Why were pendulums important to Charles Sanders Peirce’s research on gravity?

For Charles Sanders Peirce, pendulums were essential tools for conducting a gravimetric survey of North America, a project he supervised to determine the Earth’s ellipticity with greater precision.1

Following the 1871 appropriation to connect the geodetic surveys of the Atlantic and Pacific coasts, Peirce contributed significantly to both the theory and practice of pendulum swinging as a method for measuring the force of gravity. Because the period of a pendulum is governed by its length and the local value of gravity, these experiments allowed him to gather critical data across approximately 20 stations in the United States and Europe.12

Furthermore, the rigorous requirement for accurate length measurements during his pendulum research led Peirce to perform a pioneering determination of the length of the metre based on a wavelength of light. His experimental and theoretical work in this field earned him international recognition within the scientific community.1