Epstein then carried out a rather simple and clever calculation involving the mass of a continental block, the distance between the floor of the ocean and the surface of the continental block, and the angular (rotational) velocity of Earth, to calculate the coefficient of viscosity of the Sima, based on an estimated velocity of the continents—using the extreme (as Wegener said) value of 33 meters (108 feet) per year. He obtained a value of the order of 1016, roughly three times as great as the viscosity of steel at room temperature. He concluded, however, that based on the masses involved, “we can summarize the results in the statement that the centrifugal force of the rotation of the earth can produce a drift from the poles of the magnitude indicated by Wegener and, in fact, must produce it.”106
This was not the only such support. Walter Lambert (1879–1968) of the U.S. Coast and Geodetic Survey published an article on the same topic in September 1921. He mentioned both Taylor and Wegener in a footnote, citing Taylor’s paper of 1910, Wegener’s 1912 paper, and Wegener’s 1915 book.107 The article was apparently based on an address he had given at a mathematical meeting in 1920, in Annapolis, Maryland. With all due respect for coincidence, Lambert had almost certainly seen Wegener’s second edition with its postulation of a “pole-fleeing force”; it would have been impolitic for a U.S. Army lieutenant recently returned from service in France to give a positive discussion of a German theory: anti-Germanism was extremely powerful in the United States in the immediate postwar years.
Lambert came to the same conclusion as Epstein, that such a force was possible and indeed necessary: “the equatorward force is present, but whether it has had in geologic history an appreciable influence on the position and configuration of our continents, is a question for geologists to determine.”108 He also pointed out that “according to the classical theory a liquid, no matter how viscous, will give way before force, no matter how small, provided sufficient time be allowed for the force to act in.… But the viscosity of the liquid may be of a different nature from that postulated by the classical theory, so that the force acting might have to exceed a certain limiting amount before the liquid would give way before it, no matter how long the small force in question might act.”109
That was the good news. The bad news was that Epstein also declared that in spite of the ability of such a force to move the continents toward the equator, it would be incapable of producing great fold mountain chains around the equator, since the force between the pole and the equator was equivalent to a “fall” of only 10–20 meters (33–66 feet), while raising up mountain chains constituted work against gravity on the scale of kilometers, for which the pole-fleeing force was not sufficient.110 Even so, Epstein declared that his calculations should be in no way interpreted as opposition to Wegener’s theory, which could certainly be true of Earth.
Schweydar had read Epstein and declared that Epstein’s velocity for the continents was too great and his estimate for the coefficient of viscosity too small, such that the viscosity ought to be on the order of 1019 and the velocity of the continent something like 20 centimeters (8 inches) per year.111 Further, he had reiterated his opposition to the notion that there was any westward component to the pole-fleeing force. Not only that, but he also argued that the masses of the continents were so inconsequential compared to the mass of Earth as a whole that they were unlikely to be responsible for the displacements of the pole of rotation, thus undercutting Wegener’s entire theory of dynamic interplay; this was a severe blow. Lambert had come to the same conclusion, though Wegener did not mention this in his discussion of Lambert’s work.112
Wegener therefore had to reformulate his position on the displacing forces. “It seems to me therefore highly probable that in fact, as a consequence of the pole-fleeing force, in the course of geological time the continents have undergone considerable displacement through the Sima. Contrarily, it now seems doubtful whether this force can also explain the equatorial fold mountains although perhaps Epstein’s result is not yet the last word in this matter.”113 This was a considerable retreat from one of the main points of Wegener’s theory, that the forces responsible for moving the continents were also the forces responsible for creating the great tertiary fold mountain belts. Moreover, having given up the notion that the Westwanderung of the Americas was a component of the pole-fleeing force, he was thrown back on highly speculative ideas concerning tides in the solid Earth, or perhaps flow in the Sima to move the continents westward, along with unnamed “cosmic forces.” Finally, the dynamic interplay of pole displacement and continental motion was not only uncertain but likely improbable. Wegener put a brave face on it, but his unified pole-fleeing force was now effectively canceled out, and this aspect of his theory, like measurement, moved from fact to inference.
One last major subject remained for Wegener to rework for this edition: the paleoclimatic arguments. Most of the major novelty in the second edition came directly from work in this area with Köppen. All of it concerned, in one way or another, the displacement (or migration) of the pole. The pole-fleeing force had become the mechanism for the displacement of the continents, and such continental displacements the mechanism for the further migration of the pole. The linkage between them was the Ariadne’s thread through the labyrinth of paleoclimatology: the explanation of the anomalies in the fossil record in the Northern Hemisphere, and even greater anomalies for the Southern Hemisphere in the Carboniferous. Working out the pole positions had absorbed most of the time it took Wegener to rewrite the book, and this remained unfinished as the manuscript deadline approached in April 1920.
Wegener and Köppen had continued to work together on this problem through the summer and fall of 1920, and they were still working on it when the Berlin symposium took place in February 1921. The work points they added to their plan, published with Köppen’s second article in September 1921, show that they were still hard at work in the summer and fall of 1921, as does the content of the notes Wegener had continued to accumulate in his research notebook.
Early in the winter of 1922, however, they decided that the defense of the displacement theory and the role of the displacement theory as the “Ariadne’s thread through the labyrinth of paleoclimatology” were two different undertakings. The former was a work of advocacy for a hypothesis, and the latter was a descriptive reconstruction of Earth’s history based on the assumption that the theory was true. They resolved to continue their collaboration on the climates of Earth’s past, but to move all but the bare essentials needed to defend the displacement theory out of the planned third edition and reserve the climate material for a separate, jointly authored book on past climates.114 Wegener’s notebook shows that throughout all of 1922 he continued to collect material on the climates of the past from a variety of sources, and he was still making extracts well after the third edition of his book had appeared.115
With the burden of a complete climatic history of Earth removed, Wegener was able to move forward rapidly, rewriting his chapter on paleoclimatology. Once again, compared with his coverage of the same material in 1920, his treatment is simpler and more colloquial, as well as both more cautious and more compelling. In 1920 he had attempted to provide evidence for all the pole positions from the Carboniferous forward. Now, he was concerned exclusively with two matters: the necessity of moving Earth’s pole in order to explain the distribution of climate zones in the Tertiary, and the necessity of adding relative continental displacements to these migrations of the pole in the Carboniferous period in order to explain the ice and climate evidence without creating absurd contradictions.
“This is not,” he began, “the place to wrap up the discussion of the complete problem of the climates of the past. It is nevertheless necessary for our presentation of the case [for continental displacement], to provide at least a rapid orientation. Only in this way will it become clear how the evidence of paleoclimatology verifies the displacement theory.”116 If, he continued, paleoclimatology is in a very undeveloped state, this is not from a la
ck of evidence. We have a great body of evidence from plant and animal fossils, and we have ways to turn this evidence into evidence of climate. We can relate temperature to vegetation; we know where trees will grow at all, we know where trees with annual rings will grow, we know that palm trees, of which we have many fossil remains, will only grow in a certain temperature regime as well. We know that corals are only found today in water, the temperature of which never falls below 20°C, and that reptiles cannot live in polar climates. If we take these species one by one, of course the indications would be very uncertain, because we see many plants and animals adapt to climates very different from the rest of their families. “But here, just as in the calculation of the path of a meteor from a great number of inexact estimates, the individual data can be quite uncertain, and contradictory, but when the ensemble is treated according to the theory of errors, a reliable result is obtained.”117
To this organic evidence, Wegener wished to add “inorganic evidences of climate,” by which he meant geology. Boulder-clay (till, ground moraine; German: Blocklehme) polished rock and striations in rock taken together indicate Inland Ice. Coal and peat, forming at different temperatures but wherever there is more rainfall than evaporation, and salt deposits, forming wherever there is more evaporation than rainfall, indicate wet and dry climates, respectively. Thick red sandstones with no fossils mean hot deserts; yellow colored sandstones, more temperate arid areas.118
Wegener is here leapfrogging over, and reserving for a later time, a huge number of controversies: where some particular plant or animal might have lived in the past, whether all supposedly glacial deposits are really glacial deposits, whether all coals are formed in the tropics in temperate regions, where salt deposits and massive sandstones come from, and so on. Even ignoring all this, he is saying, we still may infer the past from the present, as we know what sorts of climates the majority of certain groups of animals and plants live in today. Wherever coal forms, it has to be where there is more rain than evaporation; wherever salt forms, there has to be more evaporation than rain.
When, he continued, we take what we know about the environments of living animals and plants and the conditions under which glacial deposits, coal, salt, and sandstones form today and apply to the past this ensemble of evidence, they form a pattern suggesting shifts in latitude, as there are always different climates in every period, but they change location from one period to another. “It is not to be wondered that in the attempt to explain the systematic alteration of the Earth’s climate in the past, recourse was had early, and increasingly, to changes in the positions of the Earth’s pole.” Whatever the imagined mechanism, “today the majority of geologists take the standpoint formulated in E. Kayser’s Lehrbuch, that the assumption of a great Tertiary displacement of the poles is, in any case, ‘difficult to avoid.’ This can indeed be considered as established, in spite of the remarkable vehemence with which some of its opponents struggle against it.”119
Once the movement of Earth’s pole is established, he said, there is remarkably good agreement on the climate zones for the more recent periods, with a position for the North Pole at the beginning of the Tertiary in the neighborhood of the Aleutian Islands, and from there movement toward Greenland, where it is found in the Quaternary. However, “the situation is entirely different for the periods before the Cretaceous. Here not only do the views of the best-known authors differ widely, but every one of their reconstructions, consequential on their inattention to continental displacements, leads to hopeless contradictions, indeed contradictions of an order that they form a barrier to every conceivable placement of the pole.”120
Finally, the point of his argument has arrived. “The riddle of the Carboniferous glaciation finds an extremely compelling solution in the displacement theory; once the different portions of the earth which today bear traces of ice action are pushed together concentrically around South Africa, the entire ice-covered area becomes no larger in extent than that of the Pleistocene glaciation [diluvialen Eisspuren].”121 Then, having redeployed the evidence from the second edition, with an increased reliance on the disposition of coal (divided into tropical and subtropical coal), the Glossopteris flora, trees with tree rings, salt, gypsum, and other desert deposits, he argues that this solves the problem of all the data for the Carboniferous.
All of this writing and thinking about the continents happened in the course of the summer and winter semesters of 1921–1922, against the background of full-time work at the observatory, research on climate, and university teaching. Now that he was pushing the work on climates of the past forward to a prospective volume on which he and Köppen would collaborate, he had reduced the number of major efforts from four to three, but there was still not enough time. The extensive commuting—among Großborstel, the university, the observatory, and the Geological Institute—was, with Kurt gone to Berlin, completely lost time. Living in a household with seven full-time residents (four adults and three children), with constant visits from colleagues, neighbors, and the other children of the elder Köppens, gave him no respite at home; he had to find a way out if he were ever to finish this book.
There was a way. Wegener and Kuhlbrodt had gone to sea briefly in the summer of 1921 to test the prototype of their new balloon theodolite, and they continued to work on it through the fall and winter. It was a good design, combining a standard balloon theodolite with a marine sextant. One need not go too much into the details, except to say that the sextant could be adjusted by sliding a large armature along an inscribed arc while looking through the telescope. This allowed very precise adjustments to happen rapidly and to be read off easily, in contrast with turning a thumbscrew on a standard instrument. Even better, a sextant had a split mirror that allowed one always to be looking both at the horizon and at a celestial object (in this case a balloon); historically its principal use has been the determination of latitude by measuring the maximum altitude of the Sun at noon.
Wegener and Kuhlbrodt’s highly mobile theodolite for tracking pilot balloons on their sea voyage to Mexico and the United States in 1922. The instrument itself is on the left, and on the right is Wegener’s photograph of Kuhlbrodt making an observation with it, using the novel control arm from a sextant allowing fine adjustments of the telescope with large adjustments on the arc. From Erich Kuhlbrodt and Alfred Wegener, “Pilotballonaufsteige auf einer Fahrt nach Mexico, März bis Juni 1922,” Archiv der Deutschen Seewarte 30, no. 4 (1922).
Applied to the problem of following a pilot balloon, one could get a constant reading on the altitude of the balloon above the horizon without ever losing sight of the balloon, while simultaneously making fine adjustments of the telescope. With a second observer to record the angle at every moment and to keep track of the compass direction and speed of the ship, it was possible to determine within a few hundred meters the absolute altitude of a balloon and, from its motion, to track the direction and velocity of the upper atmospheric winds.
So at about the time that the intellectual work for the third edition was largely completed, January and February 1922, Wegener sought and obtained permission from Adm. Kohlschütter to make a voyage across the Atlantic with Kuhlbrodt and try out the instrument. There was no question of having a research vessel, and Germany was not allowed to have naval vessels at sea under the terms of the armistice ending the war, so Wegener and Kuhlbrodt hit upon the expedient of finding a ship headed for the Americas in the spring and early summer, on which they would be nominal members of the crew but devote themselves to their scientific work.
Germany’s merchant fleet, though decimated by the demands of the Allies for reparations, still existed, and as a meteorologist at a naval observatory, Wegener hardly had to present credentials to make his case. The steamer Sachsenwald was scheduled to depart in mid-March, and it was no great work to sign on (nominally) as the purser, given his position and the backing from the Admiralty. Kuhlbrodt also took a nominal role as a member of the crew; they were, however, simply scientific passen
gers.122 The voyage would take about three months, with a scheduled return around 15 June. Wegener and Kuhlbrodt planned to send up two balloons a day while at sea, one in the morning and one in the afternoon, and one balloon a day while in harbor, the latter as a check on the velocity calculations concerning the ship, to provide correction for the balloon flights made while the ship was under way.
They also would take a long focal-length camera for photographing cloud forms and documenting the flights. Kuhlbrodt would take a series of water temperatures at different depths, and Wegener would take some preliminary measurements of gravity at sea.123 This program still left many hours each day with no duties whatever: no teaching, no commuting, no family life, no visitors, no research trips to a library, no entertaining speakers at a colloquium, no conferences with PhD students, no correspondence, no filing of reports at the observatory. All of this time could be and would be devoted to the preparation of a consistent, clear, and balanced manuscript. Wegener was accustomed to writing at sea, was rarely seasick, and was used to cramped quarters and odd hours. What he needed was time alone.
17
The Paleoclimatologist
HAMBURG, 1922–1924
Before beginning my lecture on the criteria by which ancient glaciations can be recognized I want to remind you of the curious fact that it would be impossible to give such a lecture without the existence of recent glaciers. If we did not live so near an Ice Age with glacier-ice on the poles and in the higher mountains, but in a warm period of Earth history with green trees right up to the polar regions, no one would be able to give a correct interpretation of the polishing and striations of rocks which we attribute to glacial action, for no one would imagine that ice can stream like a river and be a most important geological factor.
MARTIN SCHWARZBACH (1963)
Alfred Wegener Page 86
