Jed Z. Buchwald

Descartes's experimental journey past the prism and through the invisible world to the rainbow

Summary Descartess model for the invisible world has long seemed confined to explanations of known phenomena, with little if anything to offer concerning the empirical investigation of novel processes. Although he did perform experiments, the links between them and the Cartesian model remain difficult to pin down, not least because there are so very few. Indeed, the only account that Descartes ever developed which invokes his model in relation to both quantitative implications and to experiments is the one that he provided for the rainbow. There he described in considerable detail the appearances of colours generated by means of prisms in specific circumstances. We have reproduced these experiments with careful attention to Descartess requirements. The results provide considerable insight into the otherwise fractured character of his printed discovery narrative. By combining reproduction with attention to the rhetorical structure of Descartess presentation, we can show that he worked his model in conjunction with experiments to reach a fully quantitative account of the rainbow, including its colours as well as its geometry. In this one instance at least, Descartes produced just the sort of explanatory novelties that the young Newton later did in optics. That Descartess results in respect to colour are in hindsight specious is of course irrelevant.

Thomas S. Kuhn, 1922-1996

Thomas S. Kuhns singular voice was stilled by cancer on June 17, 1996, some 49 years after his initial encounters with past science had drawn him into a career in the history and philosophy of science. One of the most widely-read and influential academics of the 20th century, Kuhn was educated at Harvard University, where he received an S.B. (summa cum laude) in Physics in 1943 and a Ph.D. in the subject in 1949. He remained there until 1956, first as a Junior Fellow in the Society of Fellows from 1948 to 1951, when he in effect retrained himself as a historian of science, and then as an Assistant Professor of General Education and History of Science. He joined the faculty of the University of California, Berkeley, in 1956, becoming Professor of History of Science in 1961. From 1964 to 1979 he was on the faculty of the History of Science Program of Princeton University, and from 1972 to 1979 also a member of the Institute for Advanced Study. He moved to the Department of Linguistics and Philosophy of Massachusetts Institute of Technology in 1979, where he became Professor Emeritus in 1991. He was President of the History of Science Society in 196870 and of the Philosophy of Science Association in 1988-90. He received the George Sarton Medal of the History of Science Society in 1982 and the John Desmond Bernal Award of the Society for the Social Studies of Science in 1983.

Incommensurability and the Discontinuity of Evidence

Incommensurability between successive scientific theoriesthe impossibility of empirical evidence dictating the choice between themwas Thomas Kuhns most controversial proposal. Toward defending it, he directed much effort over his last 30 years into formulating precise conditions under which two theories would be undeniably incommensurable with one another. His first step, in the late 1960s, was to argue that incommensurability must result when two theories involve incompatible taxonomies. The problem he then struggled with, never obtaining a solution that he found entirely satisfactory, was how to extend this initial line of thought to sciences like physics in which taxonomy is not so transparently dominant as it is, for example, in chemistry. This paper reconsiders incommensurability in the light of examples in which evidence historically did and did not carry over continuously from old laws and theories to new ones. The transition from ray to wave optics early in the nineteenth century, we argue, is especially informative in this regard. The evidence for the theory of polarization within ray optics did not carry over to wave optics, so that this transition can be regarded as a prototypical case of discontinuity of evidence, and hence of incommensurability in the way Kuhn wanted. Yet the evidence for classic geometric optics did carry over to wave optics, notwithstanding the fundamental conceptual readjustment that Fresnels wave theory required.

The battle between Arago and Biot over Fresnel

The rapid development of the wave theory of light at the hands of Fresnel early in the nineteenth century was accompanied by an equally rapid acceptance of Fresnels empirical success, though not of the wave theory itself. This was substantially due to the eager promotion of Fresnels work by Arago, whose interest in it was, in part as least, stimulated by personal interests. Several years before Fresnel visited and wrote to him, Arago had been professionally sabotaged by Biot. He used Fresnel to revenge himself in almost the same manner that he believed Biot had wounded him. Paradoxically this nasty, personal conflict served very well to promote the wave theory at a critical time in its development.

Optics and the theory of the punctiform ether

The fundamental principles of the wave theory of light had all been developed by 1822, when Fresnel completed his theory of polarisation and birefringence. On the bases of the principle of interference and the principle that the optical vibration is perpendicular to the light ray Fresnel had been able to account quantitatively for many optical phenomena which had previously been explained, if at all, purely qualitatively. One might therefore conclude that what remained to be done in the wave theory was primarily the extension and application of these two principles. Much work of this kind was indeed accomplished during the nineteenth century, and it constitutes an essential aspect of the maturation of the wave theory. However, even a cursory survey of the literature between 1830 and 1890 indicates that a vastly greater effort was expended on attempts to construct a mathematical system from which Fresnels principles could be analytically deduced. The goal of this work was one which Fresnel had only briefly addressed: namely, to discover a general differential equation of wave propagation which could be applied to all optical phenomena, and especially to those phenomena, such as dispersion, which escaped explanation on the sole basis of Fresnels two principles. Described in this fashion the search for a general propagation equation seems to be purely formal. In fact, from the first detailed attempt in 1830 to discover the equation, to the last efforts in the late 1880s before the elec-

The Training of German Research Physicist Heinrich Hertz

Just over a century ago a young German physicist of moderate though hardly overpowering reputation announced that he had successfully generated electric waves. In Germany and England replications of Heinrich Hertz’s discovery rapidly followed; in France and Switzerland controversy over precisely what Hertz had found swirled for about five years. Scarcely a decade after the original finding, Hertz’s laboratory devices were being rapidly transformed into technological apparatus as Oliver Lodge, Guglielmo Marconi and others concentrated on sending signals through, and extracting them from, the new world of the electromagnetic spectrum. By then Hertz was dead, having succumbed to septicemia in 1895 at the age of thirty-eight. He had however ceased experimenting nearly five years before, having turned his attention instead to abstract questions that had long bothered him concerning the foundations of mechanics, and indeed of all of physics.

The Background to Heinrich Hertz’s Experiments in Electrodynamics

One hundred years ago an ambitious young German physicist demonstrated that electromagnetic radiation exists and that it behaves like light. Heinrich Hertz’s experiments had, without doubt, the widest impact outside the scientific community of any in physics up to that time. Within physics they surprised the British, who did not expect to find this kind of radiation quite so simply. His results were surprising to the Germans as well, but they were also perplexing and difficult to grasp, an effect that Hertz sought to overcome through an elaborate series of theoretical articles. Then, just as his influence within German physics seemed destined to reach heights hitherto achieved only by his mentor Hermann von Helmholtz, Hertz succumbed to an extremely painful jaw malady that he had suffered from even in the midst of his most intricate experiments and complex theorizing.

Reflections on Hertz and the Hertzian Dipole

Heinrich Hertz has for some time attracted the attention of philosophers of science who are interested in the impact of his highly abstract Principles of Mechanics. Yet he has not until recently been much investigated by historians of physics, who, in considering electrodynamics, have for the most part concentrated on figures such as Kelvin, Maxwell, or Lorentz. There is a nice symmetry between the philosophers’ interest and the historians’ lack of it, because both interests exhibit a long-standing concern with figures who were deeply engaged in the production of new theories or who developed influential abstractions. Hertz himself never did produce a theoretical system comparable to Maxwell’s or to Lorentz’s, but he did generate an elaborate scheme for the foundations of mechanics that had a substantial impact on foundational thinking in late 19th and early 20th century philosophy.

Michael S. Mahoney, 1939–2008

Perhaps the clearest testimony to the scholarly range and depth of Princetons now‐lamented Michael S. Mahoney lies in the dismay of his colleagues in the last few years, as they contemplated his imminent retirement. How to maintain coverage of his fields? Fretting over this question, the program in history of science that he did so much to build recently found itself sketching a five-year plan that involved replacing him with no fewer than four new appointments: a historian of mathematics with the ability to handle the course on Greek antiquity, a historian of the core problems of the Scientific Revolution, a historian of technology who could cover the nineteenth‐century United States and Britain, and, finally, a historian of the computer-and-media revolution. In his passing we have lost a small department.

HEINRICH HERTZ'S ATTEMPT TO GENERATE A NOVEL ACCOUNT OF EVAPORATION

Although Heinrich Hertz is known primarily for his discovery in 1888 of electric waves and for his canonical formulation of field theory over the next several years, he had spent much of the 1880s searching for other ways to produce novel effects in the laboratory.1 These investigations, which did not have much impact on his contemporaries, nevertheless provide uniquely revealing insight into Hertz’s characteristic methods of thinking and of working in the laboratory. Among the earliest of the areas that he tried to evolve into something novel was evaporation, which became interesting to him as a byproduct of a brief investigation he did early in 1882 on hygrometry (Hertz 1882a). He had developed a new method for measuring absolute or relative humidity by weighing a hygroscopic substance. Such a substance absorbs water from the air until its vapour pressure becomes equal to the partial pressure of the unsaturated vapour “actually present in the air.” Hertz built a simple device to measure relative humidity that employed a torsion-balanced glass rod carrying on one of its ends tissue-paper saturated with calcium chloride. Shortly afterwards Hertz became interested in the process of evaporation itself, as a vehicle for discovery.