The Problem of the Earth's Figure: Measurement, Theory, and Evidence in Physical Geodesy

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).

Name dc:type.qualificationname

Doctor of Philosophy (PhD)

Level dc:type.qualificationlevel

Doctoral

Grantor dc:publisher.institution

University of Cambridge

Year dc:date.issued

2024

Author dc:creator

• Ohnesorge, Miguel

Advisor dc:contributor.advisor

• Chang, Hasok

• Celestial Mechanics
• Evidence
• Geodesy
• Gravitational Physics
• History of Physics
• Measurement
• Philosophy of Physics
• Philosophy of Science

Licence

• https://apollo8-f-pro.lib.cam.ac.uk/bitstreams/435c01e2-c4e8-4aa1-97f0-86562dd2549e/download
• https://creativecommons.org/licenses/by-nd/4.0/

Language dc:language

eng

Author Identifier

0000-0003-4583-4124

OAI identifier oai:identifier

oai:www.repository.cam.ac.uk:1810/369776