the land, a water hemisphere and a land hemisphere holding the single protocontinent.
The land-hemispheric part of the Lambert projections, with the North Pole obliquely facing the viewer, gives a clear visualization of that which Diener and others had found impossible to understand about the separation of the continents. Diener had claimed that Wegener’s theory required a 35° longitudinal gap between Siberia and Alaska which would later have to be closed. Wegener’s maps here make it easy to see that North and South America did not slide to the west uniformly but rotated away from Eurasia and Africa, first in the southern part, while Siberia and Alaska always remained connected by land or separated only by a shallow shelf sea, never by deep ocean.
Wegener’s maps of continental displacement, shown in the Hammer equal-area projection, from the third ed
ition of Alfred Wegener, Die Entstehung der Kontinente und Ozeane (Braunschweig: Friedrich Vieweg & Sohn, 1922). The three periods of geological history shown are the late Carboniferous, the Eocene, and the older Quaternary. Following his practice, Wegener held Africa in its current position (latitude and longitude) and moved the other continents away from it. The map therefore shows relative rather than absolute continental displacements.
The change in tone and attitude and the economy of expression are evident once again in the next chapter, in which he discusses the relationship of the displacement theory to the contraction theory (Theorie) and to the doctrines (Lehre) of land bridges and permanence. The change of emphasis here is subtle but telling: the shrinking of Earth was a general theory meant to explain everything—continents and oceans, connection and lack of connection between landmasses, the origin of mountains. Therefore, Wegener said, “the historical service of this theory cannot be denied; and for a long time it allowed us to construct a serviceable synthesis of our geological knowledge. In consequence of the long period in which the contraction theory allowed the integration of a very large quantity of individual research results, the great simplicity of its fundamental conception and the multiplicity of its applications, it retains a strong hold even today.”89
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