As a natural philosopher, Count Rumford is best known for his vehement advocacy of a motion or mechanical hypothesis of heat and for the dramatic experiments that he performed to support this hypothesis. Although a motion hypothesis which held that heat was merely the motion of the ultimate particles of a body had a distinguished history, with advocates that included Bacon, Boyle, Hooke, and Newton, most British natural philosophers by the beginning of the nineteenth century believed that the phenomena associated (...) with heat were caused by an imponderable fluid. William Henry reflected contemporary opinion in 1803, when he wrote:The former of these opinions [i.e. the existence of caloric], though far from being universally admitted, is now generally received; and the peculiar body, to which the phenomena of heat are referred, has been denominated by M. Lavoisier [as] caloric. (shrink)

Ultraviolet radiation is generally considered to have been discovered by Johann Wilhelm Ritter in 1801. In this article, we study the reception of Ritter’s experiment during the first decade after the event—Ritter’s remaining lifetime. Drawing on the attributional model of discovery, we are interested in whether the German physicists and chemists granted Ritter’s observation the status of a discovery and, if so, of what. Two things are remarkable concerning the early reception, and both have to do more with neglect than (...) with reception. Firstly, Ritter’s observation was sometimes accepted as a fact but, with the exception of C. J. B. Karsten’s theory of invisible light, it played almost no role in the lively debate about the nature of heat and light. We argue that it was the prevalent discourse based on the metaphysics of Stoffe that prevented a broader reception of Ritter’s invisible rays, not the fact that Ritter himself made his findings a part of his Naturphilosophie. Secondly, with the exception of C. E. Wünsch’s experiments on the visual spectrum, there was no experimental examination of the experiment. We argue that theorizing about ontological systems was more common than experimenting, because, given its social and institutional situation, this was the appropriate way of contributing to physics. Consequently, it was less clear in 1810 than in 1801 what, if anything, had been discovered by Ritter.Keywords: Johann Wilhelm Ritter; Carl Johann Bernhard Karsten; Christian Ernst Wünsch; Ultraviolet radiation; Conceptions of heat and light. (shrink)

Hardly any ontological result of modern science is more firmly established than the fact that infrared radiation differs from light only in wavelength; this is part of the modern conception of the continuous spectrum of electromagnetic radiation reaching from radio waves to gamma radiation. Yet, like many such evident truths, the light-infrared unity was an extremely difficult thing to establish. We examine the competing arguments in favour of the unified and pluralistic theories of radiation, as put forward in the first (...) half of the nineteenth century by three of the most important early pioneers of the study of radiation: Herschel, Melloni and Draper. In this part of the paper, we conclude that there were no compelling reasons of observational adequacy to prefer the unified theory to the pluralistic theory. Keywords: Macedonio Melloni; John William Draper; William Herschel; Infrared; Observation; Theory-choice. (shrink)

Research on thermal “black-body” radiation played an essential role in the origin of the quantum theory at the beginning of the twentieth century. This is a well-known fact, but historians of science up to now have not generally recognized that studies of radiant heat were also important in an earlier episode in the development of modern physics: the transition from caloric theory to thermodynamics. During the period 1830–50, many physicists were led by these studies to accept a “wave theory of (...) heat”, although this theory subsequently faded into obscurity. (shrink)