An Account of Experiments to Determine the Figure of the Earth by Means of the Pendulum Vibrating Seconds in Different Latitudes : As Well As on Various Other Subjects of Philosophical Inquiry

By the early nineteenth century, it was widely accepted that gravity varied at different points across the Earth's surface, and that the Earth could not be perfectly spherical. This 1825 work documents the groundbreaking experiments of Edward Sabine (1788–1883), the first physicist to produce accurate measurements of this ellipticity.

As early as the seventeenth century, scientists realised that a pendulum swings more slowly at the equator than it would at the North Pole. Newton predicted that gravity increased with latitude, and that the Earth could not be perfectly spherical. Although various experiments were undertaken to determine the exact degree of this ellipticity, none proved successful until physicist Edward Sabine (1788–1883) embarked on a series of expeditions across the world. Based on pendulum measurements from a wide range of latitudes, from Jamaica to Spitsbergen, his results were very different to mathematical predictions, and far more accurate; Charles Babbage would even complain that they were too good to be true. In this account, which first appeared in 1825, Sabine explains his methodology and presents his findings. His book opens a fascinating window into nineteenth-century geodesy for students in the history of science.