Following Einstein's prediction of the gravitational bending of light, and in the course of experimental work aimed at its verification, only sporadic and at times misleading references have been made to Johann Georg von Soldner. In a paper published in 1804, Soldner derived the gravitational bending of light on the classical Newtonian basis and calculated its value around the sun with remarkable accuracy. Soldner's paper, inaccessible even in German, is now presented in English translation and put in the perspective of (...) Soldner's life and the science of his day and ours. (shrink)

This article seeks to provide a historically well-informed analysis of an important post-Newtonian area of research in experimental physics between 1798 and 1898, namely the determination of the mean density of the earth and, by the end of the nineteenth century, the gravitational constant. Traditionally, research on these matters is seen as a case of “puzzle solving.” In this article, the author shows that such focus does not do justice to the evidential significance of eighteenth- and nineteenth-century experimental research on (...) the mean density of the earth and the gravitational constant. As Newton’s theory of universal gravitation was mainly based on astronomical observation, it remained to be shown that Newton’s law of universal gravitation did not break down at terrestrial distances. In this context, Cavendish’ experiment and related nineteenth-century experiments played a decisive role, for they provided converging and increasingly stronger evidence for the universality of Newton’s theory of gravitation. More precisely, the author shall argue that, as the accuracy and precision of the experimental apparatuses and the procedures to eliminate external disturbances involved increasingly improved, the empirical support for the universality of Newton’s theory of gravitation improved correspondingly. (shrink)

In 1786, Robert Blair, an unknown astronomer from Edinburgh, wrote a paper that would remain unpublished. In his manuscript, Blair gives a systematic treatment of the Newtonian kinematics of light, taking into account in the absolute space of Newton the motion of the light source, that of the observer, and the velocity of the corpuscles of light. Two years before, in the context of Newton's corpuscular theory of light, John Michell had pointed out that the velocity of light could be (...) measured with the help of refraction experiments. Blair went a step further and inferred the existence of what we now call the Doppler effect: a variation of refraction due to a relative motion of the source and the observer. Blair's proposal is at the roots of Arago's well‐known 1806–10 experiments on the velocity of light. In the context of the undulatory theory of light, Blair proposed an experiment to determine the absolute motion of the Earth, laying the bases for the famous experiment performed by Albert Michelson 100 years later. In fact, this manuscript contains the very questions of light relativity, the roots of spectroscopy, and addresses the very problems that would be hotly debated in the nineteenth century, only to be solved by Einstein in 1905. (shrink)

The ArgumentThe question of the possible existence of black holes is closely related to the question of the action of gravitation on the propagation of light. It has been raised recurrently from the when that Newton referred to a possible bending of light in hisOpticks. And it relies on apparently simple questions: Is light subject to gravitation? What is the effect of a gravitational field on the propagation of light? Could a particle of light emitted by a star be retained (...) by its gravitational field?From the end of the 1960s, the black hole idea has had a very important place in the relativistic literature, not to speak of the popularization of the theory. It turned out to be not only an important concept but also a tool that permitted us to understand general relativity better, indeed a tool that contributed greatly to changing the interpretation of Einstein's theory of gravitation. Here too I want to use this concept of the black hole to assist our understanding of the history of general relativity: the black hole is a fundamental milestone in the evolution of general relativity. (shrink)