Newton wrote in thePrincipiathat all bodies are to be regarded as subject to the principle of gravitation. Every body, however great or small, is related to every other body in the universe by a mutual attraction. It was this postulated universality of the force of gravity which contributed so greatly to the order and unity of the Newtonian world. This unity was, for its followers, an untested article of faith for nearly a century after thePrincipia. During this time the evidence (...) of gravitational attraction continued to be drawn from the motions of the earth, moon, planets, comets, and falling bodies—phenomena which span an intermediate range of masses, sizes, and distances. In three domains of experience, involving the extreme upper and lower limits of masses and dimensions, the action of gravity had not yet been observed: the gravity of the “fixed” stars; the mutual attraction of terrestrial bodies; and the gravitation of light. The task of deducing observable consequences from each of these supposed instances of universal gravitation fell to the Reverend John Michell (1724–1793), a teacher at Cambridge (1749–1763) and afterwards Rector of Thornhill, Yorkshire. His renowned London friend Henry Cavendish (1731–1810) encouraged him in these researches and became involved in the resulting observational and experimental questions. The immersion of Michell and Cavendish in gravitational studies was an essential feature of their commitment to a unified Newtonian world. Their commitment had yet a broader significance: Newton's theory of gravitation inspired their image of physical reality, and it served as their model of an exact science. This paper is an attempt to relate the personal friendship of Michell and Cavendish, their scientific collaboration, and their common Newtonian philosophy. Its chief focus is on Michell's 1784 plan for weighing the stars by the gravitational retardation of their light; his project of weighing the world by means of a torsion balance is treated by way of an epilogue. (shrink)

Summary The object of this study is to analyse certain aspects of the debate between David Brewster and William Whewell concerning the probability of extra-terrestrial life, in order to illustrate the nature, constitution and condition of natural theology in the decades immediately preceding the publication in 1859 of Charles Darwin's Origin of species. The argument is directed against a stylised picture of natural theology which has been drawn from a backward projection of the Darwinian antithesis between natural selection and certain (...) forms of the design argument. Contrary to the popular image of natural theology as an essentially static, autonomous and monolithic set of presuppositions about the existence of design in nature, the paper underlines the existence of a fundamental divergence of strategies within natural theology, a divergence that, in the case of Brewster and Whewell, can be correlated with the religious cultures to which they most closely belonged. The fact that, in the plurality of worlds debate, their respective positions became mutually exclusive suggests that the fragmented and disordered state of natural theology, only too apparent before the Darwinian impact, was occasioned as much by the ulterior problem of rationalising the excessive space of the astronomers and the excessive time of the geologists as it was by any principle of the uniformity of nature in the biological sphere. The argument is substantiated with particular reference to the breakdown in communication as Brewster and Whewell developed conflicting strategies to expose the ?development hypothesis? that had appeared in Vestiges. Their altercation also reveals a certain conflict of status concerning the conclusions of astronomy and geology which, in turn, suggests that tensions between the physical and life sciences were not peculiar to the period following the publication of Darwin's theory. (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)

The years between 1660 and 1800 were important ones in the study of light. For most of the period the work, especially in this country, was largely dominated by the theories advanced by Newton; unfortunately the protagonists of these theories were much more rigid in their approach than was Newton himself. There was, in effect, almost a century of ‘rear-guard actions’ to maintain the corpuscular theory at all costs.Fortunately, the advance of geometrical optics and the design of optical instruments was (...) not retarded to a very great degree by this partisan approach. The workers in these fields were not, as a rule, too involved in speculation, and worked largely empirically.Some of the modifications to the original corpuscular theory are interesting. Attempts were made to explain, with varying degrees of success, total internal reflection, dispersion, interference effects, diffraction and phosphorescence. Considerable speculation about the velocity of light occurred in connection with these topics. At the same time, wave theories never completely died out and, although they were not developed until the early part of the nineteenth century, their influence was felt even in this country. (shrink)