The lovely phrase “figure of the earth” evokes for me the wonderful photographs of earth from space taken by the Apollo 11 and Apollo 17 astronauts. The phrase, however, originates more than three hundred years ago, and refers to measurement of the precise shape of the earth. More specifically, to determine of the “figure of the earth” means to measure the amount by which a degree of latitude varies from equator to pole along a meridian. We understand now that the earth is approximately an oblate spheroid with flattening at the poles. By the seventeenth century it was suspected that the earth was not precisely spherical, so the distance that corresponds to a degree of latitude is not the same near the equator as it is near the poles. But is it larger toward the poles, or smaller?
In The Quest for the True Figure of the Earth , Michael Hoare explores the tempestuous history of the art and science of land surveying that gave rise to the science of geodesy. A central part of his story is the “Figure of the Earth” controversy, an extraordinary contest of ideas and philosophies that involved the leading scientific figures of the age — Descartes, Newton, Voltaire, Maupertuis, Cassini and many others. Newton argued in favor of an oblate spheroid model for the figure of the earth, but Descartes and his partisans favored a prolate spheroid. The controversy developed well beyond the scientific and technical into political, theological and philosophical arenas. Yet this was not purely an intellectual confrontation. Resolution of the controversy involved daring expeditions to some of the most inhospitable parts of the earth.
In the 1730s, two expeditions sponsored by the Académie Royale des Sciences left Paris for what must have seemed like the ends of the earth. Louis Godin led an expedition to the equatorial region of Peru to carry out measurements across three degrees of latitude. Pierre-Louis Moreau de Maupertuis headed to Lapland and the Arctic Circle with his party for a measurement across one degree of latitude. Both expeditions had to carry out their surveys while dealing with extremes of climate, capricious weather conditions, complicated logistics, and personal rivalries. Yet both expeditions were successful.
One of the curious aspects of the “Figure of the Earth” controversy is its essential irrelevance to practical navigation. Far more important was the problem of developing a practical method for determining longitude at sea. This was not resolved until the eighteenth century. (See, for example, Dava Sobel’s Longitude.)
The current book focuses on the historical aspects of the expeditions and offers only a little on the technical aspects of geodesy. A reader interested in the history of geodesy and the controversy over the figure of the earth will find much of interest here. For those more focused on the mathematical aspects of geodesy, this book provides fascinating background, but a book such as Theory of the Earth’s Shape by Dragomir et al. would be more suitable.
Bill Satzer (firstname.lastname@example.org) is a senior intellectual property scientist at 3M Company, having previously been a lab manager at 3M for composites and electromagnetic materials. His training is in dynamical systems and particularly celestial mechanics; his current interests are broadly in applied mathematics and the teaching of mathematics.