Wegener’s maps of continental displacement, shown in the Lambert oblique equal-area projection, from the third edition of Die Entstehung der Kontinente und Ozeane (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. This map, like its partner above, shows relative rather than absolute continental displacements.
Contrasted with the contraction theory, the doctrines of great sunken land bridges and of the permanence of continents and oceans are much more limited in scope. “The relation of the displacement theory to both these doctrines is different from the contraction theory. To anticipate the results, the arguments that are led out into battle by both of these doctrines are correct. Each is based on only that portion of the facts necessary for a favorable judgment and receives its refutation immediately once the other portion of the facts is introduced. The displacement theory will fit the entire facts and therefore prepares the way for a reconciliation of these hostile doctrines in a manner which satisfies all reasonable demands of both parties.”90
Wegener had now completely recast the theoretical situation once again. The contraction theory was a universal theory that explained all the known facts of geology and paleontology in terms of a single organizing principle: the contraction of Earth. The doctrine of great land bridges became a foundation of paleontology because its adherents assumed that the contraction theory was true, self-evidently so, and did not require further proof.91 The contrary doctrine of permanence of continents and oceans was not a biological but a geophysical doctrine. The principle of the general permanence of the continental blocks was sound, wrote Wegener; the present continents, with but a few exceptions, have never in the history of Earth been part of the floor of the ocean but have been as they are in the present: continental platforms.92 He continued, “While we thus must completely reject the contraction theory we need only to scale back the doctrine of land bridges, and the doctrine of permanence, to the conclusions that can be legitimately drawn from the argument advanced for them, in order to reconcile these apparently so opposed doctrines by means of the displacement theory. That theory says: land connections, yes, but not via former bridge-continents, rather by direct contact; permanence, not of individual continents and oceans as such, but of the oceanic areas and the continental areas taken as a whole.”93
Wherever possible, Wegener defended his ideas with the ideas of his supporters and, preferentially, with ideas from his opponents. To point out the weaknesses of the idea that land bridges rise and sink “as needed,” he cited the misgivings of Bailey Willis and Albrecht Penck, both strong supporters of the permanence of continents and oceans. When defending his choice of Airy’s “roots of mountains” and the floating-continent version of isostasy, he used as an authority Schweydar’s remarks in the Berlin symposium in February, not his own explanations.
These extracts from the first pages of Wegener’s third edition convey the different tone of this version of his theory and the extent to which the role of arbiter has replaced the role of a partisan combatant. In place of brash certainty, startling novelty, and individual effort, we see generosity toward opponents, caution in assertion, gratitude for the efforts of the great geologists of the past, hope for reconciliation of views, awareness of difficulties, and finally the characterization of displacement as an idealistic attempt to bring back together the unity of geology lost in the fall of the contraction theory. This approach and voice continue in the next section of the book, entitled simply “Beweisführung” (Presentation of the evidence).
In this next section Wegener radically reformulated what counted in his theory as evidence (Beweis). He made a firm decision to strip out conjecture and inference to things that could not be seen, in favor of observational evidence. Everything outside the ensemble of visible evidence he moved to a different category: Erläuterungen und Schlußfolgerungen. There are a number of reasonable translations of these two words; many English translators like “explanations and conclusions.” In this context, it would be more accurate to say “elucidations and inferences.”
Into this new category of “elucidations and inferences” went all of Wegener’s ideas about the viscosity of Earth and its paradoxical properties, temperature distributions in Earth’s interior, Earth tides, transgressions and regressions of the seas caused by polar shifts, whatever might lie beneath the ocean floors, the character of the underside of the continental blocks, the way in which folds and rifts might take place in the displacement of continents, the form and structure of the continental shelves, the causes of island arcs and ocean trenches, the differences between the Atlantic and Pacific coasts, and finally all speculations concerning the mechanisms and forces bringing about displacement of the continents. Most or all of these had been offered in both the first and the second editions of the book as evidences; they were now remanded to the realm of interpretations.
This third edition of Wegener’s Origin of Continents and Oceans was by far the most influential version of his theory ever published, as well as the only one widely translated and read outside Germany. His original articles in 1912 have only recently been translated into English, and the first and second editions of his book on continents and oceans have never been translated into English at all. The only other of his publications to find its way into English is a translation of Die Entstehung der Mondkrater by the geologist and historian of geology A. M. Celal Sengör.94
Wegener was generally well served by his first English translator, J. G. A. Skerl, and since Wegener reviewed the translation of the third edition of his book into English, he must bear the responsibility. Nevertheless, in a variety of ways the book gives a misleading impression of Wegener’s tone and replaces the tentativeness of his approach with a certain vehemence, which works very much against Wegener’s intention at the time. Throughout the book, Wegener used a variety of expressions to calibrate the depth of his confidence in his evidence: “these arguments imply,” or “this evidence would be difficult to shake,” or the “documented evidence for this is … ,” or “This is to my knowledge the first certain evidence for the soundness … ,” and so on. In each instance, Skerl translated the word in question as “proof”: “this proves,” “This is to my knowledge the first proof,” the “paleontological and biological proofs,” and so on. Similarly, he translated a phrase such as “confirmation of a long asserted principle” as “confirmation of the long postulated law.” Talk of presentations, evidences, and principles is very different from talk of demonstrations, proofs, and laws. The latter suggest mathematical and logical certainty, whereas the former merely suggest the balance of evidence that would likely produce a favorable verdict.
This question of attitude toward evidence is also of some historical importance because in this edition Wegener was above all trying to convince geologists, an audience that he had nearly abandoned two years before. In 1920, geophysics explained everything, and every geological detail was but an idiosyncratic departure from some general geophysical principle. In 1922, the geophysical explanations are still there, but everywhere there are complications, exceptions, and reservations. For instance, in this edition, as in every previous version of the theory, Wegener drew a cartoon schematic cross section through a continental block in the form of a large cube, perfectly rectilinear, with sharp borders, immersed in a medium, and adjacent to a thin rectilinear section of ocean water. There are three substances (Sial, Sima, water), three densities, and three behaviors—no ambiguity. In this edition, however, this schematic is accompanied by the following gloss:
It is essential to immediately exercise caution not to exaggerate this new conception of the ocean floors. As in the case of our comparison with tabular icebergs we must certainly also consider that the upper surface of the sea [here the Sima in which the Sial bergs float] between them can be again covered with new ice, and also further,
that small fragments of the iceberg that have become detached from its upper surface or have broken off from its foot can also cover the surface. In a similar manner this will occur at many places on the ocean floors.95
This is a response to the charge by Penck that his theory could not be true because fragments of continental material are found scattered across large sections of the ocean floor. Wegener hoped that reservations like the above, which accounted for the overwhelming portion of added text in this edition, would make it more rather than less compelling to geologists. In the 1922 edition the world was again varied, local, and detailed: it was the world of geology, not the exclusive “bulk property” world of thermodynamics and gravity. To balance these many reservations, Wegener urged his audience to steer a middle course on the question of detail: “The ever-increasing stream of separate discoveries allows the picture of these connections to grow under our eyes, and today a very far-reaching agreement prevails already among various experts about the most important land bridges, although there are those also who cannot ‘see the forest for the trees.’”96
Dividing the book into two separate sections, one concerned with firm observational data and the other with all other matters, allowed Wegener to go far beyond the “forest and the trees” to discuss things buried deep beneath the forest floor, as it were. Consider the following diagram, which appears as figure 30 of the new edition in a chapter titled “The Sialsphere.” Here instead of the ice cube version of the floating continent, there is a “mash” of Sial and Sima, of the kind that Cloos had advocated in 1915. The diagram as drawn by Wegener (in the lower left of the accompanying figure) appears to be a merging of two different conceptions into a new view of the continental block. One of these is from a 1915 drawing by Dacqué of what he took to be a more plausible version of Wegener’s continental blocks. The second, also by Dacqué, and also from his 1915 book, is a picture of the complex mixing of rock caused by lateral pressure in the formation of fold mountains. Wegener appears to have worked these visualizations together into a conception that united ideas about the continents with ideas about fold mountains.
“Such a structure,” Wegener wrote concerning this picture, “of the continental blocks offers an explanation of many phenomena.”97 He then went on with a complex speculation to show how such a ragged trailing underlayer could explain sedimentary loading of shelf seas, predisposition to folding, extrusion of lava, fold structures incorporating different kinds of rock, island festoons, volcanic islands, and anomalous gravity data.98 Removing these speculations to the latter part of the book (elucidations and inferences) would, he hoped, differentiate them from the “essentials of the theory” and allow him to continue to develop his ideas without damaging the presentation of secure evidence.
There were, however, two major areas of the theory in which Wegener was forced to give significant ground, based on research spurred by his own theory. The first of these was the geodetic evidence for shifts in latitude and longitude of the various continents. Wegener’s claim for the unique advantage of the displacement theory, over all other theories of similar wide-ranging ambition, was that it could be tested by astronomical position finding, so this was a rather hard blow.99
Top left: Wegener’s 1912 cross section of the continents as redrawn by Edgar Dacqué in Grundfragen und Methoden der Paläogeographie (Jena: Gustav Fisher Verlag, 1915). Top right: Dacqué’s suggestion of a more plausible version of a continental cross section, also from 1915. Bottom left: Wegener’s cross section of the continents, from Die Entstehung der Kontinente und Ozeane (1922), which seems to combine some of Dacqué’s ideas. Bottom right: genesis of fold mountains, under tangential pressure, again from Dacqué, Grundfragen und Methoden der Paläogeographie.
Since 1912 he had asserted that comparison of longitude observations made in East Greenland in 1823, 1870, and 1906/1907 showed the westward drift of the observing stations. In 1912 and 1915 he had also used telegraphic time signals exchanged between Cambridge, Massachusetts, and Greenwich, England, in 1866, 1872, and 1892; in 1920 he dropped the 1866 measurement but added the measurements made in 1914. These measurements appeared, he claimed, to show discernible shifts in the longitude of North America. Finally, in 1920, he had added observations made by the International Latitude Service suggesting a decrease in the latitude of these stations since 1870, lending support to his idea of a “flight from the poles.”
In 1921–1922 he was forced to abandon all of these claims. The hardest was the claim for Greenland, since he had participated in the measurements and their publication had come from his expedition colleague and good friend Koch. Greenland was the only place, Wegener believed, still spreading fast enough in the present to provide really accurate measurements of displacement. In 1920 he had recalculated, using recent estimates of geological time, the spreading rates for displacement of all the major continental blocks, reducing most of these to centimeters per year; only in the far north—England, Iceland, Scotland, Labrador, Greenland—did he hold out for estimates of displacements of several meters per year.
The question of the accuracy of these measurements had dominated the discussion after his lecture in Frankfurt in May 1921, and subsequently Friedrich Burmeister (1890–1959), a geophysicist at the Geomagnetic Observatory in Munich and an expert on precise geophysical measurements, had written an article in Petermanns challenging the means by which Koch had reduced the estimate of error in his calculations. He had also raised the problem of making such measurements with single observers, far apart in time, under difficult conditions, without reporting the “personal equation” of each observer. The “personal equation” of an observer is the difference—often a matter of fractions of a second, but sometimes of several seconds—between the assessments by two different observers making the same observation with the same instrument of when an astronomical event (something reaching a maximum altitude, or passing a certain point) has actually happened. Burmeister pointed out that the personal equations alone of these observers could easily swamp the measurements.
There were other sources of error as well, including printing errors in the ephemerides that reported the expected, as opposed to the observed, time of a celestial event. Burmeister had ended his critique by saying that it should in no way be interpreted as a criticism of Wegener’s hypothesis of displacements, merely an elucidation of the inaccuracy of the method used to measure them, and urging the promise of radio time signals to provide definitive evidence for the displacement of Greenland.100
Wegener accepted this critique, while suggesting that Burmeister’s account of the inaccuracy of the observations was exaggerated. Hence, in this third edition he still presented the results for the Greenland measurements from 1823, 1870, and 1907, but he admitted that they were insufficiently accurate to claim that the displacements of Greenland had been demonstrated. Still, “if the exact quantitative proof [Nachweis] must be reserved for more accurate measurements, Koch would still have priority for the measurement of the change in the coordinates.”101
For the case of the telegraphic time signals between Cambridge, Massachusetts, and Greenwich, England, the news was also bad. Galle, in his 1916 article on Wegener’s hypothesis in Deutsche Revue, had said that the 1866 measurement Wegener had invoked was now considered to be unreliable; Wegener had therefore already discarded it in 1920. Further, in his 1912 paper Wegener had made a copying error for the 1892 measurement which made its difference from the 1872 measurement ten times the actual value. He had repeated this erroneous value in 1915 but corrected it in 1920. Wegener now acknowledged “the possibility that even after new measurements, the displacement is still too small to be detectable with any degree of certainty.”102
In 1920, to shore up his measurement claims and to promote the idea of the pole-fleeing force suggested by Köppen, he had excitedly reported that the latitude stations in the Northern Hemisphere seem to be moving toward the equator. Now it appeared that all of these conjectural shifts were the result of similar
errors made at all component observatories, the errors in question being insufficient correction for atmospheric refraction. If anything, the more recent measurements of latitude shifts in Europe and North America showed an increase of latitude.103
As if this were not enough, Wegener was forced into a major retreat (if not retraction) on the question of the displacing forces. First, it turned out that the pole-fleeing force was not even their idea: Köppen was not the first to think of it. In July 1920, Kohlschütter had told Köppen that the Hungarian geophysicist, Roland von Eötvös (1848–1919), had mentioned the possibility of such a force at the International Geodetic Conference in Hamburg in 1912.104 Köppen had insisted to Wegener that he include this information in the third edition of his book, but Wegener, intensely loyal to Köppen, referred to Eötvös’s work as a “brief, obscure reference.”105
Wherever one wishes to assign priority, the idea of such a mechanism caught the imagination of a number of scientists, not least the young physicist Paul Epstein (1883–1966), about to depart Germany for an appointment at Caltech. Epstein wrote a letter to the editor of Die Naturwissenschaften noting that not only were the readers of that journal well informed in the spring of 1921 about Wegener’s theory, but in Berlin it had been hard to escape the public excitement over it. Nonscientists (“the general public”), Epstein wrote, seemed to be swept away by the idea, and so many geographers and geologists approved of it that one had to take it seriously. Yet, he said, the physicist still has a question: will the force he proposes to drive these continents work?
Alfred Wegener Page 85
