Richard Feynman (1918–1988) loved to tell the story of his close encounter with poetry while a graduate student in physics at Princeton. Sitting in on a colloquium in which “somebody” analyzed the structural and emotional elements of a poem, Feynman was set up as an impromptu respondent by the graduate dean, who was confident that the situation would elicit a strong reaction. To the literary scholar’s inquiry, “Isn’t it the same in mathematics …?” Feynman was asked to relate the problem to theoretical physics. He tells us about his reply:

Like other anecdotes in Feynman’s memoirs, this story – in both its enactment and retelling – is framed upon a frequently recurrent motif of clever one-upmanship that displays several constituent characteristics of his psychology and personality. The special notice he takes of the smile he is about to wipe off the speaker’s face participates in the kind of intellectual sadism that Feynman later enjoyed as the perpetrator of elaborate practical jokes, some with near life-and-death consequences.

During the past decades, the historiography of nineteenth-century chemistry has become increasingly complex and at the same time more interesting. Rising on the sound “internalistic” foundations laid by Aaron J. Ihde’s The Development of Modern Chemistry (1964) and, of course, by James R. Partington’s A History of Chemistry (four volumes, 1961–1970), the edifice of more recent historiography depicts chemistry as an endeavor in close interaction with the cultural and intellectual currents of that time. Departing from the question of the disciplinary identity of chemistry during the nineteenth century and thus joining “the separate analyses of schools, disciplines, and traditions into an integrated analytical matrix,” Mary Jo Nye has with a sure hand sketched out the framework of this chemical edifice. As reflected in her book, new problems have moved to the forefront, among them the question of the disciplinary development of chemistry and its subdisci-plines, such as biochemistry, stereochemistry, and physical chemistry, as well as questions of the emergence of scientific schools and of science policy in general. Last but not least are the questions of the metaphysical background and of the internal discourses among chemists. In this context, two questions are of eminent importance: What is “chemical” in chemistry, that is, what distinguishes chemistry from its neighbor sciences? And how does chemistry arrange the objects of its scientific experiences?

CHEMICAL VERSUS PHYSICAL ATOMS

One may well say that it is the notion of units of matter showing certain measurable relations of their weight and possessing certain characteristics to explain the specificity of chemical reactions (that is, the notion of “chemical atomism”) that distinguished chemistry from its close relative, physics. This may sound a little strange, as we are used to seeing atoms as the same entities in all sciences. From the time of Democritus (ca. 410 b.c.) up to the first decades of the nineteenth century, atoms were considered to be little indivisible lumps of matter, which, when forming compounds, are attached to one another either by their respective shapes or by “affinities.”

There is a common trait in reviews by plasma- and solid-state physicists of their specialties: an emphasis on the ubiquity of the subject matter with which they are concerned. “As we now know, planet Earth is but a small non-plasma island in a vast sea of plasma. Though tenuous in outer space, plasma is dense and omnipresent in the stars and in their coronas. In fact this ‘fourth state of matter’ – plasma – is seen as the dominant form of matter in the Universe,” a pioneer of plasma physics writes in a review about his discipline. With the same zeal but a slightly different emphasis, a German solid-state protagonist has created a link between the omnipresent solid matter and human culture: “Solid substances have given their names to the great historical epochs of mankind. Stone, bronze, and iron have caused epochal changes,” he begins in a book on the history of solid-state electronics. Now, at the end of the iron age, we are entering a new era. “Probably this epoch will be given the name of the crystal.… This new epoch perhaps will be called silicon age.”

What is the message behind such a “ubiquity” rhetoric? Beyond the pleading for recognition, funds, and other means of furthering plasma and solid-state physics, are we supposed to consider research in those omnipresent substances as a cultural obligation? In contrast to specialties like elementary particle physics, which appear to the public as more fundamental, the study of plasmas is regarded as a corollary to the quest for controlled thermonuclear fusion. Similarly, solid-state physics seems to derive its importance more from technological applications than from intellectual curiosity.

Four different, but related, topics will be examined in this chapter: first, the debate between the emission theory and the undulatory theory of light; second, the discovery of new kinds of radiation, such as heat (infrared) and chemical (ultraviolet) rays at the beginning of the nineteenth century, and the gradual emergence of the consensus that heat, light, and chemical rays constituted the same continuous spectrum; third, the development of spectroscopy and spectrum analysis; and finally, the emergence of the electromagnetic theory of light and the subsequent laboratory creation of electromagnetic waves, as well as the discovery of x rays at the end of the nineteenth century.

The account given here is based on current scholarship in the history of nineteenth-century physics and, in particular, optics and radiation. However, as the current status of historical research on each of these topics is not homogeneous, different historical and historiographical points will be stressed for each topic. The first subject will stress historiographical issues in interpreting the optical revolution, with reference to Thomas Kuhn’s scheme of the scientific revolution. The second and third subjects, which have not yet been thoroughly examined by historians, will stress the interplay among theory, experiment, and instruments in the discovery of new rays and the formation of the idea of the continuous spectrum. The fourth subject, Maxwell’s electromagnetic theory of light, is rather well known, but the account here concentrates on the transformation of a theoretical concept into a laboratory effect, and then on the transformation of the laboratory effect into a technological artifact.

In the years between 1800 and the end of the twentieth century, astronomy was fundamentally transformed. That which had been at heart a science of position, in which astronomers strove to say where an object is, not what it is, became in many ways a vastly more wide-ranging and large-scale enterprise in terms of the questions asked of nature, the number of astronomers it engaged, the level of public and private support it enjoyed, and the size and sophistication of the instruments employed, as well as the remarkable extension of observations beyond the narrow window of optical wavelengths.

The focus of this chapter is on those changes in observational astronomy that comprised central elements in this remaking of astronomy between 1800 and 2000: the reform of positional astronomy in the early nineteenth century, the rise of astrophysics (although little attention is devoted to the study of the Sun, as that is discussed elsewhere in this volume), and the ways in which shifting forms of patronage provided new opportunities for state-of-the-art instruments. In all of these areas, the history of the telescope, the key instrument in observational astronomy in the last four centuries, will be key. We shall also see that the improvement of telescopes was often not tied to answering particular theoretical questions, but was rather seen as a worthy goal in itself that would, in turn, lead to novel results. It should be noted, too, that we are concerned with astronomy in the Western world at the cutting edge of research. I shall therefore not address very interesting questions about the development of instruments for use primarily in demonstrations (e.g., planetaria) or employed chiefly for recreational uses.

Surveying the history of nineteenth-century science in his magisterial A History of European Thought in the Nineteenth Century (1904–12), John Theodore Merz concluded that one “of the principal performances of the second half of the nineteenth century has been to find … the greatest of all exact generalisations – the conception of energy.” In a similar vein, Sir Joseph Larmor, heir to the Lucasian Chair of Mathematics at Cambridge once occupied by Newton, wrote in the obituary notice of Lord Kelvin (1824–1907) for the Royal Society of London in 1908 that the doctrine of energy “has not only furnished a standard of industrial values which has enabled mechanical power … to be measured with scientific precision as a commercial asset; it has also, in its other aspect of the continual dissipation of energy, created the doctrine of inorganic evolution and changed our conceptions of the material universe.” These bold claims stand at the close of a remarkable era for European physical science, which saw, in the context of British and German industrialization, the replacement of earlier Continental (notably French) action-at-a-distance force physics with the new physics of energy.

This chapter traces the construction of the distinctively nineteenth-century sciences of energy and thermodynamics. Modern historical studies of energy physics have usually taken as their starting point Thomas Kuhn’s paper on energy conservation as a case of simultaneous discovery. Kuhn’s basic claim was that twelve European men of science and engineering, working more or less in isolation from one another, “grasped for themselves essential parts of the concept of energy and its conservation” during the period between 1830 and 1850.

“Global environmental change,” three words heard with increasing frequency in both science and policy circles, is shorthand for the inevitability of change in the geosphere-biosphere. It also expresses the realization that human activities have now reached the level of a planetary force. Since 1945, we have grown increasingly apprehensive about a number of global environmental issues, including population, energy consumption, pollution, and the health of the biosphere. At the beginning of a new millennium, instead of standing firmly on the technoscientific foundations of our “enlightened” predecessors, we find ourselves apprehensive about global environmental change, teetering on the uncertainties of a new century and unsure about the future quality and even habitability of the global environment.

Much of the concern is rightfully focused on changes in the atmosphere caused by human activities. Only a century after the discovery of the stratosphere, only five decades after the invention of chlorofluorocarbons (CFCs), and only two decades after atmospheric chemists warned of the destructive nature of chlorine and other compounds, we fear that ozone in the stratosphere is being damaged by human activity. Only a century after the first models of the carbon cycle were developed, only three decades after regular carbon dioxide (CO,) measurements began at Mauna Loa Observatory, and only two decades after climate modelers first doubled the CO, in a computerized atmosphere, we fear that the earth may experience a sudden and possibly catastrophic warming caused by industrial pollution.

Mathematical knowledge has long been regarded as essentially stable and, hence, rooted in a world of ideas only superficially affected by historical forces. This general viewpoint has profoundly influenced the historiography of mathematics, which until recently has focused primarily on internal developments and related epistemological issues. Standard historical accounts have concentrated heavily on the end products of mathematical research: theorems, solutions to problems, and the technical difficulties that had to be mastered before a well-posed question could be answered. This kind of approach inevitably suggests a cumulative picture of mathematical knowledge that tells us little about how such knowledge was gained, refined, codified, or transmitted. Moreover, the purported permanence and stability of mathematical knowledge begs some obvious questions with regard to accessibility – known to whom and by what means? Issues of this kind have seldom been addressed in historical studies of mathematics, which often treat priority disputes among mathematicians as merely a matter of “who got there first.” By implication, such studies suggest that mathematical truths reside in a Platonic realm independent of human activity, and that mathematical findings, once discovered and set down in print, can later be retrieved at will.

If this fairly pervasive view of the epistemological status of mathematical assertions were substantially correct, then presumably mathematical knowledge and the activities that lead to its acquisition ought to be sharply distinguished from their counterparts in the natural sciences. Recent research, however, has begun to undercut this once-unquestioned canon of scholarship in the history of mathematics. At the same time, mathematicians and philosophers alike have come increasingly to appreciate that, far from being immune to the vicissitudes of historical change, mathematical knowledge depends on numerous contextual factors that have dramatically affected the meanings and significance attached to it.

Dismissed as inconsequential before the 1970s, the history of the contributions of women to the physical sciences has become a topic of considerable research in the last two decades. Best known of the women physical scientists are the three “great exceptions” from central Europe – Sonya Kovalevsky, Marie Sklodowska Curie, and Lise Meitner– but in recent years, other women and other countries and areas have been receiving attention, and more is to be expected in the future. The overall pattern for most women in these fields, the nonexceptions, has been one of ghettoization and subsequent attempts to overcome barriers.

PRECEDENTS

Before 1800 there were several self-taught and privately-tutored “learned ladies” in the physical sciences. Included were the English self-styled “natural philosopher” Margaret Cavendish (1623–1673), who wrote books and in the 1660s visited the Royal Society of London, which had not elected her to membership; the German astronomer Maria Winkelmann Kirch (1670– 1720), who worked for the then-new Berlin Academy of Sciences in the early 1700s; the Frenchwoman Emilie du Chatelet (1706–1749), who translated Newton’s Principia into French before her premature death in childbirth in 1749; the Italians Laura Bassi (1711–1778), famed professor of physics at the University of Bologna, and Maria Agnesi (1718–1799), a mathematician in Bologna; Ekaterina Romanovna Dashkova (1743–1810), the director of the Imperial Academy of Sciences in Russia; and Marie Anne Lavoisier (1758– 1836), who helped her husband Antoine with his work in the Chemical Revolution.

During the nineteenth and twentieth centuries, astronomy has changed from a relatively homogeneous discipline to one of tremendous diversity. Before this period, the main business of astronomy had been the measurement and prediction of planetary motion and stellar position. Earlier astronomers depended on a limited range of observational equipment – the optical telescope and various instruments for measuring angles and positions against the sky – in order to map the locations of the stars and to track the motions of the planets as they wandered against this fixed background. By the early nineteenth century, astronomers had, as theoretical tools, not only Newtonian gravitation but also the fruits of a century’s further refinement of celestial mechanics. Not only could astronomers calculate the orbits of individual planets around the Sun; they could also investigate the mutual perturbations of the various bodies and the stability of the solar system as a whole, far into the future. Within their well-defined realm, early-nineteenth-century astronomers congratulated themselves on possessing a predictive power exceeding that of all other fields of natural science.

Yet astronomers were eventually to trade their sure grasp of their traditional portion of the world for a much less certain hold on broad, new domains: the study not just of position and motion but also of the physical nature of celestial objects of all kinds, from the Sun, stars, and planets to nebulae and galaxies. This expansion of subject was, in significant part, technology driven, and many new observational technologies contributed to making it possible, including the building of telescopes with tremendously increased light-gathering power and finer resolution, and the introduction of photography as an astronomical tool.

Until the mid-1950s, the word “computer” commonly referred to a woman employed in operating a calculating machine in a business office or a scientific calculating laboratory. With the invention in 1945 of the stored-program computer, several months after the Second World War ended, and with the publicity surrounding the introduction in 1952 of the first commercial computer (the Universal Automatic Computer, or UNIVAC), the word computer became associated with a machine, rather than a human.

This machine had three attributes that rendered prior calculating technologies obsolete in less than two decades. The electronic switching of its components eventually made the computer billions of times faster than its mechanical ancestors. The digital storage of information enhanced precision to practically unrestricted levels. The stored program capability, that is, the ability to store instructions as well as data inside the machine and to have the machine process those instructions during the course of a computation without human intervention, had two advantages: First, it enabled almost any computer to be used as a universal machine, in other words, to carry out virtually any computation possible by a machine. Second, stored programming was critical to the automation of the computational process, so that the overall speed of computation could reflect the electronic speed of the components.

The nineteenth century saw enormous advances in electrical science, culminating in the formulation of Maxwellian field theory and the discovery of the electron. It also witnessed the emergence of electrical power and communications technologies that have transformed modern life. That these developments in both science and technology occurred in the same period and often in the same places was no coincidence, nor was it just a matter of purely scientific discoveries being applied, after some delay, to practical purposes. Influences ran both ways, and several important scientific advances, including the adoption of a unified system of units and of Maxwellian field theory itself, were deeply shaped by the demands and opportunities presented by electrical technologies. As we shall see, electrical theory and practice were tightly intertwined throughout the century.

EARLY CURRENTS

Before the nineteenth century, electrical science was limited to electrostatics; magnetism was regarded as fundamentally distinct. In the 1780s, careful measurements by the French engineer Charles Coulomb established an inverse-square law of attraction and repulsion for electric charges, and electrostatics occupied a prominent place in the Laplacian program, based on laws of force between hypothetical particles, then beginning to take hold in France. The situation was soon complicated, however, by Alessandro Volta’s invention in 1799 of his “pile,” particularly as attention shifted from the pile itself to the electric currents it produced. Much of the history of electrical science in the nineteenth century can be read as a series of attempts to come to terms with the puzzles posed, and the opportunities presented, by currents like those generated by Volta’s pile.

Throughout the late eighteenth and nineteenth centuries, there were two distinctly different ways of thinking about the earth – two different evidentiary and epistemic traditions. Such men as Comte Georges de Buffon and Léonce Elie de Beaumont in France, William Hopkins and William Thomson (Lord Kelvin) in the United Kingdom, and James Dwight Dana in the United States tried to understand the history of the earth primarily in terms of the laws of physics and chemistry. Their science was mathematical and deductive, and it was closely aligned with physics, astronomy, mathematics, and, later, chemistry. With some exceptions, they spent little time in the field; to the degree that they made empirical observations, they were likely to be indoors rather than out. In hindsight, this work has come to be known as the geophysical tradition. In contrast, such men as Abraham Gottlob Werner in Germany, Georges Cuvier in France, and Charles Lyell in England tried to elucidate earth history primarily from physical evidence contained in the rock record. Their science was observational and inductive, and it was, to a far greater degree than that of their counterparts, intellectually and institutionally autonomous from physics and chemistry. With some exceptions, they spent little time in the laboratory or at the blackboard; the rock record was to be found outside. By the early nineteenth century, students of the rock record called themselves geologists. These two traditions – geophysical and geological – together defined the agenda for what would become the modern earth sciences. Geophysicists and geologists addressed themselves to common questions, such as the age and internal structure of the earth, the differentiation of continents and oceans, the formation of mountain belts, and the history of the earth’s climate.

Until about 1840, the theory of probability was used almost exclusively to describe and to manage the imperfections of human observation and reasoning. The introduction of statistical methods to physics, which began in the late 1850s, was part of the process through which the mathematics of chance and variation was deployed to represent objects and processes in the world. If this was a “probabilistic revolution,” it was a multifarious and gradual one, the vast scope of which went largely unremarked. Yet it challenged some basic scientific assumptions about explanation, metaphysics, and even morality. For this reason, it sometimes provoked searching reflection and debate within particular fields, including physics, over what, in retrospect, appears as an important new direction in science.

At the most basic level, statistical method meant replacing fundamental laws whose action was universal and deterministic with broad characterizations of heterogeneous collectives. Statistics, whether of human societies or of molecular systems, involved a shift from the individual to the population and from direct causality to mass regularity. In social writings, it was linked to bold claims for scientific naturalism. Statisticians claimed to have uncovered a lawlike social order governing human acts and decisions that had so far been comprehended by Christian moral philosophy in terms of divine intentionality and human will. Their science seemed to devalue moral agency, perhaps even to deny human freedom. In other contexts, and especially in physics, statistical principles appeared, rather, to limit the domain of scientific certainty. They directed attention to merely probabilistic regularities, the truth of which was uncertain and approximate.

For over three millennia, cosmology had closer connections to myth, religion, and philosophy than to science. Cosmology as a branch of science has essentially been an invention of the twentieth century. Because modern cosmology is such a diverse field and has ties with so many adjacent scientific disciplines and communities (mathematics, physics, chemistry, and astronomy), it is not possible to write its history in a single chapter. Although there is no complete history of modern cosmology, there exist several partial histories that describe and analyze the main developments. The following account draws on these histories and presents some major contributions to the knowledge of the universe that emerged during the twentieth century. The chapter focuses on the scientific aspects of cosmology, rather than on those related to philosophy and theology.

THE NINETEENTH-CENTURY HERITAGE

Cosmology, the study of the structure and evolution of the world at large, scarcely existed as a recognized branch of science in the nineteenth century; and cosmogony, the study of the origin of the world, did even less. Yet there was, throughout the century, an interest, often of a speculative and philosophical kind, in these grand questions. According to the nebular hypothesis of Pierre-Simon de Laplace and William Herschel, some of the observed nebulae were protostellar clouds that would eventually condense and form stars and planets in a manner similar to the way in which the solar system was believed to have been formed. This widely accepted view implied that the world was not a fixed entity, but in a state of evolution.

The modern historical period from the Enlightenment to the mid-twentieth century has often been called an age of science, an age of progress or, using Auguste Comte’s term, an age of positivism.

Volume 5 in The Cambridge History of Science is largely a history of the nineteenth- and twentieth-century period in which mathematicians and scientists optimistically aimed to establish conceptual foundations and empirical knowledge for a rational, rigorous scientific understanding that is accurate, dependable, and universal. These scientists criticized, enlarged, and transformed what they already knew, and they expected their successors to do the same. Most mathematicians and scientists still adhere to these traditional aims and expectations and to the optimism identified with modern science.

By way of contrast, some writers and critics in the late twentieth century characterized the waning years of the twentieth century as a postmodern and postpositivist age. By this they meant, in part, that there is no acceptable master narrative for history as a story of progress and improvement grounded on scientific methods and values. They also meant, in part, that subjectivity and relativism are to be taken seriously both cognitively and culturally, thereby undermining claims for scientific knowledge as dependable and privileged knowledge.