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Issue No.03 - July-September (2004 vol.26)
pp: 78-84
Published by the IEEE Computer Society
Raul Rojas , Free University of Berlin
Charles P. Bourne and Trudi Bellardo Hahn, A History of Online Information Services: 1963–1976, MIT Press, 2003, $45, 496 pp., ISBN 0-262-02538-8.
A historical account of online information services can be more than just a detailed chronology of who did what when. Charles Bourne and Trudi Bellardo Hahn show this unequivocally with their engaging account of the formative years in this important area of computing. The reader is immediately drawn into the spirit of the narrative with a lively prologue that pays tribute to the 1950s Hepburn and Tracy movie Desk Set and its helpful computer, which frees the librarian from mundane tasks. This foray into Hollywood in no way presupposes the depth and treatment of the topic as the authors relentlessly dissect a complex and complicated history. In fact, Bourne and Hahn present it in a way that illuminates an era that is quickly slipping into the past. The authors' direct involvement in this history adds a dimension of authority to the writing that readers will appreciate. They embed nuggets of wisdom and personal insight throughout the text, making even the most excruciatingly detailed passages palatable.
The book is logically broken into several sections. The first chapter stands alone to provide a sense of the rigor and research approach taken in this work's development. In addition to using a vast array of published sources, more than 90 citations list the authors' interviews and personal communication with pioneers of online services. The authors caution, however, that they used these interviews primarily to flavor the narrative. They validated chronological facts and drew them from multiple sources to ensure accuracy. Chapter 1 also provides a historical backdrop for the years being documented. This gives the readers a sense of relevant world events and urgency that stimulated the development of online services.
Chapter 2 begins coverage of nascent online information services and the early years of experimentation, idea formation, and prototypes that would later form the basis for academic and commercial applications. Chapters 3 and 4 carry the information services story ahead from the late 1960s into the 1970s, against the backdrop of the Vietnam War and various technical constraints. The authors point out the challenges faced by online information services pioneers and the sheer genius of many compromises made in an age of slow machines, low memory, and large data sets. Chapter 3 looks at university applications, while Chapter 4 covers advances in nonacademic research laboratories.
The next four chapters provide detailed chronologies of four major online initiatives through transformations, changes, and eventually, their emergence as a coherent set of systems in the early 1970s. The next two chapters look at the operational online information services of the 1970s and how the industry stimulated by these services expanded from an academic curiosity into a vibrant reality. The last chapter summarizes the book's research questions and main findings.
Overall, this book leaves the reader feeling satisfied that the authors have made every effort to create a historical record that will stand the test of time. Not only are the milestones and major developments chronicled with accurate detail, the human side of the equation is carefully covered as well. However, developers, end users, marketers, and others are all cast in their roles in a way that only a person working in the early years of online information services would understand. This book promises to be a valuable reference for years to come.
Roger McHaney, Kansas State University; mchaney@ksu.edu
Erdmann Thiele, Telefunken nach 100 Jahren. Das Erbe einer deutschen Weltmarke [Telefunken after 100 Years: The Legacy of a Global German Brand], Nicolai Verlag, 400 pp., €29.90, ISBN 3-87584-961-2. (Available only in German.)
When translated into English, the name Telefunken is Tele-Spark. Already this hints at the roots of a company, that at its height, expanded all over the world from Germany to Brazil and the Philippines. During the 1960s, Telefunken AG earned revenues of more than a billion deutsche marks, even though the communication technology enterprise ceased to exist in 1967, when it was integrated into Allgemeine Elektricitäts Gesellschaft (AEG). Nearly 40 years later, former employees established the Initiative Telefunken nach 100 Jahren [Telefunken after 100 Years Initiative] with the goal of writing a book in celebration of the 100th anniversary of the company's founding. Felix Herringer, the corporation's last president, finds the reason for this still vivid remembrance in a special company spirit that he calls Telefunken-Geist (see page 9). The commemorative volume consists of almost 40 articles written by former employees that deal with the company's history, products, technical achievements, and research activities.
The story begins in 1896, in a small village near Bologna, with Guglielmo Marchese Marconi's wireless transmission of Morse signals over approximately 2 kilometers—the first long distance wireless transmission ever. In his home country, however, nobody was interested in his technological innovation, so Marconi migrated to Great Britain.
In 1897, he conducted further successful experiments at the Bristol Channel, which were followed with interest by both the British navy and Adolf Slaby, who was a professor at what is now the Technische Universität Berlin and held the first chair of electrical engineering. Slaby repeated the experiments and aroused the curiosity of the German emperor Wilhelm II. The emperor even made his private gardens available for Slaby's experiments, and several antennas were placed on towers of the royal palaces. At the same time, professor Ferdinand Braun succeeded in improving Marconi's technology in Strassburg. Braun used a sparkless antenna circuit (patented in 1899) that linked the transmitter power to the antenna circuit inductively. This invention greatly increased the broadcasting range. The company Siemens & Halske AG recognized the invention's economic potential and began to support Braun. The AEG, which was founded in 1887, began to support Slaby.
Before long, there were heavy conflicts about patent priorities. Slaby's systems were supplied mainly to the navy, while the systems by Siemens & Halske were used by the army. Great Britain's military was already using a uniform system: the one supplied by the Marconi Wireless Telegraph and Signal Company. Emperor Wilhelm II therefore ordered the two German companies to quit the patent quarrels and develop a single standardized radio system for both the navy and army.
On 27 May 1903, the radio system departments of the Gesellschaft für Drahtlose Telegraphie, System Braun und Siemens & Halske GmbH [Wireless Telegraphy Company, System Prof. Braun and Siemens & Halske, Ltd.], and the AEG/Slaby/Arco group merged, and a new company called Gesellschaft für drahtlose Telegraphie mbH. [Wireless Telegraphy Ltd.] was founded. Wilhelm Bargmann and Slaby's research assistant Count Georg von Arco were appointed as the new company's directors, and on 11 November 1903, the trademark Telefunken was registered. This name had been used as the telegram address by the company that sold Braun's systems. In 1904, the word Telefunken also became part of the company's name.
The story that follows the foundation seems to interact with everything of historical importance that has happened during the last 100 years. The Titanic disaster in 1912, for example, led to a resolution that all ships carrying more than 50 passengers must be equipped with a radio communication system. This directly increased Telefunken's revenue. Their technical innovations were used in World War I. However, the Treaty of Versailles had a negative impact on Telefunken because all their transmitting stations outside Germany were confiscated. In 1923, Telefunken built the first radio-broadcasting station in Germany and the appropriate receivers for the public. The world tour of the Graf Zeppelin airship in 1929 was achieved using Telefunken transmitters, receivers, and onboard directional equipment. In 1935, Telefunken equipped the Olympic Stadium in Berlin with electrical-acoustic equipment. On 1 August 1936, an electronic TV camera, the Ikonoskop camera, was used for the first direct transmission of the Olympic Summer Games in Berlin. In 1941, Telefunken became a subsidiary of AEG because they took over 50 percent of Siemens & Halske shares. During World War II Telefunken built the famous Würzburg-Riese, a predecessor of modern radar units. The reconstruction after the war posed a difficult challenge. All production facilities were destroyed, dismantled, or confiscated, and many valuable experts were scattered worldwide.
Nevertheless, by 1952, the product range had already grown to a considerable size. It consisted of long-range communications systems as well as radio and TV transmitters and receivers, directional and navigation systems, radar devices, mobile and portable radio systems, high-frequency heat generators, measuring equipment, electro-acoustical systems, record players, all kinds of tubes, and quartz crystals.
In 1955, the company's name was changed to Telefunken GmbH, and in 1963, it went public and became Telefunken AG. In 1966, the general shareholder meeting of AEG passed a resolution to integrate Telefunken AG. Thereafter, the business activities of Telefunken were transferred to AEG (effective 1 January 1967) and were continued under the combined name AEG-Telefunken. Further advancements and innovations were distributed under the new brand name; among them was a series of computers, the first model of which (the TR-4) having already been sold by Telefunken in 1962. Further models include the TR-440 and TR-86, which was used for air-traffic control. However, AEG-Telefunken, unable to stand competition from IBM and other overseas companies, halted new computer development in 1980.
Daimler-Benz AG entered the company in 1985 and decided to dissolve the legal entity 11 years later. It transferred the remaining assets to EHG Electroholding GmbH. The company's history was then complete, although the brand survives. The name Telefunken continues to be used under license agreements.
As I stated earlier, the book is a collection of articles written by former employees, each describing the history of a group of products. Because Telefunken was involved in almost every aspect of radio technology, the volume serves well as a reference book. For example, if readers are interested in the history of, the radar system, the vacuum tube, or the color TV, they can use the book to get a thorough introduction from those directly involved. The articles are easily understandable, even for the lay reader. A glossary explains most of the technical terms and the bibliography contains approximately 250 references. It's a pity that the book is only available in German.
Gerald Friedland, Free University of Berlin; fland@inf.fu-berlin.de
Alice Rowe Burks, Who Invented The Computer? The Legal Battle That Changed Computing History, Prometheus Books, 2003, 463 pp., $35, ISBN 1-59102-034-4.
Suppose one of my students asked me who invented the computer? When I introduce the history of computing in introductory computer science classes, I define "the computer" as a collection of computing devices used over the years to make "brain work" easier. My "computer" consists of fingers, rocks, and the abacus. It is marks on cave walls. It includes calculating machines such as those from Leibnitz and Pascal. It is made up of the contributions of Ada Lovelace and Jacquard's looms. I try to condense the important contributions in the 20th century to cover many of the events that played a role in our computers of today, including contributions from other countries. As one student put it, I don't just rely on "Mauchly, Eckert, and those guys" in my approach. Among the other contributors are Turing, von Neumann, Atanasoff, and Berry. Although I probably should include more people from other countries, I single out Grace Hopper and Konrad Zuse's contributions.
In this book, Alice Rowe Burks answers the invention question with Atanasoff and his Atanasoff-Berry Computer. (Berry, being a graduate student, is often left out when the ABC is discussed.) She bases her decision on the documents from the legal battle between Honeywell and Sperry Rand, Sperry Rand and Control Data, and many other documents and interviews.
In 1964, a patent was issued for the ENIAC to Mauchly and Eckert, who eventually sold their company and rights to Remington Rand. Remington Rand merged with Sperry Gyroscope. Sperry Rand, as this new company was called, began to demand royalties from almost all other competitors. One competitor, Honeywell, challenged the patent with evidence that the basis for the patent came from Atanasoff's ABC. In June 1941, Mauchly had paid a visit to Atanasoff at Iowa State College. There was some speculation that Mauchly came back from his visit to Atanasoff with information about the ABC, which he used to build the ENIAC.
This was not the first patent trial involving the ENIAC. In 1967, Sperry Rand had challenged Control Data over who had created regenerative memory. Mauchly and Eckert had the patent for this also. Did the rights belong to Sperry Rand, based on their purchase of the rights to these patents? Or had Atanasoff been the one who created regenerative memory and provided information from which the ENIAC was derived making the patents illegal?
The first half of the book is based on Mauchly's difficulty in recalling many facts and Atanasoff's detailed memory recollections. Berry, unfortunately, had committed suicide and could not contribute to the testimony. In any event, Judge Earl R. Larson based his ruling on the evidence supporting the ENIAC as being derived from ABC. Furthermore, Larson ruled that the patents for the regenerative memory patent and certain other components were unenforceable due to the derivation of these components from ABC.
The next half of Burks' book supports her thesis and controversy surrounding a declaration that Atanasoff was the father of computing, not Mauchly and Eckert. She starts with Eckert threatening to sue her and her husband Arthur if they published an article about the ENIAC in the October 1981 issue of Annals of the History of Computing. The suit did not happen, and another article was published in the April 1984 issue of Annals by Kathleen (Kay) R. Mauchly covering her husband's version of the ENIAC's development. (Mauchly died in 1980.) Scholars of the history of computing continue to argue over Larson's ruling, and will continue arguing for and against this topic.
Think about the words of Arthur W. Burks, in his paper "From Eniac to the Stored-Program Computer: Two Revolutions in Computers" found in A History of Computing in the Twentieth Century (Academic Press, 1980):
There has been a long controversy over "who invented the store-program computer?" Unfortunately, this question is over simplistic. The development of the stored-program computer took place in many steps and involved many people. I shall trace this development through its main stages, starting with the first generation of stored program computers: EDVAC, IAS, WHIRLWIND, EDSAC, UNIVACI, and many others.
What if the Alice Rowe Burks book had been written to describe the computer as a generalization of computers of today and went on to discuss the importance of the Larson ruling in favor of Atanasoff and ABC? Perhaps she might have borrowed the words of her husband and started the book with this:
There has been a long controversy over who invented the first computer. Unfortunately, this question is over simplistic. The development of the computer took place in many steps and involved many people. I shall trace this development through its main stages, starting with the first generation of ABC, COLOSSUS, Z3, ENIAC, EDVAC, IAS, WHIRLWIND, EDSAC, UNIVACI, and many others and then discuss the importance of the controversial Larson ruling in the development of the computer as we know it today.
While I had difficulty reading the second half of the book, I found the testimony and transcripts interesting. The book convinced me that, in all probability, Mauchly did use some of the Atanasoff–Berry ideas in creating the ENIAC. I am not convinced that Atanasoff should be given credit for the invention of the first computer. However, it left me with one thought. What would have happened if Larson had ruled in favor of Mauchly and Eckert, and how would this have changed the history of computing?
Noni McCullough Bohonak, University of South Carolina Lancaster; nbohonak@gwm.sc.edu
Charlotte Froese Fischer, Douglas Rayner Hartree: His Life in Science and Computing, World Scientific, 2003, 244 pp., $67, ISBN 981-238-577-0.
Charlotte Fischer has filled a significant gap in the biographical literature with this well-researched account of Douglas Hartree's scientific career. Born in 1897, Hartree is most known for his Self Consistent Field method in atomic physics, further developed by Vladimir Fock and now generally referred to as the Hartree–Fock method. In addition to this achievement, he made fundamental contributions to many other areas, such as the theory of the magnetron, atmospheric electromagnetic propagation, and the early development of control theory, all centered around the common theme of the numerical solution of differential equations. After World War II, his interests shifted more to the process of computation, and he played a prominent role in the early development of computing hardware and computing services in the UK. During his career, he held professorships at Manchester University in applied mathematics, theoretical physics, and engineering physics and at Cambridge University in mathematical physics. In 1932, Hartree was elected a Fellow of the Royal Society. He died suddenly in 1958 at 61.
Fischer begins with an overview of Hartree's family history, tracing three generations of distinguished engineers, physicians, and literary figures. This is followed by a brief chapter covering Hartree's early education at Bedales School, where his lifelong hobby interests in music and railways (both model and real) developed. In his private life, we learn he was shy. Fischer quotes Rudolf Peierls: "In mixed company his red face would acquire a darker hue before he managed an utterance." (Peierls is a famous theoretical physicist, and he overlapped with Hartree in Manchester and was professor at Birmingham from 1945–1963 and Oxford from 1963–74.) Perhaps because of this, Fischer has been unable to unearth much information on his social life and, following these introductory chapters, concentrates almost exclusively on his professional accomplishments, with only the occasional anecdote to give us insight into his private personality. Fischer does a good job of outlining the technical and historical context of each of Hartree's many contributions, but in consequence, the general reader without a background in the physical sciences might find some of the book difficult to read.
Two significant events shaped Hartree's early career. First, World War I interrupted his undergraduate degree at Cambridge. In support of the war effort, he became involved in ballistics calculations, where he first worked on numerical solutions to differential equations. Second, when he returned to Cambridge in 1921, Niels Bohr visited and gave an influential series of lectures on quantum theory. Hartree set the course of his research in the area of atomic physics, where after the development of wave mechanics, he made his major contribution of the Self Consistent Field method for the numerical computation of atomic wave functions.
Beginning in the early 1930s, three events combined, causing Hartree to significantly broaden his research interests. First, he was pre-empted by Fock in generalizing his method to include quantum mechanical exchange interactions, and Fischer concludes he simply did not want to compete. Second, his appointment to the chair of applied mathematics in Manchester meant that much of his time was taken up with administration and teaching duties so he could no longer be personally involved in the numerical work. Third, on a visit to the US, he was introduced to the differential analyzer, newly invented by Vannevar Bush at the Massachusetts Institute of Technology. Hartree immediately recognized its potential for application to atomic physics and many other areas of scientific endeavor where progress was hampered at the time by the growing amount of numerical computation required. Having returned to Manchester, he determined that a similar machine should be built as soon as possible in the UK. He constructed a model machine, largely from Meccano parts. After successfully demonstrating this model, Hartree secured funding for a full-scale machine. At the outbreak of World War II, this was probably the most powerful computing facility available in the UK.
Hartree at once offered the differential analyzer to the government for war-related work. He oversaw several groups working in diverse areas including ballistics; radio propagation; heat flow; and the magnetron, a critical component of radar systems. Because of wartime secrecy considerations, little of this work was ever published, and Fischer does not claim to have been able to provide an exhaustive list. These examples show how Hartree was able to turn his hand quickly to a new subject and bring his extensive practical experience of numerical methods to bear with great impact.
By the end of the war, Hartree was fully involved in developing digital computers. He was appointed to an influential National Physical Laboratory committee, which gave him considerable influence behind the scenes to promote computer developments in the UK. He also visited the Moore School at the University of Philadelphia for several months, where he had the opportunity to become one of the earliest ENIAC programmers. He returned to Cambridge to take up the Plummer Chair in Mathematical Physics, a position he held until his untimely death.
He was much in demand around the world to lecture on the latest advances in digital computers and in the emerging subject of numerical analysis. These lectures, and his now-classic book Calculating Instruments and Machines, have been reprinted as part of the Charles Babbage Institute Reprint Series for the History Of Computing (vol. 6, 1984), in recognition of the seminal nature of his contributions.
Hartree was generous with his time, offering advice and assistance to all who sought it, sometimes to the detriment of his own work. He was an excellent lecturer and teacher, and he was particularly admired by his research students. Fischer concludes with a short chapter on his legacy, with comments on and remarks by, some of the individuals for whom Hartree was a strong influence on their professional lives.
The author provides extensive references to primary sources as well as a complete listing of Hartree's publications, amounting to six books and 113 papers.
While much of the book is devoted to Hartree's work in physics, Annals readers interested in the broader scientific context leading up to his significant contributions to analog and early digital computing will find much of interest here.
Tim Robinson, Boulder Creek, Calif.; tbr00@pacbell.net
Martin Campbell-Kelly, Mary Croarken, Raymond Flood, and Eleanor Robson (eds.), The History of Mathematical Tables From Sumer to Spreadsheets, Oxford Univ. Press, 2003, 361 pp., $89.50, ISBN 019-850-841-7.
Who hasn't used a mathematical table? In our modern world, tables are ubiquitous. Any single edition of a newspaper contains stock listings, weather forecasts, sports results, and so on. Unfortunately, the history of everyday objects often remains untold as, by definition, these objects are so embedded in our environment that they seem to have always been there. In this sense, this book fills an important gap in the history of mathematical instruments (as far as tables are concerned) and provides abundant food for thought on the connections between table making and the invention of the computer.
This volume is the outcome of the summer meeting of the British Society for the History of Mathematics, held in Oxford in September 2001. Twelve papers recount the history of mathematical tables almost from the beginning of writing and civilization, all the way up to the "rise and rise" (as Campbell-Kelly puts it) of the computer spreadsheet. Although following the history of a mathematical object through the last four or five thousand years is an ambitious undertaking, the editors have done a wonderful job of harmonizing the narrative and interconnecting the papers so that a coherent picture emerges. We can only wonder if mathematical tables are as universal as the Platonic solids. They were discovered and rediscovered, emerging time and again in many cultures and different application fields.
Eleanor Robson, telling the story of tables in Sumer, Babylonia, and Assyria, opens her article with a gorgeous illustration of a clay table from Mesopotamia. Were it not for the cuneiform characters, there would be nothing to tell it apart from a modern spreadsheet. The cuneiform data is carefully divided into columns and rows, with six-month subtotals for wages and one-year totals. In the text, we learn that tables were discovered multiple times in these Middle Eastern societies that were absorbed with accounting. It seems that tables first became an everyday document in the 19th century BC, possibly due to the invention of the sexagesimal system—that is, numbers written in base 60 instead of base 10. Tables were used not just for accounting purposes but also for education in mathematics, scholarship, and astronomy.
From Mesopotamia, the volume takes us straight to Edinburgh, John Napier, and the invention of logarithms in the 17th century. Many of the mathematical tables still being produced in the 20th century, before electronic calculators gained the upper hand, were tables of logarithms and trigonometric functions. Graham Jagger, this chapter's author, reviews the original definition of the logarithm, as stated by Napier, and its transformation into a form that is easier to understand and more useful for table production. Napier published his original treatise in Latin in 1614. It was immediately translated and became a useful aid to seafarers. The earliest printed table of base-10 logarithms was edited and printed by Henry Briggs, who together with Napier, invented these around 1617. Other mathematicians continued on with the work of Napier and Briggs, and the use of logarithms as a calculating aid became widespread in the ensuing years. As for all articles in this volume, a further reading section lists some books and papers that the reader can consult to learn more about the subject.
The industrialization of table making and its influence on the development of mechanical calculators is investigated in three closely related articles. Ivor Grattan-Guiness recounts the story of the logarithmic and trigonometric tables computed in a project started by Gaspard Riche de Prony in the 18th century. Michael Williams describes several difference engines that were specially conceived for table making, and Doron Swade reviews the most famous of them all, Charles Babbage's 19th-century differential engine.
As we learn in the Grattan-Guiness article, the work-division methods of the Industrial Revolution could also be applied to the "manufacture" of mathematical tables. The engineer and mathematician de Prony organized the computation of mathematical tables using three management-and-work ranks. At the first level, a handful of mathematicians selected the algorithms that were to be used. At the next, mathematicians defined the individual steps and laid out the forms that were necessary for proceeding with the calculations. The third and last level consisted of 60 to 80 unskilled workers, unemployed hairdressers in this particular case, who only had to perform elementary calculations, sometimes just addition, to fill the forms. To check the results, tables were computed using two different methods. Obviously, such a dissection of table making into elementary operations opened the door for the mechanization of the whole process. If hairdressers only needed addition to obtain results, this surely could be done by a series of coupled mechanical adders.
Michael Williams describes such machines and portrays some of the now-forgotten inventors. A boxed text in this article (insets are used throughout the whole book and provide useful background information for the reader) reveals the basic idea behind difference engines—that is, the method of differences. This paper clearly shows that Charles Babbage's machine was not created in a vacuum. Although Babbage conceived the idea independently, others had thought in the same direction—the time was ripe for such types of computing machines. Doron Swade, who directed the reconstruction of Babbage's difference engine at the Science Museum in London, describes Babbage's machine using CAD drawings. It is interesting to see that we can always learn something more about Babbage's machine—for example, about the printing mechanism and how important this was, independent of the mathematical work the machine had to perform.
Three other articles deal with the history of special types of tables: actuarial tables (Christopher Lewin and Margaret de Valois), astronomy in general (Arthur L. Norberg), and astronomy tables for HM (Her Majesty/His Majesty) Nautical Office (George A. Wilkins). Actuarial tables have to do with banking (compound interest) and with statistics (life tables, for example). It seems that the first scientifically based mortality table was published by John Graunt in 1662. In 1693, none other than Edmund Halley published a life table and the method for computing life annuities, which the author pinpoints as the starting point of actuarial science. Astronomy tables, on the other hand, have a long history, and many renowned scientists dealt with their computation. Nevertheless, astronomy tables also have important earthly applications, such as navigation and empire building.
Three articles deal with a point that is sometimes overlooked: Table manufacturing has led to the creation of whole offices and bureaucracies in charge of producing them. Table making has its own managerial and organizational history, as Mary Croarken describes in an article about table making by committee in the UK. Also, David Alan Grier writes about the Mathematical Tables Project in the US. This last endeavor, which was conceived as a labor relief program for white collar workers within the framework of the New Deal, ran from 1937 until 1949. It was as ambitious a project as de Prony's, but it took place at the exact watershed between the era of human "computers" and our information age. A photograph on page 276 shows many human computers wearing suits and ties, bent over their respective calculating forms.
Martin Campbell-Kelly closes this volume with a reflection on the evolution of tables in our computer age, where tables have become spreadsheets, responsive to our commands and ready to recompute a whole array of numbers. He describes the main industrial players in the relatively short history of the personal spreadsheet, and how companies rose, succeeded, and failed. Clearly, the last word on table making has not yet been spoken. Mathematical tables will continue to evolve, and there will be new surprises in the future.
This book is useful and interesting for anyone interested in the origins of calculating aids, especially about the connection between mathematical table making and computing machines. It makes a wonderful lecture for the scientifically inclined—and although it is certainly not a book written for the specialist, specialists can gain new valuable insights. Numerous photographs, diagrams, insets, and literature lists complement the main body of material.
Tania Rojas-Esponda, Princeton University; trojas@princeton.edu
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