John Henry Poynting

This paper appeared in Archive for History of Exact Sciences, vol. 65(2), 2010, pp. 181-227. Abstract: 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.

Note: Unfortunately, the reconstruction of the Cavendish experiment in this paper contains a mishap that does however not affect the overall argument of the paper. The error is corrected in Steffen Ducheyne, The Cavendish experiment as a tool for historical understanding of science, Science & Education 21(1), 2012, pp 87-108 (https://www.academia.edu/2524605/The_Cavendish_experiment_as_a_tool_for_historical_understanding_of_science).