There is more to this letter that concerns us, but before going on to discuss it in detail, it is important that we stop here to consider what it reflects about Wegener’s thought processes and imaginative style. Once again we see this characteristic pattern evident since his work on atmospheric layering. An article “falls into his hands” which contains information on a problem with which he is already concerned, but which does not contain the conclusion that he would draw from the same data. A quick survey of the relevant literature at hand provides “surprising or astonishing simplifications and corroborations.” A conviction of the “fundamental correctness” of his intuition forms in his mind well in advance of a detailed survey of the evidence and sends him off on an enthusiastic pursuit of further confirmatory evidence, but not before leading him to assert a bold new working hypothesis that reorganizes the data in a novel way, to produce an argument about the structure of some geophysical entity, dependent to a large extent on analysis of surfaces of discontinuity.
Wegener was decidedly an “enthusiast.” His interest, curiosity, and even ardor were easily aroused. Enthusiasm is a double-edged sword and carries both favorable and unfavorable connotations. It may mean someone vitally animated and interested, especially in novelty, or it may mean someone whose judgment is subordinate to his excitement. Wegener was, more often than not, an enthusiast of the former kind. In spite of Köppen’s fear that he would be diverted from his core task in atmospheric physics by taking on a “sideline” like the study of former continents, Wegener embraced new enthusiasms without abandoning old ones, by partitioning his interest and increasing his workload. It was this immense capacity for concentrated work that, in part, kept him from superficiality and dilettantism. Once interested in a topic, he pursued it relentlessly.
There is a sense in which the word “enthusiasm” is in danger of trivializing the affective component of scientific investigation, in the case of someone like Wegener. There is a sense in which what we are talking about is more like “love” than “enthusiasm.” Sometimes, there is an intermingling of actual romantic love and intellectual productivity, and Erwin Schrödinger is a famous case of this, with bursts of scientific creativity following upon the formation of new romantic attachments.68 There may be some link like that here. Else Köppen was the first person and for a long time the only person whom Wegener told (so far as we know) of his intuition concerning former continents, and he did so in the first stages of a romance that would result in an engagement within a few months and his marriage within a few years.
Yet there is a more firmly anchored and thoroughly intellectual aspect to his pursuit of the idea of continental displacements at the end of 1911 and in the beginning of 1912. Wegener was very much a “theoretical physicist” who, though he had collected data in Greenland in 1906–1908, did most of his work by linking together the data produced by others. Theoretical physics, in the tradition in which he was trained by Planck at Berlin, as well as by Bezold, had a very definite answer to a pressing question that faces all scientists. That question is, when will it be time to gather up everything that we know and make a coherent and synthetic presentation of it in the form of a unified theory? The answer for Planck and for Wegener was that that time is always now. For Wegener, a theory was simply an imaginative construct used to order the data in our possession at any given moment. It is an architectural assembly of component elements into a unified picture with the aim of clarifying our thought and guiding further investigation.
For Wegener, a theory was a promising working hypothesis that would lead to new understanding, and nothing more. Thus, when he spoke of his idea of former continents, he spoke in terms of not demonstrated fact but the “fundamental correctness,” and therefore heuristic value, of an idea. It was this that led Wegener to say to Köppen, “Why should one refrain from expressing these ideas for 10 or for that matter 30 years?” A theoretical idea (or a hypothesis) is apposite not when it is “confirmed” but when it is likely to lead science in a productive direction. Under such circumstances, hesitation is nothing but procrastination in the face of intellectual urgency.
In terms of the two epigraphs at the beginning of this chapter, we are more concerned with the second, Houston Stewart Chamberlain’s characterization of Galvani, and the speed with which exposure to a new physical fact could lead him to make “extensive connections with all kinds of known and still unknown facts and this spurred him on to endless experiments and variously adapted theories.” We may recall that Chamberlain’s work was part of Wegener’s regular inspirational reading while a university student.
Wegener, at the time he came upon these articles by Krenkel and Keilhack, was preparing to return to Greenland and thinking about a scientific program, inherited from Nansen, that could help solve the riddle of the ice ages. Nansen, as we have seen, had entertained the idea of displacements of Earth’s pole of rotation as a way to map Northern Hemisphere glacial deposits within some reasonable compass, but he felt in the end that this strategy was insufficient because it could not explain, with continents and landmasses in their present position, how the distribution of flora and fauna in the Northern Hemisphere could be made compatible with any given pole position; he was especially concerned about the inability to have a pole position that could simultaneously produce a semitropical flora in Greenland and a cold-weather flora in Japan.
The extensive quotation from Keilhack, which Wegener sent on to Köppen, dealt with exactly this problem. For his Carboniferous glaciation, Keilhack was unable to come up with any pole position that covered all the glacial deposits without putting some of these regions (showing clear marks of glaciation) within 30°–35° of the paleoequator—the latitude of Buenos Aries, the Kalahari Desert, and Sydney, Australia. A similar distance from the equator in the Northern Hemisphere, with the continents in their current positions, would have required glacial deposits in Los Angeles, Algiers, Baghdad, and Shanghai. Wegener said, at the conclusion of his quotation of Keilhack’s article, “What my implication is here, you can see for yourself.”69
What he meant for Köppen to “see for himself” was that the ice age in the Southern Hemisphere and the distribution of deposits were absolutely confirmed by geology and paleontology. At the same time, no pole position, with continents in their current location, could account for the distribution of glacial deposits, without bringing the ice cap absurdly close to the equator. Thus, the most plausible hypothesis was that the relocation of the pole of rotation of Earth would have to be considered in tandem with the relative displacement of continental masses from some former configuration. It is for this reason that Wegener insisted to Köppen that he should consider the idea of an “Urkontinent” not as an unfounded or fantastic speculation but as a matter of accounting for all the available data in a way that made things simpler and more plausible. The appeal to simplicity, of course, marks him as a physicist; no geologist of his time would have made a similar claim.
The other essential datum or idea that drove him to consider continental displacements was his astonished discovery that geologists and paleontologists were willing to consider that large stretches of the current abyssal ocean floor were former continental surfaces that had somehow sunk to the bottom of the ocean. The principle of isostasy, to which Wegener refers in this regard, and which we shall consider in more detail in the next chapter, was a way of accounting for many thousands of well-confirmed gravity observations, of the kind he had studied as a graduate student with Helmert at Berlin. These could only be explained by assuming that the crust of Earth floated on the interior of Earth, which must, because of the increase of temperature with depth, be deprived of strength at some point. Astronomical calculations of the mass of Earth, universally accepted and many times reconfirmed, absolutely required that a large portion of its interior must have a much higher specific gravity than any rocks available at the surface, and therefore that this molten, or at least yielding, interior be more dense than the solid rock at the surface. Under t
hese conditions, the idea that huge blocks of Earth’s surface could sink into the interior was as physically impossible as the idea that an ice cube should sink to the bottom of a glass of water.
The driving force of Wegener’s rapid elaboration of the idea of continental displacements in the next two months, along with his immediate publication of a theory of the origin of continents and oceans, was his recognition that the universally accepted and undeniable geological and paleontological evidence of former connections between continents now separated by thousands of miles of ocean was explained by these very geologists and paleontologists in terms of a theory that appeared to be physically impossible. Therefore, the idea of continental displacements seemed to him not a wild or fantastic postulation but simply a means of putting together well-confirmed geology and well-confirmed geophysics into a single working theory.
He closed his letter to Köppen with the following remark: “It is eight days until I begin really to ‘collect’ [evidence for my hypothesis]. Till then I don’t have the time. But I don’t intend to take 30 years to do it!”70 He intended this as a rapid foray into a new field leading to a rapid publication. Instead, the work he embarked on that December would take him the rest of his life, dominate his career and posterity, and overshadow everything he thought of as his “own work.”
10
The Theorist of Continental Drift (1)
MARBURG, DECEMBER 1911–FEBRUARY 1912
I refer to this new principle [of horizontal displacement of continents], in spite of its broad foundation, as a working hypothesis, and would like to see it treated as such, at least until the persistence of these horizontal displacements in the present shall have been demonstrated, by means of astronomical position fixing, with a precision that eliminates all doubt.
ALFRED WEGENER, 1912
A Copernican Revolution
Wegener had asked Köppen, concerning his hypothesis of continental displacements, “Is this, perhaps, revolutionary?”1 It is a commonplace that the notion of “scientific revolutions” guides much of the writing of the history of science and has for at least a century. Scientists of the first rank are those who are seen to have precipitated revolutions. Thus, Copernicus, Kepler, Galileo, Newton, Lavoisier, Darwin, and Einstein are each written about as the authors of revolutions. The first modern, and therefore the archetypical, scientific revolution was that precipitated by Nicholas Copernicus (these other towering figures notwithstanding). It is no accident that Thomas S. Kuhn’s (1922–1996) book The Structure of Scientific Revolutions (1962), certainly the best-known book in the recent history of science, was written by a man whose PhD dissertation was published in 1957 as The Copernican Revolution.2
We celebrate the “Copernican Revolution” as the beginning of not only our current view of the world but also our approach to doing science. This Copernican Revolution, which displaced Earth from the center of the universe and radically simplified the picture of the cosmos, had other revolutionary consequences. In the hands of Johannes Kepler, the idea of perfect circular orbits, an image of cosmic perfection inherited from Plato, gave way to very slightly elliptical orbits. More importantly, Kepler gave up these beloved circles reluctantly, but he did so because he believed absolutely in the accuracy of the numerical data collected by Tycho Brahe, upon which Kepler based his orbital calculations. Historians of science emphasize this event as the first important instance in which a beloved scientific theory was rejected because it conflicted with reliable data, rather than the data being adjusted to fit the treasured theory.
Copernicus’s new theory might have been more immediately persuasive had it been better at predicting planetary positions than the old system, but it was not more accurate. It retained, in addition, residual elements of the old theory, which were to be abandoned by subsequent investigators. It contradicted both biblical and classical authority. It advanced itself in terms of complicated mathematical arguments; then and now these are accessible only to the fully numerate (Copernicus himself scornfully rejected the objections of “idle talkers” who would take it upon themselves to pronounce judgment on the theory, though wholly ignorant of mathematics). The theory failed a crucial empirical test—the inability of supporters and opponents alike to observe any stellar parallax. If Earth were actually moving around the Sun at a great distance, it seemed that the relative position of the stars should be different on one side of the Sun than on the other, but no such relative shift was visible. The ad hoc explanation offered by Copernicus, that this was because the stars were so far away, sounded ludicrously improbable given their large apparent diameters viewed (of necessity before 1610) with the unaided eye.
Copernicus’s theory nevertheless had from the outset a great virtue to recommend it: with a single comprehensive principle it explained a great number of facts either left unexplained in the old theory or explained in an ad hoc, heterogeneous, and metaphysical way—the retrograde motion of the planets, their varying brightness, the permanent stations of Venus and Mercury close to the Sun. Copernicus solved these problems by centering all motion in the solar system on (or very near) the Sun, now supposed to stand still. This is to say, it made a virtue of simplicity and unity of explanation and, in so doing, established a criterion of adequacy for physical theories—both aesthetic and cognitive—in which unity and simplicity came to have a central place.
By the later eighteenth century a “Copernican Revolution” was already a trope, and Immanuel Kant (1724–1804), in the introduction to his Critique of Pure Reason, could celebrate, with the confidence of being universally understood, the “Copernican Revolution” brought about in his thinking by reading the philosophy of David Hume (1711–1776).
Now let us turn these remarks and ideas in the direction of Alfred Wegener. Wegener was himself not only an astronomer by training but also a published author in the history of astronomy. He understood in great detail the sequence from Ptolemy to Copernicus, from Copernicus to Kepler, from Kepler to Newton, and from Newton to Laplace, Lagrange, and Gauss. He had, after all, written a “Copernican” PhD dissertation on planetary tables, specifically to transform a geocentric system written in sexagesimal notation to a heliocentric system written in decimal notation, so that modern astronomers might use the data. Along the way he mathematically modernized and simplified these planetary tables, throwing out a number of spurious “corrections” introduced in the fourteenth century by astronomers desiring to bring observations into harmony with theory.3
In considering Wegener’s concept of a “revolutionary” development, it is quite sensible to assume that he was speaking of such a “Copernican” move in geophysics. We may recall that Wegener had had university training in the psychology of perception and had studied what we now call “Gestalt reversals,” in which the eye rapidly switches from one visual configuration of an image to another, radically reorganizing the data into a new form. He had written to Köppen, in early December 1911, that his hypothesis of continental displacements was not an imaginative creation or a fantasy but a consequence of just such a radical reorganization of existing observational data into a new picture, producing simplification and coordination in the place of previous complexity and contradiction.4
Let us then consider Wegener’s idea of continental displacements in Copernican terms. In the standard hypothesis of Wegener’s time, the geological and paleontological continuity across deep oceans was explained by the sinking of large continental fragments to form ocean bottoms, while what we call “the continents” were the surviving remnants of formerly much more extensive continents, remnants that remained fixed in place. Wegener’s Copernican rewriting explained these continuities not by the sinking of vast continental fragments, creating new oceans in their subsidence, but by continents splitting and drifting apart across the face of Earth and creating ocean basins by their lateral motions.
Wegener’s hypothesis was Copernican both in its form and in its revolutionary intent; in consequence, it shared nearly every single problem
that had beleaguered the new theory of Copernicus. Wegener’s hypothesis was certainly no better than the old hypothesis at explaining the continental positions. It contradicted classical geological authority. It defied both aspects of physical theory (especially a leading version of solid mechanics) and common sense. It was based on complicated, numerically framed arguments in a broad range of sciences—some of them, like radioactivity and seismology, very new and unfamiliar to all but a few pioneering specialists. Like the Copernican theory, it failed a crucial observational test—no one could produce compelling, confirming evidence of continental motions continuing in the present, a problem very like Copernicus’s problem of stellar parallax. If there were lateral continental motions, then not only certain consequences of these motions but the motions themselves should be observable today.
Wegener’s hypothesis of continental displacements nevertheless had from the outset the same great virtue to recommend it as had the theory of Copernicus. It explained with a single comprehensive principle a great number of facts either left unexplained by the old hypothesis or explained in an ad hoc, heterogeneous, and metaphysical way: the jigsaw puzzle geometry of the continental shelves, the different densities of continental and ocean floor rock, the existence of similar life-forms on continents separated by abyssal oceans, the continuations of geological structures and sedimentary sequences on both sides of the Atlantic, the odd dispersal of the Southern Hemisphere remnants of the Carboniferous glaciation, the appearance of tropical fossil biota in high latitudes and temperate fossil biota at the equator, the existence and locations of mountain ranges, the location of volcanoes at continental margins, and a great many similar questions.
Wegener’s Sources
Wegener began to work on the question of continental displacements on 14 December 1911, and by 6 January 1912 he was prepared to give a public lecture in Frankfurt, entitled “Die Herausbildung der Grossformen der Erdrinde (Kontinente und Ozeane) auf geophysikalische Grundlage” (The geophysical foundations of the development of the large features of Earth’s crust [continents and oceans]). The audience was a plenary session of the German Geological Association, founded two years before by Emanuel Kayser, Wegener’s dean at Marburg, who was both chair of the Geological Association and editor of its journal, Geologische Rundschau, from 1910 to 1920. It was Kayser who arranged for Wegener to give the lecture. This initial presentation of Wegener’s hypothesis was followed four days later by a lecture in Marburg before the Gesellschaft zur Beforderung der gesamten Naturwissenschaften, under the title “Horizontalverschiebung der Kontinente” (Horizontal displacement of the continents).
Alfred Wegener Page 45
