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The Problem of the Earth's Figure: Measurement, Theory, and Evidence in Physical Geodesy https://doi.org/10.17863/CAM.109451 Ohnesorge, Miguel 0000000345834124 Chang, Hasok This thesis tells the story of a surprisingly difficult problem in gravitational physics: deriving and measuring the shape of our planet. Chapter 1 reconstructs the emergence of gravitational theories of planetary equilibrium figures and quantitative measurements of the Earth’s shape and surface gravity (c. 1660-1730). I show that early geodesists made substantial empirical progress despite deep theoretical disagreements about the nature of gravitation. Chapter 2 reconstructs how geodesy came to offer a decisive test of the interactive nature and compositionality of gravitation (c. 1740-1825). I retell how Pierre-Simon Laplace established that the Earth’s external attraction is the resultant force of the mutual attractions between its constituent particles; a momentous but overlooked achievement in the history of gravitational physics. Chapter 3 traces the numerical conflicts in the measurement of the central quantity characterising Earth’s figure: its ellipticity. These conflicts persisted throughout the nineteenth century and complicated the coordination between geodetic models and measurements. Chapter 4 reconstructs how geodesists finally achieved convergent measurements of Earth’s ellipticity between 1880 and 1924. Jointly, the four chapters illustrate key steps in obtaining strong evidence for quantitative claims about a complex and partially inaccessible system: using measurements to initiate theoretical inquiry (chapter 1), using measurements to conduct severe tests of theoretical laws (chapter 2), using discordant measurements to study second-order phenomena (chapter 3), and using multiple alternative measures to identify the sources of persistent errors (chapter 4). University of Cambridge 2024-02-22 Thesis Doctoral Doctor of Philosophy (PhD) eng This thesis has been supported by a Cambridge Trust and Darwin College Vice Chancellor's Studentship (10556463), and a Freer Prize Fellowship by the Royal Institution of Great Britain and Northern Ireland. https://www.repository.cam.ac.uk/handle/1810/369776 https://apollo8-f-pro.lib.cam.ac.uk/bitstreams/93935232-08ac-47e2-8864-9d926427afe3/download 7532d98105d88b80579e60cd2bea533b https://apollo8-f-pro.lib.cam.ac.uk/bitstreams/435c01e2-c4e8-4aa1-97f0-86562dd2549e/download 87eda9de84448d1f82354d60eee3eb5f https://creativecommons.org/licenses/by-nd/4.0/ Celestial Mechanics Evidence Geodesy Gravitational Physics History of Physics Measurement Philosophy of Physics Philosophy of Science