The Earth Inside and Out phần 7 ppt

222 CATHY BARTON Fig. 3. Section of a colour-coded province map of the Mid-Atlantic Ridge in the equatorial Atlantic. The red, yellow and green areas show highest elevation. Reproduced from a map worksheet in the Heezen Collection, Library of Congress (photographer Gary North, authors Bruce C. Heezen, Marie Tharp, Date 1960). Fig. 4. The World Ocean Floor Panorama, authors Bruce C. Heezen and Marie Tharp, Date 1977 and copyright by Marie Tharp 1977. Reproduced by permission of Marie Tharp, 1 Washington Ave., South Nyack, NY 10960. MARIE THARP AND OCEAN FLOOR CARTOGRAPHY 223 sequential or 'genetic' development of oceans from mid-ocean ridges. The Indian and Atlantic Oceans supposedly began as continental rifts and slowly grew, and the rifts in East Africa, the Red Sea and the Gulf of Aden were comparable features at different stages of development (Heezen 1962). Physiographic diagrams: a reflection of changing scientific attitudes Many scientific disciplines, not least geology, frequently proceed by the use of visual thinking and aesthetic considerations rather than deduc- tively through logic or inductively from empiri- cal data (Miller 1981). This 'aesthetic' method contributed significantly to the reintroduction of the notion of continental drift. The rifted Mid- Atlantic Ridge suggested that the Earth's crust had moved laterally and the diagrams contributed to the demise of geology's old perma- nence theory. But Heezen and Tharp did not propose that continental drift caused the rift. Rather, the diagrams attracted the attention of other geoscientists who made an acceptable case for continental drift and later for plate tectonic theory, which incorporated 'drift' (Le Grand 1988). In 1958, Heezen acknowledged that palaeomagnetic studies and other new data implied lateral continental motion, but he advocated expansionism, not drift. Expansion had been proposed previously in the twentieth century. 27 In 1960, Heezen and Tharp promoted expansion while Harry Hess (1906-1969) proposed what became, after modifications, an acceptable model for continental drift. By that time, tectonics had begun to play a key role in the collaborators' research programme and Heezen used maps of the Earth's major tectonic features to bolster his argument for expansion. Accord- ing to Heezen, the most important tectonic factors influencing sea-floor topography were crustal extension, strike-slip faulting, normal faulting, and subsidence (Heezen 1962). The work of the Australian geologist S. Warren Carey of the University of Tasmania, a staunch expansionist, influenced Heezen. In 1956, Carey organized a major conference on continental drift and Heezen participated (Carey 1956). He and Carey advocated a relatively rapid rate of expansion (Le Grand 1988). The Columbia structural geologist Walter Bucher (1889-1965), who in 1933 had proposed that the Earth under- went alternating periods of expansion and con- traction, also advised Ewing and his students at Lament. 28 The collaborators believed that mantle material welled up between the separ- ating continents, which were pushed aside as the Earth expanded, and produced the mid-oceanic ridges by a form of sea-floor spreading. A promi- nent factor in Heezen's advocacy of expansion was that he, and most of his Lamont colleagues, believed that oceanic rifts and trenches were similar crustal features produced by tension. In addition, he did not accept that excess crust could be subducted back into the Earth's inte- rior at the oceanic trenches. Heezen rejected subduction as he could not visualize the geome- try of convection cells or currents as being such as to cause compression at the trenches (Heezen 1962). The early physiographic diagrams reflected his tensional hypothesis: the ocean basins were supposedly stretched apart as the Earth expanded, with rifts opening in all directions (Heezen et al. 1959; Menard 1986). The collaborators believed that an ocean basin was structurally one unit, with all major features, including the mid-ocean ridge system and the continental margins, being minor splinters and fissures in the floor of one 'grand crack': the ocean basin. According to Felix Vening-Meinesz (1887-1966), another pioneer of sea-floor research, the presence of negative gravity anomalies over deep-sea troughs, accompanied by seismic activity in these regions, indicated down-buckling of the Earth's crust. Vening- Meinesz, Harry Hess and Ewing had accompanied the 1936-1937 cruise of the submarine Barracuda to the Caribbean, with Ewing collecting trench gravity data (Bowin 1972). After this expedition, he concentrated on equipment and the technical aspects of data collection rather than the development of theories. Hess, however, immediately began to develop Vening- Meinesz's ideas on down-buckling and convection currents (Le Grand 1988). He called these regions of crustal compression 'tectogenes' (Oreskes 1999). Lamont scientists, however, especially Ewing, did not accept crustal compression at the trenches, as they believed that the gravity data collected over trenches were inconclusive (Heezen 1962). The 'confusion' at Lamont continued until the evidence for 27 Heezen was familiar with the literature on expansion. He cited Taylor (1910) and Eyged (1957) in his most descriptive work on the topic, the paper The deep-sea floor' (Heezen 1962). 28 Marie Tharp, pers. comm., October 1999. 224 CATHY BARTON Fig. 5. Physiographic diagram of the South Atlantic, authors Bruce C. Heezen and Marie Tharp, Date 1961 and copyright by Marie Tharp 1961. Reproduced by permission of Marie Tharp, 1 Washington Ave., South Nyack, NY 10960. continental drift became overwhelming in the mid-1960s. The Heezen and Tharp physiographic diagrams, especially of the Atlantic, reflected the rapidly changing comprehension of processes shaping the ocean basins, during a brief period of revolutionary scientific activity as defined by Thomas Kuhn (Kuhn 1962). In 1961, the diagram of the South Atlantic, with the excep- tion of a few equatorial fracture zones, illus- trated few departures from the theories that prevailed during the 1950s (see Fig. 5). The early physiographic diagrams had land-like features, while later versions pictured a different world. Late in the 1960s, continental drift was becom- ing acceptable and plate tectonic theory was MARIE THARP AND OCEAN FLOOR CARTOGRAPHY 225 quickly developing as a viable alternative to the old paradigm. The appearance of the diagrams changed drastically in the 1968 Geological Society of America's edition of the North Atlan- tic after decisive geomagnetic core studies had convinced the majority at Lamont of continental drift, although Heezen and Tharp did not com- pletely abandon expansion (Heezen & Hollister 1971). The most significant change in the appearance of their diagrams was the style of topographic symbolism. The edges of many features, especially mountain peaks, 'became' jagged and sharp (see Fig. 6). The pronounced angularity, emphasized by thicker black lines, and the ordered definition of the later editions contrasts with the more random, 'softer' edges of peaks in the early maps. On the rifted Mid- Atlantic Ridge, the incorporation of many regu- larly spaced offsets gave this great feature a new and forbidding appearance. Offsets along the ridge were exaggerated to emphasize the extent of displacement. 29 Eventually, the Mid-Atlantic Ridge region became filled with sharp, closely spaced peaks. The appearance of light and shadow in the diagrams also changed as the new paradigm was adopted. In the early diagrams, the shadowing was not as strong as in later editions and there were no sharply defined sources of light. In the 1968 diagram, the floor of the central Atlantic Ocean was represented as if it were brightly illu- minated from a point to the south, with light impinging on the face of the peaks, and high- lighting the appearance of the fracture zones. The sketched lines and shading of these features was dark, accentuating their angularity and depth. These changes reflected the significance of these features in the development of plate tectonics theory and the understanding of the Earth's behaviour, even though the collaborators were not themselves supporters of plate tectonics. The collaborators' years of research and analysis of offset fracture zones intersecting the Mid-Atlantic Ridge inspired others, such as J. Tuzo Wilson, to consider their origin and the direction of crustal motion at these features. While fracture zones had been discovered on the floor of the eastern Pacific by H. W. Menard of the Scripps Institution, in California, Heezen and Tharp established their existence in the Atlantic. During the drafting process, Tharp noticed trends and the collaborators looked for Fig. 6. Section of a physiographic diagram of the North Atlantic ocean floor, showing the jagged nature of the offset fracture zones on the Mid- Atlantic Ridge, c. 1968. Reproduced from the Heezen Collection, Library of Congress (photographed by Gary North, authors Bruce C. Heezen and Marie Tharp). additional fracture zones using the earthquake data (Heezen et al. I964b). They discovered irregular patterns along the central rift valley, which led them to believe that offsets on the ridge occurred at angular breaks of between 80 and 100° (Heezen & Tharp 1965). Tuzo Wilson cited this and other data, when he proposed that these features were not ordinary offset faults, but a new class of faults that occurred on mid- ocean ridges and are locally transformed into zones of crustal movement. According to Wilson, the motion along these faults was oppo- site to that of the usual strike-slip faults. The 'new' type of fault did not extend across the ridge, but joined the next segment of the rifted ridge. He named these features 'transform faults' (Wilson 1965) and they were soon incorporated into the emerging new theory of global tectonics. 30 29 Archival source: Tharp 19990, Tanya Levin interview, 24 May 1997,142. 30 In this important paper Wilson cited Bucher (1933), Carey (1956), Heezen (1962) and several other works that laid the foundation for the concept of transform faults. 226 CATHY BARTON The collaborators' analysis of the data collected during the International Indian Ocean Expedition illustrates that scientific observations are theory-laden (cf. Hanson 1961); theoretical assumptions can dictate what is dis- cerned in or inferred from data. While the relative symmetry of the Mid-Atlantic Ridge had inspired Heezen and Tharp to consider expansion, the complex and asymmetric nature of the Indian Ocean topography failed to change their expansion model. Rather, the new data strength- ened their belief that continental drift, utilizing a simple pattern of convection currents inside the Earth, was not a feasible option and they continued to advocate expansion (Heezen & Tharp 1965). According to Tharp, Heezen was essentially a uniformitarian, who believed that observable processes could be used to explain the geological record (Tharp 1982a). Many scientific disciplines employ analogy (Hesse 1981) and as geologists, Heezen and Tharp gath- ered data and often used analogies to help in their analysis. However, to comprehend all the forces shaping ocean-basin topography, these tools were not sufficient as: (1) subduction does not occur on the continents; (2) the movement of the offset fracture zones intersecting the Mid- Atlantic Ridge differed from existing examples of fault systems on land; and (3) it was necessary to consider physical laws and go beyond geological fieldwork at the surface in order to understand how the Earth's crust behaves, as Wilson (1951) had suggested. In addition, researchers who were not deeply involved in data collection were able to distance themselves from specific research problems and propose broad explanatory theories (Menard 1986). Conclusions While Heezen and Tharp helped revive Wegener's mobilism, and their physiographic diagrams reflected the latest findings by leaders in the field of oceanographic research, visual representation and analogy could take the collaborators only so far and they were not involved in establishing plate tectonics per se (Le Grand 1988). The collaborators' carto- graphic endeavours stimulated scientific change by revealing critical elements of sea-floor topography and behaviour. These included: (1) the rifted Mid-Atlantic Ridge; (2) the extension of the mid-oceanic ridges around the planet; (3) the idea of the sequential or genetic development of oceans from continental rifts; and (4) the angled nature of the faults intersecting the Mid-Atlan- tic Ridge. But this newly documented know- ledge, no matter how essential, could not in itself propel ideas beyond a certain point and tran- scend assumptions that were firmly established in the collaborators' minds. Nevertheless, Heezen and Tharp successfully continued their mapping and data gathering into the 1970s. Their efforts were vital to scientific change, even though, after the plate tectonics revolution, their method remained the same and their theoretical ideas did not change radically. Even if the collaborators are not usually acknowledged for substantial theoretical contributions to the revolution in the Earth sciences, their physiographic diagrams, globes and related artifacts may well be considered milestones in the history of cartography, and their work undoubtedly contributed to the eventual grand change in geological theory that occurred in the 1960s. Perhaps one might say that Heezen and Tharp were (together) the Tycho Brahe of the Earth sciences revolution, providing essential empiri- cal information but not able to break free of older ways of thinking. Or insofar as they did so, they pursued an idea that (so far as most geologists are concerned) led to a dead-end. I wish to thank S. Herbert for her invaluable assist- ance; G. Fitzpatrick, at the Library of Congress, for encouraging my interest in the physiographic diagrams; G. North, at the Library of Congress, for taking the photographs of the diagrams in the Heezen Col- lection; and Marie Tharp for her encouragement and giving me the opportunity to interview her. Appendix Archival sources THARP, M. 1997. Interview conducted by Gary North, 21 November. One session, one video-cassette; preliminary transcript. The Heezen Collection, The Library of Congress, Washington DC. THARP, M. 19990. Reminiscences of Marie Tharp: interviews conducted in four sessions by Ronald Doel on 14 December 1995 and 18 December 1996, and by Tanya Levin on 24 May 1997 and 28 June 1997. Preliminary transcript. (These are part of the Lamont-Doherty Earth Observatory Oral History Project. Oral History Research Office, Columbia University. On file at the American Institute of Physics Neils Bohr Library, College Park, MD.) THARP, M. 1999b. Interviews conducted by the author on 25-26 October. Three sessions, three audio- tapes; preliminary transcript. The Heezen Collec- tion, The Library of Congress, Washington DC. References BOWIN, C. 1972. Puerto Rico trench negative anomaly belt. In: SHAGAM, R., HARGRAVES, R. B., MORAN, W. J., VAN HOUTEN, F. B., BURK, C. A., HOLLAND, MARIE THARP AND OCEAN FLOOR CARTOGRAPHY 227 H. D. &. HOLLISTER, L. C. (eds) Studies in Earth and Space Sciences: A Memoir in Honor of Harry Hammond Hess. The Geological Society of America, Memoir 132, 339-362. BUCHER, W. H. 1933. The Deformation of the Earth's Crust: An Inductive Approach to the Problems of Diastrophism. Princeton University Press, Prince- ton. CAREY, S. W. (ed.) 1956 (reprinted 1959). Continental Drift: A Symposium being a Symposium on the Present State of the Continental Drift Hypothesis, held in the Geology Department of the University of Tasmania, March 1956. Geology Department, The University of Tasmania, Hobart. 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GOOD History Department, West Virginia University, Morgantown, WV 26506-6303, USA Abstract: In 1900, researchers interested in Earth's magnetism generally proclaimed all facets of magnetic phenomena to be within their purview. Most researchers in this field referred to themselves as 'magneticians' first and physicists or geologists second. After World War II, specialization increased. A number of distinct research areas appeared over several decades: the geodynamo theory and the study of the core-mantle boundary; palaeomagnetism and its growing connection to geology; the production of induced fields in Earth's crust; and, among others, the electromagnetic phenomena of the upper atmosphere and near space. The former unity dissolved and the field fragmented. One result of frag- mentation has been a loss of memory and a consequent misinterpretation of an important part of the history of geoscience. This paper relates the challenges of recovering a history obscured by later events. When most geologists think of studies of Earth's magnetism in the twentieth century, they think of palaeomagnetism, and with good reason. The investigation of, for example, reversals of direction of Earth's magnetism played a critical role in the acceptance of continental drift and plate tectonics, one of the central developments in geology during the century (Le Grand 1998; Frankel 1998). It's a dramatic story, and magnetic reversals themselves, seeming simultaneously unexpected and unsettling, have caught the imagination of a broader public. The many facets of the story of continental drift and plate tectonics, including the role of palaeomagnetism, are thoroughly analysed in Naomi Oreskes' The Rejection of Continental Drift (1999, pp. 263-267). One must remember, however, that there is much more to Earth's magnetism than palaeomagnetism's importance in plate tectonics. When most geophysicists think of this broad phenomenon, they think toward one of two extremes of Earth's environment: the depths of the core-mantle boundary where the main geomagnetic field is produced, or the heights of the magnetosphere where the planet's magnetic field interacts with the solar wind and begins the chains of events that lead to magnetic disturb- ances and the aurora polaris. Investigations of the phenomena of these two realms relate to two other critically important stories of twentieth- century geoscience. Interestingly, all the major streams of geomagnetic research explored in this paper - palaeomagnetism, the origin of Earth's main magnetic field, fields induced in Earth's crust and mantle, and ionospheric-magnetospheric phenomena - witnessed their great periods of dramatic success simultaneously in the mid-twentieth century. From roughly the end of World War II until the landing on the Moon in 1969, one dramatic discovery followed another. In palaeomagnetism, the work in the 1950s and 1960s of Allan Cox, Richard Doel, Brent Dalrymple, Donald H. Tarling and Ian McDougall, among others, established a timescale for reversals in the main geomagnetic field. This ultimately supported the famous Vine-Matthews-Morley hypothesis, which linked palaeomagnetism firmly to sea- floor spreading and plate tectonics. Concerning the origin of the main geomagnetic field, important developments in this story occurred in the 1940s and 1950s, with the first theories of a self- sustaining dynamo, proposed by Walter Elsasser and Edward Bullard, and the rotational theory of P. M. S. Blackett. These theories, while not immediately successful, started a new direction in geomagnetic research. The third major stream, of fields induced in Earth's crust and of conductivity, included both global and local investigations (Parkinson 1998). The fourth stream, the study of near-Earth space, included the investigation of the interaction of Earth's magnetic field in that region with the solar wind by Eugene Parker, the discovery of polar substorms and aurora polaris, of whistlers, and more (see, for example, Akasofu 1996; Hufbauer 1998; Stern 1989,1996; Van Allen 1983; Cliver 1998). All these areas of magnetic research, however, are much larger than these descrip- tions imply. Scientists and historians alike tend to be blinded by the bright lights of successful research. The successes of mid-twentieth century geomagnetic research helped drive the From: OLDROYD, D. R. (ed.) 2002. The Earth Inside and Out: Some Major Contributions to Geology in the Twentieth Century. Geological Society, London, Special Publications, 192, 229-239. 0305-8719/02/$15.00 © The Geological Society of London 2002. 230 GREGORY A. GOOD historical process of specialization. Palaeomag- netic researchers, main field theorists, conductivity/induced field researchers, and space scientists began moving in progressively more independent directions. Despite some continu- ing overlap in instrumentation and/or theory, the rigours of their respective fields demanded ever more concentration. As this specialization has continued, people looking back have had a hard time seeing past the bright lights of the mid- century to a time before, when researchers in geomagnetism conducted their research for reasons unconnected with plate tectonics, the geodynamo, crustal conductivity or magnetospheric interactions. This does not imply that the different specializations were or are mutually irrelevant, since indeed palaeomagneticians (to borrow a word from W. D. Parkinson), for example, have placed significant constraints on viable theories of the origin of the main field. And while a palaeomagnetician quite likely would not understand the calculations of flow patterns in the outer core, the results would still be of interest. Specialisation has been partial and primarily methodological and institutional. This paper tells a straightforward story of these events and places the drama of mid-twentieth- century geomagnetism in the context of the longer story of generations of successful and interesting research (cf. Parkinson 1998). The story told, moreover, concentrates on research questions and methods, leaving aside crucial social, institutional and cultural issues related to the development of geophysics. Unde- niably, industrial/economic interests, the military use and support of geophysics, and the politics of the World Wars and the Cold War all played important roles in this history. The Inter- national Geophysical Year, the establishment of World Data Centres and space exploration also influenced the development of geophysics in many ways. Doel (1997), among others, has begun investigation of the history of these matters, which require much more vigorous pursuit. Terrestrial magnetism In 1900, investigations of Earth's magnetism flourished as never before. All the major Euro- pean powers and their colonial empires, along with the United States, Japan, and several other nations, established magnetic observatories and sent out teams of researchers to map magnetic declination and other variables (Merlin & Somville 1910; Chapman & Bartels 1940, pp. 955-957). In 1904, Louis Agricola Bauer established the Department of International Research in Terrestrial Magnetism, better known as the DTM, at the Carnegie Institution of Washington, to fill in the gaps in these surveys around the world. The DTM also brought regular observations of the changing magnetic field to places that were previously bereft of observatories (Good 1994; Bauer 1912-1927). The explicit goal of this frenetic global activity was to understand Earth's magnetism in its entirety. Many geomagnetic scientists at the beginning of the twentieth century were inspired by the two nineteenth-century giants, Alexander von Humboldt (Rupke 1997) and Carl Friedrich Gauss (Dunnington 1955). Humboldt had attempted the impractical: to grasp the dynamic phenomena of the Earth and the Cosmos in one mind, and to reveal and revel in their intercon- nections. This included both magnetic and electric phenomena. From his work sprang the institutionalization of 'terrestrial physics' and 'cosmic physics', which continued as well recog- nized branches of physics into the early twentieth century (Walker 1866; Conrad 1938). Magnetic researchers in 1900 saw their chosen phenomena in this context and directed their research in such a way as to endeavour to fulfil Humboldt's vision. Researchers in 1900 had a critically important practical advantage over Humboldt. Geomag- netic research, with its requirements of observatories, instruments and international activity, was expensive. During the half century since Humboldt's last magnetic researches, the fiscal and organizational vitality of many nations had increased significantly. They could now afford not only to survey their home territories, but their extensive colonial empires. Germany, France, the Netherlands, Britain and the United States, in particular, did this (Pyenson 1985, 1989). A few nations and ambitious individuals like Roald Amundsen and Robert F. Scott, in the rush for the polar regions, likewise equipped their expeditions for magnetic research (e.g. Chree 1903; Good 1991). The DTM took advantage of the largess of Andrew Carnegie's private fortune to launch the most far-ranging and systematic of these global enterprises. Magnetic researchers in the early twentieth century tended to be interested in all aspects of Earth's magnetic phenomena. Consider two of the more important theorists: Adolf Schmidt and Arthur Schuster. Schmidt, who directed the Prussian magnetic observatory in Potsdam, followed in the footsteps of Edward Sabine by pub- lishing an extensive compendium of magnetic data. Whereas Sabine's numerous 'Contri- butions to Terrestrial Magnetism' assembled data from magnetic surveys of many countries FROM TERRESTRIAL MAGNETISM TO GEOMAGNETISM 231 and individuals, Schmidt collected tables of data from many observatories for the systematic study of time variations (Schmidt 1903-1926). Schmidt assembled these and other data to answer diverse theoretical questions. What were the causes of magnetic storms (Schmidt 1899)? Did electric currents flow through the surface of the Earth (Schmidt 1939)? What caused secular variation (Schmidt 1932)? Schuster, trained as a physicist by Helmholtz and Maxwell, published his first important magnetic work in 1889: an application of Gauss's spherical harmonics to the problem of the diurnal variation of Earth's magnetism (Schus- ter 1889). This work provided the basis for future studies of induced electromagnetic fields in the crust and in the upper atmosphere. This gave rise to two apparently independent, yet closely related, areas of research: electrical conductivity of the crust and electrical currents in the ionosphere and beyond. Schuster also published on the causes of magnetic storms (Schus- ter 1911) and on the causes of Earth's main magnetic field (Schuster 1912). This inclusivity was common to leading researchers around 1900. Sydney Chapman presented a most useful guide to geomagnetic research in the early twentieth century in his acceptance speech for the first Chree Medal in 1941. Charles Chree, who died in 1928, had been Director of the Kew (meteorological and magnetic) Observatory from 1893 to 1925. In his Chree Address, Chapman related the research careers of Chree, Schmidt and Bauer, saying that these three - plus the Dutch Willem van Bemmelen, the Indian N. A. F. Moos, and Edward Walter Maunder and Arthur Schuster in England - 'epitomise the progress of earth magnetic science during nearly half a century' (Chapman 1941, p. 630). He characterized the different 'gifts' that each researcher brought to the science: Moos and Chree's mathematical ability and indefatigable treatment of data; Bauer's 'fiery enthusiasm' and 'wide views'; Maunder's familiarity with events on the surface of the Sun, and Schuster's 'brilliant sorties' and 'striking theoretical conclusions' (Chapman 1941, pp. 632-633). Chapman divided the rest of his discussion into the consideration of time relationships and distribution of geomagnetism over space, a traditional division that closely parallels the studies of solar-terrestrial relationships and deep-Earth magnetic phenomena today. These traditions of terrestrial and cosmic physics relate intimately to the multifaceted development of geophysics and space physics. This, however, is not the place to pursue the story of the physical study of the Earth in extenso (Doel 1997; Good 2000). As the cases of Schmidt and Schuster indicate, geomagnetic research in 1900 was not merely 'Baconian' or inductive, as, indeed, it was not in earlier centuries either. That is, scientists were not aimlessly collecting reams of data. (This popular characterization of 'Baconianism' does not do justice to Francis Bacon, but this issue need not be entered into here.) Their data collection was directed by theory. Even the activity of the Carnegie's DTM - with its dozens of tech- nician-expeditionaries off around the world, with its magnetic survey vessels cruising the oceans, and with its observatories in Peru and Australia automatically generating extensive data relating to numerous types of phenomena - was undertaken to answer questions. Bauer had written his dissertation at Berlin on the analysis of the main magnetic field and secular variation (Good 1994; Bauer 1895). The data available, he lamented, were inadequate to the theoretical studies that needed to be undertaken. In order to explain the production of the main field, the cause of secular variation, the diurnal variations and magnetic storms, data collection guided by theory was required. Primarily, the theories of Carl Friedrich Gauss and James C. Maxwell (Garland 1979; Harman 1998; Hunt 1991) provided that guidance. Geo- magnetic research from the 1890s onwards was in the hands of investigators trained in physics. They exploited the data obtained during the 'Magnetic Crusade' (Morrell & Thackray 1981) and the first International Polar Year (Mill- brooke 1998). They applied Gauss's spherical harmonic analysis with ever-greater sophisti- cation. Schmidt, Bauer, Schuster and others firmly entrenched the habit of treating geomagnetism and geoelectricity exclusively in terms of field theory; and they made it clear that the future of explaining the main field and disturb- ance fields lay in this direction. Geomagnetism We no longer remember, and it seems unlikely today, but in 1938 'geomagnetism' was a new word in English. Germans had written of Erd- magnetismus for nearly a century, but to anglo- phone and francophone researchers the subject had long been 'terrestrial magnetism' and 'mag- netisme terrestre\ Sydney Chapman suggested the change. Although his reasons were linguistic and pragmatic, numerous changes were sweep- ing through this research community, which made the change more than a matter of linguistic convenience. [...]... material from the Meteor Cruise 1925/ 27 to the South Atlantic (Correns 19 37) ; and, to look ahead, Francis P Shepard (18 97- 1985) used it for the study of sediments in the Gulf of Mexico (Shepard et al 1960) and an outstanding application was published in 1 971 by Michael Sarnthein from the Persian/Arabian Gulf Up to now the study of fabrics, too, has been and still is useful in sediments and sedimentary... years G E Backus and others pointed out defects in the earlier theories and developed improved dynamo models in the late 1950s Others involved in this included Stephen Childress and Glynn Roberts, A Herzenberg and E N Parker In the 1960s, Raymond Hide developed the 'magnetohydrodynamic wave hypothesis' as an alternative to motion of the outer core relative to the mantle In this hypothesis, waves oscillating... in clay on right These sands, younging to the south, are variously younger to the right and centre and older to the left (Buckman 1889, Fig 1 - the distance between Cols 1 and 2 is about 50 km while the maximum between Cols 2 and 3 is about 90 km) Houghton Brunn has informed me (in lit July, 2000) that in France 'the teaching of Historical Geology is practically abandoned except for the efforts of some... rocks can tell us about the past condition of the Earth This is certainly part of the story, but so are two other main topics: the connection of remanent magnetism to local anomalies and the study of rock magnetism as a subject in its own right Nevertheless, consider the pre-1950s history of palaeomagnetism first The utility of rock magnetism for revealing the history of the main field and secular variation... magnetic anomalies and related it to the mapping of gravitational anomalies and the locating of ore bodies Chapman and Bartels described Schmidt's field balance, the use of local variometers, and the reduction of observations They did not ask what rock magnetism had to say about any large theoretical matter - not the history of the magneticfield;not drift or polar wander; not even theories of magnetization... physics and the mainly more local terrestrial science of meteorology, on the one hand, and on the other, the universal science of physics' Indeed, it encompassed parts of each of the neighbouring fields The topics covered in the book reflected this, including for example: Earth' s main field; secular variation; magnetic anomalies and geological prospecting; periodic variations due to the Sun and Moon;... faithful to the contexts of their times Special thanks are due to all of the participants in the Rio sessions for discussions that broadened and deepened this investigation, and to R E Doel, W D Parkinson, and A Jonkers for their critiques of the draft manuscript I didn't address all of their recommendations in the final revision, but I have taken them to heart and will be considering their other suggestions... directions Their compendium not only incorporated the accomplishments of Gauss and Maxwell and the data of the expeditions and observatories of the nineteenth and early twentieth centuries, it also incorporated elements of the 'new physics' Many theories based in older natural philosophy did not merit discussion even in the final historical chapter of the book (Chapman & Bartels 1940, Vol 2, pp 898-9 37) The. .. authors faced the future and their book provided the platform for launching the next generation of researchers These new researchers carried their investigations along diverging trajectories: palaeomagnetism; theories of the main geomagnetic field; investigations of induced fields and currents (and conductivity); and studies of the upper atmosphere and near space This paper recounts the 'stories' of... rule out permanent magnetization since the effect of very high pressures on magnetization were not understood The possibility of an inductive effect from electrical currents inside the Earth was, he thought, overrated The first of these explanations had roots in William Gilbert and Edmond Halley's ideas, and the second in those of Andre-Marie Ampere Schuster rejected another idea, popular in the nineteenth . reflected the significance of these features in the development of plate tectonics theory and the understanding of the Earth& apos;s behaviour, even though the collaborators were not themselves. the peaks, and high- lighting the appearance of the fracture zones. The sketched lines and shading of these features was dark, accentuating their angularity and depth. These changes. gathering into the 1 970 s. Their efforts were vital to scientific change, even though, after the plate tectonics revolution, their method remained the same and their theoretical ideas